STEEL SHEET AND METHOD OF MANUFACTURING THE SAME

20220389531 · 2022-12-08

Assignee

Nippon Steel Corporation (Tokyo, JP)

Inventors

Cpc classification

International classification

Abstract

A steel sheet has a predetermined chemical composition, in which a microstructure in a ¼ width portion, a microstructure in a ½ width portion, and a microstructure in a ¾ width portion, include, by area %, ferrite: 80% or more, martensite: 2% or less, and residual austenite: 2% or less, in which a proportion of unrecrystallized ferrite in the ferrite is 5% to 60%, an average grain size of carbonitrides is 6.0 nm to 30.0 nm, and Expressions (2) to (5) are satisfied.

Δ.sub.SF/μ.sub.SF≤0.10 (2)

Δ.sub.dF/μ.sub.dF≤0.20 (3)

Δ.sub.SUF≤20 (4)

Δ.sub.dC/μ.sub.dC≤0.50 (5)

Claims

1.-10. (canceled)

11. A steel sheet comprising, as a composition, by mass % comprising: C: 0.035% to 0.150%; Si: 0.010% to 1.500%; Mn: 0.10% to 3.00%; Al: 0.005% to 1.000%; P: 0.100% or less; S: 0.0200% or less; N: 0.0150% or less; O: 0.0100% or less; V: 0% to 0.50%; Cr: 0% to 1.00%; Ni: 0% to 1.00%; Cu: 0% to 1.00%; Mo: 0% to 1.00%; W: 0% to 1.00%; B: 0% to 0.0100%; Sn: 0% to 1.00%; Sb: 0% to 0.20%; Nb: 0% to 0.060%; Ti: 0% to 0.100%; Ca: 0% to 0.0100%; Mg: 0% to 0.0100%; Zr: 0% to 0.0100%; REM: 0% to 0.0100%; and a remainder: Fe and impurities, wherein Expressions (1-1) to (1-3) are satisfied; a microstructure in a ¼ width portion at a ¼ width position from a sheet width direction end portion in a sheet width direction and at a ¼ thickness position from a surface in a sheet thickness direction, a microstructure in a ½ width portion at a ½ width position from the sheet width direction end portion in the sheet width direction and at the ¼ thickness position from the surface in the sheet thickness direction, and a microstructure in a ¾ width portion at a ¾ width position from the sheet width direction end portion in the sheet width direction and at the ¼ thickness position from the surface in the sheet thickness direction include, by area %, ferrite: 80% or more, martensite: 2% or less, and residual austenite: 2% or less, and the remainder in microstructure, a proportion of unrecrystallized ferrite in the ferrite is 5% to 60%, an average grain size of carbonitrides is 6.0 nm to 30.0 nm, Expressions (2) to (5) are satisfied, a 0.2% proof stress is 280 MPa to 600 MPa, a tensile strength is 450 MPa to 800 MPa, a yield ratio is 0.50 to 0.90, and a uniform elongation is 10.0% or more,
1.5×Nb+Ti≥0.015 (1-1)
0.03≤{(Ti/48−N/14)+Nb/93}/(C/12)≤0.40 (1-2)
Ca+Mg+Zr+REM≤0.0100 (1-3)
Δ.sub.SF/μ.sub.SF≤0.10 (2)
Δ.sub.dF/μ.sub.dF≤0.20 (3)
Δ.sub.SUF≤20 (4)
Δ.sub.dC/μ.sub.dC≤0.50 (5) each of Ti, N, Nb, C, Ca, Mg, Zr, and REM in Expressions (1-1) to (1-3) represent a content by mass % of the element, when the element is not included, 0% is substituted as the content of the element, and when a value of (Ti/48−N/14) is negative, 0 is substituted as the value of (Ti/48−N/14), μ.sub.SF in Expression (2) represents an average value of an area ratio of ferrite in the microstructure in the ¼ width portion, an area ratio of ferrite in the microstructure in the ½ width portion, and an area ratio of ferrite in the microstructure in the ¾ width portion, and Δ.sub.SF represents a difference between a maximum value and a minimum value of area ratio of ferrite in the microstructures in the ¼ width portion, the ½ width portion, and the ¾ width portion, μ.sub.dF in Expression (3) represents an average value of an average grain size of ferrite in the microstructure in the ¼ width portion, an average grain size of ferrite in the microstructure in the ½ width portion, and an average grain size of ferrite in the microstructure in the ¾ width portion, and Δ.sub.dF represents a difference between a maximum value and a minimum value of average grain size of ferrite in the microstructures in the ¼ width portion, the ½ width portion, and the ¾ width portion, Δ.sub.SUF in Expression (4) represents a difference between a maximum value and a minimum value of area ratio of unrecrystallized ferrite in the microstructures in the ¼ width portion, the ½ width portion, and the ¾ width portion, and μ.sub.dC in Expression (5) represents an average value of an average grain size of carbonitrides in the microstructure in the ¼ width portion, an average grain size of carbonitrides in the microstructure in the ½ width portion, and an average grain size of carbonitrides in the microstructure in the ¾ width portion, and AK represents a difference between a maximum value and a minimum value of average grain size of carbonitrides in the microstructures in the ¼ width portion, the ½ width portion, and the ¾ width portion.

12. The steel sheet according to claim 11 wherein the composition, includes Mn: 0.70% to 3.00% by mass %.

13. The steel sheet according to claim 11, wherein the average grain sizes of ferrite in the ¼ width portion, the ½ width portion, and the ¾ width portion is 5.0 μm to 15.0 μm.

14. The steel sheet according to claim 12, wherein the average grain sizes of ferrite in the ¼ width portion, the ½ width portion, and the ¾ width portion is 5.0 μm to 15.0 μm.

15. The steel sheet according to claim 11, comprising a galvanized layer on the surface.

16. The steel sheet according to claim 11, comprising a zinc alloy plated layer on the surface.

17. The steel sheet according to claim 15, wherein a Fe content in the galvanized layer is 7.0% to 13.0% by mass %.

18. The steel sheet according to claim 16, wherein a Fe content in the zinc alloy plated layer is 7.0% to 13.0% by mass %.

19. A method of manufacturing the steel sheet according to claim 11, comprising: a hot rolling process of heating a steel piece having the composition of said steel sheet to 1150° C. to 1320° C., completing hot rolling such that a hot rolling completion temperature is 850° C. to 930° C., starting cooling after 1.5 s or longer, cooling the steel piece to a temperature range of lower than 450° C. to obtain a hot-rolled steel sheet such that an average cooling rate in a temperature range of 800° C. to 450° C. is 20° C./s or higher; a reheating process of heating the hot-rolled steel sheet to a temperature range of 450° C. to 700° C.; a cooling process of cooling the hot-rolled steel sheet to room temperature; a cold rolling process of cold-rolling the hot-rolled steel sheet to obtain a cold-rolled steel sheet such that a total rolling reduction is 30% to 80% and a cold rolling completion temperature is 120° C. or higher; and an annealing process of heating the cold-rolled steel sheet to an annealing temperature of 720° C. to 850° C. and cooling the cold-rolled steel sheet to a temperature range of 500° C. or lower, wherein in the hot rolling process, Expression (6) is satisfied in a temperature range of 1000° C. or lower, in the reheating process, Expression (7-1) and Expression (8) are satisfied in the temperature range of 450° C. to 700° C., in the annealing process, in the process of heating to the annealing temperature, Expression (9) is satisfied in a temperature range of 550° C. to 720° C., a tension of 15 MPa or higher is applied and Expression (10) is satisfied in a temperature range of 720° C. to the annealing temperature, and in the process of cooling from the annealing temperature, Expression (11) is satisfied in a temperature range of 720° C. to 500° C., $\begin{matrix} g_{n} = (0.5 + \frac{h *}{h}) .Math. (1 + a_{1} \sqrt{Nb} + a_{2} \sqrt{T i}) & (6) \end{matrix}$ $K_{n} = (T_{n} + 273) .Math. (a_{3} + a_{4} \sqrt{N b} + a_{5} \sqrt{Ti})$ $R_{n} = (T_{n} + 273) .Math. (a_{6} + a_{7} \sqrt{N b} + a_{8} \sqrt{Ti})$ $J_{n} = {(\frac{h *}{h})}^{1.5} .Math. (a_{9} + a_{1 0} \sqrt{N b} + a_{1 1} \sqrt{Ti})$ $f_{n} = [f_{n - 1} .Math. \exp (- K_{n} .Math. t_{n}) + g_{n} .Math. {1 - \exp (- K_{n} .Math. t_{n})}] .Math. \exp (- R_{n} .Math. t_{n}) + J_{n} \leq 1.$ in Expression (6), f.sub.n represents an index representing a degree of progress of precipitation of a fine carbide in the temperature range of 1000° C. or lower of the hot rolling process, reference numerals in Expression (6) are as follows, n: the number of rolling passes at 1000° C. or lower, h: a sheet thickness [mm] before an n-th pass rolling, h*: a sheet thickness [mm] after the n-th pass rolling, Nb and Ti: contents [mass %] of Nb and Ti, T.sub.n: an average steel sheet temperature [° C.] from the n-th pass rolling to an n+1-th pass rolling, t.sub.n: a shorter time among a time [s] from the n-th pass rolling to the n+1-th pass rolling and a time [s] taken until the steel sheet temperature decreases to 800° C. from the n-th pass rolling, a.sub.1 to 11: constants (a.sub.1=2.28×100, a.sub.2=1.25×100, a.sub.3=7.86×10.sup.−4, a.sub.4=1.36×10.sup.−3, a.sub.5=6.76×10.sup.−4, a.sub.6=7.86×10.sup.−4, a.sub.7=2.13×10.sup.−3, a.sub.8=1.14×10.sup.−3, a.sub.9=6.70×10.sup.−2, a.sub.10=1.11×10.sup.0, and a.sub.11=5.27×10.sup.−1), $\begin{matrix} b_{1} .Math. {1 .00 - \exp (- \frac{b_{2} + b_{3} .Math. \sqrt{Nb} + b_{4} .Math. \sqrt{Ti * - T_{\max}}}{b_{5} + b_{6} .Math. \sqrt{Nb} + b_{7} .Math. \sqrt{Ti *}})} .Math. \sqrt{D_{2 0} .Math. t_{2 0}} \geq 1. & (7 - 1) \end{matrix}$ reference numerals in Expression (7-1) are as follows, b.sub.1 to 7: constants (b.sub.1=6.82×10.sup.6, b.sub.2=1.00×10.sup.3, b.sub.3=8.70×10.sup.1, b.sub.4=1.25×10.sup.2, b.sub.5=1.00×10.sup.2, b.sub.6=−1.50×10.sup.1, and b.sub.7=−2.50×10.sup.1), Nb: a Nb content [mass %], Ti*: an effective Ti content represented by Ti−42/14×N, where each of Ti and N represents a content by mass % of the element, and when the element is not included, 0 is substituted as the content of the element, T.sub.max: a highest heating temperature [° C.], t.sub.20: an effective heat treatment time [s] in a 20th period when a residence time in the temperature range of 450° C. to 700° C. is divided into 20 periods, D.sub.20: an index representing an effective diffusion rate in a 20th period when a residence time in the temperature range of 450° C. to 700° C. is divided into 20 periods, where an m-th effective heat treatment time t.sub.m and an index D.sub.m representing an m-th effective diffusion rate are represented by Expression (7-2), $\begin{matrix} D_{m} = \frac{T i *}{4 2} .Math. {(\frac{Ti *}{4 2} + \frac{N b}{9 2})}^{- 1} .Math. b_{8} .Math. \exp (- \frac{b_{9}}{T_{m}}) + \frac{N b}{9 2} .Math. {(\frac{Ti *}{4 2} + \frac{N b}{9 2})}^{- 1} .Math. b_{1 0} .Math. \exp (- \frac{b_{1 1}}{T_{m}}) & (7 - 2) \end{matrix}$ $t_{m} = t^{'} + \frac{D_{m - 1}}{D_{m}} .Math. t_{m - 1}$ reference numerals in Expression (7-2) are as follows, m: an integer of 1 to 20, b.sub.9 to 11: constants (b.sub.8=6.81×10.sup.1, b.sub.9=2.61×10.sup.5, b.sub.10=5.60×10.sup.0, and b.sub.11=2.86×10.sup.5), Nb: a Nb content [mass %], Ti*: an effective Ti content represented by Ti−42/14×N, where each of Ti and N represents a content by mass % of the element, and when the element is not included, 0 is substituted as the content of the element, T.sub.m: an average steel sheet temperature [° C.] in an m-th period when a residence time in the temperature range of 450° C. to 700° C. is divided into 20 periods, t.sub.m: an effective heat treatment time [s] in an m-th period when a residence time in the temperature range of 450° C. to 700° C. is divided into 20 periods, where t.sub.1=t′, t′: 1/20 [s] of an entire residence time in the temperature range of 450° C. to 700° C., $\begin{matrix} K_{j} = T_{j} .Math. (log10 (s_{j}) + 20 / (1 + 0.1 5 \times Si - 0.08 \times Mn - 0.05 \times Cr - 0.13 \times Mo)) & (8) \end{matrix}$ $s_{j} = t^{'} + 10^{\frac{T_{j - 1}}{T_{j}} .Math. \log_{10} s_{j - 1} + \frac{20}{T_{j}} .Math. \frac{T_{j} + T_{j - 1}}{1 + 0.15 Si - 0.08 M𝔫 - 0.05 Cr - 0.13 Mo}}$ $K_{2 0} ≦ 2.0 0 \times 1 0^{4}$ in Expression (8), K.sub.20 represents an index representing a degree of stabilization of cementite in a 20th period when a temperature history in the temperature range of 450° C. to 700° C. of the reheating process is divided into 20 periods with respect to time, reference numerals in Expression (8) are as follows, j: an integer of 1 to 20, each of Si, Mn, Cr, and Mo: a content [mass %] of the element, T.sub.j: an average steel sheet temperature [° C.] in a j-th period when a residence time in the temperature range of 450° C. to 700° C. is divided into 20 periods, s.sub.j: an effective heat treatment time [s] in a j-th period when a residence time in the temperature range of 450° C. to 700° C. is divided into 20 periods, where s.sub.1=t′, t′: 1/20 [s] of an entire residence time in the temperature range of 450° C. to 700° C., $\begin{matrix} E = d_{1} .Math. {(1 - \frac{h *}{h})}^{1.5} .Math. T_{R}^{- 1} .Math. {(1 + d_{2} .Math. {Nb}^{0.5} + d_{3} .Math. Ti *^{0.5})}^{- 1} .Math. K_{2}^{0.5} & (9) \end{matrix}$ $q_{n} = d_{3} .Math. E .Math. \exp (- \frac{d_{4}}{T_{n}^{'} + 273})$ $t_{n} = Δ t - \frac{\ln (1 - p_{n - 1})}{q_{n}}$ $p_{n} = 1 - \exp (- q_{n} .Math. t_{n})$ $0.1 \leq p_{1 0} \leq 1.0 0$ in Expression (9), p.sub.10 represents an index representing a degree of progress of recrystallization in a 10th period when a residence time in the temperature range of 550° C. to 720° C. in the process of heating in the annealing process is divided into 10 periods, reference numerals in Expression (9) are as follows, d.sub.1 to 4: constants (d.sub.1=4.24×10.sup.2, d.sub.2=2.10×10.sup.0, d.sub.3=1.31×10.sup.3, and d.sub.4=7.63×10.sup.3), h: a sheet thickness [mm] before cold rolling, h*: a sheet thickness [mm] after cold rolling, T.sub.R: a cold rolling completion temperature [° C.], Nb: a Nb content [mass %], Ti*: an effective Ti content represented by Ti−42/14×N, where each of Ti and N represents a content by mass % of the element, and when the element is not included, 0 is substituted as the content of the element, K.sub.2: a value obtained by Expression (7-1), n: an integer of 1 to 10, T.sub.n′: an average temperature [° C.] in an n-th period when a residence time in the temperature range of 550° C. to 720° C. is divided into 10 periods, Δ.sub.t: a time [s] in one of 10 periods into which an elapsed time until a steel sheet temperature reaches 720° C. from 550° is divided, where t.sub.1=Δt, $\begin{matrix} y_{m} = {\frac{e_{1}}{K_{2}} .Math. \exp (- \frac{e_{2}}{T_{m} + 2 7 3}) .Math. \frac{A_{c 3} - T_{m}}{A_{c 3} - A_{c 1}} .Math. t_{m}}^{1 / 2} .Math. e_{3} .Math. {(\frac{T_{m} - e_{4}}{A_{c 3} - e_{4}})}^{3} & (10) \end{matrix}$ $t_{m} = Δ t + y_{m - 1}^{2} .Math. {\frac{e_{1}}{K_{2}} .Math. \exp (- \frac{e_{2}}{T_{m} + 2 7 3}) .Math. \frac{A_{c 3} - T_{m}}{A_{c 3} - A_{c 1}}}^{- 1} .Math. {e_{3} .Math. {(\frac{T_{m} - e_{4}}{A_{c 3} - e_{4}})}^{3}}^{- 2}$ $1. 0 \leq e_{4} .Math. y_{m} .Math. {(K_{3} .Math. K_{4})}^{- \frac{1}{2}} \leq 5.0$ in Expression (10), y.sub.m represents an index representing a degree of progress of reverse transformation in an m-th period when a residence time in the temperature range of 720° C. to the annealing temperature is divided into 10 periods, reference numerals in Expression (10) are as follows, e.sub.1 to 4: constants (e.sub.1=4.50×10.sup.2, e.sub.2=2.85×10.sup.4, e.sub.3=2.24×10.sup.0, and e.sub.4=8.56×10.sup.−8), K.sub.2: a value on the left side of Expression (7-1), K.sub.3: a value of K.sub.20 obtained by Expression (8), K.sub.4: a value of p.sub.10 obtained by Expression (9), Ac.sub.1: an austenite transformation start temperature [° C.] during heating, Ac.sub.3: an austenite transformation completion temperature [° C.] during heating, T.sub.m: an average temperature [° C.] in an m-th period when a residence time in the temperature range of 720° C. to the annealing temperature is divided into 10 periods, t.sub.m: an effective heat treatment time [s] in an m-th period when a residence time in the temperature range of 720° C. to the annealing temperature is divided into 10 periods, $\begin{matrix} {.Math.}_{i = 1}^{1 0} (g_{1} + g_{2} .Math. {Nb}^{0.5} + g_{3} .Math. Ti *^{0.5}) .Math. {(1 + g_{4} .Math. {Mo}^{0.5})}^{- 1} .Math. K_{4}^{1 / 3} .Math. {(\frac{A_{c 3} - T_{\max}}{A_{c 3} - A_{c 1}})}^{1 / 3} .Math. (Δ_{i} + g_{5} .Math. Δ_{i}^{0.5}) .Math. \exp (- \frac{g_{6}}{T_{i} + 2 7 3}) .Math. t^{′0 .5} \geq 1.0 0 & (11) \end{matrix}$ reference numerals in Expression (11) are as follows, i: an integer of 1 to 10, Δ.sub.i: 750−18×Si−17×Mn−10×Cr−8×Ni+15×Al−T.sub.i, where each of the elements represents a content by mass % of the element, and when the element is not included, 0 is substituted as the content of the element, when a calculated value of Δ.sub.i is a negative value, Δ.sub.i set to 0, g.sub.1 to 6: constants (g.sub.1=1.00×10.sup.1, g.sub.2=1.46×10.sup.1, g.sub.3=1.14×10.sup.1, g.sub.4=2.24×10.sup.0, g.sub.5=4.53×10.sup.0, and g.sub.6=4.83×10.sup.3), each of Nb, Mo, Si, Mn, Cr, Ni, and Al: a content [mass %] of the element, Ti*: an effective Ti content represented by Ti−42/14×N, where each of Ti and N represents a content by mass % of the element, and when the element is not included, 0 is substituted as the content of the element, K.sub.4: a value of p.sub.10 obtained by Expression (9), Ac.sub.1: an austenite transformation start temperature [° C.] during heating, Ac.sub.3: an austenite transformation completion temperature [° C.] during heating, T.sub.max: an annealing temperature [° C.], T.sub.i: an average temperature [° C.] in an i-th period when a residence time in the temperature range of 720° C. to 500° C. is divided into 10 periods, and Δt: a time [s] in one of 10 periods into which an entire residence time in the temperature range of 720° C. to 500° C. is divided.

20. The method of manufacturing a steel sheet according to claim 19, wherein in the process of cooling in the annealing process, hot-dip galvanizing is performed on the cold-rolled steel sheet.

21. The method of manufacturing a steel sheet according to claim 19, wherein in the process of cooling in the annealing process, hot-dip zinc alloy plating is performed on the cold-rolled steel sheet.

22. The method of manufacturing a steel sheet according to claim 20, wherein in the process of cooling in the annealing process, alloying is performed after the hot-dip galvanizing.

23. The method of manufacturing a steel sheet according to claim 21, wherein in the process of cooling in the annealing process, alloying is performed after the hot-dip zinc alloy plating.

Description

EXAMPLES

[0397] Next, examples of the present invention will be described, but conditions of the examples are merely exemplary to confirm the operability and the effects of the present invention. The present invention is not limited to these condition examples. The present invention can adopt various conditions within a range not departing from the scope of the present invention as long as the object of the present invention can be achieved under the conditions.

[0398] Molten steel having a chemical composition shown in Tables 1-1 and 1-2 were cast to manufacture steel pieces. Next, hot-rolled steel sheets were obtained by hot-rolling the steel pieces under conditions shown in Tables 2-1 and 2-2. Tables 2-1 and 2-2 show f.sub.n obtained from the temperature history at 1000° C. or lower in the hot rolling process and Expression (6).

[0399] Next, the steel pieces were reheated under conditions shown in Tables 2-1 and 2-2. Tables 2-1 and 2-2 show the left side of Expression (7-1) obtained from the temperature history in a temperature range of 450° C. to 700° C. in the reheating process and Expressions (7-1) and (7-2), and show K.sub.20 obtained from the temperature history in a temperature range of 450° C. to 700° C. in the reheating process and Expression (8).

[0400] Next, steel sheets were obtained by performing cold rolling, a heat treatment (annealing), and optionally temper rolling on the hot-rolled steel sheets under conditions shown in Tables 3-1 to 3-3. For annealing, the steel sheets were heated to annealing temperatures shown in Tables 3-1 to 3-3, were retained at the temperatures for 3 s to 200 s, and subsequently were cooled.

[0401] Tables 3-1 to 3-3 show p.sub.10 obtained from the temperature history in the temperature range of 550° C. to 720° C. in the process of heating in the annealing process and Expression (9), and show e.sub.4.Math.y.sub.m.Math.(K.sub.3.Math.K.sub.4).sup.−2/1 obtained from the temperature history in the temperature range of 720° C. to the annealing temperature in the process of heating in the annealing process and Expression (10).

[0402] The plating process in Tables 3-1 to 3-3 is as follows.

[0403] Zn alloy plating: a process of cooling the steel sheet to a temperature range of 500° C. or lower in the annealing process, dipping the steel sheet in a molten zinc alloy bath, and cooling the steel sheet to room temperature to obtain a zinc alloy plated steel sheet.

[0404] Alloy Galvannealing: a process of cooling the steel sheet to a temperature range of 500° C. or lower in the annealing process, dipping the steel sheet in a molten zinc alloy bath and reheating the steel sheet to 580° C. for alloying and cooling the steel sheet to room temperature to obtain an alloy galvannealed steel sheet.

[0405] GA: a process of cooling the steel sheet to a temperature range of 500° C. or lower in the annealing process, dipping the steel sheet in a molten zinc bath and reheating the steel sheet to 560° C. for alloying and cooling the steel sheet to room temperature to obtain a hot-dip galvannealed steel sheet (GA).

[0406] GI: a process of cooling the steel sheet to a temperature range of 500° C. or lower in the annealing process, dipping the steel sheet in a molten zinc bath, and cooling the steel sheet to room temperature to obtain a hot-dip galvanized steel sheet (GI).

[0407] Deposition: a process of performing deposition plating after the annealing process to obtain a galvanized steel sheet.

[0408] EG: a process of performing electrogalvanizing after the annealing process to obtain an electrogalvanized steel sheet (EG).

[0409] Test pieces (three in total) having, as an observed section, a cross section parallel to a rolling direction of the steel sheet and perpendicular to a steel sheet surface were collected from the ¼ width portion, the ½ width portion, and the ¾ width portion of each of the steel sheets obtained under the manufacturing conditions shown in Tables 4-1 to 4-6 and Tables 1-1 to 3-3, and microstructures were observed. As the results of the structure observation performed using the above-described method, Tables 4-1 to 4-6 show the area ratio of ferrite, the proportion of unrecrystallized ferrite in ferrite, the area ratio of martensite, the volume percentage of residual austenite, the average grain size of carbonitrides, the average grain size of ferrite, and the left sides of Expressions (2) to (4). The sheet thickness of the steel sheet was the same as the sheet thickness after rolling shown in Tables 3-1 to 3-3.

[0410] Regarding the alloyed steel sheet, The Fe content in the alloyed hot-dip galvanized layer (galvannealed layer) or the alloyed hot-dip zinc alloy plated layer (alloy galvannealed layer) was measured using the above-described method.

[0411] The plated layers shown in Tables 4-1 to 4-6 are as follows.

[0412] Zn alloy plated: zinc alloy plated layer

[0413] Alloy Galvannealed: alloy galvannealed layer

[0414] GA: hot-dip galvannealed layer formed by dipping the steel sheet in a molten zinc bath and alloying the steel sheet

[0415] GI: hot-dip galvanized layer formed by dipping the steel sheet in a molten zinc bath

[0416] Deposited: galvanized layer formed by deposition plating EG: galvanized layer formed by electrogalvanizing

[0417] Tables 5-1 to 5-3 show the properties of the steel sheets obtained under the manufacturing conditions of Tables 1-1 to 3-3. Regarding the tensile properties, the 0.2% proof stress (YS: yield strength), the tensile strength (TS), the yield ratio (YR), and the uniform elongation (uEl) were evaluated. The 0.2% proof stress, the tensile strength, the yield ratio, and the uniform elongation were obtained by performing a tensile test. A 13B test piece was prepared according to JIS Z 2241:2011, and the rolling direction of the steel sheet is set as a tension axis to perform the tensile test. The rolling direction of the steel sheet was set as the tension axis, and tensile test pieces were collected from a ¼ width position from a sheet width direction end portion in the sheet width direction, a ½ width position from the sheet width direction end portion in the sheet width direction, and a ¾ width position from the sheet width direction end portion in the sheet width direction. By calculating the average values of the 0.2% proof stress, the tensile strength, and the uniform elongation obtained from the three tensile test pieces, the 0.2% proof stress, the tensile strength, and the uniform elongation were obtained. By dividing the average value of tensile strength by the average value of 0.2% proof stress, the yield ratio was obtained.

[0418] A steel sheet in which the 0.2% proof stress was 280 MPa to 600 MPa, the yield ratio was 0.50 to 0.90, and the uniform elongation was 10.0% or more was determined to have excellent formability and as “Pass”. A steel sheet in which the 0.2% proof stress was lower than 280 MPa or higher than 600 MPa, the yield ratio was lower than 0.50 or higher than 0.90, or the uniform elongation was less than 10.0% was determined to have poor formability and as “Fail”.

[0419] A steel sheet in which the tensile strength was 450 MPa to 800 MPa was determined to have an excellent strength and as “Pass”. On the other hand, a steel sheet in which the tensile strength was lower than 450 MPa was determined to have a poor strength and as “Fail”.

[0420] The homogeneity of the steel sheet was evaluated from Expressions (12), (13), and (14). A steel sheet that satisfied Expressions (12), (13), and (14) was determined to be homogeneous, to have excellent dimensional accuracy during press forming, and as “Pass”. A steel sheet that did not satisfy any one of Expressions (12), (13), and (14) was determined to be inhomogeneous, to have poor dimensional accuracy during press forming, and as “Fail”.

[0421] YS in Expression (12) was the average value of 0.2% proof stress obtained using the above-described method at the ¼ width position from the sheet width direction end portion in the sheet width direction, the ½ width position from the sheet width direction end portion in the sheet width direction, and the ¾ width position from the sheet width direction end portion in the sheet width direction. Δ.sub.YS in Expression (12) was obtained using the above-described method by calculating a difference between a maximum value and a minimum value among the values of 0.2% proof stress at the ¼ width position from the sheet width direction end portion in the sheet width direction, the ½ width position from the sheet width direction end portion in the sheet width direction, and the ¾ width position from the sheet width direction end portion in the sheet width direction.

[0422] uEl in Expression (13) was the average value of uniform elongation obtained using the above-described method at the ¼ width position from the sheet width direction end portion in the sheet width direction, the ½ width position from the sheet width direction end portion in the sheet width direction, and the ¾ width position from the sheet width direction end portion in the sheet width direction. Δ.sub.uEl in Expression (13) was obtained using the above-described method by calculating a difference between a maximum value and a minimum value among the values of uniform elongation at the ¼ width position from the sheet width direction end portion in the sheet width direction, the ½ width position from the sheet width direction end portion in the sheet width direction, and the ¾ width position from the sheet width direction end portion in the sheet width direction.

[0423] In order to obtain am in Expression (14), one tensile test piece is collected from each of the ¼ width position from the sheet width direction end portion in the sheet width direction, the ½ width position from the sheet width direction end portion in the sheet width direction, and the ¾ width position from the sheet width direction end portion in the sheet width direction, that is, three test pieces in total were collected. A deformation at a bending angle of 90° was applied to the test pieces in a bending test defined by the standard 238-100 of Verband der Automobilindustrie (VDA) in December, 2010, and plastic bending angles α of the test pieces after removing the load were measured. α.sub.M was an angle of the test piece having the maximum difference from 90° among the measured values of the plastic bending angles α. That is, am is the maximum value of the absolute value of “α−90°”, and α.sub.M/90 is an index representing the size of a dimensional dispersion after press forming obtained by non-dimensionalizing the plastic bending angle α.sub.M by 90°. In addition, conditions were set in the VDA bending test.

[0424] Roll diameter; ϕ30 mm

[0425] Distance between rolls: 2×sheet thickness+0.5±0.05 mm

[0426] Punch shape: tip end R=0.4 mm

[0427] Punch pressing-in speed: 20 mm/min

[0428] Test piece dimension: sheet thickness×60 mm×60 mm

[0429] Bending direction: direction perpendicular to the rolling direction The plastic bending angle is a measured value of a bending inner angle among angles formed by extended lines of two flat portions of the test piece that is deformed in a “V-shape” in the bending test.

Δ.sub.YS/YS≤0.20 (12)

Δ.sub.uEl/uEl≤0.25 (13)

0.90≤α.sub.M/90≤1.10 (14)

TABLE-US-00001 TABLE 1-1 Middle Side in Composition, mass %, Remainder including Fe and Impurities Expression Steel C Si Mn Al P S Ti Nb N O Others (1-2) Ac.sub.3 Ac.sub.1 Note A 0.095 0.018 1.23 0.039 0.023 0.0036 0.037 0.012 0.0058 0.0006 0.06 838 704 Example B 0.038 0.256 1.72 0.014 0.006 0.0049 0.063 0.0035 0.0018 0.34 843 715 Example C 0.078 0.048 0.48 0.091 0.013 0.0009 0.035 0.0045 0.0012 0.06 865 723 Example D 0.105 1.374 1.71 0.009 0.015 0.0038 0.034 0.031 0.0016 0.0016 0.11 862 733 Example E 0.046 0.066 1.18 0.249 0.009 0.0014 0.025 0.0043 0.0022 B: 0.0032 0.06 882 725 Example F 0.104 0.932 0.75 0.091 0.021 0.0017 0.023 0.047 0.0025 0.0008 0.09 879 734 Example G 0.088 0.099 2.17 0.067 0.016 0.0039 0.089 0.0074 0.0015 0.18 825 697 Example H 0.135 0.179 1.60 0.472 0.009 0.0043 0.044 0.0026 0.0008 0.04 862 720 Example I 0.123 0.694 0.98 0.076 0.018 0.0012 0.034 0.024 0.0027 0.0011 Cr: 0.65 0.08 852 738 Example J 0.058 0.038 1.07 0.184 0.046 0.0067 0.025 0.017 0.0057 0.0007 Ca: 0.0033 0.06 864 715 Example K 0.064 0.357 1.64 0.073 0.008 0.0019 0.075 0.012 0.0036 0.0018 Mo: 0.33 0.27 846 707 Example L 0.118 0.013 0.78 0.037 0.021 0.0082 0.018 0.056 0.0041 0.0013 0.07 843 710 Example M 0.072 0.154 0.16 0.042 0.006 0.0018 0.057 0.0067 0.0018 Ni: 0.59 0.12 856 712 Example N 0.077 0.045 1.82 0.867 0.007 0.0045 0.008 0.047 0.0016 0.0024 0.09 998 745 Example O 0.085 0.599 2.83 0.071 0.009 0.0014 0.046 0.007 0.0042 0.0015 0.10 821 684 Example P 0.114 0.153 1.26 0.050 0.015 0.0037 0.048 0.0055 0.0016 V: 0.15 0.05 838 708 Example Q 0.081 0.214 1.94 0.096 0.003 0.0008 0.036 0.015 0.0034 0.0030 W: 0.20 0.10 842 698 Example The underline represents that the value is outside of the range of the present invention, and the blank represents that the value is less than the lower detection limit.

TABLE-US-00002 TABLE 1-2 Middle Side in Composition, mass %, Remainder including Fe and Impurities Expression Steel C Si Mn Al P S Ti Nb N O Others (1-2) Ac.sub.3 Ac.sub.1 Note R 0.057 0.054 0.62 0.033 0.021 0.0058 0.029 0.037 0.0115 0.0014 Mg: 0.08 864 715 Example 0.0024 S 0.091 1.097 1.22 0.038 0.013 0.0059 0.050 0.0026 0.0008 Sb: 0.11 874 727 Example 0.13 T 0.046 1.038 2.32 0.023 0.009 0.0017 0.068 0.027 0.0036 0.0007 0.38 854 707 Example U 0.113 0.428 1.05 0.080 0.018 0.0050 0.058 0.0082 0.0017 Sn: 0.07 850 720 Example 0.17 V 0.122 0.089 2.34 0.134 0.015 0.0035 0.021 0.019 0.0022 0.0009 Ce: 0.05 821 689 Example 0.0019, La: 0.0011 W 0.059 0.057 0.38 0.064 0.021 0.0039 0.070 0.0056 0.0010 Cr: 0.22 867 724 Example 0.20, Mo: 0.07, B: 0.0011 X 0.103 0.066 1.09 0.257 0.014 0.0026 0.036 0.0085 0.0010 Cu: 0.05 860 717 Example 0.22, Ni: 0.08 Y 0.071 0.942 1.37 0.075 0.008 0.0045 0.065 0.026 0.0051 0.0016 Cu: 0.21 868 722 Example 0.34 Z 0.067 0.435 2.00 0.075 0.010 0.0011 0.025 0.0032 0.0020 0.05 840 700 Example AA 0.102 0.194 1.21 0.097 0.013 0.0061 0.015 0.013 0.0058 0.0011 0.02 846 712 Comparative Example AB 0.050 0.374 1.32 0.091 0.009 0.0049 0.073 0.045 0.0038 0.0014 0.42 862 713 Comparative Example AC 0.084 0.136 1.36 0.082 0.009 0.0059 0.117 0.0055 0.0017 0.29 843 706 Comparative Example AD 0.069 0.180 1.41 0.074 0.023 0.0029 0.079 0.0052 0.0007 0.15 848 703 Comparative Example AE 0.013 0.214 1.44 0.098 0.021 0.0058 0.037 0.0065 0.0017 0.28 878 762 Comparative Example AF 0.189 0.174 1.49 0.099 0.007 0.0280 0.058 0.031 0.0044 0.0012 0.08 820 705 Comparative Example AG 0.082 0.088 0.69 0.014 0.012 0.0021 0.0032 0.0011 — 845 712 Comparative Example AH 0.051 1.223 0.22 0.038 0.012 0,0018 0.061 0.0029 0.0011 0.25 886 703 Example The underline represents that the value is outside of the range of the present invention, and the blank represents that the value is less than the lower detection limit.

TABLE-US-00003 TABLE 2-1 Cold Rolling Process Time Average Required Cooling Rate in Reheating Process Hot- Steel Piece Rolling for Temperature Maximum Left side Rolled Heating Completion Start of Range of 800° C. Reheating in Steel Temperature Temperature Cooling to 450° C. Temperature Expression K.sub.20 Steel Sheet ° C. ° C. f.sub.n s ° C./s ° C. (7-1) ×10.sup.4 Note A A1 1276 903 0.57 2.3 37 658 6.00 1.84 Example A A2 1260 891 0.88 2.0 50 608 40.20 1.94 Example A A3 1233 831 0.66 2.4 45 582 15.72 1.85 Comparative Example B B1 1253 873 0.68 1.7 47 584 41.59 1.92 Example B B2 1239 904 0.63 2.2 61 657 10.77 1.88 Example B B3 1140 912 0.42 3.5 33 575 15.21 1.91 Comparative Example C C1 1269 894 0.58 1.7 30 593 1.90 1.79 Example C C2 1242 878 0.24 1.8 49 539 1.59 1.75 Example C C3 1247 918 0.27 2.3 14 629 4.64 1.88 Comparative Example D D1 1216 913 0.71 2.2 34 471 1.52 1.38 Example D D2 1240 864 0.31 5.1 36 605 3.66 1.46 Example E E1 1275 880 0.14 4.1 47 525 3.61 1.68 Example E E2 1244 872 0.56 1.7 23 568 1.30 1.63 Example F F1 1282 890 0.59 1.6 27 550 1.91 1.40 Example F F2 1308 892 0.33 4.2 34 693 9.34 1.59 Example F F3 1274 876 1.11 1.6 60 602 7.66 1.52 Comparative Example G G1 1288 907 0.44 2.3 25 626 4.99 1.93 Example G G2 1259 880 0.77 1.9 54 539 3.25 1.84 Example H H1 1252 889 0.37 3.3 38 585 2.57 1.95 Example H H2 1226 863 0.47 1.8 73 635 1.83 1.96 Example I I1 1181 897 0.76 1.9 39 685 35.60 1.83 Example I I2 1266 880 0.39 3.4 41 540 11.10 1.64 Example I I3 1300 916 0.45 3.2 31 612 9.37 1.66 Example J J1 1204 890 0.73 1.8 53 549 4.48 1.72 Example J J2 1229 874 0.25 3.1 79 522 9.65 1.76 Example K K1 1259 889 0.75 2.1 43 594 1.99 1.75 Example K K2 1226 900 0.41 4.6 49 641 5.00 1.85 Example K K3 1211 905 0.48 1.2 63 592 1.92 1.75 Comparative Example L L1 1214 895 0.33 4.8 29 578 11.26 1.89 Example L L2 1206 875 0.31 4.2 83 537 5.91 1.82 Example L L3 1257 877 0.34 3.1 47 726 — — Comparative Example M M1 1254 899 0.27 4.3 30 594 6.35 1.58 Example M M2 1253 875 0.52 2.2 42 595 2.84 1.52 Example M M3 1355 901 0.60 4.2 49 672 17.28 1.71 Comparative Example N N1 1253 904 0.63 1.7 38 498 3.44 1.84 Example N N2 1168 893 0.63 1.7 44 599 1.40 1.85 Example The underline represents that the value is outside of the range of the present invention.

TABLE-US-00004 TABLE 2-2 Cold Rolling Process Average Cooling Time Rate in Required Temperature Reheating Process Hot- Steel Piece Rolling for Start Range of Maximum Rolled Heating Completion of 800° C. to Reheating Left side in Steel Temperature Temperature Cooling 450° C. Temperature Expression K.sub.20 Steel Sheet ° C. ° C. f.sub.n s ° C./s ° C. (7-1) ×10.sup.4 Note O O1 1245 919 0.75 1.8 42 650 5.97 1.92 Example O O2 1284 863 0.55 2.5 32 574 1.84 1.77 Example O O3 1238 898 0.54 2.4 36 435 — — Comparative Example P P1 1249 876 0.76 1.9 39 540 1.84 1.85 Example P P2 1232 902 0.41 2.5 67 615 4.13 1.96 Example Q Q1 1250 905 0.80 1.8 32 540 2.62 1.75 Example Q Q2 1241 889 0.78 1.9 41 464 3.39 1.73 Example R R1 1245 905 0.41 2.1 57 611 1.70 1.81 Example R R2 1248 912 0.46 2.0 60 665 4.89 1.94 Example S S1 1193 919 0.57 2.1 29 643 49.42 1.68 Example S S2 1263 887 0.74 1.5 41 519 4.51 1.45 Example T T1 1266 897 0.68 3.0 52 538 2.33 1.56 Example T T2 1264 886 0.92 1.9 42 565 3.82 1.61 Example T T3 1245 943 0.80 1.7 35 623 12.15 1.72 Comparative Example U U1 1240 887 0.42 2.5 23 605 8.48 1.66 Example U U2 1225 882 0.37 2.4 34 575 4.85 1.61 Example V V1 1286 921 0.67 1.9 61 627 3.10 1.96 Example V V2 1275 925 0.36 3.5 47 527 1.22 1.81 Example W W1 1273 908 0.48 2.5 29 586 7.69 1.68 Example W W2 1308 886 0.42 3.5 38 597 33.46 1.80 Example X X1 1219 892 0.40 2.3 36 623 2.65 1.93 Example X X2 1295 904 0.39 3.3 25 517 1.14 1.80 Example X X3 1267 914 0.42 2.5 37 663 5.21 2.02 Comparative Example Y Y1 1254 878 0.38 4.0 36 574 23.87 1.64 Example Y Y2 1255 881 0.46 3.6 48 636 73.40 1.76 Example Z Z1 1221 911 0.12 5.1 35 625 2.14 1.95 Example Z Z2 1224 878 0.25 4.2 47 558 1.09 1.85 Example Z Z3 1258 901 0.49 2.1 41 579 0.79 1.84 Comparative Example AA AA 1223 894 0.23 3.2 32 594 1.19 1.83 Comparative Example AB AB 1244 896 0.81 2.1 57 644 6.89 1.73 Comparative Example AC AC 1270 867 0.57 3.2 40 633 6.44 1.79 Comparative Example AD AD 1274 900 0.40 3.6 40 618 1.94 1.92 Comparative Example AE AE 1242 888 0.40 2.5 54 579 2.29 1.67 Comparative Example AF AF 1245 916 0.82 2.1 43 612 3.98 1.76 Comparative Example AG AG 1222 906 0.50 3.3 53 624 — 1.44 Comparative Example AH AH 1204 894 1.06 1.6 56 450 — — Comparative Example The underline represents that the value is outside of the range of the present invention.

TABLE-US-00005 TABLE 3-1 Annealing Cold Rolling Process Temperature Sheet Sheet Process of Hot- Thickness Thickness Total Rolling Heating Rolled before after Rolling Completion Annealing Experiment Steel Rolling Rolling Reduction Temperature Temperature Example Steel Sheet mm mm % ° C. ° C. 1 A A1 3.9 2.2 44 175 779 2 A A1 3.9 2.2 44 99 770 3 A A2 2.8 1.0 64 190 814 4 A A3 3.3 1.2 64 196 789 5 B B1 3.5 1.0 71 154 790 6 B B2 2.1 0.7 67 175 770 7 B B3 2.9 1.0 66 172 787 8 C C1 4.3 1.8 58 170 804 9 C C1 4.3 1.8 58 188 813 10 C C1 4.3 1.8 58 188 810 11 C C2 1.8 0.8 56 185 795 12 C C3 1.9 0.8 58 183 811 13 D D1 4.9 2.0 59 136 789 14 D D2 4.7 1.4 70 164 775 15 E E1 2.0 0.6 70 168 789 16 E E2 2.8 1.8 36 196 784 17 F F1 3.5 1.4 60 202 796 18 F F1 3.5 0.6 83 190 806 19 F F1 3.5 1.4 60 202 791 20 F F2 2.4 0.8 67 161 807 21 F F3 4.8 2.0 58 173 797 22 G G1 2.6 0.8 69 164 769 23 G G2 3.2 0.7 78 191 771 24 H H1 3.5 1.8 49 143 809 25 H H2 1.6 0.4 75 174 805 26 I I1 2.1 0.5 76 180 779 27 I I2 3.3 1.6 52 136 812 28 I I3 4.0 2.3 43 160 776 29 J J1 5.2 2.4 54 156 767 30 J J2 1.8 1.0 44 121 786 Annealing Temperature Temper Process of Rolling Cooling Process Left Total Process of Heating Side of Rolling Experiment Tension e.sub.4 .Math. ym Expression Reduction Plating Example MPa p.sub.10 (K.sub.3 .Math. K.sub.4).sup.−1/2 (11) % Process Note 1 18 0.58 1.8 1.40 0.50 Example 2 41 0.12 2.3 1.54 0.20 Comparative Example 3 16 0.76 1.4 1.11 0.83 Example 4 19 0.67 1.5 1.18 0.36 Comparative Example 5 26 0.53 1.6 1.19 0.14 GA Example 6 29 0.97 1.1 1.06 0.58 Example 7 21 0.62 1.5 1.47 0.34 Comparative Example 8 28 0.69 3.7 1.31 1.35 Example 9 22 0.08 4.3 2.43 0.42 Comparative Example 10 18 0.75 6.4 1.55 0.33 Comparative Example 11 20 0.65 4.2 1.80 0.33 GA Example 12 28 0.85 4.4 1.17 0.21 Comparative Example 13 23 0.30 2.0 1.11 0.44 GA Example 14 24 0.45 2.4 1.18 0.43 Example 15 21 0.54 1.7 1.40 0.18 GI Example 16 27 0.35 3.4 1.36 0.73 Example 17 28 0.32 4.5 1.27 0.40 Example 18 29 0.39 3.5 1.17 0.52 Comparative Example 19 26 0.32 3.5 0.84 0.56 Comparative Example 20 34 0.77 2.3 1.24 0.26 Zn Example Alloy Plating 21 25 0.76 2.0 1.56 0.19 Comparative Example 22 26 0.54 1.5 1.32 0.28 Example 23 30 0.96 1.8 1.35 0.46 Example 24 30 0.52 4.2 1.47 0.19 GI Example 25 26 0.86 3.5 1.17 0.67 Example 26 23 0.20 1.7 1.25 0.14 Example 27 26 0.69 4.8 1.16 0.18 Example 28 18 0.39 1.4 1.11 — Example 29 25 0.58 1.5 1.12 0.22 Example 30 28 0.15 2.2 2.29 0.47 GA Example The underline represents that the value is outside of the range of the present invention.

TABLE-US-00006 TABLE 3-2 Annealing Cold Rolling Process Temperature Sheet Sheet Process of Hot- Thickness Thickness Total Rolling Heating Rolled before after Rolling Completion Annealing Experiment Steel Rolling Rolling Reduction Temperature Temperature Example Steel Sheet mm mm % ° C. ° C. 31 K K1 4.2 2.2 48 149 745 32 K K1 4.2 2.2 48 191 759 33 K K2 3.3 2.2 33 160 759 34 K K3 3.8 1.4 63 147 750 35 L L1 2.0 1.0 50 185 825 36 L L2 1.4 0.4 71 189 752 37 L L2 1.4 0.4 71 167 765 38 L L3 1.8 0.6 67 200 795 39 M M1 4.8 2.6 46 188 799 40 M M2 3.8 1.0 74 145 782 41 M M3 3.8 1.6 58 168 801 42 N N1 3.4 2.0 41 127 838 43 N N2 2.2 0.6 73 126 813 44 O O1 24 1.0 58 158 746 45 O O2 5.5 1.8 67 179 735 46 O O2 5.5 1.8 67 142 857 47 O O3 3.7 2.0 46 159 730 48 P P1 5.3 2.4 55 130 770 49 P P1 5.3 2.4 55 179 707 50 P P1 5.3 2.4 55 130 780 51 P P2 2.3 1.0 57 169 774 52 Q Q1 2.5 1.2 52 192 747 53 Q Q2 3.9 1.8 54 209 787 54 R R1 2.9 1.8 38 188 762 55 R R2 3.5 1.8 49 175 810 56 S S1 3.3 1.2 64 185 826 57 S S2 2.9 1.0 66 148 796 59 T T1 4.6 2.3 50 151 780 60 T T2 4.5 2.4 47 145 770 Temper Annealing Temperature Rolling Process of Process Cooling Total Process of Heating Left Side of Rolling Experiment Tension e.sub.4 .Math. ym Expression Reduction Plating Example MPa p.sub.10 (K.sub.3 .Math. K.sub.4).sup.−1/2 (11) % Process Note 31 20 0.24 1.3 1.08 0.59 Example 32 — 0.24 1.3 1.08 0.22 Comparative Example 33 33 0.19 2.0 1.17 0.55 Example 34 35 0.32 1.6 1.04 0.30 Comparative Example 35 30 0.92 1.7 1.07 0.25 Example 36 19 0.13 1.5 2.34 0.44 Example 37 35 0.66 0.7 1.34 0.19 Comparative Example 38 38 — — — 0.34 Comparative Example 39 34 0.46 2.6 1.79 0.87 GA Example 40 17 0.52 3.2 1.31 0.28 GA Example 41 29 0.85 2.3 1.50 0.28 Comparative Example 42 23 0.43 3.3 1.51 0.28 Example 43 29 0.49 2.8 2.14 0.34 GI Example 44 24 0.13 1.2 1.43 0.47 Example 45 29 0.12 1.2 1.70 0.21 GI Example 46 29 0.85 — 0.00 0.24 Comparative Example 47 26 — — — 0.57 Comparative Example 48 29 0.42 2.0 1.29 0.22 Alloy Example Galvannealing 49 26 — — — 0.50 Comparative Example 50 20 0.12 6.0 2.63 0.41 Comparative Example 51 19 0.52 1.3 1.43 0.33 Example 52 20 0.14 3.0 2.18 0.37 Alloy Example Galvannealing 53 22 0.35 3.1 1.68 0.43 Example 54 25 0.18 2.0 2.13 0.35 EG Example 55 25 0.32 2.2 1.55 1.78 Example 56 29 0.82 1.6 1.09 1.41 Example 57 23 0.25 3.8 1.47 0.48 Deposition Example 59 25 0.22 3.6 1.55 1.31 Example 60 31 0.82 1.2 1.23 0.49 Example The underline represents that the value is outside of the range of the present invention.

TABLE-US-00007 TABLE 3-3 Annealing Cold Rolling Process Temperature Sheet Sheet Process of Hot- Thickness Thickness Total Rolling Heating Rolled before after Rolling Completion Annealing Experiment Steel Rolling Rolling Reduction Temperature Temperature Example Steel Sheet mm mm % ° C. ° C. 61 T T3 4.0 2.2 45 164 773 62 U U1 3.4 1.8 47 203 779 63 U U2 4.5 1.8 60 146 730 64 V V1 2.0 0.8 60 162 762 65 V V2 2.9 1.8 38 161 760 66 W W1 3.3 1.4 58 172 799 67 W W2 3.6 1.6 56 206 802 68 X X1 3.0 1.0 67 157 804 69 X X1 3.0 2.3 23 221 809 70 X X2 2.4 0.6 75 226 764 71 X X3 3.0 1.6 47 209 764 72 Y Y1 2.2 0.6 73 153 828 74 Z Z1 2.9 1.0 66 199 742 75 Z Z2 3.0 1.0 67 185 785 76 Z Z3 4.6 2.6 43 170 743 77 AA AA 3.7 2.0 46 176 758 78 AB AB 2.1 1.2 43 183 784 79 AC AC 3.9 1.6 59 176 784 80 AD AD 4.6 1.8 61 183 774 81 AE AE 4.0 1.6 60 174 783 82 AF AF 4.0 1.6 60 190 768 83 AG AG 3.0 1.2 60 146 778 84 AH AH 1.7 0.8 53 93 771 Annealing Temperature Temper Process of Rolling Cooling Process Left Total Process of Heating Side of Rolling Experiment Tension e.sub.4 .Math. ym Expression Reduction Plating Example MPa p.sub.10 (K.sub.3 .Math. K.sub.4).sup.−1/2 (11) % Process Note 61 28 0.47 1.5 1.27 0.32 Comparative Example 62 18 0.60 1.9 1.50 0.26 GI Example 63 27 0.33 1.7 1.90 0.59 Example 64 18 0.16 1.5 1.50 0.15 Example 65 19 0.14 1.7 1.84 0.30 Example 66 23 0.61 2.8 1.10 0.43 Example 67 27 0.72 2.0 1.09 0.45 EG Example 68 24 0.61 4.3 1.19 0.46 Example 69 27 0.25 2.1 1.44 0.73 Comparative Example 70 20 0.69 1.5 1.29 0.27 Zn Example Plating 71 27 0.25 1.4 1.19 0.24 Comparative Example 72 39 0.77 2.1 1.10 0.42 Example 74 30 0.13 1.1 1.08 0.34 Example 75 29 0.51 4.0 1.32 1.22 Example 76 32 0.17 1.5 1.19 0.88 Comparative Example 77 27 0.22 1.7 1.40 0.26 Comparative Example 78 29 0.32 2.7 1.45 0.38 Comparative Example 79 28 0.76 1.3 1.21 0.14 Comparative Example 80 22 0.23 3.2 1.29 0.34 Comparative Example 81 21 0.33 1.7 1.22 0.32 Comparative Example 82 22 0.28 2.4 1.41 0.11 Comparative Example 83 25 — — — 0.25 Comparative Example 84 22 — — — 0.28 Comparative Example The underline represents that the value is outside of the range of the present invention.

TABLE-US-00008 TABLE 4-1 Properties of Steel Sheet ¼ Width Portion Average Grain Size of Hot- Proportion of Carbonitrides Rolled Unrecrystallized Residual including Ti Experiment Steel Ferrite Ferrite Martensite Austenite and/or Nb Example Steel Sheet Vol % % Vol % Vol % nm 1 A A1 89 18 0 0 7.5 2 A A1 86 71 0 0 8.6 3 A A2 88 7 0 0 22.5 4 A A3 85 17 0 0 15.4 5 B B1 90 35 0 0 16.3 6 B B2 92 35 1 0 10.7 7 B B3 91 14 0 0 28.7 8 C C1 82 12 0 0 8.7 9 C C1 89 59 1 0 8.3 10 C C1 83 8 0 0 8.6 11 C C2 90 11 0 0 7.5 12 C C3 81 15 0 0 6.2 13 D D1 83 20 0 1 8.3 14 D D2 88 29 0 0 12.5 15 E E1 91 26 0 0 14.4 16 E E2 90 15 0 0 8.7 17 F F1 81 18 0 0 8.0 18 F F1 81 16 0 0 8.8 19 F F1 82 23 0 4 10.9 20 F F2 83 29 0 0 8.6 21 F F3 90 29 0 0 10.1 22 G G1 83 22 1 0 9.6 23 G G2 92 11 0 0 10.9 24 H H1 89 24 0 0 6.1 25 H H2 86 13 0 0 6.9 26 I I1 82 35 0 0 16.6 27 I I2 86 30 0 0 8.6 28 I I3 86 43 0 0 9.6 Properties of Steel Sheet ¼ Width ½ Width Portion Portion Average Average Grain Size of Average Grain Proportion of Carbonitrides Grain Size of Unrecrystallized including Ti Size of Experiment Ferrite Ferrite Ferrite Martensite Residual and/or Nb Ferrite Example μm Vol % % Vol % Austenite nm μm 1 7.6 87 20 0 0 8.1 8.2 2 6.2 87 73 0 0 8.9 6.7 3 6.9 85 8 0 0 23.7 7.8 4 9.7 86 19 0 0 16.2 8.4 5 6.5 95 36 0 0 16.3 6.5 6 5.3 96 35 1 0 11.8 5.6 7 6.8 96 14 0 0 31.7 7.7 8 8.6 87 13 0 0 9.5 8.7 9 6.7 86 65 1 0 8.4 6.3 10 9.0 87 9 0 0 9.5 9.5 11 10.5 87 11 0 0 8.1 10.6 12 10.1 86 16 0 0 6.9 10.6 13 8.6 87 20 0 1 8.4 8.6 14 9.3 88 30 0 0 13.6 9.9 15 12.4 93 28 0 0 15.2 13.0 16 11.7 94 12 0 0 9.2 11.9 17 7.1 86 17 0 0 7.0 7.0 18 7.9 86 14 0 0 8.9 8.0 19 6.9 87 19 0 4 10.9 7.5 20 9.5 86 30 0 0 9.4 10.3 21 6.8 87 31 0 0 11.0 6.9 22 6.7 90 25 1 0 9.8 7.2 23 6.2 90 13 0 0 11.4 6.3 24 9.0 81 26 0 0 6.8 9.3 25 7.9 82 10 0 0 7.3 8.3 26 7.2 85 42 0 0 17.1 7.6 27 9.2 83 29 0 0 9.1 8.9 28 10.5 85 50 0 0 10.1 11.1 The underline represents that the value is outside of the range of the present invention or is not preferable.

TABLE-US-00009 TABLE 4-2 Properties of Steel Sheet ¾ Width Portion Average Grain Size of Average Hot- Proportion of Carbonitrides Grain Rolled Unrecrystallized Residual including Ti Size of Experiment Steel Ferrite Ferrite Martensite Austenite and/or Nb Ferrite Example Steel Sheet Vol % % Vol % Vol % nm μm 1 A A1 85 22 0 0 9.1 8.3 2 A A1 83 49 0 0 11.2 5.9 3 A A2 81 11 0 0 31.6 6.9 4 A A3 97 20 0 0 18.4 7.9 5 B B1 93 46 0 0 19.8 7.7 6 B B2 95 26 1 0 14.1 5.8 7 B B3 95 22 0 0 42.8 7.8 8 C C1 85 16 0 0 10.3 8.1 9 C C1 87 47 1 0 10.7 5.8 10 C C1 93 24 0 0 10.1 9.6 11 C C2 91 14 0 0 9.1 9.2 12 C C3 94 22 0 0 8.8 9.9 13 D D1 84 25 0 1 10.8 9.8 14 D D2 84 38 0 0 15.0 10.3 15 E E1 91 31 0 0 18.6 13.7 16 E E2 94 20 0 0 11.5 11.1 17 F F1 82 21 0 0 6.6 6.0 18 F F1 85 30 0 0 11.1 10.0 19 F F1 80 17 0 4 13.5 8.1 20 F F2 91 23 0 0 10.8 10.3 21 F F3 90 32 0 0 18.1 8.5 22 G G1 83 19 1 0 13.3 7.4 23 G G2 92 17 0 0 13.9 6.9 24 H H1 88 28 0 0 7.3 10.2 25 H H2 86 18 0 0 9.2 8.6 26 I I1 85 44 0 0 21.8 7.6 27 I I2 86 35 0 0 10.8 8.3 28 I I3 80 56 0 0 12.4 11.5 Properties of Steel Sheet Fe Left Left Left Left Content in Side of Side of Side of Side of Plated Experiment Expression Expression Expression Expression Plated Layer Example (2) (3) (4) (5) Layer mass % Note 1 0.05 0.09 4 0.19 Example 2 0.05 0.13 24 0.27 Comparative Example 3 0.08 0.13 4 0.35 Example 4 0.13 0.21 3 0.18 Comparative Example 5 0.05 0.17 11 0.20 GA 10.3 Example 6 0.04 0.09 9 0.28 Example 7 0.05 0.13 8 0.41 Comparative Example 8 0.06 0.07 4 0.17 Example 9 0.03 0.14 18 0.26 Comparative Example 10 0.11 0.06 16 0.16 Comparative Example 11 0.04 0.14 3 0.19 GA 8.7 Example 12 0.15 0.07 7 0.36 Comparative Example 13 0.05 0.13 5 0.27 GA 12.6 Example 14 0.05 0.10 9 0.18 Example 15 0.02 0.10 5 0.26 GI 0.4 Example 16 0.04 0.07 8 0.29 Example 17 0.06 0.16 4 0.19 Example 18 0.06 0.24 16 0.24 Comparative Example 19 0.08 0.16 6 0.22 Comparative Example 20 0.09 0.08 7 0.23 Zn 4.2 Example Plated 21 0.03 0.23 3 0.61 Comparative Example 22 0.08 0.10 6 0.34 Example 23 0.02 0.11 6 0.25 Example 24 0.09 0.13 4 0.18 GI 1.8 Example 25 0.05 0.08 8 0.29 Example 26 0.04 0.05 9 0.28 Example 27 0.04 0.10 6 0.23 Example 28 0.07 0.09 13 0.26 Example The underline represents that the value is outside of the range of the present invention or is not preferable.

TABLE-US-00010 TABLE 4-3 Properties of Steel Sheet ¼ Width Portion Average Grain Size of Hot- Proportion of Carbonitrides Rolled Unrecrystallized Residual including Ti Experiment Steel Ferrite Ferrite Martensite Austenite and/or Nb Example Steel Sheet Vol % % Vol % Vol % nm 29 J J1 90 30 0 0 7.7 30 J J2 90 43 1 0 10.1 31 K K1 92 40 0 1 11.1 32 K K1 81 28 0 0 8.8 33 K K2 92 52 0 0 8.6 34 K K3 92 33 0 0 9.8 35 L L1 87 6 1 0 12.1 36 L L2 83 54 0 0 8.8 37 L L2 87 27 3 0 7.4 38 L L3 95 12 0 0 9.0 39 M M1 82 20 0 0 14.2 40 M M2 86 24 0 0 10.5 41 M M3 84 22 0 0 9.7 42 N N1 87 49 0 0 8.0 43 N N2 89 26 1 0 7.2 44 O O1 87 55 0 0 7.6 45 O O2 89 25 0 0 9.2 46 O O2 76 0 0 0 8.3 47 O O3 87 51 0 0 8.0 48 P P1 85 20 0 0 9.8 49 P P1 82 4 0 0 8.6 50 P P1 81 22 5 0 7.9 51 P P2 86 23 1 0 8.3 52 Q Q1 93 36 0 0 11.7 53 Q Q2 89 17 0 0 9.0 54 R R1 89 20 0 0 7.1 55 R R2 83 19 0 0 6.4 56 S S1 85 14 0 0 16.9 Properties of Steel Sheet ¼ Width ½ Width Portion Portion Average Average Grain Size of Average Grain Proportion of Carbonitrides Grain Size of Unrecrystallized Residual including Ti Size of Experiment Ferrite Ferrite Ferrite Martensite Austenite and/or Nb Ferrite Example μm Vol % % Vol % Vol % nm μm 29 9.2 93 32 0 0 8.0 9.7 30 11.7 91 46 1 0 10.8 12.1 31 5.8 94 44 0 1 11.5 5.9 32 8.4 94 30 0 0 9.7 9.2 33 8.5 93 57 0 0 9.5 8.5 34 6.9 94 33 0 0 10.3 7.4 35 9.0 80 7 1 0 12.3 9.1 36 9.9 85 55 0 0 9.1 10.7 37 8.2 84 29 3 0 7.4 8.9 38 5.3 84 13 0 0 10.0 5.6 39 9.3 83 21 0 0 14.5 9.5 40 7.9 87 26 0 0 10.9 8.4 41 7.7 85 23 0 0 10.3 7.9 42 7.8 90 51 0 0 6.6 7.4 43 6.3 91 21 1 0 7.5 6.9 44 5.8 90 57 0 0 8.4 6.1 45 6.3 90 27 0 0 9.5 6.5 46 12.2 71 0 0 0 8.4 13.0 47 12.8 91 66 0 0 4.9 12.8 48 7.7 85 21 0 0 10.4 7.8 49 9.0 87 2 0 0 9.1 9.4 50 9.1 84 23 6 0 7.9 9.3 51 10.0 84 25 1 0 9.2 10.6 52 6.8 90 39 0 0 11.8 7.6 53 7.6 88 19 0 0 10.0 7.7 54 9.5 91 26 0 0 7.4 9.5 55 9.8 89 20 0 0 6.8 10.4 56 10.4 87 16 0 0 17.0 10.8 The underline represents that the value is outside of the range of the present invention or is not preferable.

TABLE-US-00011 TABLE 4-4 Properties of Steel Sheet ¾ Width Portion Average Grain Size of Average Hot- Proportion of Carbonitrides Grain Rolled Unrecrystallized Residual including Ti Size of Experiment Steel Ferrite Ferrite Martensite Austenite and/or Nb Ferrite Example Steel Sheet Vol % % Vol % Vol % nm μm 29 J J1 91 37 0 0 9.7 9.7 30 J J2 90 30 1 0 13.9 12.8 31 K K1 92 51 0 1 15.0 6.5 32 K K1 81 35 0 0 11.0 9.7 33 K K2 89 39 0 0 10.8 9.6 34 K K3 92 39 0 0 11.7 8.6 35 L L1 81 10 1 0 16.6 10.4 36 L L2 84 36 0 0 10.7 10.7 37 L L2 87 32 3 0 9.2 9.0 38 L L3 99 34 0 0 15.0 5.9 39 M M1 86 24 0 0 18.3 10.2 40 M M2 89 32 0 0 13.1 9.2 41 M M3 92 27 0 0 12.0 6.1 42 N N1 91 37 0 0 6.4 7.1 43 N N2 87 20 1 0 10.5 7.1 44 O O1 82 44 0 0 9.7 6.4 45 O O2 93 31 0 0 11.0 7.5 46 O O2 77 0 0 0 9.8 13.2 47 P O3 89 78 0 0 8.7 13.7 48 P P1 89 25 0 0 13.9 9.3 49 P P1 85 3 0 0 11.1 9.7 50 P P1 84 31 5 0 11.4 9.9 51 P P2 88 29 1 0 10.2 10.5 52 Q Q1 92 32 0 0 16.2 7.6 53 Q Q2 90 14 0 0 13.8 8.7 54 R R1 91 31 0 0 8.8 10.4 55 R R2 87 12 0 0 7.9 10.3 56 S S1 89 13 0 0 20.7 11.0 Properties of Steel Sheet Fe Left Side Left Side Left Side Left Side Content of of of of in Plated Experiment Expression Expression Expression Expression Plated Layer Example (2) (3) (4) (5) Layer mass % Note 29 0.03 0.05 7 0.24 Example 30 0.01 0.09 16 0.33 GA 8.2 Example 31 0.02 0.12 11 0.31 Example 32 0.15 0.14 7 0.22 Comparative Example 33 0.04 0.12 18 0.23 Example 34 0.02 0.22 6 0.18 Comparative Example 35 0.08 0.15 4 0.33 Example 36 0.02 0.08 19 0.20 Example 37 0.03 0.09 5 0.23 Comparative Example 38 0.16 0.11 22 0.53 Comparative Example 39 0.05 0.09 4 0.26 GA 11.6 Example 40 0.03 0.15 8 0.23 GA 9.7 Example 41 0.09 0.25 5 0.22 Comparative Example 42 0.04 0.09 14 0.23 Example 43 0.04 0.12 6 0.39 GI 0.9 Example 44 0.09 0.10 13 0.25 Example 45 0.04 0.18 6 0.18 GI 2.4 Example 46 0.08 0.08 0 0.17 Comparative Example 47 0.04 0.07 27 0.53 Comparative Example 48 0.05 0.19 5 0.36 Alloy 11.5 Example Galvannealed 49 0.06 0.07 2 0.26 Comparative Example 50 0.04 0.08 9 0.39 Comparative Example 51 0.05 0.06 6 0.21 Example 52 0.03 0.11 7 0.34 Alloy 9.2 Example Galvannealed 53 0.02 0.14 5 0.44 Example 54 0.02 0.09 11 0.22 EG Example 55 0.07 0.06 8 0.21 Example 56 0.05 0.06 3 0.21 Example The underline represents that the value is outside of the range of the present invention or is not preferable.

TABLE-US-00012 TABLE 4-5 Properties of Steel Sheet ¼ Width Portion Average Grain Size of Hot- Proportion of Carbonitrides Rolled Unrecrystallized Residual including Ti Experiment Steel Ferrite Ferrite Martensite Austenite and/or Nb Example Steel Sheet Vol % % Vol % Vol % nm 57 S S2 87 39 0 0 10.0 59 T T1 97 33 0 0 9.6 60 T T2 94 39 0 0 18.8 61 T T3 91 55 0 0 7.4 62 U U1 84 27 0 0 9.9 63 U U2 83 47 0 0 11.6 64 V V1 82 30 1 0 8.5 65 V V2 82 8 0 0 7.1 66 W W1 91 26 1 0 7.5 67 W W2 86 24 0 0 16.9 68 X X1 80 14 0 1 6.4 69 X X1 81 75 0 0 8.2 70 X X2 85 12 0 0 10.3 71 X X3 93 37 4 0 6.4 72 Y Y1 88 19 0 0 11.1 74 Z Z1 86 27 1 1 8.3 75 Z Z2 89 11 0 0 9.1 76 Z Z3 89 15 0 0 5.3 77 AA AA 87 0 0 0 8.8 78 AB AB 94 78 0 0 11.8 79 AC AC 88 66 0 0 9.1 80 AD AD 85 57 0 0 9.1 81 AE AE 98 36 0 0 7.9 82 AF AF 75 21 0 0 9.1 83 AG AG 87 0 1 0 — 84 AH AH 93 18 0 0 7.5 Properties of Steel Sheet ¼ Width ½ Width Portion Portion Average Average Grain Size of Average Grain Proportion of Carbonitrides Grain Size of Unrecrystallized Residual including Ti Size of Experiment Ferrite Ferrite Ferrite Martensite Austenite and/or Nb Ferrite Example μm Vol % % Vol % Vol % nm μm 57 6.8 88 43 0 0 10.5 7.5 59 5.1 96 34 0 0 10.5 5.2 60 5.1 96 43 0 0 19.1 5.3 61 13.1 95 58 0 0 7.7 16.8 62 9.8 86 28 0 0 10.7 10.6 63 10.0 87 48 0 0 11.8 10.7 64 11.9 84 32 1 0 9.4 12.4 65 15.0 84 9 0 0 7.3 16.3 66 7.8 90 29 1 0 6.4 8.1 67 9.9 90 26 0 0 17.7 10.4 68 9.5 85 15 0 1 6.4 9.8 69 14.8 85 78 0 0 9.0 15.9 70 9.1 87 13 0 0 11.0 9.7 71 8.9 87 39 4 0 6.6 9.8 72 8.6 90 17 0 0 11.4 8.9 74 10.9 92 28 1 1 7.6 11.5 75 10.5 90 12 0 0 9.4 10.7 76 10.5 92 16 0 0 5.5 11.0 77 11.9 86 0 0 0 9.3 12.1 78 6.0 95 82 0 0 12.7 5.9 79 6.2 90 71 0 0 9.6 6.8 80 8.9 91 62 0 0 7.5 9.1 81 8.3 100 38 0 0 8.6 8.9 82 5.8 74 22 0 0 10.0 6.4 83 13.1 90 0 1 0 — 14.2 84 5.9 98 5 0 0 8.1 6.4 The underline represents that the value is outside of the range of the present invention or is not preferable.

TABLE-US-00013 TABLE 4-6 Properties of Steel Sheet ¾ Width Portion Average Grain Size of Average Hot- Proportion of Carbonitrides Grain Rolled Unrecrystallized Residual including Ti Size of Experiment Steel Ferrite Ferrite Martensite Austenite and/or Nb Ferrite Example Steel Sheet Vol % % Vol % Vol % nm μm 57 S S2 89 52 0 0 13.4 7.7 59 T T1 95 43 0 0 10.9 6.0 60 T T2 97 33 0 0 28.5 5.9 61 T T3 95 41 0 0 10.3 16.1 62 U U1 82 34 0 0 12.2 10.7 63 U U2 84 39 0 0 13.4 10.7 64 V V1 88 37 1 0 11.6 12.5 65 V V2 83 14 0 0 8.7 15.9 66 W W1 87 17 1 0 6.2 8.6 67 W W2 83 33 0 0 20.2 10.6 68 X X1 86 19 0 1 7.7 10.8 69 X X1 86 63 0 0 11.3 15.9 70 X X2 82 19 0 0 12.3 9.9 71 X X3 83 45 4 0 8.3 9.9 72 Y Y1 85 25 0 0 15.5 9.4 74 Z Z1 85 37 1 1 6.9 11.7 75 Z Z2 88 16 0 0 11.7 11.0 76 Z Z3 91 24 0 0 8.9 11.0 77 AA AA 89 3 0 0 10.2 12.4 78 AB AB 93 54 0 0 18.2 7.0 79 AC AC 87 55 0 0 11.6 7.3 80 AD AD 90 45 0 0 7.1 9.6 81 AE AE 99 29 0 0 9.8 9.0 82 AF AF 73 19 0 0 12.7 6.8 83 AG AG 86 0 1 0 — 14.5 84 AH AH 97 31 0 0 12.2 7.4 Properties of Steel Sheet Fe Left Left Left Left Content in Side of Side of Side of Side of Plated Experiment Expression Expression Expression Expression Plated Layer Example (2) (3) (4) (5) Layer mass % Note 57 0.02 0.12 13 0.30 Deposit Example 59 0.02 0.17 10 0.13 Example 60 0.03 0.15 10 0.44 Example 61 0.04 0.24 17 0.34 Comparative Example 62 0.05 0.09 7 0.21 GI 0.1 Example 63 0.05 0.07 9 0.15 Example 64 0.07 0.05 7 0.32 Example 65 0.02 0.08 6 0.21 Example 66 0.04 0.10 12 0.19 Example 67 0.08 0.07 9 0.18 EG Example 68 0.07 0.13 5 0.19 Example 69 0.06 0.07 15 0.33 Comparative Example 70 0.06 0.08 7 0.18 Zn 33 Example Plated 71 0.11 0.10 8 0.27 Comparative Example 72 0.06 0.09 8 0.35 Example 74 0.08 0.07 10 0.18 Example 75 0.02 0.05 5 0.26 Example 76 0.03 0.05 9 0.55 Comparative Example 77 0.03 0.04 3 0.15 Comparative Example 78 0.02 0.17 28 0.45 Comparative Example 79 0.03 0.16 16 0.25 Comparative Example 80 0.07 0.08 17 0.25 Comparative Example 81 0.02 0.08 9 0.22 Comparative Example 82 0.03 0.16 3 0.34 Comparative Example 83 0.05 0.10 0 — Comparative Example 84 0.05 0.23 26 0.51 Comparative Example The underline represents that the value is outside of the range of the present invention or is not preferable.

TABLE-US-00014 TABLE 5-1 Hot- Rolled Properties Experiment Steel YS TS uEl Δ.sub.YS/ Δ.sub.uEl/ Example Steel Sheet MPa MPa YR % YS uEl α.sub.M/90 Note 1 A A1 338 603 0.56 16.2 0.09 0.17 0.98 Example 2 A A1 604 689 0.88 8.2 0.21 0.40 1.14 Comparative Example 3 A A2 293 545 0.54 19.7 0.16 0.16 1.02 Example 4 A A3 309 604 0.51 14.1 0.22 0.26 1.12 Comparative Example 5 B B1 393 572 0.69 16.8 0.13 0.14 1.04 Example 6 B B2 403 604 0.67 14.9 0.12 0.17 1.01 Example 7 B B3 261 483 0.54 19.7 0.22 0.03 1.11 Comparative Example 8 C C1 292 541 0.54 16.5 0.12 0.17 1.06 Example 9 C C1 609 686 0.89 10.9 0.09 0.22 1.12 Comparative Example 10 C C1 348 563 0.62 18.6 0.25 0.27 0.88 Comparative Example 11 C C2 326 594 0.55 20.0 0.11 0.14 0.94 Example 12 C C3 301 565 0.53 18.3 0.20 0.27 1.16 Comparative Example 13 D D1 462 772 0.60 14.6 0.10 0.08 0.97 Example 14 D D2 450 701 0.64 13.2 0.12 0.15 1.01 Example 15 E E1 312 534 0.58 20.1 0.08 0.18 1.02 Example 16 E E2 324 505 0.64 19.4 0.13 0.07 1.01 Example 17 F F1 383 701 0.55 17.7 0.13 0.21 1.02 Example 18 F F1 351 674 0.52 16.1 0.23 0.12 0.89 Comparative Example 19 F F1 274 611 0.45 22.2 0.15 0.16 0.91 Comparative Example 20 F F2 421 689 0.61 12.2 0.18 0.20 1.02 Example 21 F F3 407 712 0.57 15.0 0.22 0.09 1.12 Comparative Example 22 G G1 370 616 0.60 14.7 0.19 0.06 0.97 Example 23 G G2 308 582 0.53 20.1 0.08 0.14 0.95 Example 24 H H1 411 721 0.57 12.3 0.14 0.17 1.04 Example 25 H H2 336 638 0.53 14.0 0.15 0.05 1.01 Example 26 I I1 450 714 0.63 12.2 0.09 0.14 1.03 Example 27 I I2 414 703 0.59 12.7 0.08 0.06 1.05 Example 28 I I3 526 674 0.78 13.5 0.11 0.20 1.01 Example 29 J J1 358 580 0.62 18.7 0.10 0.09 1 Example 30 J J2 435 604 0.72 13.2 0.11 0.06 0.98 Example The underline represents that the value is outside of the range of the present invention or is not preferable.

TABLE-US-00015 TABLE 5-2 Hot- Rolled Properties Experiment Steel YS TS uEl Δ.sub.YS/ Δ.sub.uEl/ Example Steel Sheet MPa MPa YR % YS uEl α.sub.M/90 Note 31 K K1 431 647 0.67 16.6 0.07 0.14 1.02 Example 32 K K1 417 598 0.70 17.0 0.15 0.26 1.16 Comparative Example 33 K K2 513 647 0.79 11.8 0.13 0.21 1 Example 34 K K3 400 591 0.68 19.9 0.21 0.17 1.16 Comparative Example 35 L L1 302 566 0.53 15.6 0.16 0.15 0.99 Example 36 L L2 486 657 0.74 11.6 0.13 0.12 0.98 Example 37 L L2 266 662 0.40 16.7 0.12 0.22 1.08 Comparative Example 38 L L3 324 637 0.51 14.6 0.31 0.26 1.14 Comparative Example 39 M M1 357 598 0.60 13.0 0.13 0.00 1.09 Example 40 M M2 358 606 0.59 16.6 0.14 0.06 0.91 Example 41 M M3 338 618 0.55 13.6 0.22 0.17 1.12 Comparative Example 42 N N1 470 650 0.72 13.2 0.15 0.09 1.04 Example 43 N N2 343 593 0.58 17.8 0.14 0.19 1.02 Example 44 O O1 561 695 0.81 12.1 0.17 0.15 1.03 Example 45 O O2 365 681 0.54 18.5 0.10 0.17 0.98 Example 46 O O2 363 647 0.56 9.4 0.11 0.15 1.09 Comparative Example 47 O O3 638 697 0.92 9.9 0.23 0.35 1.13 Comparative Example 48 P P1 318 629 0.51 14.8 0.14 0.11 1.03 Example 49 P P1 238 620 0.38 14.5 0.14 0.04 0.92 Comparative Example 50 P P1 258 731 0.35 12.4 0.19 0.15 1.09 Comparative Example 51 P P2 350 641 0.55 12.8 0.14 0.10 0.98 Example 52 Q Q1 418 654 0.64 16.9 0.10 0.18 1.05 Example 53 Q Q2 330 619 0.53 15.9 0.09 0.10 0.99 Example 54 R R1 340 587 0.58 14.8 0.13 0.11 1.05 Example 55 R R2 312 596 0.52 17.4 0.14 0.15 1.05 Example 56 S S1 383 672 0.57 17.0 0.10 0.12 1 Example 57 S S2 517 695 0.74 15.1 0.07 0.17 1.02 Example 59 T T1 456 686 0.66 18.8 0.11 0.19 1 Example 60 T T2 479 661 0.72 14.4 0.11 0.14 1.04 Example The underline represents that the value is outside of the range of the present invention or is not preferable.

TABLE-US-00016 TABLE 5-3 Hot- Rolled Properties Experiment Steel YS TS uEl Δ.sub.YS/ Δ.sub.uEl/ Example Steel Sheet MPa MPa YR % YS uEl α.sub.M/90 Note 61 T T3 516 698 0.74 15.2 0.23 0.20 1.11 Comparative Example 62 U U1 406 666 0.61 12.3 0.09 0.10 1 Example 63 U U2 473 673 0.70 14.3 0.15 0.19 1.01 Example 64 V V1 409 669 0.61 14.8 0.12 0.23 0.98 Example 65 V V2 313 629 0.50 17.6 0.07 0.05 1 Example 66 W W1 387 616 0.63 16.4 0.14 0.09 1.07 Example 67 W W2 340 538 0.63 14.5 0.14 0.01 0.93 Example 68 X X1 306 578 0.53 15.1 0.14 0.04 1.03 Example 69 X X1 629 656 0.96 9.7 0.26 0.29 0.86 Comparative Example 70 X X2 283 542 0.52 18.5 0.14 0.19 1 Example 71 X X3 440 678 0.65 14.0 0.22 0.26 1.14 Comparative Example 72 Y Y1 371 657 0.56 18.9 0.15 0.16 0.98 Example 74 Z Z1 362 640 0.57 15.6 0.17 0.12 0.96 Example 75 Z Z2 318 607 0.52 17.1 0.09 0.15 0.99 Example 76 Z Z3 607 606 1.00 16.9 0.09 0.30 1.13 Comparative Example 77 AA AA 218 448 0.49 16.1 0.10 0.15 0.91 Comparative Example 78 AB AB 655 636 1.03 10.2 0.21 0.28 1.14 Comparative Example 79 AC AC 635 650 0.98 9.7 0.10 0.22 1.08 Comparative Example 80 AD AD 610 652 0.94 13.2 0.17 0.23 0.92 Comparative Example 81 AE AE 298 352 0.85 19.8 0.14 0.14 1.07 Comparative Example 82 AF AF 428 727 0.59 9.4 0.07 0.05 1.06 Comparative Example 83 AG AG 188 407 0.47 18.0 0.14 0.14 0.92 Comparative Example 84 AH AH 391 462 0.85 18.8 0.17 0.19 1.21 Comparative Example The underline represents that the value is outside of the range of the present invention or is not preferable.

[0430] Among steels A to AH shown in Tables 1-1 and 1-2, the steels AA to AG are comparative examples where the composition was outside of the range defined by the present invention.

[0431] The steel AA did not satisfy Expression (1-2). In the steel sheet according to Experiment Example 77 obtained using this steel, the amount of unrecrystallized ferrite was small. Therefore, the 0.2% proof stress, the tensile strength, and the yield ratio were low.

[0432] The steel AB did not satisfy Expression (1-2). In the steel sheet according to Experiment Example 78 obtained using this steel, the amount of unrecrystallized ferrite was large, and Expression (4) was not satisfied. Therefore, the 0.2% proof stress and the yield ratio were high, and Expressions (12) and (13) were not satisfied.

[0433] In the steel AC, the Ti content was higher than the range of the present invention. In the steel sheet according to Experiment Example 79 obtained using this steel, the amount of unrecrystallized ferrite was large. Therefore, the 0.2% proof stress and the yield ratio were high, and the uniform elongation was low.

[0434] In the steel AD, the Nb content was higher than the range of the present invention. In the steel sheet according to Experiment Example 80 obtained using this steel, the amount of unrecrystallized ferrite was large. Therefore, the 0.2% proof stress and the yield ratio were high.

[0435] In the steel AE, the C content was lower than the range of the present invention. In the steel sheet according to Experiment Example 81 obtained using this steel, the tensile strength was low.

[0436] In the steel AF, the C content and the S content were higher than the ranges of the present invention. In the steel sheet according to Experiment Example 82 obtained using this steel, the ferrite content was low. Therefore, the uniform elongation was low.

[0437] The steel AG did not include both Ti and Nb. In the steel sheet according to Experiment Example 83 obtained using this steel, the amount of unrecrystallized ferrite was small, carbonitrides were not included, and Expression (5) was not satisfied. Therefore, the 0.2% proof stress, the tensile strength, and the yield ratio were low.

[0438] Experiment Examples 4, 7, 12, 21, 34, 41, and 61 were comparative examples where the conditions of the hot rolling process were outside of the range of the present invention.

[0439] Experiment Example 4 was a comparative example in which the hot rolling completion temperature was low. Therefore, Expressions (2) and (3) were not satisfied, and Expressions (12) and (13) were not satisfied.

[0440] Experiment Example 7 was a comparative example in which the steel piece heating temperature was low. Therefore, the average grain size of carbonitrides was large, the 0.2% proof stress was low, and Expression (12) was not satisfied.

[0441] Experiment Example 12 was a comparative example in which the average cooling rate in the temperature range of 800° C. to 450° C. was low. Therefore, Expression (2) was not satisfied, and Expression (13) was not satisfied.

[0442] Experiment Example 21 was a comparative example in which G was large and Expression (6) in a temperature range of 1000° C. or lower was not satisfied. Therefore, Expressions (3) and (5) were not satisfied, and Expression (12) was not satisfied.

[0443] Experiment Example 34 was a comparative example in which the time required for the start of cooling after hot rolling was short. Therefore, Expression (3) was not satisfied, and Expression (12) was not satisfied.

[0444] Experiment Example 41 was a comparative example in which the steel piece heating temperature was high. Therefore, Expression (3) was not satisfied, and Expression (12) was not satisfied.

[0445] Experiment Example 61 was a comparative example in which the hot rolling completion temperature was high. Therefore, Expression (3) was not satisfied, and Expression (12) was not satisfied.

[0446] Experiment Examples 38, 47, 71, and 76 were comparative examples in which the conditions of the reheating process were outside of the range of the present invention.

[0447] Experiment Example 38 was a comparative example in which the maximum reheating temperature was high. Therefore, Expressions (2), (4), and (5) were not satisfied, and Expressions (12) and (13) were not satisfied.

[0448] Experiment Example 47 was a comparative example in which the maximum reheating temperature was high. Therefore, the amount of unrecrystallized ferrite was large, the average grain size of carbonitrides was small, Expressions (4) and (5) were not satisfied, the 0.2% proof stress and the yield ratio were high, the uniform elongation was low, and Expressions (12) and (13) were not satisfied.

[0449] Experiment Example 71 was a comparative example in which K.sub.2O was high and Expression (8) in a temperature range of 450° C. to 700° C. was not satisfied. Therefore, the amount of martensite was large, Expression (5) was not satisfied, and Expressions (12) and (13) were not satisfied.

[0450] Experiment Example 76 was a comparative example in which Expression (7-1) was not satisfied. Therefore, the average grain size of carbonitrides was small, Expression (5) was not satisfied, the 0.2% proof stress and the yield ratio were high, and Expression (13) was not satisfied.

[0451] Experiment Examples 2, 18, and 69 were comparative examples in which the conditions of the cold rolling process were outside of the range of the present invention.

[0452] Experiment Example 2 was a comparative example in which the cold rolling completion temperature was low. Therefore, the amount of unrecrystallized ferrite was large, Expression (4) was not satisfied, the 0.2% proof stress was high, the uniform elongation was low, and Expressions (12) and (13) were not satisfied.

[0453] Experiment Example 18 was a comparative example in which the total rolling reduction was high. Therefore, Expression (3) was not satisfied, and Expression (12) was not satisfied.

[0454] Experiment Example 69 was a comparative example in which the total rolling reduction was low. Therefore, the amount of unrecrystallized ferrite was large, the 0.2% proof stress and the yield ratio were high, the uniform elongation was low, and Expressions (12) and (13) were not satisfied.

[0455] Experiment Examples 9, 10, 19, 32, 37, 46, 49, and 50 were comparative examples where the conditions of the annealing process were outside of the range of the present invention.

[0456] Experiment Example 9 was a comparative example in which P.sub.10 was low and Expression (9) was not satisfied. Therefore, the amount of unrecrystallized ferrite was large, and the 0.2% proof stress was high.

[0457] Experiment Example 10 was a comparative example in which Expression (10) was not satisfied. Therefore, Expressions (2) was not satisfied, and Expressions (12) and (13) were not satisfied.

[0458] Experiment Example 19 was a comparative example in which Expression (11) was not satisfied. Therefore, the amount of residual austenite was large, and the 0.2% proof stress and the yield ratio were low.

[0459] Experiment Example 32 was a comparative example in which a tension in a temperature range of 720° C. to the annealing temperature was not applied. Therefore, Expression (2) was not satisfied, and Expression (13) was not satisfied.

[0460] Experiment Example 37 was a comparative example in which Expression (10) was not satisfied. Therefore, the amount of martensite was large, and the 0.2% proof stress and the yield ratio were low.

[0461] Experiment Example 46 was a comparative example in which the annealing temperature was high. Therefore, the amount of ferrite and the amount of unrecrystallized ferrite were small, and the uniform elongation was low.

[0462] Experiment Example 49 was a comparative example in which the annealing temperature was low. Therefore, the amount of unrecrystallized ferrite was small, and the 0.2% proof stress and the yield ratio were low.

[0463] Experiment Example 50 was a comparative example in which Expression (10) was not satisfied. Therefore, the amount of martensite was large, and the 0.2% proof stress and the yield ratio were low.

[0464] Experiment Example 84 was a comparative example in which Expression (6) was not satisfied, the time required for the start of cooling in the hot rolling process was short, and the rolling completion temperature in the cold rolling process was low. Therefore, Expressions (2) to (5) were not satisfied.

[0465] Experiment Examples other than Comparative Examples described above were Examples according to the present invention. It was found that the steel sheets described as Examples were manufactured using the manufacturing method satisfying the manufacturing conditions according to the present invention and thus had excellent formability, strength, and dimensional accuracy during press forming.

[0466] Experiment Examples 5, 11, 13, 15, 20, 24, 30, 39, 40, 43, 45, 48, 52, 54, 57, 62, 67, and 70 are examples where the plated steel sheets according to the present invention were obtained by performing plating.

[0467] Experiment Examples 15, 24, 43, 45, and 62 were Examples in which a hot-dip galvanized steel sheet (GI) was obtained by cooling the steel sheet to 500° C. in the annealing process, dipping the steel sheet in a molten zinc bath, and cooling the steel sheet to room temperature.

[0468] Experiment Examples 5, 11, 13, 30, 39, and 40 were Examples in which hot-dip galvannealed steel sheet (GA) was obtained by cooling the steel sheet to 500° C. in the annealing process, dipping the steel sheet in a molten zinc bath and reheating the steel sheet to 560° C. for alloying and cooling the steel sheet to room temperature.

[0469] Experiment Examples 20 and 70 were Examples in which a zinc alloy plated steel sheet was obtained by cooling the steel sheet to 500° C. in the annealing process, dipping the steel sheet in a molten zinc alloy bath, and cooling the steel sheet to room temperature.

[0470] Experiment Examples 48 and 52 were Examples in which an alloy galvannealed steel sheet was obtained by cooling the steel sheet to 500° C. in the annealing process, dipping the steel sheet in a molten zinc alloy bath and reheating the steel sheet to 580° C. for alloying and cooling the steel sheet to room temperature.

[0471] Experiment Example 57 is an Example in which a galvanized steel sheet was obtained by performing deposition plating after temper rolling.

[0472] Experiment Examples 54 and 67 are Examples in which an electrogalvanized steel sheet (EG) was obtained by performing electrogalvanizing after the annealing process.

INDUSTRIAL APPLICABILITY

[0473] In the above-described aspects according to the present invention, a steel sheet having excellent formability, strength, and dimensional accuracy during press forming and a method of manufacturing the same can be provided. The steel sheet according to the above-described aspects is a steel sheet that is suitable for a significant reduction in the weight of a vehicle and for ensuring the protection and safety of a passenger. Therefore, the present invention is highly applicable to the steel sheet manufacturing industry and the automobile industry.

STEEL SHEET AND METHOD OF MANUFACTURING THE SAME

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