HOT-STAMPING FORMED BODY

Abstract

A hot-stamping formed body includes a steel sheet and a zinc-plated layer that is provided on the steel sheet. The steel sheet has a predetermined chemical composition, and an area % of martensite is 90% or more in microstructure at a position corresponding to ¼ of a sheet thickness of the steel sheet from a surface of the steel sheet in a sheet thickness direction. The zinc-plated layer includes a F phase and a Fe—Zn solid solution, and a cross-sectional area ratio of voids present in the zinc-plated layer is 15.0% or less.

Claims

1. A hot-stamping formed body comprising: a steel sheet; and a zinc-plated layer that is provided on the steel sheet, wherein the steel sheet has a chemical composition containing, by mass %, C: 0.18% to 0.50%, Si: 0.10% to 1.50%, Mn: 1.5% to 2.5%, sol.Al: 0.001% to 0.100%, Ti: 0.010% to 0.100%, S: 0.0100% or less, P: 0.100% or less, N: 0.010% or less, Nb: 0% to 0.05%, V: 0% to 0.50%, Cr: 0% to 0.50%, Mo: 0% to 0.50%, B: 0% to 0.010%, Ni: 0% to 2.00%, and a total of REM, Ca, Co, and Mg: 0% to 0.030%, a remainder consisting of Fe and impurities, an area % of martensite is 90% or more in microstructure at a position corresponding to ¼ of a sheet thickness of the steel sheet from a surface of the steel sheet in a sheet thickness direction, the zinc-plated layer includes a Γ phase and a Fe—Zn solid solution, and a cross-sectional area ratio of voids present in the zinc-plated layer is 15.0% or less.

2. The hot-stamping formed body according to claim 1, wherein the chemical composition contains, by mass %, one or two or more selected from the group of Nb: 0.02% to 0.05%, V: 0.005% to 0.50%, Cr: 0.10% to 0.50%, Mo: 0.005% to 0.50%, B: 0.0001% to 0.010%, Ni: 0.01% to 2.00%, and a total of REM, Ca, Co, and Mg: 0.0003% to 0.030%.

3. The hot-stamping formed body according to claim 1, wherein the chemical composition contains, by mass %, C: 0.24% to 0.50%.

4. The hot-stamping formed body according to claim 2, wherein the chemical composition contains, by mass %, C: 0.24% to 0.50%.

5. A hot-stamping formed body comprising: a steel sheet; and a zinc-plated layer that is provided on the steel sheet, wherein the steel sheet has a chemical composition containing, by mass %, C: 0.18% to 0.50%, Si: 0.10% to 1.50%, Mn: 1.5% to 2.5%, sol.Al: 0.001% to 0.100%, Ti: 0.010% to 0.100%, S: 0.0100% or less, P: 0.100% or less, N: 0.010% or less, Nb: 0% to 0.05%, V: 0% to 0.50%, Cr: 0% to 0.50%, Mo: 0% to 0.50%, B: 0% to 0.010%, Ni: 0% to 2.00%, and a total of REM, Ca, Co, and Mg: 0% to 0.030%, a remainder comprising Fe and impurities, an area % of martensite is 90% or more in microstructure at a position corresponding to ¼ of a sheet thickness of the steel sheet from a surface of the steel sheet in a sheet thickness direction, the zinc-plated layer includes a Γ phase and a Fe—Zn solid solution, and a cross-sectional area ratio of voids present in the zinc-plated layer is 15.0% or less.

Description

EXAMPLES

[0096] Next, examples of the present invention will be described. Conditions in the examples are one condition example that is employed to confirm the feasibility and effects of the present invention, and the present invention is not limited to this condition example. The present invention may employ various conditions to achieve the object of the present invention without departing from the scope of the present invention.

[0097] After steel pieces manufactured from the casting of molten steel having the chemical composition shown in Table 1 were heated to 1200° C. or more and were held for 20 minutes or more, hot rolling was performed so that a finish rolling completion temperature was 810° C. or more and cold rolling was further performed. As a result, steel sheets were obtained. A cumulative rolling reduction during the cold rolling was set in a range of 30% to 90%. Zinc plating was applied to the obtained steel sheets by a continuous hot-dip galvanizing line, so that zinc-plated steel sheets (hot-dip zinc-plated steel sheets) were obtained. The adhesion amount of a zinc-plated layer was set in a range of 5 g/m.sup.2 to 150 g/m.sup.2 per side. Hot-stamping formed bodies shown in Tables 2 and 3 were manufactured using the obtained zinc-plated steel sheets under conditions shown in Tables 2 and 3. An average heating rate during the heating performed before hot stamping was set in a range of 0.1° C./s to 200° C./s.

[0098] An underline in Tables represents that a condition is out of the range of the present invention, a condition is out of a preferred manufacturing condition, or a property value is not preferred.

[0099] With regard to the microstructure of the steel sheet of each hot-stamping formed body, the measurement of the area ratio of each structure was performed by the above-mentioned measurement method. Ferrite, pearlite, and bainite were observed as the remainder in microstructure other than martensite.

[0100] Further, the layer structure of the zinc-plated layer of the hot-stamping formed body was analyzed using the above-mentioned method, and the cross-sectional area ratio of voids present in the zinc-plated layer was measured using the above-mentioned method. In a case where a r phase was observed in the zinc-plated layer, “presence” was written in Tables. In a case where the Γ phase was not observed in the zinc-plated layer, “absence” was written in Tables. The zinc-plated layer of Example where “presence” was written in Tables with regard to the zinc-plated layer included a Fe—Zn solid solution in addition to the Γ phase, and the adhesion amount of the Γ phase was in a range of 5 g/m.sup.2 to 150 g/m.sup.2 per side.

[0101] The mechanical properties (tensile strength and spot weldability) of each hot-stamping formed body were evaluated using the following methods.

[0102] Tensile Strength

[0103] No. 5 test pieces described in JIS Z 2241:2011 were prepared from an arbitrary position of the hot-stamping formed body, and the tensile strength of the hot-stamping formed body was obtained according to a test method described in JIS Z 2241:2011. In a case where the tensile strength was in a range of 1500 MPa to 2500 MPa, the test piece was determined to be acceptable since having strength generally required for a hot-stamping formed body. Further, in a case where the tensile strength was less than 1500 MPa, the test piece was determined to be unacceptable since being insufficient in strength. Furthermore, in a case where the tensile strength exceeded 2500 MPa, the test piece was determined to be unacceptable since being insufficient in toughness and ductility due to excessively high strength.

[0104] Spot Weldability

[0105] With regard to the hot-stamping formed body, two test pieces having a size of 100 mm×30 mm were taken from a position excluding a region within 10 mm from an end surface, these test piece overlapped with each other, and spot welding was performed while current was changed under the following conditions.

[0106] Electrode force: 400 kgf

[0107] Weld time: 15 cycles

[0108] Holding time: 9 cycles

[0109] Shape of electrode tip: DR type, tip ϕ 6 mm-radius of curvature of R40 mm

[0110] Spot welding was performed while current was increased from a current I.sub.0 at which a nugget diameter was 4√{square root over (t)} (t denotes the sheet thickness of the test piece) to obtain a current at which expulsion occurred and a current at which electrode sticking occurred (electrode sticking current I.sub.s). A range between I.sub.0 and the current at which expulsion occurred was set as an appropriate current range. In a case where molten metal was splashed, it was determined that expulsion occurred. In a case where expulsion occurred when spot welding was performed at the current I.sub.0 at which a nugget diameter was 4√{square root over (t)}, it was regarded that there was no appropriate current range and “−” was written in Table 3. An example in which there was no appropriate current range was determined to be unacceptable since being inappropriate as a zinc-plated steel sheet for spot welding.

[0111] Further, spot weldability with regard to the obtained electrode sticking current Is was evaluated on the basis of the following criteria. Here, I.sub.0(kA) is the current at which a nugget diameter was 4√t (t denotes the sheet thickness of the test piece), and I.sub.a(kA) is “I.sub.0×1.4”. Examples evaluated as good and fair were determined to be acceptable since being excellent in spot weldability. On the other hand, an example evaluated as bad was determined to be unacceptable since being insufficient in spot weldability.

[0112] Good: I.sub.s>I.sub.a×1.15

[0113] Fair: I.sub.a×1.10<I.sub.s≤I.sub.a×1.15

[0114] Bad: I.sub.s≤I.sub.a×1.10

TABLE-US-00001 TABLE 1 Steel Chemical composition (mass %) Remainder Fe and impurities Ac.sub.3 No. C Si Mn sol Al Ti S P N Others (° C.) Note  1 0.19 0.20 2.4 0.030 0.025 0.0020 0.004 0.003 768 Steel of present invention  2 0.49 0.15 2.0 0.030 0.035 0.0020 0.010 0.003 729 Steel of present invention  3 0.31 0.10 1.8 0.040 0.025 0.0020 0.010 0.003 757 Steel of present invention  4 0.31 1.40 1.8 0.040 0.025 0.0020 0.010 0.003 816 Steel of present invention  5 0.33 0.20 1.5 0.040 0.025 0.0020 0.015 0.005 767 Steel of present invention  6 0.33 0.20 2.5 0.040 0.025 0.0020 0.015 0.005 737 Steel of present invention  7 0.33 0.15 1.8 0.050 0.050 0.0002 0.090 0.005 766 Steel of present invention  8 0.33 0.15 1.8 0.050 0.050 0.0100 0.090 0.005 766 Steel of present invention  9 0.34 0.18 1.5 0.040 0.010 0.0030 0.010 0.005 759 Steel of present invention 10 0.34 0.18 1.5 0.040 0.100 0.0030 0.010 0.005 795 Steel of present invention 11 0.33 0.15 1.5 0.040 0.025 0.0020 0.090 0.005 765 Steel of present invention 12 0.33 0.15 1.5 0.040 0.025 0.0020 0.001 0.005 765 Steel of present invention 13 0.22 0.20 1.8 0.090 0.025 0.0030 0.010 0.005 780 Steel of present invention 14 0.22 0.20 1.8 0.005 0.025 0.0030 0.010 0.005 780 Steel of present invention 15 0.22 0.18 1.8 0.040 0.030 0.0020 0.010 0.010 781 Steel of present invention 16 0.22 0.18 1.8 0.040 0.030 0.0020 0.010 0.003 781 Steel of present invention 17 0.33 0.20 2.0 0.040 0.024 0.0020 0.010 0.005 752 Steel of present invention 18 0.33 0.21 2.0 0.040 0.024 0.0020 0.010 0.005 Nb: 0.05 752 Steel of present invention 19 0.33 0.20 2.0 0.040 0.025 0.0020 0.010 0.005 V: 0.20 752 Steel of present invention 20 0.33 0.20 2.0 0.040 0.025 0.0020 0.010 0.005 Cr: 0.20 752 Steel of present invention 21 0.33 0.22 1.9 0.040 0.022 0.0020 0.010 0.005 Mo: 0.02 755 Steel of present invention 22 0.34 0.25 1.9 0.040 0.023 0.0020 0.020 0.005 B: 0.003 755 Steel of present invention 23 0.33 0.25 2.0 0.040 0.022 0.0020 0.020 0.005 Ni: 0.04 753 Steel of present invention 24 0.31 0.20 2.1 0.040 0.024 0.0020 0.010 0.005 Mg: 0.001 753 Steel of present invention 25 0.31 0.20 2.1 0.040 0.024 0.0020 0.010 0.005 Ca: 0.001, 753 Steel of present invention Mg: 0.001 26 0.31 0.20 2.0 0.040 0.024 0.0020 0.010 0.005 REM: 0.001, 756 Steel of present invention Co: 0.005 27 0.17 0.20 2.0 0.040 0.022 0.0020 0.010 0.005 784 Steel of present invention 28 0.52 0.20 2.0 0.040 0.022 0.0020 0.010 0.005 721 Comparative steel 29 0.23 1.60 1.8 0.050 0.023 0.0020 0.010 0.005 839 Comparative steel 30 0.22 0.20 1.3 0.050 0.025 0.0040 0.009 0.005 795 Comparative steel 31 0.49 0.20 2.6 0.050 0.025 0.0040 0.009 0.005 709 Comparative steel 32 0.22 0.20 2.0 0.040 0.020 0.0130 0.010 0.005 772 Comparative steel 33 0.22 0.20 1.6 0.040 0.008 0.0010 0.010 0.005 779 Comparative steel 34 0.22 0.20 1.6 0.040 0.110 0.0010 0.010 0.005 820 Comparative steel 35 0.22 0.20 2.0 0.040 0.020 0.0010 0.110 0.005 772 Comparative steel 36 0.33 0.20 1.8 0.110 0.020 0.0030 0.020 0.005 756 Comparative steel 37 0.22 0.20 1.8 0.020 0.030 0.0030 0.020 0.015 782 Comparative steel 38 0.33 1.20 1.9 0.040 0.025 0.0020 0.010 0.005 800 Steel of present invention 39 0.33 1.00 2.0 0.040 0.025 0.0020 0.010 0.005 788 Steel of present invention An underline represents that a condition is out of the range of the present invention.

TABLE-US-00002 TABLE 2 Galvanized Hot stamping layer Average Steel Cross- cooling sheet sectional Mechanical Heating rate Contact Marten- Presence/ area properties Manu- temper- Heating until pressure site absence ratio Tensile facture Steel ature time 250° C. P (area of Γ of voids strength No. No. (° C.) (s) (° C./s) (MPa) %) phase (%) (MPa)  1  1 880 120 130 100 100 Presence 7.0 1505  2  2 820 90 110 100 100 Presence 3.0 2480  3  3 850 60 130 100 100 Presence 5.1 1950  4  4 850 60 130 100 100 Presence 5.5 1920  5  5 880 120 130 100 100 Presence 7.5 2045  6  6 830 90 110 100 100 Presence 4.0 2030  7  7 850 60 120 100 100 Presence 5.1 1980  8  8 850 60 120 100 100 Presence 5.0 1975  9  9 920 60 150 100 100 Presence 14.2 2100 10 10 950 60 150 100 100 Presence 13.5 1980 11 11 880 90 130 100 100 Presence 8.3 2025 12 12 880 90 130 100 100 Presence 7.9 2035 13 13 830 60 100 100 100 Presence 3.3 1520 14 14 830 60 110 100 100 Presence 2.9 1545 15 15 830 90 100 100 95 Presence 3.5 1540 16 16 830 120 100 100 100 Presence 3.0 1550 17 17 830 60 100 100 100 Presence 3.9 2030 18 18 830 120 110 100 100 Presence 3.3 2020 19 19 830 120 120 100 100 Presence 4.0 2050 20 20 830 120 100 100 100 Presence 3.3 1980 21 21 830 120 100 100 100 Presence 4.0 2010 22 22 830 120 120 100 100 Presence 4.4 2040 23 23 830 120 100 100 100 Presence 4.1 2050 24 24 830 120 100 100 100 Presence 3.9 1995 25 25 830 120 100 100 100 Presence 4.0 2010 Mechanical properties Ap- Electrode propriate 4 √t sticking Deter- Manu- current current I.sub.a × I.sub.a × current mination facture range I.sub.0 I.sub.a 1.10 1.15 I.sub.a of spot No. (kA) (kA) (kA) (kA) (kA) (kA) weldability Note  1 1.40 5.80 8.12 8.93 9.34 10.00 Good Steel of present invention  2 1.20 5.70 7.98 8.78 9.18 10.00 Good Steel of present invention  3 1.50 5.80 8.12 8.93 9.34 10.00 Good Steel of present invention  4 1.50 5.80 8.12 8.93 9.34  9.50 Good Steel of present invention  5 1.30 6.00 8.40 9.24 9.66 10.00 Good Steel of present invention  6 1.80 5.70 7.98 8.78 9.18 10.00 Good Steel of present invention  7 1.40 5.60 7.84 8.62 9.02 10.00 Good Steel of present invention  8 1.40 5.80 8.12 8.93 9.34 10.00 Good Steel of present invention  9 0.90 6.00 8.40 9.24 9.66  9.50 Fair Steel of present invention 10 0.20 6.40 8.96 9.86 10.30  10.00 Fair Steel of present invention 11 1.20 5.90 8.26 9.09 9.50 10.00 Good Steel of present invention 12 1.20 5.80 8.12 8.93 9.34  9.50 Good Steal of present invention 13 1.60 5.60 7.84 8.62 9.02 10.40 Good Steel of present invention 14 1.70 5.80 8.12 8.93 9.34 10.00 Good Steel of present invention 15 1.60 5.80 8.12 8.93 9.34 10.00 Good Steel of present invention 16 1.50 6.00 8.40 9.24 9.66 10.50 Good Steel of present invention 17 1.80 5.70 7.98 8.78 9.18 10.50 Good Steel of present invention 18 1.70 5.80 8.12 8.93 9.34 10.50 Good Steel of present invention 19 1.70 5.60 7.84 8.62 9.02  9.50 Good Steel of present invention 20 1.70 5.90 8.26 9.09 9.50 10.00 Good Steel of present invention 21 1.70 6.00 8.40 9.24 9.66 10.00 Good Steel of present invention 22 1.80 5.70 7.98 8.78 9.18 10.00 Good Steel of present invention 23 1.90 5.70 7.98 8.78 9.18  9.90 Good Steel of present invention 24 1.70 5.90 8.26 9.09 9.50 10.00 Good Steel of present invention 25 1.70 5.80 8.12 8.93 9.34 10.00 Good Steel of present invention

TABLE-US-00003 TABLE 3 Galvanized Hot stamping layer Average Cross- cooling Steel sectional Mechanical Heating rate Contact sheet Presence/ area properties Manu- temper- Heating until pressure Martensite absence ratio Tensile facture Steel ature time 250° C. P (area of Γ of voids strength No. No. (° C.) (s) (° C./s) (MPa) %) phase (%) (MPa) 26 26 830 120 100 100 100 Presence 4.4 2000 27 27 850 120 120 100 100 Presence 5.2 1475 28 28 850 120 130 100 100 Presence 6.1 2550 29 29 820 120 110 100  30 Presence 3.2 1380 30 30 820  90 120 100  90 Presence 2.7 1480 31 31 920  60 120 100 100 Presence 15.5  2570 32 32 810  90 110 100  90 Presence 2.8 1480 33 33 810  90 110 100  85 Presence 1.2 1310 34 34 810  90 120 100  30 Presence 1.5 1150 35 35 810  90 110 100  85 Presence 1.9 1340 36 36 900 180 110 100  80 Absence 3.3 1790 37 37 810  90 100 100  95 Presence 2.4 1490 38 18 780 120 100 100  10 Presence 3.2 1000 39 18 960  60 140 100 100 Presence 15.4  2150 40 18 800  30 100 100  30 Presence 1.2 1380 41 18 830 630 100 100 100 Absence 4.5 2120 42 17 850 120  15 100  20 Presence 6.0 1240 43 17 920  90 120  40 100 Presence 18.0  2110 44 38 850  60 100 100 100 Presence 9.0 2020 45 39 850  60 100 100 100 Presence 8.2 2040 46 17 850  60  50 100  97 Presence 4.0 2000 47 18 850  60  50 100  98 Presence 5.3 2010 48 17 850  60  30 100  96 Presence 4.4 1980 49 18 850  60  30 100  96 Presence 4.5 1990 Mechanical properties Electrode Appropriate 4 √t sticking Manu- current current I.sub.a × I.sub.a × current Determination facture range I.sub.0 I.sub.a 1.10 1.15 I.sub.a of spot No. (kA) (kA) (kA) (kA) (kA) (kA) weldability Note 26 1.70 5.80 8.12 8.93 9.34 10.00 Good Example of present invention 27 1.30 6.00 8.40 9.24 9.66 10.00 Good Comparative Example 28 1.10 5.90 8.26 9.09 9.50 9.50 Fair Comparative Example 29 1.60 5.90 8.26 9.09 9.50 10.50 Good Comparative Example 30 1.70 5.70 7.98 8.78 9.18 10.50 Good Comparative Example 31 0.20 6.20 8.68 9.55 9.98 9.00 Bad Comparative Example 32 1.50 6.00 8.40 9.24 9.66 10.00 Good Comparative Example 33 1.70 6.00 8.40 9.24 9.66 9.90 Good Comparative Example 34 1.70 5.50 7.70 8.47 8.86 9.50 Good Comparative Example 35 1.70 5.70 7.98 8.78 9.18 10.00 Good Comparative Example 36 — 6.00 8.40 9.24 9.66 9.40 Fair Comparative Example 37 1.30 5.70 7.98 8.78 9.18 10.00 Good Comparative Example 38 1.80 5.80 8.12 8.93 9.34 11.00 Good Comparative Example 39 — 6.30 8.82 9.70 10.14 8.50 Bad Comparative Example 40 1.70 5.70 7.98 8.78 9.18 10.00 Good Comparative Example 41 — 6.10 8.54 9.39 9.82 9.50 Fair Comparative Example 42 1.30 5.60 7.84 8.62 9.02 9.50 Good Comparative Example 43 — 6.00 8.40 9.24 9.66 8.50 Bad Comparative Example 44 1.40 5.80 8.12 8.93 9.34 10.00 Good Example of present invention 45 1.50 5.80 8.12 8.93 9.34 10.00 Good Example of present invention 46 1.60 5.80 8.12 8.93 9.34 10.50 Good Example of present invention 47 1.70 5.90 8.26 9.09 9.50 10.00 Good Example of present invention 48 1.60 6.00 8.40 9.24 9.66 10.00 Good Example of present invention 49 1.60 5.80 8.12 8.93 9.34 10.00 Good Example of present invention An underline represents that a condition is out of the range of the present invention, a manufacturing condition is not preferred, or properties are not preferred.

[0115] It is found from Tables 2 and 3 that a hot-stamping formed body of which the chemical composition and microstructure of a steel sheet and the layer structure and cross-sectional area ratio of voids of a zinc-plated layer are in the range of the present invention has a tensile strength in a range of 1500 MPa to 2500 MPa and is excellent in spot weldability.

[0116] On the other hand, it is found that a hot-stamping formed body of which any one or more of the chemical composition and microstructure of a steel sheet and the layer structure and cross-sectional area ratio of voids of a zinc-plated layer are out of the present invention has a tensile strength out of a range of 1500 MPa to 2500 MPa and/or is inferior in spot weldability. Manufacture No. 36, 39, 41, and 43 are examples in which expulsion occurred before current reaches the current I.sub.0 at which a nugget diameter was 4√{square root over (t)}.

INDUSTRIAL APPLICABILITY

[0117] According to the aspect of the present invention, it is possible to obtain a hot-stamping formed body that is excellent in spot weldability and has strength generally required for a hot-stamping formed body.