Low-cost and high-formability 1180 MPa grade cold-rolled annealed dual-phase steel plate and manufacturing method thereof

Abstract

A low-cost and high-formability 1180 MPa grade cold-rolled annealed dual-phase steel plate and a manufacturing method thereof are provided. The dual-phase steel plate has the following chemical composition by mass percentages: C: 0.1%-0.125%, Si: 0.4%-0.8%, Mn: 2.6%-2.9%, Al: 0.01%-0.05%, Nb: 0.01%-0.03%, and Ti: 0.01%-0.03%, the remainder being Fe and unavoidable impurities. By reasonable design of alloy elements and manufacturing processes, the dual-phase steel plate of the invention achieves a strength of 1180 MPa grade at a low cost, obtains a fine and uniform martensite-ferrite dual-phase structure that ensures excellent elongation rate and cold bending performance, and has good formability. The dual-phase steel plate has a yield strength of more than 850 MPa, a tensile strength of more than 1180 MPa, an elongation rate of 8% or more, and a parameter (R/t), characterizing the 90-degree cold bending performance, of 2.5 or less.

Claims

1. A 1180 MPa grade cold-rolled annealed dual-phase steel plate, consisting of following chemical composition by mass percentages: C: 0.1%-0.125%, Si: 0.4%-0.8%, Mn: 2.6%-2.9%, Al: 0.01%-0.05%, Nb: 0.01%-0.03%, and Ti: 0.01%-0.03%, a remainder being Fe and unavoidable impurities, wherein C, Mn and Si contents satisfy that 1.73×[C]×[Mn]+[Si]≥1, and Nb and Ti contents satisfy that [Nb]+[Ti]×3≥0.047.

2. The 1180 MPa grade cold-rolled annealed dual-phase steel plate as claimed in claim 1, wherein the C content is from 0.11% to 0.125%.

3. The 1180 MPa grade cold-rolled annealed dual-phase steel plate as claimed in claim 1, wherein the Si content is from 0.5% to 0.7%.

4. The 1180 MPa grade cold-rolled annealed dual-phase steel plate as claimed in claim 1, wherein the Mn content is from 2.7% to 2.85%.

5. The 1180 MPa grade cold-rolled annealed dual-phase steel plate as claimed in claim 1, wherein the Al content is from 0.015% to 0.045%.

6. The 1180 MPa grade cold-rolled annealed dual-phase steel plate as claimed in claim 1, wherein the Nb content is from 0.015% to 0.025%.

7. The 1180 MPa grade cold-rolled annealed dual-phase steel plate as claimed in claim 1, wherein the Ti content is from 0.015% to 0.025%.

8. The 1180 MPa grade cold-rolled annealed dual-phase steel plate as claimed in claim 1, wherein the dual-phase steel plate has a fine and uniform martensite-ferrite dual-phase structure, and wherein the dual-phase steel plate contains at least 75% of martensite, and a rest is ferrite the martensite has a grain size of not more than 5 micrometers, and the ferrite has a grain size of not more than 5 micrometers.

9. The 1180 MPa grade cold-rolled annealed dual-phase steel plate as claimed in claim 1, wherein the dual-phase steel plate has a yield strength of more than 850 MPa, a tensile strength of more than 1180 MPa, an elongation rate of 8% or more, and a parameter (R/t), characterizing 90° cold bending performance, of 2.5 or less, wherein R is bend radius, and t is plate thickness in mm.

10. A method for manufacturing the 1180 MPa grade cold-rolled annealed dual-phase steel plate as claimed in claim 1, wherein the method comprises: 1) smelting and casting into a slab having a chemical composition claimed in claim 1; 2) hot rolling including firstly, heating to 1100° C.-1230° C. and holding for 0.6 hours or more, and then hot rolling at a temperature of Ar3 or more, after rolling, rapidly cooling at a rate of 30° C./s-100° C./s coiling at a temperature of 400° C.-500° C., after coiling, slowly cooling to 370° C. or less at a cooling rate of not more than 0.3° C./s; 3) cold rolling that is controlled at a reduction rate of 50%-70%; 4) annealing at a soaking temperature of 790° C.-840° C., then cooling at a rate of v=3° C./s-20° C./s to a rapid cooling start temperature T, wherein the rapid cold start temperature satisfies T≥800-30×v, and then cooling to 200° C.-270° C. at a rate of 30° C./s-100° C./s; 5) tempering at a temperature of 200° C.-270° C. for 100 s-400 s; and 6) leveling to a degree of 0%-0.3%.

11. A 1180 MPa grade cold-rolled annealed dual-phase steel plate, comprising following chemical composition by mass percentages: C: 0.1%-0.125%, Si: 0.4%-0.8%, Mn: 2.6%-2.9%, Al: 0.01%-0.05%, Nb: 0.01%-0.03%, and Ti: 0.01%-0.03%, a remainder being Fe and unavoidable impurities, wherein C, Mn and Si contents satisfy that 1.73×[C]×[Mn]+[Si]≥1, and Nb and Ti contents satisfy that [Nb]+[Ti]×3≥0.047, and wherein the steel plate does not contain Mo and does not contain Cr.

Description

DETAILED DESCRIPTION

(1) The invention will be further explained and illustrated in conjunction with the specific Examples. However, the explanations and illustrations are not intended to unduly limit the technical solutions of the present invention.

(2) The compositions of the steel of the Examples of the present invention are shown in Table 1, and the balance in the steel is Fe. Table 2 lists the process parameters of the steel plates of the Examples. Table 3 lists the performance parameters of the steel plates of the Examples.

(3) The method for manufacturing the steel of the Examples of the present invention is as follows:

(4) (1) smelting and casting: obtaining a slab with required alloy composition and minimize the contents of S and P.

(5) 2) hot rolling: firstly, heating to 1100-1230° C. and holding for 0.6 hours or more, and then hot rolling at a temperature of Ar3 or more, after rolling, rapidly cooling at a rate of 30-100° C./s; in the hot rolling process, low temperature coiling (400-500° C.) is performed in the bainite transformation zone to ensure that the final hot-rolled structure has a bainite content of 80% or more; after coiling, it is cooled to a temperature of 370° C. or less at a cooling rate of not more than 0.3° C./s, and does not enter the martensite transformation zone, to ensure that the hot rolling strength meets the requirements of cold rolling manufacturability;

(6) 3) cold rolling: the cold rolling is controlled at a reduction rate of 50-70%;

(7) 4) annealing: annealing at a soaking temperature of 790-840° C., preferably 800-820° C.; then cooling at a rate of v=3-20° C./s to the rapid cooling start temperature T, wherein the rapid cold start temperature T≥800−30×v, and then cooling to 200-270° C. at a rate of 30-100° C./s;

(8) 5) tempering: tempering at a temperature of 200-270° C. for 100-400 s;

(9) 6) leveling: leveling to a degree of 0-0.3%.

(10) Table 3 shows the mechanical properties of Examples 1-18 (i.e., low-cost and high-formability 1180 MPa grade cold-rolled annealed dual-phase steel plates obtained according to the compositions and processes of the present invention). The steel plate of the present invention has a yield strength of more than 850 MPa, a tensile strength of more than 1180 MPa, an elongation rate of 8% or more, and a parameter (R/t), characterizing the 90° cold bending performance, of 2.5 or less. It can be seen that the low-cost and high-formability 1180 MPa grade cold-rolled annealed dual-phase steel plate according to the present invention achieves a tensile strength of more than 1180 MPa, a good elongation rate, and excellent cold bending property without adding precious alloying elements such as Mo and Cr.

(11) TABLE-US-00001 TABLE 1 Unit: mass percentage Number C Si Mn Al P S N Nb Ti Example 1 0.101 0.562 2.817 0.032 0.013 0.0016 0.0035 0.023 0.021 Example 2 0.101 0.562 2.817 0.032 0.013 0.0016 0.0035 0.023 0.021 Example 3 0.101 0.562 2.817 0.032 0.013 0.0016 0.0035 0.023 0.021 Example 4 0.102 0.56 2.740 0.028 0.011 0.0020 0.0045 0.021 0.021 Example 5 0.102 0.56 2.740 0.028 0.011 0.0020 0.0045 0.021 0.021 Example 6 0.102 0.56 2.740 0.028 0.011 0.0020 0.0045 0.021 0.021 Example 7 0.110 0.63 2.760 0.045 0.009 0.0022 0.0037 0.025 0.021 Example 8 0.110 0.63 2.760 0.045 0.009 0.0022 0.0037 0.025 0.021 Example 9 0.110 0.63 2.760 0.045 0.009 0.0022 0.0037 0.025 0.021 Example 10 0.120 0.63 2.760 0.038 0.011 0.0015 0.0031 0.026 0.021 Example 11 0.120 0.63 2.760 0.038 0.011 0.0015 0.0031 0.026 0.021 Example 12 0.120 0.63 2.760 0.038 0.011 0.0015 0.0031 0.026 0.021 Example 13 0.124 0.57 2.80 0.026 0.008 0.0012 0.0043 0.023 0.021 Example 14 0.124 0.57 2.80 0.026 0.008 0.0012 0.0043 0.023 0.021 Example 15 0.124 0.57 2.80 0.026 0.008 0.0012 0.0043 0.023 0.021 Example 16 0.115 0.65 2.68 0.033 0.013 0.0010 0.0035 0.021 0.023 Example 17 0.115 0.65 2.68 0.033 0.013 0.0010 0.0035 0.021 0.023 Example 18 0.115 0.65 2.68 0.033 0.013 0.0010 0.0035 0.021 0.023

(12) TABLE-US-00002 TABLE 2 Annealing Hot rolling Cold Rapid Hot Cooling rolling Rapid cooling Tempering Heat- roll- Coil- rate after Cold Anneal- cooling termi- Temper- ing Hold- ing Cool- ing coiling rolling ing start Rapid nation ing Temper- temper- ing temper- ing temper- (cooling to reduction temper- temper- cooling temper- temper- ing ature time ature rate ature 370° C.) rate ature v1 ature T rate ature ature time Number (° C.) (h) (° C.) (° C./s) (° C.) (° C./s) (%) (° C.) (° C./s) (° C.) (° C./s) (° C.) (° C.) (s) Exam- 1230 1 880 50 450 0.3 60 800 5 670 50 240 240 200 ple 1 Exam- 1230 1 880 50 450 0.3 60 820 5 670 50 240 240 200 ple 2 Exam- 1230 1 880 50 450 0.3 60 840 5 670 50 240 240 200 ple 3 Exam- 1230 1 880 50 450 0.3 60 800 5 670 50 240 240 200 ple 4 Exam- 1230 1 880 50 450 0.3 60 820 5 670 50 240 240 200 ple 5 Exam- 1230 1 880 50 450 0.3 60 840 5 670 50 240 240 200 ple 6 Exam- 1230 1 880 50 450 0.3 60 800 5 670 50 240 240 200 ple 7 Exam- 1230 1 880 50 450 0.3 60 820 5 670 50 240 240 200 ple 8 Exam- 1230 1 880 50 450 0.3 60 840 5 670 50 240 240 200 ple 9 Exam- 1230 1 880 50 450 0.3 60 800 5 670 50 240 240 200 ple 10 Exam- 1230 1 880 50 450 0.3 60 820 5 670 50 240 240 200 ple 11 Exam- 1230 1 880 50 450 0.3 60 840 5 670 50 240 240 200 ple 12 Exam- 1230 1 880 50 450 0.3 60 800 5 670 50 240 240 200 ple 13 Exam- 1230 1 880 50 450 0.3 60 820 5 670 50 240 240 200 ple 14 Exam- 1230 1 880 50 450 0.3 60 840 5 670 50 240 240 200 ple 15 Exam- 1150 0.6 880 40 400 0.2 70 810 5 650 40 220 220 250 ple 16 Exam- 1200 1 890 50 460 0.25 60 810 10 670 60 240 240 200 ple 17 Exam- 1250 1.5 900 60 500 0.3 50 810 15 690 80 260 260 150 ple 18

(13) TABLE-US-00003 TABLE 3 90° Yield Tensile Elongation bending Plate strength strength rate radius R thickness t Number (MPa) (MPa) (%) (mm) (mm) R/t Example 1 858 1180 9.3 2.0 1.1 1.8 Example 2 855 1183 8.6 2.0 1.1 1.8 Example 3 874 1196 8.2 2.0 1.1 1.8 Example 4 901 1197 8.6 2.0 1.2 1.7 Example 5 954 1225 8.3 2.0 1.2 1.7 Example 6 913 1217 8.2 2.0 1.2 1.7 Example 7 855 1288 9.1 2.0 1.1 1.9 Example 8 902 1191 8.4 2.0 1.0 2 Example 9 886 1231 8.2 2.0 1.0 2 Example 10 853 1242 10.3 2.0 1.0 2 Example 11 858 1228 8.4 2.0 1.1 1.9 Example 12 931 1258 8.6 2.0 1.0 2 Example 13 894 1278 9.4 2.0 1.1 1.8 Example 14 882 1269 8.6 2.0 1.1 1.8 Example 15 1021 1324 8.5 2.0 1.3 1.6 Example 16 874 1232 9.0 2.0 1.0 2 Example 17 883 1223 9.1 2.0 1.0 2 Example 18 867 1234 8.7 2.0 1.0 2