Ultrahigh-strength hot-rolled steel sheet and steel strip having good fatigue and reaming properties and manufacturing method therefor
11578380 · 2023-02-14
Assignee
Inventors
Cpc classification
C22C38/002
CHEMISTRY; METALLURGY
C21D8/021
CHEMISTRY; METALLURGY
International classification
Abstract
An ultra-high-strength hot-rolled steel plate and steel strip having good fatigue and reaming properties and a manufacturing method therefor. The weight percentages of the components of the steel plate and the steel strip are: C: 0.07-0.14%, Si: 0.1-0.4%, Mn: 1.55-2.00%, P≤0.015%, S≤0.004%, Al: 0.01-0.05%, N≤0.005%, Cr: 0.15-0.50%, V: 0.1-0.35%, Nb: 0.01%-0.06%, Mo: 0.15-0.50%, Ti≤0.02%, and the balance of Fe and unavoidable impurities. Such components need to meet: 1.0≤[(Cr/52)/(C/4)+(Nb/93+Ti/48+V/51+Mo/96)/(C/12)]≤1.6. The tensile strength of the ultrahigh-strength hot-rolled steel plate and steel strip is ≥780 MPa, the yield strength thereof is ≥660 MPa, the tensile fatigue limit (10 million cycles) FL thereof is ≥570 MPa, or the fatigue limit to tensile strength FL/Rm thereof is ≥0.72. The reaming rate meets: if an original hole is a punched hole, the reaming rate thereof is >85%; and if the original hole is a reamed hole, the reaming rate thereof is >120%.
Claims
1. A ultra-high-strength hot-rolled steel plate or steel strip with good fatigue and reaming performances, with a chemical composition based on weight percentage being: C: 0.07-0.14%, Si: 0.1-0.4%, Mn: 1.55-2.00%, P≤0.015%, S≤0.004%, Al: 0.01-0.05%, N≤0.005%, Cr: 0.15-0.50%, V: 0.1-0.35%, Nb: 0.01%-0.06%, Mo: 0.15-0.50%, and Ti≤0.02%, and a balance of Fe and unavoidable impurities, wherein the above elements meet the following relationship: 1.0≤[(Cr/52)/(C/4)+(Nb/93+Ti/48+V/51+Mo/96)/(C/12)]≤1.6, wherein in a microstructure of the ultra-high-strength hot-rolled steel plate or steel strip, lower bainite has a content of 30%-70% by volume, and wherein the ultra-high-strength hot-rolled steel plate or steel strip has a tensile strength ≥780 MPa; a yield strength ≥660 MPa; a reaming rate performance index: a reaming rate >85% if an original hole is a punched hole; or a reaming rate >120% if an original hole is a reamed hole; and a fatigue resistance performance index: a high frequency fatigue limit after 10 million cycles FL≥570 MPa, or a ratio of fatigue limit to tensile strength FL/Rm≥0.72.
2. The ultra-high-strength hot-rolled steel plate or steel strip with good fatigue and reaming performances according to claim 1, wherein in the chemical composition of the ultra-high-strength hot-rolled steel plate or steel strip, C: 0.07-0.09% based on weight percentage.
3. The ultra-high-strength hot-rolled steel plate or steel strip with good fatigue and reaming performances according to claim 1, wherein in the chemical composition of the ultra-high-strength hot-rolled steel plate or steel strip, Si: 0.1-0.3% based on weight percentage.
4. The ultra-high-strength hot-rolled steel plate or steel strip with good fatigue and reaming performances according to claim 1, wherein in the chemical composition of the ultra-high-strength hot-rolled steel plate or steel strip, Mn: 1.70-1.90% based on weight percentage.
5. The ultra-high-strength hot-rolled steel plate or steel strip with good fatigue and reaming performances according to claim 1, wherein in the chemical composition of the ultra-high-strength hot-rolled steel plate or steel strip, Cr: 0.35-0.50% based on weight percentage.
6. The ultra-high-strength hot-rolled steel plate or steel strip with good fatigue and reaming performances according to claim 1, wherein in the chemical composition of the ultra-high-strength hot-rolled steel plate or steel strip, V: 0.12-0.22% based on weight percentage.
7. The ultra-high-strength hot-rolled steel plate or steel strip with good fatigue and reaming performances according to claim 1, wherein in the chemical composition of the ultra-high-strength hot-rolled steel plate or steel strip, Mo: 0.15-0.3% based on weight percentage.
8. The ultra-high-strength hot-rolled steel plate or steel strip with good fatigue and reaming performances according to claim 1, wherein in the chemical composition of the ultra-high-strength hot-rolled steel plate or steel strip, Ti≤0.005% based on weight percentage.
9. The ultra-high-strength hot-rolled steel plate or steel strip with good fatigue and reaming performances according to claim 1, wherein in the chemical composition of the ultra-high-strength hot-rolled steel plate or steel strip, Ti≤0.003%, N≤0.003% based on weight percentage.
10. The ultra-high-strength hot-rolled steel plate or steel strip with good fatigue and reaming performances according to claim 1, wherein the ultra-high-strength hot-rolled steel plate or steel strip has a tensile strength ≥780 MPa; a yield strength ≥660 MPa; a reaming rate performance index: a reaming rate >85% if the original hole is a punched hole; or a reaming rate >120% if the original hole is a reamed hole; and a fatigue resistance performance index: a high frequency fatigue limit after 10 million cycles FL≥600 MPa, or a ratio of fatigue limit to tensile strength FL/Rm≥0.75.
11. The ultra-high-strength hot-rolled steel plate or steel strip with good fatigue and reaming performances according to claim 1, wherein the ultra-high-strength hot-rolled steel plate or steel strip has a fatigue resistance performance index: a high frequency fatigue limit after 10 million cycles FL≥640 MPa, or a ratio of fatigue limit to tensile strength FL/Rm≥0.8.
12. A method for manufacturing the ultra-high-strength hot-rolled steel plate or steel strip with good fatigue and reaming performances according to claim 1, comprising: 1) Smelting and casting the chemical composition according to claim 1; 2) Rolling, wherein a heating temperature is 1100-1250° C.; an initial rolling temperature for finish rolling is 950-1000° C., and a final rolling temperature for finish rolling is 900-950° C.; 3) Cooling, wherein a cooling rate is ≥30° C./s; and a coiling temperature is 450-580° C.; and 4) Pickling.
13. The method for manufacturing the ultra-high-strength hot-rolled steel plate or steel strip with good fatigue and reaming performances according to claim 12, wherein after the cooling and coiling in Step 3), the method further includes heat insulation and slow cooling, wherein a temperature is controlled at 450° C. or higher for 2-4 hours.
14. The ultra-high-strength hot-rolled steel plate or steel strip with good fatigue and reaming performances according to claim 8, wherein the ultra-high-strength hot-rolled steel plate or steel strip has a tensile strength ≥780 MPa; a yield strength ≥660 MPa; a reaming rate performance index: a reaming rate >85% if the original hole is a punched hole; or a reaming rate>120% if the original hole is a reamed hole; and a fatigue resistance performance index: a high frequency fatigue limit after 10 million cycles FL≥600 MPa, or a ratio of fatigue limit to tensile strength FL/Rm≥0.75.
15. The ultra-high-strength hot-rolled steel plate or steel strip with good fatigue and reaming performances according to claim 9, wherein the ultra-high-strength hot-rolled steel plate or steel strip has a fatigue resistance performance index: a high frequency fatigue limit after 10 million cycles FL≥640 MPa, or a ratio of fatigue limit to tensile strength FL/Rm≥0.8.
16. The method for manufacturing the ultra-high-strength hot-rolled steel plate or steel strip with good fatigue and reaming performances according to claim 12, wherein in the chemical composition of the ultra-high-strength hot-rolled steel plate or steel strip, C: 0.07-0.09%, Si: 0.1-0.3%, Mn: 1.70-1.90%, Cr: 0.35-0.50%, V: 0.12-0.22%, Mo: 0.15-0.3%, and Ti≤0.005%, based on weight percentage.
Description
DESCRIPTION OF THE DRAWINGS
(1)
(2)
DETAILED DESCRIPTION
(3) The disclosure will be further illustrated with reference to the following specific Examples. The steel materials of different compositions shown in Table 1 were smelted, and then subjected to the heating+hot rolling process as shown in Table 2 to obtain steel plates having a thickness of less than 4 mm. Transverse JIS 5# tensile samples were prepared to measure the yield strength and tensile strength. Central parts of the plates were taken to measure the reaming rate and fatigue limit. Transverse samples were used for the fatigue limit measurement. As regards the sample dimensions and experimental methods, reference was made to GB 3075-2008 Metal Axial Fatigue Testing Method. The test data are shown in Table 2. The reaming rate was measured using a reaming test, wherein a test piece with a hole in the center was pressed into a die with a punch to expand the central hole of the test piece until the edge of the hole in the plate necked or through-plate cracks appeared. Due to the great influence of the way for forming the original hole in the center of the test piece on the test results of the reaming rate, punching and reaming were used to form the original hole in the center of the test piece respectively. The subsequent tests and test methods were performed according to the reaming rate test method as specified in the ISO/DIS 16630 standard. The fatigue limit was measured according to the axial high-frequency tensile fatigue test. Particularly, the GB 3075-2008 metal axial fatigue test method was used, wherein the test frequency was 85 Hz. The maximum strength of the sample having no failure after 10 million cycles of loading was taken as the fatigue limit RL.
(4) In Table 1, Examples A to H are the inventive steel compositions, while the contents of carbon or manganese or other alloying elements in Comparative Examples J to P are outside of the corresponding ranges defined for the inventive compositions. Note: M (all) in the table refers to the calculated value of (Cr/52)/(C/4)+(Nb/93+Ti/48+V/51+Mo/96)/(C/12) in the composition.
(5) As shown by Tables 1 to 3, when the contents of the alloying components such as C and Mn deviate from the scope of the present disclosure, for example, when the contents of C and Mn are lower, the yield strength of the steel of Comparative Examples J and K is less than 660 MPa, and the tensile strength is less than 780 MPa. When the contents of C and Mn are higher than the corresponding ranges defined for the inventive compositions, the hot-rolled structure contains a large amount of martensite, which will have a negative influence on the formability of the steel, and the reaming performance will deteriorate. This does not meet the purpose of the present disclosure. For example, the reaming rates of Comparative Examples I and L are both lower than that of the present disclosure.
(6) When the content of the Ti element deviates from the scope of the present disclosure, the fatigue limit of the steel will be affected negatively. For example, Comparative Examples M, N, O, P may be mentioned. The Ti contents in Comparative Examples M and P are too high, so that their fatigue limits are much lower than 570 MPa, and their fatigue limit ratios are also much lower than the minimum design standard of 0.72, although the strength of the steel reaches the strength standard designed by the present disclosure. The Ti contents in Comparative Examples N and O are lower, but still exceed the upper limit defined by the present disclosure, so that their fatigue limits and fatigue limit ratios do not meet the requirements of the present disclosure. At the same time, in the compositional design of these two groups, the ratios of the alloying elements and the carbon element, namely M (all), do not fall in the range designed for the present disclosure, so that the reaming performance of these two groups of materials does not meet the standard.
(7) As shown by Tables 2 to 3, when the final rolling temperature of the coil is rather low, such as in the case of Comparative Steel Samples A-2 and F-1 in Table 2, the reaming rate does not meet the design standard of the present disclosure. When the coiling temperature is higher than 550° C., pearlite structure and a large amount of carbide precipitates are generated, which deteriorates the reaming performance, such as in the case of Comparative Example F-2. In addition, in the case that the heat insulation and slow cooling technology is utilized, when the heat insulation temperature is too low, precipitation of carbides will be suppressed, resulting in insufficient steel strength. If the heat insulation time is too long, a large amount of coarse carbides will be generated, which has a negative influence on the reaming rate, such as in the case of Comparative Examples F-3, G-3 and H-3.
(8) As shown by
(9) To sum up, by reasonably controlling the content ranges of the components, adding micro-alloying elements, and limiting the content of the Ti element on the basis of carbon-manganese steel, and further by controlling the coiling temperature on the basis of a conventional automotive steel production line, and still further by utilizing the heat insulation and slow cooling technology according to the present disclosure, an ultra-high-strength hot-rolled steel plate and an ultra-high-strength hot-rolled steel strip having good reaming and fatigue performances are produced, wherein the yield strength Rp0.2≥660 MPa, tensile strength Rm≥780 MPa, reaming rate≥85% (the original hole is a punched hole), reaming rate ≥120% (the original hole is a reamed hole), high frequency fatigue limit strength RL≤570 MPa, or tensile fatigue limit ratio RL/Rm≥0.72, suitable for manufacturing automobile chassis, suspension parts and other products.
(10) TABLE-US-00001 TABLE 1 (unit: weight %) C Si Mn P N Al S Nb Ti V Cr Mo M(all) Ex. A 0.09 0.35 1.75 0.011 0.005 0.031 0.003 0.055 0.018 0.10 0.45 0.16 1.00 Ex. B 0.07 0.24 1.87 0.011 0.004 0.027 0.003 0.030 0.015 0.20 0.35 0.21 1.54 Ex. C 0.14 0.40 1.57 0.010 0.004 0.036 0.004 0.045 0.016 0.33 0.42 0.18 1.02 Ex. D 0.07 0.28 1.59 0.010 0.005 0.034 0.003 0.025 0.009 0.15 0.44 0.19 1.41 Ex. E 0.11 0.40 1.63 0.010 0.005 0.031 0.003 0.030 0.005 0.13 0.50 0.41 1.14 Ex. F 0.09 0.15 1.55 0.010 0.003 0.036 0.003 0.025 0.004 0.27 0.46 0.27 1.52 Ex. G 0.07 0.20 1.62 0.010 0.002 0.024 0.002 0.020 0.003 0.21 0.37 0.15 1.43 Ex. H 0.09 0.29 1.55 0.011 0.004 0.026 0.002 0.015 0.005 0.16 0.39 0.20 1.06 Comp. Ex. I 0.15 0.25 1.82 0.012 0.005 0.030 0.004 0.048 0.020 0.10 0.50 0.17 0.63 Comp. Ex. J 0.057 0.39 1.64 0.014 0.004 0.018 0.004 0.034 0.014 0.11 0.34 0.16 1.40 Comp. Ex. K 0.08 0.40 1.47 0.012 0.005 0.021 0.003 0.014 0.018 0.10 0.37 0.17 0.99 Comp. Ex. L 0.08 0.38 2.20 0.016 0.004 0.014 0.002 0.026 0.019 0.16 0.50 0.16 1.30 Comp. Ex. M 0.07 0.24 1.87 0.011 0.004 0.027 0.003 0.030 0.075 0.35 0.71 Comp. Ex. N 0.08 0.30 1.57 0.010 0.005 0.036 0.003 0.046 0.027 0.25 0.45 0.30 1.80 Comp. Ex. O 0.14 0.40 1.57 0.010 0.005 0.036 0.004 0.025 0.025 0.15 0.42 0.18 0.71 Comp. Ex. P 0.10 0.35 1.90 0.010 0.004 0.038 0.004 0.030 0.12 0.15 0.44 0.24 1.33
(11) TABLE-US-00002 TABLE 2 Final Rolling Heating Temperature Cooling Coiling Heat Insulation Temperature For Finish Rate Temperature And Slow Cooling Steel (° C.) Rolling (° C.) (° C./s) (° C.) (° C., h) Ex. A-1 1240 910 40 530 No heat insulation Comp. Ex. A-2 1210 880 50 400 No heat insulation Ex. B-1 1250 910 40 520 No heat insulation Ex. B-2 1250 910 40 520 520, 4 Ex. C 1220 900 50 450 No heat insulation Ex. D 1250 910 35 570 No heat insulation Ex. E 1250 920 45 510 No heat insulation Comp. Ex. F-1 1190 870 30 500 No heat insulation Comp. Ex. F-2 1230 900 30 600 No heat insulation Comp. Ex. F-3 1250 920 40 450 420, 3 Ex. F-4 1240 910 40 550 510, 4 Ex. G-1 1250 920 45 520 No heat insulation Ex. G-2 1230 910 40 520 500, 4 Comp. Ex. G-3 1240 910 40 520 500, 8 Ex. H-1 1230 900 40 530 No heat insulation Ex. H-2 1230 900 40 530 500, 3 Comp. Ex. H-3 1220 900 40 530 500, 6 Comp. Ex. I 1220 900 40 550 No heat insulation Comp. Ex. J 1230 910 40 450 No heat insulation Comp. Ex. K 1220 910 40 510 No heat insulation Comp. Ex. L 1250 920 40 550 No heat insulation Comp. Ex. M 1230 910 45 450 No heat insulation Comp. Ex. N 1210 900 40 520 No heat insulation Comp. Ex. O 1230 910 40 520 No heat insulation Comp. Ex. P 1220 910 40 520 No heat insulation
(12) TABLE-US-00003 TABLE 3 Rp0.2 Rm Reaming Rate Reaming Rate Steel (MPa) (MPa) A50(%) FL (MPa) FL/Rm Punched Hole (%) Reamed Hole (%) Ex. A-1 701 805 16.5 600 0.75 94.2 129.0 Comp. Ex. A-2 715 846 15.1 590 0.70 75.2 93.1 Ex. B-1 682 803 16.6 600 0.75 96.4 135.2 Ex. B-2 732 839 15.5 620 0.74 88.2 123.7 Ex. C 763 870 15.1 610 0.70 85.2 120.6 Ex. D 695 813 17.0 610 0.75 89.9 125.0 Ex. E 720 825 16.2 620 0.75 87.8 122.7 Comp. Ex. F-1 707 809 17.5 600 0.74 79.8 113.4 Comp. Ex. F-2 738 848 14.8 590 0.70 70.3 88.0 Comp. Ex. F-3 652 777 18.0 570 0.73 88.3 108.9 Ex. F-4 749 842 15.5 630 0.75 86.5 120.5 Ex. G-1 671 788 17.8 630 0.80 97.7 129.8 Ex. G-2 707 809 16.5 640 0.79 93.3 127.5 Comp. Ex. G-3 725 840 15.0 600 0.71 72.0 98.8 Ex. H-1 678 789 17.5 620 0.79 100.2 138.0 Ex. H-2 703 812 15.8 620 0.76 91.7 120.1 Comp. Ex. H-3 722 833 14.0 590 0.71 74.9 110.5 Comp. Ex. I 703 916 15.1 570 0.62 75.4 98.9 Comp. Ex. J 643 757 18.1 530 0.70 89.1 127.3 Comp. Ex. K 657 764 16.5 540 0.71 84.8 118.0 Comp. Ex. L 732 885 10.0 560 0.63 79.9 104.7 Comp. Ex. M 718 842 13.5 540 0.64 61.6 88.2 Comp. Ex. N 743 899 10.8 560 0.62 60.2 86.9 Comp. Ex. O 775 934 9.0 560 0.60 50.2 77.1 Comp. Ex. P 690 901 12.8 530 0.59 60.1 82.4