MULTI-LAYER COMPOSITE COLD-ROLLED STEEL PLATE AND MANUFACTURING METHOD THEREFOR

Abstract

Disclosed is a multi-layer composite cold-rolled steel plate, provided with an upper surface layer, a lower surface layer and at least one interlayer between the upper surface layer and the lower surface layer in the thickness direction of the steel plate, wherein the phase proportion of austenite in the microstructure of the upper surface layer and the lower surface layer is ≥95%, and the at least one interlayer comprises at least one first interlayer, with the phase proportion of martensite in the microstructure of the first interlayer being ≥85%. In addition, further disclosed is a method for manufacturing the multi-layer composite cold-rolled steel plate above, the method comprising the steps of: (1) preparing billets for various layers and assembling the billets; (2) rolling; (3) acid pickling and cold-rolling; (4) annealing, involving: controlling the annealing temperature to be 830-890° C., then cooling to 700-800° C. at a rate of 3-15° C./s, and then water-cooling until the steel plate temperature is below 100° C.; and (5) acid pickling the steel plate and then heating same to 180-240° C. for tempering, with the tempering time being 200-600 s. The multi-layer composite cold-rolled steel plate of the present invention has the characteristics of a high strength, a high formability and resistance to delayed cracking.

Claims

1. A multi-layer cold-rolled clad steel plate, wherein the multi-layer cold-rolled clad steel plate comprises an upper skin layer, a lower skin layer and an interlayer between the upper skin layer and the lower skin layer in a thickness direction of the steel plate, wherein the upper skin layer and the lower skin layer each comprise a microstructure having an austenite phase proportion of ≥95%; wherein the interlayer comprises at least one first interlayer, wherein the first interlayer comprises a microstructure having a martensite phase proportion of ≥85%.

2. The multi-layer cold-rolled clad steel plate according to claim 1, wherein the microstructure of the first interlayer further comprises at least one of ferrite, bainite, retained austenite, cementite and precipitates.

3. The multi-layer cold-rolled clad steel plate according to claim 1, wherein the first interlayer has a hardness HV of ≥400; and/or the first interlayer has a tensile strength of ≥1300 MPa.

4. The multi-layer cold-rolled clad steel plate according to claim 1, wherein the interlayer further comprises at least one second interlayer, wherein the second interlayer comprises a microstructure having a ferrite phase proportion of ≥70%; optionally, the microstructure of the second interlayer further comprises at least one of ferrite, bainite, retained austenite, cementite and precipitates.

5. The multi-layer cold-rolled clad steel plate according to claim 4, wherein the interlayer comprises two second interlayers.

6. The multi-layer cold-rolled clad steel plate according to claim 1, wherein the first interlayer has a thickness accounting for 80-95% of a total thickness of the multi-layer cold-rolled clad steel plate; and/or the upper skin layer and the lower skin layer have a combined thickness accounting for 5-20% of the total thickness of the multi-layer cold-rolled clad steel plate.

7. The multi-layer cold-rolled clad steel plate according to claim 4, wherein the second interlayer has a total thickness accounting for ≤15% of the total thickness of the multi-layer cold-rolled clad steel plate.

8. The multi-layer cold-rolled clad steel plate according to claim 1, wherein the multi-layer cold-rolled clad steel plate has a total thickness of 0.7-2.5 mm.

9. The multi-layer cold-rolled clad steel plate according to claim 1, wherein the multi-layer cold-rolled clad steel plate satisfies one or more of the following performances: an overall tensile strength of ≥1180 MPa, an overall yield strength of ≥1050 MPa, an elongation a of 5%-8%, no cracking when it is soaked in 1 mol/L hydrochloric acid for 300 hours under a stress level of 0.8*TS.

10. The multi-layer cold-rolled clad steel plate according to claim 1, wherein the first interlayer comprises, in addition to Fe, the following chemical elements in mass percentages: C: 0.15-0.3%, Si: 0-0.5%, Mn: 1.0-1.8%, B≤0.004%, Al: 0.02-0.1%, N≤0.005%, Ti: 0.015-0.04%.

11. The multi-layer cold-rolled clad steel plate according to claim 4, wherein the second interlayer comprises, in addition to Fe, the following chemical elements in mass percentages: C: 0.001-0.1%, Si: 0-1.5%, Mn: 0.1-1.8%, Al: 0.02-0.1%, N≤0.005%; optionally, the second interlayer further comprises one or more of Nb, V, Ti, Mo, Cr, and B in a total amount of ≤1% by mass.

12. The multi-layer cold-rolled clad steel plate according to claim 1, wherein the upper and lower skin layers comprise, in addition to Fe, the following chemical elements in mass percentages: C: 0.4-0.8%, Mn: 14-20%, Al: 1.0-2.0%, N: 0.001-0.003%.

13. The multi-layer cold-rolled clad steel plate according to claim 12, wherein the upper and lower skin layers further comprise RE: 0.05-0.15%.

14. A manufacturing method for the multi-layer cold-rolled clad steel plate according to claim 1, wherein the method comprises steps of: (1) Preparing blanks of layers and assembling them into a slab; (2) Hot rolling; (3) Pickling and cold rolling; (4) Annealing: controlling an annealing temperature at 830-890° C., then cooling to 700-800° C. at a rate of 3-15° C./s, and then water cooling to a steel plate temperature of lower than 100° C.; (5) Tempering by reheating the steel plate to 180-240° C. after pickling, wherein a tempering time is 200-600 s.

15. The manufacturing method according to claim 14, wherein: in step (2), the slab is heated to 1150-1260° C., and then hot rolling is performed, wherein a finishing rolling temperature is controlled at 830-930° C., and a coiling temperature is controlled at 500-650° C.; and/or in step (4), the water cooling is performed at a rate of 500° C./s.

16. The manufacturing method according to claim 14, wherein: the microstructure of the first interlayer of the multi-layer cold-rolled clad steel plate further comprises at least one of ferrite, bainite, retained austenite, cementite and precipitates; and/or the first interlayer has a hardness HV of 400; and/or the first interlayer has a tensile strength of 300 MPa; and/or the first interlayer has a thickness accounting for 80-95% of a total thickness of the multi-layer cold-rolled clad steel plate; and/or the first interlayer comprises, in addition to Fe, the following chemical elements in mass percentages: C: 0.15-0.3%, Si: 0-0.5%, Mn: 1.0-1.8%, B≤0.004%, Al: 0.02-0.1%, N≤0.005%, Ti: 0.015-0.04%.

17. The manufacturing method according to claim 14, wherein the interlayer of the multi-layer cold-rolled clad steel plate further comprises at least one second interlayer.

18. The manufacturing method according to claim 17, wherein: the second interlayer comprises a microstructure having a ferrite phase proportion of ≥70%; optionally, the microstructure of the second interlayer further comprises at least one of ferrite, bainite, retained austenite, cementite and precipitates; and/or the second interlayer comprises, in addition to Fe, the following chemical elements in mass percentages: C: 0.001-0.1%, Si: 0-1.5%, Mn: 0.1-1.8%, Al: 0.02-0.1%, N≤0.005%; optionally, the second interlayer further comprises one or more of Nb, V, Ti, Mo, Cr, and B in a total amount of ≤1% by mass; and/or the second interlayer has a total thickness accounting for 5% of the total thickness of the multi-layer cold-rolled clad steel plate; and/or the interlayer comprises two second interlayers.

19. The manufacturing method according to claim 14, wherein: the upper skin layer and the lower skin layer of the multi-layer cold-rolled clad steel plate have a combined thickness accounting for 5-20% of the total thickness of the multi-layer cold-rolled clad steel plate; and/or the upper and lower skin layers comprise, in addition to Fe, the following chemical elements in mass percentages: C: 0.4-0.8%, Mn: 14-20%, Al: 1.0-2.0%, N: 0.001-0.003%, and optional RE: 0.05-0.15%.

20. The manufacturing method according to claim 14, wherein the multi-layer cold-rolled clad steel plate satisfies one or more of the following performances: an overall tensile strength of ≥1180 MPa, an overall yield strength of ≥1050 MPa, an elongation a of 5%-8%, no cracking when it is soaked in 1 mol/L hydrochloric acid for 300 hours under a stress level of 0.8*TS.

Description

DETAILED DESCRIPTION

[0064] The multi-layer cold-rolled clad steel plate and the method for manufacturing the same according to the disclosure will be further explained and illustrated with reference to the specific examples. Nonetheless, the explanation and illustration are not intended to unduly limit the technical solution of the disclosure.

Examples 1-9

[0065] The multi-layer cold-rolled clad steel plates of Examples 1-9 according to the present disclosure were all prepared by the following steps:

[0066] (1) According to the chemical compositions shown in Table 1, the blanks for the layers were prepared and assembled: the raw slab materials for the layers to be combined were rolled to thicknesses according to the thickness fractions of the layers in the clad steel plate for later use; the adjoining interfaces of the layers were cleaned to remove impurities such as oxide scales; the contact boundaries of the layers were welded and sealed, and oxygen between the layers were evacuated; and then the layers were assembled into a slab by rolling cladding.

[0067] (2) Hot rolling: the slab was heated to 1150-1260° C., and then hot rolled. The finishing rolling temperature was controlled at 830-930° C., and the coiling temperature was controlled at 500-650° C.

[0068] (3) Pickling and cold rolling.

[0069] (4) Annealing: the annealing temperature was controlled at 830-890° C.; then the steel plate was cooled to 700-800° C. at a rate of 3-15° C./s; and then the steel plate was water cooled until the temperature of the steel plate was lower than 100° C.

[0070] (5) After the steel plate was pickled, it was reheated to 180-240° C. for tempering, wherein the tempering time was 200-600 s.

[0071] Among the multilayer cold-rolled clad steel plates of Examples 1-9 according to the present disclosure, it should be noted that:

[0072] The multi-layer cold-rolled clad steel plates of Examples 1-3 each had an upper skin layer, a lower skin layer, and an interlayer between the upper skin layer and the lower skin layer. The interlayer in each of Examples 1-3 had only one first interlayer, and there was no second interlayer.

[0073] The multi-layer cold-rolled clad steel plates of Examples 4-6 each had an upper skin layer, a lower skin layer, and two interlayers between the upper skin layer and the lower skin layer. The interlayer in each of Examples 4-6 had one first interlayer and one second interlayer.

[0074] The multi-layer cold-rolled clad steel plates of Examples 7-9 each had an upper skin layer, a lower skin layer, and three interlayers between the upper skin layer and the lower skin layer. The interlayer in each of Examples 7-9 had one first interlayer and two second interlayers.

[0075] The thickness fraction of each layer in the multilayer cold-rolled clad steel plate of each of Examples 1-9 is shown in Table 1.

[0076] Table 1 lists the thickness fraction of each layer in the multi-layer cold-rolled clad steel plate of each of Examples 1-9 according to the present disclosure.

TABLE-US-00001 TABLE 1 Second First Second Upper skin interlayer interlayer interlayer Lower skin No. layer (%) 1 (%) (%) 2 (%) layer (%) Ex. 1 2.5 — 95 — 2.5 Ex. 2 5 — 90 — 5 Ex. 3 10 — 80 — 10 Ex. 4 2.5 — 80 15 2.5 Ex. 5 5 — 80 10 5 Ex. 6 5 — 85 5 5 Ex. 7 2.5 7.5 80 7.5 2.5 Ex. 8 5 5 80 5 5 Ex. 9 5 2.5 85 2.5 5

[0077] Table 2-1, Table 2-2 and Table 2-3 list the mass percentages of the chemical elements in each layer in the multilayer cold-rolled clad steel plate of each of Examples 1-9 according to the present disclosure.

[0078] Table 2-1 lists the mass percentages of the chemical elements in the upper and lower skin layers in the multilayer cold-rolled clad steel plate of each of Examples 1-9. In the microstructure of the upper and lower skin layers, the austenite phase proportion (by volume) was ≥95%.

TABLE-US-00002 TABLE 2-1 (wt %, the balance is Fe and unavoidable impurities other than P and S) Chemical composition No. C Mn P S Al N RE Ex. 1 0.5 15 0.012 0.002 1.5 0.001 0.05 Ex. 2 0.4 20 0.01 0.0014 1.0 0.0025 0.07 Ex. 3 0.45 20 0.012 0.0013 1.2 0.003 0.09 Ex. 4 0.5 19 0.01 0.0013 1.4 0.003 0.10 Ex. 5 0.55 18 0.011 0.001 1.5 0.003 0.12 Ex. 6 0.6 17 0.012 0.0015 1.6 0.0023 0.11 Ex. 7 0.65 16 0.01 0.0011 1.7 0.001 0.13 Ex. 8 0.7 15 0.011 0.0012 1.9 0.0015 0.14 Ex. 9 0.8 14 0.012 0.0016 2.0 0.003 0.15

[0079] Table 2-2 lists the mass percentages of the chemical elements in the first interlayer in the multilayer cold-rolled clad steel plate of each of Examples 1-9. Each first interlayer had a hardness HV of ≥400, a tensile strength of ≥1300 MPa, and a martensite phase proportion (by volume) of ≥85%.

TABLE-US-00003 TABLE 2-2 (wt %, the balance is Fe and unavoidable impurities other than P and S) Chemical composition No. C Si Mn B P S Al N Ti Nb Ex. 1 0.2 0.1 1.55 0.0015 0.01 0.0015 0.025 0.002 0.015 0.01 Ex. 2 0.15 0.15 1.8 0 0.011 0.001 0.035 0.003 0.02 0.015 Ex. 3 0.17 0.25 1.5 0.002 0.01 0.0012 0.045 0.0025 0.025 0.01 Ex. 4 0.19 0.35 1.35 0.0025 0.012 0.0011 0.055 0.0035 0.03 0 Ex. 5 0.22 0.45 1.6 0.0005 0.01 0.0013 0.065 0.0045 0.04 0.01 Ex. 6 0.24 0.5 1.75 0 0.011 0.0014 0.075 0.005 0.03 0.01 Ex. 7 0.26 0.15 1.65 0.001 0.01 0.001 0.085 0.003 0.02 0 Ex. 8 0.28 0.05 1.25 0.0035 0.012 0.0012 0.095 0.002 0.025 0.01 Ex. 9 0.3 0.12 1.0 0.004 0.01 0.0015 0.1 0.0027 0.02 0.02

[0080] Table 2-3 lists the mass percentages of the chemical elements in the second interlayer(s) in the multilayer cold-rolled clad steel plate of each of Examples 4-9.

[0081] It should be noted that the multi-layer cold-rolled clad steel plate of each of Examples 4-6 only had one second interlayer 2, while the multi-layer cold-rolled clad steel plate of each of Examples 7-9 had both the second interlayer 1 and the second interlayer 2. In the microstructure of the second interlayer, the ferrite phase proportion (by volume) was ≥70%.

TABLE-US-00004 TABLE 2-3 (wt %, the balance is Fe and unavoidable impurities other than P and S) Chemical composition No. Type C Si Mn P S Al N Ti Nb Ex. 4 Second interlayer 2 0.002 0.03 0.5 0.013 0.002 0.02 0.005 0.03 0.04 Ex. 5 Second interlayer 2 0.04 0.05 0.8 0.01 0.0012 0.04 0.0045 0.03 0 Ex. 6 Second interlayer 2 0.1 0.5 0.1 0.011 0.001 0.06 0.0035 0 0.04 Ex. 7 Second interlayer 1 0.004 1.5 1.8 0.013 0.002 0.1 0.0035 0.03 0.03 Second interlayer 2 0.004 1.5 1.8 0.013 0.002 0.1 0.0035 0.03 0.03 Ex. 8 Second interlayer 1 0.01 0.04 0.5 0.01 0.0015 0.04 0.005 0.03 0.045 Second interlayer 2 0.01 0.04 0.4 0.01 0.0015 0.04 0.005 0.03 0.045 Ex. 9 Second interlayer 1 0.03 0.05 0.3 0.011 0.003 0.05 0.004 0.03 0.05 Second interlayer 2 0.03 0.05 0.5 0.011 0.003 0.05 0.004 0.03 0.05

[0082] Table 3 lists the specific process parameters for the multi-layer cold-rolled clad steel plates of Examples 1-9.

TABLE-US-00005 TABLE 3 Step (4) Step (2) Starting Rapid Finishing temperature cooling Step (5) Heating rolling Coiling Annealing Cooling of rapid mode and Tempering Tempering Thickness temperature temperature temperature temperature rate cooling rate temperature time No. (mm) (° C.) (° C.) (° C.) (° C.) (° C./s) (° C.) (° C./s) (° C.) (s) Ex. 1 0.7 1150 830 500 830 3 700 Water 180 600 quenching (≥500) Ex. 2 1.2 1200 860 550 840 5 720 Water 200 400 quenching (≥500) Ex. 3 1.5 1260 880 600 850 7 740 Water 220 300 quenching (≥500) Ex. 4 1.0 1230 900 650 860 10 760 Water 240 250 quenching (≥500) Ex. 5 1.6 1200 930 600 870 12 780 Water 220 200 quenching (≥500) Ex. 6 2.0 1230 880 600 880 15 800 Water 200 200 quenching (≥500) Ex. 7 1.9 1200 880 550 890 10 750 Water 220 250 quenching (≥500) Ex. 8 2.3 1230 900 550 850 7 760 Water 200 400 quenching (≥500) Ex. 9 2.5 1200 900 550 850 5 745 Water 220 500 quenching (≥500)

[0083] The multi-layer cold-rolled clad steel plates of Examples 1-9 obtained according to the present disclosure were subjected to various performance tests. The test results are listed in Table 4.

[0084] Table 4 lists the relevant performance parameters of the multi-layer cold-rolled clad steel plates of Examples 1-9. In the present disclosure, the overall yield strength σs, overall tensile strength σb, and elongation δ of the steel plates were measured in accordance with “GB/T 228.1-2010 Metal Materials-Tensile Test”; the minimum R/T of 90-degree bend was measured in accordance with “GB/T 232-2010 Metal Materials-Bend Test”; and the hardness was measured in accordance with “GB/T 4342-1991 Metal Materials-Vickers Microhardness Test”.

TABLE-US-00006 TABLE 4 90-degree bend minimum R/T (inside radius of curvature/ Stress Stress Stress σs σb δ plate level level level No. (MPa) (MPa) (%) thickness) 0.8*TS 1.0*TS 1.2*TS Ex. 1 1150 1450 7 0.5 ◯ ◯ ◯ Ex. 2 1050 1310 8 0.5 ◯ ◯ ◯ Ex. 3 1080 1400 7 0.5 ◯ ◯ ◯ Ex. 4 1120 1410 7.2 0.5 ◯ ◯ ◯ Ex. 5 1200 1550 5 0.5 ◯ ◯ ◯ Ex. 6 1260 1600 5 0.5 ◯ ◯ ◯ Ex. 7 1130 1420 7.1 0.5 ◯ ◯ ◯ Ex. 8 1190 1570 7 0.5 ◯ ◯ ◯ Ex. 9 1230 1640 6 0.5 ◯ ◯ ◯ Note: O—no cracking, X—cracking: representing the hydrogen induced cracking results when soaking the steel plates in 1 mol/L hydrochloric acid for 300 hours under a certain internal stress level.

[0085] As it can be seen from Table 4, the multi-layer cold-rolled clad steel plates of Examples 1-9 according to the present disclosure had an overall yield strength σs of 1050-1260 MPa, an overall tensile strength 6b of ≥1180MPa, and an elongation δ of 5%-8%, preferably 6%-8%. The multi-layer cold-rolled clad steel plates of Examples 1-9 didn't crack when they were immersed in 1 mol/L hydrochloric acid for 300 hours under stress levels of 0.8*TS, 1.0*TS and 1.2*TS. The multi-layer cold-rolled clad steel plates of each Example had high strength, high formability and resistance to delayed cracking.

[0086] The austenitic high manganese steel of the upper and lower skin layers of the multi-layer cold-rolled clad steel plate according to the present disclosure has the function of blocking hydrogen diffusion, thereby effectively reducing the hydrogen content inside the steel plate and improving the hydrogen-induced cracking resistance of the multi-layer cold-rolled clad steel plate. In addition, the austenitic high manganese steel used for the upper and lower skin layers has the characteristics of high strength (HV≥240) and ultra-high formability which can effectively improve the bending performance of the clad steel plate. Compared with the existing multi-layer clad steel plate prepared by a conventional rolling cladding process, the multi-layer cold-rolled clad steel plate according to the present disclosure has better performances. The first interlayer in the multi-layer cold-rolled clad steel plate according to the present disclosure has ultra-high hardness and ultra-high tensile strength which effectively ensure its high-strength performances.

[0087] In summary, as it can be seen, the multi-layer cold-rolled clad steel plate according to the present disclosure has the characteristics of high strength, high formability and delayed cracking resistance, can be effectively used in manufacture of automobile safety parts and structural parts, and is highly valuable and promising for popularization and application.

[0088] In addition, the ways in which the various technical features of the present disclosure are combined are not limited to the ways recited in the claims of the present disclosure or the ways described in the specific examples. All the technical features recited in the present disclosure may be combined or integrated freely in any manner, unless contradictions are resulted.

[0089] It should also be noted that the Examples set forth above are only specific examples according to the present disclosure. Obviously, the present disclosure is not limited to the above Examples. Similar variations or modifications made thereto can be directly derived or easily contemplated from the present disclosure by those skilled in the art. They all fall in the protection scope of the present disclosure.