Ultra-low-carbon cold-rolled high-strength steel applicable to electrostatic dry powder enameling and manufacturing method thereof

Claims

1. Ultra-low carbon cold-rolled high-strength steel applicable for electrostatic dry powder enameling, containing Fe and unavoidable impurity elements, as well as the following chemical elements, wt.%: C 0,002-0,010 If ≤0,05 Mn 0,25-1,0 R 0,04-0,08 S 0,01-0,04 Al 0,01-0,05 Su 0,02-0,08 You 0,05-0,12 In 0,02-0,10 N 0,004-0,012 where the chemical elements satisfy at least one of the following formulas M*>0, where M*=Ti-S×1.5-N×3.4-C×4>0; N*≥0.012, where N*=(Mn+P)×Mo; where each chemical element in the formulas represents the mass percentage value of that chemical element before the percent symbol.

2. Ultra-low-carbon cold-rolled high-strength steel according to item 1, wherein the chemical elements have the following content, wt.%: C 0,002-0,010 If ≤0,05 Mn 0,25-1,0 R 0,04-0,08 S 0,01-0,04 Al 0,01-0,05 Su 0,02-0,08 You 0,05-0,12 In 0,02-0,10 N 0,004-0,012 If 0,01-0,045 Fe and unavoidable impurity elements the rest, where the chemical elements satisfy at least one of the following formulas M*>0, where M*=Ti-S×1.5-N×3.4-C×4>0; N*≥0.012, where N*=(Mn+P)×Mo, where each chemical element in the formulas represents the mass percentage value of that chemical element before the percent symbol.

3. Ultra-low-carbon cold-rolled high-strength steel according to claim 1 or 2, wherein the steel additionally contains at least one of the following chemical elements, %: B 0,0006-0,003 Nb 0,02-0,06 4. An ultra-low-carbon cold-rolled high-strength steel according to claim 1 or 2, wherein the steel has a microstructure that is exclusively ferrite.

5. Ultra-low-carbon cold-rolled high-strength steel according to claim 4, in which the ferrite has a grain size of class 9-11.

6. Ultra-low-carbon cold-rolled high-strength steel according to item 1 or 2, where the steel has a thickness of 0.7-3.5 mm.

7. Ultra-low-carbon cold-rolled high-strength steel according to claim 1 or claim 2, wherein the steel characteristics satisfy: yield strength ≥200 MPa, tensile strength ≥400 MPa, elongation ≥30% and yield strength drop <10% after high-temperature enamel firing at 840-870°C, preferably when held for 5 min during high-temperature enamel firing.

8. Ultra-low-carbon cold-rolled high-strength steel according to claim 7, wherein the steel characteristics satisfy: yield strength ≥220 MPa, tensile strength ≥410 MPa, elongation ≥34% and yield strength drop <6.5% after enamel firing by holding at 840-870°C for 5 min.

9. Ultra-low-carbon cold-rolled high-strength steel according to claim 1 or 2, where after firing the enamel by holding at 840-870°C for 5 min., the steel characteristics satisfy: yield strength ≥210 MPa, tensile strength ≥370 MPa, elongation ≥34%.

10. A method for producing ultra-low-carbon cold-rolled high-strength steel according to any one of paragraphs 1-9, comprising the following stages: (1) melting and casting; (2) heating the cast blank; (3) hot rolling; (4) Laminar cooling: adjusting the cooling rate at 10-30°C / s to cool the steel sheet to the coiling temperature; (5) Rolling: Rolling at 600-680°C, then air cooling to room temperature; (6) etching; (7) cold rolling; (8) annealing; (9) training.

11. The manufacturing method according to item 10, wherein at stage (2) the heating temperature is regulated at a level of 1180-1260°C.

12. The manufacturing method according to claim 10, wherein in step (3), the heated cast blank is first subjected to rough rolling to obtain an intermediate blank, and then the intermediate blank is subjected to finish rolling, wherein the rough rolling temperature is adjusted to 900°C or higher, preferably 900-1080°C; the initial temperature of the finish rolling is 900-1050°C; and the final temperature of the finish rolling is 860-940°C.

13. The manufacturing method according to item 10, wherein at stage (7) the degree of compression during cold rolling is adjusted at a level of 70-95%.

14. The manufacturing method according to claim 10, wherein continuous annealing is used at step (8), and the annealing temperature is 770-830°C.

15. The manufacturing method according to claim 10, wherein at step (8) bell-type annealing is used, and the annealing temperature is 690-740°C. air cooling to room temperature; (6) etching; (7) cold rolling; (8) annealing; (9) training.

11. The manufacturing method according to item 10, wherein at stage (2) the heating temperature is regulated at a level of 1180-1260°C.

12. The manufacturing method according to claim 10, wherein in step (3), the heated cast blank is first subjected to rough rolling to obtain an intermediate blank, and then the intermediate blank is subjected to finish rolling, wherein the rough rolling temperature is adjusted to 900°C or higher, preferably 900-1080°C; the initial temperature of the finish rolling is 900-1050C; and the final temperature of the finish rolling is 860-940°C.

13. The manufacturing method according to item 10, wherein at stage (7) the degree of compression during cold rolling is adjusted at a level of 70-95%.

14. The manufacturing method according to claim 10, wherein continuous annealing is used at step (8), and the annealing temperature is 770-830°C.

15. The manufacturing method according to claim 10, wherein at step (8) bell-type annealing is used, and the annealing temperature is 690-740°C.