High-strength cold-rolled steel sheet with excellent surface quality and minimal material deviation, and method for manufacturing the same.

Abstract

The present invention relates to a high-strength cold-rolled steel sheet with excellent surface quality and minimal material deviation, and a method for producing the same, and provides a high-strength cold-rolled steel sheet and a method for producing the same that ensure high strength and elongation and can be applied to automotive parts. [Solution] The material contains, by weight %, C: 0.05~0.3%, Si: 0.01~2.0%, Mn: 1.5~3.0%, Al: 0.01~0.1%, P: 0.001~0.015%, S: 0.001~0.01%, N: 0.001~0.01%, with the remainder being Fe and other unavoidable impurities. The value defined by the following relational formula 1 is 0.9 or more and less than 1.2. The microstructure, by area %, consists of bainite and martensite totaling 80% or more, with the remainder being ferrite. The average number of surface defects that satisfy one or more of the following conditions is 10 defects / m², with a depth of 100 μm or more and a short side length of 1 mm or more. 2 It is less than. [Relationship 1] C + (1.3 × Si + Mn) / 6 + (Cr + 1.2 × Mo) / 5 + 100 × B

Claims

1. In weight percent, C: 0.05-0.3%, Si: 0.01-2.0%, Mn: 1.5-3%. 0%, Al: 0.01-0.1%, P: 0.001-0.015%, S: 0.001-0 0.01%, N: 0.001-0.01%, the remainder being Fe and other unavoidable impurities. The value defined by the following relational expression 1 satisfies the condition of being 0.9 or greater and less than 1.

2. In terms of microstructure, the total area percentage of bainite and martensite is 80% or more. The remainder contains ferrite, Surface defects satisfying one or more of the following conditions: depth of 100 μm or more and short side length of 1 mm or more. The average number of pits is 10 per meter. ２ High-strength cold-rolled steel sheet that is less than [amount missing]. [Relationship 1] C+(1.3×Si+Mn) / 6+(Cr+1.2×Mo) / 5+100×B (In the above relational formula 1, C, Si, Mn, Cr, Mo, and B are relative to each element) This indicates the average content by weight percent. If none of the elements are added, 0 is substituted.

2. The microstructure comprises, by area %, less than 20% ferrite (excluding 0%), according to claim 1. The high-strength cold-rolled steel sheet described.

3. The microstructure comprises 5-9% ferrite by area percentage, as described in claim 1 for high-strength cold Rolled steel plate.

4. The microstructure comprises 31-35% bainite by area percentage, according to claim 1, for a high strength degree cold rolled steel plate.

5. The microstructure comprises, by area percentage, 56-62% martensite, as described in claim 1. High strength cold rolled steel plate.

6. Claim 1, wherein the tensile strength is 1180 MPa or more and the yield strength is 870 MPa or more. High-strength cold-rolled steel sheet as described above.

7. The high-strength cold-rolled product of tensile strength and elongation is 8,000 MPa or more, as described in claim 1. steel plate.

8. In weight percent, Cr: 1.0% or less (including 0%), Mo: 0.2% or less (including 0%), B: The claim 1 further comprises one or more selected from 0.005% or less (including 0%). High strength cold rolled steel plate.

9. In the width direction of the cold-rolled steel sheet, the difference in yield strength between both ends and the center is 100 MPa or less. The high-strength cold-rolled steel sheet according to claim 1.

10. In weight percent, C: 0.05-0.3%, Si: 0.01-2.0%, Mn: 1.5-3%. 0%, Al: 0.01-0.1%, P: 0.001-0.015%, S: 0.001-0 0.01%, N: 0.001-0.01%, the remainder being Fe and other unavoidable impurities, below Steel slabs that satisfy the value defined by the relational expression 1 to be between 0.9 and 1.2 are 1100 and 135. The step of reheating to 0°C; The step of hot-rolling the reheated steel slab at 850 to 1150°C; The hot-rolled steel sheet is cooled to 450-700°C at an average cooling rate of 10-70°C / s. The stage of doing so; The step of winding the cooled steel plate at 450 to 700°C; The step of cold-rolling the wound steel sheet at a reduction ratio of 40 to 70%; and The process includes the step of continuously annealing the cold-rolled steel sheet at 740 to 900°C; The winding step involves using the overall width of the steel plate as a reference and measuring the surface temperature (Te) of both ends in the width direction. The temperature is 601-700°C, and the central surface temperature (Tc) is 450-600°C. A method for manufacturing high-strength cold-rolled steel sheets, which involves controlling the process. [Relationship 1] C+(1.3×Si+Mn) / 6+(Cr+1.2×Mo) / 5+100×B (In the above relational formula 1, C, Si, Mn, Cr, Mo, and B are relative to each element) This indicates the average content by weight percent. If none of the elements are added, 0 is substituted.

11. After the winding step, the wound steel plate is moved into the heat-insulating cover and 400- The high-intensity cold process according to claim 10, further comprising the step of maintaining the temperature in the range of 500°C for 6 hours or more. A method for manufacturing rolled steel sheets.

12. The winding step involves the difference (Te-Tc) between the surface temperature of both ends and the surface temperature of the central part. A method for manufacturing a high-strength cold-rolled steel sheet according to claim 10, wherein the temperature is controlled to be 150°C or lower. 。

13. The aforementioned cooling step involves injecting cooling fluid into both ends in the width direction, based on the overall width of the steel plate. The amount of cooling water injected into the central part, excluding the ends, is even larger than the amount of water injected. A method for manufacturing a high-strength cold-rolled steel sheet according to claim 10, wherein the strength is controlled to increase.

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