Cold-rolled steel sheet with tensile strength larger than 900 MPa and manufacturing method thereof

Abstract

The invention discloses a cold-rolled steel sheet with tensile strength larger than 900 MPa and a manufacturing method of the cold-rolled steel sheet. The cold-rolled steel sheet is composed of the following ingredients in percentage by weight: 0.06-0.095wt% of C, 0.1-0.4wt% of Si, 1.2-1.6wt% of Mn, 0.001-0.004% of B, not larger than 0.015wt% of P, not larger than 0.004wt% of S, 0.003-0.007wt% of N, 0.01-0.03wt% of Nb, 0.03-0.06% of Ti, 0.015-0.045wt% of Al, 0.002-0.007wt% of Ca and the rest balance of Fe and inevitable impurities. Cold-rolled high strength steel with tensile strength larger than 900 MPa and excellent cold bending property and delayed cracking resistance is obtained by reasonable ingredient design and technique design in the invention, and the steel has the characteristics of small and uniform tissues and excellent cold bending property. Meanwhile, the delayed cracking resistance of the steel is excellent, so that the steel meets the manufacturing demands of safety elements and structural members of automobiles.

Description

Technical field [0001] The invention relates to a cold-rolled steel sheet and a manufacturing method, in particular to a cold-rolled steel sheet with a tensile strength above 900 MPa and a manufacturing method. The steel has the characteristics of excellent cold bending performance and excellent delayed cracking resistance. Background technique [0002] Due to the need to reduce weight, the automobile industry requires the use of higher-strength steel plates. Among them, ultra-high-strength steel with a tensile strength of 900 MPa and above has increasingly become the first choice for the automobile manufacturing industry, because this strength level of steel can effectively reduce the weight of the car body and improve safety. In the automobile manufacturing process, the deformation ability of high-strength steel plates is mainly controlled by the occurrence and expansion of cracks. Therefore, the requirements for local forming ability are very high, that is, the requirements fo...

AI Technical Summary

Problems solved by technology

When the carbon content is higher than 0.1%, the rapid growth of columnar crystals is likely to occur during the solidification process, and the gaps between columnar crystals are large, solute-enriched molten steel tends to flow into the gaps between columnar crystals, resulting in aggravation of segregation. The Mn content is high, the degree of segregation is high and it is difficult to eliminate, so it is not good for the uniformity of structure, performance and cold bending performance, and it is easy to cause fluctuations and inhomogeneity of performance microscopically, the longitudinal bending performance is not ideal, the anisotropy is large, and the resistance Unsatisfactory delayed crack performance

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