High-strength cold-rolled steel sheet excellent in stretch-flangeability and spot weldability and manufacturing method thereof

Abstract

The invention provides a high-strength cold-rolled steel sheet having excellent stretch flangeability and spot welding property and a manufacturing method of the steel sheet. The steel sheet comprises 0.03-0.15% of C, 0.30-0.10% of Si, 1.20-2.20% of Mn, not more than 0.015% of P, not more than 0.010% of S, 0.02-0.15% of Al, not more than 0.005% of N, 0.20-0.60% of Cr, 0.010-0.060% of Nb, 0.030-0.100% of V and 0.0007-0.0050% of Ca, with the balance being Fe and unavoidable impurities, and with the (Mn+2Nb+V) being not more than 2.3% and not less than 1.6%. In the manufacturing method, the start rolling temperature of hot continuous rolling precision rolling is 1000-1100 DEG C, the finish rolling temperature is 890-950 DEG C, the acid-washing cold rolling rate is 60-80%, and two-stage cooling, namely slow cooling firstly and rapid cooling secondly, are adopted after annealing and temperature maintaining steps. The tensile strength of the finally obtained steel sheet is higher than 800 MPa. The obtained steel sheet is good in strength ductility matching, and excellent in stretch flangeability and spot welding property.

Description

technical field [0001] The invention belongs to the technical field of cold-rolled high-strength thin plates for automobiles, and in particular relates to a high-strength cold-rolled steel plate with excellent stretch flangeability and spot weldability and a manufacturing method thereof. Background technique [0002] In recent years, with the rapid development of the automobile industry, automobiles, as a daily means of transportation, bring convenience to people and at the same time become a source of CO 2 , NOx and noise are the main sources of pollution, and its ensuing environmental and energy issues are increasingly being paid more and more attention by people. In order to reduce fuel consumption, save energy, and achieve sustainable development, promote the development of automobiles in the direction of environmental protection and light weight. At present, dual-phase (DP) steel, transformation-induced plasticity (DP ) steel, complex-phase (CP) steel and twinning-indu...

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Problems solved by technology

In order to obtain this composite structure, the patent adopts a process route of 930~960°C soaking, two-stage cooling and tempering. This process requires multi-point plate temperature control at 4 temperature points, and the actual operability is complicated. In addition, high temperature The soaking is also close to the limit of the existing cold rolling continuous annealing furnace, the possibility of realizing industrial continuous production is very small and the spot welding performance of the steel plate is not considered

[0007] The Japanese patent "High-strength hot-dip galvanized steel sheet with excellent processability and its manufacturing method" (PCT / JP2008 / 069699) provides a structure of ferrite, martensite, retained austenite and tempered martensite. High-strength hot-dip galvanized steel sheet with excellent workability and impact resistance and its manufacturing method, not involving spot welding performance of finished product as cold-rolled annealed sheet and steel sheet

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