Tensile strength 1000 MPa-grade cold-rolled complex phase steel and preparation method thereof

Abstract

The invention provides tensile strength 1000 MPa-grade cold-rolled complex phase steel and a preparation method thereof. The complex phase steel is composed of, by mass, 0.07-0.13% of C, 0.2-0.4% of Si, 1.8-2.5% of Mn, 0.2-0.6% of Cr, 0.1-0.4% of Mo, less than or equal to 0.02% of P, less than or equal to 0.015% of S, 0.02-0.06% of Nb, 0.02-0.06% of Ti and the balance iron and other inevitable impurity elements. The complex phase steel adopts low carbon equivalent design as composition design and has good welding performance, a small amount of microalloy elements of Nb and Ti and C elements are composited and added for forming nanometer precipitated phases, thus, grains are refined, meanwhile, the elements are dispersed and distributed in a complex phase steel ferritic matrix, sufficient precipitation strength is reached, therefore, the yield strength of a material is improved, the good bending and reaming properties are achieved, the tensile strength of the final cold-rolled complex phase steel is 1000 MPa or higher, the yield strength reaches 780 MPa or higher, the yield ratio is 0.8 or higher, the elongation after fracture is 8% or higher, the reaming ratio is 50% or higher, andthe application requirements in the field of automotive steel are met.

Description

technical field [0001] The invention belongs to the technical field of steel rolling, and in particular relates to a cold-rolled multiphase steel with a tensile strength of 1000 MPa and a preparation method thereof. Background technique [0002] As the automotive industry has increasingly stringent requirements for lightweight, safety, and low emissions, the proportion of advanced high-strength steel used in new automotive models continues to increase. In the body structure designed by the "ultra-light steel car body-advanced car concept" project, high-strength steel with a tensile strength of 1000MPa accounts for the largest proportion, accounting for about 29% to 30% of the weight of the car body. High-strength steel above 1000MPa, in addition to commonly used dual-phase steel, also includes martensitic steel, multi-phase steel, third-generation high-strength steel, etc. [0003] Different from dual-phase steel, multi-phase steel belongs to the series of ultra-high-streng...

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Problems solved by technology

This patent refers to the hot-rolled steel plate of the composite phase steel plate. Although the strength of the disclosed patented product reaches 1000MPa, the thickness of the plate is more than 1.8mm, which obviously cannot meet the current urgent requirements for lightweight automobile bodies. In addition, the carbon content of this steel type reaches 0.175 -0.215%, too high carbon content deteriorates welding performance, and it is difficult to be used in the field of automotive steel

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