Cold-rolled steel sheet with 420 MPa grade yield strength and preparation method of steel sheet

Abstract

The invention discloses a cold-rolled steel sheet with the 420 MPa grade yield strength and a preparation method of the steel sheet and belongs to the technical field of metallurgy. The steel sheet is prepared from components in percentage by mass as follows: 0.06%-0.09% of C, 0-0.2% of Si, 0.8%-1.0% of Mn, 0-0.02% of Ti, 0.01%-0.025% of Nb and the balance of Fe and inevitable impurity elements. The preparation method comprises steps as follows: (1) according to the ratio of the chemical components of the cold-rolled steel sheet, a steel ingot is obtained through smelting and is forged to form a slab; (2) heat preservation is performed on the slab, hot rolling is performed, and a hot-rolled sheet is prepared and is cooled to the proper temperature at a certain cooling rate for coiling; (3) the coiled hot-rolled sheet is pickled and then cold-rolled, and the cold-rolled sheet is prepared; (4) the cold-rolled sheet is subjected to continuous annealing treatment of low-temperature soaking and step cooling. According to the cold-rolled steel sheet, the microstructure mainly comprises ferrite, pearlite and cementite, the yield strength of the steel sheet ranges from 435 MPa to 450 MPa, the tensile strength ranges from 518 MPa to 548 MPa, and the ductility A80 ranges from 25.0% to 26.3%.

Description

technical field [0001] The invention belongs to the technical field of metallurgy, and in particular relates to a cold-rolled steel plate with a yield strength of 420 MPa and a preparation method thereof. Background technique [0002] Lightweight automobile body can reduce energy consumption and CO 2 emissions purposes. Lightweight has been proved to be the key technical route of automobile "energy saving and emission reduction". Every 10% reduction in vehicle weight can reduce fuel consumption by 6%-8% and reduce carbon dioxide emissions by 13%. China is the world's largest producer and consumer of automobiles, and lightweight has become an important issue for the sustainable development of the automobile industry. The high strength of automobile steel is an effective way to realize the lightweight of automobiles, and the high strength of automobile steel has become an inevitable trend. By strengthening the body structure by increasing the use of high-strength steel plat...

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Problems solved by technology

However, the Nb content in this method is 0.04% to 0.05%, and the cost is relatively high

[0008] All adopted high-temperature soaking in the above-mentioned method, this will bring the following problems: (1) under high temperature, hearth roll nodulation very easily takes place, thus easily causes scratch to strip steel in operation process, affects strip surface quality (2) Under high temperature soaking conditions, the precipitated particles are prone to coarsening, and at the same time, the ferrite grains are easy to grow, resulting in a decrease in strength; (3) Under high temperature, the diffusion ability of Si and Mn elements is improved, and the selective oxidation is intensified , it is more difficult to control the surface quality of strip steel; (4) The energy consumption increases at high temperature, and the heating cost is higher

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