780 MPa-grade hot-rolled dual-phase steel with excellent hole expanding performance and preparation method of 780 MPa-grade hot-rolled dual-phase steel

Abstract

The invention relates to 780 MPa-grade hot-rolled dual-phase steel with excellent hole expanding performance. The 780 MPa-grade hot-rolled dual-phase steel comprises the following chemical components including, by weight: 0.05%-0.09% of C, 0.10%-0.30% of Si, 1.40%-1.60% of Mn, less than or equal to 0.010% of P, less than or equal to 0.003% of S, 0.08%-0.12% of Ti, 0.20%-0.24% of Mo, 0.010%-0.030% of Nb and 0.08%-0.12% of V. The production method comprises the following steps of carrying out vacuum treatment after converter smelting, heating a casting blank after continuous casting is conducted to form a blank, carrying out rough rolling, carrying out finish rolling, carrying out two-stage cooling and carrying out coiling. The grain size grade of ferrite and martensite is greater than or equal to 10 grades; the area ratio of the martensite is 30%-50%, a ferrite matrix contains a large number of nanoscale cluster precipitates, the size of the nanoscale cluster precipitates is 1-8 nm, and the density of the nanoscale cluster precipitates can reach 1*10<3> / microns<2>; and the tensile strength of a hot-rolled steel plate is larger than or equal to 780 MPa, the ductility is larger than or equal to 15%, the yield ratio is smaller than or equal to 0.75, the hole expanding performance is larger than or equal to 55%, and the use requirements for high strength, high plasticity and excellent hole expanding performance of automobile steel can be completely met.

Description

technical field [0001] The invention relates to a production method of hot-rolled steel for automobiles, in particular to a 780MPa grade hot-rolled dual-phase steel with excellent hole expansion performance and a preparation method thereof. Background technique [0002] The automobile industry in the 21st century, reducing fuel consumption and reducing CO 2 And exhaust emissions have become the needs of the society. In order to adapt to this development trend, the steel industry as a material production plant has developed many types of ultra-high-strength steel plates to help reduce the weight of automobiles and meet the new requirements of the automobile industry. More and more hot-rolled products are used to make automotive components, such as automotive suspension parts and chassis parts. With the continuous development of automobile lightweight, the application of high-strength and high-hole reaming steel with good hole reaming performance is becoming more and more com...

AI Technical Summary

Problems solved by technology

The invented steel plate has a low carbon content, and the structure is pearlite and ferrite, which is easy to control during production, but the strength obtained by the composition and structure is low, which cannot meet the needs of high strength and high plasticity, and the hole expansion performance is only limited. It can reach 60-90%, because there is no composite addition of microalloy in this invention, purely by the precipitation of Ti, the size of the precipitate is large and the precipitation is not enough and dispersed

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