1200-MPa-level cold milling steel and manufacturing method thereof

Abstract

The invention discloses 1200-MPa-level cold milling steel and a manufacturing method thereof. The steel comprises, by mass, 0.15-4.0% of C, 0.3-2.0% of Si, 1.0-5.0% of Mn, S with the amount equal to or smaller than 0.01 ppm, P with the amount equal to or smaller than 0.01 ppm, H with the amount equal to or smaller than 20 ppm, 0.02-2.0% of Al, 0.01-0.04% of Nb, and the balance Fe and unavoidable impurities. As the Nb element is added to the steel, crystal grain can be effectively refined, the area of crystal boundaries is increased to adsorb hydrogen atoms, and then hydrogen spreading is effectively restrained; in addition, a precipitate Nb (C, N) formed by Nb is a hydrogen trap and can effectively adsorb hydrogen in the steel so that hydrogen can be distributed uniformly in the steel and restrained from spreading or gathering, and the hydrogen induced cracking resistant characteristic of the steel is improved; in addition, the Nb element is a stable retained austenite element and can increase the strength and ductility product of the steel; due to microalloying of Nb, the hydrogen induced cracking resistant characteristic of the steel can be effectively improved; meanwhile, the crystal grain can be refined, and the stability of austenite is improved. The steel has the advantages of being high in hydrogen induced cracking resistance, large in strength and ductility product, and capable of effectively improving the driving safety of an automobile.

Description

technical field [0001] The invention relates to a high-strength automobile steel, in particular to a 1200MPa grade cold-rolled Q&P steel and a manufacturing method thereof. Background technique [0002] Q&P steel has excellent tensile strength and elongation. The tensile strength reaches 1200MPa while the elongation reaches more than 14%. It is of great significance to improve safety performance and reduce environmental emissions. Q&P adopts 80-90% volume fraction of martensite strengthening, so it has extremely high tensile strength. At the same time, using the "carbon partition" process and principle, the steel is heated to the austenite zone, and then cooled rapidly, at the quenching temperature and Keep warm at a slightly higher partition temperature to diffuse supersaturated carbon in martensite into austenite without forming or rarely forming carbide precipitation, so that 10-20% volume fraction of stable retained austenite remains to room temperature. During the de...

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Problems solved by technology

[0003] At present, the Chinese patent publications whose publication numbers are CN103215516A, CN103805851A, CN103233161A, CN103805869A, CN102226248A, and CN101775470A all disclose the production method of hot-rolled Q&P steel, which is characterized in that the process flow is short and the production cost is low; High requirements are put forward, it is difficult to realize in industry, and it is difficult to guarantee the surface quality of products

Moreover, when the tensile strength of the Q&P steel of the existing technology exceeds 1200MPa, the very low diffusible hydrogen in the steel will cause the delayed cracking of the steel, which will be unfavorable for the driving safety of the automobile when used in the manufacture of automobiles

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