Ultrahigh-strength hot-rolled Q and P steel and production method thereof

Abstract

The invention discloses ultrahigh-strength hot-rolled Q and P steel and a production method thereof. The production method includes the procedures of smelting, casting and hot rolling. The steel comprises 0.14%-0.45% of C, 0.15%-2.0% of Si, 1.0%-5.0% of Mn, 0.010% or less of S, 0.015% or less of P, 40 ppm or less of H, 0.02%-1.5% of Al, 0.01%-0.08% of Nb, and the balance Fe and inevitable impurities. The hot rolling procedure includes the steps of heating, rough rolling, finish rolling, laminar cooling and reeling. In the heating step, the heating temperature ranges from 1100 DEG C to1200 DEG C, and heat preservation is conducted for 1-3 hours. In the rough rolling step, the rolling starting temperature ranges from 1000 DEG C to 1100 DEG C, and the overall reduction is larger than 40%. In the finish rolling step, the rolling starting temperature ranges from 900 DEG C to 950 DEG C, the rolling finishing temperature ranges from 780 DEG C to 880 DEG C, and the overall reduction is larger than or equal to 60%. In the laminar cooling step, front-end cooling is conducted, the cooling rate is larger than or equal to 45 DEG C/s, and the finish cooling temperature ranges from 150 DEG C to 350 DEG C. In the reeling step, the reeling temperature ranges from 150 DEG C to 350 DEG C. Before the steel coil temperature is 100 DEG C, the cooling rate of 5-20 DEG C/hour is kept. Through the method, the martensite plus retained austenite microstructure with a small grain size can be obtained.

Description

technical field [0001] The invention relates to a steel for automobiles, in particular to an ultra-high-strength hot-rolled Q&P steel and a production 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 widely used in automotive anti-collision bars, structural parts, chassis and other parts. Q&P is reinforced with 80-90% martensite, so its strength is very high; at the same time, it uses "carbon distribution" to improve plasticity. "Carbon distribution" process and principle: Heating the steel to the austenite zone, then rapidly cooling to the quenching temperature and a slightly higher partition temperature for heat preservation, to diffuse the supersaturated carbon in the martensite to the austenite without Form or form very few carbides, so that the stable retained austenite with a volume fraction of 5-20% remains at room temperature; ...

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Problems solved by technology

[0004] In the existing patent application, CN102226248A is a carbon-silicon-manganese-based hot-rolled Q&P steel and its preparation method. Microalloying technology is not used, and the martensite lath of the produced Q&P steel is relatively thick, and there is no requirement for delayed fracture characteristics; CN103215516A 700MPa high-strength hot-rolled Q&P steel and its manufacturing method, CN103805851A ultra-high-strength low-cost hot-rolled Q&P steel and its production method, and CN103233161A low yield ratio high-strength hot-rolled Q&P steel and its manufacturing method Patents such as C-Si-Mn and Ti micro-alloying technology have been used to obtain refined martensitic lath, but the influence of micro-alloying on phase transformation is not considered; CN101775470A production method of low-alloy multi-phase Q&P steel, It is to cool Q&P to the coiling temperature and then heat it to the distribution temperature, so it is difficult to realize on the traditional hot rolling line; CN103805869A is a kind of high-strength hot-rolled Q&P steel and its manufacturing method, which is to add Cr element to improve hardenability, increased production costs

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