180 MPa-grade cold-rolled ultralow carbon baking hardened steel and production method thereof

Abstract

The invention discloses 180 MPa-grade cold-rolled ultralow carbon baking hardened steel and a production method thereof. The steel comprises the following improved chemical components in percentage by weight: 0.0015-0.0025% of C, 0.006-0.010% of Si, 0.40-0.75% of Mn, and 0.030-0.050% of P; C%/Nb% is 0.16-0.28; the hot-rolled tapping temperature is 1240-1250 DEG C; the front section is cooled after finish rolling; the plumbing ratio is 1: 1.2; the continuous annealing soaking temperature is 830-835 DEG C; the slow cooling temperature is 680-750 DEG C; the rapid cooling temperature is 340-360 DEG C; the cooling degree is 50-85 DEG C/s; and 14.0-17.0% of high hydrogen is fed in the rapid cooling section. The steel contains no precious elements, is low in production cost, is excellent in product surface quality, and is uniform in structure; the stress strain index r value reaches 2.65; the strain hardening ratio n value is stabilized at 0.23; and the stamping forming performance is excellent.

Description

technical field [0001] The invention relates to bake-hardening steel and a preparation method thereof, in particular to a 180MPa grade cold-rolled ultra-low-carbon bake-hardenable steel and a production method thereof. Background technique [0002] With the development of the automobile industry, a series of topics such as saving energy, reducing pollution, and improving vehicle safety have become the focus of attention; in order to meet the needs of the industry, steel plates used in vehicle manufacturing need to have higher dent resistance and better In this context, ultra-low carbon bake-hardening steels have been developed for the production of automotive exterior panels. The characteristics of the steel composition are based on IF steel, by adding trace amounts of Nb, Ti and other alloying elements to control the content of solid-solution C and N elements in the matrix, so that the solid-solution atoms can diffuse to the dislocation during the subsequent processing and ...

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Problems solved by technology

Publication No. 101230437, published on July 30, 2008, discloses an ultra-low-carbon bake-hardening steel for alloyed hot-dip galvanizing. In order to obtain sufficient strength, 0.50-0.60% Mn and 0.05-0.06% Mn are added to the composition P; Yield strength 230MPa, plastic strain ratio r value 1.63~1.70; This patent has a low strip forming performance index due to the addition of more P elements in the matrix; Publication No. 101994056, Patent Publication Date 2011.3.30 Disclosed is an ultra-low carbon bake-hardening steel plate with excellent stamping performance and its production process. The process ensures the stamping performance of the strip steel by controlling the (4*C% / Ti%) value at 0.8-1.2 and reducing the P content , to increase the r value to 2.26-2.55; but its tensile strength is low, at 300-320MPa, which affects the anti-sag performance of the strip steel; the patent with the publication number of 101310031B and the publication date of 2008.11.19 discloses a simultaneously Bake-hardening steel for cold rolling and galvanizing, the steel grade adopts the composition design route of low Si (≤0.02%) and high P (0.05~0.11%), and combines Ti, Nb, Mo, B composite microalloy The product has good properties of bake hardening, room temperature aging resistance and secondary processing embrittlement resistance, but this steel type has many alloying elements, and the actual production faces the problem of high cost

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