140 MPa grade cold rolled ultra-low carbon steel with high bake hardening characteristic and production method

Abstract

The invention relates to 140 MPa grade cold rolled ultra-low carbon steel with a high bake hardening characteristic. The steel comprises the following components in percent by weight: 0.002-0.003% ofC, less than or equal to 0.3% of Si, 0.25-0.35% of Mn, 0.008-0.018% of P, less than or equal to 0.012% of S, 0.025-0.055% of Als, less than or equal to 0.003% of N, 0.007-0.013% of Nb and the balanceFe and inevitable impurities. A production method of the 140 MPa grade cold rolled ultra-low carbon steel with the high bake hardening characteristic comprises the steps of steelmaking, hot rolling, pickle-rolling and continuous annealing. In the annealing step, the soaking temperature is 840-850 DEG C and the insulation time is 75-94 s. The 140 MPa grade cold rolled ultra-low carbon steel produced by the production method has a relatively good forming ability at normal temperature and has a stable high bake hardening value greater than 50 Mpa, not only meets a forming demand of a part, but also meets a rigidity demand of the formed part, and shows a good comprehensive property.

Description

technical field [0001] The invention relates to ultra-low carbon steel and a production method, in particular to a cold-rolled ultra-low carbon steel of 140 MPa grade with high baking hardening characteristics and a production method. Background technique [0002] In order to achieve the purpose of reducing the weight of automobiles and improving safety, the modern automobile industry mostly uses high-strength steel to manufacture the body. Bake-hardening steel has the deep drawing properties similar to soft steel, and has higher strength after bake-hardening. Therefore, bake-hardening steel is widely used in many cars to replace ordinary mild steel for car bodies. Manufacture of outer covers. On the one hand, it can reduce the thickness of the outer panel to achieve the purpose of reducing the weight of the vehicle body; on the other hand, it can improve the dent resistance of the outer cover of the vehicle body through its bake hardening characteristics. [0003] At pres...

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Problems solved by technology

[0003] At present, the patents and literature reports on cold-rolled ultra-low carbon bake-hardening steel focus on products with 180MPa, 220MPa and higher strength. These products generally add more alloying elements such as C, Mn, and P, supplemented by lower Annealing temperature to obtain higher strength than 140MPa grade cold-rolled ultra-low carbon steel, but due to the higher requirements on the material forming ability of automobile panels, these higher-strength products are more difficult to form complex parts

[0004] In the current national standard, the lower limit of the bake hardening value is 30MPa. Although the bake hardening steel of 140MPa level has good forming ability, the rigidity of the formed parts is still small, so it is more considered to use ordinary steel when forming complex parts. Low-carbon steel or interstitial-free steel, etc., lead to a small range of practical applications for this product. Therefore, if a 140MPa grade cold-rolled ultra-low carbon steel with high bake-hardening properties can be developed to improve the rigidity of the formed part, it will be beneficial to the simultaneous Significant for complex body parts that require material formability and stiffness

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