High-strength steel plate and manufacturing method thereof

Abstract

The present invention provides a high-strength steel sheet having excellent workability, chemical conversion treatability, and corrosion resistance after electrodeposition coating even when the Si and Mn contents are large, and a method for producing the same. The following (Condition 1) to (Condition 3) are employed when performing continuous annealing on a steel sheet. (Condition 1) During the heating process of continuous annealing, in the temperature range of the temperature in the annealing furnace of 450°C to A°C (A: 500≤A), the steel plate is subjected to heating at a heating rate of 7°C / s or more. heating. (Condition 2) In the continuous annealing, the maximum attained temperature of the steel sheet is 600°C to 750°C. (Condition 3) In the continuous annealing, the steel sheet temperature is 600°C to 750°C for a steel sheet passing time of 30 seconds to 10 minutes, and the dew point of the atmosphere is -10°C or higher.

Description

technical field [0001] The present invention relates to a high-strength steel sheet having excellent chemical conversion treatability and corrosion resistance after electrodeposition coating even when the contents of Si and Mn are large, and a method for producing the same. Background technique [0002] In recent years, from the viewpoint of improving the fuel efficiency of automobiles and improving the collision safety of automobiles, there has been an increasing demand for reducing the weight of the body itself and increasing its strength by increasing the strength of the body material. Therefore, the application of high-strength steel sheets to automobiles is being promoted. [0003] Generally, steel sheets for automobiles are used for painting. As a pretreatment for this coating, a chemical conversion treatment called phosphate treatment is performed on steel sheets for automobiles. Chemical conversion treatment of steel sheets for automobiles is one of the important t...

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Problems solved by technology

However, in Patent Document 6, when a large amount (about 0.6% or more) of Si is contained, the oxidation amount of Si, which is more easily oxidized than Fe, increases, and the oxidation of Fe is suppressed, or the oxidation of Fe itself becomes too small.

As a result, in the technique described in Patent Document 6, the formation of the Fe reduction layer on the surface after reduction may be insufficient or SiO may exist on the surface of the reduced steel sheet. 2 while the uncovered areas of the chemical conversion coating

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