High-strength steel plate and manufacturing method thereof

Abstract

An object is to provide a high-strength steel sheet having excellent phosphatability and excellent corrosion resistance after electrodeposition coating has been performed, even in the case where the contents of Si and Mn are high and to provide a method for manufacturing the steel sheet. A method for manufacturing a high-strength steel sheet, the method including, when a steel sheet having a chemical composition containing, by mass%, C: 0.03% or more and 0.35% or less, Si: 0.01% or more and 0.50% or less, Mn: 3.6% or more and 8.0% or less, Al: 0.01% or more and 1.0% or less, P: 0.10% or less, S: 0.010% or less, and the balance being Fe and inevitable impurities is annealed by using a continuous annealing method, performing a heating process at a heating rate of 7°C / sec. or more in a temperature range in the annealing furnace of 450°C or higher and A°C or lower, controlling the maximum end-point temperature of a steel sheet in the annealing furnace to be 600°C or higher and 700°C or lower, controlling the traveling time of the steel sheet in a steel sheet temperature range of 600°C or higher and 700°C or lower to be 30 seconds or more and 10 minutes or less, and controlling the dew point of the atmosphere in a steel sheet temperature range of 600°C or higher and 700°C or lower to be -40°C or lower, where A: 500 ‰¤ A ‰¤ 600.

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 and increasing the strength of the vehicle body itself by increasing the strength of vehicle body materials to achieve thinning. Therefore, the application of high-strength steel sheets to automobiles is being promoted. [0003] Generally, steel sheets for automobiles are used after being painted, and a chemical conversion treatment called phosphate treatment is performed as a pretreatment of the painting. The chemical conversion treatment of the steel sheet is one of the important t...

AI Technical Summary

Problems solved by technology

In Patent Document 6, there is no specific description of the heating temperature of the direct fire burner, but it is considered that 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, so the Oxidation is suppressed or the oxidation of Fe itself becomes less

As a result, the formation of the Fe reduction layer on the reduced surface is insufficient, or SiO is present on the surface of the reduced steel sheet. 2 , sometimes resulting in uncovered areas of the chemical conversion coating

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