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High-strength electrogalvannealed steel sheet and method for manufacturing the same

a technology of electrogalvannealed steel and high-strength, which is applied in the direction of manufacturing tools, furnaces, heat treatment equipment, etc., can solve the problems of reducing the boundary strength of grain, degrading the formability of steel sheets, and low corrosion resistance of even galvanized steel sheets, etc., to achieve high delayed fracture resistance, good formability, and excellent surface appearance

Inactive Publication Date: 2020-11-05
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Benefits of technology

The present invention provides a high-strength electrogalvannealed steel sheet with good formability, high delayed fracture resistance, excellent surface appearance, and high coating adhesion. The steel sheet has a tensile strength of 780 MPa or higher. By reducing the hydrogen content and suppressing generation of bare spots through an alloying treatment after electrogalvanization, the coating adhesion is improved. The use of the high-strength electrogalvannealed steel sheet in automotive structural members reduces the weight of the vehicle body and improves fuel efficiency, making it a valuable industrial product.

Problems solved by technology

In Patent Literature 1, in the case of the presence of a large amount of internal oxide, the internal oxide causes a problem of low corrosion resistance in even a galvanized steel sheet.
In addition, the formation of the internal oxide at grain boundaries may reduce the grain boundary strength and thus may degrade the formability of a steel sheet.
In the method disclosed in Patent Literature 2, the steel sheet components and the annealing conditions greatly affect formation of steel sheet surface oxides, and thus in the case of addition of a large amount of Mn, it is impossible to completely suppress formation of surface oxides which inhibit coating adhesion.

Method used

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  • High-strength electrogalvannealed steel sheet and method for manufacturing the same

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[0101]Steel having the composition shown in Table 1 was smelted in a converter and continuously casted into a slab. The obtained slab was hot-rolled, and the hot-rolled steel was pickled and, as needed, then subjected to a cold-rolling step. The heat treatment step and the holding step were carried out under the conditions shown in Table 2-1, Table 2-2, Table 2-3, and Table 3. Subsequently, the electrogalvanizing step and the alloying step were carried out to produce an electrogalvannealed steel sheet. Electrogalvanization was performed in a zinc sulfate bath under the condition of a current density of 100 A / dm2. Pickling was performed in 5% sulfuric acid before electrogalvanization.

TABLE 1SteelCSiMnPSNTiAlNbBNiA0.0811.532.770.0220.0015——————B0.1211.422.150.0020.00130.0035—————C0.0781.512.750.0220.00150.0040—————D0.0851.482.150.0110.00070.0042—————E0.1140.482.510.0090.00100.00370.0200.030———F0.1950.452.620.0020.00060.00440.0180.032———G0.1450.142.850.0080.00120.00350.0020.0300.0210.0...

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Abstract

Provided are a high-strength electrogalvannealed steel sheet that has a TS of 780 MPa or higher and a method for manufacturing the high-strength electrogalvannealed steel sheet. The high-strength electrogalvannealed steel sheet has a composition including, in terms of % by mass, C: 0.030% or more and 0.250% or less, Si: 0.01% or more and 3.00% or less, Mn: 1.00% or more and 10.00% or less, P: 0.001% or more and 0.100% or less, and S: 0.0001% or more and 0.0200% or less, with the balance being Fe and unavoidable impurities. The steel sheet has an electrogalvannealed coating layer on a surface thereof. The electrogalvannealed coating layer has an Fe content of 8.0% to 15.0%. The steel sheet has a tensile strength of 780 MPa or higher. The steel sheet has a diffusible hydrogen content of 0.2 wt. ppm or less.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This is the U.S. National Phase application of PCT / JP2018 / 045856, filed Dec. 13, 2018, which claims priority to Japanese Patent Application No. 2018-005418, filed Jan. 17, 2018, the disclosures of these applications being incorporated herein by reference in their entireties for all purposes.FIELD OF THE INVENTION[0002]The present invention relates to a high-strength electrogalvannealed steel sheet that has good formability and high delayed fracture resistance, has excellent surface appearance and high coating adhesion, and is suitable as a member used in industrial fields including automotive industry, and to a method for manufacturing the high-strength electrogalvannealed steel sheet.BACKGROUND OF THE INVENTION[0003]A recent important issue for preserving the global environment is an improvement in automotive fuel efficiency. To achieve this, an attempt to reduce the weight of a vehicle body itself by strengthening and thinning vehicle b...

Claims

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Application Information

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IPC IPC(8): C21D9/46B32B15/01C22C38/38C22C38/28C22C38/12C22C38/08C22C38/06C22C38/02C22C38/00C21D6/00C25D5/36C25D5/50
CPCC25D5/50C21D6/005C22C38/001C22C38/06C21D6/008C22C38/005B32B15/013C22C38/08C21D9/46C22C38/002C22C38/38C22C38/02C22C38/12C25D5/36C21D6/002C21D6/001C22C38/008C22C38/28C22C38/04C22C38/60C22C38/14C22C38/16C25D7/0614C25D3/22C22C18/04C22C38/58
Inventor AOYAMA, MAITSUCHIMOTO, KAZUAKIFUSHIWAKI, YUSUKE
Owner JFE STEEL CORP