High tensile strength hot-dip galvannealed steel sheet having excellent coated-layer adhesiveness and method for producing same

Patent metadata

Field	Value
Publication number	US-9181613-B2
Application number	US-201114111819-A
Country	US
Kind code	B2
Filing date	Apr 20, 2011
Priority date	Apr 20, 2011
Publication date	Nov 10, 2015
Grant date	Nov 10, 2015

Abstract

A high tensile strength hot-dip galvannealed steel sheet having excellent coated-layer adhesiveness in which the hot-dip galvannealed layer does not peel off from a base steel sheet even in being subjected to working accompanied by sliding and a method for producing the same are provided. In the high tensile strength hot-dip galvannealed steel sheet, a hot-dip galvannealed layer is formed on the surface of the base steel sheet, the base steel sheet contains Si by 0.04-2.5%, and, when the surface roughness of the base steel sheet after the hot-dip galvannealed layer is removed by dissolution with an acid is measured for a plurality of locations by a laser microscope, the arithmetic mean inclination angle (RΔa) is 23.0° or more and the root mean square inclination angle (RΔq) is 29.0° or more in 60% or more of all of the locations measured.

First claim

The invention claimed is:

1. A high tensile strength hot-dip galvannealed steel sheet having excellent coated-layer adhesiveness in which a hot-dip galvannealed layer is formed on the surface of a base steel sheet, wherein
the base steel sheet contains Si by 0.04-2.5mass % and C by 0.06-0.15 mass %, and,
when the surface roughness of the base steel sheet after the hot-dip galvannealed layer is removed by dissolution with an acid and is measured at a plurality of locations by a laser microscope, the arithmetic mean inclination angle (RΔa) is 23.0° or more and the root mean square inclination angle (RΔq) is 29.0° or more in 60% or more of all of the locations measured.

2. The high tensile strength hot-dip galvannealed steel sheet of claim 1 , wherein the surface roughness results when the rate of outlet side sheet thickness relative to inlet side sheet thickness at the final stand of cold rolling is 98% or less after hot rolling and acid wash and before plating.

3. The high tensile strength hot-dip galvannealed steel sheet of claim 1 , wherein the surface roughness results when the rate of outlet side sheet thickness relative to inlet side sheet thickness at the final stand of cold rolling is 97.5% to 92% after hot rolling and acid wash and before plating.

4. A method for producing the high tensile strength hot-dip galvannealed steel sheet having excellent coated-layer adhesiveness of claim 1 , comprising the steps of:
preparing a base steel sheet in which Si is contained by 0.04-2.5 mass % and C is contained by 0.06-0.15 mass % and, when the surface roughness is measured by the laser microscope, the arithmetic mean inclination angle (RΔa) is 6.0° or more and the root mean square inclination angle (RΔq) is 12.0° or more in 60% or more of all of the locations measured;
subjecting the base steel sheet to hot-dip galvanizing; and
subsequently alloying the base steel sheet.

Assignees

• Chida Minoru
• Irie Hiroshi
• Kobe Steel Ltd

Inventors

• Chida Minoru
• Irie Hiroshi

Classifications

• C23C2/28

  Thermal after-treatment, e.g. treatment in oil bath · CPC title

• C23C2/26

  After-treatment (C23C2/14 takes precedence) · CPC title

• Y10T428/12799

  Next to Fe-base component [e.g., galvanized] · CPC title

• C23C2/06 Primary

  Zinc or cadmium or alloys based thereon · CPC title

• C23C2/29 Primary

  Cooling or quenching · CPC title