HIGH-CORROSION-RESISTANCE HOT-DIP GALVANIZED STEEL SHEET HAVING EXCELLENT APPEARANCE UNIFORMITY AND MANUFACTURING METHOD THEREOF

• US 20140127531A1
• Filed: 06/29/2012
• Published: 05/08/2014
• Est. Priority Date: 06/30/2011
• Status: Active Grant

• Current Assignee: Nippon Steel Corporation
• Original Assignee: Nippon Steel & Sumitomo Metal Corporation (Nippon Steel Corporation)
• Inventors: Yasui, Takeshi, Oohashi, Tooru, Tanaka, Satoru, Saito, Akio, Kamazu, Nayuta
• Granted Patent: US 9,481,148 B2
• Time in Patent Office: Days
• US Class Current: 428/659
• CPC Class Codes: B32B 15/01 all layers being exclusively metallic making layered metal workpieces by pressure cladding B23K20/22; making coatings with a metallic material characterised by its composition C23C30/00
• CPC Class Codes: B32B 15/013 one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium
• CPC Class Codes: C22C 18/00 Alloys based on zinc
• CPC Class Codes: C22C 18/04 with aluminium as the next major constituent
• CPC Class Codes: C23C 2/022 by heating
• CPC Class Codes: C23C 2/024 by cleaning or etching
• CPC Class Codes: C23C 2/026 Deposition of sublayers, e.g. adhesion layers or pre-applied alloying elements or corrosion protection
• CPC Class Codes: C23C 2/06 Zinc or cadmium or alloys based thereon
• CPC Class Codes: Y10T 428/12799 Next to Fe-base component [e.g., galvanized]

Abstract

The present invention provides a high-corrosion-resistance hot-dip galvanized steel sheet having excellent appearance uniformity. The steel sheet includes: a coating layer containing Al: 4 to 22 mass %, Mg: 1 to 6 mass %, and Si: 0.001 to 1 mass %, and a balance being composed of Zn and inevitable impurities formed on a surface, in which at an interface between the coating layer and a base steel sheet, Mg₂Si phases and Ca phases each mainly composed of Ca or a Ca compound exist, and at least part of the Mg₂Si phases precipitate by using the Ca phases as a nucleus.

Claims

1. A high-corrosion-resistance hot-dip galvanized steel sheet having excellent appearance uniformity, comprising:

a coating layer containing Al;

4 to 22 mass %, Mg;

1 to 6 mass %, and Si;

0.001 to 1 mass %, and a balance being composed of Zn and inevitable impurities formed on a surface, wherein

at an interface between said coating layer and a base steel sheet, Mg₂Si phases and Ca phases each mainly composed of Ca or a Ca compound exist, and at least part of the Mg₂Si phases precipitate by using the Ca phases as a nucleus.

2. The high-corrosion-resistance hot-dip galvanized steel sheet having excellent appearance uniformity according to claim 1, wherein a density of the Mg₂Si phases each having a circle-equivalent diameter of 2 μ

m or more out of the Mg₂Si phases existing at the interface between said coating layer and the base steel sheet is 10 to 1000 pieces per 0.01 mm².

3. The high-corrosion-resistance hot-dip galvanized steel sheet having excellent appearance uniformity according to claim 1, wherein

an average diameter of Al/MgZn₂/Zn ternary eutectic phases existing in said coating layer is 5 to 200 μ

m.

4. The high-corrosion-resistance hot-dip galvanized steel sheet having excellent appearance uniformity according to claim 1, wherein

said coating layer further contains 0.000001 to 0.5 mass % of one or two or more selected from Ti, Ni, Zr, Sr, Hf, Sc, and B alone or in combination.

5. A manufacturing method of a high-corrosion-resistance hot-dip galvanized steel sheet having excellent appearance uniformity, comprising:

a step of bonding Ca phases each mainly composed of Ca or a Ca compound to a surface of a base steel sheet;

a step of annealing the base steel sheet having had the Ca phases bonded to the surface; and

a step of dipping the base steel sheet into a hot-dip galvanizing bath containing Al;

4 to 22 mass %, Mg;

1 to 6 mass %, and Si;

0.001 to 1 mass %, and a balance being composed of Zn and inevitable impurities and performing hot-dip galvanizing.

6. The manufacturing method of the high-corrosion-resistance hot-dip galvanized steel sheet having excellent appearance uniformity according to claim 5, wherein

in said step of bonding Ca or a Ca compound to the surface of the base steel sheet, the base steel sheet is dipped into a hot water containing Ca of 10 to 40 mass ppm and having a temperature of 50 to 90°

C. for 1 to 100 s.