Galvannealed steel sheet and manufacturing method thereof

Patent metadata

Field	Value
Publication number	US-10040270-B2
Application number	US-201414889351-A
Country	US
Kind code	B2
Filing date	May 20, 2014
Priority date	May 20, 2013
Publication date	Aug 7, 2018
Grant date	Aug 7, 2018

Abstract

A galvannealed steel sheet includes a plating layer containing 7.2-10.6 mass % of Fe, 0.2-0.4 mass % of Al, and 0.1 mass % or more of at least one of Ni, Co, Cu, and In, and the balance of Zn and impurities. In a vertical cross-section of the plating layer, an average thickness of a ζ phase is 0.2 μm or less, and an average thickness of a Γ phase is 0.5 μm or less. In the Γ phase, at least one of Ni, Co, Cu, and In are contained at a ratio in the Γ phase of 0.5 mass % or more. A phase existing in contact with the Γ phase is a mixed phase of Γ1 phase and δ phase, and a δ phase percentage defined by “(δ phase/Γ phase contact interface length)/(δ phase/Γ phase contact interface length+Γ1 phase/Γ phase contact interface length)×100” is 10% or more.

First claim

The invention claimed is:

1. A galvannealed steel sheet, comprising:
a base iron; and
a plating layer containing 7.2 to 10.6 mass % of Fe, 0.2 to 0.4 mass % of Al, and 0.1 mass % or more in total of one type or more types selected from the group consisting of Ni, Co, Cu, and In, and the balance comprising Zn and impurities,

wherein
the plating layer is formed on a surface of the base iron,

wherein
in a vertical cross-section of the plating layer, an average thickness of a ζ phase is 0.2 μm or less, and an average thickness of a Γ phase existing in contact with the base iron is 0.5 μm or less,

wherein
the one type or more types selected from the group consisting of Ni, Co, Cu, and In contained in the plating layer are contained in the Γ phase at 0.5 mass % or more in total, and

wherein
a phase existing in contact with the Γ phase is a mixed phase of Γ 1 phase and δ phase, and a δ phase percentage defined by Expression (1) below is 10% or more,
δ phase percentage=(δ phase/Γ phase contact interface length)/(δ phase/Γ phase contact interface length+Γ 1 phase/Γ phase contact interface length)×100  (1),

wherein the δ phase/Γ phase contact interface length is the length of the interface at which the δ phase and the Γ phase are in contact, and the Γ 1 phase/Γ phase contact interface length is the length of the interface at which the Γ 1 phase and the Γ phase are in contact.

2. A manufacturing method of the galvannealed steel sheet of claim 1 to manufacture the galvannealed steel sheet that is to be subjected to press working with a sheet thickness reduction percentage (%) of 5% or more, the method comprising:
calculating a necessary pre-plating weight (g/m 2 ) based on the sheet thickness reduction percentage (%) during press working of the galvannealed steel sheet according to Expression (2) below;
pre-plating with the calculated necessary pre-plating weight (g/m 2 ) or more in total of one type or more types selected from the group consisting of Ni, Co, Cu, and In on a base iron;
dipping the pre-plated base iron into a plating bath containing 0.1 to 0.3 mass % of Al to perform galvanizing thereon to obtain a galvanized steel sheet;
heating the galvanized steel sheet in a heating furnace;
and after the temperature of the galvanized steel sheet reaching a maximum temperature at the exit of the heating furnace, performing slow cooling of the galvanized steel sheet in a soaking furnace adjusting a temperature integral value S calculated by Expression (3) below in a range of 300 or more to less than 800 and performing an alloying treatment of the galvanized steel sheet,
necessary pre-plating weight (g/m 2 )=0.0222×sheet thickness reduction percentage (%)−0.0625  (2), and

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Assignees

• Nippon Steel & Sumitomo Metal Corp

Inventors

• Kurosaki Masao
• Maki Jun
• Yamanaka Shintaro
• Tanaka Hiroyuki

Classifications

• Y10T428/12972

  Containing 0.01-1.7% carbon [i.e., steel] · CPC title

• Y10T428/12979

  Containing more than 10% nonferrous elements [e.g., high alloy, stainless] · CPC title

• B32B15/013 Primary

  one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium · CPC title

• Y10T428/12944

  Ni-base component · CPC title

• C21D6/00

  Heat treatment of ferrous alloys · CPC title