Galvannealed steel sheet, electrodeposition-coated steel sheet, automotive part, method of producing electrodeposition-coated steel sheet, and method of producing galvannealed steel sheet

Patent metadata

Field	Value
Publication number	US-12473652-B2
Application number	US-202118251242-A
Country	US
Kind code	B2
Filing date	Nov 5, 2021
Priority date	Nov 6, 2020
Publication date	Nov 18, 2025
Grant date	Nov 18, 2025

Abstract

Disclosed is a galvannealed steel sheet including: a Si-containing cold-rolled steel sheet containing Si in an amount of 0.1 mass % or more and 3.0 mass % or less; an Fe-based electroplating layer formed on at least one surface of the Si-containing cold-rolled steel sheet; and a galvannealed layer formed on the Fe-based electroplating layer, in which in an intensity profile measured by glow discharge optical emission spectrometry, I Si,Fe /I Si,bulk is 0.30 or more, and an average value of C concentration in a region ranging from 10 μm to 20 μm in the thickness direction from the interface between the galvannealed layer and the Fe-based electroplating layer towards the Fe-based electroplating layer is 0.10 mass % or less.

First claim

The invention claimed is:

1 . A galvannealed steel sheet comprising:
a Si-containing cold-rolled steel sheet containing Si in an amount of 0.1 mass % or more and 3.0 mass % or less; an Fe-based electroplating layer formed on at least one surface of the Si-containing cold-rolled steel sheet; a galvannealed layer formed on the Fe-based electroplating layer, and a decarburized layer extending from the interface between the galvannealed layer and the Fe-based electroplating layer towards the Fe-based electroplating layer, wherein in an intensity profile measured by glow discharge optical emission spectrometry, a value of I Si,Fe /I Si,bulk is 0.30 or more, where I Si,Fe denotes an average Si intensity in a region ranging from a position shifted from an interface between the galvannealed layer and the Fe-based electroplating layer towards the galvannealed layer, by a distance corresponding to a thickness obtained by converting an Fe content (mass %) in the galvannealed layer into a thickness (μm) as a plating layer, to an interface between the Fe-based electroplating layer and the Si-containing cold-rolled steel sheet, and I Si,bulk denotes an average Si intensity in the Si-containing cold-rolled steel sheet, an average value of C concentration in a region ranging from 10 μm to 20 μm in the thickness direction from the interface between the galvannealed layer and the Fe-based electroplating layer towards the Fe-based electroplating layer is 0.10 mass % or less, the number of crystal grain boundaries in the Fe-based electroplating layer that are in contact with the Si-containing cold-rolled steel sheet at the interface between the Fe-based electroplating layer and the Si-containing cold-rolled steel sheet is 10 or more per 10 μm in a sheet transverse direction in an observation field of view of the Si-containing cold-rolled steel sheet, and a coating weight (g/m 2 ) per surface of the Fe-based electroplating layer, denoted by C.W. Fe1 , and a thickness (μm) of the decarburized layer, denoted by Ca, satisfy the following formula (1):
0.8×(C.W. Fe1 )+( C d )≥70(1).

2 . The galvannealed steel sheet according to claim 1 , wherein the Si-containing cold-rolled steel sheet contains Si in an amount of 0.50 mass % or more and 3.0 mass % or less.

3 . The galvannealed steel sheet according to claim 1 , wherein the decarburized layer has a thickness of 30 μm or more.

4 . The galvannealed steel sheet according to claim 1 , wherein the coating weight (g/m 2 ) per surface of the Fe-based electroplating layer C.W. Fe1 is 2 g/m 2 or more.

5 . The galvannealed steel sheet according to claim 1 , wherein the Si-containing cold-rolled steel sheet has a chemical composition containing, in addition to Si, in mass %,
C: 0.8% or less, Mn: 1.0% or more and 12.0% or less, P: 0.1% or less, S: 0.03% or less, N: 0.010% or less, and Al: 1.0% or less, with the balance being Fe and inevitable impurities.

6 . The galvannealed steel sheet according to claim 5 , wherein the chemical composition further contains, in mass %, at least one element selected from the group consisting of
B: 0.005% or less, Ti: 0.2% or less, Cr: 1.0% or less, Cu: 1.0% or less, Ni: 1.0% or less, Mo: 1.0% or less, Nb: 0.20% or less, V: 0.5% or less, Sb: 0.020% or less, Ta: 0.1% or less, W: 0.5% or less, Zr: 0.1% or less, Sn: 0.20% or less, Ca: 0.005% or less, Mg: 0.005% or less, and REM: 0.005% or less.

7 . The galvannealed steel sheet according to claim 1 , wherein the Fe-based electroplating layer has a chemical composition containing at least one element selected from the group consisting of B, C, P, N, O, Ni, Mn, Mo, Zn, W, Pb, Sn, Cr, V, and Co, in a total amount of 10 mass % or less, with the balance being Fe and inevitable impurities.

8 . An electrodeposition-coated steel sheet comprising:
a chemical conversion layer formed on the galvannealed steel sheet as recited in claim 1 ; and an electrodeposition coating layer formed on the chemical conversion layer.

9 . An automotive part at least partially made from the electrodeposition-coated steel sheet as recited in claim 8 .

10 . A method of producing an electrodeposition-coated steel sheet, the method comprising:
subjecting the galvannealed steel sheet as recited in claim 1 to chemical conversion treatment to obtain a chemical-conversion-treated steel sheet with a chemical conversion layer formed thereon; and subjecting the chemical-conversion-treated steel sheet to electrodeposition coating treatment to obtain an electrodeposition-coated steel sheet with an electrodeposition coating layer formed on the chemical conversion layer.

11 . A method of producing the galvannealed steel sheet according to claim 1 , the method comprising:
subjecting a cold-rolled steel sheet containing Si in an amount of 0.1 mass % or more and 3.0 mass % or less to Fe-based electroplating to obtain a pre-annealing Fe-based electroplated steel sheet with a pre-annealing Fe-based electroplating layer formed on at least one surface thereof; then heating the pre-annealing Fe-based electroplated steel sheet with an average heating rate of 10° C./sec or higher in a temperature range from 400° C. to 650° C., and holding the pre-annealing Fe-based electroplated steel sheet in the temperature range in an atmosphere with a dew point above −30° C., to obtain an Fe-based electroplated steel sheet; then subjecting the Fe-based electroplated steel sheet to galvanization to obtain a galvanized steel sheet; and then subjecting the galvanized steel sheet to alloying treatment to obtain a galvannealed steel sheet comprising an Fe-based electroplating layer having a coating weight per surface of more than 0 g/m 2 and a galvannealed layer formed on the Fe-based electroplating layer.

12 . The method of producing a galvannealed steel sheet according to claim 11 , wherein the cold-rolled steel sheet contains Si in an amount of 0.50 mass % or more and 3.0 mass % or less.

13 . The method of producing a galvannealed steel sheet according to claim 11 , wherein a coating weight (g/m 2 ) per surface of the pre-annealing Fe-based electroplating layer, denoted by C.W. Fe0 , satisfies the following formula (2):
(C.W. Fe0 )−(C.W. Zn )×[mass % Fe]/100>0  (2),

where C.W. Zn denotes a target value of a coating weight (g/m 2 ) per surface of the galvannealed layer, provided:
25.0 g/m 2 ≤C.W. Zn ≤80.0 g/m 2 , and
[mass % Fe] denotes a target value of an Fe content (mass %) in the galvannealed layer.

14 . The method of producing a galvannealed steel sheet according to claim 11 , wherein a coating weight (g/m 2 ) per surface of the pre-annealing Fe-based electroplating layer, denoted by C.W. Fe0 , and the dew point, denoted by D.P., satisfy the following formula (3):
0.83×{(C.W. Fe0 )−(C.W. Zn )×[mass % Fe]/100}+(D.P.)≥−5  (3),

where C.W. Zn denotes a target value of a coating weight (g/m 2 ) per surface of the galvannealed layer, provided:
25.0 g/m 2 ≤C.W. Zn ≤80.0 g/m 2 , and
[mass % Fe] denotes a target value of an Fe content (mass %) in the galvannealed layer.

15 . The method of producing a galvannealed steel sheet according to claim 11 , wherein a coating weight (g/m 2 ) per surface of the pre-annealing Fe-based electroplating layer, denoted by C.W. Fe0 , satisfies the following formula (4):
(C.W. Fe0 )−(C.W. Zn )×[mass % Fe]/100≥2  (4)
where C.W. Zn denotes a target value of a coating weight (g/m 2 ) per surface of the galvannealed layer, provided: 25.0 g/m 2 ≤C.W. Zn ≤80.0 g/m 2 , and [mass % Fe] denotes a target value of an Fe content (mass

Assignees

• Jfe Steel Corp

Inventors

• Yamamoto Shunsuke
• Takashima Katsutoshi
• Okumura Yusuke
• Kanazawa Tomomi
• Hoshino Katsuya
• Kawano Takashi
• Yamashita Takako
• Matsuda Hiroshi
• Makimizu Yoichi

Classifications

• C21D8/02

  during manufacturing of plates or strips (C21D8/12 takes precedence) · CPC title

• C25D3/20

  of iron · CPC title

• C23C2/06 Primary

  Zinc or cadmium or alloys based thereon · CPC title

• C22C38/06

  containing aluminium · CPC title

• C22C38/04

  containing manganese · CPC title