Coated steel product

Patent metadata

Field	Value
Publication number	US-10982303-B2
Application number	US-201816480967-A
Country	US
Kind code	B2
Filing date	Jan 26, 2018
Priority date	Jan 27, 2017
Publication date	Apr 20, 2021
Grant date	Apr 20, 2021

Abstract

There is provided a coated steel product having a steel product and a coating layer including a Zn—Al—Mg alloy layer disposed on a surface of the steel product, in which the Zn—Al—Mg alloy layer has a Zn phase, the Zn phase contains a Mg—Sn intermetallic compound phase, and the coating layer consists of Zn: more than 65.0%, Al: from more than 5.0% to less than 25.0%, Mg: from more than 3.0% to less than 12.5%, Sn: 0.1% to 20.0% in terms of percent (%) by mass, given amounts of optional elements, and impurities, and has a chemical composition that satisfies the following Formulas 1 to 5:

Bi+In<Sn  Formula 1:

Y+La+Ce≤Ca  Formula 2:

Si<Sn  Formula 3:

0≤Cr+Ti+Ni+Co+V+Nb+Cu+Mn<0.25  Formula 4:

0≤Sr+Sb+Pb+B<0.5.  Formula 5:

First claim

The invention claimed is:

1. A coated steel product having a steel product and a coating layer including a Zn—Al—Mg alloy layer disposed on a surface of the steel product,
wherein the Zn—Al—Mg alloy layer has a Zn phase, and the Zn phase includes a Mg—Sn intermetallic compound phase,
wherein the coating layer consists of, in terms of percent (%) by mass:
Zn: more than 65.0%,
Al: from more than 5.0% to less than 25.0%,
Mg: from more than 3.0% to less than 12.5%,
Sn: from 0.1% to 20.0%,
Bi: from 0% to less than 5.0%,
In: from 0% to less than 2.0%,
Ca: from 0.05% to 3.00%,
Y: from 0% to 0.5%,
La: from 0% to less than 0.5%,
Ce: from 0% to less than 0.5%,
Si: from 0.01% to less than 2.5%,
Cr: from 0% to less than 0.25%,
Ti: from 0% to less than 0.25%,
Ni: from 0% to less than 0.25%,
Co: from 0% to less than 0.25%,
V: from 0% to less than 0.25%,
Nb: from 0% to less than 0.25%,
Cu: from 0% to less than 0.25%,
Mn: from 0% to less than 0.25%,
Fe: from 0% to 5.0%,
Sr: from 0% to less than 0.5%,
Sb: from 0% to less than 0.5%,
Pb: from 0% to less than 0.5%,
B: from 0% to less than 0.5%, and
impurities, and
wherein the coating layer has a chemical composition that satisfies the following Formulas 1 to 5:
Bi+In<Sn  Formula 1:

Y+La+Ce≤Ca  Formula 2:

Si<Sn  Formula 3:

0≤Cr+Ti+Ni+Co+V+Nb+Cu+Mn<0.25  Formula 4:

0≤Sr+Sb+Pb+B<0.5  Formula 5:

wherein, in Formulas 1 to 5, each element symbol represents a content of a corresponding element in terms of percent (%) by mass,
wherein the Zn—Al—Mg alloy layer has at least one selected from the group consisting of a Ca—Al—Si intermetallic compound phase having an average grain size of 1 μm or more and a Mg—Al—Si intermetallic compound phase having an average grain size of 1 μm or more.

2. The coated steel product according to claim 1 , wherein the Mg—Sn intermetallic compound phase has an average grain size of less than 1 μm.

3. The coated steel product according to claim 1 , wherein, in a cross-section of the Zn—Al—Mg alloy layer, the Mg—Sn intermetallic compound phase having a grain size of less than 1 μm has an area fraction of from 10% to 50% with respect to the Zn phase including the Mg—Sn intermetallic compound phase.

4. The coated steel product according to claim 1 , wherein, in a cross-section of the Zn—Al—Mg alloy layer, the Zn phase including the Mg—Sn intermetallic compound phase is present with an area fraction of 3% or more with respect to the cross-section of the Zn—Al—Mg alloy layer.

5. The coated steel product according to claim 1 , wherein, based on an X-ray diffraction image of a surface of the coating layer, the image being measured using a Cu-Kα ray with an X-ray output at 40 kV and 150 mA, a specific intensity I (Mg—Sn intermetallic compound phase)={I (22.8° intensity (cps))+I (23.3° intensity (cps))+I (24.2° intensity (cps))}/3×I (background intensity at 20° (cps)) is 1.5 or more.

6. The coated steel product according to claim 1 , wherein the Zn phase contains, as the Mg—Sn intermetallic compound phase, a MgCaSn phase and a Mg 9 Sn 5 phase,
wherein, based on an X-ray diffraction image of a surface of the coating layer, the image being measured using a Cu-Kα ray with an X-ray output at 40 kV and 150 mA, a specific intensity I (MgCaSn+Mg 9 Sn 5 )={I (22.8° intensity (cps))+I (26.3° intensity (cps))}/I (23.3° intensity (cps)) is less than 0.3, and I (23.3° intensity (cps)) is 500 cps or more.

7. The coated steel product according to claim 5 , wherein the coating layer has a Mg content of from more than 4.0% to less than 12.5% by mass,
wherein, based on the X-ray diffraction image of the surface of the coating layer, the image being measured using a Cu-Kα ray with an X-ray output at 40 kV and 150 mA, a diffraction peak having a strongest intensity among diffraction peaks appearing at from 23.0° to 23.46° appears between 23.36° to 23.46°.

8. The coated steel product according to claim 1 ,
wherein, in a cross-section of the Zn—Al—Mg alloy layer, a Ca—Zn—Al intermetallic compound phase having a grain size of 1 μm or more is present with an area fraction of 5% or more with respect to the cross-section of the Zn—Al—Mg alloy layer.

9. The coated steel product according to claim 1 , wherein the coating layer has an Sn content of from 3.00% to 20.00% by mass, and, the following Formula is satisfied:
0.05<Sn/Zn, wherein each of Sn and Zn represents the content of the corresponding element,
wherein, in a cross-section of the Zn—Al—Mg alloy layer, a Mg—Sn intermetallic compound phase having a grain size of 1 μm or more is present with an area fraction of 3% or more with respect to the cross-section of the Zn—Al—Mg alloy layer.

10. The coated steel product according to claim 1 , wherein, in a cross-section of the Zn—Al—Mg alloy layer, a eutectoid structure composed of a Zn phase and an Al phase, and having a lamellar spacing of less than 300 nm, is present with an area fraction of 10% or more with respect to the cross-section of the Zn—Al—Mg alloy layer.

11. The coated steel product according to claim 1 , wherein a Zn—Al—MgZn 2 ternary eutectic structure has an area fraction of from 0% to 5% in a cross-section of the Zn—Al—Mg alloy layer.

12. The coated steel product according to claim 1 , wherein an Sn content of the coating layer is from 0.10% to less than 3.00%.

13. The coated steel product according to claim 1 , wherein the coating layer has an Al—Fe alloy layer between the steel product and the Zn—Al—Mg alloy layer.

14. The coated steel product according to claim 2 , wherein, in a cross-section of the Zn—Al—Mg alloy layer, the Mg—Sn intermetallic compound phase having a grain size of less than 1 μm has an area fraction of from 10% to 50% with respect to the Zn phase including the Mg—Sn intermetallic compound phase.

15. The coated steel product according to claim 2 , wherein, in a cross-section of the Zn—Al—Mg alloy layer, the Zn phase including the Mg—Sn intermetallic compound phase is present with an area fraction of 3% or more with respect to the cross-section of the Zn—Al—Mg alloy layer.

16. The coated steel product according to claim 3 , wherein, in a cross-section of the Zn—Al—Mg alloy layer, the Zn phase including the Mg—Sn intermetallic compound phase is present with an area fraction of 3% or more with respect to the cross-section of the Zn—Al—Mg alloy layer.

17. The coated steel product according to claim 2 , wherein, based on an X-ray diffraction image of a surface of the coating layer, the image being measured using a Cu-Kα ray with an X-ray output at 40 kV and 150 mA, a specific intensity I (Mg—Sn intermetallic compound phase)={I (22.8° intensity (cps))+I (23.3° intensity (cps))+I (24.2° intensity (cps))}/3×I (background intensity at 20° (cps)) is 1.5 or more.

Assignees

• Nippon Steel Corp

Inventors

• Tokuda Kohei
• Maki Jun
• Goto Yasuto
• Mitsunobu Takuya

Classifications

• C23C2/29

  Cooling or quenching · CPC title

• C23C2/28

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

• C23C2/26

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

• C23C2/024

  by cleaning or etching · CPC title

• C23C2/0224

  Two or more thermal pretreatments · CPC title