Hot-stamped steel

Patent metadata

Field	Value
Publication number	US-9932652-B2
Application number	US-201515129640-A
Country	US
Kind code	B2
Filing date	Mar 31, 2015
Priority date	Mar 31, 2014
Publication date	Apr 3, 2018
Grant date	Apr 3, 2018

Abstract

Hot-stamped steel includes: a base metal that is steel including a tempered portion having hardness corresponding to 85% or less of the highest quenching hardness, the highest quenching hardness being defined as a Vickers hardness at a depth position spaced away from a surface by ¼ times a sheet thickness in a case of performing water quenching after heating at a temperature equal to or higher than an A c3 point and retention for 30 minutes; and a Zn coating layer that is formed on the tempered portion of the base metal. The Zn coating layer includes a solid-solution layer including a solid-solution phase that contains Fe and Zn that is solid-soluted in Fe, and a lamella layer that includes the solid-solution phase and a capital gamma phase. An area ratio of the lamella layer in the Zn coating layer is 20% or less.

First claim

What is claimed is:

1. A hot-stamped steel comprising:
a base metal that is a steel sheet including a tempered portion having a hardness corresponding to 85% or less of the highest quenching hardness, the highest quenching hardness being defined as a Vickers hardness at a depth position spaced away from a surface by ¼ times a sheet thickness in a case of performing water quenching after heating to a temperature equal to or higher than an A c3 point and retaining for 30 minutes;
wherein either a part of the base metal may be the tempered portion or an entirety of the base metal is the tempered portion, and
a Zn coating layer that is formed on the tempered portion of the base metal,
wherein the Zn coating layer includes:
a solid-solution layer including a solid-solution phase that contains Fe and Zn that is solid-soluted in Fe, and
a lamella layer that includes the solid-solution phase and a capital gamma phase, and
an area ratio of the lamella layer in a vertical cross section in the Zn coating layer is 20% or less.

2. The hot-stamped steel according to claim 1 ,
wherein the hardness of the tempered portion is 60% or less of the highest quenching hardness, and the area ratio of the lamella layer in the vertical cross section in the Zn coating layer is 5% to 20%.

3. The hot-stamped steel according to claim 1 or 2 ,
wherein the hardness of the tempered portion is 50% or less of the highest quenching hardness.

4. The hot-stamped steel according to claim 1 or 2 ,
wherein the hardness with a load of 10 kgf of the tempered portion is 180 Hv to 450 Hv.

5. The hot-stamped steel according to claim 1 or 2 ,
wherein the hot-stamped steel is produced by heating for a predetermined heating time so that the highest heating temperature is the A c3 point or higher, working and quenching simultaneously through pressing by using a die, and tempering at a predetermined tempering temperature, and
when an A c1 point of the base metal is represented by A c1 , the tempering temperature is represented by T in degrees ° C., and a concentration of Zn in the solid-solution phase after the quenching and before the tempering is represented by C in a unit of % by mass, the following Equation 1 is satisfied,
A c1 ≥T≥ 700−4.0×(35.0− C )  (1).

6. The hot-stamped steel according to claim 5 ,
wherein the tempering temperature is 700° C. to the A c1 point of the base metal.

7. The hot-stamped steel according claim 1 or 2 ,
wherein a part of the base metal is the tempered portion.

8. The hot-stamped steel according to claim 5 ,
wherein a part of the base metal is the tempered portion.

9. The hot-stamped steel according to claim 6 ,
wherein a part of the base metal is the tempered portion.

Assignees

• Nippon Steel & Sumitomo Metal Corp

Inventors

• Sengoku Akihiro
• Takebayashi Hiroshi

Classifications

• C23C30/005

  on hard metal substrates · CPC title

• Y10T428/12972

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

• Y10T428/24983

  Hardness · CPC title

• B32B15/18

  comprising iron or steel {(B32B15/011, B32B15/012 and B32B15/013 take precedence)} · CPC title

• C21D9/46 Primary

  for sheet metals · CPC title