Hot press-formed article and a method for its manufacture

• US 20060121305A1
• Filed: 10/21/2005
• Published: 06/08/2006
• Est. Priority Date: 04/23/2003
• Status: Active Grant

• Current Assignee: Nippon Steel Corporation, Toyoda Iron Works Company Limited, Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Sumitomo Metal Industries Limited (Nippon Steel Corporation), Toyoda Iron Works Company Limited, Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Imai, Kazuhito, Toki, Tamotsu, Yoshikawa, Yukihiro, Ichikawa, Masanobu, Sudo, Shuntaro, Fukui, Kunihiro, Obayashi, Akira
• Granted Patent: US 7,399,535 B2
• Time in Patent Office: Days
• US Class Current: 428/629
• CPC Class Codes: C21D 1/673 for die quenching
• CPC Class Codes: C23C 2/26 After-treatment C23C2/14 takes precedence
• CPC Class Codes: C23C 2/261 in a gas atmosphere, e.g. inert or reducing atmosphere
• CPC Class Codes: C23C 2/28 Thermal after-treatment, e.g. treatment in oil bath
• CPC Class Codes: C23C 2/29 Cooling or quenching
• CPC Class Codes: Y10T 428/1259 Oxide
• CPC Class Codes: Y10T 428/12611 Oxide-containing component
• CPC Class Codes: Y10T 428/12799 Next to Fe-base component [e.g., galvanized]
• CPC Class Codes: Y10T 428/12951 Fe-base component
• CPC Class Codes: Y10T 428/264 Up to 3 mils
• CPC Class Codes: Y10T 428/27 Web or sheet containing structurally defined element or component, the element or component having a specified weight per unit area [e.g., gms/sq cm, lbs/sq ft, etc.]

Abstract

A hot press-formed article having improved corrosion resistance and coating adhesion when coated is obtained by hot press forming of a zinc-based plated steel material. It has a zinc-based plating layer comprising an iron-zinc solid solution phase and atop it a zinc oxide layer. The average thickness of the zinc oxide layer which is the outermost layer is at most 2 μm. A hot press-formed article having a good appearance and excellent corrosion resistance, coating adhesion, post-coating corrosion resistance, and weldability has a layer (2) consisting essentially of an iron-zinc solid solution phase atop a base material steel sheet (1). It also has a zinc oxide layer (3) with an average thickness of at most 5 μm as an uppermost layer, but it does not have a substantial amount of an iron-zinc intermetallic compound phase. The total amount of Al contained in the iron-zinc solid solution layer (2) and the zinc oxide layer (3) is at most 0.5 g/m², and/or the total amount of Al oxides contained in these layers is at most 5 mg/m².

Claims

1. A hot press-formed article formed by hot press forming of a zinc-based plated steel material, the formed articles having on its surface a zinc-based plating layer which comprises an iron-zinc solid solution phase and which has a thickness of at least 1 μ

m and at most 50 μ

m, with the average thickness of a zinc oxide layer, which may be present atop the zinc-based plating layer, being at most 2 μ

m.

2. A hot press-formed article as set forth in claim 1 wherein substantially no zinc oxide layer is present atop the zinc-based plating layer.

3. A hot press-formed article as set forth in claim 1 wherein the zinc-based plating layer consists essentially of an iron-zinc solid solution phase.

4. A hot press-formed article as set forth in claim 1 wherein the total amount of zinc in the zinc-based plating layer and the zinc oxide layer present on the surface of the steel material is at least 10 g/m² and at most 90 g/m².

5. A method of manufacturing a hot press-formed article including a step of hot press forming a zinc-based plated steel material to form a hot press-formed article having a zinc-based plating layer comprising an iron-zinc solid solution phase and a zinc oxide layer atop it, and a step of removing all or a portion of the zinc oxide layer so that the average thickness of the zinc oxide layer which is the outermost layer of the resulting hot press-formed article is at most 2 μ

m.

6. A method as set forth in claim 5 wherein the step of hot press forming simultaneously achieves hardening of the steel material.

7. A method as set forth in claim 5 wherein the step of removing the zinc oxide layer is carried out by a method selected from the group consisting of shot blasting and liquid honing.

8. A method as set forth in claim 7 wherein the shot blasting uses steel spheres having an average diameter of 100-500 μ

m as shot.

9. A method as set forth in claim 5 wherein the step of removing the zinc oxide layer is performed so as to leave a zinc-based plating layer having a thickness of at least 1 m and at most 50 μ

m.

10. A hot press-formed article having a zinc oxide layer as an uppermost layer and having beneath it an iron-zinc solid solution layer consisting essentially of an iron-zinc solid solution phase and not having a layer including a substantial amount of an iron-zinc intermetallic compound phase, wherein the average thickness of the zinc oxide layer is at most 5 μ

m, and at least one of the following (1) and (2) is satisfied;

(1) the total amount of Al contained in the iron-zinc solid solution layer and the zinc oxide layer is at most 0.5 g/m²; and

(2) the total amount of Al oxides contained in the iron-zinc solid solution layer and the zinc oxide layer is at most 5 mg/m² as Al.

11. A hot press-formed article as set forth in claim 10 wherein the average thickness of the iron-zinc solid solution layer is 10-40 μ

m.

12. A method of manufacturing a hot press-formed article including a heating step in which a steel material is heated to a predetermined temperature and a pressing step in which the steel material is then press-formed at a high temperature, wherein:

the steel material is a hot-dip galvanized steel material or a galvannealed steel material having a plating film with an Al content of at most 0.35 mass % and a coating weight of at least 40 g/m² and at most 80 g/m²,

in the heating step, the temperature of the steel material is increased from room temperature to a temperature range of 850°

C.-950°

C. in an oxidizing atmosphere at an average rate of at most 15°

C. per second, and then it is held in this temperature range for at least 30 seconds, with the total of the time for temperature increase and the holding time being at least 3 minutes and at most 10 minutes, and

in the pressing step, the steel material is press-formed in a temperature range of 700°

C.-950°

C.

13. A method as set forth in claim 12 wherein the steel material is a galvannealed steel material having an Fe content in the plating film of 10-20 mass %.

15. A method as set forth in claim 12 wherein hardening is carried out in the pressing step by cooling at least a portion of a die used in the pressing step.

16. A method as set forth in claim 12 wherein after the pressing step, the formed article obtained in the pressing step is treated by shot blasting or liquid honing to remove all or a portion of a zinc oxide layer on the surface.

14. A method of manufacturing a hot press-formed article including a heating step in which a steel material is heated to a predetermined temperature and a pressing step in which the steel material is then press-formed at a high temperature, wherein:

the steel material is an electrogalvanized steel material or a steel material electroplated with a Zn—

Fe alloy having an Fe content in the plating of at most 20 mass %, the coating weight of plating being at least 40 g/m² and at most 80 g/m²,

in the heating step, the temperature of the steel material is increased from room temperature to a temperature range of 850°

C.-950°

C. in an oxidizing atmosphere at an average rate of at most 15°

C. per second, and then it is held in this temperature range for at least 30 seconds, with the total of the time for the temperature increase and the holding time being at least 3 minutes and at most 10 minutes, and

in the pressing step, the steel material is press-formed in a temperature range of 700°

C.-950°

C.