HOT STAMPED HIGH STRENGTH PART EXCELLENT IN POST PAINTING ANTICORROSION PROPERTY AND METHOD OF PRODUCTION OF SAME

• US 20140030544A1
• Filed: 03/30/2012
• Published: 01/30/2014
• Est. Priority Date: 04/01/2011
• Status: Active Grant

• Current Assignee: Nippon Steel Corporation
• Original Assignee: Nippon Steel & Sumitomo Metal Corporation (Nippon Steel Corporation)
• Inventors: Maki, Jun, Kusumi, Kazuhisa, Abe, Masayuki, Kurosaki, Masao
• Granted Patent: US 8,986,849 B2
• Time in Patent Office: Days
• US Class Current: 428/632
• CPC Class Codes: B21B 1/26 by hot-rolling , e.g. Steckel hot mill
• CPC Class Codes: C21D 1/673 for die quenching
• CPC Class Codes: C21D 2211/004 Dispersions; Precipitations
• CPC Class Codes: C21D 7/13 by hot working
• CPC Class Codes: C21D 8/0226 Hot rolling
• CPC Class Codes: C21D 8/0236 Cold rolling
• CPC Class Codes: C21D 8/0263 following hot rolling
• CPC Class Codes: C21D 9/46 for sheet metals
• CPC Class Codes: C22C 38/001 containing N
• CPC Class Codes: C22C 38/02 containing silicon
• CPC Class Codes: C22C 38/04 containing manganese
• CPC Class Codes: C22C 38/06 containing aluminium
• CPC Class Codes: C22C 38/14 containing titanium or zirconium
• CPC Class Codes: C22C 38/20 with copper
• CPC Class Codes: C22C 38/22 with molybdenum or tungsten
• CPC Class Codes: C22C 38/28 with titanium or zirconium
• CPC Class Codes: C22C 38/32 with boron
• CPC Class Codes: C22C 38/38 with more than 1.5% by weight of manganese
• CPC Class Codes: C22C 38/44 with molybdenum or tungsten
• CPC Class Codes: C22C 38/50 with titanium or zirconium
• CPC Class Codes: C22C 38/54 : with boron
• CPC Class Codes: C22C 38/60 : containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
• CPC Class Codes: C23C 2/0038 : characterised by the pre-treatment chambers located immediately upstream of the bath or occurring locally before the dipping process
• CPC Class Codes: C23C 2/02 : Pretreatment of the material to be coated, e.g. for coating on selected surface areas C23C2/30 takes precedence
• CPC Class Codes: C23C 2/0222 : in a reactive atmosphere, e.g. oxidising or reducing atmosphere C23C2/024 takes precedence
• CPC Class Codes: C23C 2/12 : Aluminium or alloys based thereon
• CPC Class Codes: C23C 2/26 : After-treatment C23C2/14 takes precedence
• 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: C23C 2/34 : characterised by the shape of the material to be treated C23C2/14 takes precedence
• CPC Class Codes: Y10T 428/12611 : Oxide-containing component
• CPC Class Codes: Y10T 428/12757 : Fe
• CPC Class Codes: Y10T 428/12951 : Fe-base component
• CPC Class Codes: Y10T 428/12972 : Containing 0.01-1.7% carbon [i.e., steel]
• CPC Class Codes: Y10T 428/31678 : Of metal

Abstract

A hot stamped high strength part in which the propagation of cracks which form at the plating layer at the time of hot stamping when hot stamping aluminum plated steel sheet is suppressed and the post painting anticorrosion property is excellent even without adding special ingredient elements which suppress formation of cracks in an aluminum plating layer is provided.

A hot stamped high strength part which is excellent in post painting anticorrosion property, which hot stamped high strength part has an alloy plating layer which includes an Al—Fe intermetallic compound phase on the surface of the steel sheet, wherein the alloy plating layer is comprised from phases of a plurality of intermetallic compounds, a mean linear intercept length of crystal grains of a phase containing Al: 40 to 65 mass % among the phases of the plurality of intermetallic compounds is 3 to 20 μm, an average value of thickness of the Al—Fe alloy plating layer is 10 to 50 μm, and a ratio of the average value of thickness to the standard deviation of thickness of the Al—Fe alloy plating layer satisfies the following relationship:

0<standard deviation of thickness/average value of thickness≦0.15.

Claims

1. A hot stamped high strength part which is excellent in post painting anticorrosion property, comprising an alloy plating layer comprising an Al—

Fe intermetallic compound phase on the surface of the steel sheet,

said alloy plating layer is comprised from phases of a plurality of intermetallic compounds,

a mean linear intercept length of crystal grains of a phase containing Al;

40 to 65 mass % among said phases of the plurality of intermetallic compounds is 3 to 20 μ

m,

an average value of thickness of said Al—

Fe alloy plating layer is 10 to 50 μ

m, and

a ratio of the average value of thickness to the standard deviation of thickness of said Al—

Fe alloy plating layer satisfies the following relationship;

0<

standard deviation of thickness/average value of thickness≦

0.15.

2. The hot stamped high strength part which is excellent in post painting anticorrosion property as set forth in claim 1 characterized in that said ratio of the average value of thickness to the standard deviation of thickness is 0.1 or less.

3. The hot stamped high strength part which is excellent in post painting anticorrosion property as set forth in claim 1 or 2 characterized in that said Al—

Fe alloy plating layer contains, by mass %, Si;

2 to 7%.

4. The hot stamped high strength part which is excellent in post painting anticorrosion property as set forth in claim 1 or 2 characterized in that a surface film layer which contains ZnO is laid on the surface of said Al—

Fe alloy plating layer.

5. The hot stamped high strength part which is excellent in post painting anticorrosion property as set forth in claim 4 characterized in that a content of ZnO of said surface film layer is, converted to mass of Zn, 0.3 to 7 g/m² per side.

6. The hot stamped high strength part which is excellent in post painting anticorrosion property as set forth in claim 1 or 2 characterized in that said steel sheet is comprised of a steel sheet of chemical ingredients which comprise as ingredients, by mass %,

C:

0.1 to 0.5%,

Si;

0.01 to 0.7%,

Mn;

0.2 to 2.5%,

Al;

0.01 to 0.5%,

P;

0.001 to 0.1%,

S;

0.001 to 0.1%,

N;

0.0010% to 0.05%, and

a balance of Fe and unavoidable impurities.

7. The hot stamped high strength part which is excellent in post painting anticorrosion property as set forth in claim 6 characterized in that said steel sheet further comprises, by mass %, one or more elements selected from

Cr:

over 0.4 to 3%,

Mo;

0.005 to 0.5%,

B;

0.0001 to 0.01%,

W;

0.01 to 3%,

V;

0.01 to 2%,

Ti;

0.005 to 0.5%,

Nb;

0.01 to 1%

Ni;

0.01 to 5%,

Cu;

0.1 to 3%,

Sn;

0.005% to 0.1%, and

Sb;

0.005% to 0.1%.

8. A method of production of an aluminum plated steel sheet for a hot stamped high strength part, comprising steps of:

providing an aluminum plated steel sheet obtained characterized by

hot rolling a steel which comprises chemical ingredients which comprise, by mass %,

C;

0.1 to 0.5%,

Si;

0.01 to 0.7%,

Mn;

0.2 to 2.5%,

Al;

0.01 to 0.5%,

P;

0.001 to 0.1%,

S;

0.001 to 0.1%,

N;

0.0010% to 0.05%, and

a balance of Fe and unavoidable impurities,

cold rolling said hot rolled steel to obtain a cold rolled steel sheet,

heating said cold rolled steel sheet on a hot dipping line to an annealing temperature of 670 to 760°

C.,

holding said heated steel sheet in a reducing furnace for 60 sec or less, and

aluminum plating said steel sheet; and

temper rolling said aluminum plated steel sheet to give a rolling rate of 0.5 to 2%;

raising the temperature of said temper rolled aluminum plated steel sheet by a temperature elevation rate of 3 to 200°

C./sec;

hot stamping the aluminum plated steel sheet under conditions of a Larson-Miller parameter (LMP) expressed by the following formula;

LMP=T(20+log t)

(wherein, T;

heating temperature of aluminum plated steel sheet (absolute temperature K), t;

holding time in heating furnace after reaching target temperature (hrs)) of 20000 to 23000; and

quenching said aluminum plated steel sheet after hot stamping at a 20 to 500°

C./sec cooling rate in the die.

9. The method of production of an aluminum plated steel sheet for a hot stamped high strength part as set forth in claim 8 characterized in that said steel furthermore comprises, by mass %, one or more of the elements selected from

Cr:

over 0.4 to 3%,

Mo;

0.005 to 0.5%,

B;

0.0001 to 0.01%,

W;

0.01 to 3%,

V;

0.01 to 2%,

Ti;

0.005 to 0.5%,

Nb;

0.01 to 1%

Ni;

0.01 to 5%,

Cu;

0.1 to 3%,

Sn;

0.005% to 0.1%, and

Sb;

0.005% to 0.1%.

10. The method of production of an aluminum plated steel sheet for a hot stamped high strength part as set forth in claim 8 or 9 characterized in that in the temperature elevation rate in said hot stamping step is 4 to 200°

C./sec.

11. The method of production of an aluminum plated steel sheet for a hot stamped high strength part as set forth in any one of claims 8 to 10 characterized in that in the step of producing said aluminum plated steel sheet, a plating bath for aluminum plating comprises Si in an amount of 7 to 15%, and either a bath temperature or a sheet temperature upon entering the bath is 650°

C. or less.