Hot stamped article, method of producing hot stamped article, energy absorbing member, and method of producing energy absorbing member

Patent metadata

Field	Value
Publication number	US-10023925-B2
Application number	US-201214112584-A
Country	US
Kind code	B2
Filing date	May 11, 2012
Priority date	May 13, 2011
Publication date	Jul 17, 2018
Grant date	Jul 17, 2018

Abstract

A hot stamped article has a component composition containing, in terms of % by mass, 0.002% to 0.1% of C, 0.01% to 0.5% of Si, 0.5% to 2.5% of Mn+Cr, 0.1% or less of P, 0.01% or less of S, 0.05% or less of t-Al, 0.005% or less of N, and 0.0005% to 0.004% of B which is optionally contained in a case where the Mn+Cr is 1.0% or more, the remainder being Fe and unavoidable impurities. The hot stamped article has a microstructure composed of, in terms of an area ratio, 0% or more and less than 90% of martensite, 10% to 100% of bainite, and less than 0.5% of unavoidable inclusion structures, or a microstructure composed of, in terms of an area ratio, 99.5% to 100% of bainitic ferrite, and less than 0.5% of unavoidable inclusion structures.

First claim

The invention claimed is:

1. A hot stamped article that is obtained by hot stamping a steel sheet for hot stamping, the hot stamped article having a component composition comprising, in terms of % by mass:
0.002% to 0.1% of C;
0.01% to 0.5% of Si;
0.5% or more and less than 1.0% of Mn+Cr;
0.1% or less of P;
0.01% or less of S;
0.05% or less oft-Al;
0.005% or less of N; and
remainder being Fe and unavoidable impurities,
wherein the hot stamped article has a microstructure consisting of, in terms of an area ratio, 70% or more and less than 90% of martensite, 10% to 30% of bainite, and less than 0.5% of unavoidable inclusion structures, or a microstructure consisting of, in terms of an area ratio, 99.5% to 100% of bainitic ferrite, and less than 0.5% of unavoidable inclusion structures, by performing cooling at a cooling rate exceeding 100° C./second during hot stamping,
wherein λ obtained by a method described in JIS Z 2256 (2010) is 50% or more, and
wherein a tensile strength of the hot stamped article is less than 980 MPa.

2. The hot stamped article according to claim 1 ,
wherein a plated layer is provided on a surface of the hot stamped article.

3. The hot stamped article according to claim 1 , wherein the component composition further comprises one or more kinds selected from, in terms of % by mass,
0.001% to 0.1% of Ti,
0.001% to 0.05% of Nb,
0.005% to 0.1% of V, and
0.02% to 0.5% of Mo.

4. The hot stamped article according to claim 1 , wherein the component composition further comprises, in terms of % by mass, 0.0005% to 0.004% of B.

5. An energy absorbing member, comprising:
the hot stamped article according to any one of claims 1 to 4 ; and
a joint member which is joined to the hot stamped article and has tensile strength of 1180 MPa or more,
wherein a difference in tensile strength between the hot stamped article and the joint member is 200 MPa or more.

6. A method of producing a hot stamped article, the method comprising:
a heating process of heating a slab in order for a surface temperature to be in a temperature range of Ar3 point to 1400° C., the slab having a component composition comprising, in terms of % by mass, 0.002% to 0.1% of C, 0.01% to 0.5% of Si, 0.5% or more and less than 1.0% of Mn+Cr, 0.1% or less of P, 0.01% or less of S, 0.05% or less of t-Al, 0.005% or less of N, remainder being Fe and unavoidable impurities;
a hot rolling process of subjecting the heated slab to finish rolling in which a total rolling reduction at a final stand and an immediately previous stand of the final stand is set to 40% or more in a temperature range state in which the surface temperature is Ar3 point to 1400° C., and initiating cooling within one second after the finish rolling to produce a hot-rolled steel sheet;
a coiling process of coiling the hot-rolled steel sheet in a temperature range of 650° C. or lower; and
a hot stamping process of using the hot-rolled steel sheet as a steel sheet for hot stamping, forming the steel sheet for hot stamping using a die in a state in which the steel sheet is heated to a temperature of Ac3 point or higher, cooling the steel sheet for hot stamping in the die at a cooling rate exceeding 100° C./second to produce a hot stamped article having a microstructure consisting of, in terms of an area ratio, 70% or more and less than 90% of martensite, 10% to 30% of bainite, and less than 0.5% of unavoidable inclusion structures, or a microstructure consisting of, in terms of an area ratio, 99.5% to 100% of bainitic ferrite, and less than 0.5% of unavoidable inclusion structures, wherein the hot stamped article has a tensile strength of less than 980 MPa.

7. The method of producing a hot stamped article according to claim 6 , the method further comprising:
a plating process of carrying out a plating treatment with respect to the hot-rolled steel sheet before the hot stamping process,
wherein in the hot stamping process, the hot-rolled steel sheet to which the plating treatment is carried out is used as the steel sheet for hot stamping.

8. The method of producing a hot stamped article according to claim 6 , the method further comprising:
a cold rolling process of producing a cold-rolled steel sheet by carrying out cold rolling with respect to the hot-rolled steel sheet before the hot stamping process,
wherein in the hot stamping process, the cold-rolled steel sheet is used as the steel sheet for hot stamping.

9. The method of producing a hot stamped article according to claim 6 , the method further comprising:
a cold rolling process of producing a cold-rolled steel sheet by carrying out cold rolling with respect to the hot-rolled steel sheet before the hot stamping process; and
a plating treatment process of carrying out a plating treatment with respect to the cold-rolled steel sheet,
wherein in the hot stamping process, the cold-rolled steel sheet to which the plating treatment is carried out is used as the steel sheet for hot stamping.

10. The method of producing a hot stamped article according to claim 6 , the method further comprising:
a cold rolling process of producing a cold-rolled steel sheet by carrying out cold rolling with respect to the hot-rolled steel sheet before the hot stamping process; and
a continuous annealing process of carrying out continuous annealing with respect to the cold-rolled steel sheet,
wherein in the hot stamping process, the cold-rolled steel sheet to which the continuous annealing is carried out is used as the steel sheet for hot stamping.

11. The method of producing a hot stamped article according to claim 6 , the method further comprising:
a cold rolling process of producing a cold-rolled steel sheet by carrying out cold rolling with respect to the hot-rolled steel sheet before the hot stamping process;
a continuous annealing process of carrying out continuous annealing with respect to the cold-rolled steel sheet; and
a plating treatment process of carrying out a plating treatment with respect to the cold-rolled steel sheet to which the continuous annealing is carried out,
wherein in the hot stamping process, the cold-rolled steel sheet to which the continuous annealing and the plating treatment are carried out is used as the steel sheet for hot stamping.

12. The method of producing a hot stamped article according to claim 6 ,
wherein the slab further comprises one or more kinds selected from, in terms of % by mass, 0.001% to 0.1% of Ti, 0.001% to 0.05% of Nb, 0.005% to 0.1% of V, and 0.02% to 0.5% of Mo.

13. The method of producing a hot stamped article according to claim 6 , wherein the slab further comprises, in terms of % by mass, 0.0005% to 0.004% of B.

14. A method of producing an energy absorbing member, the method comprising:
a joining process of joining the steel sheet for hot stamping according to any one of claims 6 to 13 to a steel sheet for joint to produce a joined steel sheet; and
a hot stamping process of forming the joined steel sheet using a die in a state in which the joined steel sheet is heated to a temperature of Ac3 point or higher, and cooling the joined steel sheet in the die at a cooling rate exceeding 100° C./second so as to set a difference in tensile strength between a portion corresponding to the steel sheet for hot stamping and a portion corresponding to the steel sheet for joint in the joined steel sheet to 200 MPa or more.

Assignees

• Kawasaki Kaoru
• Nippon Steel & Sumitomo Metal Corp

Inventors

• Kawasaki Kaoru

Classifications

• C22C38/26

  with niobium or tantalum · CPC title

• Y10T428/1241

  Nonplanar uniform thickness or nonlinear uniform diameter [e.g., L-shape] · CPC title

• C22C38/12

  containing tungsten, tantalum, molybdenum, vanadium, or niobium · CPC title

• C21D2211/008

  Martensite · CPC title

• C22C38/14

  containing titanium or zirconium · CPC title