Warm press forming method and automobile frame component

Abstract

A method of forming a steel sheet having a tensile strength of 440 MPa or more into a press-formed part including a flange portion and other portions by press forming includes: heating the steel sheet to a temperature of 400° C. to 700° C.; and press-forming the heated steel sheet using draw forming to obtain a press-formed part, with the steel sheet being held at a press bottom dead point in the die for one second to five seconds. Geometric changes such as springback that occur in a panel can thus be suppressed, the dimensional accuracy of the panel can be enhanced, and the desired mechanical properties can easily be obtained in the press-formed part.

1 - 12 . (canceled) 
     
     
         13 . A warm press forming method of forming a steel sheet having a tensile strength of 440 MPa or more into a press-formed part including flange portions and other portions by press forming, the method comprising:
 heating the steel sheet to a temperature of 400° C. to 700° C.; and   press-forming the heated steel sheet using draw forming to obtain a press-formed part, with the steel sheet being held at a press bottom dead point in a die for one second to five seconds.   
     
     
         14 . The method according to  claim 13 , wherein a difference in average temperature among flange portions and other portions of the press-formed part immediately after draw forming is kept within 150° C. 
     
     
         15 . The method according to  claim 13 , wherein the press-formed part has a tensile strength of 80% to 110% of a tensile strength of the steel sheet. 
     
     
         16 . The method according to  claim 13 , wherein the steel sheet has a chemical composition containing, by mass %,
 C: 0.015% to 0.16%,   Si: 0.2% or less,   Mn: 1.8% or less,   P: 0.035% or less,   S: 0.01% or less,   Al: 0.1% or less,   N: 0.01% or less, and   Ti: 0.13% to 0.25%,   
       provided that a relation defined by Expression (1) is satisfied, and
 the balance including Fe and incidental impurities, and 
 wherein the steel sheet has a microstructure containing a ferrite phase by 95% or more on an area ratio basis with respect to the entire microstructure, ferrite crystal grains constituting the ferrite phase have an average grain size of 1 μm or more, and carbides having an average particle size of 10 nm or less are dispersed and precipitated in the ferrite crystal grains
   2.00≧([% C]/12)/([% Ti]/48)≧1.05  (1)
 
 
 
       where [% M] indicates the content by mass % of element M. 
     
     
         17 . The method according to  claim 14 , wherein the press-formed part has a tensile strength of 80% to 110% of a tensile strength of the steel sheet. 
     
     
         18 . The method according to  claim 14 , wherein the steel sheet has a chemical composition containing, by mass %,
 C: 0.015% to 0.16%,   Si: 0.2% or less,   Mn: 1.8% or less,   P: 0.035% or less,   S: 0.01% or less,   Al: 0.1% or less,   N: 0.01% or less, and   Ti: 0.13% to 0.25%,   
       provided that a relation defined by Expression (1) is satisfied, and
 the balance including Fe and incidental impurities, and 
 wherein the steel sheet has a microstructure containing a ferrite phase by 95% or more on an area ratio basis with respect to the entire microstructure, ferrite crystal grains constituting the ferrite phase have an average grain size of 1 μm or more, and carbides having an average particle size of 10 nm or less are dispersed and precipitated in the ferrite crystal grains
   2.00≧([% C]/12)/([% Ti]/48)≧1.05  (1)
 
 
 
       where [% M] indicates the content by mass % of element M. 
     
     
         19 . The method according to  claim 17 , wherein the steel sheet has a chemical composition containing, by mass %,
 C: 0.015% to 0.16%,   Si: 0.2% or less,   Mn: 1.8% or less,   P: 0.035% or less,   S: 0.01% or less,   Al: 0.1% or less,   N: 0.01% or less, and   Ti: 0.13% to 0.25%,   
       provided that a relation defined by Expression (1) is satisfied, and
 the balance including Fe and incidental impurities, and 
 wherein the steel sheet has a microstructure containing a ferrite phase by 95% or more on an area ratio basis with respect to the entire microstructure, ferrite crystal grains constituting the ferrite phase have an average grain size of 1 μm or more, and carbides having an average particle size of 10 nm or less are dispersed and precipitated in the ferrite crystal grains
   2.00≧([% C]/12)/([% Ti]/48)≧1.05  (1)
 
 
 
       where [% M] indicates the content by mass % of element M. 
     
     
         20 . The method according to  claim 19 , wherein the steel sheet comprises a coating or plating layer on a surface thereof. 
     
     
         21 . The method according to  claim 20 , wherein the chemical composition further contains at least one group selected from (A) to (F), wherein
 (A) by mass %, at least one selected from
 V: 1.0% or less, 
 Mo: 0.5% or less, 
 W: 1.0% or less, 
 Nb: 0.1% or less, 
 Zr: 0.1% or less, and 
 Hf: 0.1% or less, 
   
       provided that a relation defined by Expression (1)′ is satisfied:
   2.00≧([% C]/12)/([% Ti]/48+[% V]/51+[% W]/184+[% Mo]/96+[% Nb]/93+[% Zr]/91+[% Hf]/179)≧1.05  (1)′
 
 
       where [% M] indicates the content by mass % of element M,
 (B) by mass %, B: 0.003% or less, 
 (C) by mass %, at least one selected from Mg: 0.2% or less, Ca: 0.2% or less, Y: 0.2% or less, and REM: 0.2% or less, 
 (D) by mass %, at least one selected from Sb: 0.1% or less, Cu: 0.5% or less, and Sn: 0.1% or less, 
 (E) by mass %, at least one selected from Ni: 0.5% or less and Cr: 0.5% or less, 
 (F) by mass %, at least one selected from O, Se, Te, Po, As, Bi, Ge, Pb, Ga, In, Tl, Zn, Cd, Hg, Ag, Au, Pd, Pt, Co, Rh, Ir, Ru, Os, Tc, Re, Ta, Be and Sr, in a total amount of 2.0% or less. 
 
     
     
         22 . An automobile frame component produced by the method according to  claim 21 . 
     
     
         23 . The method according to  claim 15 , wherein the steel sheet has a chemical composition containing, by mass %,
 C: 0.015% to 0.16%,   Si: 0.2% or less,   Mn: 1.8% or less,   P: 0.035% or less,   S: 0.01% or less,   Al: 0.1% or less,   N: 0.01% or less, and   Ti: 0.13% to 0.25%,   
       provided that a relation defined by Expression (1) is satisfied, and
 the balance including Fe and incidental impurities, and 
 wherein the steel sheet has a microstructure containing a ferrite phase by 95% or more on an area ratio basis with respect to the entire microstructure, ferrite crystal grains constituting the ferrite phase have an average grain size of 1 μm or more, and carbides having an average particle size of 10 nm or less are dispersed and precipitated in the ferrite crystal grains
   2.00≧([% C]/12)/([% Ti]/48)≧1.05  (1)
 
 
 
       where [% M] indicates the content by mass % of element M. 
     
     
         24 . The method according to  claim 23 , wherein the chemical composition further contains at least one group selected from (A) to (F), wherein
 (A) by mass %, at least one selected from
 V: 1.0% or less, 
 Mo: 0.5% or less, 
 W: 1.0% or less, 
 Nb: 0.1% or less, 
 Zr: 0.1% or less, and 
 Hf: 0.1% or less, 
   
       provided that a relation defined by Expression (1)′ is satisfied:
   2.00≧([% C]/12)/([% Ti]/48+[% V]/51+[% W]/184+[% Mo]/96+[% Nb]/93+[% Zr]/91+[% Hf]/179)≧1.05  (1)′
 
 
       where [% M] indicates the content by mass % of element M,
 (B) by mass %, B: 0.003% or less, 
 (C) by mass %, at least one selected from Mg: 0.2% or less, Ca: 0.2% or less, Y: 0.2% or less, and REM: 0.2% or less, 
 (D) by mass %, at least one selected from Sb: 0.1% or less, Cu: 0.5% or less, and Sn: 0.1% or less, 
 (E) by mass %, at least one selected from Ni: 0.5% or less and Cr: 0.5% or less, 
 (F) by mass %, at least one selected from O, Se, Te, Po, As, Bi, Ge, Pb, Ga, In, Tl, Zn, Cd, Hg, Ag, Au, Pd, Pt, Co, Rh, Ir, Ru, Os, Tc, Re, Ta, Be and Sr, in a total amount of 2.0% or less. 
 
     
     
         25 . The method according to  claim 23 , wherein the steel sheet comprises a coating or plating layer on a surface thereof. 
     
     
         26 . An automobile frame component produced by the method according to  claim 23 . 
     
     
         27 . The method according to  claim 24 , wherein the steel sheet comprises a coating or plating layer on a surface thereof. 
     
     
         28 . An automobile frame component produced by the method according to  claim 24 . 
     
     
         29 . An automobile frame component produced by the method according to  claim 27 . 
     
     
         30 . The method according to  claim 16 , wherein the steel sheet comprises a coating or plating layer on a surface thereof. 
     
     
         31 . The warm press forming method according to  claim 30 , wherein the chemical composition further contains at least one group selected from (A) to (F), wherein
 (A) by mass %, at least one selected from
 V: 1.0% or less, 
 Mo: 0.5% or less, 
 W: 1.0% or less, 
 Nb: 0.1% or less, 
 Zr: 0.1% or less, and 
 Hf: 0.1% or less, 
   
       provided that a relation defined by Expression (1)′ is satisfied:
   2.00≧([% C]/12)/([% Ti]/48+[% V]/51+[% W]/184+[% Mo]/96+[% Nb]/93+[% Zr]/91+[% Hf]/179)≧1.05  (1)′
 
 
       where [% M] indicates the content by mass % of element M,
 (B) by mass %, B: 0.003% or less, 
 (C) by mass %, at least one selected from Mg: 0.2% or less, Ca: 0.2% or less, Y: 0.2% or less, and REM: 0.2% or less, 
 (D) by mass %, at least one selected from Sb: 0.1% or less, Cu: 0.5% or less, and Sn: 0.1% or less, 
 (E) by mass %, at least one selected from Ni: 0.5% or less and Cr: 0.5% or less, 
 (F) by mass %, at least one selected from O, Se, Te, Po, As, Bi, Ge, Pb, Ga, In, Tl, Zn, Cd, Hg, Ag, Au, Pd, Pt, Co, Rh, Ir, Ru, Os, Tc, Re, Ta, Be and Sr, in a total amount of 2.0% or less. 
 
     
     
         32 . An automobile frame component produced by the method according to  claim 31 .