Steel for high-speed cold working and method for production thereof, and part formed by high-speed cold working and method for production thereof

Abstract

Disclosed herein is a steel for high-speed cold working which exhibits good cold workability during working and also exhibits high hardness after working. The steel for high-speed cold working contains C: 0.03 to 0.6% (by mass), Si: 0.005 to 0.6%, Mn: 0.05 to 2%, P: no more than 0.05% (excluding 0%), S: no more than 0.05% (excluding 0%), and N: no more than 0.04% (excluding 0%), with the remainder being iron and inevitable impurities and the amount of dissolved nitrogen in the steel being no less than 0.006%.

1 . A steel for high-speed cold working, comprising:
 C: 0.03 to 0.6% (by mass),   Si: 0.005 to 0.6%,   Mn: 0.05 to 2%,   P: no more than 0.05% (excluding 0%),   S: no more than 0.05% (excluding 0%), and   N: no more than 0.04% (excluding 0%).   
       with the remainder being iron and inevitable impurities and the amount of dissolved nitrogen in the steel being no less than 0.006%. 
     
     
         2 . The steel for high-speed cold working as defined in  claim 1 , wherein the C content is 0.03 to 0.15%. 
     
     
         3 . The steel for high-speed cold working as defined in  claim 1 , wherein the C content is more than 0.15% up to 0.6%. 
     
     
         4 . The steel for high-speed cold working as defined in  claim 1 , wherein the N content is no less than 0.007%. 
     
     
         5 . The steel for high-speed cold working as defined in  claim 1 , wherein the Al content is no more than 0.1% (excluding 0%). 
     
     
         6 . The steel for high-speed cold working as defined in  claim 1 , further comprising at least one species selected from the group consisting of:
 Zr: no more than 0.2% (excluding 0%),   Ti: no more than 0.1% (excluding 0%),   Nb: no more than 0.1% (excluding 0%),   V: no more than 0.5% (excluding 0%),   Ta: no more than 0.1% (excluding 0%), and   Hf: no more than 0.1% (excluding 0%).   
     
     
         7 . The steel for high-speed cold working as defined in  claim 1 , further comprising:
 B: no more than 0.0015% (excluding 0%) and/or   Cr: no more than 2% (excluding 0%).   
     
     
         8 . The steel for high-speed cold working as defined in  claim 1 , which satisfies the formula (1) below.
   [N]−(14[Al]/27+14[Ti]/47.9+14[Nb]/92.9+14[V]/50.9+14[Zr]/91.2+14[B]/10.8+14[Ta]/180.9+14[Hf]/178.5)≧0.006  Formula (1)   
       where the square brackets [ ] represent the total amount (in mass %) of each element contained in the steel. 
     
     
         9 . The steel for high-speed cold working as defined in  claim 1 , which contains inevitable impurities as follows:
 Al: no more than 0.001% (including 0%),   Ti: no more than 0.002% (including 0%),   Nb: no more than 0.001% (including 0%),   V: no more than 0.001% (including 0%),   Zr: no more than 0.001% (including 0%),   B: no more than 0.0001% (including 0%),   Ta: no more than 0.0001% (including 0%), and   Hf: no more than 0.0001% (including 0%);   
       and also satisfy the formula (2) below.
   14[Al]/27+14[Ti]/47.9+14[Nb]/92.9+14[V]/50.9+14[Zr]/91.2+14[B]/10.8+14[Ta]/180.9+14[Hf]/178.5≦0.002%  Formula (2) 
 
       where the square brackets [ ] represent the total amount (in mass %) of each element contained in the steel. 
     
     
         10 . The steel for high-speed cold working as defined in  claim 9 , further comprising:
 Cr: no more than 2% (excluding 0%).   
     
     
         11 . The steel for high-speed cold working as defined in  claim 1 , further comprising:
 Cu: no more than 5% (excluding 0%).   
     
     
         12 . The steel for high-speed cold working as defined in  claim 1 , further comprising:
 Ni: no more than 5% (excluding 0%) and/or   Co: no more than 5% (excluding 0%).   
     
     
         13 . The steel for high-speed cold working as defined in  claim 1 , further comprising:
 Mo: no more than 2% (excluding 0%) and/or   W: no more than 2% (excluding 0%).   
     
     
         14 . The steel for high-speed cold working as defined in  claim 1 , further comprising at least one species selected from the group consisting of:
 Ca: no more than 0.05% (excluding 0%),   Rare earth elements: no more than 0.05% (excluding 0%),   Mg: no more than 0.02% (excluding 0%),   Li: no more than 0.02% (excluding 0%),   Pb: no more than 0.1% (excluding 0%), and   Bi: no more than 0.1% (excluding 0%).   
     
     
         15 . A method for producing parts by high-speed cold working, said method comprising performing high-speed cold working at a working temperature no higher than 200° C. on the steel for high-speed cold working as defined in  claim 1 . 
     
     
         16 . A method for producing parts by high-speed cold working, said method comprising performing high-speed cold working at a strain rate no lower than 100/s on the steel for high-speed cold working as defined in  claim 1 . 
     
     
         17 . A method for producing a steel for high-speed cold working, said method comprising subjecting the steel stock having the composition defined in  claim 1  consecutively to heating at a temperature above Ac 3  point plus 30° C., hot rolling at a temperature above Ac 3  point plus 30° C., and quenching to 500° C. or below at a cooling rate no smaller than 0.5° C./s. 
     
     
         18 . A method for producing a steel for high-speed cold working, said method comprising subjecting the steel stock having the composition defined in  claim 1  to heating at a temperature above Ac 3  point plus 30° C. and subsequent quenching to 500° C. or below at a cooling rate no smaller than 0.5° C./s. 
     
     
         19 . A machine part formed from the steel for high-speed cold working as defined in  claim 1  by high-speed cold working at a working temperature no higher than 200° C. and a strain rate no lower than 100/s, said machine part being characterized in having a value of H and a value of DR which satisfy the formula (3) below
     H ≧(DR+1000)/6  formula (3)   
       where H denotes the part strength (in terms of Hv) after high-speed cold working and DR denotes the maximum value of deformation resistance (in terms of MPa) during high-speed cold working.