Cold-work die steel and dies for cold pressing

Abstract

The present invention provides a cold-work die steel useful as a material of dies for cold pressing, which has basic properties such as hardness, toughness and dimensional change by heat treatment, and besides, which causes no problem in terms of machined surface roughness and cutting tool life, and also its dies for cold pressing. The invention relates to a cold-work die steel comprising: 0.5 to 0.7 mass % of C; 5.0 to 7.0 mass % of Cr; 0.5 to 2.0 mass % of Si; 0.1 to 2.0 mass % of Mn; 0.001 to 0.010 mass % of Al; 0.25 to 1.00 mass % of Cu; 0.25 to 1.00 mass % of Ni; 0.5 to 3.0 mass % of Mo+0.5×W; 0.5 mass % or less of V; 0.05 mass % or less of P; 0.1 mass % or less of S; 0.005 mass % or less of O, wherein the following requirements are satisfied: [C]×[Cr]≦4; FP=[Si]/5+[Cr]/5+2×[Mo]+[W]+2×[V]+10×[Al]≦5.0; and AP=[Mn]+3×([Cu]+[Ni])≦2.5, and also relates to a die for cold pressing which is manufactured by using the cold-work die steel.

1 . A cold-work die steel comprising:
 0.5 to 0.7 mass % of C;   5.0 to 7.0 mass % of Cr;   0.5 to 2.0 mass % of Si;   0.1 to 2.0 mass % of Mn;   0.001 to 0.010 mass % of Al;   0.25 to 1.00 mass % of Cu;   0.25 to 1.00 mass % of Ni;   0.003 to 0.025 mass % of N;   more than 0 to 0.05 mass % of P;   more than 0 to 0.1 mass % of S;   more than 0 to 0.005 mass % of O; and   at least one of Mo and W,   wherein the following requirements are satisfied:
   0.5≦[Mo]+0.5×[W]≦3.0; 
   [C]×[Cr]≦4; 
   FP=[Si]/5+[Cr]/5+2×[Mo]+[W]+2×[V]+10×[Al]≦55.0; and 
   AP=[Mn]+3×([Cu]+[Ni])≦2.5; 
   wherein FP is a parameter associated with the ferrite-forming elements, AP is a parameter associated with the austenite-forming elements, and the bracket represents a content (mass %) of an element written therein.   
     
     
         2 . The cold-work die steel according to  claim 1 , further comprising more than 0 to 0.5 mass % of V. 
     
     
         3 . The cold-work die steel according to  claim 1 , further comprising at least one element selected from the group consisting of Ti, Zr, Hf, Ta and Nb in a total content of more than 0 to 0.5 mass %. 
     
     
         4 . The cold-work die steel according to  claim 1 , further comprising more than 0 to 10 mass % of Co. 
     
     
         5 . A die for cold pressing, which is manufactured by working the cold-work die steel according to  claim 1  and giving surface treatment thereto. 
     
     
         6 . The cold-work die steel according to  claim 2 , further comprising at least one element selected from the group consisting of Ti, Zr, Hf, Ta and Nb in a total content of more than 0 to 0.5 mass %. 
     
     
         7 . The cold-work die steel according to  claim 2 , further comprising more than 0 to 10 mass % of Co. 
     
     
         8 . The cold-work die steel according to  claim 3 , further comprising more than 0 to 10 mass % of Co. 
     
     
         9 . The cold-work die steel according to  claim 6 , further comprising more than 0 to 10 mass % of Co. 
     
     
         10 . A process of making a die comprising working the cold-work die steel according to  claim 1 , and giving surface treatment thereto.