Low alloy high speed tool steel having constant toughness

Abstract

Disclosed is an improved low alloy high speed tool steel, which exhibits constant toughness with small dispersion of the properties after heat treatment and regardless of the size of the products. The steel consists essentially of, by weight %, C: 0.50-0.75%, Si: 0.02-2.00%, Mn: 0.1-3.0%, P: up to 0.050%, S: up to 0.010%, Cr: 5.0-6.0%, W: 0.5-2.0%, V: 0.70-1.25%, Al: up to 0.1%, 0: up to 0.01% and N: up to 0.04% and the balance of Fe. In the steel [Mo+0.5W](Mo-eq.) is 2.5-5.0%, [Mo-eq.]/V is 2-4. In the annealed state the steel contains carbides of [MC+M 6 C]-type and/or M 23 C 6 (M 7 C 3 )-type, and after quenching from a temperature of 1100-1200° C., it contains substantially no remainig carbide or, even contains, almost all the carbides are of MC-type.

We claim:  
     
         1 . A low alloyed high speed tool steel, which consists essentially of, by weight %, C: 0.50-0.75%, Si: 0.02-2.00%, Mn: 0.1-3.0%, P: up to 0.050%, S: up to 0.010%, Cr: 5.0-6.0%, W: 0.5-2.0%, V: 0.70-1.25%, Al: up to 0.1%, 0: up to 0.01% and N: up to 0.04% and the balance of Fe, provided that [Mo+0.5W](Mo-eq.) is 2.5-5.0%, that Mo-eq./V is 2-4, and that it contains carbides of, in the annealed state, [MC+M 6 C]-type and/or M 23 C 6 (M 7 C 3 ) -type, and after quenching from a temperature of 1100-1200° C., substantially no remaining carbide or, even contained, almost all the carbides being of MC-type.  
     
     
         2 . The low alloy high speed tool steel according to  claim 1 , wherein Si-content is 0.2-0.8%.  
     
     
         3 . The low alloy high speed tool steel according to  claim 1 , wherein the steel further contains at least one of the group consisting of Ni: up to 2.0%, Cu: up to 1.0% and Co: up to 3.0%.  
     
     
         4 . The low alloy high speed tool steel according to  claim 1 , wherein the steel further contains B: up to 0.01%.  
     
     
         5 . The low alloy high speed tool steel according to  claim 1 , wherein the steel further contains Nb: up to 0.1%, and wherein Mo-eq./(V+5Nb) is 2-4.  
     
     
         6 . The low alloy high speed tool steel according to  claim 1 , wherein the steel further contains at least one of the group consisting of Ni: up to 2.0%, Cu: up to 1.0% and Co: up to 3.0%, and B: up to 0.01%.  
     
     
         7 . The low alloy high speed tool steel according to  claim 1 , wherein the steel further contains at least one of the group consisting of Ni: up to 2.0%, Cu: up to 1.0% and Co: up to 3.0%, and Nb: up to 0.1%, and wherein Mo-eq./(V+5Nb) is 2-4.  
     
     
         8 . The low alloy high speed tool steel according to  claim 1 , wherein the steel further contains B: up to 0.01% and Nb: up to 0.1%, and wherein Mo-eq./(V+5Nb) is 2-4.  
     
     
         9 . The low alloy high speed tool steel according to  claim 1 , wherein the steel further contains at least one of the group consisting of Ni: up to 2.0%, Cu: up to 1.0% and Co: up to 3.0%, B: up to 0.01%, and Nb: up to 0.1%, and wherein Mo-eq./(V+5Nb) is 2-4.