High strength steel for induction hardening

Abstract

A steel product which, while minimizing an increase in hardness after forging to ensure machinability and cold workability, is improved, for example, in fatigue strength in its nonhardened portion and is improved, in its hardened portion, in rolling resistance level, anti-pitting level, abrasion resistance, and fatigue strength. The high strength steel for induction hardening comprises, by mass, carbon (C): 0.5 to 0.7%, silicon (Si): 0.5 to 0.9%, manganese (Mn): 0.5 to 1.0%, chromium (Cr): not more than 0.4%, and sulfur (S): not more than 0.035%, with the balance consisting of iron (Fe) and unavoidable impurities, the steel being forged to produce a component at least a part of which is then inductively hardened before use.

The invention claimed is:  
     
         1 . A high strength steel for induction hardening, comprising, by mass: 
 carbon (C): 0.5 to 0.7%,    silicon (Si): 0.5 to 0.9%,    manganese (Mn): 0.5 to 1.0%,    chromium (Cr): not more than 0.4%, and    sulfur (S): not more than 0.035%,    with the balance consisting of iron (Fe) and unavoidable impurities, said steel being forged into a component at least a part of which is then inductively hardened before use.    
     
     
         2 . The high strength steel for induction hardening according to  claim 1 , wherein the equivalent of carbon C eq  represented by formula (1) satisfies a requirement represented by formula (2):  
       C eq =C %+{fraction (1/7)} Si %+⅕ Mn %+{fraction (1/9)} Cr %−{fraction (5/7)} S %  (1) 0.75≦C eq ≦0.90  (2)  
     
     
         3 . A component produced by inductively hardening at least a part of a product produced by casting the steel according to  claim 1 .  
     
     
         4 . The component according to  claim 3 , wherein the component is a hub unit or a joint.  
     
     
         5 . The high strength steel of  claim 1  having a Si content of 0.59 to 0.9%.  
     
     
         6 . A high strength steel for induction hardening, having improved machinability, said steel comprising, by mass: 
 carbon (C): 0.5 to 0.7%,    silicon (Si): 0.5 to 1.0%,    manganese (Mn): 0.5 to 1.0%,    chromium (Cr): not more than 0.4%,    sulfur (S): not more than 0.035%, and    vanadium (V): 0.01 to 0.15%    with the balance consisting of iron (Fe) and unavoidable impurities, said steel being cast and forged to produce a component at least a part of which is then inductively hardened before use.    
     
     
         7 . The high strength steel for induction hardening according to  claim 6 , having a Si content of 0.59 to 0.9% and wherein the equivalent of carbon C eq  represented by formula (1) satisfies a requirement represented by formula (2):  
       C eq =C %+{fraction (1/7)} Si %+⅕ Mn %+{fraction (1/9)} Cr %−{fraction (5/7)} S %+V %  (1) 0.75≦C eq ≦0.90  (2)  
     
     
         8 . A component produced by inductively hardening at least a part of a product produced by casting the steel according to  claim 6 .  
     
     
         9 . The component according to  claim 8 , wherein the component is a hub unit or a joint.  
     
     
         10 . An induction hardened hub made from a high strength steel comprising, by mass: 
 carbon (C): 0.5 to 0.7%,    silicon (Si): 0.5 to 0.9%,    manganese (Mn): 0.5 to 1.0%,    chromium (Cr): not more than 0.4%, and    sulfur (S): not more than 0.035%,    with the balance consisting of iron (Fe) and unavoidable impurities, said steel being forged into a component at least a part of which is then inductively hardened before use.    
     
     
         11 . The induction hardened hub of  claim 10  wherein the high strength steel contains 0.59 to 0.9% Si.