Steel Article Having Improved Contact Fatigue Resistance

Abstract

A steel article with resistance to contact fatigue having a martensitic stainless steel body with a hardened surface layer and a core. The hardened surface layer is tempered martensite and M 7 C 3 carbides, has at least 1.6 wt. % carbon, and has a depth equal to or greater than the depth where the steel article experiences the maximum shear stress when placed in service.

The invention claimed is: 
     
         1 . A steel article having resistance to contact fatigue comprising a martensitic stainless steel body having a hardened surface layer and a core, wherein the hardened surface layer comprises M 7 C 3  carbides in a tempered martensite matrix. 
     
     
         2 . The steel article of  claim 1 , wherein the hardened surface layer comprises at least 1.6 wt. % carbon. 
     
     
         3 . The steel article of  claim 2 , wherein the hardened surface layer comprises 1.6-2.4 wt. % carbon. 
     
     
         4 . The steel article of  claim 1 , wherein the hardened surface layer has a depth equal to or greater than a depth where the steel article will experience a maximum shear stress when placed in service. 
     
     
         5 . The steel article of  claim 4 , wherein the hardened surface layer has a depth of at least 0.001 inches. 
     
     
         6 . The steel article of  claim 1 , wherein the steel article comprises one or more of Cr, Ni, Mo, Co, Mn, and V. 
     
     
         7 . The steel article of  claim 6 , wherein the steel article comprises 11-15 wt. % Cr, 1.5-3.5 wt. % Ni, 1-3 wt. % Mo, 3-8 wt. % Co, up to 1.5 wt. % Mn, and 0.1-1 wt. % V. 
     
     
         8 . The steel article of  claim 6 , wherein the tempered martensite matrix in the hardened surface layer is enriched in Ni and Co as compared to the core.