Method of steel processing combining thermal and mechanical surface treatment to control metallurgical phase and mechanical response

Abstract

A method of steel processing combining thermal and mechanical processing of steels in controlled sequences. The method of the present invention combines thermal and mechanical processing in controlled sequences to achieve material property results that are superior to existing methods. The method allows for manipulation of steel processing variables, which promotes further elimination of retained austenite, additional residual compression, reduced surface tension, increased material strength, increased compressive stresses at the surface, and significantly improved bending fatigue and wear resistance. By varying the sequence of mechanical processing of the steel, desired residual compressive stress responses and hardness levels may be achieved. In addition, this processing can reduce embrittlement caused by late stage phase transformation.

What is claimed is: 
     
         1 . A method of treating steel, comprising:
 heating the steel;   applying a quench hardening to the steel;   applying a mechanical treatment to the steel after the quench hardening; and   applying one or more cycles of a deep freeze and a tempering sequence to the steel.   
     
     
         2 . The method of  claim 1 , wherein the mechanical treatments are selected from the group consisting of shot peening, laser peening, low plasticity burnishing, cavitation peening, and vibratory processing. 
     
     
         3 . The method of  claim 1 , wherein the steel comprises:
 a non-carburized steel.   
     
     
         4 . The method of  claim 1 , wherein the steel comprises: carburized, a nitrocarburized, a carbonitrided, a nitrided, a precipitation hardened, an induction hardened, and a flame hardened. 
     
     
         5 . The method of  claim 1 , wherein the mechanical treatment is applied immediately following the quench hardening step. 
     
     
         6 . A method of treating steel, comprising:
 heating the steel;   applying a quench hardening to the steel to thermally destabilize retained austenite in the steel;   applying a first cycle of a deep freeze and a tempering sequence to the steel;   applying a mechanical treatment to the steel; and   applying one or more cycles of a subsequent deep freeze and a subsequent tempering sequence to the steel.   
     
     
         7 . The method of  claim 6 , wherein the mechanical treatment is selected from the group consisting of shot peening, laser peening, low plasticity burnishing, cavitation peening, and vibratory processing. 
     
     
         8 . The method of  claim 6 , wherein the steel comprises:
 a non-carburized steel.   
     
     
         9 . The method of  claim 6 , wherein the steel is selected from the group consisting of a carburized, a nitrocarburized, a carbonitrided, a nitrided, a precipitation hardened, an induction hardened, or a flame hardened steel. 
     
     
         10 . The method of  claim 6 , wherein the mechanical treatment is applied immediately following immediately after the first cycle. 
     
     
         11 . A method of treating steel, comprising:
 heating the steel;   applying a quench hardening to the steel;   applying a first cycle of a deep freeze and a tempering sequence to the steel;   applying an intermediate mechanical treatment to the steel after the first cycle;   applying a subsequent cycle of the deep freeze and the tempering sequence to the steel, after the intermediate mechanical treatment; and   applying a second mechanical treatment sequence to the steel.   
     
     
         12 . The method of  claim 11 , wherein the mechanical surface treatment is selected from the group consisting of shot peening, laser peening, low plasticity burnishing, cavitation peening, and vibratory processing. 
     
     
         13 . The method of  claim 11 , wherein the steel comprises:
 a non-carburized steel.   
     
     
         14 . The method of  claim 11 , wherein the steel is selected from the group consisting of a carburized, a nitrocarburized, a carbonitrided, a nitrided, a precipitation hardened, an induction hardened, or a flame hardened steel. 
     
     
         15 . The method of  claim 11 , wherein the mechanical surface treatment is applied immediately following each subsequent cycle of the deep freeze and the tempering sequence.