High-hardness, highly ductile ferrous articles

Abstract

Ferrous articles are austenitized, then converted to at least 60% bainite, and the balance substantially converted to martensite by quenching; the articles are then cold worked, preferably by both compression and tensile deformation to at least 60% yield strength. The articles have improved serviceability, particularly fatigue life.

1 . Method of making a ferrous article comprising (a) forming said ferrous article (b) austenitizing said ferrous article at a temperatures between 1450-1800° F. (c) quickly transferring said ferrous article to a thermal bath (d) holding said ferrous article in said thermal bath for a period of at least 10 minutes whereby said ferrous article comprises at least 60% bainite (e) quenching said ferrous article to ambient temperature to convert substantially all of the remaining austenite to martensite, whereby said article has a hardness of at least Rc52, an elongation at failure of at least 5%, and a serviceability ratio Rc/E1% of at least 3.5 and (f) plastically deforming said article.  
     
     
         2 . Method of  claim 1  wherein said ferrous article is a steel article.  
     
     
         3 . Method of  claim 1  wherein said ferrous article is a steel chain link.  
     
     
         4 . Method of  claim 1  wherein step (c) is conducted in twenty seconds or less.  
     
     
         5 . Method of  claim 1  wherein step (f) comprises both compression deformation and tensile deformation.  
     
     
         6 . Method of  claim 5  wherein said compression deformation comprises shot peening.  
     
     
         7 . Method of  claim 5  wherein said compression deformation comprises the application of compressive stress in the range of −50,000 psi to 200,000 psi.  
     
     
         8 . Method of  claim 5  wherein the tensile deformation comprises dynamic stress to at least 60% of yield strength.  
     
     
         9 . Method of  claim 1  wherein said serviceability ratio is in the range of 3.5-8.0.  
     
     
         10 . Method of  claim 1  wherein said article has a serviceability ratio at the end of step (e) in the range of 3.6 to 6.  
     
     
         11 . Method of  claim 1  wherein said article has a fatigue life at the end of step (f) at least 20% greater than at the end of step (e).  
     
     
         12 . Method of making a steel chain link comprising (a) forming said steel chain link of steel (b) austenitizing said steel chain link at a temperatures between 1450-1800° F. (c) transferring said steel chain link to a thermal bath in a period less than 60 seconds (d) holding said steel chain link in said thermal bath for a period from 10 minutes to three hours whereby said steel chain link comprises at least 60% bainite (e) quenching said steel chain link in a bath to convert substantially all of the remaining austenite to martensite, whereby said steel chain link has a hardness of at least Rc 52, an elongation at break of at least 5%, and a serviceability ratio Rc/E1% of at least 3.5, and (f) plastically deforming said steel chain link by (i) compression deformation and (ii) tensile deformation to at least 60% of its yield strength, whereby the fatigue life of said steel chain link is increased by at least 100% compared to its fatigue life without plastic deformation.  
     
     
         13 . An article made by the method of  claim 1 .  
     
     
         14 . A steel chain link made by the method of  claim 12 .  
     
     
         15 . Method of  claim 12  wherein said compression deformation comprises shot peening.  
     
     
         16 . Method of  claim 12  wherein said compression deformation comprises the application of compressive stress in the range of −50,000 psi to −200,000 psi.  
     
     
         17 . Method of  claim 12  wherein said tensile deformation is applied to said chain link as a part of a chain.  
     
     
         18 . Method of  claim 12  wherein step c is performed in 20 seconds or less.  
     
     
         19 . Method of  claim 12  wherein the hardness of said chain link at the end of step (e) is at least Rc54 and said serviceability ratio Rc/E1% is in the range of 3.6 to 8.  
     
     
         20 . A steel chain link of hardness at least Rc52 whose fatigue life has been increased 100% by plastic deformation.