Induction heat treatment method and article treated thereby

Abstract

A method of induction heat-treating certain surfaces of an article comprising a hub and a plurality of trunnions or shafts extending therefrom, wherein the surfaces to be heat-treated comprise the surfaces of the trunnions. The method employs an induction coil that provides a planar magnetic field that is adapted to the irregular shape of the article, such that the induction coil produces magnetic fields that are adapted to induce currents in, and thereby heat, the trunnion surfaces of the article. The method and induction coil are particularly adapted to provide an induction hardening heat treatment for trunnion surfaces of trunnions used in steel spiders of spider or tripod-type constant velocity joints.

1 . A method of induction heat treatment, comprising the steps of: 
 (1) selecting an article for heat treatment comprising a hub having a hub surface and a plurality of angularly spaced trunnions extending from a corresponding plurality of trunnion shoulders formed in the hub surface, each trunnion shoulder having a trunnion shoulder surface, and each trunnion having a trunnion axis and a trunnion surface;    (2) selecting an induction coil, which is adapted to receive a trunnion for heat treatment and apply a magnetic field to the trunnion surface and trunnion shoulder surface;    (3) placing a trunnion within the induction coil with its corresponding trunnion shoulder adjacent to the induction coil;    (4) rotating the trunnion within the induction coil about the trunnion axis at a selected speed;    (5) energizing the induction coil to apply the magnetic field and produce induction currents within the trunnion shoulder surface and trunnion surface of the article for a time sufficient to induce heating them to a heat treatment temperature (T H ) to at least a selected case depth;    (6) withdrawing the trunnion from the induction coil at a selected rate;    (7) cooling the trunnion surface and the trunnion shoulder surface of the article to a temperature (T C ) to the selected case depth; and    (8) repeating steps (3)-(7) for a selected number of the trunnions.    
     
     
         2 . The method of  claim 1 , wherein the article comprises a spider.  
     
     
         3 . The method of  claim 2 , wherein the spider has a barrel-shaped outer surface, a plurality of angularly spaced cylindrical shoulders extending from the outer surface, and a plurality of cylindrical trunnions extending from the cylindrical shoulders.  
     
     
         4 . The method of  claim 2 , wherein the spider comprises a pearlitic/ferritic steel.  
     
     
         5 . The method of  claim 4 , wherein the steel comprises AISI 1050 steel.  
     
     
         6 . The method of  claim 4 , wherein T H  is greater than the austenite transition temperature.  
     
     
         7 . The method of  claim 6 , wherein the T H  is in the range of 1700-2000° F.  
     
     
         8 . The method of  claim 6 , wherein said step of cooling comprises quenching the trunnion.  
     
     
         9 . The method of  claim 8 , wherein T C  is less than the martensite start temperature and greater than the martensite finish temperature.  
     
     
         10 . The method of  claim 9 , further comprising stopping the quenching when the trunnion surface and the trunnion shoulder surface of the spider is less than or equal to T C  to the selected case depth, and then permitting the trunnion surface to cool under ambient conditions.  
     
     
         11 . The method of  claim 10 , further comprising the step of (9) shielding any previously heated trunnion surface and trunnion shoulder surface during step (7) from additional quenching, wherein all of the trunnion surfaces are cooled from T C  under ambient conditions.  
     
     
         12 . A method of induction heat treatment of a spider having a barrel-shaped outer surface, a plurality of cylindrical trunnion shoulders formed in the outer surface of the hub and a corresponding plurality of angularly spaced cylindrical trunnions extending from the shoulders, each trunnion shoulder having a trunnion shoulder surface, and each trunnion having a trunnion axis and a trunnion surface, comprising the steps of: 
 (1) selecting an induction coil, which is adapted to receive a trunnion for heat treatment and apply a magnetic field to the trunnion surface and the trunnion shoulder surface;    (2) placing a trunnion within the induction coil with its corresponding trunnion shoulder adjacent to the induction coil;    (3) rotating the trunnion within the induction coil about the trunnion axis at a selected speed;    (4) energizing the induction coil to apply the magnetic field and produce induction currents within the trunnion shoulder surface and trunnion surface of the article for a time sufficient to induce heating them to a heat treatment temperature (T H ) to at least a selected case depth;    (5) withdrawing the trunnion from the induction coil at a selected rate;    (6) cooling the trunnion surface and the trunnion shoulder surface of the article to a temperature (T C ) to the selected case depth; and    (7) repeating steps (2)-(6) for a selected number of the trunnions.    
     
     
         13 . The method of  claim 12 , wherein the spider comprises a pearlitic/ferritic steel.  
     
     
         14 . The method of  claim 13 , wherein the steel comprises AISI 1050 steel.  
     
     
         15 . The method of  claim 13 , wherein T H  is greater than the austenite transition temperature.  
     
     
         16 . The method of  claim 15 , wherein T H  is in the range of 1700-2000° F.  
     
     
         17 . The method of  claim 15 , wherein said step of cooling comprises quenching the article.  
     
     
         18 . The method of  claim 17 , wherein said step of cooling comprises quenching until T C  is lower than the martensite start temperature.  
     
     
         19 . The method of  claim 18 , wherein T C  is less than the martensite start temperature and greater than the martensite finish temperature.  
     
     
         20 . The method of  claim 19 , further comprising stopping the quenching when the temperature of the trunnion surface and the trunnion shoulder surface reaches T C  to the selected case depth, and then permitting the spider to cool under ambient conditions.  
     
     
         21 . The method of  claim 20 , further comprising the step of (8) shielding any previously heated trunnion surface during step (6) from additional quenching, wherein all of the trunnion surfaces and trunnion shoulder surfaces are cooled under ambient conditions.  
     
     
         22 . An article, comprising: 
 a steel spider comprising a hub, a plurality of angularly spaced trunnion shoulders extending from the hub, each having a trunnion shoulder surface, and a corresponding plurality of angularly spaced trunnions extending from the plurality of trunnion shoulders, each trunnion having a trunnion axis and a trunnion surface, the trunnion surfaces and the trunnion shoulder surfaces comprising a hardened case, wherein the hardened case is formed by an induction heat treatment.    
     
     
         23 . The article of  claim 22 , wherein the induction heat treatment comprises the steps of (1) selecting an induction coil, which is adapted to receive a trunnion for heat treatment and apply a magnetic field to the trunnion surface and the trunnion shoulder surface; (2) placing a trunnion within the induction coil with its corresponding trunnion shoulder adjacent to the induction coil; (3) rotating the trunnion within the induction coil about the trunnion axis at a selected speed; (4) energizing the induction coil to apply the magnetic field and produce induction currents within the trunnion surface and trunnion shoulder surface of the article for a time sufficient to induce heating them to a heat treatment temperature (T H ) to at least a selected case depth; (5) withdrawing the trunnion from the induction coil at a selected rate; (6) cooling the trunnion surface and the trunnion shoulder surface of the article to a temperature (T C ) to the selected case depth; and (7) repeating steps (2)-(6) for a selected number of the trunnions.  
     
     
         24 . The article of  claim 23 , wherein the induction hardened case comprises a martensitic microstructure and the core comprises a microstructure that is a mixture of pearlite and ferrite.  
     
     
         25 . The article of  claim 24 , wherein the induction hardened case has a hardness of about R C 58-63, and the core has a hardness of about R C 15-30.  
     
     
         26 . The article of  claim 24 , wherein the martensitic microstructure is a tempered martensitic microstructure.  
     
     
         27 . The article of  claim 26 , wherein the tempered martensitic microstructure is formed by the induction heat treatment.  
     
     
         28 . The article of  claim 27 , wherein the tempered martensitic microstructure has a hardness of about R C 58-63.  
     
     
         29 . The article of  claim 28 , wherein the depth of the case is about 1-2 mm.