Contact pressure-resistant member and method of making the same

Abstract

A contact pressure-resistant member including a rolling contact portion having a carbon concentration ranging from 0.8 to 1.2%. The contact pressure-resistant member is made of a steel material containing 0.15 to 0.40% by mass of C, 0.50 to 1.50% by mass of Si, 0.20 to 1.50% by mass of Mn, 0.50 to 1.50% by mass of Cr, and 0.05 to 0.50% by mass of Mo, 0.010% by mass or less of P, at least one element selected from the group consisting of 0.50 to 3.50% by mass of Ni, 0.03 to 0.20% by mass of Ti, 0.03 to 0.15% by mass of Nb and 0.01 to 0.10% by mass of Al, and the balance of Fe and inevitable impurities.

1 . A contact pressure-resistant member, comprising: 
 a rolling contact portion having a carbon concentration ranging from 0.8 to 1.2%, the rolling contact portion being located on a surface of the contact pressure-resistant member and adapted to come into rolling contact with a counterpart,    the contact pressure-resistant member being made of a steel material containing 0.15 to 0.40% by mass of C, 0.50 to 1.50% by mass of Si, 0.20 to 1.50% by mass of Mn, 0.50 to 1.50% by mass of Cr, and 0.05 to 0.50% by mass of Mo, 0.010% by mass or less of P, at least one element selected from the group consisting of 0.50 to 3.50% by mass of Ni, 0.03 to 0.20% by mass of Ti, 0.03 to 0.15% by mass of Nb and 0.01 to 0.10% by mass of Al, and the balance of Fe and inevitable impurities.    
     
     
         2 . The contact pressure-resistant member as claimed in  claim 1 , wherein the steel material contains 0.16 to 0.40% by mass of C.  
     
     
         3 . The contact pressure-resistant member as claimed in  claim 1 , wherein the steel material contains 0.50 to 1.25% by mass of Si.  
     
     
         4 . The contact pressure-resistant member as claimed in  claim 1 , wherein the steel material contains 0.20 to 1.31% by mass of Mn.  
     
     
         5 . The contact pressure-resistant member as claimed in  claim 1 , wherein the steel material contains 0.50 to 1.31% by mass of Cr.  
     
     
         6 . The contact pressure-resistant member as claimed in  claim 1 , wherein the steel material contains 0.05 to 0.45% by mass of Mo.  
     
     
         7 . The contact pressure-resistant member as claimed in  claim 1 , wherein the steel material contains 0.50 to 3.00% by mass of Ni.  
     
     
         8 . The contact pressure-resistant member as claimed in  claim 1 , wherein a concentration ratio Cr/Si between Cr and Si is in a range of 0.8 to 2.0% by mass, and a concentration ratio (Mn+Ni)/Mo of Mn and Ni to Mo is 20 or less.  
     
     
         9 . The contact pressure-resistant member as claimed in  claim 1 , wherein the steel material further comprises 0.05 to 0.5% by mass of V.  
     
     
         10 . The contact pressure-resistant member as claimed in  claim 1 , wherein the rolling contact portion has a concentration of carbon forming a solid solution of carbon and Fe, in a range of 0.60 to 0.95% by mass.  
     
     
         11 . The contact pressure-resistant member as claimed in  claim 1 , wherein the rolling contact portion has a total concentration of carbon plus nitrogen which ranges from 0.8 to 1.2%.  
     
     
         12 . The contact pressure-resistant member as claimed in  claim 1 , wherein the surface of the contact pressure-resistant member contains carbide particles having a mean particle diameter of 1.2 μm or less.  
     
     
         13 . The contact pressure-resistant member as claimed in  claim 1 , wherein the surface of the contact pressure-resistant member has a carbide area ratio of 2 to 8%.  
     
     
         14 . The contact pressure-resistant member as claimed in  claim 1 , wherein the rolling contact portion comprises a Ni plating layer formed on at least a part thereof.  
     
     
         15 . The contact pressure-resistant member as claimed in  claim 14 , wherein the Ni plating layer has a thickness of 0.1 to 20 μm.  
     
     
         16 . The contact pressure-resistant member as claimed in  claim 1 , wherein the contact pressure-resistant member is adapted for use in a rolling contact for an automobile.  
     
     
         17 . The contact pressure-resistant member as claimed in  claim 1 , wherein the contact pressure-resistant member is adapted for use in a rolling element of a toroidal continuously variable transmission.  
     
     
         18 . A method of making a contact pressure-resistant member having a rolling contact portion on a surface thereof, the rolling contact portion being adapted to come into rolling contact with a counterpart, the method comprising: 
 subjecting a workpiece made of a steel material containing 0.15 to 0.40% by mass of C, 0.50 to 1.50% by mass of Si, 0.20 to 1.50% by mass of Mn, 0.50 to 1.50% by mass of Cr, and 0.05 to 0.50% by mass of Mo, 0.010% by mass or less of P, at least one element selected from the group consisting of 0.50 to 3.50% by mass of Ni, 0.03 to 0.20% by mass of Ti, 0.03 to 0.15% by mass of Nb and 0.01 to 0.10% by mass of Al, and the balance of Fe and inevitable impurities, to either carburizing or carbonitriding to control a carbon concentration on a surface of the workpiece to a range of 0.8 to 1.2%; and    subjecting the workpiece to quenching and tempering.    
     
     
         19 . The method as claimed in  claim 18 , further comprising: 
 holding at least the surface of the workpiece at a first temperature ranging from an Ac 1  transformation point to less than a temperature of an Acm transformation point plus 150° C., after the carburizing or carbonitriding;    heating the workpiece to a second temperature ranging from 550° C. to less than an Ar 1  transformation point, after holding the at least the surface of the workpiece at the first temperature;    holding the workpiece at the second temperature;    holding the workpiece at a third temperature ranging from the Ac 1  transformation point to less than the Acm transformation point; and    subjecting the workpiece to rapid cooling.    
     
     
         20 . The method as claimed in  claim 18 , further comprising forming a Ni plating layer on at least a part of the surface of the workpiece which is adapted to act as the rolling contact portion of the contact pressure-resistant member.