Mechanical structural shaft component and method of manufacturing the same

Abstract

The invention is to provide a method of manufacturing a mechanical structural shaft component improved in the fatigue strength and maintained in the manufacturability, and a mechanical structural shaft component manufactured by the method. The shaft component is manufactured by blending and melting a raw material so as to achieve a steel material composition of, in % by mass, Fe: 96% or more, C: 0.45% or more and 0.55% or less, Si: 0.02% or more and 0.15% or less, Mn: more than 0.50% and 1.20% or less, P: 0.005% or more and 0.020% or less, S: 0.005% or more and 0.030% or less, Cr: 0.10% or more and 0.30% or less, Al: 0.002% or more and 0.050% or less, Ti: 0.020% or more and 0.050% or less, B: 0.0005% or more and 0.0030% or less and Nb: 0.020% or more and 0.100% or less; by allowing the raw material to solidify, while keeping cooling rate of the center portion of a bloom at 2° C./min or above; and by subjecting the resultant steel material to product rolling or forging at a heating temperature of 950° C. to 1,050° C., and at a working temperature of 800° C. to 1,050° C., to thereby make the steel material having a geometry of shaft component, and further to induction hardening and tempering.

1 . A method of manufacturing a mechanical structural shaft component comprising the steps of: 
 blending and melting a raw material so as to achieve a steel material composition of, in % by mass, Fe: 96% or more, C: 0.45% or more and 0.55% or less, Si: 0.02% or more and 0.15% or less, Mn: more than 0.50% and 1.20% or less, P: 0.005% or more and 0.020% or less, S: 0.005% or more and 0.030% or less, Cr: 0.10% or more and 0.30% or less, Al: 0.002% or more and 0.050% or less, Ti: 0.020% or more and 0.050% or less, B: 0.0005% or more and 0.0030% or less and Nb: 0.020% or more and 0.100% or less;    allowing the raw material to solidify within a temperature range from 1,200° C. to 1,400° C., both ends inclusive, while keeping cooling rate of the center portion of a bloom at 2° C./min or above;    subjecting the resultant steel material to product rolling or forging at a heating temperature of 950° C. to 1,050° C., both ends inclusive, and at a working temperature of 800° C. to 1,050° C., both ends inclusive, to thereby make the steel material into a processed matter having a geometry of shaft component;    subjecting the processed matter to induction hardening; and    subjecting the induction-hardened processed matter to tempering.    
     
     
         2 . The method of manufacturing a mechanical structural shaft component as claimed in  claim 1 , wherein the induction hardening is carried out so as to adjust hardened layer ratio expressed by t/R to 0.4 to 0.8, both ends inclusive, where “t” is thickness defined by a distance from the surface of the mechanical structural shaft component to a position in the radial direction thereof where a hardness equivalent to that of 50% martensite formation is achieved, and “R” is radius of the shaft component, and the tempering is carried out at 150° C. to 220° C., both ends inclusive, for 2 to 150 minutes, both ends inclusive.  
     
     
         3 . The method of manufacturing a mechanical structural shaft component as claimed in  claim 1 , using a material containing, in % by mass, Mo: 0.05% or more and 0.50% or less as the steel material.  
     
     
         4 . The method of manufacturing a mechanical structural shaft component as claimed in  claim 2 , using a material containing, in % by mass, Mo: 0.05% or more and 0.50% or less as the steel material.  
     
     
         5 . The method of manufacturing a mechanical structural shaft component as claimed in  claim 1 , using a material containing at least any one of, in % by mass, Pb: 0.01% or more and 0.20% or less, Bi: 0.01% or more and 0.10% or less, and Ca: 0.0005% or more and 0.0050% or less as the steel material.  
     
     
         6 . The method of manufacturing a mechanical structural shaft component as claimed in  claim 2 , using a material containing at least any one of, in % by mass, Pb: 0.01% or more and 0.20% or less, Bi: 0.01% or more and 0.10% or less, and Ca: 0.0005% or more and 0.0050% or less as the steel material.  
     
     
         7 . The method of manufacturing a mechanical structural shaft component as claimed in  claim 3 , using a material containing at least any one of, in % by mass, Pb: 0.01% or more and 0.20% or less, Bi: 0.01% or more and 0.10% or less, and Ca: 0.0005% or more and 0.0050% or less as the steel material.  
     
     
         8 . The method of manufacturing a mechanical structural shaft component as claimed in  claim 4 , using a material containing at least any one of, in % by mass, Pb: 0.01% or more and 0.20% or less, Bi: 0.01% or more and 0.10% or less, and Ca: 0.0005% or more and 0.0050% or less as the steel material.  
     
     
         9 . A mechanical structural shaft component manufactured by blending and melting a raw material so as to achieve a steel material composition of, in % by mass, Fe: 96% or more, C: 0.45% or more and 0.55% or less, Si: 0.02% or more and 0.15% or less, Mn: more than 0.50% and 1.20% or less, P: 0.005% or more and 0.020% or less, S: 0.005% or more and 0.030% or less, Cr: 0.10% or more and 0.30% or less, Al: 0.002% or more and 0.050% or less, Ti: 0.020% or more and 0.050% or less, B: 0.0005% or more and 0.0030% or less. and Nb: 0.020% or more and 0.100% or less; 
 by allowing the raw material to solidify within a temperature range from 1,200° C. to 1,400° C., both ends inclusive, while keeping cooling rate of the center portion of a bloom at 2° C./min or above; and by subjecting the resultant steel material to product rolling or forging at a heating temperature of 950° C. to 1,050° C., and at a working temperature of 800° C. to 1,050° C., to thereby make the steel material having a geometry of shaft component, and further to induction hardening and tempering, wherein torsional strength y (MPa) and average hardness x (Hv) defined by the equation below:            x   =       3     a   3       ⁢   a   ⁢       ∫   0   a     ⁢       h   ⁡     (   r   )       ⁢     r   2     ⁢           ⁢     ⅆ   r                   where “a” is radius of the shaft, r is distance from the center, and h(r) is hardness at distance r from the center, satisfy a relation of y>2.5x.    
     
     
         10 . The mechanical structural shaft component as claimed in  claim 9 , using a material containing, in % by mass, Mo: 0.05% or more and 0.50% or less as the steel material.  
     
     
         11 . The mechanical structural shaft component as claimed in  claim 9 , using a material containing at least any one of, in % by mass, Pb: 0.01% or more and 0.20% or less, Bi: 0.01% or more and 0.10% or less, and Ca: 0.0005% or more and 0.0050% or less as the steel material.  
     
     
         12 . The mechanical structural shaft component as claimed in  claim 10 , using a material containing at least any one of, in % by mass, Pb: 0.01% or more and 0.20% or less, Bi: 0.01% or more and 0.10% or less, and Ca: 0.0005% or more and 0.0050% or less as the steel material.