Spring Steel Wire

Abstract

The present invention provides a spring steel wire which has a tempered martensitic structure brought about by quenching-tempering. The present spring steel wire has a 40% or higher reduction of area and a 1,000 MPa or higher shear yield stress after subjected to heat treatment for at least hours at a temperature ranging from 420° C. to 480° C. The present steel wire preferably constitutes, based on mass %, C: 0.50-0.75%, Si: 1.80-2.70%, Mn: 0.1-0.7%, Cr: 0.70-1.50%, Co: 0.02-1.00%, and remnants consisting of Fe and impurities, or constitutes, based on mass %, C: 0.50-0.75%, Si: 1.80-2.70%, Mn: over 0.7-1.50%, Cr: 0.70-1.50%, and remnants consisting of Fe and impurities.

1 . A spring steel wire having a tempered martensitic structure brought about by quenching-tempering, the spring steel wire comprising:
 a 40% or higher reduction of area; and   a 1,000 Mpa or higher shear yield stress after subjected to heat treatment for at least 2 hours at a temperature ranging from 420° C. to 480° C.   
     
     
         2 . The spring steel wire according to  claim 1  consisting of, based on mass %, C: 0.50-0.75%, Si: 1.80-2.70%, Mn: 0.1-0.7%, Cr: 0.70-1.50%, Co: 0.02-1.0%, and remnants consisting of Fe and impurities. 
     
     
         3 . The spring steel wire according to  claim 1  consisting of, based on mass %, C: 0.50-0.75%, Si: 1.80-2.70%, Mn: over 0.7-1.5%, Cr: 0.70-1.50%, and remnants consisting of Fe and impurities. 
     
     
         4 . The spring steel wire according to  claim 1  consisting of, based on mass %;
 C: 0.50-0.75%, Si: 1.80-2.70%, Mn: over 0.7-1.5%, Cr: 0.70-1.50%;   at least one element of Ni: 0.1-1.0% and Co: 0.02-1.00%; and   remnants consisting of Fe and impurities.   
     
     
         5 . The spring steel wire according to  claim 1  consisting of, based on mass %;
 C: 0.50-0.75%, Si: 1.80-2.70%, Mn: 0.1-0.7%, Cr: 0.70-1.50%, Co: 0.02-1.00%;   at least one element selected from the group of 5 elements consisting of V: 0.05-0.50%, Mo: 0.05-0.50%, W: 0.05-0.15%, Nb: 0.05-0.15% and Ti: 0.01-0.20; and   remnants consisting of Fe and impurities.   
     
     
         6 . The spring steel wire according to  claim 1  consisting of, based on mass %;
 C: 0.50-0.75%, Si: 1.80-2.70%, Mn: over 0.7-1.5%, Cr: 0.70-1.50%;   
       at least one element selected from the group of 5 elements consisting of V: 0.05-0.50%, Mo: 0.05-0.50%, W: 0.05-0.15%, Nb: 0.05-0.15% and Ti: 0.01-0.20%; and
 remnants consisting of Fe and impurities. 
 
     
     
         7 . The spring steel wire according to  claim 1  consisting of, based on mass %, C: 0.50-0.75%, Si: 1.80-2.70%, Mn: over 0.7-1.5%, Cr: 0.70-1.50%, at least one element of Ni: 0.1-1.0% and Co: 0.02-1.00%, at least one element selected from the group of 5 elements consisting of V: 0.05-0.50%, Mo: 0.05-0.50%, W: 0.05-0.15%, Nb: 0.05-0.15% and Ti: 0.01-0.20%, and remnants consisting of Fe and impurities. 
     
     
         8 . The spring steel wire according to  claim 1  comprising austenite grains (prior austenite grains) which have an average grain size in the range of 3.0-7.0 μm. 
     
     
         9 . A spring manufactured from the spring steel wire according to  claim 1 . 
     
     
         10 . A spring manufactured from the spring steel wire according to  claim 8 . 
     
     
         11 . A method of manufacturing a spring steel wire, comprising the steps of:
 patenting a steel consisting of chemical compositions given below;   drawing the thus patented steel into a steel wire; and   subjecting the resultant steel wire to quenching-tempering;   wherein said patenting process comprises:
 an austenization step in which the steel is heated at 900-1,050° C. for 60 to 180 seconds; and 
 an isothermal transformation step in which the thus austenized steel is heated at 600-750° C. for 20 to 100 seconds; 
   Chemical compositions (based on mass %):   
       C: 0.50-0.75%, Si: 1.80-2.70%, Mn: 0.1-0.7%, Cr: 0.70-1.50%, Co: 0.02-1.00%, and remnants consisting of Fe and impurities. 
     
     
         12 . A method of manufacturing a spring steel wire, comprising the steps of:
 patenting a steel consisting of chemical compositions given below;   drawing the thus patented steel into a steel wire; and   subjecting the resultant steel wire to quenching-tempering;   wherein said patenting process comprises:
 an austenization step in which the steel is heated at 900-1,050° C. for 60 to 180 seconds; and 
 an isothermal transformation step in which the thus austenized steel is heated at 600-750° C. for 20 to 100 seconds; 
   Chemical compositions (based on mass %):   
       C: 0.50-0.75%, Si: 1.80-2.70%, Mn: over 0.7-1.5%, Cr: 0.70-1.50%, and remnants consisting of Fe and impurities. 
     
     
         13 . A method of manufacturing a spring steel wire, comprising the steps of:
 patenting a steel consisting of chemical compositions given below;   drawing the thus patented steel into a steel wire; and   subjecting the resultant steel wire to quenching-tempering;   wherein said patenting process comprises:
 an austenization step in which the steel is heated at 900-1,050° C. for 60 to 180 seconds; and 
 an isothermal transformation step in which the thus austenized steel is heated at 600-750° C. for 20 to 100 seconds; 
   Chemical compositions (based on mass %):   
       C: 0.50-0.75%, Si: 1.80-2.70%, Mn: over 0.7-1.5%, Cr: 0.70-1.50%, at least one element of Ni: 0.1-1.0% and Co: 0.02-1.00%, and remnants consisting of Fe and impurities.