High Strength Spring Steel Wire and High Strength Spring and Methods of Production of the Same

Abstract

The present invention provides high strength spring and high strength spring steel wire superior in corrosion fatigue characteristics and methods of production of the same, that is, a high strength spring steel wire and high strength spring containing, by mass %, C: 0.35 to 0.50%, Si: 1.00 to 3.00%, and Mn: 0.10 to 2.00%, restricting P to 0.015% or less and S to 0.015% or less, having a balance of Fe and unavoidable impurities, and, when raising the temperature in the range from 50° C. to 600° C. by 0.25° C./s and measuring the differential scanning calories, having the only peak of the exothermic reaction present at 450° C. or more. A method of production of high strength spring characterized by tempering under conditions where the tempering temperature T[K], tempering time t[s], and content Si % [mass %] of Si satisfy the following: 16000≦(T−40×[Si %])×(31.7+log t)≦23000.

1 . A high strength spring steel wire characterized by containing, by mass %,
 C, 0.35 to 0.50%,   Si: 1.00 to 3.00%, and   Mn: 0.10 to 2.00%,   restricting   P to 0.015% or less and   S to 0.015% or less,   having a balance of Fe and unavoidable impurities, and   when raising the temperature in the range from 50° C. to 600° C. by 0.25° C./s and measuring the differential scanning calories, having the only peak of the exothermic reaction present at 450° C. or more.   
   
   
       2 . A high strength spring steel wire as set forth in  claim 1  characterized by further containing, by mass %,
 Ti: 0.100% or less and   B: 0.0010 to 0.0100%,   restricting   N to 0.0100% or less, and   having contents of Ti and N satisfying   Ti≧3.5N   
   
   
       3 . A high strength spring as set forth in  claim 1  characterized by further containing, by mass %,
 one or more of Mo: 0.05 to 1.00%, Cr: 0.05 to 1.50%, Ni: 0.05 to 1.00%, Cu: 0.05 to 1.00%, Nb: 0.010 to 0.100%, V: 0.05 to 0.20%, and Sb: 0.001 to 0.050%.   
   
   
       4 . A high strength spring characterized by using as a material a high strength spring steel wire as set forth in  claim 1 . 
   
   
       5 . A high strength spring characterized by containing, by mass %,
 C, 0.35 to 0.50%,   Si: 1.00 to 3.00%, and   Mn: 0.10 to 2.00%,   restricting   P to 0.015% or less and   S to 0.015% or less,   having a balance of Fe and unavoidable impurities, and   when raising the temperature in the range from 50° C. to 600° C. by 0.25° C./s and measuring the differential scanning calories, having the only peak of the exothermic reaction present at 450° C. or more.   
   
   
       6 . A high strength spring as set forth in  claim 5  characterized by, further containing, by mass %,
 Ti: 0.100% or less and   B: 0.0010 to 0.0100%,   restricting   N to 0.0100% or less, and   having contents of Ti and N satisfying   Ti≧3.5N   
   
   
       7 . A high strength spring as set forth in  claim 5 , characterized by further containing, by mass %,
 one or more of Mo: 0.05 to 1.00%, Cr: 0.05 to 1.50%, Ni: 0.05 to 1.00%, Cu: 0.05 to 1.00%, Nb: 0.010 to 0.100%, V: 0.05 to 0.20%, and Sb: 0.001 to 0.050%.   
   
   
       8 . A method of production of high strength spring steel wire characterized by heating steel wire comprised of the ingredients as set forth in  claim 1  to 850 to 1000° C., quenching it, then tempering it under conditions where the tempering temperature T[K], tempering time t[s], and content Si % [mass %] of Si satisfy the following formula 1:
   16000≦( T− 40×[Si %])×(31.7+log  t )≦23000  (1)   
   
   
       9 . A method of production of a high strength spring characterized by cold forming steel wire comprised of the ingredients as set forth in  claim 5  to a spring shape, heating it to 850 to 1000° C., quenching it, then tempering it under conditions where the tempering temperature T[K], tempering time t[s], and content Si % [mass %] of Si satisfy the following formula 1:
   16000≦( T− 40×[Si %])×(31.7+log  t )≦23000  (1)   
   
   
       10 . A method of production of a high strength spring characterized by heating steel wire comprised of the ingredients as set forth in  claim 5  to 850 to 1000° C., hot forming it into a spring shape, then quenching it, then tempering it under conditions where the tempering temperature T[K], tempering time t[s], and content Si % [mass %] of Si satisfy the following formula 1:
   16000≦( T− 40×[Si %])×(31.7+log  t )≦23000  (1)