Steel for cold punching and steel element for steel belt using the same

Abstract

A steel used in a belt-type CVT that is superior in wear resistance and toughness, and a steel for cold punching, that provides the same. The steel satisfies the following: 10.8 [C]+5.6 [Si]+2.7 [Mn]+0.3 [Cr]+7.8 [Mo]+1.4 [V]≦13. The steel contains C within the range of 0.50 to 0.70%, Si within the range of 0.03 to 0.60%, Mn within the range of 0.50 to 1.00%, Cr within the range of 0.20 to 1.00%, Ti within the range of 0.01 to 0.10%, and B within the range of 0.0005 to 0.0050% by mass as required additional elements, P within the range of 0.025% or less and S within the range of 0.015% or less by mass as optional additional elements, and the remainder as Fe and unavoidable impurities.

1 . A steel for cold punching comprising a steel of a component composition that satisfies 10.8 [C]+5.6 [Si]+2.7 [Mn]+0.3 [Cr]+7.8 [Mo]+1.4 [V]≦13,
 given [M] as the percent by mass of the chemical element M, further comprising: 
 a component composition of
 C within the range of 0.50 to 0.70%, 
 Si within the range of 0.03 to 0.60%,. 
 Mn within the range of 0.50 to 1.00%, 
 Cr within the range of 0.20 to 1.00%. 
 Ti within the range of 0.01 to 0.10%, and 
 B within the range of 0.0005 to 0.0050% 
 
 by mass as required additional elements,
 P within the range of 0.025% or less and 
 S within the range of 0.015% or less 
 
 by mass as optional additional elements, 
 and the remainder as Fe and unavoidable impurities, wherein: 
 a hardness of 88 HRB or less is provided in a structure achieved by heating and maintaining the steel in an austenite single-phase temperature range and subsequently performing cooling at a predetermined rate to disperse fine carbides in a mainly ferrite+pearlite mixed structure. 
 
     
     
         2 . The steel for cold punching according to  claim 1  wherein the steel is characterized by the suppression of coarse carbides with a circle-equivalent diameter of 0.5 μm or greater to 1.2×10 5  carbides or less per 1 mm square in a sectional structure. 
     
     
         3 . An element for steel belts wherein the element is characterized by the provision of a quenching and tempering heat treatment after the steel for cold punching according to  claim 1  is cold punched into a predetermined shape, thereby providing a hardness of 640 Hv or greater. 
     
     
         4 . The element for steel belts according to  claim 3  wherein the steel element is characterized by the suppression of coarse carbides with a circle-equivalent diameter of 0.5 μm or greater to 1.3×10 4  carbides or less per 1 mm square in a sectional structure. 
     
     
         5 . An element for steel belts wherein the element is characterized by the provision of a quenching and tempering heat treatment after the steel for cold punching according to  claim 2  is cold punched into a predetermined shape, thereby providing a hardness of 640 Hv or greater.