Steel and method for manufacturing steel

Abstract

The present disclosure relates to a steel and a method for manufacturing the steel. Specifically, the present disclosure is characterized by providing a method for providing optimal alloy components that can reduce carburizing thermal deformation by reducing contents of Cr and Mo elements compared to the existing ones, and improving the physical property with fatigue resistance of a carburized steel by adjusting a rolling thermal treatment temperature, a carburizing thermal treatment condition, and the like to increase a fraction of a fine MX precipitate and improve a precipitation strengthening effect.

What is claimed is: 
     
         1 . A steel comprising:
 C: 0.17 to 0.23 wt %, Si: 0.6 to 0.8 wt %, Mn: 0.35 to 0.65 wt %, Cr: 1.35 to 1.65 wt %, Ni: 0.25 to 0.45 wt %, Mo: 0.15 to 0.25 wt %, Nb: 0.015 to 0.035 wt %, and V: 0.02 to 0.04 wt %; and   residues comprising iron and other inevitably mixed impurities,   wherein the steel satisfies the following formula:
   6.7≤5[C]+2[Si]+2[Mn]+2[Cr]+2[Ni]+5[Mo]≤9.5
 
   wherein [C], [Si], [Mn], [Cr], [Ni], and [Mo] are amounts of addition (wt %) of C, Si, Mn, Cr, Ni, and Mo, respectively, and   wherein a fraction of a precipitate satisfies 0.025% to 0.045%.   
     
     
         2 . The steel of  claim 1 ,
 wherein a contact fatigue L10 life of the steel satisfies 2,980,000 cycles or more and a bending fatigue life satisfies 31,000 cycles or more.   
     
     
         3 . A method for manufacturing a steel, the method comprising:
 preparing a carburized steel comprising C, Si, Mn, Cr, Ni, Mo, Nb, and V;   rolling the carburized steel at a temperature of 1180 to 1460° C.;   carburizing and hardening the rolled carburized steel at a temperature of 850 to 920° C. for 150 to 300 minutes; and   precipitating an MX precipitate comprising V and Nb at a fraction of 0.025 to 0.045%.   
     
     
         4 . The method of  claim 3 ,
 wherein the carburized steel comprises:
 C: 0.15 to 0.25 wt %. Si: 0.5 to 0.9 wt %, Mn: 0.3 to 0.7 wt %, Cr: 1.3 to 1.7 wt %, Ni: 0.2 to 0.5 wt %, Mo: 0.1 to 0.4 wt %, Nb: 0.01 to 0.04 wt %, and V: 0.03 to 0.05 wt %; and 
 residues including iron and other inevitably mixed impurities, and 
   wherein the carburized steel satisfies the following formula:
   6.7≤5[C]+2[Si]+2[Mn]+2[Cr]+2[Ni]+5[Mo]≤9.5
 
   wherein [C], [Si], [Mn], [Cr], [Ni], and [Mo] are amounts of addition (wt %) of C, Si, Mn, Cr, Ni, and Mo, respectively.