High-toughness steel and method for manufacturing the same

Abstract

A method for manufacturing high-toughness steel includes the following steps. A steel billet is provided. The steel billet is subjected to a heating step, a hot rolling step, a spheroidizing step and a quenching and tempering heat treatment step to obtain the high-toughness steel. The steel billet includes a specific proportion of composition. After the steel billet undergoes the heating step, the hot rolling step and the spheroidizing step, the obtained spheroidized steel has good processability and formability. The high-toughness steel has good hardness and impact toughness.

What is claimed is: 
     
         1 . A method for manufacturing high-toughness steel, comprising:
 providing a steel billet, wherein a total weight of the steel billet is as 100 weight percent, the steel billet comprises:
 0.3 weight percent to 0.35 weight percent of carbon; 
 0.01 weight percent to 0.1 weight percent of silicon; 
 0.8 weight percent to 1.4 weight percent of manganese; 
 0.6 weight percent to 0.8 weight percent of chromium; 
 0.025 weight percent to 0.045 weight percent of niobium; 
 0.02 weight percent to 0.03 weight percent of titanium; 
 0.0015 weight percent to 0.0025 weight percent of boron; and 
 a balance being iron and inevitable impurities, wherein the steel billet excludes nickel, copper, molybdenum, vanadium and aluminum; 
   performing a heating step on the steel billet, so as to obtain a heated steel billet;   performing a hot rolling step on the heated steel billet, so as to obtain a rolled steel;   performing a spheroidizing step on the rolled steel, so as to obtain a spheroidized steel; and   performing a quenching and tempering heat treatment step on the spheroidized steel, so as to obtain the high-toughness steel.   
     
     
         2 . The method for manufacturing high-toughness steel according to  claim 1 , wherein a heating temperature in the heating step is 1150° C. to 1250° C., and a heating temperature holding time in the heating step is 1.0 hour to 2.5 hours. 
     
     
         3 . The method for manufacturing high-toughness steel according to  claim 1 , wherein a rolled temperature in the hot rolling step is 800° C. to 900° C., and a post-rolling cooling rate in the hot rolling step is 0.3° C./second to 0.5° C./second. 
     
     
         4 . The method for manufacturing high-toughness steel according to  claim 1 , wherein the rolled steel consists of a ferrite microstructure with a volume fraction of 40% to 50% and a balanced amount of pearlite microstructure. 
     
     
         5 . The method for manufacturing high-toughness steel according to  claim 1 , wherein a spheroidizing temperature in the spheroidizing step is 765° C. to 775° C., and a spheroidizing temperature holding time in the spheroidizing step is 2 hours to 4 hours. 
     
     
         6 . The method for manufacturing high-toughness steel according to  claim 5 , wherein a post-spheroidizing cooling rate in the spheroidizing step is 10° C./hour to 12° C./hour. 
     
     
         7 . The method for manufacturing high-toughness steel according to  claim 1 , wherein a spheroidization rate of the spheroidized steel is classified as grade 1, and a hardness of the spheroidized steel is HRB70 to HRB73 according to Rockwell hardness B scale. 
     
     
         8 . The method for manufacturing high-toughness steel according to  claim 1 , wherein the quenching and tempering heat treatment step comprises:
 an austenitization treatment, wherein an austenitization temperature of the austenitization treatment is 840° C. to 870° C., and an austenitization temperature holding time of the austenitization treatment is 1 hour to 2 hours; and a tempering treatment after the austenitization treatment, wherein a tempering temperature of the tempering treatment is 200° C. to 250° C., and a tempering temperature holding time of the tempering treatment is 1 hour to 2 hours.   
     
     
         9 . The method for manufacturing high-toughness steel according to  claim 1 , further comprising:
 before performing the spheroidizing step on the rolled steel, a wire drawing step is performed on the rolled steel; and   before performing the quenching and tempering heat treatment step on the spheroidized steel, a forming step is performed on the spheroidized steel.   
     
     
         10 . A method for manufacturing high-toughness steel, comprising:
 providing a steel billet, wherein a total weight of the steel billet is as 100 weight percent, the steel billet further comprises:
 0.3 weight percent to 0.35 weight percent of carbon; 
 0.01 weight percent to 0.1 weight percent of silicon; 
 0.8 weight percent to 1.4 weight percent of manganese; 
 0.6 weight percent to 0.8 weight percent of chromium; 
 0.025 weight percent to 0.045 weight percent of niobium; 
 0.02 weight percent to 0.03 weight percent of titanium; 
 0.0015 weight percent to 0.0025 weight percent of boron; and 
 a balance being iron and inevitable impurities, wherein the steel billet excludes nickel, copper, molybdenum, vanadium and aluminum; 
   performing a hot rolling step, so as to obtain a rolled steel;   performing a wire drawing step on the rolled steel, so as to obtain a drawn rolled steel;   performing a spheroidizing step on the drawn rolled steel, so as to obtain a spheroidized steel; and   performing a quenching and tempering heat treatment step on the spheroidized steel, so as to obtain the high-toughness steel, wherein the quenching and tempering heat treatment step comprises:   an austenitization treatment, wherein an austenitization temperature of the austenitization treatment is 840° C. to 870° C., and an austenitization temperature holding time of the austenitization treatment is 1 hour to 2 hours; and a tempering treatment after the austenitization treatment, wherein a tempering temperature of the tempering treatment is 200° C. to 250° C., and a tempering temperature holding time of the tempering treatment is 1 hour to 2 hours.   
     
     
         11 . The method for manufacturing high-toughness steel according to  claim 10 , wherein a rolled temperature in the hot rolling step is 800° C. to 900° C., and a post-rolling cooling rate in the hot rolling step is 0.3° C./second to 0.5° C./second. 
     
     
         12 . The method for manufacturing high-toughness steel according to  claim 10 , wherein the rolled steel consists of a ferrite microstructure with a volume fraction of 40% to 50% and a balanced amount of pearlite microstructure. 
     
     
         13 . The method for manufacturing high-toughness steel according to  claim 10 , wherein a spheroidizing temperature in the spheroidizing step is 765° C. to 775° C., and the spheroidizing temperature holding time in the spheroidizing step is 2 hours to 4 hours. 
     
     
         14 . The method for manufacturing high-toughness steel according to  claim 13 , wherein a post-spheroidizing cooling rate in the spheroidizing step is 10° C./hour to 12° C./hour. 
     
     
         15 . The method for manufacturing high-toughness steel according to  claim 10 , wherein a spheroidization rate of the spheroidized steel is classified as grade 1, and a hardness of the spheroidized steel is HRB70 to HRB73 according to Rockwell hardness B scale. 
     
     
         16 . The method for manufacturing high-toughness steel according to  claim 10 , further comprising:
 before the quenching and tempering heat treatment step on the spheroidized steel, a forming step is performed on the spheroidized steel.   
     
     
         17 . A high-toughness steel made by the method for manufacturing high-toughness steel according to  claim 1 , wherein a hardness of the high-toughness steel is HRC47 to HRC49, and an impact toughness of the high-toughness steel is 55.7J to 60.3J.