Material heating method

Abstract

A material heating method includes: a step of charging a silicon-containing carbon steel material into a heating furnace; a step of preheating the material; a first heating step of raising the temperature of the material; a second heating step of lowering the temperature of the material so as to reduce a temperature difference between the surface and inside of the material; a third heating step of raising the temperature of the material; and a soaking step of reducing the temperature difference between the surface and inside of the material. The temperature of the material in the heating furnace is maintained at the melting point of fayalite or lower.

1 . A material heating method comprising:
 a step of providing a silicon-containing carbon steel material in a heating furnace;   a step of preheating the material;   a first heating step of raising the temperature of the material;   a second heating step of lowering the temperature of the material so as to reduce a temperature difference between the surface and inside of the material;   a third heating step of raising the temperature of the material; and   a soaking step of reducing the temperature difference between the surface and inside of the material,   wherein the temperature of the material in the heating furnace is maintained at the melting point of fayalite or lower.   
     
     
         2 . The material heating method of  claim 1 , wherein the material contains carbon of 0.15 to 1.20 wt % and silicon of 0.10 wt % or more. 
     
     
         3 . The material heating method of  claim 1 , wherein a temperature T 1  of a first heating zone of the heating furnace for performing the first heating step, a temperature T 2  of a second heating zone of the heating furnace for performing the second heating step, a temperature T 3  of a third heating zone of the heating furnace for performing the third heating step, and a temperature T 4  of a soaking zone of the heating furnace for performing the soaking step are set to satisfy the relation of T 2 <T 4 <T 3 <T 1 . 
     
     
         4 . The material heating method of  claim 3 , wherein the temperature T 1  ranges from 1,190 to 1,210° C. 
     
     
         5 . The material heating method of  claim 3 , wherein the temperature T 2  ranges from 1,130 to 1,160° C. 
     
     
         6 . The material heating method of  claim 3 , wherein the temperature T 3  ranges from 1,170 to 1,190° C. 
     
     
         7 . The material heating method of  claim 3 , wherein the temperature T ranges from 1,160 to 1,180° C. 
     
     
         8 . The material heating method of  claim 3 , wherein the temperature T 1  is 1,200° C., the temperature T 2  is 1,150° C., the temperature T 3  is 1,180° C., and the temperature T 4  is 1,170° C. 
     
     
         9 . The material heating method of  claim 1 , wherein a residence time of the material ranges from 160 to 230 minutes. 
     
     
         10 . The material heating method of  claim 1 , wherein a temperature difference ΔT 1  between the surface and inside of the material after the first heating step, a temperature difference ΔT 2  between the surface and inside of the material after the second heating step, a temperature difference ΔT 1  between the surface and inside of the material after the third heating step, and a temperature difference ΔT 4  between the surface and the inside of the material after the soaking step satisfy the relation of ΔT 4 <ΔT 2 and ΔT 3 <ΔT 1 .