| 摘要 |
PURPOSE:To give an evenly spheroidized structure to a bar steel material by a short-period heat treatment in which a stranded bar steel material is subjected to an annealing treatment involving heating and cooling under specific conditions. CONSTITUTION:A bar steel material, e.g., of carbon steel for the structures of machinery, cold rolling, etc., is made into a strand form, and then heated to a target temperature of Ac1+30 deg.C to Ac1+150 deg.C at an average heating rate of 50 deg.C/min or more. Then, the bar steel material is held at the target temperature for 5min or less, cooled for 10min or less to the transformation point Ar1, and then cooled at an average cooling rate of 0.5 to 5 deg.C/min in a temperature region of Ac1 to 40 deg.C for spheroidization. Thus, high temperatures can be effectively utilized because the rate, time, and temperature of heating the bar steel material can be exactly controlled, so that a bar steel material having evenly spheroidized structure can be obtained by a short-period heat treatment. |
