| 摘要 |
PURPOSE:To obtain a medium-carbon steel having improved ruputurability of swarf and good machineability by utilizing the difference which arises between the austenitization rate of the old ferrite phase and the penetration rate of the carbide into pearlite under quick heating. CONSTITUTION:The middle-carbon steel contg. 0.4-0.5% C is heated to 820-900 deg.C and is then cooled down to the temp. higher by 10-20 deg.C than the A1 point of said steel and after the steel is held at said temp., the steel is cooled to form the mixed structure of coarse ferrite and pearlite phases. The steel is then quickly heated up to 820-870 deg.C at >=0.6 deg.C/sec heating rate and is held at the constant temp. within 5 minutes; thereafter the steel is cooled down to 640+ or -20 deg.C within 30 minutes and is held at said temp. to convert the coarse ferrite part to ferrite + pearlite structure and to convert the pearlite part to sheroidizing-annealed structure.
|
