| 摘要 |
PURPOSE:To improve the resistance to delayed fracture of steel materials by rapid heating for a short duration of time for softening the limiting surface area of the high strength steel material which is specified in its strength. CONSTITUTION:The surface of the steel material being applied drawing working, etc. to have tensile strength of 120kg/mm.<2> or over, is heated by high frequency induction heating or flame heating methods. With this heating, the surface, within 1mm. from the surface, is formed with softend layer having micro-Vickers hardness of under 350. Thus, high strength steel materials having excellent resistance to delayed fracture can be supplied without deteriorating quality performance such as strength and toughness of the steel material. |
