| 摘要 |
PURPOSE:To improve the fatigue strength and toughness in a state of non- refining, after forging, by bringing steel for machine structure or low alloy steel to hot rolling, and thereafter, quenching it, forming a quench hardening depth layer on the surface by a prescribed sectional area rate, and thereafter, executing the forging in a specified temperature range. CONSTITUTION:Steel for machine structure, etc., are brought to hot rolling, and thereafter, only the surface layer is quenched by cooling in a short time by comparatively small quantity of water, and a quench hardening depth layer is generated on the surface, by 20-70% by a sectional area rate. Also, the inside is made to remain ferrite and pearlite structures. Subsequently, by bringing the steel for machine structure, etc., which have been quenched, to forging at a temperature between 550 deg.C-Ac1, a non-refining forgings whose tensile strength is >=70kgf/mm<2> and whose Charpy absorption energy at a room temperature is >=5kgfm is obtained. This non-refining forgings has characteristics which are excellent in the fatigue strength and toughness, even if the subsequent heat treatment is omitted.
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