| 摘要 |
PURPOSE:To produce a steel of improved hardness, abrasion resistance and fatigue strength by heating a spheroidal graphite cast iron blank material then cooling and normalizing the same, followed by machining and quickly cooling the same down to a prescribed temp. after reheating, thence maintaining the same at that temp. CONSTITUTION:After a spheroidal graphite cast iron blank material having ordinary composition ratios is cast, it is heated to 850-950 deg.C, and is maintained at these temp. for 0.5-5hr according to the differences in wall thickness to allow the carbon in the base to diffuse. Next, the cast iron blank material in this state is allowed to cool in the atmosphere or forcibly cooled, so that the structure is converted to pearlite ground or pearlite ground contg. a small amount of pearlite. Next, this normalized blank material is machined to get rid of deformation and is held for 0.5-5hr at 850-950 deg.C, to austenitize the base. Thereafter, it is immediately hardened in a hot bath of salt or like of 250-400 deg.C, and is maintained at these temp. for >=0.5hr. As a result, the base is turned to bainite structure and the steel of improved hardness, abrasion resistance and fatigue strength of the material is obtained. |
