| 摘要 |
PURPOSE:To obtain a superior product without adding expensive elements in large quantities by reheating a casting to a temp. in the austenitizing temp. range above the A1 transformation range, and rapidly cooling the casting under specified conditions. CONSTITUTION:Molten metal having the composition of vermicular graphite cast iron is charged into a casting mold and solidified. The resulting casting is reheated to a temp. in the austenitizing temp. range above the A1 transformation range, and it is rapidly cooled. At this time, the casting is rapidly cooled from said temp. at a cooling rate at which pearlitic transformation is not caused, and it is held at a temp. at which a mixed structure consisting of bainite and austenite is stably formed. After the lapse of a prescribed time, the casting is allowed to cool, or it is rapidly cooled. Thus, vermicular graphite cast iron having extremely superior mechanical properties such as high strength and toughness is obtd. |
