| 摘要 |
PURPOSE:To form a casting mold with superior durability by centrifugally casting a low-Ni alloy cast steel into a casting mold and by melting the surface layer part of the inside of the mold with plasma. CONSTITUTION:A low-Ni alloy cast steel consisting of <=0.2% C, <=0.55% Si, <=1.5% Mn, 0.8-1.2% Ni, 0.3-0.4% Mo and the balance essentially Fe is centrifugally cast into a casting mold. 0.07-0.09% V and/or <=0.2% Cr may be substituted for part of Fe in the steel. The surface layer part of the inside of the mold is melted with plasma to provide superior durability. Conditions during the melting include 300-450A electric current; 30-40V voltage; pure Ar as a plasma gas; 1.0- 3.0l/min flow rate of the plasma gas; a gaseous mixture of Ar with 5-10% H2 as a shield gas; and 25-50l/min flow rate of the shield gas. The melting is carried out at about 50-200mm./min melting rate, and the thickness of the layer to be melted is adjusted to about 2-4mm.. |
