| 摘要 |
PURPOSE:To improve the toughness of a high chromium steel having a cavity by pouring core material molten metal from the lower part of the outer layer of the high chromium of the specific Cr amount and allowing the same to overflow from the upper part thereby keeping the Cr amount less than the specific. CONSTITUTION:A vertical mold 12 is constituted by a high chromium outer layer 1 containing 13-27wt% Cr held provided within a centrifugally casting mold 4 and upper, lower dies 7, 6. Next, core molten metal of ductile cast iron is continuously poured into the mold 12 through a pouring basin 13, a pouring pipe 14 and a pouring cross gate 10 and the molten metal is allowed to overflow from the discharge port 11 of the upper die 7. The previously poured molten metal of increased Cr contents is then substituted with the post poured molten metal of which the Cr amount has become <=0.9wt%. Thence, strain relief heat treatment is applied after the freezing of the core material 2 to apply roughing, after which a heater insertion hole 2' is pierced in the central part thereof. The reason for limiting the Cr amount of the high chromium material of the outer layer 1 is: The one within this range has both abrasion resistance and surface roughening resistance. |
