| 摘要 |
PURPOSE:To obtain the title plug wherein the peeling resistance of an oxide layer is improved by heating a high-Cr plug material which has been machined to form an oxide layer on the surface, cooling the material while specifying the temp. range and velocity of cooling and then again forming an oxide layer. CONSTITUTION:A plug material made of a high Cr-Ni alloy steel contg. at least 12-20wt% Cr and 1-2.5wt% Ni and whose surface has been machined is heated in an oxidizing atmoshere to form an oxide layer on the surface. Then the material is cooled as the primary heat treatment in the temp. range of >=350 deg.C at a velocity higher than the velocity obtained when the material is allowed to cool in the air and the treatment is carried out more than once. Consequently, cracks are generated in the oxide layer and a poorly stuck oxide is released. The plug material is heated again in an oxidizing atmosphere to form an oxide layer on the surface. A fresh oxide is generated and grown from the cracks and the released part, the formation of Ni-enriched base iron particles is increased and a tougher oxide layer is formed.
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