| 摘要 |
PURPOSE:To improve a resistance to oxidation in a high temperature by a method wherein first and second heating bodies are connected in series and the second heating body is formed by a low carbon steel, added with the special metal of specified % or less and specified in the content of carbon. CONSTITUTION:The first heating body 5 is used for a heating element and the second heating body 6 is used for a control element controlling an electric power supplied to the first heating body 5. The first heating body 5 is made of a low carbon steel having enough positive resistance temperature coefficient and containing 0.05-0.30wt% of carbon while the second heating body 6 is made of low carbon steel added with 0.5wt% or less of special metallic material such as yttrium, aluminum or the like. According to this method, the resistance to oxidation of the plug may be improved and the strength of it in a high temperature may also be improved. |
