| 摘要 |
PURPOSE:To form a dense black coating with good protectivity by heating the sheath heater to predetermined temp. in a wet hydrogen atmosphere with a predetermined dew point or more. CONSTITUTION:The sheath heater having an alloy pipe containing 5wt% or more of Cr as a protective pipe is heated to 900-1,200 deg.C in a wet hydrogen atmosphere with a dew point of 5 deg.C or more and, according to circumstances, heated further at 900-1,200 deg.C in the air to form an oxide coating based on Cr with a thickness of 0.5-6mu. Thereby, dense Cr2O3 is formed and a black coating with excellent corrosion resistance and oxidation resistance is obtained. |
