METHOD FOR IMPROVING SURFACE HARDNESS OF MARTENSITIC STAINLESS STEEL

摘要

PPROBLEM TO BE SOLVED: To improve surface hardness of a martensitic stainless steel to the maximum by controlling the amount to be carburized. PSOLUTION: A continuous furnace 4 is composed of: a heating furnace 41 consisting of a preheating region 411 and an austenitizing region 312; and a cooling furnace 45, nitrogen and hydrogen produced by subjecting ammonia 42 to heating decomposition by a modification furnace 43 are passed through a drying apparatus 44, propane 46 is added thereto by a gas mixing apparatus 47, and it is introduced into the continuous furnace. An oxide film in stainless steel is reduced by hydrogen in the mixed gas, carburization of carbon atoms in the propane 46 into the stainless steel base material is promoted, and the flow rate of the propane 46 is controlled to 0.05 to 0.08 liter/min, thus the surplus carbon atoms form carbide with chromium, and the fact that the corrosion resistance of the stainless steel is influenced by sensitization is prevented. By controlling the amount of the carbon to be infiltrated, only solid solution treatment in the stainless steel base material is performed, and carbide is not formed in addition. The hardness of the surface in a martensitic stainless steel is improved by carburization. PCOPYRIGHT: (C)2009,JPO&INPIT