PURPOSE: To form a diffused Al layer with low hardness, superior workability and superior strength at high temp., by diffusing Al at a specified temp. in the surface of each of parts made of high alloy steel used in an atmosphere of hot combusting gas and by carrying out after-heat-treatment at the same temp.
CONSTITUTION: Al is diffused at 1,000W1,250°C in the surface of each of parts made of stainless steel or higher alloy steel used in an atmosphere of hot combustion gas such as parts of a boiler or a heat exchanger to form an Al-enriched layer having ≥10μm thickness. Afterheat-treatment is then carried out by heating at the same temp. of 1,000W1,250°C in a nonoxidizing atmosphere. A surface treated layer having lower surface hardness than a material subjected to conventional Al diffusion is formed. The layer has superior strength at high temp. as well as supeiror workability.
MAKIURA HIROFUMI
MURAYAMA JIYUNICHIROU
