| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 89 === Replacement of damaged steam turbine blades is quite often and costly in the operation of power plants. With the improved welding techniques, laser repairing of damaged blades appears to be cost effective together with good quality. AISI 403 stainless steel is a special quality grade used particularly for turbine blades. It has excellent corrosion resistance with the ability to develop hardness and mechanical properties similar to 4130 alloy steel. However, 403 S.S. is subject to hydrogen-induced cracking in the same manner as low alloy steels. Consequently, appropriate precautions must be taken in welding procedures to avoid hydrogen pickup during welding and associated cracking problems. Apparently, weld repairing of 403 S.S. by lasers has advantages such as low heat input and less distortion over conventional repairing methods. In this research, a 5KW CO2 laser was employed in the repairing process. The weld repairing procedure and the selection of alloy powders (filler metals) on the repaired quality of 403 S.S. were performed. Mechanical tests such as fatigue crack growth propagation, impact toughness, and tensile tests along with microstructural analyses of repaired welds were included in the evaluation process. The results indicated that the use of 410 S.S. powder with the adjustment of carbon content by mixing of alloy powders to the level of base material seemed to be very promising in the laser repairing process. It is suggested that the application of laser welding technique to restorate damage 403 turbine steam blades is not only feasible but also practical.
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