Development of a superalloy with excellent fatigue property

An attempt has been made to develop new alloys with high thermal fatigue re sistance and interpret the thermal fatigue behavior based on the relation b etween plastic strain range and related elongation in tension test at eleva ted temperatures. The thermal stresses that lead to thermal fatigue failure s are generally induced by rapid change in temperature due to start and sto p of plants, so that the rotal number of cycles involved is relatively smal l. Resistance to thermal fatigue depends on the material properties such as a coefficient of thermal expansion, heat conductivity and resistance to th e strains incidental to temperature change. At present work, three types of modified NCF625 alloys were candidated to control the material properties by changing the contents of elements such as aluminum, titanium and iron, a nd were cast as ingots for the test. Thermal fatigue behaviors of examined alloys were evaluated at elevated temperatures between 773K and 1073K, and between 773K and 1073K. As a result, it was derived that the modified NCF62 5 alloy containing 1% titanium, 1% aluminum, and 1% iron showed the highest thermal fatigue strength. It was found, form the thermal fatigue rests, th at this alloy had thermal fatigue resistance about two times that of NCF625 . The alloy thus selected was gas atomized to powder and PTA welded on a ca rbon steel plate, and it was confirmed that there was no problem found on t he metallurgical structure and hardness distribution.