Original paper(Vol.46 No.9 pp.1051)
Fatigue strength of SUS303/SUS303 friction welded joints
Fukuchi Yusuke; Okita Kozo; Nozaki Mineo
Abstract:Fatigue tests were conducted on the free cutting stainless steel SUS303/SUS303 friction welded joints under pulsating zero-tension load to study the effects of microstructure produced by friction welding process. The specimens with circumferential notch machined near the welding interface were used in the fatigue tests. Fatigue crack initiation and propagation were examined by using direct current potential drop method.
The fatigue limit of the friction welded joints is the same as that of the base metal. But the difference in fatigue strength between the base metal and the joints increased with increasing stress level. The crack initiation strength of the joints is lower than that of the base metal and the non-propagating cracks were found in the specimens of the joints which did not fracture above 107 stress cycles. The fatigue crack growth rate of the joints was decreased and reached the minimum value near cracl length od 0.2 mm. The crack growth rate of the joints was smaller than that of the base metal in the low stress intensity factor range, while it increased and gained upon that of the base metal. The degradation of fatigue strength of the joints, especially for the fatigue crack initiation strength, was mainly caused by the shape, size, direction and distribution of non-metallic inclusions which differed from those of the base metal.
Key Words:fatigue, fatigue strength, friction welding, notched-specimen, D.C. potential method, crack initiation, non-propagating crack, crack growth rate, non-metallic inclusion