STUDIES OF THE FATIGUE BEHAVIOR OF BUTT-WELDED JOINTS IN HY-80 AND HY-100 STEELS

Abstract
The results of axial fatigue tests of transverse butt welded joints in HY-80 steel containing internal defects are reported. The tests were conducted on 3/4 in. and 1-1/2 in. thick material under stress cycles of zero- to-tension and complete reversal. The types of weld defects studied include porosity, slag inclusions, and artificially produced pores, and show that the existence of weld defects measurably decreases the fatigue life of a joint at a given stress cycle when compared to sound welded specimens (with reinforcement removed). However, there does not appear to be a simple correlation between type of defect or amount of defective area and fatigue strength. As part of the study of weld defects, radiographic and ultrasonic techniques were employed to determine the time to initiation and propagation of fatigue cracks in welded joints. The subsequent crack propagation progresses slowly and erratically at first, but the rate of growth is rapidly accelerated from the time it reaches the specimen surface until complete failure occurs. Metallurgical studies were conducted to examine the effect of restraint during welding on the formation of internal microcracks (sulfide inclusions) in welded joints, and the behavior of these joints under conditions of fatigue.

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