The effect of small flaws on the fatigue strength of HAZ at the weld toe

Abstract

The effects of small artificial surface flaws on the fatigue strength of HAZ material are studied. The samples of coarse grain HAZ material were prepared using a welding thermal-cycle simulator. The artificial flaws were produced by indenting with a Vickers pyramid at different loads as either single indentations or as a series. The size of the flaws did not exceed the primary austenitic grain size of the material, which is the most relevant microstructural unit of carbon steels. The dependence of the experimentally determined bending fatigue strength of treated coarse grain HAZ materials on the properly evaluated size of the artificial flaws was compared with the law of long-crack propagation. The biggest flaws evaluated with the flaw-size parameter √area ≅ 100 m are still small for the studied coarse grain HAZ. In further experimental work, the effects of flaw size and the effects of residual stresses should be analysed separately.