Abstract
X-ray diffraction observation of metal fractures provides us with useful information on the mechanisms and mechanical conditions of fracturing. This method has been developed especially as an engineering tool for fracture analysis. (α+γ) dual phase stainless steel JIS-SUS329J4L is a composite material which consists of ferrite αFe and austenite γFe phases. This material excels in corrosion-resistance in the chlorinated environment, and is used for chemical plant and the oil pipes. In this study, X-ray fractogarphy technique is applied to fatigue fracture surface of dual phase stainless steel. Fatigue crack propagation tests were conducted under stress ratios of 0.5 and 0.7. Residual phase and macro stresses near the fracture surface were measured using X-ray diffraction method to the depth direction. In addition, the distribution of the misfit of plastic strain ΔeP between αFe and γFe phase obtained from micromechanics beneath the fracture surface was calculated. From the distribution of these X-ray parameters, the depth of the maximum plastic zone ωy was determined. Relations between ωy and fracture mechanics parameter were examined. As the result, ΔeP was related with the maximum stress intensity factor Kmax divided by the 0.2% proof stress σ0.2. Moreover, it is suggested that ΔeP is more effective parameter than residual stresses for determination of ωy of dual phase stainless steel.
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