X-Ray Fractography for (ƒ¿+ƒÁ) Dual Phase Stainless Steels Using Parameter ƒ¢ƒÃP Obtained from Micromechanics
Hajime HIROSE, Toshihiko SASAKI and Masumi SAKA
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. (ƒ¿+ƒÁ) dual phase stainless steel JIS-SUS329J4L is a composite material which consists of ferrite ƒ¿Fe and austenite ƒÁFe 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 ƒ¢ƒÃP between ƒ¿Fe and ƒÁFe 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 ƒÖy was determined. Relations between ƒÖy and fracture mechanics parameter were examined. As the result, ƒ¢ƒÃP was related with the maximum stress intensity factor Kmax divided by the 0.2% proof stress ƒÐ0.2. Moreover, it is suggested that ƒ¢ƒÃP is more effective parameter than residual stresses for determination of ƒÖy of dual phase stainless steel. Key Words:X-ray diffraction, Fractography, Micromechanics, Dual phase stainless steel, Misfit of plastic strain, Macro stress