2020 年 106 巻 7 号 p. 457-464
The demand for a reliable and quantitative method to determine phase fractions has been increasing due to the developments of multi-phase materials, such as TRIP steels. The authors conducted a mutual verification between the two methods for phase fraction analysis, the saturation magnetization measurement and the newly developed neutron diffraction technique, neutron-diffraction-based Rietveld texture analysis (NDRTA). The chemical compositions of the current samples were Fe-18Cr-8Ni-1Mn-0.5Si (mass%) with 0, 0.1 or 0.2 mass% of C or N. The α’-martensite volume fractions analyzed by both methods showed a good linear correspondence. The analysis based on the saturation magnetization measurement required an accurate evaluation of the volume saturation magnetization of α’-martensite, which was a function of the chemical composition. The comparison with the result of NDRTA can be an effective method to calibrate the volume saturate magnetization of α’-martensite, especially in the case that a fully transformed standard sample cannot be obtained. NDRTA is also an effective method to determine the fraction of ε-martensite, which is non-magnetic and has a hexagonal close-packed (hcp) structure. Since the hcp phase tends to develop a sharp texture, the conventional X-ray diffraction method without care of texture underestimated its volume fraction. Hence, the simultaneous evaluation of volume fraction and texture by NDRTA is the optimum method to determine the fraction of ε-martensite.
