Evaluation of Quench Hardening in Steel from Three-Dimensional Magnetic Flux Vectors

抄録

Since austenite shows paramagnetic properties and ferrite and martensite do ferromagnetic ones, magnetic evaluation can be a good candidate for detecting phase transition. However, hence coercive force cannot distinguish ferrite from martensite under external magnetic field, magnetic measurement has not been used for quench hardening evaluation. By contrast, ferromagnetic specimens have inverse-magnetostriction properties, which can cause spontaneous magnetization under phase-transition stress during quenching process. Therefore, in this study, we have tried to develop a technique for quench hardening distribution analysis by sensing spontaneous magnetization caused from inverse-magnetostriction. From the results of the experiments, large spontaneous magnetizations were appeared in the specimen, which indicates partial martensite transformation in that area. However, residual magnetizations were observed in whole martensite or ferrite phase. Especially, high magnetic intensity was obtained in the area of multiple phases with residual austenite and martensite. The residual stress caused from the different molar volume between fcc austenite and bct martensite phase has an influence to the inverse magnetostriction phenomena emerging high spontaneous magnetization after quenching.