Inductive measurements of the stress assisted and strain induced martensite transformations of Sandvik maraging steel 1RK91 before, during and after metal forming

摘要

Measurements of transformation behaviour are very important to get a good knowledge of the material behaviour of metastable stainless steels during metal forming processes. A convenient way of measuring this kind of transformations is inductive measurement. This article describes a possible solution for this kind of measurements, together with the developed sensors and electronics. The first part of the article focuses on the electronics, calibration and the development of the sensors. The equipment is also used for multi sensor measurements. The second part of the article shows results of measurements on the Sandvik maraging steel 1RK91. The results are shown for three examples: ·strain induced transformation during tensile testing, · Stress assisted transformation. · Amount of strain induced transformations after cold rolling and the homogeneity of those transformations in relation with the coil length and width. A problem that occurs during inductive measurements is that more parameters than the martensite content have influence on the output of the signal. Elastic stresses, temperature and plastic deformation have also a big influence on the signal output. Some results of measurements are shown to demonstrate the influence together with a calibration method. The measuring device is fully automatic and connected to a computer to make sample logging possible during testing.