MICROSTRUCTURE AND BARKHAUSEN JUMPS IN AN NI-CR EUTECTOID STEEL

The decomposition of austenite following the initial rapid formation of bainitic ferrite in a eutectoid steel containing nominally 1 wt\% Ni and 1 wt\% Cr isothermally transformed in the bainitic region of the time-temperature transformation diagram has been studied. The microstructure and kinetics were studied using both optical and electron microscopy. Also, the mean potential difference V(B) and the frequency F(B) of Barkhausen jumps were measured for various bainitic transformation products. Lower bainite with fine carbides shows the higher values of F(B) and V(B). The formation of upper bainite with coarser carbides leads to a considerable decrease of F(B) and V(B), while in the region of upper bainite and spiky pearlite F(B) and V(B) increase slightly. The relative amount of the eddy currents depends on the transformation products.