Studies on Martensite Transformation in a Metastable Austenitic Cr-Mn Stainless Steel

Abstract

The influences of the heating rate and annealing duration on martensite formation and its reversion to austenite have been investigated in a 60% cold-rolled metastable high-manganese austenitic Type 204Cu stainless steel. A Gleeble 3800 thermomechanical simulator was used for dilatometric measurements. Cold-rolled steel pieces were either heated up to 1000 °C at various heating rates between 5 °C/s and 150 °C/s followed by quenching to room temperature, or heated and held at temperatures in the range of 450 620 °C for different durations between 0.1 600 s. In heating experiments, dilatation curves revealed an expansion of a specimen starting around 550 °C followed by contraction, both processes depending on the heating rate. These dimensional changes could be correlated to the formation and reversion of a ferromagnetic phase, α-martensite. Some martensite was also formed during isothermal holding in connection with tempering of the pre-existing α-martensite before the following reversion, as established by magnetic measurements. Tempering of martensite was revealed by microhardness behaviour, X-ray diffraction analysis and transmission electron microscopy.

Demonstrating the Effect of Precipitation on the Mechanical Stability of Fine-Grained Austenite in Reversion-Treated 301LN Stainless Steel

“…A high heating rate of 200 • C/s and cooling rate of 35 • C/s was used. The effect of a high heating rate on the reversion mechanism in metastable cold-rolled austenitic steels has been investigated, e.g., [26,27]. It is also known that ultrahigh heating rates can result in grain size refinement and improved formability in low carbon steels, see e.g., [28].…”