The progress of the martensite (α') to austenite (γ) phase transformation has been thoroughly investigated at different temperatures during the continuous heating of a cold-rolled precipitation hardening metastable stainless steel at a heating rate of 0.1 K/s. Heat treated samples have been characterized using different experimental complementary techniques: highresolution dilatometry, magnetization and thermoelectric power (TEP) measurements, microhardness Vickers testing, optical/scanning electron microscopy and tensile testing. The two-step transformation behavior observed is thought to be related to the presence of a pronounced chemical banding in the initial microstructure. This banding has been characterized using electron probe microanalysis (EPMA). Unexpectedly, dilatometry measurements seem unable to locate the end of the transformation accurately, as this technique does not detect the second step of this transformation (last 20 % of it). It is shown that once the starting (A S) and finishing (A F) transformation temperatures have been estimated by magnetization measurements, the evolution of the volume fractions of austenite and martensite can be evaluated by TEP or micro-hardness measurement quite reliably as compared to magnetization measurements. The mechanical response of the material after being heated to temperatures close to A S , A F and (A F-A S)/2 is also discussed.