Investigation Of Plastic Properties Of Hotvar Hot-Work Tool Steel During Martensitic Transformation

This article presents the investigation of transformation plasticity (especially high permanent plasticity) of Uddeholm Hotvar hot-work tool steel (C = 0.55 %, Cr = 2.60 %, Mo = 2.30 %, V = 0.90 %, Si = 1.0 %, Mn = 0.80 %) that has high wear resistance and resistance to thermal fatigue. The steel is used for manufacturing of hot working tools, i.e., dies, punches and other deforming parts. The tests were performed during martensitic transformation of steel. For the investigation of steel transformation plasticity the specimens were austenized at 1050 degrees C, 1070 degrees C and 1090 degrees C and air quenched. The load that was generated 100 MPa bending stress (<= 10 % x(R-P0.2) of material at the temperature of the test) was applied on specimens got out from the heating furnace and placed in the bending device. The start of bending was at 550 degrees C - 530 degrees C temperature. Plastic deflection was observed through all cooling process till room temperature and was measured with 0.01 mm accuracy. It was determined that bending of specimen in the temperature range of similar to 220 degrees C to similar to 30 degrees C gave the deflection 5 - 7 times higher than after bending in 550 degrees C - 30 degrees C temperature range. The magnitude of deflection is related with austenitic-martensitic transformation and with phenomenon of transformation plasticity, as well.