Influência da taxa resfriamento/aquecimento no tratamento criogênico do aço AISI M2: propriedades mecânicas tribológicas e análise microestrutural.

Abstract

This study investigates the influence of the cryogenic treatment (DCT) cooling/heating rate on the mechanical and tribological properties of AISI M2 steel. The samples were austenitized at 1200 °C and cooled in oil, subjected to cryogenic treatment for 24 hours, varying the heating/cooling rate (0.5 °C/min, 1.67 °C/min; direct immersion) and, finally, tempered twice at 550 °C for 2 hours each. A group of samples without application of cryogenic treatment (CT) was also analyzed, considering the same parameters of conventional heat treatments (CHT) (austenitization, quenching and tempering). HRC hardness, HV1 microhardness, charpy impact toughness and wear resistance were investigated and related to the microstructure of the material accessed via Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Raman Microscopy and x-ray diffraction characterization (XRD). The results demonstrate the importance of the DCT cooling/heating rate on the properties of AISI M2 steel. The rate of 0.5 °C/min resulted in the highest impact toughness and wear resistance among the tested samples, while direct cooling in liquid was harmful. Samples submitted to DCT, with controlled cooling/heating rates, showed improvement in all observed parameters, in relation to samples without DCT. The behavior is associated with the retained austenite content being reduced by cryogenic treatment. The DCT modifies the behavior of secondary carbide precipitation, refining them and increasing their quantity and population density. This leads to a more uniform precipitation.