Martempering of high carbon powder metal steels and investigation of wear behavior

Powder metallurgy applications are one of the widely used production methods in which engineering parts are produced. These applications provide high quality production of parts with complex geometry. Therefore, it is necessary to investigate the mechanical properties and microstructures of materials produced by powder metallurgy. In this study, the effects of different heat treatments applied to specimens produced from high carbon powder metal steel on the microstructure and mechanical properties of the samples are investigated. For this purpose, the specimens are produced using pure iron powder and graphite powder as a source of carbon. 1.5% by weight of natural graphite powder are mixed to ATOMET 1001 pure iron powder produced by water atomization method, and 0.5% by weight of powder Zn stearate as a lubricant. The mixture powders are pressed by applying uniaxial pressure of 700 MPa, and then sintered in an argon gas environment for 20 minutes at 1200 ˚C. Sintered specimens are austenitized at 950 ˚C for 4 minutes, after this process, which each specimen is held at different periods in the neutral salt baths with temperatures of 210 ˚C, 350 ˚C and 400 ˚C. After that, the martempering heat treatment is applied by quenching with specimens. Microstructure and mechanical properties of the high carbon powder metal steel produced by applying martempering process are studied. Micro-hardness measurements and phase transformations of the heat-treated specimens are examined. However, the transformation time of martensitic structure formed as a result of heat treatment applied to high carbon powder metal steels into bainite phase is investigated. The results of the study are analyzed based on microstructure characterization studies and hardness tests involving optical and scanning electron microscope (SEM) images. Also, X-Ray diffraction analyzes (XRD) are performed to determine the chemical composition. Dry sliding wear tests are carried out under 10 N load and 500 m-1000 m sliding distance to evaluate the mechanical strength of the specimens in ambient air at room temperature. After the wear test, the wear surfaces of the specimens are examined and their wear resistance is evaluated. As a result of the studies, the transformation time of high carbon powder metal steels from martensite phase to bainite phase is obtained according to the Time-Temperature-Transformation diagram. It is determined that the most wear-resistant specimen is the one with the least salt bath temperature.