A New Heat Treatment Cycle Design for High Wear Resistant in PM Steels

Abstract

In this study, 1.5% by weight of natural graphite powders were added to Atomet 1001 pure iron powders and unalloyed high carbon powder metallurgy steel specimens were obtained. After the mixture was uniaxial pressed at room temper-ature and 700 Mpa pressing pressure, it was sintered in Ar protected atmosphere controlled oven at 1150 ° C for 20 minutes. The densities of the specimens before and after sintering were measured using precision scales and electronic calipers and presented graphically. After sintering, microstructure specimens containing primary cementite and typical dense perlite colonies were produced. The sintered specimens having primary cementite plus lamellar pearlitic structures were fully quenched from 950 °C temperature and then over-tempered at 705 °C temperature for 60 minutes to produce spherical-fine cementite particles in the ferritic matrix. After by this treatment, these specimens annealed at 735 °C temperature for 3 minutes were austempered at 300 °C salt bath for a period of 1 to 5 hours. After the heat treatment, dry sliding wear tests of specimens were carried out under 10N constant load and 500-1500m wear distance. At the end of the dry sliding wear test, the weight losses of the specimens were measured and it was determined that the dry sliding wear resistance increased with increasing austempering time after spheroidization annealing.

Keywords

• austempering
• spheroidization
• powder metallurgy steel
• microstructure