The Effect of Post Sintering Cooling Rate on Microstucture and Machinability of a PM Sinter Hardened Steel

摘要

The effect of post sintering cooling rate on the microstructure of a PM sintered steel was investigated by assigning three different cooling conditions to the same alloy. The various microstructures produced by these different cooling conditions were evaluated and quantitatively analyzed for volume fraction of bainite, martensite, and retained austenite. Machinability tests were also performed on samples from all three cooling conditions to determine how these microstructures affected tool life. This was done using a turning operation and the tool life machinability criteria. It was found that the volume fraction of martensite was the most important factor in determining machinability. Lower martensite contents produced much higher machinability and vice versa. Lower martensite contents also resulted in decreased hardness. Bainite was found to be a much more favorable phase from a machinability standpoint. It was also observed that the trajectory of the chips during the turning operation was an indicator of the condition of the tool edge.