Effect of cooling rates on sinter-hardened steels

Purpose: Purpose of this paper was to evaluate the differences between rapid, medium and low cooling rates on three systems and also to study cooling mechanism of known materials. Design/methodology/approach: Two different systems have been tested in order to investigate how the cooling rates influence on the microstructure and properties. The powders used in the present invention are pre-alloyed iron-base powders containing low amounts of chromium and molybdenum. The amount of graphite that was admixed to the iron-base powder was 0.6% and lubricant 0.75%. The amount of graphite which is mixed with the iron-base powder is 0.6% and lubricant is 0.75%. Green compact were sintered in a vacuum furnace at 1120şC for 30 minutes in vacuum atmosphere and rapidly cooled in nitrogen with three different rates: rapid cooling (7şC/s) and medium cooling (1.6şC/s), slow cooling (0.3şC/s). Next the samples were tempered in vacuum in the same furnace at 200şC for 60 minutes and then were cooled to room temperature in nitrogen, with the exception of slow cooling cycle. Findings: The effect of cooling and applied sintering were studied in terms of mechanical properties, hardness and wear resistance. The results achieved after the investigation sinter-hardened steels with low carbon content proved that applied process of sintering and different cooling rates brought expected outcome. Practical implications: According to the powders characteristic, the applied rapid and medium cooling rate seems to be a good compromise for mechanical properties and microstructure, nevertheless further tests should be carried out in order to examine different cooling rates. Originality/value: The effect of cooling rates on mechanical properties of pre-alloyed Astaloy CrL and CrM powders was investigated.