Effect of Cooling Rate after Solution Heating on the Mechanical Properties and Age Hardening Properties of 21-12N Steel

Abstract

The effects of various cooling procedures from solution temperature, i. e. water quenching, air cooling and furnace cooling, etc., on the mechanical properties of 21-12N steel before and after ageing were investigated.
It was found that the tensile strength and 0.2% proof stress of specimens before aging were not affected by the cooling rate, whereas the maximum hardness was obtained after water quenching. The ductility and the type of fractures after solution treatment were also affected by the shape of grain boundaries as well as by the amount of grain boundary precipitates formed during cooling at various rates.
It was also found that the age-hardening characteristics changed appreciably with cooling procedure. According to the transmission electron microscopy the remarkable hardening during high-temperature aging after water-quenching was attributed to the fact that the high dislocation density resulted in large amount of fine precipitates of M₂₃C₆ which are formed mostly on dislocations.