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Evolution of microstructure and hardness in 42CrMo4 steel during quenching under the different cooling conditions were investigated. Mineral oil, polymer solution and water were selected as quenchants to provide different cooling conditions. Quenching experiments were also conducted under magnetic stirring and ultrasonic agitation of polymer solution. Cooling conditions during quenching had significant effect on phase transformation and hardness of 42CrMo4 steel. The quench hardened samples show martensite microstructure along with other micro-constituents. Needle like/acicular ferrite was observed with water quenching due to diffusion less transformation. Sample quenched under ultrasonic agitated medium showed formation of network of carbides. Higher hardness values were obtained with water quenching and ultrasonic agitated polymer quenching.
Ramesh et al. (Fri,) studied this question.