In the present study, medium carbon low alloy (MCLA) steels like AISI 5140 (EN18) and AISI 4140 (EN19) are treated in different quenching media under solutionizing temperature of 855°C. Quenched in SAE 250 oil, polyethylene glycol (PEG) (10% and 30%), and water. The quenched samples are step-tempered at 575°C and at 220°C sequentially with 60 minute soaking time. BHN, YS, UTS and tensile toughness are determined for the untreated and heat-treated samples. It is found that there is an excellent correlation, with correlation coefficients of 0.97. The standard generalized equation for these two steels are established. Tensile toughness = 19000 + 12 BHN- 215 El. The study revealed that the PEG is better in terms of cost, fire-resistant and biodegradable. 30% polymer quenched samples result in better tensile toughness properties as compared to 10% polymer quenched samples.