Evaluation of As-Quenched Hardness of 1.2% Carbon Steels in Different Quenching Media

Abstract

The As-quenched hardness behaviour of 1.2% carbon steels in different quenching media was investigated. The hardness values were studied on two grades of high carbon steel materials, namely 1.2% carbon and low-alloy 1.2% carbon steels respectively. Specimens were prepared and given both spheroidizing and normalizing heat treatments before they were hardened. Hardening was done at both 800oC and 850oC and quenching was carried out in water, cold water, brine, cold brine and SAE engine oil. Then hardness measurements were carried out on the specimens in the pre-hardening and as-quenched conditions, results obtained showed that in the as-quenched condition, oil quenching resulted in partial hardening in both steels; the addition of 1.2% tungsten to the 1.2% carbon steel was not sufficient to cause full hardening. Full hardening was only attained when quenched in water or brine. Cold brine quenching produced maximum as-quenched hardness values in both steels; in conclusion, higher as-quenched hardness values were obtained for the case of normalized prehardening structure than the other case of spheroidized pre-hardening structure when quenched from 800oC, it is the reverse when they were quenched from 850oC. The two steels did not attain full hardening when quenched from 800oC or 850oC in SAE engine oil. Quenching in more severe media such as water and brine was found to result in adequate hardening, where hardness values of over 600VHN were obtained.