Quenching Media Effects on Carbide Microstructure and Microhardness of Locally Manufactured AISI D2 Steel during tempering process

Abstract

Cold work tool steel is essential in manufacturing and suitable for many applications, including punching, forming, and cold rolling. This steel distinguished by a high carbon and chromium content and exhibits mechanical properties significantly influenced by heat treatment processes. It contains higher hard phases like carbides and plate martensite than other steel alloys, posing a continual challenge in balancing strength and toughness to prevent immediate fracture. The primary problems of hardening treatment of this steel include the risk of crack distortion and formation in various media. In this study, the effect of different quenching media on the microstructural evaluation and microhardness of locally manufactured AISI D2 tool steel was investigated to possibility improving microstructure and mechanical properties, where the AISI D2 tool steel was austenitized at a temperature of 900°C, quenched in different media (water and oil), and finally tempered. Microstructural analysis was conducted using optical microscopy along with quantitative image assessment through ImageJ software, and Vickers microhardness was carried out. The results showed that oil-quenched specimens exhibited coarser carbides and higher retained austenite content, whereas water-quenched specimens showed finer and more uniformly distributed carbides. Quantitative image analysis confirmed significant variation in carbide size and area fraction depending on the quenching medium. The measured Vickers microhardness values were 197.9, 248.2, and 225.9 HV for the locally manufactured base steel and for the water- and oil-quenched samples, respectively. Statistical analysis indicated a weak positive correlation between carbide distribution and microhardness (R = 0.213, 0.123, 0.169). These findings emphasize the importance of optimizing heat treatment in mechanical applications.