Microstructure–hardness relationship in quenched and partitioned medium-carbon and high-carbon steels containing silicon

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 498; no. 1; pp. 442 - 456
• Main Authors: Nayak, S.S., Anumolu, R., Misra, R.D.K., Kim, K.H., Lee, D.L.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 20.12.2008; Elsevier
• Subjects: Applied sciences; Exact sciences and technology; Hardening. Tempering; Hardness; Heat treatment; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Production techniques; Quenching and partitioning; Retained austenite; Silicon; Transition carbide; Retained austenite; Silicon; Quenching and partitioning; Hardness; Transition carbide; High carbon steel; Phase composition; Medium carbon steel; Quenching; Alloy steel; Precipitation; Spheroidizing; Property structure relationship; Microstructure
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2008.08.028

We describe here the effects of quenching and partitioning (Q&P) process on the evolution of microstructure and consequent changes in hardness in a set of medium-carbon and high-carbon steels containing varying percentage of chromium, manganese, and silicon, with the aim to advance our understanding of Q&P process. The study suggests that in medium-carbon steels, higher partitioning of carbon from martensite to retained austenite and stabilization of austenite occurs when martensite has a higher supersaturation of carbon after quenching, which is obtained at low quench temperature. Another important aspect that emerges from the study is that the transition ( ɛ) carbide decreases hardness and its formation is promoted in medium-carbon steels with higher silicon-content such that the precipitation occurs at lower temperature of 250 °C. However, in contrast to medium-carbon steels, the high chromium content in high-carbon steels has a negative impact on the Q&P process because of the formation of large cementite during the spheroidizing treatment that reduces the ability of austenite to be enriched with carbon. The decrease in hardness in high-carbon steels during partitioning is a cumulative effect of austenite stabilization, softening of martensite, and decrease in carbon supersaturation of martensite.