High Carbon Steel Microcracking Control During Hardening

Abstract

When high carbon, low alloy steels, such as AISI 52100, are conventionally quenched or marquenched from an austenitizing temperature that dissolves all of the carbon in the austenite, many of the martensite crystals in the quenched microstructure are fractured or microcracked. This paper describes a process in which a limited amount of martensite is formed by quenching the steel to a temperature between the Ms temperature and conventional quench temperatures. This martensite is then tempered for a short time to toughen it before again cooling the steel to complete the formation of martensite from austenite. When the limited amount of martensite formed, and intermediately tempered, and the martensite formed on cooling from the intermediate tempering temperature are appropriately balanced by the processing, micro-cracking is essentially avoided. The process can be done in equipment and with procedures commonly used commercially.