Interrelation of Steel Composition, Hardening Route, and Tempering Response of Medium Carbon Low-Alloy Steels

摘要

Four medium carbon and low-alloy steels were hardened through oil and forced air cooling. Tempering was then performed in the temperature range 250-600 A degrees C. The martensite content increased with an increased hardenability and/or the rate of cooling. Tempering at T > M (s) caused a gradual decline in both hardness and strength and an improvement in the Charpy V-notch impact toughness. The low-alloy steels underwent tempered martensite embrittlement (as a result of the formation of carbides at the martensite interlaths and prior austenite grain boundaries) and enhancement of phosphorus segregation (particularly in the presence of Ni). Higher hardenability steels were found to be better hardened via the more recent forced air quenching rather than the conventional oil quenching. In this work, a modest, novel attempt is presented to empirically correlate the impact toughness with the hardness measurements to enable future prediction of impact toughness from hardness measurements.