Influence of Preforging Treatments on Mechanical Properties of Two Low-Alloy Powder-Forged Steels

Abstract

This paper gives an indication of the influence of inclusion content on the mechanical properties of two powder-forged low-alloy steels. The powders used were Höganäs ATST–D (0·3–0·4Mn–0·1–0·25Cr–0·2–0·3Ni–0·25–0·35Mo) and Höganäs ATST–A (0·25–0·35Mn–0·1 max. Cr–1·8–2·2Ni–0·45–0·55Mo). The inclusion content and distribution were modified by subjecting the powder preforms to different preforging treatments. Different matrices were produced for the ATST–D material by tempering at different temperatures after quench-hardening in oil. A number of fatigue samples were nitrocarburized to examine the effect of surface treatment on fatigue behaviour. An improvement in the fatigue endurance limit of 14% was achieved in the ATST–D material following a 60% reduction in the percentage area of inclusions. In comparison, nitrocarburizing improved the endurance limit of the higher inclusion content material by 43%. A combination of reduced inclusion content and nitrocarburizing produced an increase of 50% in endurance limit. Although the monotonie tensile strength of the ATST–A material was much higher than that of the ATST–D, the fatigue endurance limit was only slightly greater and was only marginally improved by nitrocarburizing. PM/0170