Microstructure of Tool Steel X37CrMoV5 after Cryogenic Treatment and its Effect on Wear Resistance

Abstract

<p>A deep cryogenic heat treatment (DCT) was applied to X37CrMoV5 steel, which included soaking at -160°C for 12 and 30 hours followed by tempering at 180°C. Microstructures were compared with those after conventional heat treatment (HT). Microstructures with conspicuous dendritic segregation were observed in all specimens. After HT coarser and finer tempered martensite occurred in depleted and enriched areas of carbon and alloying elements respectively. Coarse molybdenum and vanadium carbides, fine secondary Fe2MoC carbides and retained austenite were identified after HT. Deep freezing resulted in microstructure refinement, transformation of retained austenite into twinned martensite, spinodal decomposition of martensite plates and precipitation of semicoherent h-carbide. The mechanism of h-carbide precipitation was discussed. Wear rate was measured using pin-on-disc test. The best results were obtained after DCT with cryosoaking for 12 hours.</p>