Influence of Cryoprocessing on Mechanism of Carbide Development in Cobalt-Bearing High-Speed Steel (M35)

Cryogenic treatment has been used commonly to high-speed tool steels to enhance the wear resistance of the materials. In the current research study, specimens of complex alloyed high-speed tool steel (M35) were hardened at 1473 K (1200 A degrees C), triple tempered at 673 K (400 A degrees C) and then cryogenically treated at 88 K (-185 A degrees C) for varying lengths of period starting from 16 to 48 hours of cryosoaking followed by soft tempering at 373 K (100 A degrees C). These treated specimens were studied as a function of cryosoaking period for their electrical resistivity, residual compressive stress, and its correlation with carbide density was established. TEM analysis indicated carbide size 0.156 to 1 mu m, which confirms that the cryogenic treatment enhances the precipitation of finer carbides. Lower residual stresses in the higher carbide density regimes identified in 2D contour map were explained by the stress relaxation in the matrix through precipitation of incoherent carbides. (C) The Minerals, Metals & Materials Society and ASM International 2013