Application of Deep Cryogenic Treatment to Uncoated Tungsten Carbide Inserts in the Turning of AISI 304 Stainless Steel
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AS a complementary process to conventional heat treatment, cryogenic treatment is currently used to improve the mechanical properties of some materials.[1,2] Prior to 1937, the beneficial effects of cold treatment on tool performance were reported in early studies.[3] In cryogenic treatment, a material is gradually cooled to a cryogenic temperature [in general, 77 K ( 196 °C)] at a constant cooling rate, held for a given period (in general, for 24 hours) at this temperature and then gradually returned to room temperature at a constant heating rate.[4,5] Thus, the wear resistance of the material is improved by the transformation of retained austenite into martensite and the subsequent formation of fine carbide particles in new nucleation sites in the microstructure.[6–8] Cryogenic treatment is generally divided into two subclasses: shallow cryogenic treatment (SCT) and deep cryogenic treatment (DCT). In SCT, the materials are cooled to temperatures in the range of 223 K to 173 K ( 50 °C to 100 °C), whereas in DCT, they are treated at temperatures ranging from 148 K to 77 K ( 125 °C to 196 °C).[4,6,9] Nowadays, cryogenic treatment is applied to many workpiece and tool materials because of such beneficial outcomes as the
NURSEL ALTAN O¨ZBEK, Assistant Professor, is with the Cumayeri Vocational School of Higher Education, Du¨zce University, _ ¸ lEK, Professor, is with the 81700 Du¨zce, Turkey, ADEM C¸IC Department of Mechanical Engineering, Faculty of Engineering and Natural Sciences, Yıldırım Beyazıt University, 06050 Ankara, Turkey. _ Professor, Contact e-mail: [email protected] MAHMUT GU¨LESIN, is with the Department of Manufacturing Engineering, Faculty of Technology, Gazi University, 06500 Ankara, Turkey, ONUR O¨ZBEK, Lecturer, is with the Gu¨mu¨¸sova Vocational School of Higher Education, Du¨zce University, 81850 Du¨zce, Turkey. Manuscript submitted July 7, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
enhancement of tool life, relief of residual stresses, and improvement of mechanical properties.[1,10–12] Tungsten carbide is one of the materials commonly used in the industrial manufacturing of cutting tools. Stewart[13] declared that cryogenic treatment led to increases in the wear resistance of tungsten carbide tools during the turning of medium-density fiberboard. The author reported that cryogenic treatment appeared to have an effect on the cobalt binder by changing the phase or crystal structure so that more cobalt binder was retained during cutting. Bryson[14] attributed the wear resistance, and hence the increase in tool life, of carbide tools to the improvement in the holding strength of the binder after cryogenic treatment. He believed that cryogenic treatment also acted to relieve the stresses introduced during the sintering process by which carbide tools are produced. In their study, Gill et al.[15] proved that cryogenically treated tungsten carbide inserts performed better in both interrupted machining mode and continuous machining mode under both dry and wet cutting conditions. The extent of the advan
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