Effects Of Alloying Elements On Microstructure And Mechanical Properties Of Steel Bonded Carbide

Steel bonded carbide, a brand new engineering material, is widely used in many national economic fields for excellent properties such as high hardness, high wear resistance, good toughness, machinability and heat-treatability. In this paper, microstructure evolution of steel bonded carbide, mainly focused on the influences of hard phase composition and alloying elements Mo, Cr, C, was investigated by Scanning Electron Microscope(SEM), Energy Dispersive Spectrometer(EDS), X-Ray Diffraction(XRD) and Optical Microscope(OM), respectively. Also, macrohardness test, transverse rupture strength(TRS) test and impact toughness test were carried out to explore the processes improving the toughness of steel bonded carbide.In this paper, the steel bonded carbide was fabricated by means of the vacuum liquid phase sintering technique. On the one hand, different pressing pressure of the green body and sintering temperature were applied to gain the selective preparation process of steel bonded carbide. On the other hand, changing the contents of Mo, Cr, C to find out the effects of which on the microstructure and the mechanical properties of the steel bonded carbide. Furthermore, the relationship among hard phase, microstructure and mechanical properties was also studied by adjusting the added proportions of the hard phase WC and TiC.The results can be concluded as follows: Firstly, the most appropriate pressing pressure is considered as around 200 MPa, and delaminate defects appeared in the green bodies for overly pressed. Secondly, the sintering temperature should be controlled properly in order to obtain a good density as well as fine and uniform grain size; Thirdly, favorable comprehensive mechanical properties with a HRC hardness of 70, TRS of 1270 MPa and toughness of 10J/cm3 could be obtained in WC steel bonded carbide, when the Cr content reached 10%. However, the strength and toughness would significantly decrease if the Cr content is excessively high. Then, in WC-TiC steel bonded carbide, a relatively high hardness value of 91 HRA and a best TRS of 2430 MPa were achieved when the molar ratio σ of TiC and WC is between 0.8 and 1.0. Too much or too less TiC is harmful to the performance of the alloy. Moreover, it is noteworthy that a slight addition of Mo about 1% can obviously strengthen the material due to the improving wetability of TiC in ferrous base binder phase. But the additive amount of Mo should not be too much, otherwise the TRS of the alloy would dramatically decrease. In addition, when the molar ratio of C and W adding Ti is 1.1, a fine and uniform microstructure was obtained, meanwhile the(W,Ti)C solid solutions were preferably sintered as well. As a result, a maximum TRS of 2570 MPa could be achieved. By changing the preparation processes and alloying composition, strength and toughness of the steel bonded carbide were better than most domestic typical alloys.