Effect Of Chromium And Tungsten On The Microstructure And Properties Of Hardfacing Metal On Medium-High Carbon Steel

Medium-high carbon steel workpieces, such as hot rollers, are key ones used in metallurgy industry. After servicing for periods of time, they fail because of thermal fatigue and excess wear. However, the failed workpieces can be repaired in size and properties by hardfacing method. Currently, the development of material used in medium-high carbon steel workpieces has atendancy to alloying, such as with high Cr and W content. Whereas, the research on related hardfacing metal have not been reported. Therefore, the aim of the present work is to investigate the effect of the Cr and W content on the microstructure and properties of hardfacing material.The microstructure of hardfacing metals was observed by optical microscopy (OM) and field emission scanning electron microscopy (SEM). Macro and micro hardnesses of the hardfacing metal were determined by using of Rockwell hardness tester and nano-indenter hardness tester respectively. The type of carbide in the hardfacing metal carbide was identified by X-ray diffraction analysis. The fracture morphology and compositions of inclusions of hardfacing metal were observed and identified using scanning electron microscopy and X-ray spectrometer respectively. Moreover, the types and compositions of the equilibrium phases of the hardfacing metal with different contents of C, Cr and W at different temperatures were calculated by the Thermal-Calc software.The results show that, with the increasing of the ferrochrome, the microstructures of the hardfacing metals are widmanstatten, strip ferrite, lath martensite and plate martensite respectively. The white network microstructure after hardfacing cooled in air is highalloyed martensite formed along the grain boundary. With the increasing of the ferrochrome, the number of high-alloy martensite in the hardfacing metal gradually increases at the grain boundaries.With the increasing of the ferrotungsten, the microstructures of hardfacing metals are lath martensite, flake martensite, the mixture of bainite and pearlite, and pearlite, respectively. The hardness of hardfacing metals with different ferrotungsten additions is firstly increased, and then decreased. After tempering hardfacing metal at 450℃, secondary hardening in the hardfacing metal occurs and the maximal hardness is about 51HRC.Carbide content at phase diagrams with different Cr content in mass are calculated. The results show that, with the increasing of Cr content, the M7C3 carbide is increased gradually, while the M3C carbide is firstly increased and then decreased. For different W contents, phase diagrams and the the mass fraction of MC at different temperature are calculated. The results show that, with the increaseing of W content, the mass fraction of the precipitated MC carbide is increased and its solidification temperature is increased too significantly. Their laws are consistent with X-ray results of hardfacing metal.