New Type Of Surfacing Electrode And Study On The Structure And Properties Of Hardfacing Layer

In this paper, on base of the principle of alloy design and a large number of tests, a new type of surfacing electrode has been designed and developed successfully. This type of electrode uses ZX7-630 direct current inverse electic welding machine as power and has the advantage of low dilution rate and easy manufacture. So it is particularly suitable to experiment carried out in the laboratory scale with different alloy powder or surface hardening of components of small batch production.The metallurgical process of surfacing has been discussed, which is a course of quick and non-equilibrium freezing. With the shift of welding arc, melting and freezing occur simultaneously, and the process of surface metallurgy can be regarded as a phasing and continuous reaction process. The freezing mechanics, characteristic and influence on structure of melting pool have been analyzed in full.Making use of optical microscope, SEM, electron probe, X-ray diffraction etc., morphology and component features have been studied in detail. Transverse section of the hardfacing layer consists of heat affected zone, decarburization layer, cellular branch crystal layer and equiaxed crystal layer. Chemical composition changes from hypoeutectic to hypereutectic with eutectic as the transition composition. The first precipitates in the hypoeutectic and the decarburization layer are a-Fe dissolved with large amount of Cr. Both eutectic and hypereutectic structures are composed of Fe3C or M7C3 and Fe-Cr solid solution. When the welding speed increases, the dilution gets lower, and the main spindle of the grain changed to perpendicular to the weld fusion line.Some defects appeared in the coating. Segregation, gas cavity and crack have been involved in this paper. Their reasons and mechanics have been discussed in detail.