Refinement Of Nitrogen On Primary M₇C₃ Carbides In Hypereutectic Fe-Cr-C-Ti Hardfacing Alloy

With the rapid development of industrial modernization,more and more attention has been paid to the service life of mechanical components serving under harsh conditions,and higher requirements have been put on the surface performance of the components.Hardfacing technology is one of the key technologies in surface engineering,which can make the surface of the mechanical components remanufactured and strengthened.Hardfacing technology can not only recover the shape and size of failure workpieces,but also enhance the surface performance of the workpieces to obtain more excellent wear resistance,heat resistance and corrosion resistance.With the rapid development of the hardfacing technology,the hardfacing materials applied for different fields have also developed rapidly.In addition,the wear-resistant components made by flux cored wire have been widely applied in modern industrial production with high deposition rate,good economy and reliability.The hypereutectic Fe-Cr-C-Ti hardfacing alloys were taken in this work.By optimizing the chemical composition of the self-shield flux cored wire of Fe-Cr-C-Ti hardfacing alloys,the hypereutectic Fe-Cr-C-Ti hardfacing alloys with different N content were prepared by hardfacing technology.The content of each element in hardfacing alloy were tested by X ray fluorescence spectrometer and carbon sulfur analyzer.The phases of the hardfacing alloys precipitated in solidification process were predicted by Thermo-Calc software.The microstructure of the hardfacing alloys with different composition were observed and analyzed by optical microscope?OM?,scanning electron microscope?SEM?,X-ray diffraction?XRD?and transmission electron microscope?TEM?and so on.The hardness and wear resistance of the hardfcing alloys were respectively tested by rockwell hardness tester and abrasive belt friction and wear tester.On this basis,the first principles method was used to calculate the interfacial behavior between the primary M₇C₃ carbide in the hardfacing alloy and the precipitated phase TiN in the solidification process,in order to analyze the refinement mechanism of the primary M₇C₃ carbide with TiN.The phase in the hypereutectic Fe-Cr-C-Ti hardfacing alloy with N content consists of primary M₇C₃ carbides,?-Fe and Ti?C,N?.During the solidification process,the Ti?C,N?phase precipitates earlier than the primary M₇C₃ carbide.The primary M₇C₃ carbides in the hardfacing alloy microstructure are refined with increase of N content.By observing the microstructure of the hardfacing alloy,it can be found that the element N is distributed in the hardfacing alloy,mainly in the form of Ti?C,N?,and the Ti?C,N?is formed in the interior and edge position of the primary M₇C₃ carbide.The macrohardness of the hardfacing alloy is decreased slightly with increase of N content,while the wear resistance of the hardfacing alloy is increased with the increase of the N content.Therefore,the refinement of the primary M₇C₃ carbide is the main factor to enhance the wear resistance of the hardfacing alloy.The first-principles calculation showed that the bonding between TiN and M₇C₃carbide is complex mixure of covalent,metallic and ionic characters.The atomic layers of TiN surface configurations and the Fe₃Cr₄C₃ surface models are respectively nine and seventeen when building TiN/Fe₃Cr₄C₃ interface.By calculating the electronic structure and the bonding properties between different TiN?111?/Fe₃Cr₄C₃?0001?interface,it is found that the bonding between different atoms was stronger,and the interface exhibites good stability,which provides a theoretical basis for TiN to become the primary M₇C₃carbide nuclei.