Study On Open-arc Self-shielded Hardfacing Flux-cored Wire Of Coal Grinding Roller

Coal grinding roller is one of important equipment to fabricate hardfacing layers with good abrasion resistance. Flux-cored wire arc welding has become an economic and reliable method to improve the service life of the milling. Based on the research of iron based high Geming arc surfacing alloy,this paper try to develope Flux-cored wire arc welding alloy so as to meet the practical applications of the coal grinding roller through adjusting the composition of flux cored wire.The hardfacing alloy layers is fabricated by self shielded open arc welding on Q235 A steel. The microstructure and property are investigated by optical microscope, scanning electron microscope, X-ray diffraction,macro-hardness testing and wet sand abrasive wear testing.Firstly, the effect of carbon content on microstructure and property of hypereutectic high Geming arc surfacing alloy organization and property of different content is studied.The results show that, the microstructure of the hardfacing alloy mainly is primary carbides M7C3 and eutectic structure. With the increasing of carbon content in the alloy, the content and size of primary carbides of M7C3 increased, The volume fraction of carbides increased and while the volume fraction of substrate reduced, resulting in toughness of the alloy significantly declining. When the carbon content is higher, the micro exfoliation has become the main reason for the decrease of wear resistance of high chromium hardfacing alloy, the toughness of alloy must be noticed when wear resistance improved.Secondly, respectively adding different content of ferroboron, ferrovanadium, ferrotitanium, ferrotungsten and ferroniobium into flux-cored wire,the effect of alloy element boron, tungsten, vanadium, titanium and niobium on the microstructure and mechanical properties of high chromium bright arc surfacing welding alloy is studied. Results show that the boron can make the eutectic point shift to the left, and promote the formation of primary M7C3 carbide, and generate high hardness boride or carbon boron compounds in the organization, significantly improve the hardness surfacing welding alloy, but too much of boron alloy increased brittleness and wear resistance decrease; Vanadium have a reunion effect on the carbon atom and can change the melt carbon concentration distribution, increase the volume fraction of primary M7C3 phase, inhibit the generation of brittle tissue and a moderate amount of V can improve the wear resistance of open-arc surfacing welding alloy significantly; Tungsten can make the eutectic point of high chromium alloy shift to the left and increase primary M7C3 carbide volume fraction, reduce the number of eutectic carbides, austenite in the matrix was increased and beneficial to the improvement of the alloy toughness; The TiC phase separate out prior of melt with the addition of titanic, TiC acts as the heterogeneous nucleation core of primary M7C3 and γ- Fe and improve their nucleation rate, refining primary phase and matrix organization, beneficial to the improvement of the alloy ductile, but too much titanium will make the remaining melt lean carbon, then inhibit the generation of primary M7C3;High chromium alloy of niobium all exist in the form of NbC and distribution are diffuse. It can refine the grain, increase metal toughness and beneficial to improve the surfacing alloy hardness and abrasion resistance.