Research On Submerged-arc And Self-shielded Open-arc Hardfacing High Chromium Flux-cored Wire

High chromium alloys without expensive elements such as Nb, Mo, and Ni have been widely used to manufacture or remanufacture wear-resisting coatings of the advanced machine parts not only for the economy, but also due to containing hard phase particle such as M₇C₃ with high microhardness, which helps them acquire excellent abrasion resistance. However, in China, high chromium alloys are mainly provided with cast ones and the total material cost is still higher comparing to the high chromium hardfacing alloys deposited on low carbon steel Q235 substrates, whose cost is lower and can be easily repaired even if they are out of work. In view of the situation, high chromium alloys were deposited by the methods of flux-cored wire submerged-arc welding and self-shielded open-arc welding. Their microstructure and phase compositions as well as wear resistance and wear mechanism were respectively researched by optimizing alloy systems, adjusting the welding process parameters together with optical microscopy (OM), scanning electron microscope (SEM), X-ray diffractometer (XRD) and energy dispersive spectrometer (EDS).Firstly, the effects of hardfacing velocityυ, alloying element such as V and C on the microstructure and abrasion resistance of Fe-Cr-C-V-Ti hardfacing alloys deposited by flux-cored wire submerged-arc welding were studied. The experimental results show that the hardfacing velocityυhas a significant effect on the microstructure and abrasion resistance. Asυwas 30 cm/min which suggests low heat input of weld beads, the grains were apparently refined but the distributing of alloy composition was uniform. When hardfacing velocity was reduced to 28.3 cm/min, primary M₇C₃ grains homogeneously and directionally distributed, and it improved the abrasion resistance. As the hardfacing velocity was continuously reduced, the volume fraction of cellarγ-Fe matrix increased but the amount of carbides such as primary M₇C₃ phase decreased due to the solutionizing effect of excess alloying elements such as Cr, V, which made abrasion resistance decreased. The traditional direct proportional relation between experimental loads and wear mass losses can't be met due to excessively inhomogenous distribution of microstructure and chemical composition. Proper V and C contents can refine M₇C₃-type carbide for promoting its nucleation rate to improve the abrasion resistance.Then, the effects of such alloy elements as Si, Ti, B, C on the processing properties of flux-cored wires and the properties of high chromium alloys hardfaced by self-shielded open-arc welding were researched. It shows that appropriate Si and B contents have improved the shapes of weld beads and reduced the splattering. With the increase of Ti content, the reducibility of molten pool is so strong as to decrease the self-generated shielded gases greatly and appear easily no oxided carbon powders as well as to lead to the increase of remained slag adhered on weld beads. Excessive Si can promote the aggregation of primary carbides, which improves the abrasion resistance in some degree but the continuous decrease of the toughness due to Si makes against the improving of abrasion resistance. In the same words, excessive Ti content can make grain refinement disappeared and lead to the aggregation and coarsening of primary M₇C₃ grains. The volume fraction and the size of primary M₇C₃ and primary M₂B have increased but the crack resistance has decreased with C content.