Argon Arc Surfacing With Flux-cored Wires For New Type Of Casting High Cr Hot-Working Die Steels

With the improvement of automation degree in manufacturing technology,moulds as the processing tools of high-speed forging machines were developed at arapid speed because few or none cutting processing can be achieved by using them.There are a series of advantages to process components by moulds such as highproduction efficiency, good quality, raw materials used economically and low cost.That makes it used widely. And the study on mould materials and manufacturingprocedures has become a hotspot in the field of materials processing. Themanufacturing technology of casting hot-working-die steels according to theresearch results of the national "863" project is casting raw castings by thenear-net-shape technique, heat treatment, finish machining, hardened and ductileheat treatment and polishing. Its purpose is to take place of the laggard technologyof mould processing, i.e., alloyed steel billet, forging, heat-treatment, coarsemachining, hardened and ductile heat-treatment, fine machining. The newtechnology has many advantages such as longer service life of moulds, simplerworking procedures, higher efficiency of raw materials in use, shorter producingperiod, easier rebirth of disused dies, lower cost and less resource dissipation andso forth. This technology is the up-to-date representation in the field of diemanufacturing and will bring about a great advance in the development ofhot-working dies in automobiles and machine manufacturing industries. But thehot-working-die steels sometimes exist some casting defects such as shrinkagevoids, shrinkage porosity, air holes, inclusion and so on by casting. Repair weldingis one of the feasible measures. The research literatures on repair welding ofcasting hot-working-die steels were hardly found due to seldom application inpractice at present. But the development of repair welding materials and techniquesfor the new type casting high Cr hot-working-die steels is an imperative task to theindustrialization.The research in this thesis is designing flux-cored wires which fit for repairwelding or surfacing of the new type of casting high Cr hot-working-die steels withdifferent TIG and MIG welding parameters. Then the same heat treatment as that ofthe base metals is done for the specimens. So the manufacturing procedures can beconcluded as follows: casting rough castings by the near-net-shape technique,annealing, repair welding, heat treatment, finish machining, hardened and ductileheat-treatment and polishing. After repair welding, the differences between the TIGand MIG surfacing layers were analyzed and compared by chemical compositionanalyses, microstructure and hardness tests. Different welding parameters of TIG orMIG welding were experimented and then conclusion was made on the differencesbetween them. Further more, the directions of flux-cored wires and weldingprocedures fitted for the new type of casting high Cr hot-working-die steels weredesigned.Flux-cored wires were designed by computer aided design (CAD) andconfirmed by experiments, whose veracity was higher. This program fits not onlyfor the die steels but also for flux-cored wires available for the other steels.The transfer coefficients of main alloying elements were achieved for TIG andMIG surfacing processes. For TIG surfacing, C transfer coefficients are from 0.87to 0.93, Cr transfer coefficients are from 0.94 to 0.98, and Mo coefficients are from0.91 to 0.95. While for MIG welding, transfer coefficients of C are from 0.85 to0.91, those of Cr are from 0.94 to 0.99 and those of Mo are from 0.96 to 0.99. Inthe experimental condition, transfer coefficients of C, Cr, Ni, Si, Mo and V by TIGwelding were higher than those by MIG welding.Welding parameters affect the transfer coefficients. With the increasing ofwelding currents, the transfer coefficients of C, Cr and Mo were all decreased forTIG surfacing. But the alloying element composition in MIG surfacing layerschanged irregularly. The compositions of all surfacing layers were near to that ofbase metals.The microstructures of surfacing layers were finer by TIG surfacing butcoarser by MIG surfacing. The composition and microstructures of TIG surfacinglayers were more uniform than those by MIG. MIG surfacing layers had biggerdefect susceptibility. Microstructures of surfacing layers were mainly temperedtroostite. The microstructures became not only finer and finer from top to bottom ofsurfacing layers but also more and more uniform. And microhardness was higherand higher.The flux cored wires were designed and surfacing procedures were workedout for the casting high Cr hot-working-die steels.