The wear behavior between hardfacing materials
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I.
INTRODUCTION
HARDFACE welding has already been adapted for applications in Europe and America for many years.[1] Hardfacing is welded to the base material (usually low or medium carbon steels, or low-alloy steels) to protect against abrasives or to combine with materials in special applications. The cladding thickness depends on the crack susceptibility of the cladding material. Usually one to three layers are accumulated, according to the following factors: environmental design, base-material properties, and work investment. This welding not only utilizes the special characteristics of the hardfacing layer (e.g., resistance to high-temperature deformation, wear, and corrosion) to extend the workpiece lifetime, it also creates significant savings for material costs (especially evident with large workpieces). Hardface welding technology can recover the worn workpiece, giving a longer lifetime than the original design. The most common hardface welding technologies implemented are the early oxyacetylene gas welding (OAW), gas tungsten arc welding (GTAW) or tungsten inert-gas welding (TIG), submerged arc welding (SAW), and the present plasma transferred arc welding (PTA). Among them, the most important differences lie in the welding efficiency and the weld plate dilution rates.[2] First, SAW has a very high fill rate (up to 15 kg/h). However, the material selection is relatively limited. Serious deformations and dilution (15 to 30 pct) are caused in the workpiece because of significant heat input. Second, OAW has a low dilution rate. Yet, tell-tale signs of manual welding are evident because the difficulty of automation or semi-automation is prohibitive. Also, its weld rate is quite slow (3 kg/h). Third, GTAW produces relatively few defects. Still, its dilution rate is high (about 10 to 20 pct) and fill rate low (below 2 kg/h). Finally, PTA covers the broadest range of materials, including almost all hardface weld materials. Most of the heat is absorbed by the cladding material in the PTA process. Thus, heat input for the whole WEITE WU, Associate Professor, is with the Department of Materials Engineering, Kaohsiung Polytechnic Institute, Taiwan 84008, Republic of China. LUNG-TIEN WU, Engineer, is with the Welding Division, Metal Industries Research and Development Centre, Taiwan 81103, Republic of China. Manuscript submitted February 13, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS A
piece is low and postweld dilution is low (4 to 10 pct). Consequently, deformation is low, the fill rate is extremely high (10 kg/h), and the potential for automation is good. The weld is of uniform quality, the surface smooth, finishprocessing requirements low, and it is even economical. The PTA technology was developed as early as 1960.[3] However, it was not until the 1980s that PTA became widely applied in the industries of developed areas like America, Europe, and Japan. Typical applications include plastic extruder screws and valve seat and engine valves.[2,4] The primary materials in the PTA process are cobalt alloys, nicke
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