| Martensitic precipitation hardening stainless steel has good corrosion resistance and the advantages of high intensity, so PH17-4stainless steel can be used as ultra high strength and corrosion resistant materials in nuclear industry and aerospace industry. Martensitic precipitation hardening stainless steel has complex microstructure and excellent comprehensive performance, these features are affected by heat treatment process in addition to material chemical composition. But application environment is almost of air flow or corrosion in the solution, so the surface of workpiece exposures to lasting impact and high temperature corrosion in long-term. So the surface treatment is very necessary in order to improve surface performance. Cobalt base alloy, which is with high wear resistance and high temperature resistant corrosion, is considered to be a very optimized surface strengthening alloy for PH17-4. PH17-4deposited with Co-based alloy hardfacing coating by plasma surfacing welding technology is an excellent choice for surface strengthening PH17-4.The heat treatment is used to improve the performance of martensitic precipitation hardening stainless steel. At the same time, PH17-4stainless steel is deposited with Co-based alloy hardfacing coating by plasma surfacing welding technology to improve its surface properties. Influence of different heat treatment on microstructure and properties of17-4PH steel is measured by scanning electron microscope equipped with energy dispersive spectroscopy (SEM-EDS), electronic probe (EPMA), X-ray diffraction (XRD), transmission electron microscope (TEM) and microhardness tester; Microstructure and properties of17-4PH stainless steel after plasma-transferred arc welding and the influence of post-weld heat treatment are studied. The experimental results are as follows:1. After solution+aging treatment, precipitate can be found in the martensite matrix and the hardness value is improved; With the increase of aging temperature, precipitate is coarse, the formation of reversed austenite is observed and the hardness is decreasing; after secondary aging treatment, refinement of grain is happened, but corresponding microstructure doesn’t happen to change, with the changing of the secondary aging temperature, corresponding microstructure and properties(impact toughness, strength and plasticity) doesn’t change significantly, but there is a peak hardness when the temperature is620℃.2. The adjustment between the solution treatment and ageing treatment can change the corresponding microstructure obviously (martensite refinement and clear-cut grain boundary); the hardness, strength and plasticity is between the value of lower temperature aging (480℃) and higher temperature aging (620℃), it can achieve good hardness and strength, accompanying with relatively higher plasticity; with the increasing of adjustment temperature, corresponding microstructure almost doesn’t happen to change and the plasticity is almost not affected, but, the strength is increased, the impact toughness is decreased and there is a peak hardness when the temperature is780℃.3. After the plasma-transferred arc welding (PTAW), the interface between weld metal and base metal is favorable. The hardness of the coating improves a lot. Microstructural gradient and microhardness gradient are observed both in the coating and HAZ.4. Post-weld solution treatment at1050℃, heat affected zone disappears, organization is homogenized, organization of the coating is refined and the hardness is improved; solution followed by aging at different temperature, the precipitation of hard phase in the base metal and the increasing of hardness turn up; but with the increasing of the aging temperature, the hardness is decreased; the coating isn’t affected by aging treatment. |
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