| Surfacing is an effective method for modifying the surface properties of metal parts,which is a lower cost process method and has a wide range of applications in practical production.For example,high-temperature valve sealing surface used in the field of coal chemical industry require good corrosion resistance,high temperature resistance,wear resistance and thermal fatigue resistance.But it is difficult for conventional stainless steel materials to meet all the above performance requirements.Therefore,it is a relatively reasonable technological process to build up a high temperature valve sealing surface by surfacing a cobalt-based alloy on the surface of stainless steel.However,there is a large difference in mechanical properties and thermophysical parameters between the substrate and the surfacing layer because of its difference in chemical composition,which leads to cracking in the surfacing layer due to large stress during welding.Consequently,the temperature field and stress field under different welding conditions were studied to provide a theoretical basis for the process optimization and production of large-scale seal ring cobalt-based surfacing layer by plasma arc surfacing technology,which has important academic significance and engineering application value.The research and modeling object is 347 H stainless steel sealing ring surfaced Co-CrMo-Si system Co based alloy,whose center line radius is 24 inches in this paper.The process of welding arc movement and alloy powder deposition during the surfacing process was simulated through the combination of the birth-and-death technology and the isothermal heat source movement.The model under different welding process conditions was established to simulate the effects of different welding preheating temperatures,welding sequences,and post-weld heat temperature on the distribution of seal ring weld overlay temperature field and stress field after verifying the effectiveness of the heat source through experiments.The experimental results verified the welding residual stress in the surfacing layer.The numerical simulation results of the temperature field show that,welding preheating can increase the overall temperature of the workpiece.The higher preheating temperature,the higher peak temperature of the heat source,and the temperature gradient near the heat source has decreased.After section welding,the latter track has heating effect on the previous track,and some nodes undergo secondary thermal cycles and the temperature field of the whole ring is more uniform.After post-weld heat treatment,the sealing ring absorbs or dissipates heat for a short period of time,reaching the corresponding heat treatment temperature and remaining constant,and eventually drops to room temperature at the same cooling rate.The numerical simulation results of the stress field show that,the radial residual stress on the surfacing layer of the seal ring undergoes a tensile stress-compressive stress-tensile stress change with increasing radius,and the compressive stress is greatest at the center.The circumferential residual stress on the surfacing layer is tensile stress,and the tensile stress on the center is larger than on both sides.With the increase of preheat temperature,the stress distribution trend is basically same and the stress peak value is decreased.When the welding sequence is segmented after welding,the welding residual stress is minimal.After the seal ring is post-heat treated,the stress distribution trend remains unchanged,the radial residual compressive stress on the surfacing layer increases,and the residual tensile stress decreases.The stress drops heaviest when the preheating temperature is 400 °C.With the increase of the preheating temperature,the stress reduction decreases.The residual stress distribution on the surface of the seal ring was measured by X-ray diffractometry.The results agree well with the simulation results of the stress field under the same process conditions. |
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