Thermal fatigue study of hardfaced hot forging tool using numerical analysis and residual stress evaluation

摘要

Hot forging tools are exposed to severe thermo-mechanical load which cause their failure.The main failure mechanisms are mechanical fatigue, thermal fatigue, plastic deformation and abrasive wear.The use of hardfacing is an effective solution to increase tool life and consequently reducing the cost of forged part.In this work the use of a cobalt-base hard-facing obtained by Plasma Transferred Arc process is studied.The hardfacing is used for tool failed by thermal cracking.The high rate of temperature variation and high temperature gradient at the tool surface induce material softening and surface plastic deformation.These plastic deformations are accumulated during each cycle and eventually cause cracks in the most exposed zones and then tool failure after a few thousand cycles.Microstructure characterization and mechanical behavior analyses are required to prove the quality of coating.Finite element method is used to calculate stress distribution in tool resulting from external loading in order to optimize the thickness and the choice of coating used.Evaluation of residual stresses by ultrasonic technique is used to validate the finite element results and analyze the stress state by non destructive method.