Numerical Simulation and Process Optimization of Hot Extrusion of FGH98 Alloy

Hot extrusion is one of the key forming processes for manufacturing nickel-based powder superalloy turbine discs. However, cracking tends to occur during the hot extrusion of FGH98 alloy, and the process parameters are critical factors affecting its forming quality. Finite element simulation was adopted to investigate the effects of die angle, extrusion ratio, extrusion speed and initial billet temperature on the forming quality of FGH98 alloy. Meanwhile, the hot extrusion process parameters were optimized via the response surface method. The results show that the extrusion die angle ranging from 35° to 45° can effectively avoid equivalent stress concentration. With the increase of the extrusion ratio and extrusion speed, the equivalent stress rises and the temperature distribution of the extruded bar becomes non-uniform. Increasing the extrusion temperature can improve the uniformity of stress and temperature distribution in the bar. With the aim of achieving lower and uniformly distributed equivalent stress, a response surface optimization model was established. The optimal combination of hot extrusion process parameters is obtained: extrusion ratio of 4.63, extrusion temperature of 1098 ℃, and extrusion speed of 26 mm/s.