Microstructure and susceptibility to hot tearing of K424 nickel-based superalloys for turbocharger turbine wheels

Hot tearing tends to occur when K424 superalloy is used for a turbocharger turbine wheel. To solve this problem,the alloy characteristics of K424 and K418 superalloys and the factors impacting the susceptibility to hot tearing were studied by microstructure observations and casting simulations. The research proposed the main factors which affected the susceptibility to hot tearing and also the method to reduce hot tearing in the turbine wheel. It is found that the susceptibility to hot tearing of the turbine wheel is influenced by both the alloy characteristics and casting characteristics. K424 superalloy shows a higher susceptibility to hot tearing when compared with K418. Because of high amount of aluminum and titanium in K424 superalloy,the size and the amount of γ + γ' eutectics increase,resulting in more prior forming and propagating areas of hot tearing. On the other hand,due to a smaller thickness and a larger curvature change in the blade margin of the turbine wheel,the uneven distribution of the thermal stress is induced in the end of the solidification process,which leads to hot tearing in this paper. In order to decrease the susceptibility to hot tearing of the turbine wheel,the contents of aluminum and titanium should be controlled,and the reasonable technological parameters of casting should be set to ensure the final effect.