The Mechanical Properties Of Fine-grained Superalloy K4169

On the basis of the previous work, a new refiner is developed to refine a Fe-Ni based superalloy K4169 under different casting parameters in this thesis. By this way, the grain size was obviously refined. We have analyzed the changes of the microstructure, measured tensile and low cyclic fatigue properties at room temperature and at 700 D, observed the fracture of the test bars by SEM and analyzed the fracture mechanism.The results are as follows:Trace addition of the new refiner to the melt can obviously refine the grains of the alloy. At a conventional pouring temperature of 1400D, the grains could be refined to the order of ASTM1.7, the proportion of equiaxed grains at traverse cross-section could be improved to 96%. Under this process, the granulation phenomenon was found and the cast have much less casting defects. The size of porosity and the interdendritic segregation level of main elements was reduced with grain refinement.The yield and tensile strength of the test bars of fine grains is higher than that of the coarse ones at room temperature and at 700 D, and the plasticity is also superior for fine grains at room temperature, but debase at 70011. The improvement of strength of fine ones can be attributed not only to the retardation of dislocation by grain interface, but also to the uniformity of microstructure, the reduction of segregation and the refinement of the secondary phase after grain refinement.The fatigue lives of the test bar of fine grains are longer than that of coarse ones at room temperature. The results reveal that the improvement of the fatigue lives of fine grained ones was attributed to that the extend of fatigue crack had been decelerated. Whereas at moderate-high temperature, the strain amplitude has great effect on the fatigue life. Only at a lower strain amplitude the disposal of grain refinement improve the mechanical of LCF. The study also reveals that some unstable place such as phase interface and grain interface and grain interface can be provenance ofinside fatigue cracks at this temperature and at high strain.The results show that the fine grain process of casting has some effects on the behavior of response to cyclic stress, such as the increase in rigidification exponential of fine grains.