Adopting bar type with cylindrical or conical shape and molding method with shell or sand-filling

the effects of cooling rate on solidification microstructure and precipitation phase formation of K438 superalloy were investigated.Moreover

the relationship between high temperature mechanical properties and microstructure characteristics of the alloy was analyzed according to the observation of fracture morphology.The results show that columnar grain is prone to be generated in form of bar because of its high solidification rate.The shortened solidification time further reduces the feeding capacity of melt

resulting in non-denser microstructure casting.Due to the thick cross-section for conical shape rod

the solidification cooling rate and the growth rate of grain are decreased

which is beneficial for the formation of coarse equiaxed grain and the corresponding high temperature rupture time with 980℃ and 150 MPa is longer than 45 h

accompanied by the obvious improvement of elongation.Homogeneous fine precipitateγ′is formed under shell molding because of accelerated cooling rate

which modifies the coarse columnar grain and irregular precipitate in sand-filling molding.As a result

the high temperature tensile strength and plastic deformation behavior at 650℃ are improved significantly.