Effect Of Carbon Content And Pouring Temperature On Microstructure And Mechanical Properties Of Cast Ni-base Superalloy K4750

K4750 is a new nickel-based cast superalloy,which is based on ? matrix and strengthened by ?' phase.Due to excellent high temperature performance and good microstructure stability at 700-750?,this alloy can be applied to manufacture aeroengine parts used at high temperature.To obtain the excellent properties,the composition and processing technology of this alloy are still need to be studied and optimized.In this dissertation,the solidification process,element segregation,the effect of pouring temperature and the carbon content on the microstructure and properties of K4750 alloy are all exhasustively analized.It could support the basic data by the way of determining the best carbon content and the pouring temperature,which has scientific significance and application value.The main results obtained in this dissertation are as follows:(1)The pouring temperature has a significant influence on the microstructure and mechanical properties of K4750 alloy.With the increase of pouring temperature,the grain size of K4750 alloy is increased obviously,the dendrites are more developed.And the aggregation of residual liquid phases between dendrites leads to MC carbides precipitation,which causes the MC carbides accumulated seriously.This kind of MC carbide deteriorated the mechanical properties with high pouring temperature.The increase of the pouring temperature may led to degradation of the mechanical properties of K4750 alloy,and the best temperature of this alloy is 1410?.(2)It proves that the main precipitated phases of the K4750 alloy,with different carbon contents,are all ? phase,?' phase,MC carbide and M23C6 carbide.The amount of MC carbides is increased with the increasing C content,and M23C6 carbide and phase have no change with the increasing C content.With the increase of C content from 0.02 to 0.10wt.%,the room temperature tensile strength and yield strength increase from 894MPa and 719 MPa,to 982 MP and 756 MPa,respectively;the 750? temperature tensile strength and yield strength increase from 855MPa and 676MPa,to 891 MP and 712 MPa,respectively;the stress rupture life under increases from 19.5h to 161h,and the elongation increases from 0.84%to 12%.When C content is 0.10wt.%,the strength,the creep rupture life and the tensile ductility have reached the best match.(3)The isothermal solidification experiment has been performed.The liquidus of K4750 alloy is 1350?,and the solidus is 1270?.Its solidification sequence can be identified as follow:L?? at 1350?;L??+MC at 1320?.During the solidification of K4750 alloy,becomes from 1310? to 1290?.During the solidification,W,Fe,Cr element tend to segregate to the solid,which are identified as negative segregation elements;C,Ti,Nb,Mo element are prone to segregate to the residual liquid,which are regarded as positive segregation elements and promote the nucleation and growth of MC carbide at the initial stage liquid.