Research On The Control Of The Microstructure And Properties Of GE1014 Ultra-high Strength Steel

Transmission shaft is the key component of the aero engine.With the improvement of aero engine performance,the critical requirements of high power,high speed,large deformation and high maneuver overload are put forward for the transmission shaft material.GE1014 steel is applied to aero-engine drive shaft with super high strength,good plastic toughness matching and fatigue fracture resistance.The domestic research on GE1014 steel is less.In order to promote the progress of our country in the field of aero engine drive shaft and support the rapid development of China's aviation industry,it is imperative to study the basic research of GE1014 ultra high strength steel.The phase transformation point,mechanical propertiese and microstructure of a new type of aeroengine transmission shaft steel,the GE1014 were studied thoroughly through thermal expansion test,mechanical tests,and metallography,SEM,TEM,XRD respectively.The curves of the mechanical properties of the test steel varying with the heat treatment process are obtained,the evolutions of carbides and reverted austenite during tempering were systematically concluded,by means of which the optimum heat treatment process of GE1014 steel was determined.The main achievements of this paper include:Tests show that the temperature of Ac_1,Ac_3,Ms of GE1014 were 520?,780?,and 150?,respectively,GE1014 has a very good hardenability,which means that Martensite could be obtained with a 200?/s cooling rate to room temperature.The phase transformation point.The phase transition points of the GE1014 steel alloy system with high Co and Ni content are calculated by Andrews's empirical formula,the calculated values are in good agreement with the measured values,and the deviations are not more than 70?.After quenching at 860?,there were still many small undissolved carbides on the martensitic matrix,and fine grain structure was obtained by the grain boundary pinning of fine undissolved carbides at this time.When the quenching temperature is higher than 900?,the martensite structure was obtained completely,but the microstructure of the quenched grains became coarsened.The optimum quenching temperature and tempering temperature for GE1014steel are 900?and 520?.After tempering at 420?,the carbide precipitated from GE1014 steel is mainly composed of thick lamellar cementite,at this time,the toughness of steel reached a valley bottom value.When the tempering temperature raised to 480?,a large number of fine dispersed M₂C carbide and thin film reverted austenite precipitated on the lath martensite matrix.In the meanwhile,the tensile strength of the test steel reached the peak value.As the tempering temperature reached to 520?,although the M₂C carbide had grown up,it can still maintain the distribution state of fine dispersion,the matrix remained as lath martensitic structure,and the reverted-austenite remained thin film like,which makes the toughness of test steel at 520?the best.The reverted-austenite's volume fraction increased rapidly when the tempering was higher than 520?,and the morphology of the reverted austenite was changed from thin film to large lump,and the strength and toughness of the test steel were reduced.