Composition Optimization and Heat Treatment Study of Carbide-Strengthened Novel Invar Alloys
Invar alloys have attracted widespread attention in the aerospace and precision instrument fields in recent years due to their low thermal expansion coefficient.However,their relatively low strength limits their application range.Currently,researchers generally believe that grain refinement,solid solution strengthening,and precipitation strengthening are the main ways to improve the strength of Invar alloys.This paper mainly studies the effects and mechanisms of vanadium and carbide compounds(VC)on the microstructure of the typical hot-rolled Invar alloy Fe-36Ni,and solves the problem of grain secondary growth during the heat treatment process by changing the existing heat treatment methods.The microstructure of the Invar alloy is characterized by metallographic microscopy,scanning electron microscopy,transmission electron microscopy,and other means.The results show that adding appropriate amounts of V and C elements can form fine and uniform VC particles,which precipitate to strengthen the matrix and improve the uniformity of the matrix austenite structure.Excessive addition of V and C elements not only leads to the agglomeration of VC particles but also causes the accumulation of silicon elements at grain boundaries,forming large silicon inclusions,which reduces the plasticity and increases the thermal expansion coefficient of the alloy.In addition,through appropriate heat treatment processes,the growth of the matrix structure during VC precipitation can be effectively prevented.This study adopts a low-temperature solution treatment plus ultra-long aging heat treatment method,which effectively enables the carbide to uniformly precipitate in the alloy matrix to form precipitation strengthening,while also avoiding abnormal growth of the austenite structure in the alloy.
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