Microstructure and properties of V-N microalloyed hot-rolled invar alloy
Invar alloys have an extremely low coefficient of thermal expansion,but their low mechanical strength seriously restricts their application in the field of structural materials.In order to further enhance the strength of the invar alloys,V-N microalloyed invar alloys were designed based on the concept of microalloying.The effects of trace amounts of V and N on microstructure and mechanical properties of hot-rolled invar alloys were studied using Vickers hardness tester,tensile testing machine,electron backscatter diffraction(EBSD)technique,X-ray diffraction(XRD),scanning electron microscopy(SEM)and transmission electron microscopy(TEM),and their action mechanisms were analyzed.The results show that the hot-rolled microstructure of the V-N microalloyed invar alloys is significantly refined,and the hardness and tensile strength are significantly increased.As the N content increases,the grain size is further refined and the distribution is more uniform,resulting in a further increase in tensile strength.A large amount of small and dispersed V(C,N)second phase with a size of about 400 nm is precipitated in the matrix of the V-N microalloyed invar alloys,which pins grain boundaries and dislocations.Fine grain strengthening,precipitation strengthening and dislocation strengthening are the main reasons for the significant improvement in mechanical properties of the V-N microalloyed invar alloys.
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