Refinement On Primary Austenite In Hypoeutectic Fe-Cr-C Alloy And First Principles Calculation

Hardfacing technology is one of the important means of surface engineering technology.By hardfacing technology,the alloy coatings with special properties such as wear resistance,heat resistance or corrosion resistance can be obtained on the surface of workpieces.At present,it is widely used in the field of additive manufacturing.The primary phase of hypoeutectic Fe-Cr-C hardfacing alloy is austenite.It is not easy to flake and crack,compared with hypereutectic Fe-Cr-C hardfacing alloy,whose primary phase is M₇C₃ carbide.However,its wear-resistance is low.Therefore,in this paper,the micro-alloying elements M?M=V,Nb,Ti?was added to hypoeutectic Fe-Cr-C hardfacing alloy.By refining the primary austenite,the plasticity and hardness of the alloy will be improved,so that the wear resistance of the alloy will be increased too.The hypoeutectic Fe-Cr-C hardfacing alloy was taken in this paper.The six kinds of alloys with different C and Nb contents respectively,the ratio of C and Nb to 1:2,and different elements such as Ti,V addtives were prepared.The microstructure and wear resistance of the hypoeutectic Fe-Cr-C hardfacing alloys with the micro-alloying elements M?M=V,Nb,Ti?were investigated.The Bramfitt lattice mismatch theory was used to verify that NbC is an effective heterogeneous core of austenite.By primary principles,the elastic constants,microhardness,young's modulus,the anisotropy factor,poisson's ratio of NbC were calculated,and the interface combine work and interface bonding properties of NbC/g-Fe wrer calculated.Lastly,the refinement mechanism of primary austenite by NbC was analyzed.In this work,the fluorescence and sulfur carbon tests were carried out for the samples of the alloy.The actual content of the samples was agreement with the expected requirements.According to the phase diagram calculation element content,the primary phase isg-Fe,which is hypoeutectic microstructure.XRD results show that,in#1 and#2samples,the main phase of the samples areg-Fe and M₇C₃;In#3 and#4 samples,those areg-Fe,M₇C₃ and NbC;In#5 sample,those areg-Fe,M₇C₃ and TiC;In#6 sample,those areg-Fe,M₇C₃ and VC.The hardness results show that the hardness of#4 is the highest.The nanometer indentation analysis shows that the nano indentation hardness of NbC is the highest,and that of TiC is the second,and tthat of VC is the smallest.The wear curves show that the weightlessness of#4 sample is the smallest after 24 hours of abrasive wear,and that of#6 sample is the second.The mismatch degree of NbC/g-Fe is 8.35%,which indicates that NbC as heterogeneous nucleation of austenitic core is medium effective.The interface atomic spacing of NbC-C?Nb?-OT,NbC-C?Nb?-MT and NbC-C-?Nb?-HCP are3.461?,2.924?and 2.924?.The interface binding energy ofg-Fe are 0.59J/m²,0.72J/m²and 1.07J/m²,respectively,which indicates that the atomic bonding force of NbC-C?Nb?-HCP interface is the strongest,and the interface is the most stable.