Study On Vanadium Carbide Coating On 3Cr13 Stainless Steel By Thermal Diffusion Process With Fluoride Salt Bath

3Cr13 is a kind of martensitic stainless steel,with good mechanical performance and strong corrosion-resistance.It is widely used as plastic mold,springs,cutting tools,etc.,which suffer from the high loading and corrosion medium.After quenching and tempering heat treatment,the hardness of this alloy is under HRC30.So,its wear-resistance is poor.The surface plasma nitriding technology can solve this problem effectively,but is invalid for the shape complex workpieces.Among surface strengthening technologies,the thermal diffusion（TD）process can solve these problems well.Unfortunately,the traditional thermal diffusion process has many shortcomings as well,for example,the high liquid viscosity,composition segregation of the salt bath.Salt tends to be adhere on the workpiece surface and difficult to clean.FLi Na K salt（LiF-NaF-KF 29.2%,11.7%,59.1% wt.%）is stable and easy to be cleaned from the workpiece after reaction,which showing potential advantages.This study will try to use the FLiNaK as a new kind of base salt in TD process on 3Cr13 stainless steel to obtain VC coating.Salt bath formula as follow:86% FLiNaK+10% V₂O₅+4%（Si +BC）（wt.%）The experiment temperature is 900 oC,treatment time are 10 h,24h,48 h and 90 h,respectively.The main conclusions are listed as follows :1)The morphologies of the surface and cross-section of the coating were obtained by scanning electron microscope（SEM）.The results showed that there is a small amount of SiO₂ layer on the surface of the coating.The coating can fully covered on the matrix flatly and densely.2)The coating composition,structure and elements distribution were analyzed by X-ray diffractometer（XRD）and energy dispersive X-ray spectroscopy（EDS）.Results showed that the phase of the coating is VC carbide.The content of carbon slightly increase from the interphase of matrix /coating to the surface of the coating in the 90h-treated sample.3)With the friction abrasion testing machine,the friction and wear performance of the matrix and coating were examined.The results showed that the wear-resistance property of coating is about 6 times of matrix under the same condition.This fact indicated that the VC coating can greatly improve the wear-resistance property for matrix by the TD process technology.4)The corrosion-resistance tests of coating and matrix by electrochemical workstation showed that the performance of corrosion-resistance has been improved about 31% after TD process.5)The growth kinetics curve of vanadizing coating at 900 oC has been researched and showed its approximately follows similar parabolic equation: d2 =0.511 t.