High Precision Slender Tube Parts Study On Surface Modification Of Inner Wall

High-precision parts of elongated tubing are the newly developed parts of Chongqing Jianshe Industry Group Co.,Ltd.(hereinafter referred to as the “Factory”)in recent years,which requires the inner wall of the surface be wear-resistant,corrosion-resistant,some kind of high temperature resistant,and requires keep the same inner size after surface modification.In the past,the inner wall of the parts was treated with chrome plating in Factory.However,those parts require high precision with very low pass rate after chrome plating.Therefore,after many rounds of experiments and exploration were conducted,the QPQ salt bath process technology was finally adopted instead of the chrome plating process.QPQ salt bath composite process technology(also referred to as QPQ Technology)has emerged in recent years as a new surface modification technology.Compared with the traditional surface treatment technology,the QPQ technology is more superior in the fields in: surface nitriding,soft nitriding,chrome plating,high frequency quenching,with wear resistance and corrosion resistance of the prominent,which is widely used in the field of automobile industry,mold,agricultural machinery,military firearms etc.In this paper,the commonly used 50 B steel tubing parts as the material,to process the QPQ treatment and chrome plating,respectively.QPQ treatment with different nitriding time(2hours,3hours,and 4hours)was used to investigate the effect of different nitriding time on the morphology and properties of the infiltrated layer.The microstructure of the modified 50 B steel was studied by means of metallographic microscope,Vickers microhardness tester,X-ray diffraction(XRD),scanning electron microscope(SEM)and energy dispersive spectroscopy(EDS),Hardness gradient of infiltrating layer,phase composition of the surface layer,microstructure and microstructure of the layer were analyzed.At the same time,the effects of QPQ process and chrome plating process on the performance were studied by wear test,neutral salt spray test and electrochemical experiment.The results show that the infiltration layer of QPQ treated 50 B steel tubing parts is divided into three parts: oxide layer,loose layer and compounds layer.The oxide layer is mainly composed of Fe3O4,which improves the corrosion resistance and wear resistance.The compound layer is composed of Fe3 N and Fe4 N,and the compound layer is thicker and thicker with the increase of nitriding time;while the loose layer is a porous layer,and the layer has a significant influence on the corrosion resistance.With the increase of nitriding time,the degree of porosity became more and more serious,and the corrosion resistance became worse and worse.The surface hardness of QPQ treated with nitriding for 4h reached 700HV0.1,which was twice that of the matrix;the results show that the QPQ treated sample has a smaller wear amount and a smaller friction coefficient than the chrome plated sample,and has a friction coefficient of 0.522.Electrochemical experiments show that as the QPQ nitriding time increases from 2hours to 4hours,the corrosion rate is constant Improve,so nitriding 2hours QPQ process corrosion resistance than nitriding 4hours good corrosion resistance.QPQ process and chrome plating process can significantly improve the corrosion resistance,but QPQ treatment has more excellent corrosion resistance.In order to verify that whether the QPQ process can meet the use of indicators or not,batch production was conducted and random samples were taken for all aspects of performance testing.Compared with the chrome plating process,QPQ process in the surface hardness,corrosion resistance,wear resistance,accuracy and Production costs and environmental pollution is much better than chrome plating process.And the QPQ process is available to meet the high-precision tubing parts requirements.