Study On Titanium-assisted Enhanced Plasma Nitriding Technology

Plasma nitriding is a clean and efficient surface modification technology,which can significantly improve surface hardness and wear resistance.After conventional plasma nitriding treatment,the characteristics of nitrided layer change with the process of plasma nitriding.With the thickening of nitrided layer,the compound layer,diffusion layer and effective hardening layer are all thickened,and the hardness of surface layer is also increased.Unfortunately,the thickening of compound layer will lead to the increase of brittleness.For parts bearing impact and heavy-duty wear,such as hot stamping dies,hot forging dies and heavy-duty gears,the conventional plasma nitriding treatment often has the problem that the characteristics of nitriding layer conflict with the service requirements,that is,with the thickening of nitriding layer,the surface hardness will increase,but the compound layer will also thicken,which will lead to the increase of brittleness of nitriding layer,and local cracking and shedding will easily occur during service,resulting in early failure of parts;However,the nitrided layer with few compound layers is thin,and the high hardness nitrided layer is easy to be worn away,so it is difficult to meet the requirements of long service life.Therefore,the research and development of innovative plasma nitriding technology,which can significantly improve the effective hardened layer thickness and surface hardness on the premise of reducing the compound layer thickness,has significant scientific research and application value.Based on this,in this study,quenched and tempered 45 steel,42CrMo steel and 38CrMo Al steel were selected as materials,which were treated by conventional plasma nitriding,plasma nitriding with trace titanium and plasma nitriding+post oxidation respectively.The effects of titanium addition and nitriding temperature on the characteristics of nitrided layer after titanium enhanced plasma nitriding were studied and analyzed.The changes of phase and properties of different materials after adding trace titanium plasma nitriding were studied and analyzed,and verify the consistency of adding trace titanium plasma nitriding treatment;Research and analysis of the effect of post-oxidation process on the characteristics of nitriding layer by titanium enhanced plasma nitriding compound treatment.The research on titanium enhanced plasma nitriding of 42CrMo steel shows that the effective hardening layer thickness and compound layer thickness can be significantly increased and decreased by adding trace titanium at 540?/4 h.When the amount of titanium is 0.8 g,the thickness of effective hardening layer increases from 255?m to 360?m,that is,the nitriding efficiency increases by nearly 50%;When the thickness of effective hardening layer increases,the thickness of compound layer decreases from16.1?m of conventional plasma nitriding to 8.8?m,that is,the thickness of compound layer decreases by about 50%;The ratio of compound layer to effective hardening layer in the infiltrated layer is reduced from 8.5%in conventional plasma nitriding to 2.6%.At the same time,a high hardness strengthening phase Ti N is formed in the titanium reinforced plasma nitriding layer,which increases the surface hardness of the layer from 703 HV_0.05 to894 HV_0.05.After adding a small amount of titanium,the wear resistance and impact resistance of the samples are also improved.At the same time,titanium enhanced plasma nitriding is carried out at different temperatures.It is found that titanium enhanced plasma nitriding at different temperatures can also achieve the effects of reducing the thickness of compound layer,increasing the thickness of effective hardening layer and improving the hardness of surface and section.The research on titanium enhanced plasma nitriding of 45 steel?42CrMo steel and 38CrMo Al steel shows that titanium enhanced plasma nitriding has the same effect on different materials,that is,it reduces the thickness of compound layer,increases the thickness of effective hardening layer,and improves the hardness of surface and section.Under the same plasma nitriding process parameters(540?/4 h),the effective hardening layer thickness of 45 steel,42CrMo steel and 38CrMo Al steel is increased from100?m,255?m and 240?m of conventional plasma nitriding treatment to121?m,360?m and 388?m respectively.The surface hardness is increased from 470 HV_0.05,703 HV_0.05 and 1027 HV_0.05 treated by conventional plasma nitriding to 525 HV_0.05,889 HV_0.05 and 1137 HV_0.05 respectively.The thickness of compound degree is reduced from 19.9?m,16.1?m and 10.6?m treated by conventional plasma nitriding to 12.1?m,8.8?m and 6.0?m respectively.The research of plasma nitriding+post-oxidation shows that when the post-oxidation temperature is 400?and the post-oxidation time is 60 min,The corrosion resistance of the sample is the best,with the lowest corrosion current of 0.2429×10^-5 A/cm² and the maximum corrosion potential of-386.13 m V;meanwhile,the surface hardness of the sample reaches the highest value of 630 HV_0.05,and compared with conventional plasma nitriding+post-oxidation treatment,the corrosion resistance is further improved under the same post-oxidation process parameters(400?/60 min).The corrosion current decreases from 0.2429×10^-5 A/cm² to 0.12755×10^-5 A/cm² and the corrosion potential increases from-386.13 m V to-325.40 m V.The surface hardness and effective hardening layer thickness increased from 645 HV_0.05and 175?m to 713 HV_0.05 and 230?m,respectively,and the compound layer thickness decreased from 7.2?m to 3.7?m.