Effect Of Carburizing And Quenching Process And Cryogenic Treatment On Friction And Wear Properties Of 20CrNi2Mo Steel

As an important realization end of the intelligent manufacturing "cloud-networkend" architecture,industrial robots have been developing rapidly in recent years.Bearings are important moving parts of the reducer for industrial robot joints,and their wear resistance greatly affects the service life of the reducer.At present,the rolling fatigue life of the crank shaft of the domestic robot RV reducer is generally short,which severely restricts the development of the domestic robot industry.This paper takes the common hot-rolled commercial crankshaft steel 20 Cr Ni2Mo as the research object,aiming to compare the structure and properties of crankshaft steels at home and abroad,and discuss the effect of carburizing and quenching process and cryogenic treatment on the mechanical properties of 20 Cr Ni2Mo steel.Conclusions are as below:(1)The crankshaft steels at home and abroad are all low-carbon steels,but there are certain differences in the ratio of Ni and Cr content.In addition,the inclusions in the steel structure of foreign bearings are relatively small and evenly distributed,and the control of inclusions is generally better than that of domestic ones.The structure of the crank shaft at home and abroad is similar,all of which are low-carbon lath martensite,but the surface structure is quite different.Among them,the domestic one is high-carbon acicular martensite and a small amount of retained austenite,while the foreign one is mainly composed of fine cryptocrystalline martensite with evenly distributed fine carbides.The hardness value of the carburized layer of crankshaft abroad is about 100 HV higher than that of domestic.(2)The relationship between the structure and mechanical properties of 20 Cr Ni2Mo steel under the traditional carburizing quenching and cyclic carburizing quenching and gas quenching + oil quenching process was comparatively studied.Among them,after traditional carburizing and quenching and cyclic carburizing and quenching,the surface structure of 20 Cr Ni2Mo steel is mainly high-carbon acicular martensite,with some austenite and a small amount of carbide remaining,and after gas quenching + oil quenching treatment Its structure is remarkably refined,mainly cryptocrystalline martensite.In addition,the overall hardness gradient,core hardness,tensile properties and wear resistance of the surface carburized layer after gas quenching and oil quenching are better than the other two.(3)After cryogenic treatment,the main microstructure types of the sample surface of the three carburizing and quenching processes did not change significantly,but the austenite content was significantly reduced compared with that before the treatment,which was reduced by 2.3%,5.1%,and 3.9%,respectively.After cryogenic treatment,the overall surface hardness of the three samples is increased by about 50 HV compared with that before cryogenic treatment.After cryogenic treatment,the lower austenite content in the structure leads to a decrease in the proportion of austenite transformation induced by deformation during the friction process,so that the friction coefficient of the sample during the entire friction process is more stable than before treatment.In addition,under a load of 100 N,no obvious furrows appeared on the worn surfaces of the three specimens after cryogenic treatment.Under a load of 200 N,the surface of the sample is relatively flat and covered with a large amount of oxide film.The presence of oxide film may promote the improvement of the wear resistance of the sample.