Effect Of Cryogenic Treatment On Microstructure And Performance Of DLC Coated M35 High Speed Steel

High speed steel is widely used in industrial production and is an important tool material.The preparation of surface coating on the basis of traditional heat treatment can effectively improve the service life and other comprehensive properties of high speed steel tools,which is of great significance.Diamond like carbon(DLC)film is a kind of hard coating with excellent performance,but its application is limited by the problems of poor adhesion,high internal stress and poor thermal stability.As a simple,safe and environmental protection technology,cryogenic treatment has been widely studied in metal materials,but the application and research of cryogenic treatment in coating field is not sufficient,and there are few related research reports at home and abroad.In this research,taking M35 high speed steel as the research object,a kind of coated high speed steel tool with high wear resistance was prepared by cryogenic treatment,heat treatment and DLC coating preparation technology.The main research work and achievements are as follows.Firstly,the effects of tempering and cryogenic treatment sequence,tempering temperature,tempering times and cryogenic treatment on microstructure and properties of M35 high speed steel were studied.The fine near-circular carbides precipitated from the grains of the sample by quenching+3 tempering+deep cryogenic treatment,showing good wear resistance.After tempering at different temperatures,the hardness of M35 high speed steel first decreased,then increased to the peak value of 67.1 HRC,and finally decreased sharply.Compared with tempered samples,the peak hardness was increased by 0.7 HRC and tempering temperature was reduced by nearly 30?.Compared with three times tempering,more fine and nearly round carbides could be obtained in once tempering at 525?.After cryogenic treatment,the agglomeration of carbides in once tempering sample was reduced,the distribution of carbides was more uniform,and the red hardness of 63.6 HRC was maintained.Secondly,diamond like carbon(DLC)film was deposited on M35 high speed steel by plasma enhanced chemical vapor deposition(PECVD).The effects of tempering times and cryogenic treatment of substrate and cryogenic temperature on the structure and mechanical properties of DLC coating were studied.The results showed that the tempering times of the substrate had no effect on the content of sp³bond in the DLC coating.But the adhesion of the coating was the best when the substrate was treated with once tempering at 525?and cryogenic treatment,the maximum nanohardness reached 28.3 GPa,and the minimum wear was 0.44×10^-3mm³.The structure of DLC coating changed after cryogenic treatment at different cryogenic temperatures.After cryogenic treatment at-140?,the content of sp³bond in DLC coating was the most with the sp²/sp³value of 0.524,then decreased gradually with the decrease of temperature.With the decrease of cryogenic temperature,the adhesion of DLC coating first increased and then decreased rapidly,and the critical load reached the peak value of 40.54 N at-180?.Finally,the effects of cyclic and magnetic field on the structure and properties of DLC coating were studied by changing the cryogenic times under the condition of a certain total holding time and introducing the applied static magnetic field.After twice cryogenic treatments at-140?and-196?,the content of sp³bond decreased.The adhesion of DLC coating increased after several times of cryogenic treatment,but the wear resistance of DLC coating decreased with the increase of cryogenic times.The surface of DLC coating was easy to absorb impurity particles after vertical magnetic field cryogenic treatment,while the internal defects of DLC coating increased and the surface quality deteriorated after parallel magnetic field cryogenic treatment.After magnetic field cryogenic treatment,the adhesion and wear resistance of DLC coating decreased,the disorder of sp²bond decreased and the size of sp²cluster increased,resulting in the nanohardness decreased from 30.4 GPa to 25.8 GPa.This research has obtained the deep cryogenic treatment and heat treatment technology which can refine the structure and improve the comprehensive mechanical properties of M35high speed steel through the research of the deep cryogenic treatment technology.The influence of different deep cryogenic treatment on the structure and performance of DLC coating on the surface of M35 high speed steel was also studied,which had important theoretical and practical significance for improving the adhesion and wear resistance of DLC coating.