| 35CrMo and 40Cr low-alloy steels are the main steels to create a variety of all kinds ofmechanical parts (such as bearing parts,and gear, etc.), and receive much concern because oftheir excellent comprehensive properties. However in the practical application, thephenomenon of their friction and wear becomes serious under the harsh mining environment,and the results of economic losses and waste of materials arouse people's more and moreattention.In this paper, the samples of 35CrMo tempered steel and 40Cr tempered steel wereprocessed by TJU-UMSNT-I ultrasonic surface nanocrystallization device, and nitrided at 550℃for 2 and 10 hours before and after surface nanocrystallization.Then observe microstructure on the treated sample by Transmission Electron Microscope,and the result showed that Equiaxed crystal nanostructured surface layers about 100μm werefabricated on 35CrMo and 40Cr tempered steel by ultrasonic processing, with grain size of25nm at the top surface and random distribution of their orientation, at the same time, thegrain was highly refined.Examine and analyse the nitriding layers on the specimens before and afternano-treatment by metalloscope and hardness tester. And the results showed that about 140μmand 150μm flow layers were formed on two kinds of material by ultrasonic processing, andwith nitriding time different nitrided diffusion layers(35CrMo:100μm,130μm,200μm,450μmand 40Cr :150μm,200μm,175μm,450μm) were formed on the samples before and after surfacenoncrystalline processing. So, the effects of nano-nitriding samples were obviously better thannitriding with nitriding time.The surface hardness of 35CrMo tempered steel about 695HV and 40Cr tempered steelabout 706HV highly increased after ultrasonic surface processing and gas nitriding before and after surface nanocrystalline, compared with the center of the samples increased about 2.6times and 2.5 times. Hardness fell as the distance to the surface increases, and the range ofhardness region was prolonged with nitriding time after surface nanocrystalline.In the last, evaluate the abrasive resistance through measuring lost weights and averagefriction coefficient about materials after different processing, and analyze abrasion degree onthe samples treated through the different processing by Scanning Electron Microscope andasana microscope. Lost weights and average friction coefficient about materials by ultrasonicprocessing and gas nitriding treatment were obviously lower than unprocessed specimens, andsurface resistance to abrasion was enhanced．And the anti-wear performance of the samplesby ultrasonic processing were better. And wear mechanism changes from adhesive wear toabrasive wear.So Ultrasonic surface nanocrystallization treatment can significantly improve frictionand wear properties of low-alloy steel, and it is an effective way to improve other surfacehardening methods.
|
PDF Full Text Request