Surface Nanocrystallization of Steel 20 Induced by Fast Multiple Rotation Rolling

Xingdong Yuan^1,2, Bin Xu²,Yucheng Cai²

(1. School of Materials Science and Engineering£¬Shandong University£¬Jinan 250061£¬China;2. School of Materials Science and Engineering£¬Shandong Jianzhu University£¬Jinan 250101£¬China)



Abstract:

In order to expand the application of steel 20 in precision device, fast multiple rotation rolling (FMRR) is applied to fabricate a nanostructured layer on the surface of steel 20. The FMRR samples are then Cr-Rare earth-boronized under low-temperature. The microstructure of the top surface layer is characterized by transmission electron microscopy (TEM). Microhardness of the top surface is measured by a Vickers microhardness tester. The boride layer is characterized by using scanning electron microscopy (SEM). Experimental results show that a nanostructured layer with their grain size range from 200 to 400 nm is obtained in the top surface layer. The microhardness of FMRR sample changes gradiently along the depth from about 274HV in the top surface layer to about 159HV in the matrix, which is nearly 1.7 times harder than that of the original sample. The penetrating rate is enhanced significantly when the FMRR samples are Cr-Rare earth-boronized at 600 ¡æ for 6 h. Thickness of the boride layer increases to around 20 ¦Ìm, which is nearly twice thicker than that of the original sample.

Key words:  fast multiple rotation rolling  steel 20  surface nanocrystallization  dislocation  Cr-Rare earth-boronizing

DOI£º10.11916/j.issn.1005-9113.2015.05.006

Clc Number:TG156.87

Fund: