Effect of Surface Nanocrystallization on Cr-Rare Earth-Boriding for Steel Q235 at Low-Temperature

A nanostructured layer was fabricated on the surface of steel Q235 by using fast multiple rotation rolling( FMRR). The Cr-Rare earth-boriding process was carried out followed at different temperatures.Experimental results showed that the thickness of the boride layer was significantly increased by surface nanocrystallization. The morphology of the boride layer was saw-toothed. An uniform,continuous and dense boride layer was obtained and adhered well to the substrate. The penetrating speed of FMRR specimens was enhanced by 1.9,1.7 and 1.5 times when the Cr-Rare earth-boriding temperature was 843,873 and 923 K.Severe plastic deformation,which grain size was approximately 100 nm,was observed on steel Q235 surface.Mechanism of Cr-Rare earth-boriding was also studied.