Effect of Surface Nanocrystallization Induced by Fast Multiple Rotation Rolling on Cr-Rare Earth-Boronizing for Steel 45 under Low-Temperature

In this paper, fast multiple rotation rolling （FMRR） is applied to fabricate a nanostructured layer on the surface of steel 45. The FMRR samples are then Cr-Rare earth-boronized under low-temperature. The boride layer is characterized by using Scanning electron microscopy （SEM） and X-ray diffraction （XRD）. Experimental results indicate that the thickness of the boride layer is greatly increased by surface nanocrystallization. The boride layer with relatively continuous structure instead of the zigzag teeth structure is obtained, and the penetrating rate is enhanced by 2. 5-3.7 times when the FMRR samples are Cr-Rare earth- boronized at the temperature of 570 %, 600℃ and 650℃ for 6 h. The boride layer fabricated on the FMRR sample consists of single phase Fe2B. Severe plastic deformation with the grain size of approximately 100 nm in the top surface layer of steel 45 is observed, and the thickness of the plastic deformation layer is about 30 6xm. The microstructure in the top surface layer is characterized by Transmission electron microscopy （TEM）. Grain boundaries are largely increased with high stacking fault energy after FMRR, leading to a significant enhancement of RE boron-chromizing speed.

Surface Nanocrystallization of Steel 20 Induced by Fast Multiple Rotation Rolling

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 about274 HV in the top surface layer to about 159 HV 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 earthboronized at 600 ℃ for 6 h. Thickness of the boride layer increases to around 20 μm,which is nearly twice thicker than that of the original sample.

Phase Analysis of Cemented Carbide WC-Co Boronised with Yttrium

Phase analysis for the coated surface with B 4C and Y 2O 3 of cemented carbide WC-20Co in vacuum-heating was carried out by high-temperature X-ray diffraction from ambient temperature to 1300 ℃. The results show that, the high-concentration active boron atoms are released from the boron-supply agent B 4C located on the alloy surface and diffused into the γ-phase, leading to forming the three-element boron-bearing compound W 2Co 21B 6 beside forming boron-bearing compounds on the blank surface. By contrast with boronising only, the element yttrium in boronization broadens the boronising temperature range during vacuum-sintering, catalyzes the decarbonisation decomposition of B 4C and promotes diffusion of active boron atoms into the bulk of WC-Co.