Papers by Keyword: Chromizing

Abstract: Diffusion chromizing of tool steel has been investigated, using a powder method modified by the use of low pressure during the process for the avoidance of the oxidation of the batch. Innovative chromizing novel processes have been carried out in a hot-wall vacuum oven. The processes have been performed in a chromium chloride atmosphere at a low pressure range from 1 to 800 hPa, with treatment temperatures of 850 to 950°C. Studies of layer thickness, its phase composition, and Cr, Fe, and C depth profiles in the diffusion zone of chromized layer have been conducted. The effect of the process parameters, such as time and temperature, on the growth kinetics of diffusion layers has also been investigated. A comparison was made between the layer thickness produced on the tool steel surface using the novel chromizing method, under low pressure, and a traditional chromizing process, by the pack powder method. Chromizing conducted at low pressure was found to be more effective for maximizing the growth rate of diffusion layers than that for chromizing by the traditional pack cementation method.

Abstract: In this study, the friction and wear properties of the siliconized, chromized and borochromized SS 400 steel/Si₃N₄ tribopairs were investigated in ethyl alcohol at 298 K. The surface of the siliconized plate specimens mainly consisted of Fe₃Si, while the surfaces of the chromized and borochromized steel plate specimens were mainly composed of Fe-Cr alloy and Cr₂B phases, respectively. The borochromized specimens exhibited the highest microvickers hardness of all the plate specimens. Also, it was found that both the chromized and borochromized steel specimens exhibited friction coefficients as low as 0.2 in ethyl alcohol, and that the friction coefficients of the siliconized steel specimens were slightly lower than those of the non-coated steel specimens.

Abstract: Q195 steel was conducted by plasma chromizing and Cr-Ni surface alloying process to research the relationship between unit diffusion and binary diffusion. After studying the thickness, composition, phase component of the layer and diffusion coefficients of alloying elements, results showed that (1) the thickness of chromizing layer was 150μm; the surface phase component was Fe-Cr solid solution; the surface chromium contents was 21.4%. The thickness of Cr-Ni co-diffusion layer was 40μm; the surface phase component was Fe-Cr-Ni solid solution; the surface contents were: Cr 16.14%, Ni 48.16%. The alloying elements distributed in downward gradient from the outside to the inside. (2) Compared with plain surface alloying technique, using plasma surface alloying technique can get higher diffusing speed and shorten production cycle time. (3) The diffusion coefficients decreased as the diffusion distance increased. (4)Compared with chromizing, Cr-Ni co-diffusion increased the utilization ratio of alloying elements but decreased the diffusion speed of alloying elements, thus the surface alloying content increased and the thickness of alloying layer decreased.

Abstract: The present investigation is on the microstructure evolution and hardness of powder metallurgically processed Al- 0.5 wt.%Mg base 10 wt.% short steel fiber reinforced composites. The 0.38 wt.% C short steel fibers of average diameter 50μm and 500-800μm length were nitrided and chromized in a fluid bed furnace. Nitriding was carried out at 525°C for 90, 30 and 5 min durations. Chromizing was performed at 950°C for 53 and 7 min durations, using thermal reactive deposition (TRD) and diffusion technique. The treated fibers and resulting reaction interfaces were characterized using metallographic, microhardness and XRD techniques.

Abstract: Two types of Ni-base nanocomposites were prepared by co-deposition of Ni with nano-sized particles of Cr or CeO2, respectively. Both Ni-Cr and Ni-CeO2 nanocomposites were mainly composed of nanocrystalline Ni matrix, in which certain content of nanoparticles of Cr or CeO2 randomly dispersed. The Ni-Cr nanocomposite was used as a precursor for preparing a novel hard Ni/CrN coating by plasma nitriding at 560oC. The Ni-CeO2 nanocomposite was used as a precursor to develop a novel oxidation-resistant chromia-forming coating by low temperature chromizing using a conventional pack-cementation method. The microhardness of the nitrided layer on the Ni-Cr nanocomposite and the oxidation resistance of the chromizing coating on the Ni-CeO2 nanocomposite were both greatly increased, in comparison to the corresponding counterparts, which were obtained by plasma nitriding on a conventional coarse-grained Ni-Cr alloy with similar Cr content and by chromizing on a coarse-grained Ni metal, respectively. The relationships among the microstructures of the nanocomposite precursors and the nitrided/or chromized coatings, and their properties were investigated and discussed.