Papers by Keyword: Cr Addition

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Authors: Kyeong Hwan Choe, Sang Mok Lee, Kyong Whoan Lee
Abstract: High temperature oxidation behavior of Si-Mo ferritic ductile cast iron was investigated in the point of the effect of chromium and vanadium addition. The addition of Cr promoted the formation of as-cast pearlite around carbide which exists in cell boundary, which was eliminated during annealing process. The addition of vanadium promoted the precipitation of tiny carbide and reduced the grain size of ferrite. As the test temperature increased, the change of volume increased, on the other hand, the change of weight decreased above 1173K. In the case of Cr added specimen, the change of weight decreased with the increase of test temperature because of the presence of Cr oxide layer. The vanadium added specimens showed higher increase in the weight and volume change. The oxide layer of vanadium added specimen had very porous structure and showed severe internal oxidation. It is due to the catastrophic oxidation characteristic of vanadium alloyed ferrous alloy.
542
Authors: Chihiro Watanabe, Fumiya Nishijima, Ryoichi Monzen, Kazue Tazaki
Abstract: The effects of P and Cr addition and two-step aging on the microstructure and mechanical properties of a Cu-4wt%Ni-0.95wt%Si alloy have been examined. The addition of 0.02wt%P improves both strength and elongation because it suppresses discontinuous precipitation reaction. The Cr addition to the Cu-Ni-Si-P alloy decreases greatly the grain size, resulting in an increase in elongation. Two-step aging, pre-aging at 300 or 350oC and subsequent second-step aging at 450oC, causes an increase in strength without reducing elongation. The increase in strength is attributable to the decrease in inter-precipitate spacing by the two-step aging. The two-step aged Cu-4wt%Ni- 0.95wt%Si-0.02wt%P-0.02wt%Cr alloy attains a tensile strength of 830MPa, an elongation of 13% and an electrical conductivity of 35%IACS.
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Authors: Azdiar A. Gazder, Vladimir Bata, Sujoy S. Hazra, Elena V. Pereloma
Abstract: The effects of 0.74wt% Cr addition on the recrystallisation kinetics of low carbon (LC) steel was investigated using Vickers hardness testing, optical metallography and Electron Back-Scattering Diffraction (EBSD). Compared to the unalloyed steel, Cr addition significantly delays the time for recrystallisation and increases the JMAK pre-exponential factor (k) by an order of magnitude. During initial softening, EBSD returned similar orientations for nucleated and growing grain fractions in both steels. However with longer annealing times the micro-texture of recrystallised grains differs from their earlier counterparts. Overall, the effect of fine Cr carbides on grain boundary mobility in the LC-Cr steel causes variations in recrystallisation kinetics, grain morphology and micro-textures.
679
Authors: Kyeong Hwan Choe, Kyoung Mook Lim, Sang Mok Lee, Kyong Whoan Lee
Abstract: Carbide precipitation behavior in Si-Mo ferritic ductile cast iron was investigated as functions of vanadium and chromium contents. Vanadium addition promoted the precipitation of carbides both in ferrite grains and at its grain boundaries. Pearlite was found to form near the cell boundary next to the eutectic carbides in the as-cast chromium alloyed specimens, and was fully decomposed by an annealing heat treatment. Vanadium addition led to the formation of fine precipitates, prohibiting the ferrite growth, resulting in smaller ferrite grains. The precipitate phase at grain boundaries in vanadium alloyed specimens was identified as vanadium carbide (VC1-x) and the stoichiometry of the eutectic carbide was almost same as that in Si-Mo ferritic ductile cast iron except for a higher vanadium content. However, in the case of chromium alloyed specimen, the ratio of iron in the composition of eutectic carbide was higher than those of Si-Mo and Si-Mo-0.5V cast irons.
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