Micro-properties of (Nb,M)C carbide (M = V, Mo, W and Cr) and precipitation behavior of (Nb,V)C in carbide reinforced coating

In this work, the Micro-properties such as stability, mechanical parameter and bonding structures of (Nb,M)C carbides (M = V, Mo, W and Cr) were calculated. And the misfit and interfacial combination between (Nb,M)C carbides and Fe matrix were investigated by first principles calculation. The precipitation behavior of (Nb,V)C carbides were studied. The element V distribution of the carbide in the coatings were analyzed by experiments. The calculation results show that, in the (Nb,M)C carbides, the lattice constant and formation energy of Nb0.75V0.25C carbide are the smallest, and its hardness and brittleness are the largest. According to bonding analysis, Nb-C covalent bonds are the main factor for its high hardness in Nb0.75V0.25C carbide. The combination between carbide and Fe matrix is improved from the results of misfit and adhesion work. Based on the diagrams of the hardfacing alloys with different V contents, the fraction of MC carbides is increased with increase of V contents, and VC carbide can precipitate when V content is high enough. It indicates that element V can be introduced into NbC carbide from the chemical elements analysis experiments

Sintered silicon carbide molded body and method for its production

Sintered silicon carbide shapes are described. They are produced by using a composition containing an oxide of at least one element chosen from the group: Li, Be, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Nb, Mo, Ba, Tc, Ta, W and Th as a supplement to known sintering aids

ВЗАИМНАЯ РАСТВОРИМОСТЬ КАРБИДОВ В МНОГОКОМПОНЕНТНЫХ ДИФФУЗИОННЫХ СЛОЯХ, ОБРАЗОВАННЫХ НА ТВЕРДОМ СПЛАВЕ

An optimization of powder mixtures has been performed with respect to wear resistance of  diffusive carbide coatings on hard alloy Т15К6 (79% WC, 15% TiC and 6% Co) for four three-component systems, viz. Cr–Ti–V, Cr–V–Mo, Cr–Ti–Mo and Cr–V–Nb,). The «composition-properties» diagrams have been plotted using the obtained mathematical models. Optimum three-component diffusive saturation of a hard alloy using carbide-forming elements permits to increase its service life by the factor of 2.2–3.1 as compared with one-component saturation. This significant improvement of wear resistance of three-component diffusive carbide coatings is due to formation of heterogeneous microstructure containing complex alloyed carbides of IV-VI-group metals with 2–30% mutually soluble one- or two- saturating elements. Выполнена оптимизация составов насыщающих смесей по износостойкости диффузионных карбидных слоев на твердом сплаве Т15К6 (79 % WC, 15 % TiC и 6 % Co) в четырех трехкомпонентных системах на основе Cr–Ti–V, Cr–V–Mo, Cr–Ti–Mo и Cr–V–Nb. Используя математические модели построены диаграммы «состав–свойства». Оптимальное трехкомпонентное насыщение твердого сплава карбидообразующими элементами позволяет повысить его работоспособность по сравнению с однокомпонентным (Сr, Ti, V, Nb) в 2,2–3,1 раза. Такое значительное улучшение износостойкости трехкомпонентных диффузионных карбидных покрытий достигается путем формирования гетерогенной структуры на основе сложно легированных карбидов металлов IV-VI групп, в которых взаимно растворены 2–30 % одного или двух насыщающих элементов

Physical metallurgy of modern creep-resistant steel for steam power plants: microstructure and phase transformations

The fact that the microstructure of steel depends on its composition and the heat treatment given to it has been heavily exploited in the design of steel for power plant applications. To obtain a steel that can function at the higher temperature where power plants operate without failure for extended life, heat treatment is needed to produce fine and highly stable dispersion of carbides, nitrides, and intermetallic compounds in the microstructure of the material. A significant contribution also comes from solid solution strengthening by substitutional solutes. We review here various types of phases, microstructures, functions, and interacting effects of the various alloying elements in the design of steel for modern power plant application

The influence of Widmanstätten ferrite, martensite and grain boundary carbides on the strength and impact behaviour of high Al (0.2%) and Nb containing hot rolled steels

The influence of Al and Nb on the strength and impact behaviour of hot rolled 0.06%C, 1.4%Mn steels has been determined after hot rolling to 15 and 30 mm thick plate. When 0.16%Al was added to the plain C-Mn steel, the impact behaviour significantly improved even though Widmanstätten ferrite (WF) was present. This improvement was due to refinement of the grain boundary carbides and removing the N from solution as AlN. The hot rolled steels all contained WF but when Nb was added more WF formed as well as MA giving poor impact behaviour. Reducing the hardenability from that shown in previous work by decreasing C from 0.1 to 0.06%, Nb from 0.03 to 0.02%, and cooling rate from 33 to 17 K/min had no effect in improving the impact performance of hot rolled Nb steels. To ensure optimum properties not only is it necessary to reduce the hardenability, but WF formation must be discouraged by having a high Ar3. This can only be presently achieved by refining the austenite grain size via control rolling the Nb containing steels; the benefit of adding Al can then, readily be seen. Suggestions are made as to how this might be achieved for hot rolling

Subsurface microstructural changes in a cast heat resisting alloy caused by high temperature corrosion

A cast HP ModNb alloy (Fe–25Cr–35Ni–1Nb, wt.%) was oxidised and carburised in CO–CO2 corresponding to aC = 0.1 and pO2 = 3 1016 atm at 1080 C. Formation of an external, chromium-rich oxide scale led to depletion of this metal in a deep alloy subsurface zone. Within that zone, secondary chromium-rich carbides dissolved, primary carbides oxidised, solute silicon and aluminium internally oxidised, and extensive porosity developed. Pore volumes correspond to the difference between metal loss by scaling and metal displacement by internal oxidation, assuming the scale–metal interface to be fixed. The pores are concluded to be Kirkendall void

Processes, microstructure and properties of vanadium microalloyed steels

Vanadium as an important alloying element in steels was initially associated with the properties achieved following tempering. Interest in the microstructure was stimulated by the advent of transmission electron microscopes with a resolution of ~1nm together with selected area electron diffraction techniques. A second timely development was that of controlled rolling, particularly of plate and sheet products. The scope of this review will include the historical background on quenched and tempered vanadium steels, precipitation during isothermal aging, conventional controlled rolling and during thin slab direct charging and the development of strength and toughness in vanadium microalloyed steels. The characterisation of microstructure, in particular the methods for the analysis of the chemical composition of precipitates, has progressed since the availability of X-ray energy dispersive analysis in the 1970s, and the role played by electron energy loss spectroscopy in providing quantitative analysis of carbon and nitrogen in vanadium microalloyed steels will be presented. There are still many topics involving vanadium microalloyed steels that are controversial. These include the nucleation sequence of homogeneous precipitates of vanadium carbonitride and whether this occurs coherently, the composition of the vanadium precipitates, the nucleation mechanism for interphase precipitation, the importance of strain induced precipitation in austenite of vanadium carbonitride, the contributions of both interphase precipitation and random precipitation in ferrite to the yield strength, and the role of the process route parameters in developing properties. These topics will be considered in this paper which concentrates on hot rolled vanadium microalloyed steels placed in the context of pertinent research on other alloys