反应温度对纳米碳化钒(V_8C_7)制备的影响

使用偏钒酸铵和纳米炭黑为原料,先制备前驱体粉末,再将前驱体粉末在一定温度下热处理得到纳米V8C7粉末.采用X射线衍射仪(XRD)和扫描电镜(SEM)对不同温度下反应产物的相组成和微观结构进行了分析.结果表明:反应温度对纳米碳化钒制备过程中的相组成和微观结构具有重要影响;随着温度升高,将发生NH4VO3→V2O5→V2→V5O9+V407→V2O3→VC1-x→V8C7的相转变,反应产物的粒度呈增大→减小→增大的变化趋势,1100℃时粉末显示较好的分散性,并且主要由直径100nm左右的球形颗粒组成.     

Evolution of secondary phases in Cr-V low-alloy steels during aging

The influence of both bulk vanadium content and aging conditions on the evolution of secondary phases in Cr-V low-alloy steels was studied. Three 0.1C-0.9Cr-V steels with different vanadium contents (0, 0.258, and 0.512 wt pct) were aged for 100 to 5,000 hours at 773, 853, 953, and 993 K. In the investigation, a limited experimental program (transmission electron microscopy (TEM)) was combined with credible thermodynamic predictions (ThermoCalc). Going out from the good agreement between the predicted and experimental results, behavior of the iron-rich M₇C₃ carbide in time-temperature scale was characterized. The influence of bulk vanadium content was determined on appearance of the M₃C carbide in equilibrium, temperature of the M₇C₃ carbide precipitation, metal compositions of M₃C or M₇C₃ carbides, and vanadium portion in the metallic part of the MX phase.     

Deformation substructure and strain-hardening characteristics of metastable Fe−Mn austenites

The 500° and 550°C strain-hardening characteristics of manganese austenites based on Fe-14 pct Mn-0.4 pct C with carbide forming elements (Cr, V, Mo), were determined and deformation substructures were examined by transmission electron microscopy. Of the carbide formers investigated, molybdenum is the most effective in enhancing the strain-hardening rate of manganese austenite, followed closely by vanadium. The effect of chromium is relatively small. The effectiveness of carbide formers is independent of the strain-induced precipitation reaction, though this varies greatly in extent. Examination of thin foils revealed widely extended stacking faults which persist after heavy deformation, indicating a low stacking fault energy. It is tentatively suggested that the essential role of molybdenum, vanadium, and chromium is to progresively lower the stacking fault energy of a manganese austenite, and thereafter enhance its strain-hardening rate. The lower stacking fault energy postpones cross-slip and, as a result of stacking fault-dislocation interaction, increases the dislocation density and strain-hardening rate. It is concluded that the precipitates play only a minor role in strain-hardening manganese austenites.     

Interaction of tungsten with tungsten carbide in a copper melt

The chemical interaction between tungsten and tungsten carbide in a copper melt with the formation of W₂C at 1300°C is studied. It is shown that the mechanical activation of a composition consisting of copper melt + W and WC powders by low-temperature vibrations initiates not only the chemical interaction of its solid components but also their refinement.     

Synthesis of Fine Vanadium-Carbide (VC<Subscript>0.88</Subscript>) Powder Using Carbon Nanofiber

The synthesis of fine vanadium-carbide (VC_0.88) powder is considered. To produce the vanadium carbide, vanadium(III) oxide is reduced by means of carbon nanofiber in an induction furnace with an argon atmosphere. The carbon nanofiber is produced by the catalytic decomposition of light hydrocarbons. The specific surface of the carbon nanofiber is very high: ~150000 m²/kg, as against ~50000 m²/kg for soot. The impurity content in the carbon nanofiber is 1 wt %. By analysis of the phase diagram of the V–C system, the batch composition and the upper temperature limit in carbide formation may be determined such that vanadium carbide is formed as powder. Thermodynamic analysis yields the initial temperature at which the vanadium( III) oxide is reduced in a furnace with different CO pressures. The characteristics of the vanadium carbide are determined by the following methods: X-ray phase and elementary analysis; pycnometric analysis; scanning electron microscopy with local energy dispersion X-ray microanalysis (EDX); low-temperature nitrogen adsorption with subsequent determination of the specific surface by the BET method; sedimentation analysis; and synchronous thermogravimetric analysis and differential scanning calorimetry (TG/DSC). The material obtained with optimal reduction parameters consists of a single phase: vanadium carbide VC_0.88. The powder particles are predominantly clumped together in aggregates. The mean size of the particles and aggregates is 9.2–9.4 μm, with a broad size distribution. The specific surface of the samples is 1800–2400 m²/kg. Oxidation of vanadium carbide begins at about 430°C and is practically over at 830°C. Optimal synthesis requires stoichiometric proportions of the reagents in the production of vanadium carbide VC_0.88 at 1500–1600°C, with 20-min holding. In this process, carbon nanofiber effectively produces the carbide as the reduction product. The vanadium(III) oxide is reduced practically completely to VC_0.88.     

Preparation and properties of VC + Ni cermets with controlled carbon-to-metal ratio

A series of VC + Ni cermets was prepared where the carbon to metal (C / M) ratio of the carbide was varied from 0.86 to 0.75. Transmission electron microscopy and diffraction were used to determine the C/M ratio of the carbide and binder microstructure. At high C/M ratios, the carbide was principally V₈C₇ or V₈C₇ + V₆C₅, while at low C/M ratios the carbide was V₆C₅ or V₆C₅ + V₄C₃. The vanadium content of the binder increases as the C/M ratio of the carbide is decreased. The mechanical behavior of the cermets was evaluated by crack resistance and hardness measurements. In inverse crack resistancevs hardness plots, the VC + Ni cermets exhibit three types of behavior (labeled Type I, II, and III) in order of decreasing fracture toughness for a given hardness. Auger electron spectroscopy and scanning electron microscopy show that the three behavior types are characterized by differences in the dominant fracture mode. The fracture mode is principally transgranular fracture through the binder for Type I, transgranular cleavage of carbides for Type III, and intergranular or mixed fracture mode for Type II. The differences in fracture mode and mechanical behavior are induced by changes in microstructural features, as well as changes in the binder composition and formation of second phases. These results suggest that binder strengthening is a viable means to improving cermet performance only in systems when the cleavage energy of the carbide is sufficiently high to withstand the stresses generated by plastic flow in the binder. Formerly with Martin Marietta Laboratories, Baltimore     

Effects of Cr and V additions on the microstructure and properties of high-vanadium wear-resistant alloy steel

The effects of chromium and vanadium additions on the microstructure, hardness and wear resistance of high-vanadium alloy steel (containing 5–10 wt-% V and 2–10 wt-% Cr) were studied by means of optical microscopy, scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), Vickers hardness and Rockwell-hardness tester & M-200 ring block wear tester. Researching results showed that the solidification structure of high-vanadium wear-resistant alloy steel was mainly consisted α-Fe (martensite), vanadium carbide (VC), M₃C and M₇C₃. Vanadium is mainly distributed over VC, and certain amount of vanadium exists in the matrix and M₇C₃ type eutectic carbide. Chromium is mainly distributed over the M₇C₃, and the matrix also contains a small quantity of chromium. It is found that the content of VC increases with the increase of vanadium content when carbon and chromium contents are constant. The change of micro- and macro-hardness was not obvious with the increase of vanadium content. The content of M₇C₃ type eutectic carbides increases gradually with the increase of chromium content when carbon and vanadium contents are constant. The micro- and macro-hardness increases with the increase of chromium content. The increase of vanadium content brings to the increase of wear resistance of alloy steel when carbon and chromium contents are constant. The change of chromium content had no obvious effect on wear resistance of high-vanadium alloy steel when carbon and vanadium contents. The increase of vanadium content brings to the increase of wear resistance of alloy steel when carbon and chromium contents are constant. The wear resistance of as-cast high-vanadium alloy steel is the best when the content of vanadium and chromium is 10 wt-% and 5 wt-% respectively.     

Low carbon manganese steels microalloyed with vanadium and nitrogen

With the objective of studying the effect of vanadium and nitrogen microalloying on microstructure and strength of low carbon steels with different manganese contents, three series of low carbon steels (0.1% C) with manganese content (between 0.8 and 3.5%), vanadium content (up to 0.17%) and nitrogen content (up to 0.025%) have been designed and investigated in the hot forging condition using a preheating and finish forging temperatures of 1200 and 950°C, respectively. Steels with a manganese content up to 2.3% revealed ferrite-pearlite structures, whereas higher manganese contents from 2.7 to 3.5% resulted in the formation of bainitic structures. A pronounced effect of manganese on the mechanical properties of steels was detected at lower manganese contents < 1.5%, due to solid solution and grain refining effects, and higher manganese contents > 2.3, due to bainite formation. Manganese content in the range of 1.5-2.3% had less pronounced effect due to solely solid solution hardening. Vanadium microalloying effectively increased the strength of steels through solely precipitation strengthening or both precipitation strengthening and grain refining effect. The effectiveness of vanadium was greatly enhanced by increasing the nitrogen content. The grain refinement of vanadium-nitrogen microalloying seems to be due to inhibition of austenite grain growth as a result of precipitation of vanadium nitride in austenite during forging. Precipitation strengthening of these steels is achieved by precipitation of vanadium carbide and nitride in ferrite or bainite. Nitrogen enhanced the precipitation strengthening of vanadium microalloyed steels which could be attributed to the finer vanadium nitride dispersion precipitates compared with vanadium carbide. Up to 70% of the total nitrogen content of steel precipitates as vanadium nitride which could be achieved with V/N ratio of about 6-7. Microalloying of low carbon-manganese steels (0.1% C and 1.8% Mn) with 0.15% vanadium and 0.025% nitrogen was found to be effective in attaining high levels of yield and ultimate tensile strengths of 835 and 940 N/mm², respectively in the forging condition.     

Interaction of vanadium carbide with a nickel-molybdenum alloy

Melting and solidification temperatures for Ni-Mo alloys (the ratio of these elements is 3:1) containing 10% (by weight) of vanadium carbide are determined. Introduction of vanadium carbide into Ni-Mo alloy reduces the melting temperature by 20°C. The alloys consist of two phases: a solid solution based on nickel and a carbide component resembling needle-shaped inclusions of the eutectic type. Traces of eutectic are observed with 1% VC in a sample. Dissolution of vanadium in the Ni-Mo alloy mentioned does not exceed 1% (by weight). The presence of two phases and their approximate composition in the alloys are confirmed by x-ray diffraction analysis. The solid solution based on nickel contains molybdenum (10–20%) and vanadium (1–6%). The carbide component is a vanadium-containing phase based on molybdenum with a crystal lattice of the Mo₂C type.Scientific Research Institute of Refractory Metals and Hard Alloys. Moscow. Translated from Poroshkovaya Metallurgiya, Nos. 1–2, pp. 59–62, January–February, 1994.     

Characterisation of functionally graded and VC/steel surface alloyed composites produced using powder metallurgy

Abstract

In this study, low carbon steel specimens with surface alloyed composites were produced by means of powder metallurgy. Vanadium carbide, graphite (1·2 wt-%) and Fe were used for the surface alloyed composite, while Fe and graphite (0·2 wt-%) were used for the low carbon steel side. The powder mixtures were compacted together in the same mould. On the surface alloyed side the vanadium carbide content was changed from 5 to 25 wt-%. Microstructural investigations including EDX and X-ray, hardness measurement and abrasive wear tests were performed. The results showed that V₈C₇ formed in the alloyed surface and carbon diffusion from the alloyed surface to the parent metal created a functionally graded material. The hardness values decreased towards the parent metal. Wear resistance increased as the vanadium carbide increased in the surface alloyed composite. Thus, a functionally graded steel having a surface composite that is resistant to abrasive wear can be obtained via the powder metallurgy route.     

V2O5碳热还原合成碳化钒粉末的反应过程

为了实现小批量连续化制备碳化钒粉末,以工业级V2O5和纳米炭黑为原料,利用碳热还原法,在常压下碳管炉中得到了V8C7。通过X射线衍射仪(XRD)、扫描电镜(SEM),分析了合成过程。结果表明:在较低的温度下,纳米炭黑将V2O5还原为VO2;随着合成温度的升高,还原为更低价的V2O3,但没有VO生成;接着发生碳化反应,生成VC1-x、V8C7,合成的各阶段相互重叠;在合成过程中,试样的显微组织因物相不同而有所不同,生成的钒氧化物为炭黑附着的颗粒状大团聚体,VC1-x粉末颗粒呈类球形,但大小不均匀;随着温度升高,合成的最终产物V8C7粉末颗粒呈球形或类球形,大小均匀,粒度为1μm左右;还原碳化过程中,产生的气体有CO、CO2。     

Physicochemical interaction and structure development during the formation of metal gas-transfer coatings on diamond (review). 1. Kinetics

Work devoted to studying the phase composition and thickness of chromium, titanium, molybdenum, vanadium, and tungsten coatings which form on diamond powder during vacuum annealing of this powder mixed with chromium powder or oxidized powders of Ti, Mo, V, and W is analyzed. Coatings consist of metal (Cr, Ti, Mo, V, W) and carbide (Cr₇C₃, Cr₃C₂, TiC, -Mo₂C, V₂C, VC, W₂C, WC) phases. Diffusion of carbon during coating growth with increased metallizing time and temperature causes carbidization of chromium, titanium, and vanadium (it causes a reduction in the content of metal phase and an increase in carbide phases is coatings), growth of higher carbides (Cr₃C₂, VC, WC) at the expense of lower carbides (Cr₇C₃, V₂C, W₂C), and filling of carbon vacancies in the lattices of TiC and VC. Saturation of coatings with carbides correlates with the temperature-time range in which a further increase in coating weight slows down.Translated from Poroshkovaya Metallurgiya, No. 7(355), pp. 34–40, July, 1992.     

The effect of nitrogen on precipitation and transformation kinetics in vanadium steels

The isothermal decomposition of austenite has been studied in a series of vanadium steels containing varying amounts of carbon and nitrogen, (in approximately stoichio-metric proportions), in the temperature range 700 to 850°C. In the basic alloy, Fe-0.27V–0.05C (composition in wt pct), below 810°C the austenite to polygonal ferrite trans-formation is accompanied by interphase precipitation of vanadium carbide, the finer dis-persions being associated with the lower transformation temperatures. However, below 760°C there is an additional precipitation reaction where dislocation precipitation of vanadium carbide predominates; this is shown to occur in association with Widmanstätten ferrite. Above 810° C, a proeutectoid ferrite reaction results, the ferrite being void of precipitates; evidence is provided to show that partitioning of vanadium from ferrite to austenite occurs during the transformation. In the two steels containing nitrogen, namely Fe-0.26V-0.022N-0.020C and Fe-0.29V-0.032 N the basic interphase precipitation re-action is unchanged, but the resultant precipitate dispersions are finer at a given trans-formation temperature. The temperature range over which interphase precipitation oc-curs is expanded by the presence of nitrogen, since the Widmanstätten start tempera-ture is depressed and the proeutectoid ferrite reaction is inhibited. Precipitation in austenite prior to transformation and twin formation during transformation are both en-couraged by the presence of nitrogen.     

Synthesis of hafnium carbide by mechanochemistry and irradiation

The interaction in the Hf–C system during mechanical activation performed in a high-energy planetary ball mill and the irradiation-assisted fabrication of hafnium carbide from an Hf/C mechanocomposite are studied by synchrotron X-ray diffraction (at a quantum energy of 33.7 keV) and high-resolution scanning electron microscopy. The mechanochemical interaction results in the formation of an Hf/C mechanocomposite at the first stage and mechanical activation for ≥8 min forms hafnium carbide. The irradiation of the Hf/C mechanocomposite with a high-energy electron beam (~150 W/mm²) causes melting and spreading of hafnium over the carbon particle surface and the crystallization of hafnium carbide.     

Pilot plant manufacture of vanadium carbide

Conclusions A manometric study was carried out of the reduction of vanadium oxide with carbon, and it was found that the pressure vs time curve exhibits three discontinuities, at temperatures of 1200°C (formation of the monoxide VO), 1400°C (formation of VC_X-VO solid solutions), and 1700°C (formation of the carbide VC_X).An investigation of the vacuum reduction of vanadium oxide confirmed that it is impossible to obtain a vanadium carbide with a carbon content in excess of that represented by the formula VC_0.9.It was found that the optimum conditions for the preparation of large, pilot plant scale, batches of a vanadium carbide phase with a composition corresponding to VC_0.9 by the reduction of the oxide V₂O₃ with graphite heating elements and a reducing gas atmosphere are as follows: heating to a temperature of 1900°C in 40 min and subsequent holding for 60 min.Translated from Poroshkovaya Metallurgiya, No. 11(71), pp. 83–88, November, 1968.     

Composite magnetoabrasive TiC-Fe,VC-Fe,and Cr-C-Fe powders

Conclusions A study was made of the conditions of direct synthesis of composite MAMs from the simple substances. It has been established that the heating of mixtures of powdered carbide-forming transition metals (Ti, V, and Cr), carbon black, and iron in the temperature range 1300–2000°C results in preferential formation of titanium and vanadium carbides which are uniformly distributed in an iron matrix in the form of globules. The shape and size of the globules are determined by the carbide concentration in the composite and synthesis conditions. The chromium carbide Cr₃C₂ is not easy to synthesize in the presence of iron. The boundaries of fields of synthesized titanium and vanadium carbides in an iron matrix are clearly defined. The extent of carbide-iron interpenetration is negligible, not exceeding 3–7% of the carbide grain (globule) diameter. In the series Ti-V-Cr the degree of chemical reaction of these carbide-forming metals and their carbides with iron increases from titanium to vanadium and chromium. On the basis of data yielded by this investigation, a method is proposed for producing titanium carbide- and vanadium carbide-containing iron-base composite MAMs; the optimum compositions and conditions of synthesis of such composites have been determined. Pseudofused composite MAPs containing titanium and vanadium carbides possess excellent physicomechanical properties (grain strength, abrasive ability, and specific saturation magnetization intensity), and can be recommended for machining various materials, in particular steels. The results obtained have been utilized in the development of TU 6-09-4575-78 for MAMs, on the basis of which such materials are now being produced on an industrial scale at the Donetsk Chemical Reagents Factory.Translated from Poroshkovaya Metallurgiya, No. 3(243), pp. 94–100, March, 1983.     

电感耦合等离子体原子发射光谱法测定碳化钒中铁磷钛

准确、快速地测定碳化钒中Fe、P、Ti等杂质元素含量,对碳化钒产品质量判定意义重大。试验采用酸溶后碱熔回渣方法溶解样品,即先用王水溶解样品,再过滤,滤渣及滤纸经灰化后再用混合熔剂(碳酸钠-硼酸)熔融。采用基体匹配法绘制校准曲线消除基体效应的影响,使用电感耦合等离子体原子发射光谱法(ICP-AES)测定Fe、P、Ti。方法中Fe、P和Ti校准曲线的线性相关系数均大于0.999,方法检出限分别为0.00036%、0.00082%和0.0012%。实验方法用于3个碳化钒实际样品中Fe、P、Ti的测定,结果的相对标准偏差(RSD,n=7)小于0.90%,加标回收率为96%~103%,测定值与其他方法(Fe采用GB/T 20255.2—2006火焰原子吸收光谱法、P采用YB/T 4566.6—2016铋磷钼蓝分光光度法、Ti采用GB/T 20255.3—2006火焰原子吸收光谱法)测定值相吻合。有效解决了碳化钒中低含量Fe、P、Ti的同时测定问题,可用于碳化钒中0.015%~0.113%Fe、0.016%~0.046%P、0.015%~0.088%Ti的测定。     

电感耦合等离子体原子发射光谱法测定碳化钒中铁磷钛

准确、快速地测定碳化钒中Fe、P、Ti等杂质元素含量,对碳化钒产品质量判定意义重大。试验采用酸溶后碱熔回渣方法溶解样品,即先用王水溶解样品,再过滤,滤渣及滤纸经灰化后再用混合熔剂(碳酸钠-硼酸)熔融。采用基体匹配法绘制校准曲线消除基体效应的影响,使用电感耦合等离子体原子发射光谱法(ICP-AES)测定Fe、P、Ti。方法中Fe、P和Ti校准曲线的线性相关系数均大于0.999,方法检出限分别为0.00036%、0.00082%和0.0012%。实验方法用于3个碳化钒实际样品中Fe、P、Ti的测定,结果的相对标准偏差(RSD,n=7)小于0.90%,加标回收率为96%~103%,测定值与其他方法(Fe采用GB/T 20255.2—2006火焰原子吸收光谱法、P采用YB/T 4566.6—2016铋磷钼蓝分光光度法、Ti采用GB/T 20255.3—2006火焰原子吸收光谱法)测定值相吻合。有效解决了碳化钒中低含量Fe、P、Ti的同时测定问题,可用于碳化钒中0.015%~0.113%Fe、0.016%~0.046%P、0.015%~0.088%Ti的测定。     

粉末热等静压9.75％钒成分冷作模具钢组织与力学性能的研究

通过气雾化制粉-热等静压工艺成功制备了含钒9.75％冷作模具钢.借助X射线衍射仪、扫描电镜、电子能谱分析仪、透射电镜等研究了该成分钢种不同热处理状态的相组成、组织形貌.研究表明:退火态相组成为铁素体和MC型碳化物及少量M7C3型碳化物,碳化物呈近球形颗粒状、粒径大多在2μm以下,分布均匀;1 120℃真空淬火条件下,随...     

An evaluation of vanadium oxycarbide as ladle addition to molten steels

The present paper deals with a process involving carbothermic reduction of vanadium trioxide to produce vanadium oxycarbide. The vanadium, oxygen and carbon constituents of the oxide-carbon reaction product of the present work satisfy the empirical formula VO(0.67-0.44)C(0.20-0.70) ⋅ The paper also presents results of additions of the various grades of vanadium oxycarbide to steel melts. Results of additions have been compared with those obtained with vanadium carbide and ferro-vanadium additions. Such studies have pointed towards the suitability of VO(_0.52-0.46)C(_0.23-0.37) for introducing negligible amounts of additional carbon into steel melts. An attempt has also been made on the electroextraction of vanadium using vanadium oxycarbide as soluble anode.