Preparation and Properties of Ultra-fine Chromium Carbonization of High Performance Mechanical Activation

The preparation of hydroxyl chromium oxide by hydrogen reduction of disodium chromate and particulate hydroxyl mechanical activation features were studied. Then with self-made hydroxyl chromium as the raw material, a direct reduction and carburization process was used to prepare ultra-fine chromium carbonization. Through SEM and XRD, the high performance mechanical activation, key coefficients, microstructure, hardness and wear-resisting property were investigated. The results reveal that suitable mechanical activation and carbon reducing carbonization temperature, carbonization time, carbon content are beneficial to obtaining ultra-fine chromium carbonization. Typically, when the time of high performance grinding is 5 min, the carbon reducing temperature is 1100 ℃, the carbon reducing time is 1h, the carbon content is 28%, and finally the particle size of chromium carbide powder is 1 μm. Under this condition of preparation of ultra-fine chromium carbide, both the hardness and wear resistance are better than those in the industrialization of chromium carbide coating.

Microstructure and properties of in-situ chromium carbide composite coating by laser cladding

Using Ni/Cr/graphite powder blends as raw powders,a Ni matrix composite coating reinforced by in-situ carbide,was fabricated on the surface of Q235 by means of laser cladding. These microstructure and properties were discussed. The result of phase analysis( XRD) and microstructure investigation( SEM) showed that the coatings consist mainly of CrC,CrCand γ-( Ni,Cr),which are consistent with the thermodynamic calculations. The wear morphology of the coatings was also examined. The results of dry sliding wear tests of different Cr/C ratio show that the wear resistances of the CrC-reinforced coating,respectively,are 13. 4,9. 5,9. 1 and 6. 5 times higher than that of the substrate and the main wear mechanisms of the coatings are adhesion and abrasive wear with slight oxidation.

Spheroidization and Ostwald Growth of Carbide in Isothermal Process of Hot-Deformed High Carbon Chromium Cast Steel

In isothermal spheroidizing process,the spheroidization and growth of the carbide formed in hot-deformed high-carbon chromium cast steel at high temperature were investigated.The results showed that the spheroidizing growth of carbide proceeds in such a way that the bigger carbide particles swallow the smaller ones,and the short rhabdoid carbides dissolve and are spheroidized by itself.When the samples were held at 720℃ for more than 3 h,the spheroidization is not obvious.The feature of the process is the size increment and the amount decrement of carbide particles.The empirical equation for growth rate of carbides was obtained.The volume fraction of carbides keeps constant.The growth process agrees well with Ostwald Ripening Law.

Development of gas tungsten arc welding using current pulsing technique to preclude chromium carbide precipitation in aerospace-grade alloy 80A

Weldments were produced using gas tungsten arc welding(GTAW) and pulsed current gas tungsten arc welding(PCGTAW) techniques with ERNiCr-3 filler wire. Macro examination revealed that the resultant weldments were free from defects. A refined microstructure was observed in the weldment fabricated through PCGTAW. Scanning electron microscopy(SEM) analysis revealed secondary phases in the grain boundaries. Energy-dispersive X-ray spectroscopy(EDS) analysis revealed that microsegregation of Cr carbide precipitates was completely eradicated through PCGTAW. The microsegregation of Nb precipitates was observed in the GTA and PCGTA weldments. X-ray diffraction(XRD) analysis revealed the existence of M_(23)C?_6 Cr-rich carbide and Ni_8Nb phases in the GTA weldments. By contrast, in the PCGTA weldments, the Ni_8Nb phase was observed. The Cr_2Ti phase was observed in both the GTA and the PCGTA weldments. Tensile tests showed that the strength and ductility of the PCGTA weldments were slightly higher than those of the GTA weldments.

Effect of vanadium and chromium on the microstructural features of V–Cr–Mn–Ni spheroidal carbide cast irons

The objective of this investigation is to study the influence of vanadium（5.0wt%–10.0wt%） and chromium（0–9.0wt%） on the microstructure and hardness of Cr-V-Mn-Ni white cast irons with spheroidal vanadium carbides. The alloys＇ microstructural features are presented and discussed with regard to the distribution of phase elements. The structural constituents of the alloys are spheroidal VC, proeutectoid cementite, ledeburite eutectic, rosette-shaped carbide eutectic（based on M7C3）, pearlite, martensite, and austenite. Their combinations and area fraction（AF） ratios are reported to be influenced by the alloys＇ chemical composition. Spheroidized VC particles are found to be sites for the nucleation of carbide eutectics. Cr and V are shown to substitute each other in the VC and M7C3 carbides, respectively. Chromium alloying leads to the formation of a eutectic（γ-Fe ＋ М7С3）, preventing the appearance of proeutectoid cementite in the structure. Vanadium and chromium are revealed to increase the total carbide fraction and the amount of austenite in the matrix. Cr is observed to play a key role in controlling the metallic matrix microstructure.

Preparation and Property of Chromium Carbide Thermal Diffusion Coating on Cold Working Die Materials

Thermal diffusion （TD） salt bath chromizing of cold working dies was studied. Firstly, it obtained an ideal salt bath formula by comparing with a variety of formulas, and then obtained the influence rule of coating thickness based on studying of some process parameters. The microstructure morphologies and phase structures of the TD chromizing coating were investigated by X-ray diffraction （XRD）, energy-dispersive spectrometry （EDS） and other modern analysis methods. Meanwhile, it carried out a system of testing and analysis of coating, such as hardness, wear resistance, etc.

Effect of Rare Earth on theFormation of Liquid ZincCorrosion ResistantChromium-carbide Layer

The effect of rareearth reducing agent on the thickness of layer and properties of bathduring the forming process of liquidzinc corrosion resistant chromiumcarbide layer through the thermalreaction deposition and diffusionmethod was studied. The resultsshow that the addition of 8%RE-SiFe-Mg can make the borax systemwith 15% Cr2O3 have better chromium-carbide layer-formation abilityand excellent technical propertiesthan those of Al or Si at 950 ℃.

The Effect of Chemical Composition and Thermal Sprayed Method on the Chromium and Tungsten Carbides Coatings Microstructure

The microstructure, phase consistence and microhardness of thermal sprayed coatings were investigated. The tungsten and chromium carbide coatings and also composite NiCrSiB coating were analyzed. The microstructure of coatings were observed by using optical microscopy (MO), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Almost equiaxial carbide particles settled inside the surrounded material of coating were found. The cracks propagating thorough the particles and along boundaries between the particles and surrounded material were observed. This phenomenon was connected with the porosity of coatings. The decarburization process was detected in coatings by phase composition investigation using X-ray method. The decarburization process was the reason due to which beside initial Cr3C2 the Cr7C3 and Cr23C6 particles were found. In the tungsten coatings beside the initial WC carbides the W2Cones were found.

Properties and microstructure of VC/Cr_3C_2-doped WC/Co cemented carbides

This paper deals with the effects of codoped VC/Cr3C2 and sintering temperature on the magnetic and mechanical properties of ultra-fine grained WC-12%Co alloys. Results show that the synergistic action of doped VC/Cr3C2 in optimal proportion enhances both the hardness and transverse rupture strength （TRS） of the alloys, with more homogeneous microstructtLre. When the alloy is sintered at 1430℃ and with 0.5% Cr3C2/0.2% VC, the TRS reaches 3786 MPa, the hardness is 91.7 HRA and the grain size smaller than 0.6 μm. The numerical analyses on grain growth during the sintering process show that both VC precipitating on the WC grain boundary and Cr3C2 dissolving in the Co phase decrease the solid/liquid interfacial energy γ, the process of dissolution and reprecipitation is greatly retarded and the coarsening of WC grains is inhibited.

Influence of secondary carbide precipitation and transformation on abrasion resistance of a 3Cr15Mo1V1.5 white iron

The relationship between the secondary carbide precipitation and transformation of the 3Cr15Mo1V1.5 white iron and abrasion resistance was investigated by using optical microscope （OM）, transmission electron microscopy （TEM） and X-ray diffrac- tion （XRD）. The results show that the properties of secondary carbides precipitated at holding stage play an important role in the abrasion resistance. After certain holding time at 833 K subcritical treatment, the grainy （Fe, Cr）23C6 carbide precipitated and the fresh martensite transformed at the holding stage for 3Cr15Mo1V1.5 white iron improve the bulk hardness and abrasion resistance of the alloy. Prolonging holding time, MoC and （Cr, V）2C precipitations cause the secondary hardening peak and the corresponding better abrasion resistance. Finally, granular （Fe, Cr）23C6 carbide in situ transforms into laminar M3C carbide and the matrix structure transforms into pearlitic matrix. These changes weaken hardness and abrasion resistance of the alloy sharply.

EFFECT OF MODIFICATION ON CARBIDE GRANULATION AND ITS MECHANISM

By the modification, network carbide is disconnected at 1100 degree C through uneven dissolution at higher energy places in carbide, where there is twin or lattice distortion, and is granulated at 1130 degree C through element diffusion. The stability of M//7C//3 carbide is decreased because of the modification reducing the segregation of Cr and Mo, thus the temperature, at which uneven dissolution of carbide commenced, is decreased. Also lattice distortion or defect such as twin in carbide is increased by the modification, which prompts widespread disconnections in carbide. In addition, the modification prompts element diffusion to accelerate the kinetics process of carbide granulation. (Edited author abstract) 6 Refs.

高速火焰喷涂VC-CuNiCr涂层的耐腐蚀性能

本研究采用高速火焰喷涂(HVOF)沉积技术,将碳化钒(VC)和铜镍铬(CuNiCr)复合涂层应用于SS316不锈钢上,以解决不锈钢在海洋环境中的腐蚀问题。在室温环境下,在3.5%氯化钠溶液中进行电化学腐蚀,通过扫描电子显微镜(SEM)和能量色散光谱(EDS)对有涂层和未覆涂层样品的表面形貌进行检测。结果表明,涂层内由铜(Cu)、镍(Ni)和铬(Cr)组成的金属间黏合剂在氯化钠介质的影响下发生变质,从而导致出现衬底间的局部点蚀现象。有趣的是,在涂层配方中加入碳化钒(VC)显著地增强了表面的耐腐蚀性能,从而阻止了密闭腐蚀凹坑的出现。在不同类的涂层中,加入VC的效果最好,最小的腐蚀速率为72.38×10^(-3)mm/a,相比之下,SS316基底的腐蚀速率最快。

Growth mechanisms of interfacial carbides in solid-state reaction between single-crystal diamond and chromium

Interfacial bonding is one of the most challenging issues in the fabrication,and hence comprehensively influences the properties of diamond-based metal matrix composites(MMCs)materials.In this work,solid-state(S/S)interface reaction between single-crystal synthetic diamond and chromium(Cr)metal was critically examined with special attention given to unveil the role of crystal orientation in the for-mation and growth of interfacial products.It has been revealed that catalytically converted carbon(CCC)was formed prior to chromium carbides,which is counterintuitive to previous studies.Cr 7 C 3 was the first carbide formed in the S/S interface reaction,aided by the relaxation of diamond lattices that re-duces the interfacial mismatch.Interfacial Cr 7 C 3 and Cr 3 C 2 carbides were formed at 600 and 800℃,respectively,with the growth preferred on diamond(100)plane,because of its higher density of surface defects than(111)plane.Interfacial strain distribution was quasi-quantitively measured using windowed Fourier Transform-Geometric Phase Analysis(WFT-GPA)analysis and an ameliorated strain concentration was found after the ripening of interfacial carbides.Textured morphologies of Cr_(3)C_(2) grown on diamond(100)and(111)planes were perceived after S/S interface reaction at 1000℃,which is reported for the first time.The underlying mechanisms of Cr-induced phase transformation on diamond surface,as well as the crystal orientation dependent growth of interfacial carbides were unveiled using the first-principles calculation.The formation and growth mechanisms of Cr_(3)C_(2) were elucidated using SEM,TEM and XRD analyses.Finally,an approach for tailoring the interfacial microstructure between synthetic diamond and bonding metals was proposed.

Influence of vanadium and chromium additions on the wear resistance of a gray cast iron

A low-alloy gray cast iron containing hard carbide-forming elements, such as vanadium and chromium, was cast by sand mould casting. Its wear resistance was compared with that of an untreated gray cast iron. Three different loading conditions were tested under a con- stant speed. It was observed that this alloy could reduce the wear loss of standard gray cast iron by up to 89%, which was much greater than what was achieved in previous reports. Scanning electron microscopy （SEM） was used to determine the predominant wear mechanism of both the alloys. In a mild wear regime, the oxidative mechanism was predominant; however, in a severe wear regime, this mechanism was not predominant and the adhesive mechanism was involved. EDX analysis was conducted to evaluate the quantitative amounts of elements in the tribochemical films formed on the wear tracks.

Influence of Rare Earth on Property of Low Chromium Semi-Steel

The influence of rare earth( RE) content on mechanical properties and abrasion resistance of low chromium semi-steel was studied by means of metallographic examination,scanning electron microscopic examination and mechanical property test. The experiment results show that RE can improve the comprehensive properties,especially in combination with proper heat treatment. The optimum properties of low chromium semi-steel modified by RE of 0. 25 % could be obtained by normalization at 950 ℃ for 3 h. The main reason is the change in morphology and distribution of eutectic carbide and the precipitation of granular carbides.

基于Ti_(3)C_(2)量子点@罗丹明B荧光探针对Cr(Ⅵ)的传感检测研究

采用刻蚀和水热法合成了碳化钛量子点(Ti_(3)C_(2) QDs),该量子点与罗丹明B(RhB)之间由于静电作用产生荧光共振能量转移(FRET)形成荧光探针,Cr(Ⅵ)的内滤效应(IFE)导致探针荧光猝灭,构建了一种“开-关”型荧光探针用于Cr(Ⅵ)的传感检测.在优化实验条件下,该荧光探针对Cr(Ⅵ)的线性响应范围为0.05-500μmol/L,检出限为0.014μmol/L (S/N=3).构建的荧光探针具有制备简单、稳定性和选择性好,对Cr(Ⅵ)的检测灵敏度高等特点,对环境水样中Cr(Ⅵ)测定的回收率为94.3%-104.0%.研究为水体中重金属离子Cr(Ⅵ)的快速和准确测定提供了一种新方法.

淬火温度对Cr23高铬铸铁组织性能的影响

通过光学显微镜、显微硬度、洛氏硬度及冲击试验,研究了不同淬火温度对Cr23高铬铸铁组织性能的影响,并采用MMW-1立式万能磨损试验机对Cr23的磨损性能进行了测试分析。结果表明:900℃淬火后Cr23高铬铸铁中铸态组织未完全消失;950℃淬火回火后Cr23高铬铸铁的组织为白色的块状、条状碳化物和回火马氏体,二次碳化物弥散分布在基体上;1000℃淬火回火后Cr23高铬铸铁中的组织由回火马氏体、残余奥氏体及长条状碳化物组成,残余奥氏体及回火马氏体都呈现灰黑色。随着淬火温度的增加,高铬铸铁的硬度先升后降,冲击韧性呈下降趋势。高铬铸铁中弥散分布的碳化物可有效提高其耐磨性,回火马氏体基体为碳化物提供支撑,防止其剥落。试样经过950℃淬火+250℃回火后抗磨性最好,较l000℃淬火+250℃回火处理的试样提高了41.4%。

改善高铬铸铁力学性能的研究方法

综述了高铬铸铁的基体组织和碳化物,介绍了近年来国内外研究学者最常用的提高高铬铸铁力学性能的方法:热处理和合金化。发现高铬铸铁的高磨损性能及其他力学性能主要取决于共晶碳化物的数量、类型及基体组织。可通过热处理、合金化等方法,在高铬铸铁凝固过程中改变高铬铸铁的基体结构、改善碳化物的形貌、控制碳化物的生长等方面对高铬铸铁的性能进行优化。最后,对未来的研究方向提出了展望。

Effect of rare earth oxides on the morphology of carbides in hardfacing metal of high chromium cast iron

The flux cored wires with different amounts of rare earth （RE） oxides additions for hardfacing （harden-face-welding） the workpieces of high chromium cast iron were studied in this work.The morphology of carbides in hardfacing metal was observed,and the type of the carbides was determined by optical microscopy,scanning electron microscopy （SEM）,energy dispersive spectrometer （EDS） and X-ray diffraction （XRD）.Based on the data of effect of RE on carbides morphology,the refined reason for carbide by RE oxide was discussed with the misfit theory.The results showed that,the microstructure of hardfacing metal was composed of martensite,residual austenite and M7C3 carbides.With the increasing amount of RE oxide additions,the volume fraction and roundness of the carbides were increased,however,the area and perimeter of carbides were decreased.It indicated that carbides in hardfacing metal could be refined and spheroidized by adding RE oxides in flux cored wires.