披覆含鉻質硬層之Fe-Mn-Al合金鋼耐蝕性研究

Chromium carbide coatings deposited by the salt bath method have a lot of technologically interesting characteristics. This method produces hard, wear–resistant, oxidation and corrosion–resistant coating layers on steel substrates. In the present study, the kinetics of chromium carbide formation on carburized and uncarburized AISI 1020 steel substrates has been compared. The presence of the Cr7C3 phase on the surface of steel substrates was confirmed by X-ray diffraction. Cross–sectional observation of optical and SEM images showed that chromium carbide layers formed on the steel substrates were rather compact and smooth. The kinetics of chromium carbide coating by salt bath immersion indicated a parabolic relationship between carbide layer thickness and treatment time. The activation energy of the formation of carbide on the surface of carburized and uncarburized steel was calculated to be 87.9 and 225.6 kJ/mol, respectively. Moreover, an attempt was made to present contour diagrams for predicting the thickness of the chromium carbide layer. In addition, the possibility of establishing and using some mathematical relationships between process parameters and chromium carbide layer thickness was investigated.

The purpose of this work was to study the hot-corrosion behavior of dissimilar weldments of AISI 304 stainless steel and AISI 1015 low carbon steel assembled with consumable-309L stainless steel wires at 750 °C in static air with 2 mg/cm^2 mixture of various ratios of NaCl-Na_2SO_4 deposits. It was found that the HAZ of weldments revealed the coarse grain structure and the around 304 HAZ. Moreover, the carbon migrated from the substrate of low carbon steel of the higher chromium weld metal side and formed chromium carbide adjacent to the interface between the low carbon steel HAZ and weld metal. The results of hot corrosion showed that both 304 and 309L appeared the subscale attack while low carbon steel revealed the uniform corrosion. The depth of attack increased with increasing exposure duration of time. The 309L weld metal had the smallest metal loss because of its high chromium content. Due to sensitized reaction the 304 HAZ had the highest metal loss and the total depth of attack. The galvanic effect to the low carbon steel resulted in a serious corrosion with sufficient molten salts at low carbon steel HAZ/WM interface.

This study investigated the effect of the chromium on the hot corrosion behavior of Cr-Mo steels in a mixed molten salt. The corrosion test was performed by immersing Cr-Mo steels with different chromium content (0, 2.25, 5, 9, 12 wt% Cr) in static molten LiNO_3-NaNO_3-KNO_3 eutectic salt at 550℃ for 250, 500 and 1000 hours with nitrogen cover gas. The results show the weight gains of the steels are directly proportional to the duration of time while those are inversely proportional to the chromium content. The microstructure analyses of the corroded steels show the corrosion scales on the steels are composed of an outer LiFeO_2 and an inner (Fe,Cr)_3O_4 layers. Also, the thickness of the scales decreased with increasing chromium content. According to the result of this study, it has been confirmed that the corrosion resistance of steels in the molten slat can be dramatically improved when the chromium content reached 9 wt%.

In solar thermal storage system, the mixed chloride molten salt with the higher conversion efficiency than a single molten salt, but they are more corrosive than the often used nitride molten salts. In the presents work, aluminide and chromate coating were prepared on the surface of Inconel625 alloy by thermal packing method. The corrosion behaviors of thermal diffusion coating on the surface of Inconel625 alloy in mixed molten salts at 900°C were studied by using XRD and SEM equipped with EDS in the present work. The results showed that both of the two thermal diffusion coatings have sever corrosion in the mixed chloride molten salts, but thermal diffusion Al coating in the mixed chloride molten salt corrosion is more serious than thermal diffusion Cr coating, because Cr2O3is more easily dissolved in the molten salt than Al2O3.

High-temperature corrosion behavior of austenitic stainless steel in quaternary nitrate molten salt nanofluids for concentrated solar power

Molten salt chlorination process in the titanium industry is difficult to apply on a large scale because of producing a large amount of environmentally polluting molten salt chloride slag. The phase transition method is an effective novel method to achieve the separation of the impurity components and recovery of NaCl from the molten salt chloride slag, which is mainly composed of ternary mixed molten salt NaCl-MgCl2-CaCl2. This study investigated how the physical properties of the liquid phase influence the separation behavior of NaCl during the phase transition of chloride salt slag. Molecular dynamics simulations were used to study the physical properties of the liquid phase of molten salt chloride slag with Na2SiO3 additive, including radial distribution function, ion self-diffusion coefficient, density and viscosity. The ternary mixed molten salt NaCl-MgCl2-CaCl2 system with oppositely charged ion pairs exhibits a more stable coordination structure, with the interaction strengths following the order Mg-Cl > Ca-Cl > Na-Cl. The recovery of NaCl at different temperatures was investigated by phase transition method using Na2SiO3 additive. The additive of Na2SiO3 leads to a decrease in the ionic self-diffusion coefficients, density and viscosity of the mixed molten salt. The determination coefficients R2 for the fitted models of density/viscosity (mixed molten salt with Na2SiO3) and NaCl recovery during the phase transition of molten salt chloride slag were 0.9626 and 0.9073, respectively. The regression equation describing the relationship between density and NaCl recovery showed better agreement. The experimental results provide a reliable validation of the calculated results. These research results provide important insights to solve the pollution problem of molten salt chloride slag.

After preliminary thermodynamic calculations for verifying their refractoriness, six (Ni,Co)-based alloys were synthesized by casting. They contain chromium, carbon and tantalum to achieve interesting chemical and mechanical high temperature properties. Their microstructures in the as-cast state were observed by electron microscopy (SEM) to discover the carbides characteristics. Differential thermal analysis (DTA) was carried out for all of them to assess their melting points notably, for having better knowledge about the level of high temperature at which they can be used potentially. Thereafter thermomechanical analyses (TMA) were run to explore their behaviour in thermal expansion. As shown by the thermodynamic calculations all the alloys are theoretically possible to be shaped by conventional foundry due to liquidus temperatures all below 1400°C. According to these same results, the solidus temperatures of all alloys would stay over 1250°C, this suggesting that all alloys would be able to be used under moderate mechanical stresses at temperatures as high as 1200°C. As suggested by calculations, the as-cast microstructures are all dendritic and the interdendritic spaces are occupied by carbides. According to calculations again, the Ni-richest alloys contain chromium carbides, but tantalum carbides are also present, a presence which was not expected. In contrast the Co-richest versions contain only TaC carbides. The DTA experiments show that the solidus and liquidus temperatures both increase by going from the Ni-richest alloys to the Co-richest ones. The TMA experiments demonstrate that the thermal expansions and thermal contractions are rather continuous, without any irregularities, and the average thermal expansion coefficients, all close to 20 × 10-6 K-1 , do not systematically depend on the respective proportions of nickel and cobalt. This first part of the whole work will be followed by two other parts dealing with the effect of these Ni and Co proportions on the high temperature oxidation phenomena, for temperature variations and for isothermal conditions respectively.

The aggressive environment corrosion at increasing temperature is the major problem in the components of boiler and gas turbine, etc. This degradation occurs by application of large variety of fuels like coal and oil, etc., at higher temperature. Boiler steel materials were found to be good corrosion resistance, but they lacked to corrosion at higher temperature in aggressive environment. The detonation gun Cr 3 C 2 -25NiCr sprayed coating provides an appropriate solution to minimize the problem of hot corrosion such that enhances the life of the components of boiler and gas turbine, etc. The Cr 3 C 2 -25NiCr coating provides dense microstructure and low porosity which improves the material resistance to hot corrosion. The thermo-gravimetric processes were involved to find reaction rate. The scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) techniques were used to estimate the corrosion products and oxides of uncoated and coated specimens. It was seen that boiler steel SA213 showed excellent corrosion resistance than SA516 at higher temperature in aggressive environment. Keywords: Corrosion environment, detonation-gun method, energy dispersive spectrometry (EDS), scanning electron microscopy (SEM), surface coating Cite this Article Anil Kumar, N.K. Mishra, Vivek Srivastava. Effect of Hot Corrosion on SA-213 and SA-516 Boiler Steels in Na 2 SO 4 -50%NaCl Molten Salts Environment at 800 ° C. Journal of Aerospace Engineering & Technology . 2018; 8(2): 1–6p.

Electroplating of chromium and Cr-carbide coating for carbon fiber

The effect of formic acid concentration on the conductivity and corrosion resistance of chromium carbide coatings electroplated with trivalent chromium

Hollow spherical 0.5Li2MnO3·0.5LiMn1/3Ni1/3Co1/3O2 prepared by facile molten salt method for enhanced long-cycle and rate capability of lithium-ion batteries

On the formation and properties of chromium carbide and vanadium carbide coatings produced on W1 tool steel through thermal reactive diffusion (TRD)

In order to control the required surface quality, generally it is vital to have the choice of optimized cutting factors in various industrial machining operations. The trait of surface finish is a vital concern for most of the turned parts in an industry. The present research work is focused on the optimization of cutting process parameters (depth of cut, feed rate, spindle speed) in wet turning of High Carbon High Chromium Steel (2.2% C) having hardness 50+2 HRC. Therefore turning operations were performed on High Carbon High Chromium Steel by carbide P-30 cutting tool in wet condition and the combination of the optimal levels of the parameters was obtained. Analysis of Variance (ANOVA) and SN (Signal-to-Noise) ratio were implemented to analyze the performance characteristics in wet turning operation. The results of the analysis show that none of the factors was found to be significant. Taguchi method showed that spindle speed contributed the highest effect on the surface roughness followed by depth of cut and feed rate while turning High Carbon High Chromium Steel by carbide cutting tool in wet turning. The useful results obtained by this research can be the eye openers for other similar type of future research works.

Six chromium-rich M-based alloys (M=Co, Ni or Fe) with conventional carbon contents (0.25 and 0.50wt.%) and containing near 4wt.% of hafnium were elaborated in foundry. As expected, dense precipitation of hafnium carbides was achieved, with repartitions and shapes similar to what it is generally obtained with tantalum carbides. Chromium carbides were also obtained in some alloys. After exposure of samples at 1200°C for about 48 hours the HfC carbides network was kept without significant changes of morphology and surface fractions, in the cobalt-based and nickel-based alloys, in contrast with the iron alloys which appeared less stable. Indentation performed in as-cast and aged samples showed that these HfC-containing alloys display various hardness values. The HfC-containing cobalt alloys are the hardest ones and the high temperature exposure induced a limited lowering of this property. The cast HfC-containing cobalt alloys are potentially very interesting for applications at very high temperature requiring foundry equi-axed chromium-rich alloys.

In situ formation of chromium carbide in a mullite matrix through reaction of Cr2O3, SiC and A2O3 has been studied. Three different chromium compounds, Cr3Si, Cr3C2, Cr7C3, and mullite were formed. In a vacuum environment, the Cr3Si particles formed first and were retained below 1550 °C, while the Cr7C3 phase was only dominant above 1600 °C. The Cr3C2 phase was the dominant dispersed phase at temperatures of 1450–1500 °C. In an argon environment, the Cr3C2 phase was the main product component at temperatures ranging from 1450 to 1550 °C. The mullite phase formed concurrently through the diffusion of the SiO2 phase into the Al2O3. SiO2 was the product of the reaction between Cr2O3 and SiC. The composite hot-pressed at 1450 °C in vacuum gave a flexural strength and fracture toughness of up to 457 MPa and 4.1 MPa m1/2, respectively.