气淬处理钢渣中C2S等温析晶动力学研究

将气淬处理钢渣在不同温度条件下进行恒温热处理,利用金相显微镜和金相分析软件统计分析气淬渣中C₂S等温析晶和长大的规律,使用电子扫描电镜和能谱分析仪研究渣样的显微形貌和元素赋存状态,采用Arvami等人提出的JMAK方程研究C₂S等温析晶动力学。结果表明：气淬钢渣等温结晶的适宜温度是1 450 ℃,恒温时间是30 min,采用此温度和时间,C₂S的平均粒径为34.80 μm,结晶面积为60.97%,30 min后生长缓慢;气淬钢渣中C₂S等温析晶的析晶活化能为-31.34 kJ/mol。     

Interfacial phenomena between fluxes for continuous casting and liquid stainless steel

Abstract

Casting powders melt on the surface of the liquid metal forming a liquid slag layer. Samples taken during casting revealed convective flows in the flux layer and mass exchange with the liquid metal. It is demonstrated that concentrations of certain elements are considerably higher at the phase boundary than in the bulk of the metal and slag phase. Disturbances of interfacial tension produced by mass and charge transfer evidently cause strong shearing forces which act in parallel with the phase boundary. These forces induce convective movements in the flow boundary layer. Convective flows next to the interface between two liquids have been studied in laboratory experiments using various liquids. The results show that the movement velocity of volume elements next to the interface (due to disturbances of interfacial tension) are dependent on liquid layer thickness and on liquid properties. A new dimensionless number describing this manner of convective flow and suitable for evaluation of experimental results is introduced. Its contribution to the total mass transfer will be shown. A dimensionless function describing the relation between convective flows in the slag layer and mass transport is theoretically developed. Coefficients of this function for Ti transfer into the flux layer have been determined empirically.     

Growth of phosphorus concentrating phase in modified steelmaking slags

Abstract

Recycling steel slag to metallurgical process requires removing phosphorus from slag. In this paper, solidification experiments of converter slag modified by SiO₂ at three isothermal temperatures with several durations were performed at air conditions from superheating temperature (1520°C). Grain size evolution of P concentrating phase (C₂S, dicalcium silicate) was investigated. Results show that crystal size distributions of C₂S can be fitted by lognormal distributions, the average size of C₂S increases with increasing dwelling time and grows faster at higher holding temperature, and the relationship between average size of C₂S and holding time can be best described by equation D?=?kt^m. It is concluded that the growth mechanism of C₂S is diffusion controlled, and higher isothermal temperature promotes the growth of C₂S.

Le recyclage de la scorie de l’acier par un procédé métallurgique nécessite l’enlèvement du phosphore de la scorie. Dans cet article, on discute d’expériences de solidification de scorie de convertisseur modifiée par du SiO₄ à trois températures isothermes avec durées variées, effectuées à l’air à partir d’une température de surchauffage (1520°C). On a examiné l’évolution de la taille de grain de la phase de concentration du P (C₂S, silicate dicalcique). Les résultats montrent que l’on peut ajuster les distributions de la taille de cristal (CSD) du C₂S à une distribution log-normale, que la taille moyenne du C₂S augmente avec l’augmentation du temps de résidence et croît plus vite à une température plus élevée de rétention et que la relation entre la taille moyenne du C₂S et la durée de rétention est bien décrite par l’équation D?=?kt^m. On conclut que le mécanisme de croissance du C₂S est contrôlé par la diffusion et que la température isotherme la plus élevée favorise la croissance du C₂S.     

High modulus steels: new requirement of automotive market. How to take up challenge?

Since the last decade, lightening of automotive structure was mainly achieved by gauge reduction using ultrahigh strength steels such as dual phase and transformation induced plasticity grades. However, gauge reduction can significantly reduce the stiffness. Limits are today reached for some applications such as chassis/suspension part. Development of steel with improved specific stiffness becomes more and more relevant to go further in weight reduction. Development of steel matrix composites (SMCs) with ceramic reinforcements is a promising solution. With an appropriate selection of the ceramic, eutectic solidification can be achieved. This natural production route guarantees a good cohesion of the steel/reinforcement interface and the control of the main parameters, which provide final properties of the product (size, shape, clustering of reinforcement). Significant fraction of ceramic can be obtained (10–25 vol.-%). Eutectic SMC can be produced with conventional industrial process such as continuous casting and hot strip mill which guarantees high productivity and low cost.

Depuis la dernière décennie, l’allègement des structures automobiles a été réalisé en grande partie par la réduction des épaisseurs au travers l’utilisation d’aciers à très haute résistance tels que les aciers DP (biphasés) et TRIP (à plasticité induite par transformation). Cependant, cette réduction des épaisseurs peut entraîner une baisse de rigidité. Aujourd’hui, les limites ont été atteintes pour certaines applications telles que les composantes châssis et suspension. Le développement d’acier à rigidité spécifique améliorée devient une voie de développement de plus en plus pertinente pour progresser dans la réduction de poids. Le développement de composites à matrice d’acier et renfort céramique est une solution prometteuse. Au travers d’une sélection appropriée de la céramique, on peut obtenir une solidification eutectique. Cette route naturelle de production des aciers garantit une bonne cohésion de l’interface acier/renfort ainsi que la maîtrise des principaux paramètres qui contrôlent les propriétés finales du produit (taille, forme, agglomération du renfort). Des fractions significatives de renfort céramique peuvent être atteintes (10–25% en volume). Les composites à matrice métallique (CMM) eutectique peuvent être élaborés par des procédés industriels conventionnels tels que la coulée continue ou le laminage à chaud qui garantissent une productivité élevée et un faible coût.     

Inclusion evolution during refining and continuous casting of 316L stainless steel

The formation and characteristics of non-metallic inclusions in 316L stainless steel produced by the AOD (argon oxygen decarburization)–ladle furnace–continuous casting process were investigated. The morphology and composition of inclusions changed significantly during the refining and casting processes. After de-oxidation with Si/Mn additions, spherical complex inclusions mainly consisting of calcium silicates were observed. The contents of MgO and Al₂O₃ in these inclusions continuously increased as the steel moved from the AOD through ladle processing to the tundish. As the temperature decreased from the tundish through to solidification, harmful crystals of MgO/Al₂O₃ spinel were precipitated within the steel melt as well as within the calcium silicate matrix of existing inclusions. The results obtained from thermodynamic calculations carried out using FactSage? commercial software agreed well with the information derived from evaluation of the industrial samples enabling recommendations to be made for the avoidance of detrimental spinel inclusions.     

连接层和退火对 HVAF 喷涂Cr3C2-NiCr 涂层性能的影响

本文使用HVOF和HVAF技术在铜合金上喷涂Cr_3C_2-50wt%Ni Cr涂层,并就NiCr连接层和退火对HVAF喷涂层的耐磨性和耐腐蚀性进行研究。通过对涂层物相组成、显微结构、力学性能、摩擦磨损性能以及电化学动力学曲线进行测试。结果发现:HVAF喷涂层具有比HVOF更高的结合强度,且磨损体积差异较小,但致密的HVOF喷涂层其耐腐蚀性能优于HVAF喷涂层;NiCr连接层的添加提高了复合涂层的结合强度,且致密的连接层结构可阻碍腐蚀液向基体的侵蚀,使复合涂层的耐腐蚀性能提升;退火处理通过消除涂层内部缺陷提高组织致密性,使得耐腐蚀性增强,并且退火处理降低了涂层内部残余应力,导致涂层结合强度和耐磨性能提升;300℃磨损条件下,喷涂层的磨损机制包括黏着磨损、磨粒磨损和局部氧化磨损。     

Estimation of liquidus temperature for B2O3- and TiO2- containing fluoride free mould fluxes from activation energy for viscous flow and DTA measurements

Abstract

Liquidus temperatures of fluoride free mould fluxes simultaneously containing B₂O₃ and TiO₂ have been estimated from two methods, the activation energy for viscous flow and the DTA technique. Generally, the liquidus temperatures determined from the two methods are in good agreement. With the increase in B₂O₃ and TiO₂ content, the variation of liquidus temperatures for fluoride free mould fluxes estimated from the two methods is consistent. As the TiO₂ content increases, liquidus temperatures of the slags initially decrease and then increase. With the increase in B₂O₃ content, the liquidus temperatures of the slags decrease. Further quenching experiments reveal that there is no crystal precipitation in the slag at the liquidus temperature determined from DTA, while some crystal can be observed in the slag at the liquidus temperature determined from the activation energy for viscous flow. Superheating and supercooling effects which could bring errors in determining liquidus temperature by using the two methods are discussed.

On a estimé les températures du liquidus de fondants sans fluorure pour moule contenant simultanément du B₂O₃ et du TiO₂, à partir de deux méthodes, l’énergie d’activation pour écoulement visqueux et la technique de DTA. Généralement, les températures de liquidus déterminées à partir des deux méthodes étaient en bon accord. Avec l’augmentation de la teneur en B₂O₃ et en TiO₂, la variation des températures de liquidus des fondants sans fluorure pour moule, estimée à partir des deux méthodes, va de pair. À mesure que la teneur en TiO₂ augmente, les températures de liquidus des scories diminuent initialement et ensuite, augmentent. Avec l’augmentation de la teneur en B₂O₃, les températures de liquidus des scories diminuent. Des expériences additionnelles de trempe révèlent qu’il n’y a pas de précipitation de cristal dans la scorie à la température de liquidus déterminée à partir du DTA, alors qu’on peut observer quelques cristaux dans la scorie à la température de liquidus déterminée à partir de l’énergie d’activation pour écoulement visqueux. On discute des effets de surchauffe et de surfusion qui peuvent conduire à des erreurs dans la détermination de la température de liquidus au moyen de deux méthodes.     

Effect of CaO/Al2O3 ratio on viscosity and crystallisation behaviour of mould flux for high Al non-magnetic steel

In order to facilitate the development of CaO–Al₂O₃ based mould flux for casting high aluminium, non-magnetic steel, the effect of CaO/Al₂O₃ ratios from 0.6 to 3.2 on viscosity and crystallisation characteristics were investigated with the aid of a rotational viscometer, Fourier transform infrared spectroscopy, a single hot thermocouple technique and X-ray diffraction analysis. The results showed that, at temperatures above 1543?K (1270°C), the viscosity first decreased and then became stable with increase in the CaO/Al₂O₃ ratio. At temperatures below 1543?K (1270°C), the viscosity again first decreased but then increased, with the CaO/Al₂O₃ ratio. This viscosity behaviour can be attributed to changes in the network structure characteristics and the precipitation of solid particles within the liquid flux. Increase in the CaO/Al₂O₃ ratio also first inhibited and then enhanced crystallisation as demonstrated by the changes in initial crystallisation temperatures and incubation times. The X-ray diffraction results confirmed that, at both low and high CaO/Al₂O₃ ratios, the dominant precipitates were compounds with high melting points. On the other hand, with CaO/Al₂O₃ ratios in the midrange, the dominant precipitates were compounds with relatively low melting temperatures. It is concluded that mould flux with a CaO/Al₂O₃ ratio in the range 1.1–1.6 is the most appropriate for casting high aluminium, non-magnetic steels.     

工艺参数对高速火焰喷涂 NiCr-Cr3C2 涂层性能的影响

基于正交回归实验设计工艺参数的方法,本实验研究了喷涂距离、氧气流量和送粉量对高速火焰喷涂NiCr-Cr_3C_2涂层性能的影响,获得了喷涂工艺参数与涂层孔隙率、硬度、结合强度的关系。结果表明:喷涂距离、氧气流量和送粉量对涂层性能具有交互的影响,优化的喷涂距离、氧气流量和送粉量有利于获得性能较好的涂层。     

Investigation on viscosity of mould fluxes during continuous casting of aluminium containing TRIP steels

Abstract

Transformation induced plasticity steel with a high content of Al (Al-TRIP) is an advanced high strength steel. The reaction between Al and SiO₂ would lead to compositional changes in mould fluxes, which results in a decrease in SiO₂ content and an increase in Al₂O₃ content, and influences the physical properties of the molten fluxes. In the present study, the changes of viscosities of a series of mould fluxes with different additives and addition amounts were examined by a rotating viscometer and the crystals in the D series mould fluxes were analysed by scanning electron microscopy and X-ray diffraction. The results show that (a) the Al₂O₃ in mould fluxes containing Li₂O presents amphoteric characteristic; (b) the viscosity of the fluxes with 8% B₂O₃ decreases with the increase in w(Al₂O₃)/w (SiO₂) ratio, the result shows that the Al₂O₃ presents alkaline; (c) the viscosity of flux containing both 4% Li₂O and 5% B₂O₃ changes a little with the increase in w(Al₂O₃)/w(SiO₂) ratio. When the Al₂O₃ content is 30%, the viscosity is 0·204 Pa s and the break temperature is 1130°C; (d) mould fluxes used for Al-TRIP steel precipitate CaF₂ crystals; (e) base on the Riboud model, a suitable viscosity mathematical model for the mould fluxes with high Al₂O₃ content is established.     

Surface tension of pseudo binary and ternary sulphide matte phase systems Ni3S2, Cu2S and FeS by sessile drop technique

Abstract

The surface tensions of pseudo binary systems Ni₃S₂–FeS, Cu₂S–FeS and Cu₂S–Ni₃S₂ and pseudo ternary system FeS–Cu₂S–Ni₃S₂ as a function of composition, at a constant temperature of 1200°C, have been determined. For the Ni₃S₂–FeS and Cu₂S–Ni₃S₂ pseudo binary systems, the surface tensions increased with an increase in Ni₃S₂ content. The amount of Cu₂S has a small effect on the surface tension of the Cu₂S– containing pseudo systems investigated in this study.

On a déterminé la tension superficielle de systèmes pseudo binaires Ni₃S₂–FeS, Cu₂S–FeS, Cu₂S–Ni₃S₂ et du système pseudo ternaire FeS–Cu₂S–Ni₃S₂ en fonction de la composition, à une température constante de 1200°C. Pour les systèmes pseudo binaires Ni₃S₂–FeS et Cu₂S–Ni₃S₂, la tension superficielle augmentait avec une augmentation de la teneur en Ni₃S₂. La quantité de Cu₂S avait un petit effet sur la tension superficielle des pseudos systèmes contenant du Cu₂S, examinés dans cette étude.     

Thermal physical properties and dephosphorisation kinetics of rare earth oxides containing slags

ABSTRACT

The melting properties and viscosity of CaO–SiO₂–MnO–La₂O₃–CeO₂ slags, with mass ratios of 0.97 and 1.05 between CaO and SiO₂, were measured using the hot stage microscopy method and rotating cylinder method, respectively. In addition, the dephosphorisation kinetics of rare earth (RE) oxides containing slags was studied. For increasing mass contents of the RE oxides, La₂O₃ and CeO₂ (0, 3, 6, 9, and 12?wt.%), in the slag, the melting temperature initially decreases and then increases. Minimum values appeared for mass contents of 6?wt.%. RE oxide concentrations below 9?wt.% are beneficial to the decrease in viscosity, which increases significantly with the mass fraction of RE oxides in molten slags with a basicity of 1.05. In slags with a basicity of 0.97, the RE oxides favour the decrease in viscosity, which does not change noticeably as their mass fraction is increased above 6?wt.%. Finally, it was found that the rate-limiting step of the dephosphorisation process is the diffusion of phosphorus.     

Cr_7C_3-(Ni,Cr)_3(Al,Cr)热喷涂涂层残余应力状态及其来源分析

采用热喷涂方法在灰铸铁基体沉积Cr_7C_3-(Ni,Cr)_3(Al,Cr)涂层。通过X射线衍射(XRD)、扫描电子显微镜(SEM)分析涂层的形貌及结构,涂层厚度约235μm,涂层主要相成分为Cr_7C_3相和Ni_3Al相。纳米压痕仪测定涂层硬度为16.022±2.125 GPa,弹性模量为247.75±16.873 GPa。利用sin~2ψ法分析Cr_7C_3相在(522)晶面在不同夹角(Ψ=0°、±9°、±18°、±27°、±36°和±45°)下的残余应力。结果表明涂层表面为残余压应力,残余应力大约为-1375.9MPa,其中本征应力为主要来源约-1267.9 MPa,热应力为次要来源约-108 MPa。     

Viscosity of low silica CaO–5MgO–Al2O3–SiO2 slags

Abstract

The viscosity of CaO–5MgO–Al₂O₃–SiO₂ slag with low silica was measured by rotating cylinder method up to 1823 K. Slag compositions were chosen based on five different levels of SiO₂ content between 0 and 11·80%. The MgO content was 5·0%. The mass ratio of CaO/Al₂O₃ was varied from 0·66 to 1·95. It was shown that viscosity decreased with increasing temperature and decreased with increasing the mass ratio of CaO/Al₂O₃, following by an increase with further increasing the mass ratio of CaO/Al₂O₃. The viscosity decreased with the NBO/T ratio increasing, and the trend that flow activation energy changes with the NBO/T ratio of slag was the same as the trend that viscosity changes with the NBO/T ratio. Based on the experimental data as the boundary of the homogenous phase region, the mass triangle model was used to calculate the viscosity of low silica region.     

Formation and decomposition of C4F7 type calcium ferrites in superfluxed magnetite based pellets during oxidation and reduction

Abstract

In the current work the reactions of magnetite based pellets with large additions of calcite (3%CaO) during reduction have been investigated. This made it possible to use both X-ray diffraction (XRD) and scanning electron microscopy (SEM) to detect reaction phases that normally occur in very small amounts. The main binding phase in the pellets after oxidation was (CaO,MgO,FeO)₄(Fe₂O₃)₇, whereas the one commonly reported in the literature is (CaO)(Fe₂O₃)₂. During reduction at 500–700°C severe cracking occurred in these pellets, especially in the calcium ferrite phase. However, the decomposition of this phase began at 600°C, and therefore it is believed that the reason for the cracks is low strength of the phase itself, rather than weakness induced by reduction of the phase. Upon reduction of magnetite into wüstite at 800°C, the calcium began dissolving in the wüstite, and at 900°C porous calciowüstite had formed in the entire sample, except for some remaining magnetite left in the pellet cores.     

Thermodynamic Properties of Dilute Aluminum in Liquid Zinc

Abstract

The thermodynamic properties of the liquid zinc-aluminum system in the range of 0 to 0.36 mole fraction of aluminum and over a temperature range of 430 to 530 °C were investigated by using an electromotive force (EMF) cell of the type

Al(s)|LiCl–KCl–AlCl₃|Zn–Al(l),Mo

The activity of aluminum was found to show a significant positive deviation from Raoultian behaviour. The activity coefficient of aluminum in the dilute solution range (γ°) and the free energy of solution of aluminum based on the one weight percent (1 wt %) standard state were determined as a function of temperature and found to follow the relationships:

logγ°=(1195/T)?0.874

ΔG_s=5457?11.4T (cal/mole)

Over the temperature range investigated, the self-interaction coefficient of aluminum in liquid zinc (e^Al_Al) was found to be approximately constant at ?0.01.

On a étudié les propriétés thermodynamiques du système liquide zinc-aluminium, entre 0 et 0.36 fraction molaire d'aluminium, à des températures de 430 à 530 °C, en utilisant une cellule à force électromotrice (FEM) du type:

Al(s)|LiCl–KCl–AlCl₃|Zn–Al(l),Mo

On a trouve que l'factivite de l'faluminium montrait une deviation positive importante du comportement Raoultien. On a determine le coefficient d'factivite, γ°, de l'faluminium pour une solution diluee ainsi que l'fenergie libre de solution de l'faluminium, base sur l'fetat standard de un pour-cent en poids (1%), en fonction de la temperature. On a trouve que ceux-ci suivaient les relations suivantes:

logγ°=(1195/T)?0.874

ΔG_s=5457?11.4T (cal/mole)

Dans le domaine de température étudié, on a trouvé que le coefficient d'auto-interaction de l'aluminium dans le zinc liquide (e_Al^Al) était approximativement constant à ?0.01.     

Study on Sulfation of CeO2/γ-Al2O3 Sorbent in Simulated Flue Gas

It is well known that sulfur dioxide(SO2) , morethan50%of which arise fromcombustion of fossil fu-els ,are precursors of acidrain andtheir emission pos-es a global threat tothe atmosphere .Environmental a-gencies have ,therefore ,regulated emissions of SO…     

Partial oxidation of methane on Ni/CeO2-ZrO2/γ-Al2O3 prepared using different processes

The influences of CeO2-ZrO2 and γ-Al2O3 mixing methods on the catalytic activity and stability of partial oxidation of methane （POM） were investigated over Ni/Ce0.7Zr0.3O2-Al2O3 catalysts. The catalysts were characterized by XRD, TPR, H2-chemsorption, and TG-DTA. For fresh catalysts, the results showed that the salt precursor mixing catalyst （ATOM） presented better performance than the catalysts prepared by the precipitator mixing method （MOL） and the powder mechanically mixing method （MECH）. The result of XRD suggested that the interaction between CeO2-ZrO2 and Al2O3 in ATOM sample was stronger than the others, which led to more lattice defects and thereby better initial activity. Moreover, the MECH sample had the best stability and the least coke deposition in 24 h stability tests. The results of TPR and H2-chemsorption indicated that the intimate contact of Ni-Al in MECH sample enhanced the ability of resisting coke deposition and metal sintering.