The effect of small additions of scandium on the properties of aluminium alloys

Additions of up to 1 wt% scandium have been made to Al, Al-Mg, Al-Mg-Ag and Al-Zn-Mg alloys and the effects on age-hardening and mechanical properties studied. Scandium levels up to 1% could be retained in solution at solidification rates of about 300 K s^–1. The precipitation of Al₃Sc at ageing temperatures in the range 563–593 K (290–320 °C) gave significant additional hardening. The low solubility of Sc in the solid state makes it difficult to obtain optimum hardening from Sc and other precipitating elements because of difficulties in solution treatment. The effect of deformation prior to ageing and the temperature-dependent mechanical properties are described.     

Effect of aluminium on microstructure and mechanical properties of self-shielded flux cored welds in low carbon steel plate

Abstract

In the present paper, the results are reported of an investigation dealing with the inclusions, microstructure and mechanical properties of self-shielded flux cored welds with different aluminium contents. Results show that the total number and number density of inclusions in the low aluminium weld are higher than those of the high aluminium weld. However, the average size and the contamination rate of inclusions in the low aluminium weld are 0·77016 μm and 0·022%, which are lower than those of the high aluminium weld. The weld with a low aluminium content contains finer inclusions and the weld with a high aluminium content contains mainly coarser inclusions. There are remarkable differences in microstructure between the welds with different aluminium contents. The reheated zones in the weld made using flux no. 1 are larger than those in the weld made using flux no. 2, which are occupied by skeletal δ ferrite columnar crystals. As a result, a drastic reduction in impact toughness is observed in the high aluminium weld. Fracture examination shows that the low aluminium fracture surface consists mainly of small ductile dimples and a quasi-cleavage fracture area. The fracture surface of the high aluminium weld comprises mainly larger dimples and a cleavage fracture area. Inclusions in the low aluminium weld are mainly small Al₂O₃–MgO spinel with an approximate round shape, and some AlN inclusions. In the case of the high aluminium weld, inclusions are almost all large AlN. Finally, the results of thermodynamic analysis agree with the trends observed in the experimental data.     

The effect of niobium on the microstructure of ferritic stainless steel

The effect of different amounts of Nb and of homogenization on the ferritic stainless steels containing 17–18 wt.% Cr was investigated with scanning electron microscopy (SEM), optical microscopy, energy-dispersive spectrometry (EDS), X-ray diffraction (XRD) and differential thermal analysis (DTA). It was observed that M₂₃C₆, NbC and sigma phase formed in these steels. In addition, the formation of Nb₂C was observed in the sample containing 3.0 wt.% Nb. While the amount of Nb increased from 0.5 to 3.0 wt.% Nb, the microhardness of the matrix and the amount of M₂₃C₆ decreased and the toughness of the samples increased. After homogenization, the increase in the toughness of the samples containing 1.5–3.0 wt.%Nb was considerable and impressive.     

Predicting microstructural evolution and yield strength of microalloyed hot rolled steel plate

Abstract

A mathematical model has been developed to optimise process parameters for production of API grade steel plates by thermomechanical controlled processing at a plate mill in Bhilai Steel Plant, India. The model comprises the prediction of the microstructural evolution during hot rolling, the subsequent phase transformation, and, finally, the mechanical properties of microalloyed steels. Effects of chemistry and mill parameters on recrystallisation, grain growth, and precipitation kinetics were taken into consideration to describe the metallurgical processes. . The model has been validated through laboratory experiments as well as full-scale rolling at the plate mill.     

The effect of microstructure on hardness and toughness of low carbon welded steel using inert gas welding

The heat affected zone (HAZ), has a great influence on the properties of welded joints since it can alter the microstructure and residual stresses. In this paper, the effect of welding parameters and heat input on the HAZ and grain growth has been investigated. The role of grain size on hardness and toughness of low carbon steel has also been studied.     

含磷和钒热轧TRIP钢组织控制及力学性能研究

为探讨含磷和钒热轧TRIP钢的组织控制和力学性能,采用不同变形温度（900和800℃）,研究其相变行为,并在此基础上进行热轧试验.研究表明：随着冷速增加,变形温度对铁素体相变开始温度（Ar3）的影响逐渐增大;相同冷速条件下,变形使贝氏体相变开始温度（Bs）升高;变形对贝氏体相变的促进作用,随着变形温度的降低而减弱.终轧...     

Observation of high-temperature phase transformation in the Si-modified aluminide coating on mild steel using EBSD

Mild steel was coated by hot-dipping in a molten bath containing Al–10 wt.% Si. The phase transformation in the aluminide layer during diffusion at 750 °C in static air was analyzed by Electron Backscatter Diffraction. The results showed that the aluminide layer of the as-coated specimen consisted of an outer Al–Si eutectic topcoat and the inner Fe–Al–Si and Fe–Al intermetallic layers. The formation of τ₅-Al₇Fe₂Si and τ₆-Al₄FeSi was observed with increasing exposure time at 750 °C, while the τ₁-(Al,Si)₅Fe₃ phase precipitated into the Fe₂Al₅ phase. After 60 min of exposure, the τ₅-Al₇Fe₂Si and τ₆-Al₄FeSi phases disappeared. The FeAl phase not only formed at the interface between Fe₂Al₅ and the steel substrate, but also transformed from τ₁-(Al,Si)₅Fe₃ after diffusion for 10 h. With prolonged exposure, the growing FeAl phase decreased the thickness of Fe₂Al₅ and forced the formation of FeAl₂ phase. Finally, the aluminide layer comprised only FeAl₂ and FeAl.     

纳米MoS2轧制液摩擦特性与轧后钢板表面研究

为减少传统冷轧乳化液在轧制过程中油污污染,提高带钢表面质量,采用物理和化学方法将纳米MoS2分散在水基轧制液中替代传统极压抗磨剂添加剂,在四球摩擦磨损试验机上进行摩擦学性能实验.通过冷轧实验,考察了纳米MoS2在轧制过程中对润滑性能的影响;使用接触角测量仪检测了该轧制液的润湿性能,并通过轧后带钢表面粗糙度分析,研究了纳...     

The effect of pre-strain on the material behaviour and the Bauschinger effect in the bending of hot rolled and aged steel

Compression and bend tests were performed on an annealed and aged carbon steel that had been pre-strained by different amounts. A bending model was developed to analyse the bending response of the material. While the bending test results agreed well with some of the material trends found in previous studies focusing on the Bauschinger effect, an overly high reduction of the bending yield with pre-strain was observed. Calculation of the moment curvature diagram for the pre-strained material based on the tensile and compression test data using the analytical model did not fit the experimental curve. In the control of yield phenomena by the industrial processes of temper rolling, skin passing, tension levelling and roller levelling, the effectiveness of the treatment is usually judged from tensile testing after treatment. However, the present work shows that where the yield phenomena have been removed by pre-processing, that the tensile test will not predict the subsequent bending behaviour and that the bending test may provide greater insight. This may have important consequences in the study of cold roll forming where shape defects in the product are believed to originate from small strain forward and reverse bending deformations that will be strongly affected by the Bauschinger and yield effects.     

Cr-Si合金钢原始微观结构对表面纳米化过程的影响

利用表面机械加工法在经过调质处理的CrSi合金钢表面制备了纳米结构层,利用透射电镜(TEM)和X射线衍射(XRD)等分析技术对距表面不同深度的微观结构进行分析,研究原始微观结构对晶粒细化过程的影响.结果显示,在细化初期原始的小角度亚晶界被演化为高密度位错墙,长条形亚晶被演化为含有高密度位错的条形位错胞;一些原始的小角度...     

The effect of low temperature annealing on the mechanical behavior of cold rolled dual-phase Twinning-Induced Plasticity steel

In recent years, Twinning-Induced Plasticity (TWIP) steels with high specific strength have been developed to mainly address the unsaturated demands of transportation industries for weight reduction. To achieve the exclusive mechanical properties of TWIP steels, the understanding of their thermomechanical processing (TMP) behavior is highly necessitated. In the present work, the influence of cold rolling and post-annealing treatments on the mechanical behavior of a new dual phase (γ + α) TWIP steel have been studied. The microstructural studies indicated the presence of deformation twins in the deformed state of material. Annealing the as-rolled experimental alloy could result in the formation of Widmanstätten austenite within the ferrite grains at 500 °C. The nearly constant yield stress at high annealing durations was attributed to the opposite effects of recovery and Widmanstätten austenite formation.     

Effect of microalloying additions on steel plate to pipe property variations during UOE linepipe processing

Abstract

Composition variations have been used to generate three steels, developing plate strengths in the range 350-530 MPa for the same rolling schedules. The tensile properties of the plate have been determined and compared with those of first, pipe formed by the UOE process and second, specimens from the same pipe after flattening. It has been shown that the difference between plate and pipe strength levels for the specific pipe geometry investigated is related to the steel grade. In particular, changes have been related to the Bauschinger stress parameter, optical microstructure, fine particle distribution (from TEM replicas) and stored energy (measured using differential scanning calorimetry) differences between the steels. The trends in property variation result from the balance of work hardening behaviour and Bauschinger effect, and have been related to the presence of fine microalloying element precipitates in higher strength grades, increasing the Bauschinger effect and forming a more highly ordered dislocation structure during the various deformation stages.     

The influence of microstructure on the thermal conductivity of aluminium nitride

Starting from three different commercial powders, AIN materials were densified by pressureless sintering under various temperature and time values in order to investigate the influence of microstructure on thermal conductivity. The influence of the sintering aids (3 wt% Y₂O₃ and 2 wt% CaC₂) and of the forming processes (cold isostatic pressing and thermocompression of tape cast pieces) were also been evaluated. Thermal conductivity increased with the purity level of the starting powder and with an increasing the sintering temperature and soaking time. The highest thermal conductivity values (196 Wm^–1 K^–1) were obtained with the purest powder and high temperature (1800 °C) sintering over long periods (6 h). No influence on thermal conductivity was detected from the forming technique.     

Formation of pinch marks on pack rolled aluminium foil

The matte side of the pack rolled aluminium foils was found to contain frequent pinch marks distributed over the surface randomly with no periodicity along the rolling direction. They were judged to be material-related since only an intermittent fraction of the aluminium coils pack rolled under exactly the same process conditions has suffered this problem. Metallographic investigation of pack rolled foil sections has shown these pinch marks to be invariably associated with eutectic colonies across the section of either one of the packed webs. These lamellar eutectic colonies form due to centreline segregation typical of the twin roll casting process and have apparently survived the homogenization treatment and the downstream processing cycle. They are harder than the solid solution aluminium matrix and resist plastic deformation during cold rolling. They make an impression on the surfaces of both webs while the stacked webs pass through the roll gap. The polishing effect thus produced is retained on the inner matte surfaces that are not in contact with the work rolls producing bright spots.     

Electrocoagulation of cutting oil emulsions using aluminium plate electrodes

The treatment of very concentrated oil-water emulsions by electrocoagulation (EC) was experimentally investigated as a pre-treatment step prior to a membrane process. The oil-water emulsion was prepared from a cutting mineral oil B22 currently used for drilling and machining operations. The electrocoagulation progress was followed by the measurement of COD, turbidity and pH in a batch process with recirculation of the liquid. This study is mainly focused on the effects of operating parameters such as initial pH, current density, oil concentration and recirculation rate, on the de-emulsification efficiency. Kinetic curves showed that the EC process exhibits two phases: a "reactive phase" during which the COD and the turbidity removals increase with electrolysis, and a stationary phase for which further aluminium dissolution is useless in the pollution abatement. The results showed that the treatment efficiency increases with increasing current density, but decreases with oil concentration. It appears that treatment of the considered cutting oil is completed through dissolution of around 10mgAl/g oil, with a slight positive effect of the liquid flow rate. Best results are also obtained with initial pH near 7.     

爆炸复合板与轧制复合板界面结构的研究

用透射电镜、扫描电镜和能谱仪等手段对爆炸和轧制复合板界面组织、相结构和成分变化进行了研究。结果发现爆炸复合是由周期性熔化和非熔化构成的波状复合面，它比轧制扩散复合形成的平面积多１／３左右。两种复合方式都有越过界面的元素扩散，爆炸态扩散范围在２５μｍ左右；轧制态Ｆｅ、Ｎｉ、Ｃｒ元素扩散范围在５０μｍ左右，碳元素越过纯Ｎｉ层向不锈钢侧的扩散范围为１００μｍ左右，在此区域发现沿晶界连续析出有Ｍ２３Ｃ６型碳化物。     

The effect of Si additions on the sintering and sintered microstructure and mechanical properties of Ti-3Ni alloy

Thermodynamic predictions suggest that silicon has the potential to be a potent sintering aid for Ti-Ni alloys because small additions of Si lower the solidus of Ti-Ni alloys appreciably (>200 °C by 1 wt.% Si). A systematic study has been made of the effect of Si on the sintering of a Ti-3Ni alloy at 1300 °C. The sintered density increased from 91.8% theoretical density (TD) to 99.2%TD with increasing Si from 0% to 2%. Microstructural examination reveals that coarse particles and/or continuous networks of Ti₅Si₃ form along grain boundaries when the addition of Si exceeds 1%. The grain boundary Ti₅Si₃ phase leads to predominantly intergranular fracture and therefore a sharp decrease in ductility concomitant with increased tensile strengths. The optimum addition of Si is proposed to be ≤1%. Dilatometry experiments reveal different shrinkage behaviours with respect to different Si contents. Interrupted differential scanning calorimetry (DSC) experiments and corresponding X-ray diffraction (XRD) analyses clarify the sequence of phase formation during heating. The results provide a useful basis for powder metallurgy (PM) Ti alloy design with Si.     

Effect of zirconia additions on the reaction sintering of aluminium titanate

Yttria-stabilized zirconia was added to a chemically prepared mixture of alumina and titania. The effect of the zirconia on the microstructure and resultant properties was studied following reaction sintering to form aluminium titanate. An increase in mechanical strength was observed with little effect on the excellent thermal properties of the aluminium titanate. This was attributed to generation of extra microcracks by the transformation of the zirconia phase and the unusual microstructure produced by the presence of zirconia.