捕收剂混合使用的协同效应与其浮选性能的相关关系研究

本文是关于捕收剂混含使用所产生的协同效应大小的相关因素和相关关系研究。研究结果表明,混用组合的协同效应大小与组合中各药浮选性能差之间存在相关关系,其浮选性能差以收率档次差与品位档次差的算术和表示,并命名为CS值。利用这一相关关系,可以大致预测新的混合用药组合的协同效应,从而为选择和设计新的药剂组合提供了一定的依据。     

Serrated yielding in Cu-1 wt-%Cd alloy

Abstract

The influence of grain size and temperature on the serration patterns of the Portevin-Le Chatelier (PLC) effect and on the yield and flow stresses in a Cu-1 wt-%Cd alloy was investigated in the temperature range 150 to 360 ° C. Two kinds of serration patterns were observed in this alloy. Type I occurred at lower temperatures and its yield points are moderately spaced. Type II consists of regular jerky flow observed athigher temperatures. The Hall-Petch equation is obeyed over the temperature range in which jerky flow occurs. The Hall-Petch parameter k (?) is observed to show a local maximum in the temperature range where serrated flow is first observed. The PLC effect is associated with the solute- dislocation interactions, implying that k (?) contains a component associated with grain size dependent dislocation storage.     

Flow transitions in vacuum arc remelting

Abstract

The metallurgical structure of an ingot produced by vacuum arc remelting (VAR) depends critically on the temperature distribution within the liquid portion of the partially solidified ingot. This, in turn, depends on the fluid motion in the pool, since the dominant mechanism for transporting heat is convection. There are three primary sources of motion: buoyancy; Lorentz forces arising from the passage of current through the pool; and Lorentz forces arising from the presence of external inductors. These forces are constantly in competition with each other, and each tends to induce a quite different distribution of velocity and temperature. We examine the transition between these different flow regimes and derive dimensionless criteria which determine which regime is dominant. We show that the structure of an ingot produced by VAR depends critically on the temperature distribution within the liquid portion of the partially solidified ingot. This, in turn, depends on the fluid motion in the pool, since the dominant mechanism for transporting heat is convection. There are three primary sources of motion: buoyancy; Lorentz forces arising from the passage of current through the pool; and Lorentz forces arising from the presence of external inductors. These forces are constantly in competition with each other, and each tends to induce a quite different distribution of velocity and temperature. We examine the transition between these different flow regimes and derive dimensionless criteria which determine which regime is dominant. We show that modest changes in ingot current can produce radical changes in temperature distribution, and that weak, steady magnetic fields, of only ～1 Gs, can induce a powerful swirling motion which suppresses the normal flow.     

Inferences on plastic properties and coefficient of friction during simultaneous compression deformation of dissimilar sintered powder metallurgical preforms

Abstract

Plastic working of powder metallurgical (PM) material necessitates the development of fundamental data such as flow stress, densification behaviour, coefficient of friction, apparent strength coefficient, apparent strain hardening exponent, plastic Poisson's ratio, etc. In the present work compression and standard ring compression tests have been carried out to generate the fundamental data for simultaneous deformation of sintered steel and copper powder metallurgical preforms. The results reveal that the behaviour of individual materials during simultaneous deformation is strongly influenced by local micromechanical interactions at the metal - metal interface. In addition to this, the test conditions (iso-stress and iso-strain) strongly influence the severity of interaction. The interfacial friction coefficients are less than that of the same material when tested between hard tools. The optimal process parameters with higher interfacial friction, which can enhance the solid state joining of dissimilar materials, have been identified. The flow stress of the composite (steel - copper combination) during simultaneous deformation can be estimated if the flow stress of the individual materials comprising the combination/composite are known. With these studies, it should be possible to extend the inferences to the major deformation processes.     

Relative importance of transformation temperatures and sulphur content on hot ductility of steels

Abstract

Low (0·3%) and high manganese (1·4%) plain C – Mn steels with varying sulphur levels have had their hot ductility determined over the temperature range 700 – 1000°C, both after 'solution treatment' at 1330°C and directly after casting. It has been established that the width, depth and position of the hot ductility curves after solution treatment is more related to the transformation behaviour than either the sulphur in solution or the sulphide volume fraction or distribution. The growth of deformation induced ferrite at the austenite boundaries seems to be mainly diffusion controlled, and the higher is the transformation temperature for the γ – α phase change, the faster is the growth. Large amounts of ferrite can then form, giving good ductility. Thus, high transformation temperatures Ae ₃ or Ar ₃ are required to produce narrow ductility troughs. It is believed that any detrimental influence of the sulphides on these 'solution treated' steels is swamped by the rapid increase in ferrite volume fraction. For the as cast state, as more sulphides are able to precipitate at the interdendritic boundaries and austenite grain boundaries than in the solution treated condition, increasing the sulphur level causes a small deterioration in ductility at the high temperature end of the trough. In the present work, only narrow troughs have been found. This is in contrast to previous work on as cast C – Mn – Nb – Al steels, which exhibited wide troughs in the ductility curves, where it was shown that higher total sulphur levels lead to considerably worse ductility and that sulphur can be as detrimental to the ductility as niobium. It is recommended that, to avoid transverse cracking during continuous casting, in addition to keeping the sulphur level low, the carbon and manganese should also be as low as possible.     

Influence of cooling and reheating on the evolution of copper rich liquid in high residual low carbon steels

Abstract

This study investigates some effects of austenite microstructure on processes leading to copper hot shortness. Low carbon steels containing 0˙55 wt-% copper were subjected to two thermal profiles in an infrared image furnace with attached confocal scanning laser microscope: hold at 1150°C for 60 s; hold at 1150°C for 60 s, quench to 400°C, reheat to 1150°C. Heat treatments were conducted in dried/deoxidised argon to image microstructures. Subsequent samples were oxidised in air. The oxide/metal interface was studied in a scanning electron microscope. Additional confocal scanning laser microscope experiments involved melting copper directly on the steel. After quench/reheat, austenite grain size decreased by a factor of ～1˙7 and grain boundaries were redistributed. Copper evolved during the first heating was no longer found at boundaries. Results from direct copper exposure reveal an apparent effect of boundary character on copper penetration rate. Possible mechanisms by which hot shortness is affected are discussed.     

Microstructural and textural evolution during large strain hot rolling (LSR) of Mg–Al (AZ31) alloy

Abstract

Grain refinement has been achieved through large strain rolling (LSR) in Mg AZ31 alloy. The evolution of microstructure and texture has been found to be dependent on the amount of reduction. After the critical amount of reduction, grain refinement proceeds through continuous dynamic recrystallisation (CDRX).     

Particle break-up during heat treatment of 3000 series aluminium alloys

Abstract

In wrought aluminium alloys, the fragmentation of coarse, iron bearing intermetallic particles by hot rolling is an important development in industrial processing. Here a model 3000 series alloy is used to show that fragmentation can occur prior to hot rolling, during the homogenisation heat treatment. Some fragmented particles display a curved morphology of break-up that results from matrix wetting of two phase (or 'duplex') interfaces in Al₆(Fe,Mn) particles partially transformed to an α-Al–(Fe,Mn)–Si phase. In contrast, samples rapidly heated to temperature in a fluidised bath show an angular break-up indicative of tensile stresses induced by thermal expansion mismatch between the intermetallic particles and aluminium matrix. Although this break-up should not be industrially significant, the transformation induced break-up by wetting may be. More generally, internal boundaries resulting from the transformation to α-Al–(Fe,Mn)–Si phase may be mechanically weak fracture initiation points during hot rolling.     

Effects of homogenisation treatment on microstructure and hot ductility of aluminium alloy 6063

Abstract

Several homogenisation treatments were applied to direct chill (DC) cast ingots of aluminium alloy 6063, in order to analyse the resulting microstructures developed from these diverse conditions and their effects on the hot ductility of this alloy. Imaging was performed using scanning electron microscopy (SEM) and a focused ion beam (FIB) instrument. These techniques identified variations in distribution and morphology of second phase particles (AlFeSi and Mg₂Si). FIB results for the various AlFeSi particles correctly identify their shapes in three dimensions (3D). The particles were identified by energy dispersive spectroscopy (EDS) in the SEM, and by X-ray diffraction (XRD) for bulk samples. Hot tensile testing (HTT) was conducted between 470 and 600°C to asses the hot ductility for each condition. The inferior ductility of as cast samples was due to the poor bond strength of the β AlFeSi phase at the grain boundaries. Homogenised samples, which contain α AlFeSi, exhibited improved ductility. Samples that were water quenched following homogenisation were absent of Mg₂Si precipitates, when these elements remained in solid solution. These exhibited the highest ductility.     

Tom Bell Young Author Award Winner 2008 Influence of silicon on nitriding behaviour of hot work tool steels

Abstract

Hot work tool steels are widely used for pressure die casting moulds, die inserts, extrusion tools for aluminium processing and for steel forging. Nitriding increases the lifetime of such tools in many cases, yet delivers disappointing results in others. To optimise performance and for knowledge based surface design, it is indispensable to understand the mechanisms which occur in the near surface zone during nitriding. Nitrogen and carbon profiles obtained for X38CrMoV51 (AISI H13) steels with two silicon levels (1·1 and 0·3%), together with high resolution microscopy and electron energy loss spectroscopy, revealed that the secondary carbides are gradually transformed into nitrides during nitriding. Thermodynamic calculations confirmed the experimental observations. The near surface zone can be divided into three subzones: (1) a nitrogen enriched, almost carbon free zone with high nitride precipitation density and high hardness; (2) a nitrogen enriched and carbon depleted zone where the carbide–nitride transformation occurs; (3) a carbon enriched zone where the displaced carbon from zones 1 and 2 reprecipitates. A correlation between microstructure and microhardness and residual stress profiles was observed for all three zones. It was found that silicon, although not directly participating in the formation of nitrides, has a strong impact on the properties of the near surface zone by stabilising the secondary carbides and retarding the carbide–nitride transformation. This results in homogeneous precipitation in the transformation zone, thus avoiding micrometre sized precipitates which can act as defects and promote crack propagation. The conclusions of the present work are in accordance with literature studies on the effect of silicon on the tempering behaviour and the secondary carbide structure of 5%Cr martensitic steels.