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).     

Relative anisotropy of structures and ultrasound attenuation response between laboratory casting in permanent mould (vacuum induction melted) and casting processed through electroslag refining

Abstract

In the present study, ingots of 'modified 15CDV6' (0·3C–CrMoV) steel were laboratory melted and cast by the vacuum induction melting–electroslag refining (VIM–ESR) and VIM (water cooled steel mould) routes. The ingots have been evaluated for their relative anisotropy differences by ultrasound attenuation (UA) studies along respective radial and axial directions. The expected sources of UA are crystallographic texture and the presence of defects. These defects include inclusions, grain boundaries, segregation and microporosity. Apart from microporosity, the presence of defects has been characterised along the respective casting directions. Although both castings/ingots had gone through successive phase transformations after solidification (liquid→δferrite→austenite→ferrite), the electroslag refined (ESR) material had significantly more anisotropy in crystallographic texture, but insignificant anisotropy in inclusion distribution, as compared with the vacuum induction melted (VIM) material. The grain boundary character distributions and long range compositional fluctuations were similar and nearly isotropic between the two ingots. The ESR material, in general, was denser, which may indicate a lower presence of microporosity. Taking grain size differences into account, the UA estimated anisotropy was more for ESR material, a response clearly dominated by the anisotropy of the crystallographic texture. At a higher frequency, and correspondingly finer resolution for defects, the anisotropy owing to defects played a more dominant role, but even then the highest frequency of 2 MHz was not adequate to highlight a dominance of defect anisotropy.     

Forming characteristics of coated products for packaging applications

Abstract

A comparison of forming characteristics has been conducted on two different thickness steel substrates used in the packaging industry. Three surface conditions were studied, namely, uncoated blackplate, a lacquered electrochromium coated steel (ECCS), and a typical film laminate specification. It was found that for identical forming conditions the failure rates of both blackplate and lacquered ECCS materials were higher than in the film laminated alternative. This is shown to be related to the frictional effects of the coatings. In the film laminate material, failures were only observed at high blankholder forces near the forming limit of the material. The blackplate material produced cups, which were 0·4 mm taller than both the lacquered and film laminated coatings.     

Effect of talc and bauxite on sintering,microstructure, and refractory properties of Egyptian dolomitic magnesite

Abstract

Refractories produced from mixes of Egyptian dolomitic magnesite with talc and low cost Chinese bauxite have been assessed as potential substitutes for the high temperature basic refractory bricks currently used in steelmaking and other industries. Fifteen batches of different compositions were prepared by firing for 2 h up to 1580° C. Six samples were selected for further investigation on the basis of their phase composition and densification parameters. The mineralogical composition and microstructure, pore size distribution, and mechanical and refractory properties of these samples were investigated. All six samples consisted mainly of MgO and MA spinel refractory phases, plus some calcium silicates and aluminoferrite phases. The latter phases contribute to densification during firing by promoting liquid phase formation. Most samples showed high refractoriness under load, good spalling resistance, better mechanical properties than current refractories, and compact microstructure. It is concluded that these new refractories are good candidate materials for the production of shaped linings for industrial kilns and furnaces.     

Effect of laser fluence on surface microstructure of alumina ceramic

Abstract

The present study discusses the microstructure development during surface modifications of alumina ceramic using high power continuous wave Nd:YAG laser. Laser fluence influenced the microstructure in terms of changes in morphology and (1 1 0) crystallographic texture of the surface grains. The microstructural observations can be used to establish the guidelines for optimising the laser fluence to achieve the desired morphology of the surface grains and extent of texture in the surface modified alumina ceramic.     

Texture evolution in two phase Zr – 2.5 wt-%Nb through modified route

Abstract

Two phase Zr – 2.5 wt-%Nb is used as pressure tube material in water cooled and moderated reactors. The in service behaviour of this hcp zirconium based alloy is dependent on strong textures developed during thermomechanical processing. In the present study, the texture evolution during fabrication of this material, using a modified route, was investigated. Texture, evaluated by the orientation distribution function, was correlated to microstructure during various stages of processing. It was observed that a strong orientation fibre parallel to the working direction develops with hot working (extrusion). With subsequent cold working, the texture formed after extrusion alone becomes strengthened. This observation is attributed to the presence of a soft secondary phase (β) at the α-phase grain boundary. In contrast to the above, in the case of single phase Zircaloy 4, new components of texture are generated with cold deformation after hot extrusion, as a result of interaction between grains.     

Transformation texture of allotriomorphic ferrite in steel

Abstract

Many aspects of the crystallographic texture which develops when austenite transforms into martensite or bainite are well established because the process by which the parent lattice is transformed into that of the product is mathematically defined. This is not the case when the ferrite forms by a reconstructive mechanism. The allotriomorphic ferrite nucleates heterogeneously at austenite grain boundaries, and although a reproducible, low energy orientation relationship is expected to exist between the ferrite and one of the austenite grains with which it is in contact, there are reports that the ferrite can simultaneously adopt this orientation with more than one austenite grain. The authors examine this possibility using crystallographic theory in order to assess the probability of such events as a function of the strength of the texture within the austenite before its transformation.     

Recrystallisation textures in cold rolled low carbon steel containing ferritic and bainitic microstructures

Abstract

Low carbon steel strip was heat treated to generate four different starting microstructures (fine and coarse polygonal ferrite, acicular ferrite and bainite) for investigating their influence on texture development during cold rolling and annealing. The starting materials were cold rolled to 50–90% reduction and annealed for various times in the temperature range 853–953 K. The resultant microstructures and textures were examined mainly by electron backscatter diffraction and X-ray diffraction. The initial microstructure strongly influenced the crystallographic rotation paths during cold rolling, whereby high strain deformation generated strong {223}〈110〉 texture components in the polygonal ferritic microstructures, whereas a strong {001}〈110〉 texture was produced in the acicular/bainitic microstructures. Subsequent annealing generated, to varying degrees, the classic {111}〈uvw〉 (γ-fibre) recrystallisation texture in all materials. Unexpectedly, coarse polygonal ferrite produced the strongest γ-fibre recrystallisation texture after 70–90% cold rolling reduction. Based on arguments involving the effect of carbon in solution, initial grain size and deformation textures on recrystallisation texture development, it was shown that a strong γ-fibre texture can indeed be generated in coarse polygonal ferrite.     

Instrumentation and simulation of industrial steel wire rod cooling line

Abstract

A coupled thermal and metallurgical mathematical model has been developed to simulate the Stelmor process for controlled cooling of steel wire rod. The model predicts the through section microstructure, which is subsequently used to estimate the mechanical properties, in terms of ferrite fraction, ferrite grain size, and interlamellar pearlite spacing. Plant trials were conducted to evaluate heat transfer coefficients for the water and forced air cooling stages of the process in terms of the process parameters. To enable the development of a control model, the effect of individual process parameters, including their extreme settings, on rod temperature distribution was studied. An inverse modelling approach has been used to optimise the value of the heat transfer coefficient. The model results were compared with plant trials for a range of rod diameters, rolling speeds, number of active water boxes, and the operation ratio of the Stelmor fans. This validation was performed for three carbon–manganese steel grades (0.07–0.67%C) with rod diameters of 5.5–14.0 mm. A good agreement between the predicted and measured thermal behaviour of the rod was achieved.     

A compact planar distributed tactile display and effects of frequency on texture judgment

This paper describes the development of a planar distributed tactile display and the evaluation of the results of its effectiveness for displaying textures. The tactile display is composed of a 6 × 5 pin array actuated by 30 piezoelectric bimorphs. The distance between each pin's centers is 1.8 mm. Vertical excursion of each pin is controlled over a 0–0.7 mm range. Perceptual experiments were conducted to evaluate the performance of the system under three conditions: active touch, passive touch with vibration and passive touch without vibration. The experimental results showed that vibrational stimuli helped subjects discriminate tactile patterns. Measurements of the error rate during discrimination tasks were used to find an optimal vibration frequency for stimuli presented at a constant sensation level (32 SLdB above threshold). The experiment was repeated, this time holding the energy transferred mechanically to the fingertip tissue constant. At low frequencies, we found that the passive stimulation allowed subjects to discriminate just as well as active touch of static stimuli did. The results suggested new possibilities for displaying texture using passive touch, constant energy and spatially varied vibration frequency.