Saud Saleem

The Influence of Peritectic Reaction/Transformation on Crack Susceptibility in the Continuous Casting of Steels

The work presented here examines the surface cracks that can form during the continuous casting of near peritectic steels due to the volume changes during the peritectic reaction/transformation. The investigated samples were collected during plant trials from two different steel grades. The role and mode of the peritectic reaction/transformation are found to depend on the composition of the alloy, resulting in different types of surface cracks. The effect of the local variation in the cooling rate on the formation of the different types of cracks present in each steel grade, which can be due, for example, to the formation of oscillation marks, is demonstrated. The enhanced severity of the surface and internal oxidation, both of which depend on the alloy composition and consequent peritectic reaction, is highlighted. Experimental and theoretical studies show that different types of surface cracks can occur in peritectic steels depending upon the alloy composition and cooling rate, both of which define the fraction of the remaining liquid upon completion of the peritectic reaction/transformation.

On the formation of fold-type oscillation marks in the continuous casting of steel

Asymptotic methods are employed to revisit an earlier model for oscillation-mark formation in the continuous casting of steel. A systematic non-dimensionalization of the governing equations, which was not carried out previously, leads to a model with 12 dimensionless parameters. Analysis is provided in the same parameter regime as for the earlier model, and surprisingly simple analytical solutions are found for the oscillation-mark profiles; these are found to agree reasonably well with the numerical solution in the earlier model and very well with fold-type oscillation marks that have been obtained in more recent experimental work. The benefits of this approach, when compared with time-consuming numerical simulations, are discussed in the context of auxiliary models for macrosegregation and thermomechanical stresses and strains.

A Study of the Oscillation Marks’ Characteristics of Continuously Cast Incoloy Alloy 825 Blooms

A comprehensive experimental study of oscillation mark (OM) formation and its characteristics during the solidification of Incoloy alloy 825 in the continuous casting of blooms is investigated by plant trials and metallographic study. The experiments involved two heats with the same casting and mold conditions and sampling at different locations across the strand. The metallographic study combined macro/micro-examinations of OMs and segregation analysis of Cr, Mn, Mo, Ni, and Si by microprobe analysis. The results show that OMs have widely different characteristics, such as mark type, depth, segregation, and accompanying microstructure. Furthermore, the mark pitch can vary considerably even for the similar casting conditions, leading to different conditions for the marks’ formation in relation to the mold’s cyclic movement. Finally, a mechanism for the OM formation is discussed and proposed. Possible solutions for minimizing the observed defects by optimizing the mold conditions are suggested.

Development of an Asymptotics‐Based Numerical Model for the Formation and Evolution of Air Gaps in the Vertical Continuous Casting of Alloys

The formation of an air gap at the mould-metal interface in vertical continuous casting has long been known to have a detrimental effect on the efficiency of the process, and has therefore attracted many attempts at mathematical modelling and multi-dimensional numerical simulation. However, a recent approach has used asymptotic techniques to derive a quasi-analytical thermomechanical model that captures the essential coupling characteristics: that the formation of the air gap affects the heat transfer, whilst the heat transfer affects the stresses that lead to the formation and evolution of the air gap. In this contribution, we report on preliminary attempts to develop that model, which was for the casting of pure metals, to describe the casting of alloys.

The Effect of Superheating and Cooling Rate on Primary Precipitation of Si in Hypereutectic Al-Si Alloys

The effect of superheating and cooling rate on primary precipitation of Si was studied in hypereutectic Al-Si alloys. Alloys with compositions of 15, 18 and 20 wt% Si were solidified in unidirectional solidification equipment from different temperatures and drawing speeds. The fraction of primary silicon was measured over a certain distance of the sample in the steady state region. Results show a large variation in primary silicon fraction along the sample length and with varying cooling rate. The fraction of primary silicon and primary aluminium around silicon increases with increasing superheat. These fractions decrease with increasing cooling rate and the structure changes to a more refined dendritic-like primary silicon. Different morphologies of Si and their transformation during solidification can be seen over the sample length. An analysis of the quenched solidification front shows the possibility of strong convection ahead of the solidification front. The convection can be caused by density variation in the liquid due to the cluster structure of the melt which changes the microstructure.