This article summarizes the outcome of research work carried out to improve the performance of the oxygen lance in the LD steelmaking process. It is stated that the lack of control of the foamy slag and the augmentation of interfacial area creation between the slag and metal are the major hindrances in running the process effectively for improved turn-down steel quality. The ineffectiveness of the existing design in producing liquid metal droplets in the presence of slag foam is explained. In order to augment the droplet generation, a new oxygen lance with a central subsonic nozzle through which flow can be controlled has been introduced and its blowing performances studied using numerical and water model studies. The jet characteristics studied in the numerical simulations show no jet coalescence. The interferences of the jets with the bath have further been analyzed by hydrodynamic model studies. It has been found that the droplet generation rate improves significantly due to the presence of the central jet. Further, it has been observed that controlling the flow rate through the central hole can be used as an effective process control tool.

Supplementary cementitious materials (SCM) have turned out to be a vital portion of extraordinary strength and performance concrete. Metakaolin (MK) is one of SCM material is acquired by calcinations of kaolinite. Universally utilised as pozzolanic material in concrete to enhance mechanical and durability properties. This study investigates the fresh and hardened properties of conventional concrete (CC) and self compacting concrete (SCC) by partially replacing cement with MK in diverse percentages. In CC and SCC, partial replacement of cement with MK varies from 5-20%. Fresh concrete properties of CC are conducted by slump test and compaction factor tests and for SCC, slump flow, T500, J-Ring, L-Box, V-Funnel and U-Box tests. Hardened concrete characteristics are investigated by compressive, split tensile and flexural strengths at age of 7, 28 and 90 days of curing under water. Carbonation depth, water absorption and density of MK based CC and SCC was also computed. Fresh concrete test results indicated that increase in MK replacement increases workability of concrete in a constant w/b ratio. Also, outcomes reveal that concrete integrating MK had greater compressive, flexural and split tensile strengths. Optimum replacement level of MK for cement was 10%, which increased mechanical properties and robustness properties of concrete.

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The present work carried out an assessment of various methods for calculation of equilibrium slagmetal phosphorous partition for basic oxygen steelmaking in order to select the most acceptable procedure for estimation of the dephosphorisation capability of basic oxygen furnace (BOF) converters at Tata Steel. Equilibrium phosphorous partition was calculated by a thermodynamic approach proposed in the literature using the regular solution based quadratic formalism for slag, by semiempirical equations proposed by some investigators, as well as an optical basicity based correlation reported in literature. Turndown slag and metal composition and temperature data of a large number of BOF heats of LD-1 and LD-2 shops of Tata Steel, covering a period of several years, were employed for this purpose. Large discrepancies between the predictions of empirical correlations proposed by different investigators were found. On the basis of the assessment exercise, the correlation proposed by Turkdogan was accepted for further use and has been recommended for estimation of equilibrium slag-metal phosphorous partition for the BOF steelmaking at Tata Steel. The actual phosphorous partitions at the vessel turndown attained equilibrium only in few heats. Effectiveness of different bottom stirring systems adopted by Tata Steel over the years as well as that of post-stirring have been assessed on the basis of approach to equilibrium.

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Mixing time studies were performed on a one-fifth scale aqueous model of a single tapered ladle with different bottom purging locations. Two porous plugs were used simultaneously to purge compressed air as an analogue to argon and this was referred as dual purging. KCl solution (1 N) was used as the tracer for measuring mixing time. The scaled down gas flowrate varied from 10 to 80 L m 21 . Around 400 experiments were done including all possible dual purging locations and the location which gives least mixing time was identified. The results were compared with corresponding single purging experiments and it was found that dual purging can reduce mixing time to a great extent even in the lower flowrate range and a location better than ¡R/2 has been suggested. Effect of differential flow on mixing time has also been reported.

Variant selection during displacive transformation is popularly monitored by assessing the pole figure or orientation density function of the bulk texture or pole figures from single prior austenite grains. It can also be done by measuring the physical orientation of α′ (bainite or marteniste) plates in the microstructure. It is known that when variants of α′ form randomly, i.e. there is no variant selection, the shear strain associated with each α′ plate gets canceled and transformation strain becomes equal to the volume strain. Under this condition, orientation of sheaves of α′ also shows random distribution. In this work, it has been shown how transformation strain and orientation of sheaves change when variant selection occurs. Mathematical models have already been developed to calculate the transformation strain under various loading conditions; extensive experiments have been conducted during the course of this work to show how the nature of externally applied stress influences the transformation strain. In addition to this, it has also been shown that the variant selection might leave its trace in the microstructure by affecting the alignment of the sheaves under externally applied stress and strain. Mathematical models have been developed to show that variant selection has negligible influence on physical orientation of α′ plates when transformation occurs under external stress, but prior plastic deformation can dictate the orientation to a great extent.

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