During ladle refining process, argon gas is purged into the ladle for stirring the molten steel bath to eliminate thermal and composition gradients and to achieve inclusion flotation. Operating parameters like purging location, porous plug configuration and argon flow rate primarily affect liquid steel refining. Theefficiency of ladle processing is often quantified through mixing time. To optimize the mixing time and the associated process parameters for improved bath homogenization and inclusion flotation under different operating conditions, water modeling studies using 0.2 scale perspex model and computational fluid dynamics studies using ANSYS CFX v14.5 have been carried out through fluid profile assessment and mixing time comparison. Comparative study was made between single plug, dual plug and top lance purging configurations. The studies helped in identifying the optimum argon purging rates and configurations under normal operational practices. Under abnormal operating conditions involving purging failure from either of the two porous plugs, usage of a top lance along with the single working porous plug has been investigated and found to improvemixing and inclusion flotation in the ladle equivalent to dual plug operation. The lab scale studies have been validated on plant scale through inclusion mapping and found to be in close agreement.

The precipitation and growth behavior of titanium nitride (TiN) inclusions during the continuous casting of high carbon wire rod grade steel SWRH 72A was investigated based on the thermodynamic calculations. Titanium is a tramp element in this grade and its pick up in liquid steel mainly takes place from the ladle alloy additions. Titanium in liquid steel is the limiting factor for the growth of TiN inclusions as it diffuses slowly in steel than nitrogen and enriches in interdendritic liquid regions creating favorable conditions for TiN precipitation. It was also observed from this study that the temperature for the formation of TiN inclusion decreased with decrease in titanium for a fixed nitrogen. Titanium nitride inclusions precipitate in steel during solidification even with low titanium and nitrogen content due to the effect of elemental segregation. Solidificationsegregation of both titanium and nitrogen increased with increase in cooling rate and their segregation tendency increased rapidly with increasing solidification fraction. The effect of titanium, nitrogen and cooling rate on the growth radius of titanium nitride inclusion was studied and validated with actual inclusion measurement.

The present study aims at to study the effect of chemical composition, intercritical annealing parameters (temperature and holding time) on microstructure and mechanical properties of dual phase steels. Three normalized steels (A, B and C) with different compositions were subjected to inter-critical annealing at 760°C and 810°C for different holding times (3, 6 and 9 min). The microstructural characterization was carried out using a scanning electron microscope (SEM) and mechanical properties were evaluated using microhardness measurements and tensile tests. The strength has been found to increase from 500 MPa (steel A) to >1200 MPa (steel C) at the cost of a decrease in elongation from 25% (steel A) to 7.5% (steel C). Results havebeen analysed and discussed.

Strips of micro-alloyed steel grade 27MnSiVS6 was subjected to austenitization, followed by forced air cooling and austempering conditions. The forced air cooled condition resulted in a tensile strength of 1345 MPa and 13.5% elongation with an yield ratio of 0.41, with a microstructure consisting of ferrite, bainite with blocky martensite/austenite (M/A) constituent. The same steel was subjected to austenitization at 950 °C for 10 min followed by austempering in a salt bath at 450 °C for 5 min, showed a fully bainitic ferrite microstructure with very fine M/A constituents, where a tensile strength of 969 MPa and an elongation of 16.8% and an yield ratio of 0.82 were noticed. During austempering, the holding time at the austenitization temperature and isothermal temperature were varied which resulted in a moderate influence on the strength and the ductility. The work hardening behavior of the steel was examined using the Hollomon equation and modified C–J (Cussard–Jeoul) analysis. The work hardening initially takes place in the softer ferrite phase, which is beyond acritical strain, changes over to harder tempered martensite phases followed by void nucleation and failure. The study establishes a new range of mechanical properties in the micro-alloyed steel that can be used in flat products.

Recently, soft hot strip and hard hot strip produced through ferritic rolling are projected as a direct replacement to austenitic cold-rolled sheets for many forming applications. However, industrial hot-rolling mills, with final rolling thickness limitations cannot produce these thinner products and have to be subsequently cold-rolled to the desired application thickness and further annealed. Under ferritic rolling conditions, the hotrolling temperature of these coils governs the final properties. The temperature difference in hot-rolled sheetsgenerates the difference in the microstructure and texture of these coils after cold-rolling and annealing and variation in their formability behaviour. In the present work, an Nb–Ti stabilized IF grade steel was hot-rolled at two different temperatures in the ferritic regime and subsequently cold-rolled and annealed for structureproperty comparison. As formability is an application-specific requirement, the annealed sheets were tested for different formability characteristics. Industrially rolled samples were tested for fracture criterion, stretchflangeability, deep drawability and stretch formability through the formability limit diagram, hole expansion ratio, earing test and Erichsen cupping test respectively. These parameters were compared with those of the austenitic regime rolled sheets. High temperature ferritic rolled sheets show improved formability in all tests due to better r, higher n-value, low Δr and stronger gamma fibre maxima at 111<121>. Low temperature ferritic rolled sheets show the lowest Δr and improved n-value, but has reduced r and higher alpha fibre texture. High temperature ferritic rolled sheets show higher formability limits in uniaxial tension and low temperature ferritic rolled sheets in biaxial tension of the FLD curve. Various tests established that high temperature ferritic rolled sheets are best suited for deep drawing and stretching applications whereas low temperature ferritic rolled sheets should be preferred for stretch forming applications.

A TRIP assisted 0.22 %C steel with 2.3%Mn, 1.5 %Si, 0.05 % Nb and 0.035%Ti (wt. %), was subjected to a novel deformation quench partitioning treatment in a Gleeble thermomechanical simulator, which resulted in a homogeneously dispersed soft ferrite in tempered martensitic microstructure that gave 1470 MPa tensile strength with 13.5% elongation. The processing involves an initial 10% warm deformation followed byquenching to room temperature. The quenched steel was subject to 5% cold stretching followed by partitioning at 400°C. The processed steel, was bench marked with two types of the conventional quench partitioning heat treatments on the same steel. The steel was quenched to room temperature from full austenitization at 900°C andfrom an intercritical temperature of 770°C, followed by partitioning at 400°C. The fully austenitized quench partitioned steel gave 1499 MPa tensile strength with 8.5% elongation, while the intercritical ausatenitized quench partitioned steel gave 990 MPa tensile strength with 16.1% elongation. The structure property analysis to achieve the high properties is brought out.