9th ECCC European Continuous Casting Conference – ECCC 2017

Previous studies have shown that the application of mechanical strain over a long period of time can facilitate precipitation of microalloyed particles. Hence there is a need to clarify whether casting with a multiple straightening scheme rather than a bending/unbending design could be detrimental for the quality of CC of microalloyed steel grades, due to the time extension of the deformation and the corresponding decrease of the strain rate. Metallographic investigations have been carried out on samples of a Low Carbon Boron grade cast on three different slab casters, having very different bending and unbending strain profiles, at Tata Steel Port Talbot. The work included extensive FEG-SEM analysis using INCA Feature to characterise precipitation and numerical modelling of the industrial casting process to determine temperature profiles of the slabs during continuous casting. In particular the variation in the number of MnS inclusions with distance from the as-cast surface was determined, with unexpected results regarding the location, distribution and particle size. Comparison with data for similar grades produced on the Tata Steel Scunthorpe Slab Caster confirmed conclusions regarding the relative importance of steel chemistry and caster design on the precipitation. Using the FEI Quanta 650 FEG-SEM in combination with an Oxford Instruments Xmax80 detector made it possible to characterise the boron present. The variation in the number and size of BN inclusions with distance from the as-cast surface of slabs was determined. When the precipitate size distribution was examined at each depth, further interesting trends were revealed. Modified Gleeble tests were carried out on the same Low Carbon Boron grade. The strain and strain rate applied was calculated so as to simulate the strain in the cast strand and cooling and heating conditions of the strand below the mould in the vertical with unbending slab caster number 3 at Tata Steel Port Talbot. The results confirmed the new insights regarding particle size, location and distribution.