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Since its first implementation in the 1950’s thermo-mechanically controlled rolling has proven to be invaluable in steel industry for giving grain size refinement and hence improved strength and toughness. This led to widespread use of lab based thermo-mechanical simulators, such as Gleeble and ServoTest machines, to reproduce the strain, strain rate and temperatures of hot deformation and support the optimisation of rolling schedules for improved microstructures and steel grade development. These machines use compression samples (typically plane strain or uniaxial) to investigate the key fundamental metallurgical processes such as recrystallisation, where precise temperatures, strains and hold times can be imparted before quenching of the sample to reveal the prior austenite grain size, which is not possible on full scale plants. Whilst several research has been carried out to correct for friction and temperature variations on the flow stress behaviour, strain variation within the samples is a problem, particularly for microstructural assessment. However, as initial recrystallisation studies mainly focused on average grain size and kinetic predictions the strain non-uniformity did not give significant error. Modern recrystallisation studies focus on full grain size distribution predictions, which generally require characterization of >700 grains to give smooth histograms, in order to assess phenomena such as grain size bimodality, influence of segregation etc.
This paper reports on FE modelling and experimental verification of strain distribution in commonly used plane strain and uniaxial compression test sample geometries. Local strain was determined in the deformed Fe-3Si alloy samples by EBSD misorientation indexing, calibrated against samples with known (tensile deformed) strain. Significant strain inhomogeneity is seen for the standard compression samples, therefore a new plane strain geometry has been designed to minimize strain variability, and optimize the amount of material that exhibits uniform strain (for microstructure assessment) that matches the overall imposed macrostrain.