The paper reviews the recent works concerning the Portevin–Le Chatelier (PLC) effect in Advanced High-Strength Steels (AHSSs) with a special attention to high-strength medium-manganese steels. Theories explaining the mechanism of the plastic instability phenomenon in steels with medium- and high-Mn contents were discussed. The relationships between microstructural effects such as TRIP (Transformation-Induced Plasticity), TWIP (Twinning-Induced Plasticity) and the PLC effect were characterized. The effects of processing conditions including a deformation state (hot-rolled and cold-rolled) and strain parameters (deformation temperature, strain rate) were addressed. Factors affecting the value of critical strain for the activation of serrated flow behavior in particular in medium-manganese steels were described.

Experimental investigations of the plastic instability phenomenon in a hot-rolled medium manganese steel were performed. The effects of tensile deformation in a temperature range of 20–140°C on the microstructure, mechanical properties, and flow stress serrations were analyzed. The Portevin–Le Chatelier (PLC) phenomenon was observed for the specimens deformed at 60 °C, 100 °C, and 140 °C. It was found that the deformation temperature substantially affects the type and intensity of serrations. The type of serration was changed at different deformation temperatures. The phenomenon was not observed at room temperature. The plastic instability occurring for the steel deformed at 60 °C was detected for lower strain levels than for the specimens deformed at 100 °C and 140 °C. The increase of the deformation temperature to 100 °C and 140 °C results in shifting the PLC effect to a post uniform deformation range. The complex issues related to the interaction of work hardening, the transformation induced plasticity (TRIP) effect, and the PLC effect stimulated by the deformation temperature were addressed.

Strain hardening behavior and the corresponding microstructure evolution of the high-manganese steel with additions of Si and Al were investigated in this study. Thermomechanically processed and solution-heat-treated sheet steels were compared under conditions of interrupted tensile tests. Relationships between microstructure and strain hardening were assessed for different strain levels using light microscopy and scanning electron microscopy techniques. It was found that the deformation of both steels at low strain levels was dominated by dislocation glide before the occurrence of mechanical twinning. The amount of twins, slip lines, and bands was increasing gradually up to the point of necking. As the strain level increased, dislocation density within twinning areas becomes higher, which enhances the strength, the work hardening exponent, and the work hardening rate of the investigated high-manganese sheet steels.

The study addresses the design and optimization of chemical composition and processing routes of new quenching and partitioning medium-Mn alloy using theoretical and experimental approaches. The thermodynamic calculations using Thermo-Calc and JMatPro software were carried out to characterize the influence of Mn, Si and Al contents on cementite formation and precipitation processes. The evolution of individual phases as a function of temperature under thermodynamic equilibrium conditions was estimated. The investigations included the determination of continuous cooling transformation (CCT) and the time–temperature transformation (TTT) diagrams of a model 4Mn alloy. The calculated equilibrium diagrams were compared with the experimental diagrams determined using dilatometric tests. Microstructural observations were carried out to verify the results of dilatometric measurements. The results of thermodynamic calculations and experimental tests showed the moderate agreement. It is related to the inaccuracy of currently available models in the used software and/or non-equilibrium conditions of experimental tests.

The study addressed the microstructure and mechanical properties of hot-rolled advanced high-strength medium manganese steel. Some of the curves that were obtained in static tensile tests at deformation temperatures of 20–200 °C showed the occurrence of the heterogeneous plastic deformation phenomenon, called the Portevin-Le Chatelier (PLC) effect. The deformation temperature significantly influenced a serration character. The correlations between the deformation temperature, serration range, microstructural features, and fracture behavior were investigated. The curves showed no Lüders elongation as a result of the thermomechanical processing applied. The serrated flow phenomenon was observed at 60 and 140 °C. The serration type was different and the most enhanced at 140 °C, where the PLC effect was present in both uniform and post-uniform elongation ranges. The disappearance of serrations at 200 °C was related to the increased diffusion intensity.

This work is concerned with comparative tests involving single-spot and twin-spot laser welding of thermomechanically rolled TRIP steel. The welding tests were carried out using keyhole welding and a solid state laser. In the case of twin-spot laser beam welding, the power distribution of beams was 50%:50%. The changes in macro- and microstructures were investigated using light and scanning electron microscopy. Three main zones subjected to the tests included the fusion zone, the heat affected zone and the intercritical heat affected zone (transition zone between the base material and the HAZ). Special attention was paid to the effect of various thermal cycles on the microstructure of each zone and on martensite morphology. The tests involved hardness measurements carried out in order to investigate the effect of different microstructures on mechanical properties of welds.