Abstract
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.
Highlights
Advanced steels for automotive industry should provide the favorable combination of mechanical and technological properties, such as high strength, good formability, and weldability [1,2,3]
The medium-Mn Transformation Induced Plasticity (TRIP) steels that belong to the 3rd generation of Advanced High Strength Steels (AHSS) are of particular interest due to the higher strength and ductility than first generation TRIP steels
Σ–ε curves is related to the elevated deformation temperatures at larger strains, while serrations regularly appear on σ−ε curves fact that an increase in temperature enhances the mobility of solute C
Summary
Advanced steels for automotive industry should provide the favorable combination of mechanical and technological properties, such as high strength, good formability, and weldability [1,2,3]. It was noted in the literature that medium-Mn steels are prone to a plastic instability phenomenon related to Lüders or Portevin–Le Chatelier (PLC) band formation [6,7,8]. Both types of instabilities may lead to the occurrence of numerous cracks during forming processes or delayed cracking after deep drawing [9]. Min et al [16] reported that the PLC effect observed in 0.2C-2Mn-1.4Si steel occurred in a temperature range of 100–250 ◦ C. The DSA and TRIP effects occur at the same time in medium Mn-steels, making the analysis more advanced. The mechanisms affecting the plastic instabilities observed in the investigated steel were discussed based on theories available in literature
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