Microstructure evolution of high-manganese steel during the thermomechanical processing

Purpose: The aim of the paper is to determine the influence of hot-working conditions on microstructure evolution of new-developed high-manganese austenitic steel. Design/methodology/approach: The hot-working behaviour was determined in continuous and multi-stage compression tests performed in a temperature range of 850 to 1100°C by the use of the Gleeble 3800 thermomechanical simulator. The processes controlling work hardening and removing it were identified by microstructure evolution observations in successive stages of compression with the amount of true strain 4x0.29, 4x0.23 or 4x0.19. Findings: The investigated steel is characterized by high values of flow stresses from 250 to 450 MPa. Increase of flow stress along with decrease of compression temperature is accompanied by translation of εmax strain in the direction of higher deformation. Results of the multi-stage compression proved that applying the true strain 4x0.29 gives the possibility to refine the austenite microstructure as a result of dynamic recrystallization. In case of applying the lower deformations 4x0.23 and 4x0.19, the process controlling work hardening is dynamic recovery and a deciding influence on a gradual microstructure refinement has statical recrystallization. Research limitations/implications: To determine in detail the microstructure evolution during industrial rolling, the hot-working schedule should take into account real number of passes and higher strain rates. Practical implications: The obtained σ-ε curves can be useful in determination of power-force parameters of hot-rolling and to design a rolling schedule ensuring a fine-grained microstructure of high-manganese steel products. Originality/value: The microstructure evolution in various conditions of hot-working for the new-developed high-manganese Mn-Si-Al-Nb steel was determined.