Effect of annealing parameters on microstructure and mechanical properties of phosphorus alloyed 16%Mn-TWIP steel

The present paper covers the effect of various solution/recrystallization-annealing temperatures on the mechanical properties such as yield strength, tensile strength, and fracture elongation as well as r- and n-values of a 0.03 wt.-% phosphorus alloyed 16%Mn-TWIP steel. Small scale and large scale hot- and cold-rolled strips were produced and heat treated to simulate typical continuous annealing cycles. The microstructure was characterized by light-optical microscopy, and the influence of the thermal treatment on the austenite grain size was investigated. The mechanical properties were investigated by tensile testing. The highest tensile strength values were of about 1200 MPa at low annealing temperature of 750 °C. Total elongations greater than 80% were achieved with increasing the annealing temperature. The highest tensile elongations were associated to a significant increase of the grain size and the complete dissolution of the carbides. The steel composition showed a high work-hardening. High n10-20 values in the range of 0.45-0.55 were obtained, while the r-values were of about 0.8. In addition, the influence of the grain size on the yield strength was studied.