Austenite Stability and Its Effect on the Ductility of the Cold-rolled Medium-Mn Steel

Abstract

The mechanical and thermal stability of retained austenite in the cold-rolled medium-Mn (Fe-0.1C-5Mn) steel were studied by the tensile deformation at different temperature. The volume fractions of retianed austenite and microstructure of the starting and deformed materials were analyzed by X-ray diffraction, the scanning electron microscopy (SEM) and electron back scattered diffraction (EBSD). It was found that the volume fraction of retained austenite gradually decreased with strain increasing during tensile deformation. It showed high mechanical stability of retained austenite, which resulted in good comprehensive mechanical properties with ultrahigh strength and plasticity. Meanwhile, the tensile results at different temperature showed pretty high plasticity at low temperature (-40°C and -80°C) tensile deformation of the cold-rolled steel, which indicated the retained austenite maintained certain stability at low temperature. The results of this study indicate that the ductility in the medium-Mn steel with high contents of retained austenite can be altered by control of the austenite stability.KEY WORDS: cold-rolled medium-Mn steel; mechanical and thermal stability; retained austenite; microstructure; ultrahigh strength and plasticity.

Kinetics of Solute Partitioning During Intercritical Annealing of a Medium-Mn Steel

“…Most of the research work is concerned with experimental determination of austenite volume fraction and composition. [13][14][15][16] Mn partitioning during intercritical annealing has been studied by atom probe tomography [13,17] and experimental results have been compared with simulation predictions. Mn partitioning has also been studied by TEM [14,[18][19][20] indicating that partitioning of Mn from ferrite to the austenite is slow.…”

Effect of Deformation Temperature on Mechanical Properties in 1-GPa-grade TRIP Steels with Different Retained Austenite Morphologies

“…Here, Vγ 0 in the 0.22C and the 0.1C TRIP steels were 14.4% and 10%, respectively. 3,6) In Fig. 5, the TS-U.El balance decreased with an increase in TS.…”

“…Figure 5 shows U.El as a function of TS obtained by tensile tests at various temperatures in the present TRIP steels and other TRIP steels. 3,6) The dashed lines in Fig. 5 are contour lines for the products of TS and U.El.…”

“…8) In order to understand the TRIP effect of the 1-GPagrade TRIP steel in more detail, it is important to drastically change the DIMT behavior, which is an essential factor influencing the TRIP effect. 3,[5][6][7] One of the conditions to make a significant difference in the DIMT behavior is the deformation temperature. 6,[9][10][11][12][13][14] Various data considerably changing the deformation temperature will lead to a deep understanding of the TRIP effect of high-strength TRIP steels.…”

“…Transformation-induced plasticity (TRIP) effect due to the deformation-induced martensitic transformation (DIMT) of retained austenite (γ R ) can improve the ductility of steels and has been utilized in advanced high-strength steels (AHSS). [1][2][3][4][5][6] The tensile strength-uniform elongation balance of the third-generation AHSS is approximately 30 000-40 000 MPa%, 1) and various studies on AHSS with a tensile strength of more than 1 GPa have been reported. 1,2) We have been investigating the tensile deformation behavior of 1-GPa-grade TRIP steels with different γ R morphologies.…”