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3726641 
Book/Book Chapter 
Hot Forming Response of Medium Manganese Transformation Induced Plasticity Steels 
Rana, R; Carson, CH; Speer, JG 
2015 
CHS2-Series 
5 
391-399 
WOS:000372941900040 
A cold rolled medium Mn steel containing 9.76Mn-0.16C-1.37A1-0.19Si (mass%) was processed via a short time (3 min. soaking) continuous annealing-type treatment and then subjected to typical direct hot forming thermal cycles, with reheating at 650-800 degrees C. Excellent mechanical properties (1330-1448 MPa tensile strength; 16.7-25.3% total elongation) of the hot formed steel were obtained with reheating at 700 degrees C. The mechanical properties of the steel with reheating at lower temperatures (650 and 700 degrees C) were superior to those with higher reheat temperatures (750 and 800 degrees C) due to the transformation induced plasticity (TRIP) effect resulting from the large amount of metastable austenite retained at room temperature (18.5-56.3 vol.%), associated with Mn-enrichment of austenite in the presence of ferrite. Ultrahigh strength levels were achieved due to a combination of the TRIP effect, ultrafme grain size (< 1 mu m) of constituent phases (ferrite, austenite and martensite), and high dislocation density in the microstructure owing to the short non-equilibrium treatments used in the study. It is concluded that medium Mn TRIP steels are promising candidate material for hot forming, not only due to the potential for achieving extraordinary properties, but also due to the lower reheat temperatures required, with implications related to lower energy absorption and potentially improved behavior of Zn-based coatings. The continuous annealed microstructures generated before the hot stamping simulations were also interesting, yielding ultrahigh tensile strength levels (1619 MPa) in combination with good ductility (16.5% total elongation).