Strain Rate Effects on Martensitic Transformation in Gen 3 Steels from Synchrotron X-Ray Diffraction 2019-01-0521
The strain rate effect on martensitic transformation in two-Gen 3 Steels was investigated with synchrotron X-ray diffraction at nominal tensile strain rates of 0.5/s, 5/s, 50/s, and 500/s. Our aim was to determine which of two competing effects predominate: diffusionless shear transformation of austenite to martensite with strain or inhibition of the transformation from adiabatic heating at higher strain rates. While both steels have a minimum 1200 MPa tensile strength, their microstructures, austenite morphologies in particular, vary and contain different fractions of blocky and interlath austenite. Austenite volume fraction was measured at specific locations in fractured tensile bars and plotted as a function of strain and strain rate from digital image correlation. Reduced austenite volume fraction was measured at the highest tested strain rates for both steels. This is attributed to an enhancement of transformation induced plasticity at elevated strain rate and may partially account for concurrent increases in tensile flow stresses and elongations.
Charles Enloe, Vesna Savic, Whitney Poling, Louis Hector, Rakan Alturk