TIME-DEPENDENT MARTENSITIC TRANSFORMATION UNDER CONSTANT STRESS IN TRIP STEEL, A NOVEL PHENOMENON

摘要

The martensitic transformation from retained austenite in low-alloyed multiphase TRIP steels is often studied under "continuous loading. In this work, the time-dependent mechanical behavior under constant stress in a 0.2C-1.5Mn-0.25Si-1.8Al (wt.%) TRIP steel is systematically investigated. Step-wise tensile tests are performed and a significant increase in strain with time, typically 1-3% depending on the level of constant stress, is observed. With increasing stress, the total amount of strain variation during the holding process increases, while the time constant for the strain variation increases weakly. X-ray diffraction measurements on the volume fraction of austenite before and after each step of the holding indicate that the austenite fraction decreases with increasing time. The reason for this assumed time-dependent martensitic transformation is possibly due to the temperature variation during the loading and holding processes.