Effect of solution treatment temperature on microstructure evolution and tensile property of a medium Mn steel having a lamellar structure.

The effect of solution treatment temperature on the microstructure and tensile property of an Fe-10.62Mn-2.84Al-0.5Mo-0.177C (wt.%) medium manganese steel is investigated. The steel is subjected to two different solution treatment conditions (900 °C and 1100 °C) followed by the same subsequent heat treatments including intercritical annealing, reheating and carbon partitioning treatment. The final microstructures are characterized by lamellar morphologies of α′ martensite and austenite phases. Our results show that the fractions and compositions of each constituent phases are quite similar between both samples despite the initial difference in solution treatment temperature. However, the finer martensite substructures from the initial solution treatment at 900 °C promote finer lamellar structures after the final heat-treated step. As a result, the steel shows an increase in the yield stress from ~800 MPa to ~930 MPa. Such improvement in yield stresses is discussed based on the Hall-Petch relation and micro-yielding mechanism among the constituent phases. Besides, in-situ observation of the changes in α′ martensite fraction during tensile tests confirms that transformation induced plasticity (TRIP) effect contributes to the work hardening of both samples after yielding. [ABSTRACT FROM AUTHOR]