The Grain Refinement Mechanism Of Substitutional Fe-based Alloys

The governing of the austenite (γ) to ferrite (α) phase transformation upon cooling is essential important in the production of iron and steel. The microstructural controls during the solid-state phase transformation become the most efficiency method in developing of the new generation iron and steel materials. Among them the improvement of mechanical properties by means of the controlled rolling and controlled cooling has attracted the high interests in the field of materials.In this paper the influence of different quenching temperatures in the austenite field and applied external tiny stresses on theγ→αphase transformation behaviors of substitutional Fe-3Mn alloys were investigated by high resolution differential dilatometer. During dilatometric measurements, the phase transformation kinetic and thermodynamics information was directly obtained by the lever rule from the recorded dilatometric curves of the samples. With the aid of the microstructural analysis and the measurement of mean grain size of the samples, the phase transformation model was developed and employed to analyze the kinetics of the phase transformation. Finally, the grain refinement mechanism of substitutional Fe-base alloys was clarified. It was found out that:1. The higher the quenching temperature in the austenite field, the lower the onset temperature of theγ→αtransformation, the shorter the whole time transformation and the time interval when the transformation reaches the maximum of dfα/dt; the smaller the average grain size, the more homogeneous the grain size distribution, and the less the fraction of large grains.2. The higher the applied external tiny stress, the higher the onset temperature of theγ→αtransformation, the longer the time of the whole transformation, the smaller the average grain diameter. The sample formed with applied stress of 20 MPa exhibits the smallest grain size.3. By fitting the experimental results of theγ→αphase transformation with the phase transformation model, the initial nucleus density (N₀), the nucleation activation energy (Q_n) and the prefactor (p) of different quenching temperature in the...