Stacking Fault Energy Determination in Fe-Mn-Al-C Austenitic Steels by X-ray Diffraction

Effect of Al Additions and Cooling Rate on the Microstructure and Mechanical Properties of Austenite FeMnAlC Steels

The precipitation behavior of κ-carbide and its effects on mechanical properties in Fe-30Mn-xAl-1C (x = 7–11%) steels under water quenching and furnace cooling are studied in the present paper. TEM, XRD, EPMA were employed to characterize the microstructure, and tensile test and the Charpy impact test were used to evaluate mechanical properties. The results show that the density decreases by 0.1 g/cm³ for every 1 wt.% of Al addition. The excellent mechanical properties of tensile strength of 880 MPa and impact absorption energy of 120–220 J at −40 °C with V notch were obtained, with both solid solution and precipitation strengthening results in the yield strength increasing by about 57.5 MPa with per 1% Al addition in water-quenched samples. The increasing of yield strength of furnace-cooled samples comes from the relative strengthening of κ-carbides, and the strengthening potential reaches 107–467 MPa. The lower the cooling rate, the easier it is to promote the precipitation of κ-carbides and the formation of ferrite. The partitioning of C, Mn, Al determines the formation of κ-carbides at a given Al addition, and element partition makes the κ-carbides sufficiently easy to precipitate at a low cooling rate. The precipitation of κ-carbides improves strength and does not significantly reduce the elongation, but significantly reduces the impact absorption energy when Al addition ≥ 8%.

Microstructure, Mechanical Properties and Deformation Behavior of Fe-28.7Mn-10.2Al-1.06C High Specific Strength Steel

The microstructure, properties and deformation behavior of Fe-28.7Mn-10.2Al-1.06C high specific strength steel were studied. The results showed that the density of experimental steel is about 6.59 g/cm3 and the microstructure is austenite. With the increase in the annealing temperature, the tensile strength decreases and the elongation increases. When the annealing temperature is 950 °C, the strength-plastic product of the experimental steel is 54.82 GPa%, and the specific strength is 1.48 × 105 N·m/kg. Compared with 20Mn2CrNb high strength automobile steel, the specific strength of laboratory steel is increased by more than 20%. The deformation behavior of experimental steel is mainly: At the low strain, spacing of slip surface decreases; at high strain, dislocation walls and micro-strips are formed, and the austenite grains are segmented, increasing the dislocation density and starting more secondary slips.