In the present study, the variations of microstructure and tensile properties were investigated as a function of aging time using a Fe–11Mn–10Al-1.2C medium-Mn lightweight steel. The 1000 °C-annealed specimen revealed an austenite matrix containing nano-sized particles of intra-granular (IG) κ-carbide and a small amount of α-ferrite. After aging at 550 °C for 3 min, pre-existing IG κ-carbide grew up rapidly and relatively coarse κ-carbide formed at the γ-austenite grain boundary (GB). With aging for 10 min, the C-depleted zones, close to the coarsened GB κ-carbide particles, were transformed to filmy grain boundary ferrite (GBF). When aging time increased to 30 min, the eutectoid reaction (γ→α+κ) occurred preferentially at the coarse particles of GB κ-carbide. The eutectoid reaction continued with increasing aging time up to 720 min, and finally the specimen had a eutectoid matrix (α+κ) with a few of α-ferrite. The annealed specimen possessed high strengths (yield strength (YS) of 1242 MPa and ultimate tensile strength (UTS) of 1314 GPa) with moderate elongation (El) of 22.2%. The YS value of aged specimens was improved to ~1.35 GPa by the growth of IG κ-carbide particles after aging for 3 min, and increased further up to ~1.54 GPa by the formation of eutectoid structure after aging for 720 min.
Bibliographical noteFunding Information:
This work was financially supported by grants through the National Natural Science Foundation of China ( U1760205 ) and supported by China Scholarship Council , (CSC, Grant No. 201806080105 ).
© 2020 Elsevier B.V.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering