The precipitation behavior of j-carbide during isothermal aging was investigated in the Fe-9Mn-6Al- 0.15C (wt.%) lightweight steel through thermodynamic calculations and microstructural analyses using various microscopes and an X-ray diffractometer. No precipitates of j-carbide were observed in both hot-rolled and annealed specimens. The j-carbide started to precipitate at the grain boundaries of d-ferrite and at interphase boundaries between δ-ferrite and γ-austenite and between α-ferrite and a0-martensite after isothermal aging at 550 °C for 1 h. While the precipitation and growth of κ-carbide at the boundaries continued, new κ-carbide precipitated alongside α-ferrite by the eutectoid reaction to form a lamellar structure in austenite during 6-h aging. This result confirmed that the precipitation of κ-carbide at the boundaries preceded the precipitation of the lamellar κ-carbide due to the pre-segregation of solute atoms to the boundaries. The α'-martensite was not transformed to γ-austenite and just tempered during isothermal aging at 550 °C.
Bibliographical noteFunding Information:
This work was supported by POSCO. The authors are thankful to Dr. Jai-Hyun Kwak for discussions, and to Prof. Byeong-Joo Lee and Mr. Hyuk-Joong Lee for thermodynamic calculation.
All Science Journal Classification (ASJC) codes
- Mechanics of Materials
- Mechanical Engineering
- Metals and Alloys
- Materials Chemistry