Details

Autor(en) / Beteiligte

• Li, G.Q.
• Shen, Y.F.
• Jia, N.
• Feng, X.W.
• Xue, W.Y.

Titel

Microstructural evolution and mechanical properties of a micro-alloyed low-density δ-TRIP steel

Ist Teil von

• Materials science & engineering. A, Structural materials : properties, microstructure and processing, 2022-07, Vol.848, p.143430, Article 143430

Ort / Verlag

Lausanne: Elsevier B.V

Erscheinungsjahr

2022

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Ultrahigh tensile strength over 1200 MPa has not been reported for low-density delta-transformation-induced-plasticity (δ-TRIP) steels. In addition, the trade-off between strength and ductility is still inevitable for those steels. This study fills the gap by controlling morphology and volume fraction of δ-ferrite. A micro-alloyed low-density δ-TRIP steel with a chemical composition of Fe–3Al-0.84Cr-0.94Mn-0.31Mo-1.18Ni-0.31Si-0.25V-0.3C (weight percentage, wt.%) was prepared, and the high Al addition resulted in the reduced density of ∼5% with 7.49 g cm−3 in density. By applying varying heat treatment parameters, three steels with different microstructures, i.e. steels A, B and C were prepared. Microstructural morphologies of the three steels are significantly different. Steel A has a medium volume fraction of 56% for dendritic δ-ferrite with moderate average thickness of 3 μm while steel B contains the highest volume fraction of dendritic δ-ferrite (61%) with the smallest thickness of 1 μm. In contrast, steel C has the lowest volume fraction of dendritic δ-ferrite (32%) with the largest thickness of 4 μm. In addition, the volume fractions of lamellar RA are 14%, 8% and 19% for steels A, B and C, respectively. Steel A has an ultrahigh tensile strength of 1270 MPa, while a good ductility of 17% is retained. However, steel B shows the lower ductility of 14% in spite of the higher tensile strength of 1220 MPa. The thickness and volume fraction of δ-ferrite band influence not only the TRIP effect but also the initiation and propagation of cracks. The main reason for steel B with the lower ductility is associated with its smallest thickness and the highest volume fraction of δ-ferrite among the three steels. In contrast, the utmost strength-ductility product of steel C is attributed to its moderate thickness and the lowest volume fraction of δ-ferrite bands, which can alleviate the local stress concentration at the ferrite/martensite boundaries and leads to the improvement of ductility.