γ Decomposition in Fe–Mn–Al–C lightweight steels

Mapelli, Carlo; Barella, Silvia; Gruttadauria, Andrea; Mombelli, Davide; Bizzozero, Marco; Veys, Xavier

doi:10.1016/j.jmrt.2020.02.088

Cited by 29 publications

(22 citation statements)

References 41 publications

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“…As shown in figure 17, after holding at 1150 °C for 6 h, the austenite was completely polygonized, with fine white rod-like particles precipitating inside the austenite and at the grain boundaries. The particles can be identified as κ-carbides based on previous studies by Lu et al, Zhang et al, Mapelli et al and moon et al [23][24][25][26]. When the temperature was elevated to 1200 °C, κ-carbides were observed in the austenite after only 2 h. Extending the holding time to 6 h, δ-ferrites disappeared completely, and obvious precipitation-free zones were observed near the grain boundaries.…”

Section: Microstructurementioning

confidence: 93%

Study on as-cast microstructure of Fe-15Mn-10Al-5Ni-0.8C low density duplex steel

Guo

Zhong-jun

et al. 2022

Mater. Res. Express

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The microstructure of Fe-15Mn-10Al-5Ni-0.8C low density duplex steel ingot was studied by laser confocal scanning calorimetry (DSC), metallographic microscope (MS) and scanning electron microscope (SEM). The results show that: the microstructure of Fe-15Mn-10Al-5Ni-0.8C low density steel is mainly composed of coarse austenite dendrites and δ- ferrite phase in dendrite. When the temperature is 1100℃ and the holding time reaches 8 h, κ-carbides precipitate in austenite. When the temperature and holding time of the ingot reach or exceed 1150℃ and 2 h respectively, the austenitic dendrites transform into equiaxed grains and the δ- ferrite is distributed in bulk at austenite grain boundaries. When the temperature and holding time reach or exceed 1200℃ respectively, the δ- ferrite is distributed in smaller blocks along austenite grain boundaries. When the temperature and holding time reach 1250 ℃ respectively, δ- ferrite is no longer present in microstructure. The activation energy for austenite grain growth was calculated by Sellars’ model at 365 KJ/mol.

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Section: Microstructurementioning

confidence: 93%

Study on as-cast microstructure of Fe-15Mn-10Al-5Ni-0.8C low density duplex steel

Guo

Zhong-jun

et al. 2022

Mater. Res. Express

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“…No precipitates are visible in the EDS mapping, but higher magnification SE images shows a substructure in the austenite phase (Figure 12). The austenite substructure is formed by a spinodal transformation γ → κ + γ 0 leading to nano-sized kappa carbides [18]. The ferrite-austenite grain boundary had a more pronounced etching effect.…”

Section: Scanning Electron Microscopymentioning

confidence: 99%

“…Precipitation of the kappa-carbide phase occurs in the austenitic phase and increases the complexity of the microstructure. Precipitation of large coarse carbides or continuous strains of kappa carbides can be detrimental to mechanical properties [18,19].…”

Section: Introductionmentioning

confidence: 99%

Kappa Carbide Precipitation in Duplex Fe-Al-Mn-Ni-C Low-Density Steel

2021

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The microstructural evolution of a Fe-Mn-Al-Ni-C low-density steel was studied. The lightweight low-density steels are a promising material for the transportation industry, due to their good mechanical properties and low density. The base microstructure of the investigated steel consists of ferrite and austenite. Thermo-Calc calculations showed the formation of an ordered BCC (body-centred cubic) B2 phase below 1181 °C and kappa carbides below 864 °C. The steel was produced in a vacuum induction furnace, cast into ingots and hot forged into bars. The forged bars were solution annealed and then isothermally annealed at 350, 450, 550, 650, 750, and 850 °C. The microstructure of the as-cast state, the hot forged state, solution annealed, and isothermally annealed were investigated by optical microscopy and scanning electron microscopy. The results showed the formation of kappa carbides and the ordered B2 phase. The kappa carbides appeared in the as-cast sample and at the grain boundaries of the isothermally annealed samples. At 550 °C, the kappa carbides began to form in the austenite phase and coarsened with increasing temperature.

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“…This last feature is the most important reinforcement mechanism in austenitic Fe–Mn–Al–C steels that contain high amounts of Al and C. However, these carbides produce a complex system that makes difficult to join these steels by conventional welding processes. The kappa phase is produced by spinodal decomposition (

γ \to y_{0} + γ' \to y_{0} + L 1_{2} \to y_{0} + L' 1_{2} / E 2_{1} = γ_{0} + k

), [ 2 ] where

y_{0}

is a carbon lean γ phase, γ′ is a carbon‐rich γ phase,

L 1_{2}

is a short range‐ordered phase with Al atoms at the corners of the cube and Fe/Mn at the faces.

L 1_{2}

phase undergoes further ordering of C atoms, which settle at the octahedral site of the cube lattice, resulting in the formation of

E 2_{1}

and

L 1_{2}

structures, where

L 1_{2}

finally has the same crystallographic structure of austenite, to accomplish the requirement of the spinodal decomposition, i.e., same crystal structure of parent and product phases.…”

Section: Introductionmentioning

confidence: 99%

“…[ 3 ] However, the driving energy which promotes its precipitation can also be obtained from the hot‐rolling process and the own chemical composition. [ 2 ] Such carbides can also be formed after the welding process, [ 4 ] as the steel is exposed to a severe thermal cycles of rapid heating/cooling transformations, which can promote a complex field of internal stresses. Accordingly, the heat‐affected zone (HAZ) and the fusion zone (FZ) of LD steels present defects such as stress concentration or residual stress as a result of thermal cycles.…”

Section: Introductionmentioning

confidence: 99%

Metallographic, Structural, and Mechanical Characterization of Weld Nuggets in Fe–Mn–Al–C Low‐Density Steels Microalloyed with Ti/B and Ce/La by Gas Tungsten Arc Welding Process

Coronado-Alba

Mejı́a

Cabrera

2021

steel research int.

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The use of low‐density (LD) steels has become increasingly important due to the advantages they offer, such as high strength, high ductility, and principally weight reduction. However, there are few studies regarding their weldability by conventional processes due to the metallurgical complexity of these alloys, including kappa carbides precipitation and hot‐cracking associated with the high contents of Mn, Al, and C. Herein, the main objective is the characterization of the fusion zone and different heat‐affected zones of austenitic Fe–Mn–Al–C LD steels microalloyed with Ti/B and Ce/La. For this purpose, weld nuggets were prepared by autogenous gas tungsten arc welding process using heat inputs of 660 and 975 J. The weld nuggets were characterized metallographic, structural, and mechanically by light optical microscopy, scanning electron microscopy, X‐ray diffraction, and Vickers microhardness. In general, weld nuggets shows three well‐defined zones where γ‐austenite is the main phase and AlN and MnS particles act as nuclei of complex precipitated particles of microalloying elements such as TiC and (Ce, La)O. A considerable decrease in hot‐cracking was noticed in the microalloyed grades. A modulated structure of kappa‐carbide particles was responsible of the largest hardness values (≈450 Vickers microhardness) in the second heat‐affected zone.

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γ Decomposition in Fe–Mn–Al–C lightweight steels

Cited by 29 publications

References 41 publications

Study on as-cast microstructure of Fe-15Mn-10Al-5Ni-0.8C low density duplex steel

Study on as-cast microstructure of Fe-15Mn-10Al-5Ni-0.8C low density duplex steel

Kappa Carbide Precipitation in Duplex Fe-Al-Mn-Ni-C Low-Density Steel

Metallographic, Structural, and Mechanical Characterization of Weld Nuggets in Fe–Mn–Al–C Low‐Density Steels Microalloyed with Ti/B and Ce/La by Gas Tungsten Arc Welding Process

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