Effect of Multi-Step Austempering Treatment on the Microstructure and Mechanical Properties of a High Silicon Carbide-Free Bainitic Steel with Bimodal Bainite Distribution

Franceschi, Mattia; Bettanini, Alvise Miotti; Pezzato, Luca; Dabalà, Manuele; Jacques, Pascal

doi:10.3390/met11122055

Cited by 20 publications

(10 citation statements)

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“…These are silicon-based steels (>1.5 wt.%) characterized by ultimate tensile strength values above 2000 MPa and elongation up to 20% [19,20]. These findings have thus served as inspiration for numerous studies that have led to the development of novel steel compositions with tailored properties, which have found applications in various industrial sectors thanks to the remarkable weight reduction of the structures [21][22][23][24][25][26][27][28]. For example, currently, tunnel boring machines, high-power generators, components for wind turbines [29], and diesel injector systems [29] are manufactured with nanostructured steels.…”

Section: Introductionmentioning

confidence: 94%

“…Ausforming accelerates the bainitic transformation since the deformations modify the activation energy for the bainitic ferrite formation, leading to stress-and strain-induced transformations that enhance the transformation kinetics [28,[33][34][35][36]. Additionally, double-step treatments [24,37] lead to the acceleration of the bainitic transformation by the formation of a first population of bainitic ferrite at high temperatures, where the reaction kinetic is generally faster compared to low-temperature transformation. Moreover, this provides nucleation sites for bainitic ferrite plates, which are refined since they formed at a low temperature, significantly reducing the incubation period.…”

Section: Introductionmentioning

confidence: 99%

“…In the current investigation, an attempt was made for the L-PBF fabrication of novel carbide-free nanostructured bainitic steel with a newly developed composition of mediumcarbon, high-silicon, and carbide-free bainitic steel (0.4C-3.2Si-2.6Mn-0.1Al) [24,28] developed following the bainite transformation theory proposed by Bhadeshia. The parameter optimization had been performed to obtain high-density specimens.…”

Section: Introductionmentioning

confidence: 99%

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Laser Powder Bed Fusion Fabrication of a Novel Carbide-Free Bainitic Steel: The Possibilities and a Comparative Study with the Conventional Alloy

Franceschi,

Yazdanpanah,

Leone

et al. 2024

Metals

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A newly developed medium-carbon carbide-free bainitic steel was fabricated for the first time utilizing the laser powder bed fusion (L-PBF) technique. Process parameters were optimized, and a high density of 99.8% was achieved. The impact of austempering heat treatment on the bainite morphology and transformation kinetics was investigated by high-resolution microstructural analysis (SEM, TEM, and EDS) and dilatometric analysis, and results were compared with conventionally produced counterparts. Faster kinetics and finer microstructures in the L-PBF specimens were found as a consequence of the as-built microstructure, characterized by fine grains and high dislocation density. However, a bimodal distribution of bainitic ferrite plate thickness (average value 60 nm and 200 nm, respectively) was found at prior melt pool boundaries resulting from carbon depletion at such sites.

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Section: Introductionmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Laser Powder Bed Fusion Fabrication of a Novel Carbide-Free Bainitic Steel: The Possibilities and a Comparative Study with the Conventional Alloy

Franceschi,

Yazdanpanah,

Leone

et al. 2024

Metals

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“…The studies of Franceschi M. et al [ 16 , 17 ] dealt with the influence of different or multi-stage tempering on the resulting mechanical and corrosion-resistant properties of bainitic steel. It is clear from their results that an increase in the austenitization temperature leads to an increase in the volume fraction of retained austenite.…”

Section: Introductionmentioning

confidence: 99%

Austenite Decomposition of a Lean Medium Mn Steel Suitable for Quenching and Partitioning Process: Comparison of CCT and DCCT Diagram and Their Microstructural Changes

et al. 2022

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The present work deals with the dilatometric study of a hot-rolled 0.2C3Mn1.5Si lean medium Mn steel, mainly suitable for the quenching and partitioning (Q&P) heat treatment in both hot-rolled or cold-rolled condition, subjected to a variation of austenitization temperature. These investigations were performed in a temperature range of 800–1200 °C. In this context, the martensite transformation start temperature (Ms) was determined as a function of austenitization temperature and in turn obtained prior austenite grain size (PAGS). The results show rise in prior austenite grain size due to increasing austenitization temperature, resulting in elevated Ms temperatures. Measured dilatation curves were confronted with the metallographic analysis by means of scanning electron microscopy (SEM). The present paper also focuses on the construction of a continuous cooling transformation (CCT) and deformation continuous cooling transformation (DCCT) diagram of the investigated lean medium Mn steel in a range of cooling rates from 100 to 0.01 °C/s and their subsequent comparison. By comparing these two diagrams, we observed an overall shift of the DCCT diagram to shorter times compared to the CCT diagram, which represents an earlier formation of phase transformations with respect to the individual cooling rates. Moreover, the determination of individual phase fractions in the CCT and DCCT mode revealed that the growth stage of ferrite and bainite is decelerated by deformation, especially for intermediate cooling rates. Microstructural changes corresponding to cooling were also observed using SEM to provide more detailed investigation of the structure and present phases identification as a function of cooling rate. Moreover, the volume fractions obtained from the saturation magnetization method (SMM) are compared with data from X-ray diffraction (XRD) measurements. The discussion of the data suggests that magnetization measurements lead to more reliable results and a more sensitive detection of the retained austenite than XRD measurements. In that regard, the volume fraction of retained austenite increased with a decrease of cooling rate as a result of larger volume fraction of ferrite and bainite. The hardness of the samples subjected to the deformation was slightly higher compared to non-deformed samples. The reason for this was an evident grain refinement after deformation.

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“…

Advanced high-strength steels (AHSS) are considered very attractive materials thanks to their outstanding strength combined with high ductility. [1][2][3][4] Several authors in the literature demonstrated their capability to achieve mechanical strength higher than 1.5 GPa with elongation above 15%. [5][6][7][8] This extremely favorable combination of mechanical properties makes these steel grades new leading actors in important industrial fields such as automotive (i.e., safe and lightweight components, which allow a strong reduction in oil consumption and CO 2 emission), railways application due to their high wear resistance in comparison with standard pearlitic steels, [2,[9][10][11][12] and armor.

…”

mentioning

confidence: 99%

Influence of Austempering Temperature on Microstructure and Mechanical Properties of High‐Silicon Carbide‐Free Bainitic Steel

Franceschi

Pezzato

Gennari

et al. 2023

steel research int.

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The microstructural evolution of a novel high‐silicon carbide‐free bainitic steel at different austempering temperatures is investigated. The microstructure is evaluated by means of optical and electron microscopy, X‐ray diffraction, microhardness, and nanohardness. Results show a variation in the amount of stabilized retained austenite changing the temperature of the isothermal treatment. In particular, it is observed an increase in the retained austenite volume fraction increasing the temperature up to 350 °C, while further increase leads to a reduction. Moreover, increasing the isothermal holding temperature from 250 °C, through 300, 350, and 370 °C, a progressive bainite coarsening and an increase in the amount of stabilized carbon‐enriched retained austenite are observed. Tensile tests reveal an excellent combination of mechanical properties: mechanical strength in the range 1276–1988 MPa and total elongation 0.18–0.44.

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Effect of Multi-Step Austempering Treatment on the Microstructure and Mechanical Properties of a High Silicon Carbide-Free Bainitic Steel with Bimodal Bainite Distribution

Cited by 20 publications

References 60 publications

Laser Powder Bed Fusion Fabrication of a Novel Carbide-Free Bainitic Steel: The Possibilities and a Comparative Study with the Conventional Alloy

Laser Powder Bed Fusion Fabrication of a Novel Carbide-Free Bainitic Steel: The Possibilities and a Comparative Study with the Conventional Alloy

Austenite Decomposition of a Lean Medium Mn Steel Suitable for Quenching and Partitioning Process: Comparison of CCT and DCCT Diagram and Their Microstructural Changes

Influence of Austempering Temperature on Microstructure and Mechanical Properties of High‐Silicon Carbide‐Free Bainitic Steel

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