Recrystallization, grain growth and austenite formation in cold rolled steels during intercritical annealing

Poyraz, Okan; Ögel, Bilgehan

doi:10.1016/j.jmrt.2020.08.015

Cited by 13 publications

(9 citation statements)

References 20 publications

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“…The generation of the intergranular martensite is mainly because the experimental steel is subjected to intercritical annealing, and the austenite mainly starts to nucleate at grain boundaries (Ferrite/Ferrite and Ferrite/Cementite) due to the dissolution of lamellar carbides and the movement of carbon atoms in the ferrite. [ 20 ] Finally, in the process of air‐cooling to room temperature, austenite transforms into martensite due to the air cooling rate exceeding the critical cooling rate (0.7 °C s −1 ) of 40Mn2CrNbV steel.…”

Section: Resultsmentioning

confidence: 99%

Microstructure and Mechanical Properties of a Novel Ultra‐High Strength Hot‐Stamped Steel with High Hardenability

Chen

Chu

et al. 2022

steel research int.

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Herein, it is shown that the hot‐stamped steel exhibits high hardenability with a critical cooling rate of about 0.7 °C s−1 due to its unique chemical composition. The microstructure of the annealed sheet consists of ferrite, spherical carbides, and intergranular martensite. Thereinto, the generation of intergranular martensite can eliminate the yield point elongation and reduce the ratio of yield strength to ultimate tensile strength. Furthermore, compared with commercial 30MnB5 steel, the experimental steel (40Mn2CrNbV) quenched sheet shows excellent mechanical properties: yield strength (YS) = 1361 MPa, ultimate tensile strength (UTS) = 2422 MPa, and total elongation (TE) = 6.1%. Additionally, it is found that the Cr7C3 with a mean diameter of 240 ± 50 nm in the annealed quenching sheet can hinder dislocation movement to increase the yield strength. The coherent Nb‐rich (Nb, V)C precipitate (a mean diameter is <50 nm) in the cold‐rolled quenched sheet can improve the mechanical properties of the hot‐stamped steel.

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Section: Resultsmentioning

confidence: 99%

Microstructure and Mechanical Properties of a Novel Ultra‐High Strength Hot‐Stamped Steel with High Hardenability

Chen

Chu

et al. 2022

steel research int.

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“…Nucleation is preferred at the grain corners, so the dispersion of growing particles cannot be considered to be truly "random" [40]. Moreover, heterogeneous nucleation is more common because it can effectively reduce the interfacial energy and nucleation barrier.…”

Section: Phase-transformation Kinetics Using the Modified Jma Modelmentioning

confidence: 99%

Effect of Uniaxial Compressive Stress on Phase Transformation Kinetics of Low-Carbon Steel

et al. 2022

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To attain microstructure transformation and the kinetics of phase transformation under stress during the annealing process, dilatometric curves of phase transformation for Q235 steel were tested using a Gleeble-3500 thermal-mechanical simulator under different uniaxial compressive stresses. The Johnson–Mehl–Avrami (JMA) model considering impingement correction was applied to study the phase-transformation kinetics during annealing. The results showed that the grain size increased with increasing uniaxial compressive stresses because it provided additional energy for grain growth. Furthermore, the interfacial migration velocity decreased with increasing stress owing to grain coarsening and a decrease in the density of the α/γ boundary. Meanwhile, the stress reduces the sum of the misfit accommodation energy and interface energy caused by the transformation, and the driving force required for the transformation of austenite to ferrite decreases. Hence, it was concluded that uniaxial compressive stress plays a complex role in the phase transformation, which inhibits interfacial migration and the transformation rate while providing additional energy for the transformation.

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“…Since recrystallization processes are highly influenced by the degree of deformation that is introduced into the material in the a previous forming process [14], only a locally varying annealing would result in a homogenous softening of the material in order to reach the initial hardness distribution. Furthermore, the influence of the heat treatment strategies on the resulting hardness of the functional elements in forward extrusion are analyzed.…”

Section: Micr Microhar Ohardness Dnessmentioning

confidence: 99%

“…Overall, the application of tailored blanks is proven to be beneficial for the manufacturing of parts with integrated functional elements extruded by SBMF. In further studies, the increase of the recrystallization temperature can enable a reduction of the heat treatment time [14]. Orbital forming at high temperatures offers moreover an alternative approach to enhance the economic efficiency of the process and to reduce the production time.…”

Section: Surf Surface Int Ace Integrity Egritymentioning

confidence: 99%

Investigation on tailored blanks in a full forward extrusion process of sheet-bulk metal forming

Reck¹,

Merklein²

2021

Esaform 2021

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Due to the ongoing technological development, the demand for geometrically complicated high performance parts with great functional density is increasing. Often, the use of sheet metal is a beneficial approach in manufacturing technology to meet the requirements on components regarding material strength and lightweight construction goals. The forming of therefore required complex sheet metal part geometries with integrated functional elements cause the need for a three dimensional material flow. Sheet-bulk metal forming, characterized by the application of bulk forming operations on sheet metals, is a suitable approach to produce such components. A challenge is the material flow control, resulting in an insufficient die filling of the functional elements. The use of tailored blanks with a defined sheet thickness distribution is an auspicious approach to face this challenge in subsequent forming processes. In the presented work, semi-finished products with a continuous thickness profile manufactured by orbital forming are applied in a full forward extrusion process. By an additional implementation of a heat treatment, the tailored blanks undergo a recrystallization process that causes a softening of the strain hardened material. In this paper, the potential of a heat treatment in the process class of sheet-bulk metal forming is shown by characterizing the geometrical and mechanical properties of the functional components by applying the mild deep drawing steel DC04 with an initial sheet thickness of t0 = 2.0 mm.

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Recrystallization, grain growth and austenite formation in cold rolled steels during intercritical annealing

Cited by 13 publications

References 20 publications

Microstructure and Mechanical Properties of a Novel Ultra‐High Strength Hot‐Stamped Steel with High Hardenability

Microstructure and Mechanical Properties of a Novel Ultra‐High Strength Hot‐Stamped Steel with High Hardenability

Effect of Uniaxial Compressive Stress on Phase Transformation Kinetics of Low-Carbon Steel

Investigation on tailored blanks in a full forward extrusion process of sheet-bulk metal forming

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