Enhancing both strength and ductility of low-alloy transformation-induced plasticity steel via hierarchical lamellar structure

The ferrite/bainite dual-phase microstructure is obtained through controlling two-phase region temperature in the designed medium carbon steel. The influence of the two-phase region temperature on microstructure morphologies and volume fraction, as well as mechanical properties, is thoroughly studied. The microstructure at 795°C heat treatment process exhibits excellent strength and elongation. This is attributed to the increased proportion of large-angle misorientation, the better deformability between ferrite and bainite, and the TRIP effect of retained austenite. The strain hardening exponent curve of the sample subjected to the 795°C heat treatment process does not intersect with the straight-line n = e until the strain reaches the value of 0.1, which results in high tensile strength and high uniform elongation.

Section: Mechanical Propertiesmentioning

confidence: 99%

Section: Mechanical Propertiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Investigating microstructural properties of ferrite/bainite dual-phase steel through simple process control

Yin

Qin

Zhao

et al. 2022

“…Nevertheless, from the microstructural point of view, dynamic strain-induced ferrite was observed depending on the temperature of the finish rolling. According to a more recent study in a 0.28C–1.96Mn–1.62Cr–0.67Si–1.19Al–0.34Ni–0.23Mo TRIP steel by Qian et al, a bainitic matrix can be attained by applying the Austenite Reversion Transformation (ART) annealing during intercritical annealing followed by long-duration isothermal bainitic treatment at 320°C for 2 h [19]. They have attained 1 GPa level of UTS and 29% TE after the intercritical annealing of martensitic initial microstructure.…”

Section: Introductionmentioning

confidence: 99%

Partial austenitisation and TBF steel composed of ferrite, bainitic ferrite, and austenite

Erişir

Bilir

Sözer³

et al. 2023

A TRIP-aided bainitic-ferritic (TBF) steel with a chemical composition of Fe–0.19C–1.7Mn–1.09Si–0.51Al–0.05Nb (wt-%) was partially austenitised from a hot-rolled martensitic initial microstructure. After the hot rolling, the martensitic specimens were reheated to different intercritical temperatures and then austempered at 350°C. Thus, the effect of the initial microstructure of TBF steel on intercritical austenite formation during partial austenitisation was studied. The microstructures were investigated by scanning electron microscopy and electron backscatter diffraction (EBSD), and the tensile properties were tested. Microstructural observations revealed that a final microstructure of fine ferrite, bainitic ferrite, and retained austenite can be obtained. The steel partial austenitised at 770°C showed a good combination of ultimate tensile strength and total elongation.

“…Varshney et al found that bainite/ferrite/retained austenite multiphase structure obtained by introducing about 25% preformed ferrite before bainite transformation at 300°C, and the resulting had higher product of strength and elongation than bainite/retained austenite multi-phase microstructure [10]. Qian et al [11] have shown that the ferrite/bainite layered structure can delay the occurrence of tensile necking, resulting in high strength and high ductility of the test steel, and the product of strength and elongation exceeds the traditional TRIP steel. Wang et al studied hardening behaviour of the ferrite of dual-phase steel at different strains by using EBSD technology.…”

Section: Introductionmentioning

confidence: 99%

Study on uniaxial tensile deformation of bainite/ferrite dual phase steel

Liu

Long

et al. 2023

The microstructure evolution of a ferrite/bainite dual-phase steel during uniaxial tension was observed in-situ technology. The effects of tensile rates on microstructure, mechanical properties and fracture mechanism were studied. The result shows that stress concentration is easy to form cracks at the interfaces between ferrite and bainite. The sample exhibits high uniform elongation and strength at low-strain rate, which is attributed to the effective interaction between dislocations. The microstructure undergoes orderly and continuous high hardening rate under ‘harmonious’ conditions. Dislocations are rapidly entangled at high-strain rate and dislocation cells forms. The increased strength of the ferrite brings a reduction in its ability to coordinate more plastic deformation, which eventually leads to local plastic instability and early fracture.