Abstract:Medium-carbon dual-phase bainite/ferrite steels with different bainite and carbide volume fractions were prepared via intercritical annealing and austempering. Bainite dominated the microstructure at high intercritical temperatures, and carbides and ferrite phase dominated at low temperatures. Carbides existed in two types, undissolved alloy–cementite and vanadium carbide. The ferrite grain size was reduced to 1.22 ± 0.7 µm at 790°C. Modified Crussard–Jaoul (MC–J) model was used to analyse the strain hardening… Show more
“…Then, the ferrite is deformed under the constraint of bainite, but the bainite is still in the elastic deformation stage. The third stage is associated with the plastic deformation of ferrite and bainite [15,26].…”
Section: Mechanical Propertiesmentioning
confidence: 99%
“…Then, the ferrite is deformed under the constraint of bainite, but the bainite is still in the elastic deformation stage. The third stage is associated with the plastic deformation of ferrite and bainite [15,26]. Figure 9 (a) Relationship between strain hardening exponent and true strain of tested steel after heat treatment; (b) TEM after tensile fracture at 795°C.…”
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.
“…Then, the ferrite is deformed under the constraint of bainite, but the bainite is still in the elastic deformation stage. The third stage is associated with the plastic deformation of ferrite and bainite [15,26].…”
Section: Mechanical Propertiesmentioning
confidence: 99%
“…Then, the ferrite is deformed under the constraint of bainite, but the bainite is still in the elastic deformation stage. The third stage is associated with the plastic deformation of ferrite and bainite [15,26]. Figure 9 (a) Relationship between strain hardening exponent and true strain of tested steel after heat treatment; (b) TEM after tensile fracture at 795°C.…”
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.
“…Increasing the intercritical annealing temperature resulted in increasing V m , increased flow stress and decreased uniform elongation of DP steels [157][158][159][160][161]. Moreover, the V m of DP steels is the key factor which determines the balance between the strength and fracture strain [162].…”
In this review, effects of initial microstructure before intercritical annealing and processing routes of dual phase (DP) high strength steels are discussed. Prior-applied deformation processes as cold rolling and severe plastic deformation (SPD) including their impacts on mechanical properties of DP steels are described. Influences of heating rate, recrystallization of ferrite, nucleation and grain growth of austenite on the microstructure evolution are also presented. The intercritical annealing and thermomechanical processes of DP steels are comparatively outlined. Furthermore, post-intercritical annealing treatments, i.e., tempering, bake hardening, strain and quench aging are argued. Effects of key alloying elements on the microstructure and mechanical properties of DP steels are briefly summarized. A further development of DP steels can properly benefit from this extensive review.
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