Abstract:The work‐hardening response and mechanical properties of dual phase steels originated from different initial microstructures under low and high martensite volume fractions were investigated using a typical carbon‐manganese steel. The modified Crussard‐Jaoul analysis was used for studying the work‐hardening stages and the deformation behavior of ferrite and martensite. It was revealed that the initial martensitic microstructure before intercritical annealing is much better than the full annealed banded ferritic… Show more
“…As a result of rolling of the as-received sample, the pearlite colonies and the ferrite grains became pancaked along the rolling direction (Figure 5(b)). Subsequent isothermal heating at 775 °C results in the recrystallisation of ferrite grains and also the formation of much finer equiaxed ferrite grains and spheroidised carbides [44–46] in the former pearlite colonies (FPC) as can be seen in Figure 5(c,d). Figure 5 Microstructural evolution of IH725 sample after intercritical annealing at 775 °C.…”
Static recrystallisation of cold-rolled AISI 4130 medium carbon steel in the ferritic regime and its response to intercritical annealing treatment are studied. A fine and recrystallised microstructure with improved mechanical properties is obtained via subcritical annealing of cold-rolled sheet, where the subsequent intercritical annealing results in the enhancement of tensile strength via the formation of dual-phase microstructure. Intercritical annealing of the cold-rolled sheet is characterised by an initial drop in hardness due to recrystallisation and subsequent rise in hardness as a result of austenitisation. It is revealed that continuous martensite phase can result in a higher deformation resistance. Finally, the effects of intercritical annealing at temperatures below pearlite dissolution finish temperature (Ac1f) are discussed.
“…As a result of rolling of the as-received sample, the pearlite colonies and the ferrite grains became pancaked along the rolling direction (Figure 5(b)). Subsequent isothermal heating at 775 °C results in the recrystallisation of ferrite grains and also the formation of much finer equiaxed ferrite grains and spheroidised carbides [44–46] in the former pearlite colonies (FPC) as can be seen in Figure 5(c,d). Figure 5 Microstructural evolution of IH725 sample after intercritical annealing at 775 °C.…”
Static recrystallisation of cold-rolled AISI 4130 medium carbon steel in the ferritic regime and its response to intercritical annealing treatment are studied. A fine and recrystallised microstructure with improved mechanical properties is obtained via subcritical annealing of cold-rolled sheet, where the subsequent intercritical annealing results in the enhancement of tensile strength via the formation of dual-phase microstructure. Intercritical annealing of the cold-rolled sheet is characterised by an initial drop in hardness due to recrystallisation and subsequent rise in hardness as a result of austenitisation. It is revealed that continuous martensite phase can result in a higher deformation resistance. Finally, the effects of intercritical annealing at temperatures below pearlite dissolution finish temperature (Ac1f) are discussed.
“…There have been many similar investigations, which confirmed that intercritical annealing of the initial martensitic microstructure resulted in DP steel with better combination of strength and ductility in comparison with any other non-deformed initial microstructures due to the well distributed martensite islands within a ferritic matrix [36,39,47-51]. The reason originates from the nature of martensite, which exhibit high density of lattice defects in form of pockets, blocks, laths that are suitable sites for phase nucleation during intercritical annealing.…”
Section: Prior To Intercritical Annealingmentioning
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.
“…The martensite phase is known as one of the main constituent phases in the advanced high-strength steels, which has been extensively studied by Bleck and coworkers [18][19][20] and Mirzadeh and coworkers [21][22][23]. However, owing to their high strength and brittleness, the martensitic steels are normally used in the quenched and tempered condition.…”
Annealing of deformed martensite (high-temperature tempering) in St37 steel was studied. Different reductions in thickness were considered and compared with the behavior of as-quenched martensite during tempering. tempering of the asquenched martensite was accompanied by the formation of carbide particles, incomplete disappearance of the lath martensite morphology, and continuous decrease in hardness until reaching low values. However, during tempering of the cold rolled martensite, the precipitation of carbides in the lamellar structure, development of distinct equiaxed ultrafine grains through a continuous recrystallization mechanism, and a sudden hardness drop were characterized. the importance of cold rolling reduction and its amount were also discussed.
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