Processing-Microstructure-Property Correlation for Producing Stretch-Flangeable Grade Dual-Phase Steel

Microstructural Characteristics and Strengthening Mechanisms of Ferritic–Martensitic Dual-Phase Steels: A Review

“…Regarding the MVF effect on strengthening, it can be stated that the martensite phase acts as a reinforcement for the ferritic matrix [1,12,105]. So, MVF can control the strength of the matrix and DP steel [1,13,18,53]. An increment in MVF causes an increase in the density and area of the ferrite/martensite interface.…”

“…Meanwhile, the reason for increased ductility can result from [73]: (a) martensite softening caused by decreasing the solute carbon in it via increasing MVF, as seen in Figure 8f [73]; (b) an increase in the mean free path of martensite with an increasing MVF; (c) avoidance of spreading the strain localized in the ferrite grains to the adjacent ferrite grains via increased MVF with a chain-networked MM, and (d) a decrease in the difference between mechanical properties of ferrite and martensite through the reduction of FGS and an increment of MVF, causing an improvement in the cohesion of the ferrite/martensite interface and a postponement in the plastic instability, i.e., necking. The hole expansion test (HET) assesses the stretch-flangeability property, in other words, the formability of a material that possesses a primary defect (i.e., the preliminary central hole) [18,44]. Hole expansion ratio (HER) can be calculated using Equation (22) [44]:…”

“…finally, third-generation members are composed of medium manganese (Mn) TRIP steels, quenching and partitioning (Q&P) steels, and carbide-free bainitic (CFB) steels [8]. One of the well-known and outstanding members of AHSSs is DP steel [8,12,[18][19][20]. Although DP steels are placed in the first generation of AHSSs, as shown in Figure 1 [8], extensive research is still being conducted regarding AHSSs [21][22][23][24][25].…”

“…The main microstructural characteristics of these steels are ferrite grain size (FGS), martensite volume fraction (MVF), and martensite morphology (MM). The range of strength and ductility of DP steels can be extended as compared to other generations of AHSSs via the One of the well-known and outstanding members of AHSSs is DP steel [8,12,[18][19][20]. Although DP steels are placed in the first generation of AHSSs, as shown in Figure 1 [8], extensive research is still being conducted regarding AHSSs [21][22][23][24][25].…”