Effects of Si on Microstructural Evolution and Mechanical Properties of Hot-rolled Ferrite and Bainite Dual-phase Steels

Abstract

Based on the thermo-mechanical controlled process, the effects of Si on microstructural evolution, tensile properties, impact toughness, and stretch-flangeability of ferrite and bainite dual-phase (FBDP) steels were systematically investigated. The addition of Si from 0 to 0.95 % promoted the formation of fine and equiaxed ferrite grains, and high Si (0.95 %) also resulted in the formation of blocky martensite islands and retained austenite. Yield and tensile strengths, and uniform and total elongations all increased with increasing Si content. Therefore, the tensile strength and ductility balance was improved by Si addition due to the increasing strain-hardening rate. The fractured morphologies after hole-expansion showed that the excellent stretch-flangeability of FBDP steels was associated with the micro-cracks propagating through in ferrite phase as well as the elongated ferrite grains along the direction perpendicular to the crack. 0.95 % Si steel had a similar high combination of tensile strength and impact toughness to 0.55 % Si steel, and especially 0.95 % Si steel exhibited an excellent combination of tensile strength and stretch-flangeability.KEY WORDS: ferrite and bainite dual-phase steel; Si content; impact toughness; strain hardening rate; stretch-flangeability.

Dynamic Strain-Induced Ferrite Transformation during Hot Compression of Low Carbon Si-Mn Steels

“…In addition, Si also caused a higher dislocation density and nucleation rate during deformation. 10,21) As shown in Fig. 7(a) and (e), the ferrite grain size was significantly refined to less than 1.5 mm with Mn addition mainly due to the enhanced ferrite nucleation rate and the reduced growth rate, which was accordant with the results reported by Zhou et al 22) It was worth noting that there were no obvious deformation band structures in No.2 steel (Fig.…”

“…However, there is no literature concerning the ferrite grain refinement by the DSIT process using plain low carbon Si-added steels. In our previous study, 10) Si was considered to decrease the difference in strength of ferrite and bainite by strengthening the ferrite matrix, improving simultaneously tensile strength and stretch-flangeability of steels. In addition, Si addition not only increases Ae 3 and Ar 3 temperatures 11) but also delays austenite recrystallization, 12) probably allowing DSIT to occur at a relatively higher temperature.…”

Physically-Based Modeling and Characterization of Hot Flow Behavior in an Interphase-Precipitated Ti-Mo Microalloyed Steel

“…A new generation of advanced high strength steels (AHSSs) with both high/ultrahigh strength and good cold formability is becoming more commonly used in commercial vehicles to meet the continuous demand for better fuel economy and passenger safety [1][2][3]. However, many of the conventional AHSSs, e.g., dual-phase (DP) steel, have limited the stretch-flangeability during cold stamping in view of the notable difference in hardness between the soft ferrite and the hard martensite [2,3].…”

“…However, many of the conventional AHSSs, e.g., dual-phase (DP) steel, have limited the stretch-flangeability during cold stamping in view of the notable difference in hardness between the soft ferrite and the hard martensite [2,3]. As a solution, a ferritic matrix with interphase precipitation has been proposed to improve the stretch-flangeability of AHSSs through optimizing alloy design and thermomechanical processes [4,5].…”

Microstructure and Mechanical Properties of High Strength and Stretch-Flangeability Hot-Rolled Steels

“…신장플랜지성(hole expanding ratio, HER)에 관한 연구 는 이미 많은 문헌에서 보고되고 있으며, [1][2][3][4][5][6][7][8][9][10] 기계적 특 성보다는 미세조직에 더욱 의존하는 것으로 보고되고 있 다. [3][4][5][6] …”