Effect of nanocarbides and interphase hardness deviation on stretch-flangeability in 998 MPa hot-rolled steels

RETRACTED ARTICLE: Effect of interrupted cooling time on microstructure transformation and hardness of Ti–V–Mo composite microalloyed steel

“…Misra et al [17][18][19] developed a steel plate with yield strength up to 798 MPa by combining Ti-Nb and Nb-V composite microalloying technology with controlled rolling and cooling process and coiling interrupted at 650°C, with precipitation strengthening increment of about 355 MPa. Chun et al [20] studied the effect of coiling temperature on the mechanical properties of Nb-V-Ti composite microalloyed steel. The results show that after the test steel is interrupted at 650°C for 1 h, the precipitation strengthening amount provided by the nano precipitates distributed on the ferrite matrix exceeds 400 MPa, and the strengthening effect is very obvious.…”

Hot Strip Mill Processing Simulations on a Ti-Mo Microalloyed Steel Using Hot Torsion Testing

“…The average Vickers microhardness for the secondary phase constituents in the High T Finish and Low T Finish simulations (both evaluated at the 0.724 radial position) was approximately 550 HV (10 g). The presence of hard, secondary phase constituents negatively impacts stretch-flange formability [7,8]. Polygonal ferrite grain sizes were significantly refined for Low T Finish simulations (roughly 2.7-3.2 µm) compared to High T Finish simulations (roughly 5.2-6.0 µm).…”

“…However, the Mo and Mn additions can enhance the hardenability of the steel, resulting in slower austenite decomposition kinetics and hard secondary phase constituents (e.g., bainite and/or martensite) in the final microstructures. Hard constituents are undesirable because stretch-flange formability is markedly reduced due to the nucleation of voids at the interfaces between the relatively hard and soft phases [7,8]. Therefore, the ability to obtain both fine microalloy precipitates and a single-phase ferritic matrix in the final microstructure requires attention to thermomechanical processing, due to its effect on the austenite decomposition behavior [9].…”

Effect of Microstructural Transformation upon Edge Heat Treatment on Stretch Flangeability of Ultrahigh-Strength Steel with Sheared Edge

“…Therefore, it is considered that the softening of martensite proceeded in this heating temperature range. The improvement of the fracture toughness of martensite [19][20][21][22][32][33][34] and the reduction of the hardness difference within the DP microstructure [12][13][14][15][16][17][18] could have improved .…”

“…Factors relating to the processing technique are the work hardening of the sheared edge [5][6][7][8][9] and the roughness of the end face. 7,[9][10][11] Factors relating to the material microstructures are the heterogeneity due to the hardness difference between the soft and hard phases in the material structure, [12][13][14][15][16][17][18] low fracture toughness that indicates resistance against crack initiation and propagation, [19][20][21][22] or low local ductility. 9,23) Reducing work hardening during shearing and postprocessing of the sheared edge are reported as countermeasures to suppress stretched-flange cracking.…”