Modelling of Microstructure Evolution during Hot Rolling of a 780 MPa High Strength Steel

Abstract

The microstructure evolution during thermo-mechanical processing of a state-of-the-art Ti-Nb HSLA steel with a tensile strength of 780 MPa has been investigated with laboratory investigations. The entire hot strip rolling process was simulated with hot torsion tests. Using the Gleeble 1 500 thermomechanical simulator, constitutive behaviour, static recrystallization and austenite decompositon were quantified with single and double hit tests as well as continuous cooling transformation (CCT) tests. Precipitation strengthening was studied using aging tests. Based on the experimental results a microstructure model is proposed for hot rolling, run-out table cooling and coiling of the investigated steel. The model has been applied to predict the microstructure of industrially processed coils. The prediction of the ferrite grain size is seen to be in good agreement with that obtained during industrial hot strip rolling.

Computer Simulation of Microstructure Evolution in Low Carbon Sheet Steels

“…HSLA 80 and 90, Bϭ22.3 and Eϭ18 100 K have been determined. 44) Good agreement is obtained with grain sizes observed in industrially processed coils. Observed grain sizes are approximately 5, 4, 3 and 2 mm for the HSLA 50, 60, 80 and 90 steels, respectively.…”

“…12,[29][30][31][32][41][42][43] State-of-the-art models include HSLA grades with minimum yield strength levels of 550 MPa and higher. 31,35) Nakata and Militzer 44) have recently described such a model for a Ti-Nb steel with 780 MPa tensile strength. These high strength levels are achieved with a combination of fine, at least in part, acicular ferrite structures (ferrite grain sizes of 3 mm and below) and nano-scaled precipitates.…”

“…3. 31,85) However, some limitations of this rather simplified methodology have been noted for a 0.14wt%Ti-0.05wt%Nb steel 44) and for precipitation hardening by Cu. 87) In these cases, the complexity of nucleation, growth and coarsening of the precipitates has to be considered in more detail and a single parameter formulation, e.g.…”

Predictive Model for Austenite Grain Growth during Reheating of Alloy Steels

“…[1][2][3][4][5][6][8][9][10][11][12][13][14][15][16]18,23,[25][26][27] Among the models previously reported to predict austenite grain growth, few have considered the influence of the precipitate-forming elements in alloy steels. In the present work, a model was developed to predict the austenite grain growth during reheating including the effects of various alloying elements.…”

Development of a Hot-rolled Low Carbon Steel with High Yield Strength

“…[1][2][3][4][5][6][7][8][9] In this study, a new type of hot-rolled high strength sheet steel with excellent elongation was successfully developed. The CCT curves of this steel under deformed and undeformed conditions were investigated, and the strengthening mechanisms were also researched systematically.…”