On Factors Affecting the Phase Transformation and Mechanical Properties of Cold-Rolled Transformation-Induced-Plasticity–Aided Steel

Abstract

Two Mo-Nb microalloyed transformation-induced-plasticity (TRIP) steels, with Al contents of 0.23 and 0.65, were subjected to several hot-rolling conditions designed to generate different ferrite morphologies and grain sizes. These structures were then cold rolled and TRIP annealed under different heat-treatment conditions. To further develop TRIP steel in terms of strength and ductility, stabilizing retained austenite by isothermal bainitic transformation was studied in detail. Microstructure observation and tensile tests were conducted, and volume fractions of retained austenite were measured. It was observed that increasing the aluminum content enhances the transformation rate and increases the total amount of bainite fraction at the expense of retained austenite. The latter effect enhances formability by increasing ductility. Furthermore, it was observed that the hot-rolling schedule, prior to cold rolling and heat treatment, has a decisive effect on structure refinement, which enhances the strength-ductility balance of the final product. To study the transformation behavior, dilatometer testing was conducted under conditions similar to that of the heat treatment. Thermodynamic calculations were used to verify the results.

Effect of microstructure on retained austenite stability and tensile behaviour in an aluminum-alloyed TRIP steel

“…The main advantage of aluminumalloyed TRIP steels over silicon-based compositions is that they do not form surface oxides, which improves coatability and galvanizing properties [19]. Generally, the carbon concentration in RA is higher in aluminum-alloyed TRIP steels, which is expected to increase its mechanical stability [1,20,21]. However, it has also been reported that there is no difference in carbon enrichment of RA between silicon-alloyed vs. aluminum-alloyed TRIP steels [22].…”

Thermo-mechanically processed dual matrix ductile iron produced by continuous cooling transformation

“…On the other hand, increasing aluminum would result in increasing the stronger ausferrite on the expense of retained austenite (Soliman and Palkowski, 2008). This can justify the hardness increase with increasing the aluminum as shown in Fig.…”

“…10 that the time required for the end of stage I transformation decreased by increasing Al when applying Schedule I. This can be attributed to the effect of aluminium in accelerating the ausferritic transformation kinetics (Soliman and Palkowski, 2008) It is also obvious from Fig. 10 that, when applying Schedule I, deforming the DI resulted in accelerating the transformation.…”

“…process a wide range of intercritical region would ease controlling the pro-eutectoid volume fraction. For this purpose aluminum is added because of its effect of widening the intercritical region as reported by Soliman and Palkowski (2008). Thus the investigation aims at: 1-Studying the effect of aluminum content and the applied deformation on the kinetics of pro-eutectoid ferrite, martensite and ausferrite formation in the thermo-mechanically processed ductile iron.…”

Future Challenges in the Steel Industry and Consequences for Rolling Plant Technologies

“…Pre-rolling, using dynamic recrystallization and finishing rolling at temperature levels closely above Ac3, promotes a non-recrystallized austenite condition, which provides a high nucleation density for ferrite formation. These facts result in ferrite grain sizes in the range of some microns [7,14]. Common concepts for TM rolled HSLA steels are shown in Fig.…”