In this paper, a 0.2 C–1.6 Mn–1.5 Si wt. % TRIP-aided cold-rolled steel sheet was fabricated and the optimal heat treatment conditions (Intercritical Annealing “IA” and Bainitic Isothermal Transformation “BIT”) were investigated to maximize the volume fraction and stability of the retained austenite. The effects of temperature on IA (770, 790 and 810 ºC) and BIT (330, 350 and 370 <su...

The tempering of two–phase mixtures of bainitic ferrite and carbon–enriched retained austenite has been investigated in an effort to separate the reactions that occur at elevated temperatures from any transformation during cooling to ambient conditions. It is demonstrated using synchrotron X–radiation measurements, that the residue of austenite left at the tempering temperature partly decompose...

The stability of the retained austenite has been studied in situ in low-alloyed transformation-induced-plasticity (TRIP) steels using high-energy X-ray diffraction during tensile tests at variable temperatures down to 153 K. A detailed powder diffraction analysis has been performed to probe the austenite-to-martensite transformation by characterizing the evolution of the phase fraction, load pa...

Lath martensite reveals a specific hierarchical subgrain structure, with laths, blocks and packets of particular crystallography. The presence of interlath retained austenite layers has been reported in the literature. This paper investigates the potential influence of the interlath retained austenite on the mechanical behaviour of lath martensite subgrains. To this purpose, a martensite grain ...

with careful design, mixed microstructures consisting of fine plates of upper bainitic ferrite separated by thinfilms of stable retained austenite have exhibited impressive combinations of strength and toughness in highsiliconbainitic steels. the silicon suppresses the precipitation of brittle cementite leading to an improvement intoughness. the essential principles governing the optimisation o...

We have performed in-situ magnetization and high-energy X-ray diffraction measurements on two aluminum-based TRIP steels from room temperature down to 100 K in order to evaluate amount and stability of the retained austenite for different heat treatment conditions. We have found that the bainitic holding temperature affects the initial fraction of retained austenite at room temperature but does...

Modern TRIP assisted steels contain retained austenite with carbon concentrations in excess of 1 wt-%. Some of their mechanical properties, in particular the toughness and ductility, rely on the diffusionless transformation of this austenite into high-carbon martensite, induced by stress and strain. The properties can be excellent in spite of the fact that freshly formed high-carbon martensite ...

With careful design, mixed microstructures consisting of fine plates of upper bainitic ferrite separated by thin films of stable retained austenite have exhibited impressive combinations of strength and toughness in highsilicon bainitic steels. The silicon suppresses the precipitation of brittle cementite leading to an improvement in toughness. The essential principles governing the optimisatio...

In material selection, especially in low temperature conditions, one of very important factors it is a ductile to brittle transition temperature, i.e. the temperature when material becomes too brittle to use. In this paper transition temperature determined by impact energy in temperature interval from –196 to +100°C of unalloyed austempered ductile iron with different microstructures have been ...

High silicon (>1.5%) steels with different compositions were isothermally transformed to bainite at 220 and 250 ◦C to produce what is often referred to as nanostructured bainite. Interrupted tensile tests were carried out and the retained austenite was measured as a function of strain. Results were correlated with tensile ductility. The role of retained austenite stability is remarkably underli...