Bainite

About: Bainite is a research topic. Over the lifetime, 9520 publications have been published within this topic receiving 145305 citations.

Critical assessment: Martensite-start temperature for the γ→ε transformation

Abstract: It is increasingly important in the context of high-manganese steels of the kind that lead to twinning-induced plasticity to be able to estimate the temperature at which e -martensite forms when austenite is cooled. We find that the thermodynamic method used in similar calculations for α ′ martensite cannot in many cases be implemented because of apparently imprecise thermodynamic data, a conclusion partly validated using limited first-principles calculations. Alternative, empirical methods are also evaluated. The austenite grain size dependence of the martensite-start temperature has also been rationalised in terms of existing theory for α ′ martensite. Experiments have also been conducted to show that the problem in dealing with the e -martensite does not lie in the precision with which the transformation can be measured using dilatometry.

γ → α transformation in Fe, Fe–Ni, and Fe–Cr alloys

Abstract: Evidence is presented to show that five transformation products are possible in pure iron and dilute substitutional alloys: equiaxed ferrite, massive ferrite, bainitic ferrite, lath martensite (massive martensite), and twinned martensite. The morphology and transformation temperatures of these products are discussed. In conclusion, the chemical driving force for each of the transformations is calculated as a function of composition.

On the Spheroidized Carbide Dissolution and Elemental Partitioning in High Carbon Bearing Steel 100Cr6

Abstract: We report on the characterization of high carbon bearing steel 100Cr6 using electron microscopy and atom probe tomography in combination with multi-component diffusion simulations. Scanning electron micrographs show that around 14 vol pct spheroidized carbides are formed during soft annealing and only 3 vol pct remain after dissolution into the austenitic matrix through austenitization at 1123 K (850 °C) for 300 seconds. The spheroidized particles are identified as (Fe, Cr)3C by transmission electron microscopy. Atom probe analysis reveals the redistribution and partitioning of the elements involved, i.e., C, Si, Mn, Cr, Fe, in both, the spheroidized carbides and the bainitic matrix in the sample isothermally heat-treated at 773 K (500 °C) after austenitization. Homogeneous distribution of C and a Cr gradient were detected within the spheroidized carbides. Due to its limited diffusivity in (Fe, Cr)3C, Cr exhibits a maximum concentration at the surface of spheroidized carbides (16 at. pct) and decreases gradually from the surface towards the core down to about 2 at. pct. The atom probe results also indicate that the partially dissolved spheroidized carbides during austenitization may serve as nucleation sites for intermediate temperature cementite within bainite, which results in a relatively softer surface and harder core in spheroidized particles. This microstructure may contribute to the good wear resistance and fatigue properties of the steel. Good agreement between DICTRA simulations and experimental composition profiles is obtained by an increase of mobility of the substitutional elements in cementite by a factor of five, compared to the mobility in the database MOBFE2.

Phase-Field Modeling of Austenite Formation from a Ferrite plus Pearlite Microstructure during Annealing of Cold-Rolled Dual-Phase Steel

Abstract: The prediction of microstructure and, consequently, of mechanical properties, as a function of chemical composition and heat treatment parameters, is currently a major topic of scientific investigations There has been considerable effort to investigate the phase transformation during cooling and its modeling In comparison, the metallurgical processes of the ferrite-austenite transformation during heating and annealing have not been intensively studied However, the austenite formation during heating and annealing has a great influence on the final microstructure, as it is one of the first steps in the complex microstructure development of modern high-strength strip steels In this study, the simulation of austenite formation from a ferrite plus pearlite microstructure during heating is realized by means of a multiphase-field approach For the description of pearlite dissolution, a simple pseudo-phase approximation is used, which neglects the substitutional elements Instead, the modeling of austenite formation from ferrite is performed as a second step, taking into account the substitutional elements under LE negligible partitioning (LENP) conditions, using direct coupling to a commercial thermodynamic database The results of these two-dimensional (2-D) simulations will be presented and compared with experimental findings