Bainite

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

Formability of Al–Nb Bearing Ultra High-strength TRIP-aided Sheet Steels with Bainitic Ferrite and/or Martensite Matrix

Abstract: Microstructure, tensile properties and stretch-flangeability of 980–1470 MPa grade Al or Al–Nb bearing TRIP-aided cold-rolled sheet steels with bainitic ferrite and/or martensite matrix microstructure (TBF steels) were investigated for automotive applications such as impact member reinforcements, sheet flames and so on. In addition, these properties were related with the microstructure and the retained austenite characteristics. Complex additions of 0.5% Al and 0.05% Nb into a base steel with chemical composition of 0.2% C, 1.5% Si and 1.5% Mn (in mass%) significantly enhanced the total elongation and stretch-flangeability, especially when austempered at temperatures below martensite-start temperature. The excellent stretch-flangeability was primarily associated with (i) refined prior austenitic grain by NbC precipitates and (ii) uniform fine mixed matrix microstructure of bainitic ferrite and martensite, as well as (iii) TRIP effect of metastable retained austenite.

Kinetics modeling of austenite decomposition for an end-quenched 1045 steel

Abstract: Finite element simulations that predict the microstructure and properties of heat-treated steels can be significantly improved by incorporating appropriate models for the kinetics of various austenite transformations. In the present study the austenite decomposition kinetics for a 1045 steel was modeled using a modification of the transformation equation proposed by Li et al. [1]. The kinetics of the continuous cooling transformation were determined directly from an isothermal transformation diagram. To verify the predictions of the model, an end-quench test was used because it produces a wide range of microstructures. The microstructures predicted by the kinetics model for the end-quenched sample were confirmed by quantification of the microstructures observed in the end-quench experiments. Furthermore, the predicted hardness profile was in good agreement with the experimentally measured hardness profile. The kinetics model developed in the present study was compared to the models proposed by Kirkaldy and Venugopalan [2] and the unmodified model by Li. The present model provides a more accurate prediction. A microstructural-based hardness equation from the literature was also evaluated and it predicted hardness values that were above the experimentally measured values. The model we propose predicts the experimental hardness profile more accurately, since it is based on the calculated microstructure and experimental hardness values of martensite, bainite, and ferrite/pearlite.

New insights into crystallographic correlations between ferrite and cementite in lamellar eutectoid structures, obtained by SEM–FEG/EBSD and an indirect two-trace method

Abstract: Four different ferrite/cementite orientation relationships (ORs) in near-eutectoid steel are derived using SEM–FEG/EBSD (scanning electron microscopy–field emission gun/electron back-scatter diffraction) and an indirect two-trace method. They show a common feature of close-packed plane parallelism between ferrite and cementite. Their crystallographic compatibility with habit planes shows a variety of possible habit planes and excludes the existence of the exact conventional Bagaryatsky and Pitsch–Petch ORs. Each of these new ferrite/cementite ORs is correlated with a different edge-to-edge matching condition between austenite and pearlitic ferrite, and between austenite and pearlitic cementite, and possesses specific morphological features. The present results may give deep insight into the crystallography of pearlitic transformation and provide useful information for materials design through interface tailoring in steels.