Bainite

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

Tensile behavior of functionally graded steels produced by electroslag remelting

Abstract: Tensile behavior of functionally graded steels produced by electroslag refining has been studied. Functionally graded steels containing layers of ferrite, austenite, bainite, and martensite may be fabricatedvia diffusion of alloying elements during electroslag remelting. Tensile strength of the composites depends on the composition and number of layers and those have been modeled based on the tensile behavior of individual phases. The yield stress of each element in the composites is related to the microhardness value of that element. Considering the Holloman relation for the true stress-strain behavior of each element, the tensile strength of an individual element is also related to the microhardness value of that element. By applying the rule of mixtures, the tensile strengths of the composites were determinedvia the numerical method. The obtained results are in good agreement with the experimental results.

Interphase Precipitation of VC and Resultant Hardening in V-added Medium Carbon Steels

Abstract: Interphase precipitation of vanadium carbide (VC) accompanying ferrite and pearlite transformations and its effect on hardness have been examined by using medium carbon steels containing 0.1, 0.3 and 0.5 mass%V. Specimens transformed in a temperature range between 873 and 973 K consist of pearlite and small amount of proeutectoid ferrite. Ferrite fraction increases with raising transformation temperature or with increasing the V content. In addition to proeutectoid ferrite and pearlite, bainite is formed below 853 K, whose fraction is increased by the V addition. Hardening is significant in the V-added alloy between 873 K and 973 K and becomes larger by increasing V content in this temperature range. Meanwhile the alloying effect of V on the hardness remarkably decreases at 823 K where bainite transformation takes place partly. TEM characterization has revealed that VC are precipitated in both of proeutectoid and pearlitic ferrite with holding Baker-Nutting (B-N) orientation relationship with ferrite in the manner of fine rows parallel to the austenite / ferrite interphase boundary. Single variant of VC, whose habit plane is closer to ferrite / austenite boundary than the other two B-N variants, tends to be formed. The size of VC decreases and its number density increases by lowering transformation temperature, corresponding to the larger hardness increase.

The Influence of Bainite on Retained Austenite Characteristics in Si-Mn TRIP Steels

Abstract: Controlled rolling processes are designed to produce a desired microstructure via the control of hot rolling without subsequent heat treatment. Critical to the success of controlled rolling are the stages that occur after hot deformation, when the steel is cooled to room temperature. This can be divided into two parts: the run out table, where the material is allowed to cool relatively rapidly to a pre-determined temperature, and "coiling" at which point the rolled material is coiled, thus showing down the cooling rate considerably. Controlled rolling schedules generally finish by coiling the steel at temperatures below the bainite transformation start temperature (Bs). Any changes in coiling conditions (temperature and time) in this region can result in variations in bainite characteristics (morphology, size, carbide precipitation, etc.). This in turn, may affect the state of the retained austenite and, consequently, the mechanical properties of Si-Mn TRIP steels, which have bainite as the dominant microconstituent. The effect of changes in the bainite transformation conditions were investigated using two grades of Si-Mn TRIP steels, including one a containing Nb as a microalloy addition. The results reveal that the retained austenite volume fraction was strongly influenced by both bainite formation temperature and hold time, The highest values of total elongation (46 and 33%) and formability index (61180 and 40260 MPa·%) were observed for an intermediate hold time (5 min) and temperature (400°C), respectively. These findings are explained by considering the effect of the bainite transformation on the state of the retained austenite.

The influence of Nb on transformation behavior and mechanical properties of TRIP-assisted bainitic–ferritic sheet steels

Abstract: In this study the concept of microalloying was applied to TRIP-aided bainitic–ferritic (TBF) sheet steel. A newly designed chemical composition was introduced including significantly reduced Si content. The impact of Nb on phase transformation, microstructure and mechanical properties was investigated. Nb addition was found to indirectly accelerate transformation kinetics through grain refinement resulting in pro-eutectoid ferrite and upper bainite formation. A change in morphology of the bainitic matrix from lath-like to globular was observed as a result of grain refinement. The amount of cementite was reduced and the amount of retained austenite increased through the addition of Nb. The changes in phase transformation and microstructure resulted in significantly improved mechanical properties comprising both elevated stretch formability and edge crack resistance.