Bainite

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

Delayed Fracture Properties of 1 500 MPa Bainite/Martensite Dual-phase High Strength Steel and Its Hydrogen Traps

Abstract: It is very imperative to improve delayed fracture properties of high strength steel, which may enlarge its usage. The published literature shows that the susceptibility to hydrogen embrittlement of a novel 1 500 MPa bainite/martensite dual-phase high strength steel is inferior to that of conventional quench-tempered high strength steel. The stress corrosion cracking (SCC) in a 3.5% NaCl solution for novel 1 500 MPa bainite/ martensite dual-phase high strength steel was investigated in this paper by using modified wedge-opening-loading (WOL) specimens. The experimental results show that KISCC for novel 1 500 MPa bainite/martensite dual-phase high strength steel is larger than 50 MPa·m1/2, exceeding conventional high strength steel. Its crack growth rate (da/dt)II is about 1×10−5 mm/s, which is less than that of conventional high strength steel. Hydrogen trapping phenomena in the steel were investigated by electrochemical permeation technique. The lath boundaries and stable retained austenite are beneficial hydrogen trap, slowing down the segregation of hydrogen on the crack tip, hence KISCC increases and crack growth rate decreases.

Back calculation of parent austenite orientation using a clustering approach

Abstract: A new approach is presented for calculating the parent orientation from sets of variants of orientations produced by phase transformation. The parent austenite orientation is determined using the orientations of bainite variants that trans­formed from a single parent austenite grain. In this approach, the five known orientation relationships are used to back transform each observed bainite variant to all their potential face-centered-cubic (f.c.c.) parent orientations. A set of potential f.c.c. orientations has one representative from each bainite variant, and each set is assembled on the basis of minimum mutual misorienta­tion. The set of back-transformed orientations with the minimum summation of mutual misorientation angle (SMMA) is selected as the most probable parent (austenite) orientation. The availability of multiple sets permits a confidence index to be calculated from the best and next best fits to a parent orientation. The results show good agreement between the measured parent austenite orientation and the calculated parent orientation having minimum SMMA.

Bainite nucleation from mineral surfaces

Abstract: Experiments have been conducted to study the nucleation of bainite at interfaces between ceramic compounds and low-alloy steels. To facilitate this, chemically pure mineral powders were pressure bonded to steel samples. The resulting composite samples were then heat treated to induce transformation, and hence compare the transformation behaviour in the vicinity of the ceramic/steel interface to that within the bulk of the steel. It is found that the minerals may be categorised into three groups, according to their observed efficacy in inducing the nucleation of bainite. The dominant reason for the stimulation of bainite nucleation seems to be a chemical interaction between the mineral and the steel. One noteable exception is TiO, which, within the limits of resolution, appears to remain inert, and yet enhances bainite formation.

Evaluation of Displacive Models for Bainite Transformation Kinetics in Steels

Abstract: Several kinetic models for bainite transformation have been widely applied in industry and research. The majority of these models, that do not consider the effect of cementite precipitation during bainite transformation, were validated in high silicon bainitic steels in order to avoid the interference of cementite precipitation during bainite formation. In this work, displacive models for bainite transformation have been validated in bainitic steels with different silicon content with the aim of evaluating their applicability on steels where cementite precipitation may play an important role on bainite formation. It has been found that these models fail in the calculus of the maximum volume fraction of bainite of lean silicon steels, but lead to a reasonable accuracy in high silicon steels. This is not surprising since cementite formation reduces the carbon content in the residual austenite, stimulating the formation of a further quantity of ferrite. Likewise, an imprecise estimation of the nucleation rate of bainite must be the reason for the poor correlation in the predictions of the bainite transformation kinetics in high silicon steels. This entails a better treatment of autocatalytic nucleation, still unresolved issue in the bainite transformation kinetics theory. [doi:10.2320/matertrans.47.1492]