The influence of bainite morphology on the impact toughness behaviour of continuously cooled cementite-free low carbon bainitic steels has been examined. In these steels, bainitic microstructures formed mainly by lath-like upper bainite, consisting of thin and long parallel ferrite laths, were shown to exhibit higher impact toughness values than those with a granular bainite, consisting of equiaxed ferrite structure and discrete island of marteniste/austenite (M/A) constituent. Results suggest that the mechanism of brittle fracture of cementite-free bainitic steels involves nucleation of microcracks in M/A islands but is controlled by the bainite packet size.

The elastic diffuse neutron scattering from a Cu 17.2 atoh Mn single crystal aged at 483 K to produce an equilibrium state of atomic short-range order is measured at room temperature in a minimum separation volume of reciprocal space. Warren-Cowley short-range order parameters and coefficients of linear static displacement scattering are determined by least-squares fitting. Effective pair potentials obtained from the short-range order parameters by applying the inverse Monte-Carlo method are used to calculate the diffuse antiphase boundary energy yAPW For copper-base alloys the concentration dependence of yAPe is one of the suggested reasons for the transition of wavy to planar slip. Based on the values of yAPB, the concentration ranges for the transition in Q -M n , CL-AI, and 9 -Z n may be understood.Die elastisch diffuse Neutronenstreuung eines Cu-17,2 At% Mn-Einkristalls, der bei 483 K zur Einstellung eines Gleichgewichtszustandes der atomaren Nahordnung ausgelagert wordcn war, wird bei Zimmertemperatur in einem minimalen Separationsvolumen des reziproken Raums untersucht. Warren-Cowley-Nahordnungsparameter und lineare statische Verzerrungskoeflizienten werden nach der Methode der kleinsten Fehlerquadrate angepaI3t. Aus den Nahordnungsparametern werden effektive Paarpotentiale mit der inversen Monte-Carlo-Methode bestimmt und zur Berechnung der diffusen Antiphasengrenzenergie yApB verwendet. Fur Kupfer-Legierungen wird vorgeschlagen, daR die Konzentrationsabhangigkeit von yAPR den Ubergdng von welliger zu planarer Gleitung bestimmt. Die untcrschiedlichen Konzentrationsbereiche fur diesen Ubergang bei Q-Mn, Q -A 1 und 9 -Z n konnen auf das Verhalten von yApR zuruckgefiihrt werden.

The bainite transformation in a low-carbon Si-containing steel has been studied in situ by synchrotron X-rays. While the austenite is homogeneous prior to transformation, the carbon distribution becomes nonuniform as bainite plates form. This is because of the different degrees of physical isolation of films and blocks of residual austenite. The method for converting dilatational strain into bainite volume fraction, using lattice strain as a reference, during isothermal transformation was found to overestimate it. The bainitic and martensitic ferrite did not exhibit a tetragonal unit cell due to the low-carbon content of the steel and the high transformation temperature.

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