Papers by Keyword: TTT

Abstract: Bainitic steels, which are transformed at very low temperatures, offer an excellent combination of strength and ductility where the strength comes from the nano-structured bainitic plates and thin-film of austenite sandwiched between two bainite sheaves offers the ductility. The main drawback of this structure is the long transformation time which is not ideal for industrial application. Through the microstructural engineering, the extent and kinetics of transformation can be manipulated by judicious selection of alloy composition and process variables. The main challenge is to delay the transformation till the coiling stage and allow the formation of bainite only during the cooling of the coil. In the current work, an approach will be shown, starting from the alloy design based on thermodynamics till the cooling after coiling, which can satisfy the requirements to develop such steel with 1300 MPa UTS combined with 20% elongation (min).

Abstract: Many Aluminium alloys use the precipitation of metastable phases to generate optimum properties. The effect of including additional structures such as θ’ and GP zones is described in the context of a hierarchy of metastable structures. Extending a Thermodynamic data base that has been designed solely to deal with equilibrium conditions is a vital prerequisite to handling the heattreatment of aluminium alloys. It is then possible to generate TTT and CCT diagrams, using the Johnson-Mehl-Avrami treatment previously applied in to other materials providing provision is made for the presence of supersaturated quenched-in vacancies. Calculations using JMatPro are given for the expected behavior of commercial aluminium alloys of increasing complexity, including AA319, AA6061 and AA7075.