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Microalloyed steels have been the subject of theoretical and experimental studies revealing their exceptional mechanical response under nonlinear deformation conditions. In microalloyed steels, especially in multiphase steels, the mechanical properties are adjusted by combination of microstructure components with different levels of theirs mechanical responses, including hardness and ductility. A comprehensive studies have revealed that a transition from the development of usual bulk dislocation microstructures to more architecture ones occurs when the applied strain path allows to cumulate the deformation energy what is also strictly connected with the chemical and structural compositions of analyzed materials. The study presented here aims at understanding the complex strengthening mechanisms as well as microstructure evolution and to provide a link with the mechanical behaviour of investigated steels under nonlinear deformation conditions. The proper choice of the work hardening model for the cyclic plastic deformation is essential for predicting the inhomogeneities occurring during metal forming. Aim of the current work is to discuss the differences between various hardening models with respect to their capabilities in capturing complex deformation models and possibilities of their direct application to finite element modelling of such deformation processes. The results of experimental studies are integrated with computer modelling and dislocation theory to provide insight into the unprecedented combination of properties achieved in certain multiphase steels such as ultra-high flow strengths, good ductility and workability. Finally, based upon results obtained in performed computer simulations, conclusions regarding the possibilities of potential application of the work hardening models in the identification process parameters, trough the inverse analysis, are drawn.

The Strain-Induced Dynamic Transformation (SIDT) is an efficient way to overcome the limitation of grain refinement during the conventional thermomechanical controlled processing (TMCP) of steels. The present study deals with the effects of austenite morphology on the SIDT in microalloyed and IF steels. The discussion of the processing route in terms of chemical composition, deformation schedules, heating and cooling conditions is carried out by the means of torsion tests with deformation in metastable conditions. As it was expected, the microstructure of microalloyed steel was clearly controlled by the microalloying elements what, in turn, directly affectedthe SIDT products. Examination of water-quenched microstructures, just after deformation, revealed the morphology of "strain-induced ferrite". The kinetics of SIDT were observed and analyzed using the strain-stress curves. It is shown that presence of strain-induced precipitations in microalloyed steels accelerates kinetic of SIDT - by reducing the amount of Nb in solution. The changes in ferrite refinement of the experimental steels were explained from the view of the austenite morphology and processing parameters.

Recent studies exploring ammonia as a green hydrogen energy carrier have established its suitability for a variety of combustion technologies including gas turbines, furnaces, and internal combustion engines. Of significant interest are ammonia/hydrogen blends, which possess combustion benefits over pure ammonia, including an extended stability range and higher laminar burning velocity. Despite extensive research characterising the flame properties of these blends, very few studies explore the suitability of existing materials for the manufacture of ammonia/hydrogen combustors. The present study evaluates the impact of ammonia/hydrogen flame chemistry on the H permeation and possible loss of ductility of nickel-superalloys through exposing the samples to pure methane and ammonia/hydrogen flames at atmospheric pressure for a 5-hour period. The effect of the two flame compositions on the materials are compared through thermal desorption analysis (TDA) and room temperature tensile testing. The results showed that exposure to an ammonia/hydrogen combustion environment led to hydrogen being absorbed by the nickel superalloys but a possible variation in ductility is influenced by the combustion conditions. Furthermore, the formation of an oxide layer was shown to likely impact the hydrogen absorption rate of the materials. This work shows that ammonia/hydrogen flame chemistry on combustor materials should not be ignored and warrants further studies on material’s mechanical and environmental stability controlled by nitrogen and hydrogen species permeating at industrially relevant conditions.