Marcin Kwiecień

Characterization of UFG Microalloyed Steel Produced by Combined SPD Treatment

Studies of the effects of inhomogeneity of UFG (ultrafine-grained) microstructure evolution have been performed on severely deformed specimens produced by AAD (angular accumulative drawing), followed by wire drawing and wire flattening processes i.e. “top-down” systems of the grain refinement process. In this paper, deformation behavior and size effects are illustrated by means of UFG microalloyed steel with different combinations of microstructure length scale and deformation inhomogeneity. The refined and severely elongated structures were investigated by light microscopy, TEM and EBSD. Of particular importance was the understanding of the effects of strain path, microalloying elements and deformation inhomogeneity on grain refinement and dislocation substructure formation processes.

Mechanical Response of Microalloyed Steel Subjected to Nonlinear Deformation

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.

Comparative Analysis of Precipitation Effects in Microalloyed Austenite and Ferrite Under Hot and Cold Forming Conditions

Deformation processes of microalloyed steels, both during hot and cold processing, are characterized by complex interactions between fine strain-induced precipitates and deformation activated movement of dislocations. Disperse particles that are either forming during the deformation at elevated temperature or are already present in the material at ambient temperature can significantly affect also other strengthening mechanisms e.g. dislocation and grain size strengthening. In the current work, quantitative and qualitative analysis of the effects of second phase particles in fcc and bcc microalloyed structures subjected to severe plastic deformation (SPD) processing was performed with respect to the inhomogeneity of microstructure evolution and properties. Observed inhomogeneities of deformation mechanisms, work hardening and microstructure refinement of microalloyed ferrite much more pronounced than in the case of microalloyed austenite. Discussion of the mechanical and microstructural reasons of such differences is also presented. Conclusions regarding effects of applied complex deformation history on microstructure morphology and properties were used as a validation of performed computer modelling.

Metallic Multilayered Materials Produced by Constrained Compression

Investigation of the mechanical behaviour of multilayered metallic materials obtained during novel joining technique called Constrained Compression (CC) is presented. 316L stainless steel material was used in CC to achieve multi-layered structure. Microstructural study based on light microscopy was performed focused presumably on the joining areas of the deformed metallic laminate. The qualitative and quantitative assessment of the processing conditions, microstructure development and microhardness distributions showed the possibility of achievement good bonding quality. Experimental study was supported by numerical stress and strain analysis. It has been shown that determination of the optimum processing parameters allowed for improvement of the joining process, which in turn will enable to produce multilayered metallic materials on a larger scale.