Mechanical behaviour of hot and warm formed microalloyed steels

The aim of this work is to investigate the possibility of producing hot and warm formed steels with multiphase structures with high strength and good workability. As an example a niobium-microalloyed steel was investigated. For studying the microstructure development products that were formed in hot and inter-critical conditions, continuous and interrupted compression tests were performed. As a result the detailed indications for controlling the microstructure evolution and inhomogeneity of mechanical properties in products after hot forming were acquired. A number of direct results and conclusions were incorporated in the integrated model, considering the required distributions as well as average values of mechanical properties of deformed product. The models employed here link advanced, finite element approaches simulating metal flow and heat transfer during hot-plastic deformation with constitutive equations describing microstructural processes, phase transformation and mechanical properties. The results establish a methodology for the possible development of structural steels with both controlled microstructure and texture. These provide materials with significant increases in yield strength and a great potential value for the steel industry. The formulated conclusions may find their application in the analysis of more complex metal forming processes and grades of steels.