STRUCTURE AND PROPERTIES OF SEVERAL STEELS PRODUCED 'BY CONTROLLED SOLIDIFICATION PROCESSES

Controlled solidification has considered areat attention in the last decade with the engineering aim of developing  structures with improved properties and performance characteristics. Fundamental and applied research work in this field has led to the finding out of new processes which produce improved or novel structures. Steady state directional solidification (DS) MI stir or rheo-casting (RC) are two examples of these processes, which have been applied in this work on several types of steel. The improvements gained in structure, segregation and mechanical properties, due to the application of these processes compared to the conventional casting (CC) are briefly presented in this paper refering to author's work. In DS, plain carbon, low alloyed Mn-Ni, higly alloyed Mn, Mn-Ni and Cr and low carbon steels have been considered. Generally, the structure of these steels has dendrites aligned in the heat flow direction. A rod-like dendrite shape is obtained at high G/R values (G is the temperature gradient and R is the growth rate) while secondary and tertiary dendrite arms appear as G/R values decreases. Measurements of dendrite arm spacings show that they are functions of R-nG-m. Such relationship is useful in controlling the structure and hence the properties. Mechanical testing of some castings indicates high tensile properties for the rod-like DS structure which is even higher than that of the forged structure for the same material. In RC, a novel structure with nearly spherical primary particles is obtained for the Carbon and stainless steels used.