The influence of micro coolers on the physical-mechanical characteristics of the steels used in making railway monoblock wheels
Original scientific paper The paper introduces the possibilities of improving mechanical characteristics of the steels used in making railway monoblock wheels, by using micro coolers on steel casting. The laboratory experiments are aimed at studying the control of round cross-section steel ingot solidification by adding crystallization germs in their central area, in order to influence the internal structure and the mechanical characteristics of the steel. The stimulation of heterogeneous germination on the surfaces generated by the particles introduced in the center of the ingot, while it was in a liquid state, leads to the formation of a second solidification front and heat absorption in this area. The data we obtained during the research have been processed in Excel, in order to obtain the correlation equations that express the variation of the steel mechanical characteristics as a function of the chemical structure both for the experimental samples and for the reference ones.
THE INFLUENCE OF CARBON , MANGANESE AND SILICON CONTENT UPON THE HARDNESS OF PHOSPHORUS CAST IRON USED IN MANUFACTURING ROLLING STOCK BRAKING SHOES
Original scientific paper The paper introduces the correlations between the hardness at various points of the braking shoes, according to provisions and standards, and the carbon, manganese and silicon content of the phosphorous cast iron they are made of. The correlations are given both in analytical and graphical form. They allow the determination of the optimal variation domains for the independent parameters (the content of carbon, manganese and silicon).
Solidification of high speed steels
Abstract High speed steels are ferrous based alloys of the Fe–C–X multicomponent system where X represents a group of alloying elements comprising mainly Cr, W or Mo, V, and Co. These steels are mainly used for cutting tools, since they are characterised by their capacity to retain a high level of hardness while cutting metals at high speed. The as cast microstructure of high speed steels consists of dendrites surrounded by a more or less continuous interdendritic network of eutectic carbides. These are observed even under rapid cooling, at rates as high as 106 K s-1. The main features of the as cast microstructure are the distribution and morphology of eutectic carbides, owing to their decisive influence on mechanical properties, and on the service performance of the high speed steels, even after hot working. Hence, the most important improvements on the as cast microstructure that have been obtained through progress in alloy design concern the type, morphology, and volume fraction of the eutectic carbides, while improvements obtained by progress in solidification processing are, on the other hand, mostly related to a significant reduction in the microstructure scale. The development of the microstructure in high speed steels through solidification is reviewed, emphasising the effects of the alloy chemical composition and of the cooling rate. The formation of the eutectic carbides and the techniques used to control their morphology and distribution, both under normal and rapid cooling, are discussed. Microstructures obtained through surface remelting and surface alloying using laser and electron beams are described, and the application of highly alloyed high speed steels to the manufacture of cast hot rolling mill rolls is reviewed.