Manganese rich slag produced by the appropriate treatment of high manganese pig iron has a high manganese content and results in low fines, is low cost and gives low excess oxygen. Manganese recovery from this slag in the form of manganese ferroalloys compensates for the excess cost of the treatment process. Manganese rich slags produced from the injection of high manganese pig iron under at optimum conditions have levels of (Mn).35 wt-%, (Mn)/(Fe).7 . 65, (Mn)/(Si).2 and (Mn)/(P).285, which satisfy requirements for use as raw material in silicomanganese alloy production. Various experiments were carried out to smelt high manganese slag resulting from the treatment of high manganese pig iron to produce silicomanganese in a bench scale submerged electric arc furnace. Use of such manganese rich slag in the proportion of 40% of the blend has been found to be optimum to obtain a silicomanganese alloy with the highest metallic yield and highest manganese recovery. The silicomanganese alloy produced satisfies the standard chemical specifications, with manganese and silicon contents 68 and 18%, respectively.

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Pig iron with a high manganese content makes further processing to steel using converter technology difficult and unprofitable. In the present study, external demanganisation of high manganese pig iron before the oxygen converter process has been investigated. Pilot plant experimental heats were designed and carried out to optimise the demanganisation process, to produce hot metal adequate for the conventional LD converter, and high manganese slag suitable for the production of silicomanganese. Various high manganese pig irons with different [Si]/[Mn] contents were treated by injection of various oxidisers at varying temperatures, slag basicities and injection rates. The optimum conditions for the demanganisation process have been attained by injection of an oxygen gas-manganese ore mixture at the injection rate of 6 . 8 L min 21 kg 21 into molten high manganese pig iron with a [Si]/[Mn] ratio of 0 . 3 at an initial temperature of 1350uC and slag basicity of 0 . 3-0 . 4.

The influence of cooling rate on the microstructure and mechanical properties of two new ultrahigh-strength steels (UHSSs) with different levels of C, Cr and Ni has been evaluated for the as-cooled and untempered condition. One UHSS had higher contents of C and Cr, while the other one had a higher Ni content. On the basis of dilatation curves, microstructures, macrohardness and microhardness, continuous cooling transformation diagrams were constructed as a guide to heat treatment possibilities. Cooling rates (CRs) of 60, 1 and 0.01°C/s were selected for more detailed investigations. Microstructural characterization was made by laser scanning confocal microscopy, field emission scanning electron microscopy combined with electron backscatter diffraction, electron probe microanalysis and X-ray diffraction. Mechanical properties were characterized using macrohardness, tensile and Charpy V-notch impact tests. UHSS with the higher C and Cr contents showed lower transformation temperatures and slower bainite formation kinetics than that with the higher Ni content. Higher cooling rates led to lower volume fractions and carbon contents of retained austenite together with finer prior austenite grain size, as well as effective final grain size and lath size. These changes were accompanied by higher yield and tensile strengths. The best combinations of strength and toughness were obtained with martensitic microstructures and by avoiding the formation of granular bainite accompanied by proeutectoid carbides at low CR. For the cooling rates studied, UHSS with the higher C and Cr contents showed the higher hardness and strength but at the cost of toughness.

High‐speed steels have been used mostly for multi‐point cutting tools and for plastic working tools. High speed steels are ferrous based alloys of the Fe‐C‐X multi‐component system where X represents a group of alloying elements comprising mainly Cr, W or Mo, V, and Co. The properties of these steels can be improved by modifying their chemical composition or the technology of their production. One of the new trends in modifying the tool steels chemical composition consists in the addition of niobium and nitrogen. In this work, the effects of niobium and nitrogen on morphology of carbides and secondary hardening temperature of investigated high speed tool steels were studied. This experimental work shows that, the conventional ingots have many types of carbides of different shapes and sizes precipitate on the boundary together with thick needle like carbides. On the contrary, for nitrogen steel, the nitrogen alloying leads to form dense, fine and well distributed microstructure. While, on the case of niobium alloying, single carbide (MC), and different types of eutectic carbides were precipitated which have a major effect on the secondary hardening temperature.