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© 2015 ISIJ. The alloy/liquid Fe interaction behaviour at early stages of deoxidation/alloying have considerable influence on the mechanical properties of steel products. The interfacial reaction between FeMnSi and liquid Fe, as well as the inclusion formation, were experimentally studied at the addition early stages based on quenched FeMnSi-Fe diffusion couples. The microstructure and composition of the quenched diffusion couple were evaluated and the inclusions in the reaction zone were characterised. Five regions were distinguished in the quenched reaction zone, i.e. (1) a solidified Fe shell, (2) a α1 phase consisting of a solid α1 phase and a Fe-Mn-Si liquid melt at the experimental temperature, (3) eutectic α1+Fe5Si3 and (4) eutectic Mn5Si3+MnSi phases, which are liquid at the experimental temperature and (5) the origina FeMnSi alloy which did not melt during the interaction. Plenty of oxysulphide inclusions are observed in the reaction zone: Fe(O,S) inclusions formed in the bulk iron and an inclusion poor zone is observed in the nner part of the Fe shell. Large amounts of tiny (Mn,Si)O inclusions formed in the α1 phase near the Fe/α1 interface and large (Mn,Si)(O,S) inclusions precipitated in the liquid phase after solidification. ispartof: ISIJ International vol:55 issue:8 pages:1661-1668 status: published

It is well understood that to develop wagon wheels with higher abrasion resistance, fracture toughness, and fatigue resistance, steels with lower amounts of inclusions need to be used. Clean steels are produced with technologies that minimize the amount of inclusions in the microstructure. The demand for cleaner steels is high, and lowering of non-metallic oxide inclusions and controlling their morphology, composition, and size distribution is vital. Reduction of residual impurity elements such as sulphur, phosphorus, hydrogen, nitrogen, and trace elements is essential in the production of cleaner steel. Material cleanliness is vital for fatigue endurance, since oxide inclusions may act as stress concentrators and initiation points for fatigue cracks. To better understand the relationship between the cleanliness and toughness of the 34-inch cast wagon wheels, two samples of different levels of cleanliness were supplied for investigation. This paper presents the results of metallurgical analysis using scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), and mechanical tests for the pearlitic high-performance cast rail wagon wheel (identified as Class B) that are currently being used. The Charpy V-notch impact test results for the three samples from wagon wheels were compared. With the aid of SEM/EDS analysis system, non-metallic inclusions in these steels were detected, and it was possible to determine the position, size, shape, and composition of each particle. Alumina and manganese sulphide inclusions could be identified as the dominant inclusion types in the investigated samples. Fracture surface analysis of the Charpy specimen with high inclusions indicated that transgranular cleavage was the predominant fracture mode. Fractography of fracture surfaces of Charpy impact test samples also showed improvement of toughness properties on the clean sample.

De aanwezigheid van niet-metallische insluitsels is zeer belangrijk tijd ens de productie van hoge kwaliteitstaal, aangezien zij de microstructuu r en de structurele eigenschappen sterk kunnen beïnvloeden. Zij worden v aak beschouwd als schadelijk voor de eindproductkwaliteit en voor de pro ductiviteit van het staalproces, zodat vele industriële inspanningen naa r het verbeteren van insluitselverwijdering worden geleverd. Een andere, positievere benadering bestaat uit het gebruiken van niet-metallische i nsluitsels om staal met verbeterde of bepaalde mechanische eigenschappen te produceren. In beide gevallen, moeten de kenmerken van de insluitsel populatie in staal, zoals aantal, chemische samenstelling, morfologie, g rootte en ruimtelijke verdeling gecontroleerd worden. In dit doctorale onderzoek, werd de invloed van de belangrijkste procesp arameters in verband met de vorming en groei van insluitsels, zoals het opgeloste aluminium- (Al) en zuurstofgehalte (O) in vloeibaar ijzer (Fe) , op de vorming en de morfologie van Al2O3 insluitsels bestudeerd. Fenom enen van desoxidatie en van heroxidatie in vloeibaar Fe werden onderzoch t dankzij laboratorium experimenten onder strikt gecontroleerde omstandi gheden. Ten eerste, werd een nieuwe techniek ontwikkeld om de observatie van ins luitsels in de beginfase van het desoxidatieproces toe te laten, door ee n stuk Al in contact bij 1600 °C te brengen met vloeibaar Fe dat ve rschillende opgeloste zuurstofgehalten bevat. Een significante verhoging van het insluitselaantal en een verandering in de insluitselmorfologie van gefacetteerde tot bolvormig werden opgemerkt met een stijgende opgel oste zuurstofgehalte in het vloeibare Fe. De vormovergang werd verklaard door de evolutie van de oververzadiging en de beschikbaarheid van zuurs tof aan het reactiefront. Ten tweede, werden de vorming en de karakteris tieken van insluitsels tijdens de heroxidatie van Fe-Al smeltingen onder zocht. De Fe-Al smeltingen werden aan verschillende atmosferen met gecon troleerde zuurstofpartieeldrukken (pO2) blootgesteld. Een verandering in de insluitselmorfologie van dendrieten, clusters en staafvormige inslui tsels tot compacte en gefacetteerde insluitsels wordt waargenomen met st ijgende pO2, d.w.z. met stijgende oververzadiging. Tot slot om in de int erpretatie van de experimentele resultaten bij te wonen, werd een diffus ie-reactie model geformuleerd om de ruimte- en tijdsafhankelijke Al en O concentraties in de smelt als functie van geselecteerde experimentele v oorwaarden af te schatten. nrpages: 277 status: published

Non-metallic inclusions are a major issue during the production of high performance steels, as they influence the microstructure and structural properties to a large extent. They are often considered as harmful to the final product quality and to the steel processing productivity, so that many industrial efforts are directed towards improving inclusion removal. Another, more positive approach is to use non-metallic inclusions to produce steels with enhanced or tailored properties. In both cases, the key issue is to control the characteristics of the inclusion population in the liquid steel, such as number, composition, morphology, size and spatial distribution. In this doctoral research, the influence of the main inclusion-related process parameters, like the dissolved aluminium (Al) and oxygen (O) content in liquid iron (Fe), on the formation and morphology of Al2O3 inclusions was studied. Deoxidation and reoxidation phenomena in liquid Fe were investigated during lab-scale experiments under rigorously controlled conditions. First of all, a new technique was developed to enable the observation of inclusions in the initial stage of the deoxidation process, by bringing a piece of Al in contact at 1600°C with liquid Fe containing different dissolved O levels. A significant increase in inclusion number and a change in inclusion morphology from angular to spherical was observed with increasing dissolved O content. The shape transition was explained by the evolution of the supersaturation and the availability of oxygen at the reaction front. Secondly, the inclusion formation and characteristics during reoxidation were investigated by exposing Fe-Al melts to different oxidizing atmospheres with controlled oxygen partial pressure (pO2). Dendrites, clusters, aggregates and bars were observed near the melt surface at high pO2, while compact and faceted shapes were found at low pO2, i.e. under lower supersaturation conditions. Finally, to assist in the interpretation of the experimental results on the inclusion characteristics, a coupled diffusion/reaction model was formulated to estimate the spatial and time dependent Al and O concentration profiles as a function of selected process parameters. (FSA 3) -- UCL, 2010

The paper describes the knowledge about and results of the experimental heats performed in an electric steel plant. The aim was to verify the possibilities of a controlled desulphurization of alloy steel in a VOD (Vacuum Oxygen Decarburization) device, particularly when using chemical heating through the OVD process (Oxygen Vacuum Deoxidation/Degassing), as well as the standard slag formers. Experimental procedures were used in the production of alloy tool steel. Both, the system of making the reducing slag and optimizing the composition of individual oxides in order to achieve the desired basicity, are complicated by the products of the chemical heating. Therefore, it was necessary to develop a new production technology that would eliminate such oxide products of chemical heating and, thus, the maximum degree of desulphurization could be achieved. The main principle of the technology is to create appropriate thermodynamic and kinetic conditions required for desulphurization. In particular, this concerns a low oxygen activity in the steel, the composition of refining slag, and an intense bath stirring with argon. Web of Science 47 1 140 135