European Society of Endodontology position statement: Management of deep caries and the exposed pulp

This position statement on the management of deep caries and the exposed pulp represents the consensus of an expert committee, convened by the European Society of Endodontology (ESE). Preserving the pulp in a healthy state with sustained vitality, preventing apical periodontitis and developing minimally invasive biologically based therapies are key themes within contemporary clinical endodontics. The aim of this statement was to summarize current best evidence on the diagnosis and classification of deep caries and caries‐induced pulpal disease, as well as indicating appropriate clinical management strategies for avoiding and treating pulp exposure in permanent teeth with deep or extremely deep caries. In presenting these findings, areas of controversy, low‐quality evidence and uncertainties are highlighted, prior to recommendations for each area of interest. A recently published review article provides more detailed information and was the basis for this position statement (Bjørndal et al. 2019, International Endodontic Journal, doi:10.1111/iej.13128). The intention of this position statement is to provide the practitioner with relevant clinical guidance in this rapidly developing area. An update will be provided within 5 years as further evidence emerges

Some Challenges and Opportunities in Blast Furnace Operations

Blast furnace iron making faces a lot of pressure to decrease use of metallurgical coke and carbon footprint. In many shops around the world in the meanwhile, the convectional blast furnace process is being run at near optimum efficiency for a given set of raw material conditions. Efforts are therefore being made to generate innovative ideas. Top gas recycling and nitrogen-less blowing seem to be attracting attention. Efforts are continuing for increased pulverized coal injection (PCI) to decrease coke consumption. Several furnaces experience pressure drop problems when trying to increase coal injection due to poor burden quality. The present paper attempts to analyze few of the issues related to top gas recycling in a conventional practice and those of pressure drop during PCI. Recycling of top gas even without removal of CO2 seems to hold possibilities for enhanced PCI though with worse fuel rate. Managing layer structure and the reactivity of coke particles can be addressed in various ways to improve bed permeability

Effect of vacuum on mixing behavior in a ladle - a watermodel study

Rising inert gas bubbles in a vacuum ladle experience phenomenal expansion in the top portion of the bath due to the steep variation of absolute pressure. This makes the top layers of the melt substantially more agitated than the bottom regions. The present study is an attempt to characterize the mixing process in such a vacuum ladle by a watermodel, simulating the effect of extra stirring in the top layers of the bath. The simulation is done through a two-level blowing, in which an additional gas stream is injected into the main bubble plume at 75% of the bath height. It was found that mixing under such a simulated condition is worse than that in a bottom purged ladle, for identical total energy inputs to the bath. The study reveals that the energy imparted in the top layers of the liquid in the vacuum ladle is less effective in promoting mixing. The pattern of stirring energy input distribution along the height of the bath is an important parameter in determining the mixing behavior in a ladle, apart from the total energy input

Development of ultrahigh strength steel by electroslag refining: Effect of inoculation of titanium on the microstructures and mechanical properties

saA low alloy steel with the nominal chemical composition of C 0.3%, Mn 1%, Cr 4%, Mo 1%, V 0.4% with lower amount of P and S is prepared by electroslag refining (ESR). The result of the mechanical properties of this steel after tempering confirms that this steel may be placed in the family of ultrahigh strength steel. The tensile, yield and impact strength of this steel are 1 650 MPa, 1450 MPa and 300 kJ/m(2) respectively, coupled with good ductility and hardness. Three more steels are prepared by inoculation of titanium during the ESR process similar to above composition. The analysis values of titanium in these steels are 0.07%, 0.20% and 0.4%. The addition of titanium resulted a sharp change in both microstructures and mechanical properties. It is noticed that 0.07% titanium results a sharp increase of tensile properties compared to un-inoculated steel. The tensile and yield strength of the 0.07% titanium steel are 17:30 MPa and 1512 MPa, respectively. Further increase of titanium to 0.2% and 0.4% result a significant drop of mechanical properties compared to steel with no titanium. The optical, SEM, TEM and TEM-carbon replica studies confirms that at lower concentration of titanium (0.07%), finer T(C, N) particles are precipitated which are able to restrict the austenite grain sizes. The refinement of austenite grains and consequent finer lath martensite may be the possible reason for strenghthening. Higher titanium (>= 0.2%) led to larger carbonitride particles which has no role on grain refinement

Development of process for thermo-mechanical treatment of ultrahigh strength steel prepared by electroslag refining

Thermomechanical treatment (TMT) is the simultaneous use of work hardening, and grain refinement along with solid solution and precipitation strengthening. In this investigation, four alloys, with a base composition of 2 center dot 8%C, 1.0%Mn, 4 center dot 2%Cr, 1 center dot 0%Mo, 0 center dot 34%V, were prepared by electroslag refining (ESR) and by addition of small amounts of Ti and Nb and by increasing Cr and V to 4 center dot 8 and 0 center dot 48% respectively. In two of the alloys a yield strength in excess of 1550 Wa was obtained in the as cast quenched and tempered condition. Attempts were made to further increase the yield strength by thermomechanical treatment. The process parameters for thermomechanical treatment were optimised by adopting procedures such as calculation of stability of precipitates, hot compression test, determination of cooling rates in different coolants, and modelling of TTT and CCT diagrams. The process involved prerolling of the ESR ingot to a bar at 1200 degrees C, followed by hot rolling in two passes starting from 950 degrees C and finishing at 850 degrees C with equal deformation of 25% in each pass to convert the bar into plates. These were immediately cooled in one of the cooling media: air, polymer-water solution (1 : 1 center dot 5) and oil. Yield strength in excess of 1750 Wa was obtained in oil cooled specimens of the alloy with titanium addition and that where Cr and V were increased. The niobium added specimen gave strengths, similar to that obtained for the base alloy, in spite of the fact that the as cast alloy had shown very high strengths, presumably because of the high soaking temperatures and grain growth. Air cooling gave the lowest strengths and oil cooling the highest

Machining aspects of a high carbon Fe3Al alloy

Iron aluminide alloys containing both ferrous as well as non-ferrous (aluminum) components form unique materials from machining theory and practice point of view. While the cutting tool materials specifically required for their machining are not available, the mechanism of machining of such materials containing ferrous and non-ferrous components has not been adequately investigated. This paper deals with fundamental aspects of chip formation and tool-life in machining of an iron aluminide, Fe3Al alloy. Microstructural analysis of chips shows that the interaction of chip and tool in the secondary deformation zone, dependent upon the cutting speed mainly determines the mechanism of chip formation. Results of tool-life testing indicate that thermal softening of tool point combined with abrasion is the predominant tool failure mechanism.© Elsevie

Modeling of Reactions between Gas Bubble and Molten Metal Bath-Experimental Validation in the Case of Decarburization of Fe-Cr-C melts

A theoretical generic model describing the mass transfer phenomena between rising gas bubbles and a metal bath has earlier been developed by the present authors, to predict the composition change in the melt as consequence of blowing different oxidant gases. In order to verify the model predictions, a series of experiments involving reactions between Fe-Cr-C melts and different O(2)-CO(2) gas mixtures were carried out. The results showed that the decarburization deviates significantly from thermodynamic paths predicted on the basis of bulk compositions and that the model was able to make reasonably reliable predictions of the changes of chromium and carbon contents in the melt as a function of time. According to the model, the compositions at the vicinity of injection point as well as at the gas-melt interface in the bubble are likely to be far from that in the bulk. The results of the present set of experiments showed, with CO(2) injection, the utilization of the available oxygen for decarburization was higher as compared to O(2) injection in the case of melts containing higher carbon levels (>1mass%). Reverse is the case in low carbon melts. The results also indicate relatively less Cr-losses from the metal bath when CO(2) is used as the oxidant. As the model predictions are found to be reasonably reliable, the model predictions are extended to predict the impact of the variation of different process parameters

Processing nickel free high nitrogen austenitic stainless steels through conventional electroslag remelting process

Nickel free high nitrogen austenitic stainless steels, made through air-induction melting were processed using conventional electroslag remelting (ESR) process without application of nitrogen gas pressure over the melt, it was found possible to retain the high nitrogen contents of the original steel. The loss in nitrogen content during ESR was found to increase with increasing melt rate. Electroslag remelting was carried out on eleven steels with a base composition at around 18wt%Cr-18wt%Mn-0.1 to 0.6wt%C-0.53 to 0.9wt%N. While the air-induction melted steel had extensive porosity, the ESR ingots were all sound and free from porosity. Thus, steels made in any other process route can be successfully remelted using conventional ESR. The cast structure analysis in a typical medium carbon high nitrogen steel showed that Cr and Mn has a tendency for microsegregation. The presence of microsegregation and residual carbides affect the ductility of the cast steel

Modelling of Physico-Chemical Phenomena between Gas inside a Bubble and Liquid Metal during Injection of Oxidant Gas

Gas liquid reactors are extensively used in many metallurgical processes involving the refining of liquid metals. In these processes, reactions leading to the oxidation of various solutes in liquid metal often compete with each other, which ultimately determine the liquid metal composition. In the present paper, a model has been proposed to simulate the evolution of solute contents in a metallic melt considering mass transfer of solutes in the melt in the vicinity of the bubble, equilibrium at the gas-metal interface and gas composition evolution in the bubble during its ascent through the melt. The composition of solutes at the metal-gas interface in principle can be altered by changing the injected gas composition. The model was applied to the case of oxygen injection through a lance into liquid steel-containing C and Cr, aiming sufficient decarburization without much oxidation of Cr to the slag. The Cr loss to the slag by oxidation is generally much more than that expected based on equilibrium thermodynamics applied to the bulk metal and gas. The actual Cr loss, as shown by the present model, is determined by the composition of solutes at the metal-gas interface rather than in the bulk. The effect of change of the partial pressure of oxygen in the bubble by replacing oxygen by carbon dioxide in the injected gas and the corresponding evolution of C and Cr contents in the melt was simulated. Some preliminary experiments were conducted to validate the model predictions. The frame work of the model is generic and can be extended to many gas-liquid metal reactors in liquid metal processing