The effect of hot metal additions on the decarburization and dissolved sulfur, phosphorous, and nitrogen content in the steel of a DC EAF was investigated. The addition of hot metal of maximum 36% provided heat into the EAF allowing faster melting and reduced power on times of the furnace. The increased melting rate lowered the FeO in the slag and seems to allow faster kinetics for CaO dissolution into the slag. Hot metal utilization into the slag resulted in higher phosphorous distribution ratios compared to hot metal free heats achieving comparable phosphorous levels at the ladle metallurgical furnace even though the initial input phosphorous was much higher than hot metal free heats. The effect of hot metal on the desulfurization was not pronounced and no apparent difference could be ascertained compared with the 100% scrap charge. With the addition of carbon saturated iron units in the EAF, the evolution of CO and foaming was promoted, which inhibited the infiltration of nitrogen and lowered the overall partial pressure of nitrogen resulting in lower nitrogen levels in the steel. In addition, the dilution effect of the tramp elements Cu and Sn with hot metal ensured the critical defect index to be less than 10% resulting in a 50% reduction of the quality defect index.
The field of steelmaking has seen an increased demand in reducing and controlling the amounts of dissolved gases in steel. Hydrogen and nitrogen are two of the most important gases which, when dissolved in liquid steel, affect its properties significantly. Both of these gases can enter the liquid steel either through steelmaking additions or by reaction of the liquid metal with the atmospheric elements. At United States Steel Corporation (U. S. Steel), empirical evidence has shown that hydrated scrap, lime and coke additions are major contributors to hydrogen pickup in liquid steel. Similarly, nitrogen impurities in ferroalloys, coke and scrap are identified sources of nitrogen. In addition, the presence of measurable traces of nitrogen in oxygen gas used at the BOP and Q-BOP has also resulted in elevated levels of nitrogen pickup. There is also an increased likelihood of higher hydrogen and nitrogen in liquid steel from overblow and reblow situations. This additional pickup of hydrogen and nitrogen gases in steel will not only affect the properties of steel; there is also significant potential for hydrogen-induced sticker breakouts to occur at the continuous caster, which could result in significant maintenance costs and productivity losses. Therefore, it is imperative to accurately quantify the amounts of hydrogen and nitrogen in liquid steel. Online hydrogen measurement uses measured hydrogen partial pressure in collaboration with equilibrium constants and interaction coefficients relevant for the hydrogen dissolution reaction. To ensure accurate hydrogen readings from the instrument, those thermodynamic values were reviewed, considering the changes in chemistry and temperature in the steelmaking processes. Similarly, precautions dealing with sample preparation to ensure accurate and reproducible nitrogen measurements using optical spectrometric techniques are identified. Discussions on the potential hydrogen-induced breakouts, when uncontrolled and significantly high levels of hydrogen are present in the liquid steel, are also provided in this paper.
With advances in mold instrumentation, high performance mold fluxes, better reliability maintenance procedures, and improved operating practices, there has been a significant decline in the number of unplanned caster breakouts experienced at various production facilities. The typical breakouts of stickers and flux entrapments that were frequently observed in the past is often detected using embedded thermocouples in the mold and automatic slowdowns are initiated which inhibit excessive tearing of the partially solidified shell and prevent subsequent breakouts. However, in-mold events still occur resulting in caster downtime. Many of these occasional events have been linked to bleeders along the corners of the slabs, slab joint defects during tundish changes, and longitudinal face cracking. Considering the potential costs associated with unplanned caster breakouts, improvements have been made in the existing breakout prevention system. Major modifications of this existing breakout prevention system included, in particular, the addition of bleeder thermocouples or edge thermocouples which made possible the detection of shell containment loss near the corners of the slab. These bleeder thermocouples can also be utilized in detecting bad tundish joints related to excessive cooling and corner contraction that lead to tundish change joint defect type breakouts. In addition, changes in the location of the existing embedded thermocouples to a staggered-design extended the detection range of the breakout prevention system without increasing the total number of thermocouples.
In social network analysis, researchers are primarily interested in the "most important or most dominant" actors, an issue that is related to the position of the actors within a network. The most important or dominant player within the network is typically located at a strategic location in the network. Cohesive subgroup analysis is an analysis method that determines the network structure by grouping actors that are intimately connected with one another. By dividing a huge network into several subgroups, the network structure can be expressed more simply and the characteristics of the network can not only be understood much easier, but the relationship amongst the actors within the subgroup and the relationship between the subgroups can be identified more clearly and precisely.
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