Carbon Deoxidation Research Articles

X-ray observation of phosphorus vaporization from steelmaking slag and suppression method of phosphorus reversion in liquid iron

The behavior of phosphorus in CaO-SiO2-Al2O3-MgO-P2O5-Fe t O slag systems during solid Al and carbon deoxidation was investigated at 1873 K. Furthermore, an X-ray apparatus (vertical resistancetube furnace equipped with an X-ray inspector system, which enhances the real-time observation of the generated gas in slag) was introduced to confirm the possibility of the vaporizing phenomena of phosphorus from slag. The X-ray-assisted observations proved that phosphorus gas is produced from P2O5-containing slag during the deoxidation process and can be applied to suppress the reversion of phosphorus into the liquid iron by removing it into the air. The results of experiments between slag and metal showed that Al decreased the Fe t O and P2O5 contents in slag simultaneously because of the strong reducing power, but carbon decreased only the Fe t O content in slag to a certain extent without reducing the P2O5. For the prevention of the phosphorus-content increment in liquid iron during the deoxidation process, it was ascertained that the Fe t O content, the absorption site of phosphorus gas, should be decreased to some extent at the time of phosphorus generation. It could be proposed that it is the two-step deoxidation process that decreases the Fe t O content by carbon while maintaining the P2O5 content in the slag at a nearly constant level and then decreases the remaining P2O5 content quickly by vaporizing as a gas phase by Al, without considerable reversion of the phosphorus in hot metal.

Studies on sacrificial and carbon deoxidation of niobium

The nature and extent of oxygen removal from Nb–C–O alloys on heating to 2273 K under 2 mPa vacuum has been investigated. Correlations have been given relating the vapour pressure ratios of CO, NbO(v) and NbO 2(v) to the residual oxygen and carbon contents in niobium and the temperature of treatment. Experimental results of treating Nb pellets with initial oxygen content of 1.09 wt% and added carbon corresponding to C/O ratios of 0–1.10 in a thermogravimetry unit up to 2273 K under 2 mPa have been explained on the basis of the relevant vapour pressure ratios. The deoxidation of Nb–C–O begins at 1650 K and proceeds in three distinct steps consisting of both sacrificial deoxidation and carbon deoxidation. The first step is sacrificial deoxidation due to formation of NbO 2(v), the second step is carbon deoxidation, and the final step is sacrificial deoxidation by NbO(v) vaporization. The extent of deoxidation in each of these steps depends on C/O ratio of the charge.

Thermodynamics of Interstitial Impurities Removal from Refractory Metals

The applied thermodynamic aspects of removing hydrogen, nitrogen, oxygen, carbon, and silicon from vanadium, niobium and tantalum metals by pyrovacuum treatments are considered in this paper. Two major processes operate in refining by pyrovacuum treatment. One is distillation and the other is degassing. Distillation is mainly used to remove substitutional impurities that are either already present in the metal or have been added for removing any interstitial impurity. The success is determined by the partial pressure of the impurity element as well as by the difference in partial pressures of the impurity and the metal. The maximum rate of vaporization of impurity can then be estimated using the free evaporation equation. Interstitial impurities, particularly the gases hydrogen, nitrogen and oxygen, are removed by degassing. Thermodynamics of classical degassing, which is essentially the reverse of absorption, is described usefully by the pressure-composition isotherms. This is applicable mainly for the removal of hydrogen and nitrogen. The removal of oxygen, known as deoxidation, occurs by a more complex mechanism that involves the formation and evaporation of metal suboxides. Depending on the suboxide species responsible for deoxidation, the process is known as sacrificial deoxidation, carbon deoxidation, silicon deoxidation, or aluminium deoxidation. The applicability of these different processes to a particular metal, M is determined by the thermodynamic properties of the relevant M–O, M–C–O, M–Si–O, and M–Al–O system. It is shown in this paper that all the four processes are applicable to niobium and tantalum where as only aluminium deoxidation is useful for vanadium. For the removal of carbon and silicon also, the relevant deoxidation process can be used.

プラズマ処理によるマグクロ廃煉瓦のリサイクル

A large amount of magnesia-chromia waste bricks have been reclaimed after the use in high temperature furnace such as cement rotary kilns, steel refining furnaces and so on. For the recycle of these waste bricks, the carbon deoxidization and metal recovering was tested with high temperature plasma furnace.

Thermodynamics of Interstitial Impurities Removal from Refractory Metals

The applied thermodynamic aspects of removing hydrogen, nitrogen, oxygen, carbon, and silicon from vanadium, niobium and tantalum metals by pyrovacuum treatments are considered in this paper. Two major processes operate in refining by pyrovacuum treatment. One is distillation and the other is degassing. Distillation is mainly used to remove substitutional impurities that are either already present in the metal or have been added for removing any interstitial impurity. The success is determined by the partial pressure of the impurity element as well as by the difference in partial pressures of the impurity and the metal. The maximum rate of vaporization of impurity can then be estimated using the free evaporation equation. Interstitial impurities, particularly the gases hydrogen, nitrogen and oxygen, are removed by degassing. Thermodynamics of classical degassing, which is essentially the reverse of absorption, is described usefully by the pressure-composition isotherms. This is applicable mainly for the removal of hydrogen and nitrogen. The removal of oxygen, known as deoxidation, occurs by a more complex mechanism that involves the formation and evaporation of metal suboxides. Depending on the suboxide species responsible for deoxidation, the process is known as sacrificial deoxidation, carbon deoxidation, silicon deoxidation, or aluminium deoxidation. The applicability of these different processes to a particular metal, M is determined by the thermodynamic properties of the relevant M-Q, M-C-O, M-Si-O, and M-AI-0 system. It is shown in this paper that all the four processes are applicable to niobium and tantalum where as only aluminium deoxidation is useful for vanadium. For the removal of carbon and silicon also, the relevant deoxidation process can be used.

A Study on the Characteristics of the Boundaries in Bainitic Low Alloy Steels Using Electron Back-Scatter Diffraction (EBSD) Technique

Bainitic low alloy steel has a complex microstructure exhibiting several types of boundaries. The boundaries in bainitic steel, although certain boundaries are absent with respect to the alloy composition and the manufacturing process, could be typically divided into 4 types; dislocation cell boundary, lath boundary, packet boundary, and prior austenite grain boundary, in increasing order of size. The size and distribution of the respective boundaries are an important factor which controls the mechanical properties of the steels, including brittle fracture. In the present research, the characteristics of the boundaries in the bainitic low alloy steels were investigated in view of misorientation between grains enclosed by the respective boundaries.The alloys investigated were Mn-Mo-Ni low alloy forging steels having chemical compositions shown in TABLE 1. Steel-A was manufactured by the Vacuum Carbon Deoxidation(VCD) process. For the finer prior austenite grain size, Steel-B was produced by the aluminium addition and the silicon killing process. Before EBSD analysis, the microstructures of the alloys were observed using SEM and TEM. EBSD measurements were obtained using a Link OPAL system(Oxford) linked to a JEOL JSM 6300 SEM operating at 15KeV with the sample tilted at 70°.

Improvement of impact toughness of the SA 508 class 3 steel for nuclear pressure vessel through steel-making and heat-treatment practices

Comparative investigations of the effects of steel-making practices on impact and fracture toughness were studied. From these examinations, impact and fracture toughness of the steels by vacuum carbon deoxidation (VCD) offered the required values; however, those of the steels by modified VCD and silicon-killing practices were secure. The fracture toughness ( K IC) was significantly improved by the silicon-killing and the modified VCD. These resulted from the fineness of austenitic grain size and reduction of sulphidic inclusion. It was observed that the grain size of steels by modified VCD and silicon-killing practices was 20 μm, while that of steel by VCD was 50 μm. The sulphidic inclusion contents were reduced in the steels by modified VCD and silicon-killing practices. Furthermore, the effects of cooling rates from austenitizing temperature on the impact toughness in the steel by VCD were also investigated. The impact toughness of the steel by VCD was closely related to the cooling rate. To obtain the secure impact toughness in the steel by VCD, it seems that the recommended minimum cooling rate from the austenitizing temperature should be 15°C min −1.

低硫鋼でのMnS析出に及ぼす鋼中酸化物の影響

The behavior of MnS precipitation on oxide particles in low sulphur and low carbon steels was investigated to control the size and the distribution of MnS. The distribution of MnS became uniform by the complex deoxidation with Mn-Si-Zr, of which complex oxides dispersed finely. On the other hand, in the case of carbon deoxidation in vacuum melting, MnS precipitated less uniformly in interdendritic regions. The precipitation ratio of MnS on oxide particles was higher in the cases of Mn-Al, Mn-Si and Mn-Si-Zr deoxidations, but it depended on the oxide composition. Higher precipitation ratio was obtained in the composition range of MnO-SiO2 where liquidus temperature is low and sulphide capacity is high. The small MnS embryo formed on the surface of the liquid oxide according to its solubility limit may act as a nucleus for the further growth of MnS due to diffusion after the solidification of steels.

Optimizing deoxidation and desuIphurization during vacuum induction melting of alloy 718

AbstractWork that has helped to improve vacuum induction melting (VIM) procedures for alloy 718 is described. Three aspects of melting in a 5 t industrial VIM furnace are considered: oxygen control by carbon deoxidation; oxygen and sulphur control by alkaline earth and rare earth additions; and the effect of these additions on melt cleanness, with respect to virgin and remelt charge materials. Measurements of total oxygen content and oxygen activity have been carried out on both virgin- and remelt-charged heats. Measured and calculated activity coefficients are compared. In the absence of aluminium, good agreement is found between measured and calculated values. The fact that measured activity coefficients for a complex nickel-based superalloy agree well with predictions based on data for dilute iron alloys could indicate that such data may be useful for predicting oxygen behaviour in a wide range of iron-based and, to some extent, nickel-based alloys. A method for evaluating alkaline earth and rare earth...

Application of a new processing procedure for the further improvement of nuclear grade structural VCD steels

The enhancement of the quality of NiCrMoV-steels for turbine rotors and generator shafts by use of the vacuum carbon deoxidation (VCD) method is well known and established. So far the application of the VCD method has been limited to those steels which were not required to be made as fine grained steels and which consequently could be produced without the addition of aluminium. Klöckner Works have developed a method which allows the use of VCD — i.e. deoxidation of the steel by gaseous CO-reaction — with subsequent addition of Al for grain refinement. This new steel making process combines the advantages of a VCD steel with those of a fine grained steel. Seven production ingots of the steel 20 MnMoNi 5 5 have been produced by this process. The properties of the forgings made of these ingots are compared with forgings of Si/Al-deoxidized ingots. The VCD method has a beneficial influence of A-segregations. Sulphur prints show practically no segregation streaks. An improvement of impact properties and a greater isotropy of properties is gained by the VCD method. The excellent weldability of this steel could be demonstrated by weld simulation tests. There was be no susceptibility to cold cracking which was observed with SA 508 C1.3 forgings when the austenitic overlay cladding was welded on areas with A-segregations. In general the application of the VCD process to SA 508 C1.3 results in a remarkable improvement of material properties such as toughness and weldability and therefore renders components of higher reliability.

Refining of tantalum by sacrificial and carbon deoxidation

The removal of residual oxygen from tantalum by pyrovacuum treatment using both sacrificial deoxidation (as TaO(g)) and carbon deoxidation (as CO) was studied. The effects of various process parameters such as charge composition, temperature, pressure and time were established. The material balance of the charge indicated that the oxygen was removed primarily by carbon deoxidation until the carbon content in the charge was less than 900 ppm after which sacrificial deoxidation also occurred. Under optimum conditions a charge containing 7000 ppm oxygen with an initial carbon-to-oxygen mole ratio of 0.91 yielded tantalum metal containing less than 200 ppm of carbon and oxygen on treatment for 2 h at 2320 K and 7 × 10 −3 Pa. There was no loss of metal. The purification of the same charge by sacrificial deoxidation alone would involve a loss of 7% of the tantalum. The results are explained using available and estimated thermodynamic data for the Ta-C-O system. In view of the present observations, a modification incorporating carbon deoxidation in the refining flow sheet of tantalum is suggested.

Cr-Mo-V鋼のロータ材の品質におよぼす各種製造法の影響

Cr-Mo-V鋼のロータ材の品質におよぼす各種製造法の影響

Vacuum–Carbon Deoxidation of Iron Melts in a 70% Alumina Brick Crucible

A series of 0.20 and 1.00% C-Fe melts was processed under various reduced pressures of carbon monoxide at 1600°C in a 70% alumina crucible made from commercial quality refractory brick. The bath aluminum and oxygen contents were found to be a nonlinear function of treatment pressure, whereas the bath silicon content was found to be pressure independent. The results support a previously proposed model in which melt-refractory interactions limit oxygen removal during vacuum processing.

純鉄の溶製における炭素脱酸中のけい素の挙動

純鉄の溶製における炭素脱酸中のけい素の挙動

855. Vacuum carbon deoxidation of 265-ton openhearth heats: M H Stadler and T V Cuikaj, J Metals, 17, 1966, 533–536

855. Vacuum carbon deoxidation of 265-ton openhearth heats: M H Stadler and T V Cuikaj, J Metals, 17, 1966, 533–536

Vacuum carbon deoxidation of 265-ton open heart heats.: M H Stadler and T V Ciukej, J of Metals, 17(5), 1965, 533–536.

Vacuum carbon deoxidation of 265-ton open heart heats.: M H Stadler and T V Ciukej, J of Metals, 17(5), 1965, 533–536.

1002. Carbon deoxidation and observations on induction stirred ladle (steel) degassing: J E Fogarty,Trans Vac Metall Conference, 1964, Amer Vac Soc, Boston, Mass, (1965), pp 432–453

1002. Carbon deoxidation and observations on induction stirred ladle (steel) degassing: J E Fogarty,Trans Vac Metall Conference, 1964, Amer Vac Soc, Boston, Mass, (1965), pp 432–453

Carbon deoxidation and observations on inductions stirred ladle (steel) degassing

Carbon deoxidation and observations on inductions stirred ladle (steel) degassing

Vacuum Carbon Deoxidation of 265-Ton Open Hearth Heats

This report has described the two zone continuous stream degassing system installed at South Works’ No. 4 open hearth shop. This equipment has performed satisfactorily during its break-in period. Open hearth heats processed through this facility are upgraded by a reduction in the number and severity of the oxide type inclusions and by a lower gas content. Development work is continuing to determine the effects of vacuum carbon deoxidation on mechanical properties, and the morphology of the non-metallic inclusions remaining in the product.