Oxygen In Molten Steel Research Articles

Evaluating oxygen level of Si-deoxidized H13 die steel using ferrous oxide-containing slags at 1873 K

Laboratory-scale experiments were conducted to investigate the oxygen content of Si-deoxidized H13 die steel by ferrous oxide-containing slags at 1873 K. The calculation of thermodynamics and kinetics was performed to evaluate the oxygen level of molten steel through [Si]–[O] equilibrium and [Fe]–[O] equilibrium. The results show that as the FeO content in slag increases, the oxygen content with [Si]–[O] equilibrium (w([O])Si) has almost no change. When both the oxygen content with [Fe]–[O] equilibrium (w([O])Fe) and w([O])Si are less than the initial oxygen content in steel (w(TO)i), the oxygen content in steel (w([O])) depends on the higher value between w([O])Si and w([O])Fe. In the case of w([O])Fe > w(TO)i, the value of w([O]) is the difference between the sum of w(TO)i and w([O])Si and the value of w([O])Fe. The reaction rates of [Si]–[O] and [Fe]–[O] are equal, which are controlled by the mass transfer of oxygen in molten steel. The evaluation method is suitable to the whole smelting process of Si-deoxidized H13 die steel.

Production of Clean Steel Using the Nitrogen Elevating and Reducing Method

Nitrogen Elevating and Reducing Method (NERM) is a new technology developed to remove inclusions and oxygen in molten steel. The principle that underlies it is that nitrogenizing molten steel under low or normal pressure initially elevates the nitrogen content. Then, when the vacuum treatment is started, the nitrogen bubbles can nucleate on the surface of the inclusions and carry them to slag, reducing the number of inclusions in steel significantly. The removal effects between the new method and the conventional method were compared by industrial trials in this paper. The results show that the average oxygen content of the billet produced by the conventional method was 16 ppm, while that produced by the new method dropped to 11.5 ppm. Besides, the new method shows better removal effect of inclusions, and the number of inclusions decreased by 52.8% compared to the conventional method. The new method has obvious removal effects on inclusions in different sizes. In addition, the differences between NERM and the Pressure Elevating and Reducing Method (PERM) were compared, and the mechanism of each method was analyzed in this paper.

Source and Control of Nitrogen for X70 Pipeline Steel

The effects of some key factors on nitrogen absorption during the smelting process of X70 pipeline steel were studied, and the source of nitrogen pick-up was analyzed to find the bottleneck for nitrogen control. A series of measures were put forward to decrease the nitrogen pick-up. The results indicated that an exponential relationship existed between the nitrogen absorption index and the free oxygen in molten steel. Nitrogen absorption index could decrease below 0.3 when free oxygen in molten steel was above 100 × 10−6 after tapping. For low sulfur killed steel, the nitrogen absorption ratio and sulfur content satisfied a linear relationship with a slope of −0.007. Low free-oxygen and sulfur were beneficial to the deep desulfurization during vacuum treatment. The contradiction of high desulfurization ratio and low nitrogen pick-up during LF process could be resolved by skimming oxidizing slag after tapping and making new high basicity top slag. After optimization, the average content of nitrogen in final product decreased from 46 × 10−6 to 35 × 10−6.

Erratum to: Oxygen in Molten Iron: Deoxidation with Silicon and Aluminum

For more than 80 years, the subject of oxygen in molten steel and its removal by various agents has attracted the attention of practical and theoretical metallurgists. This review summarizes some historical data for oxygen contents of steels and some basic thermodynamics for its dissolution and elimination, primarily by the deoxidizers silicon and aluminum.

Oxygen in Molten Iron: Deoxidation with Silicon and Aluminum

For more than 80 years, the subject of oxygen in molten steel and its removal by various agents has attracted the attention of practical and theoretical metallurgists. This review summarizes some historical data for oxygen contents of steels and some basic thermodynamics for its dissolution and elimination, primarily by the deoxidizers silicon and aluminum.

Corrosion kinetics and corrosion mechanisms of BN–ZrO2–SiC composites in molten steel

Corrosion kinetics and corrosion mechanisms of BN–ZrO2–SiC composites with different ZrO2 contents of 10–40vol.% have been investigated in molten steel. The chemical reactions between dissolved oxygen in molten steel and non-oxide components of BN and SiC are key factors of corrosion process. High ZrO2 content is beneficial to the formation of a ZrO2-rich corrosion layer, which restrains molten steel from further penetrating into ceramic matrix. Corrosion kinetic obeys a nearly parabolic law, and the corrosion rate is retarded by adding ZrO2. Therefore, the addition of ZrO2 is beneficial to the enhancement of corrosion resistance against molten steel.

Deoxidation Mechanism of Al-Killed Steel during Industrial Refining Process

Deoxidation is a key step for steel refining, and it would influence the cleanliness of final product. In present study, the measured and calculated oxygen activities in Al-killed bulk steel were compared according to industrial trails, and the Fe–O equilibrium at the interface between slag and steel was also concerned by thermodynamic analysis. Finally, the deoxidation mechanism of Al-killed during industrial refining was proposed. It is found that the activity of oxygen in bulk steel is controlled by Al content, since the activity of oxygen in bulk steel is very close to the equilibrium value as the activity of Al2O3 is treated as unity. In order to keep low oxygen in molten steel, a certain Al content needs to be guaranteed. At slag-steel interface, the activity of oxygen is controlled by FeO, which is much larger than that of bulk steel, so the oxygen would transfer from slag into bulk steel. Slagging therefore presents its importance for deoxidation to reduce the oxygen transfer. Besides, the essence of SiO2 supplying oxygen is Al consumption in bulk steel, which gives rise to the increase of dissolved oxygen. So, stable refining slag is also very important to obtain low oxygen steel, and the slag basicity needs to be no smaller than 3 to reduce the Al consumption caused by SiO2 reduction. In present study, the basicity of 3–4 is recommended to refine low oxygen Al-killed steel.

Control of Aluminum Concentration on Iron Surface by Powder Eutectic Coating Using Laser-Heating

The addition of large amounts of chrome and nickel is employed to increase the oxidation and corrosion resistance of steels. Zinc or tin coating is often used for low-alloyed steels; however, the use of such elements can cause environmental problems. Some alloying elements, such as nickel and copper, are detrimental to recycling processes, due to the difficulty of removal when scrap steel is melted. Therefore, it is important to improve the corrosion and oxidation resistance of steels without the use of these elements. Aluminizing is considered to be an attractive alternative treatment in this respect. Aluminized steels are beneficial in the steel making process when they constitute part of the steel scrap, because aluminum acts as scavengers for oxygen in molten steel. A new powder liquid-coating method is proposed for the aluminization of iron.1) Phase estimation during coating process and oxidation resistance of coated layer were discussed in the previous paper.2,3) The aim of this study is control of the surface aluminum concentration in the coated layer.

Model of the relationship between properties and phase composition of zirconia solid electrolyte

The relative content of each phase at room temperature and the ratio of transformable phase at high temperature of zirconia solid electrolyte are important to its thermal shock resistance and electrical conductivity. The match of thermal shock resistance and electrical conductivity plays an important role in measuring the lower oxygen activity in molten steel. A linear model between the thermal shock resistance and the phase composition at room temperature is proposed based on this concept, another evolved relationship between the pyroconductivity and the elevated temperature transformation is also proposed. These models provide theoretical reference for the preparation of the high precision oxygen sensor for measuring the lower partial pressure of oxygen in molten steel.

Effects of BOF top blowing and bottom stirring conditions on suppressing excessive oxidation

The effects of top blowing and bottom stirring conditions during steelmaking in a 6 t basic oxygen furnace (BOF) were investigated in studies with the aim of suppressing excessive oxidation. With low oxygen feed rate and high stirring energy, the apparent partial pressure of CO P′CO was calculated from the equilibrium of carbon and oxygen in molten steel as being <1 atm. The relationship between top blowing/bottom stirring conditions and mass transfer at the slag/metal interface was analysed. It is proposed that mass transfer at the hot spot is significantly affected by the reaching rate of oxygen to the steel bath and bottom stirring. Mass transfer at the slag/metal interface, outside the hot spot, is sufficient to allow equilibrium to be attained in combined blowing BOF processes. Thus, the oxygen that is not consumed for decarburisation is distributed between steel and slag, i.e. deoxidation from steel to slag takes place, which makes it possible to obtain P′CO <1 atm under atmospheric conditions. The decarburisation model developed based on the analysis reproduces the suppression of excessive oxidation under a decreased, top blown oxygen feed rate and is in good agreement with results from both 6 t BOF experiments and 350 t commercial BOF operation.

Mathematical Model for Nitrogen Desorption and Decarburization Reaction in Vacuum Degasser.

A mathematical model for nitrogen desorption and decarburization reactions in vacuum degasser was developed. The rate controlling step is assumed to be the mass transfer of nitrogen, carbon and oxygen in molten steel and the chemical reaction of N+N=N2 and C+O=CO. The bath surface and the surface both of the injected Ar gas bubble and CO gas bubble formed inside the bath are considered as the reaction sites. This model was verified by the agreement of the calculated results with the results of small scale experiments for nitrogen desorption and absorption reaction. The following results were obtained by the analysis of a VOD process of commercial scale for degassing of stainless steel by this model. The ratio of reaction rate for nitrogen desorption and decarburization at each reaction site during operation was evaluated. The nitrogen desorption reaction occurs at the CO gas bubble formed inside steel (51%), at bath surface (36%) and injected Ar gas bubble (13%). The decarburization reaction proceeds at bath surface (90%), at CO gas bubble (8%) and at injected gas bubble in (2%).

二次精錬プロセスの開発と低酸素,低硫鋼溶製法の確立

Recently the needs of ultra low [S] and ultra low [O] steel for many kinds of products increase.Secondary refining process to achieve less than 5 ppm sulfur and less than 10 ppm oxygen in molten steel was investigated. In order to produce ultra low sulfur steel the optimum slag composition was determined as 60%CaO-32%Al2O3-8%SiO2 and the deviation of final slag composition could be decreased by the method of 2 times flux addition.In the case of producing ultra low oxygen steel, it was important for increasing deoxidation rate that the total content of FeO+MnO in slag before RH process was less than 1 wt% and then deoxidizing products were removed through RH process. On the basis of these results, the refining process, BOF-VSC-NKAP-GI-RH process, was established. By this process it became possible to achieve less than 5 ppm sulfur and less than 10 ppm oxygen in steel.

On the behaviour of oxygen and inclusions in rimming steel after refining with BOF

This study on the behaviour of inclusions in rimming steel was carried out using direct measurements of soluble oxygen in molten steel with a solid electrolyte cell. It was found that the rate of disappearance of inclusions was accelerated by the addition of Al to the steel and by gas bubbling treatment.

Control of Oxygen Content During the Reducing Period of the Electric Arc Furnace

We checked a controlling procedure of amount of oxygen in molten steel for making Cr-Mo low alloyed steels (SCM22, SCM3) by a 2 tons basic electric arc furnace with silicon semikilling during the reducing period.(1) After checking the relation between Si and O in the reducing period it was found that the correlation between Si of 0.01∼0.10% and O of 300∼100 ppm could likely be used effectively for oxygen control.(2) Furthermore, we recognized that (FeO) in slag influenced much upon the correlation between Si and O and if (FeO) was high, O raised up even under the same Si level.(3) Judging from the above mentioned results it is necessary to maintain (FeO) as the corresponding value in order to fix O.(4) In the actual trials for controlling of O by the above mentioned procedure with visual judgement of (FeO) in slag it was recognized that the probability of O expected to get itself within ±30ppm of the aimed was 80% in case of aiming at O of 100∼230ppm.

Al脱酸した18-8ステンレス鋼の酸化物系介在物

The experiments are aimed to investigate the effects of aluminum content in 18Cr-8Ni-0.9Mn-0.4/0.8Si-Fe stainless steel upon the compositions and the amount of the oxide inclusions and upon their deformation by hot-and cold-rolling. The starting material is the ingot of 10 kg which is prepared in the induction furnace under argon atmosphere. The concentration range of aluminum are from 0.007 to 0.1%. The microscopic examination is used to determine the amount and the size of the oxide inclusions in ingots and their length after rolling. The compositions of inclusions are determined by a X-ray microanalyser and the crystallographic structure is examined by the electron-diffraction method.The following results are obtained.(1) The relation between the concentrations of aluminum and oxygen in molten steel is in well agreement with that of the equilibrium experiments. It is represented by the following equation.(2) As for the ingots containing less than 0.03%Al, the oxide inclusions are Mn-silicate and their amount decreases rapidly with increasing aluminum content. On the other hand, as for the ingots containing more than 0.03%Al, the oxide phase is alumina and the amount dcreases slightly with increasing aluminum content.(3) Mn-silicate is plastically deformed by hot-rolling, but in case of cold-rolling after hot-rolling of the ingots it is crushed and arranged in a dotted line in metallic matrix. Alumina is neither deformed nor crushed by hot-and cold-rolling.

出鋼前溶鋼のガス含有量について

The molten steel in contact with air has the following chemical reaction: Steel+H2O (in air)⇔2 [H](in steel)+[O](in steel)K=[H] 2·[O]/PH2OTherefore, if the distribution of each gas in the air-slag-steel phase will be constant, the relation between PH2O in air and the gas contents in molten steel of steelmaking practice could explained only by the above equation. But the author presumed in this paper that the [H] 2·[O] value just before tap in steelmaking process with a basic electric arc furnace was not proportional to PH2O in air, because the hydrogen and the oxygen in molten steel in the steelmaking practice were controlled by each of the following phenomena:(1) As the movement of the hydrogen in the air-slag-steel phase was controlled by the velocity of diffusion in slag, which changed with CaO/SiO2 ratio of and temperature of slag, the hydrogen content ([H]) in molten steel in contact with molten slag will be effected by CaO/SiO2 ratio of and the temperature of slag.(2) As the molten steel and the molten slag were not in an ideal state, the ratio between the oxygen content ([O]) in molten steel and the Σ(FeO) content in molten slag would change with the component of steel, the CaO/SiO2 ratio of slag and the bath temperature.

眞空熔融法に依る鋼中のガス成分定量に關する研究(IV)

A rapid analytical method for hydrogen in steel was described. The method involved vacuum fusion of the steel sample and subsequent measurement of the thermoconductivity of the extracted gas. By this method, hydrogen and oxygen in molten steel could be analyzed within 17-191/2min including sampling time. Sampling method, amount of hydrogen that escaped from the sample, and comparative study to the standard 800°C vacuum extraction method are described. Applications of the apparatus in practice were also given.