Thermodynamic discussion on stripping sulfur from gear metal
How to deal with the dry air in winter?
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At present, there are many researches on the refining process of high-sulfur (w[S]=0.02-0.03) gear steel and the control of sulfur in steel, and there are few studies on desulfurization of low-oxygen and low-sulfur steel. A domestic factory has carried out experimental production on ultra-low-oxygen gear steel, using Al, Si, Mn composite deoxidation, and using high alkalinity and low oxidizing slag for slag steel refining. In this paper, the KTH model and the derivation of the sulfur distribution ratio formula are used to calculate the sulfur capacity and sulfur distribution ratio in the production process. The prediction and the measured sulfur distribution ratio are compared. The desulfurization effect of the whole refining process is studied.
1 Factory test and research method test A total of 4 furnaces, the process route is LD2LF2RH2CC.
The double slag operation of the converter, the steel is strictly slag blocking and the steel is kept; the steel is strongly deoxidized by Al, and the SiMn is deoxidized; the appropriate amount of active lime is added at the same time as the deoxidation of the tapping, so as to quickly make the alkalinity and low oxidizing slag for slag. Steel refining; LF requires 10 minutes to supply white slag, refining process to slag to spray Al particles and calcium carbide for diffusion deoxidation, requiring slag basicity control in the refining process is above 5; RH vacuum treatment requires more than 20min at 200Pa, further take off The gas and the inclusions in the steel are removed, the CaSi wire is fed after vacuum treatment, and the casting is performed after soft blowing.
A special sampler is used to extract steel water samples and slag samples for each production process of a cast steel. Chemical analysis of each steel sample and slag sample. The composition analysis results were used for calculation and comparative analysis.
2 Theoretical background 2.1 Calculation of sulfur capacity Sulfur capacity is defined by the slag gas capacity CS and the slag iron sulfur capacity CS', which can be converted by the formula (1). The definitions of the two sulfur capacities are only related to the composition and temperature of the slag, and characterize the ability of the slag to contain or absorb sulfur. In contrast, the sulfur content of the slag gas is easily measured in the laboratory, and the capacity of the slag iron and sulfur is more convenient to apply. Evaluation of slag desulfurization capacity in actual production. The calculation model for the comparison of classical sulfur capacity is RWYoung optical alkalinity model 2.2 Calculation of sulfur distribution ratio The desulfurization effect in actual production is measured by the distribution ratio of sulfur to slag steel (LS): LS=w(S)w[S] (2) From the slag iron reaction sulfur capacity definition formula: CS' = w (S) a [O] a [S] = w (S) w [S] a [O] f [S] = LSa [O] f[S](3) is obtained from equation (1)(2)(3)[6]:lgLS=-935T 1.375 lgCS lgf[S]-lga[O](4) KTH sulfur capacity calculation model introduces new The function ξ, the calculation of ξ considers the influence of the multi-component slag composition on a certain component, and uses a large number of data analysis to obtain the corresponding calculation parameters (for the specific calculation method, see [5]). In this paper, the model will be used to calculate the sulfur capacity of ultra-low-oxygen gear steel, and the distribution ratio of sulfur in the formula (4) will be predicted.
2.3 Calculation of oxygen activity in steel For Al deoxidized steel, a[O] in steel is mainly controlled by w[Al]: 2[Al] 3[O]=(Al2O3)ΔGθ5=-1202000 386.
3T=-RTlnaAl2O3a2[Al]a3[O](5) At 1873K, when the above reaction reaches equilibrium, it is deduced and formulated by formula (5): lga[O]=13lga(Al2O3)-23lgf[Al]-23lgw[ Al] ΔGθ56.909RT(6) In formula (6), a(Al2O3) is calculated by the formula: lga(Al2O3)={-0.275w(CaO) 0.167w(MgO)}w(SiO2) 0.033w(Al2O3)-1.560 (7) Calculation of 2.4f[S] and f[Al] The calculation of lgf[S] and lgf[Al] is calculated by Wagner's equation: lgf[i]=∑(ejiw[j])(8), f[i] is the activity coefficient of dissolved element i in molten steel; j represents the dissolved element in molten steel; eji represents the coefficient of action of element j in i in molten steel; and the element in sulfur liquid and aluminum in 1873K The interaction coefficient is shown in [8], and the interaction coefficient between elements at other temperatures is approximately the data at 1873K.
3 Results and discussion From the perspective of desulfurization, in the middle and late stages of LF, the desulfurization of the molten pool is reached or close to equilibrium, the sulfur content in the steel is basically unchanged, and the small fluctuation of the sulfur content of the slag is mainly due to the amount of slag. The change caused.
3.2 Theoretical calculation results Regardless of the sulfur capacity of the slag, only the ability of the slag to absorb sulfur is characterized. Iron and steel enterprises are more concerned with the removal effect of sulfur, that is, the distribution ratio of sulfur between the slag steel. The sulfur capacity and sulfur distribution of this test were theoretically calculated using the above calculation method and factory production data, and compared with the actual measured sulfur distribution ratio. It is a comparison chart between the theoretical calculation result and the measured value, and the closer to the square diagonal value, the closer to the measured value. It can be seen that the predicted value is larger than the measured value when the actual LS is small. The actual LS value in the early stage of the refining process is small. Because the desulfurization time is short, the reaction is not sufficient, and the equilibrium value is far from being reached. The theoretical calculation is the LS under equilibrium conditions, so the predicted value is greater than the measured value. When the LS value is large in the middle and the middle of refining, the predicted value is in good agreement with the measured value. This shows that it is more reliable to predict or guide the desulfurization effect of the high alkalinity low oxidizing refining slag by calculating the sulfur capacity using the KTH model and calculating the sulfur distribution ratio of the formula (4).
3.3 Analysis and discussion Both the measured value and the theoretical calculated value do not show obvious rules with the two slag characteristic indexes. This shows that after the alkalinity reaches a certain level, the increase of alkalinity has little effect on desulfurization. At this time, the thermodynamic conditions of the slag are no longer the limiting part of desulfurization. From the slag data, it can be seen that the alkalinity and MI index of the slag in the whole refining process fluctuate little, but the desulfurization effect is best in tapping and refining, and the desulfurization efficiency is the highest. This is because the tapping of the molten steel to the molten pool and LF In the early stage of refining, the relatively strong blowing of Ar for the homogenization of molten steel gives very good kinetic conditions for desulfurization.
(a) slag basicity and lgLS; (b) slag index MI and lgLS4 conclusions (1) For the refining desulfurization under the test conditions, most of the sulfur in the molten steel is removed in the early stage of LF refining, in refining Late desulfurization is basically at or near equilibrium.
(2) Calculate the sulfur capacity using the KTH model, the formula lgLS=-935T 1.
375 lgCS lgf[S]-lga[O] calculates the sulfur distribution ratio and is a reliable predictor for the desulfurization of high alkalinity and low oxidizing slag.
(3) It is very important to make good use of good kinetic conditions during tapping, and at the same time create good thermodynamic conditions, such as rapidly reducing the oxygen activity of molten steel, and making high alkalinity and low oxidizing refining slag, which can achieve good desulfurization effect.
The dryness evil in winter is so serious, what should we do?
In the north of China, the air is very dry in winter, especially indoors with heating. Xiaobian thinks that a humidifier should be prepared at home. In the past, we didn't have a humidifier. We would put a basin of water on the ground. The function of putting a basin of water was not so great, but it would feel more comfortable. At present, many humidifiers have intelligent functions. They can adjust to the humidity you set. When it reaches that range, it will automatically stop humidifying. If you live in a dry place, especially in a dry room, I suggest you prepare a humidifier.
What if there is no humidifier? If you don't have a humidifier at home, I suggest you can pour a little water on the ground before going to bed, which also has the effect of humidification. However, this method is not as effective as the humidifier. The humidifier can turn water into water vapor and beat it into the air, which can effectively change the degree of air dryness. In addition to putting a basin of water, you can also wet the towel and put it on the heating to let the water in the towel evaporate. These are the local methods of our people, and I think they are also feasible.
What should I pay attention to when I go out in a dry climate? In the face of a particularly dry external environment, you can wear a mask. The advantage of wearing a mask is to prevent the polluted air or cold air from driving directly into your nose, and it is easier to keep a wet state as the nose remains warm. Therefore, if you feel your nose is very dry, you can put on the mask quickly.
The doctor suggested that an Aroma Diffuser should be placed indoors, which can effectively and immediately solve the problem of indoor air drying, humidify the air and solve the problem of air drying. For the ultrasonic aroma diffuser, the fog is sprayed out through vibration. You can contact us to learn more about aroma diffuser