Thermodynamics of the simultaneous desulfurization and dephosphorization processes of hot metal with CaO- and BaO-based slags bearing MnO

The technical feasibility of the simultaneous desulfurization and dephosphorization process of hot metal with high basicity slags of the BaO-BaF₂ system is discussed from the thermodynamic point of view. The partition ratios as well as the degrees of removal of sulphur and phosphorus from the hot metal obtained after a single refining step with BaO-saturated slags have been compared to those achieved when typical hot metal pretreatment slags of the system CaO-CaF₂-SiO₂ (double saturated with CaO and 3CaO?SiO₂) were used. The experiments were carried out in graphite crucibles at 1573 K, under CO atmosphere. Considering that both the desulfurization degree and the dephosphorization degree of hot metal achieved with BaO-based slags, around 95 %, were much higher than those obtained when CaO-based slags were used, maximum 45 %, it was concluded that the simultaneous desulfurization and dephosphorization process of hot metal with high basicity BaO-BaF₂ slags is technically feasible. It has been verified also that the high basicity BaO-based slags led to manganese recovery degrees as high as 86 % and prevented at the same time the undesirable oxidation of carbon from the metal phase.     

Dephosphorization of Mn-based alloys

The critical oxygen partial potential of dephosphorization in liquid Mn-base alloys under oxidizing or reducing conditions has been determined by thermodynamic analysis. Under oxidizing conditions, thermodynamic conditions to achieve dephosphorization and avoid manganese oxidizing were given. The results of thermodynamic analysis show that BaO-base slag can be an effective dephosphorization agent for Mn-base alloys. Under reducing conditions, the high degree of dephosphorization in Mn-base alloys can be obtained based on thermodynamic analysis. In experimental work, BaCO₃ was added to remove phosphorus from Mn–Fe–C melts. The time needed for equilibration of the dephosphorization reaction of Mn–Fe–C melts was determined at 1573, 1623 and 1673 K. The refining results were experienced as dephosphorization efficiency ≠_p = (%[P]₀ ? %[P])/%[P]₀. Moreover, the effect of the initial content of Si and C on ≠_p was investigated. ≠_p in the Mn–Fe–C melts was also given as a function of temperature. Dephosphorization reaction in Mn–Fe–C melts is of first order.     

Study on Efficient Use of High-Manganese Pig Iron

The smelting process of high-manganese pig iron is studied to determine ways to efficiently utilize the by-product of manganese-rich slag. This process consists of two stages: 1) demanganese and carbon retention and 2) decarbonization and dephosphorization. In the first stage, oxygen is supplied at 0.5–2.0 Nm³ t⁻¹ min⁻¹. The temperature is controlled between 1300 and 1400 °C by adding iron ore to the molten bath. Ultimately, high-manganese slag, which contains more than 50% manganese oxide and semisteel with 3.2% carbon, is produced. In the second stage, oxygen is supplied at 2.0−5.0 Nm³ t⁻¹ min⁻¹ and slag-forming materials are added to the molten bath for the dephosphorization and desulfurization of the hot metal. Consequently, the iron oxide, manganese oxide, and silicon oxide contents of the high-manganese slag and the carbon, manganese, phosphorus, and sulfur contents of the semisteel are 10.8–15.3%, 70–77%, and 3–7%, and 3.2–4.2%, 0.3–1.0%, 0.12–0.22%, and 0.01–0.024%, respectively. The main mineral phases of high-manganese slag, 2MnO·SiO₂ and FeO·MnO·SiO₂, are suitable for the preparation of high-carbon ferromanganese raw materials. After further smelting, clean molten steel containing 0.03−0.08%, 0.08−0.20%, 0.005−0.02%, and 0.01−0.024% carbon, manganese, phosphorus, and sulfur, respectively, is obtained.     

100t 转炉留渣双渣法冶炼高硅高磷铁水试验

针对钢厂铁水硅和磷含量较高的特点,采用转炉留渣双渣冶炼工艺以获得稳定的铁水脱磷率。吹炼3 min后加入石灰和污泥球等造渣材料,供氧强度0～3 min时为2.5m³/（t·min）,3～4.5 min时为3.2m³/（t·min）,温度控制在约1320℃。转炉一次倒渣后,继续吹炼,加入后期造渣料,待一氧化碳体积分数稳定时,适当提高氧枪枪位,促进化渣,并进行终点碳控制。试验结果表明:脱磷期铁水平均脱磷率为58.09%,脱碳期钢水平均脱磷率为85.56%;当半钢温度为1320℃炉渣碱度为2.0,炉渣TFe含量为18%时,在脱磷期能获得较好的铁水脱磷效果;当转炉钢水一倒温度为1580℃,终渣碱度为3.5,炉渣TFe含量为20%时,在脱碳期能够获得较好的脱磷效果;转炉终点[P]_e/[P]_r为0.90;试验中得到脱磷期和脱碳期炉渣的岩相组成适合铁水脱磷。     

Studies on the removal of phosphorus and sulfur from Fe-C and Fe-C-Mn melts at 1350°C

Laboratory studies have been performed on simultaneous dephosphorization and desulfurization of Si-free Fe-4.5 % C melts with [P]_o = 0.11 wt.% and [S]_o = 0.04 wt.% in MF induction furnaces at 1 350°C. In these investigations, CaO- or Na₂CO₃-based fluxes were used and the techniques of powder injection or single top slag addition were applied. The following results have been obtained:

• – The effectiveness of lime and soda-based fluxes with regard to dephosphorization is practically the same. But a lower sulfur level is attained when Na₂CO₃-based fluxes are used.
• – In the injection experiments, efficiencies of η_P = 80% for dephosphorization and η_s = 90% for desulfurization are easily reached at a powder consumption of 50 to 60 g/kg. But a further increase of the η values requires a remarkable increase in the amount of injected powder. Top slag addition instead of powder injection is less effective, in general.
• – Apparent rate constants k_[P] and k_[S] from 0.05 to 0.3 min^?1 have been determined in the initial stage of injection depending on the relative amount of injected flux. In the top slag experiments, the k_[P] and k_[S] values were practically constant at a level of 0.1 min^?1.

Furthermore, dephosphorization of molten Fe-C-Mn alloys at 1 350°C has been studied at variable Mn content. It is predicted from thermodynamic data and confirmed by experiments that dephosphorization lessens with increasing Mn content in the range from 0 to 15 wt.%.     

液渣成分和硅酸二钙颗粒含量对铁水预处理非均相脱磷剂脱磷能力的影响简

 高磷铁水预处理脱磷的难题是脱磷剂用量太大、温降太多，急需研究脱磷能力强的脱磷剂。含有固体颗粒和液渣的非均相脱磷剂比仅含液渣的均相脱磷剂的脱磷能力强很多。为此，针对磷的质量分数为0. 5%的高磷铁水，应用FactSageTM热力学软件优选出脱磷能力强的3种液渣，添加不同数量的硅酸二钙颗粒配制非均相脱磷剂试样，脱磷剂和熔铁在1560℃下反应6h，测定熔铁中的平衡磷含量，用以评价其脱磷能力，然后在1400℃下进行了铁水脱磷预处理试验。研究结果表明，随着硅酸二钙颗粒含量的增加，非均相脱磷剂的脱磷能力明显改善；采用非均相脱磷剂有助于减少渣量和控制反应器内衬的侵蚀；采用非均相脱磷剂对铁水脱磷，仍然需要控制较高的渣铁界面FetO浓度。     

含铌铁水直接冶炼含铌微合金钢的试验

 含铌铁水通过脱碳保铌探索作为合金化元素回收铁水中铌并直接冶炼为含铌微合金钢的方法。试验在真空碳管炉内进行,铁水温度为1 500 ℃,氧化剂为Fe2O3,真空度为10 Pa,分别进行有SiO2-CaO-Al2O3系造渣剂、无渣真空氧化冶炼研究。结果表明：在无渣条件下,加入Fe2O3铁水中硅、铌和碳同时氧化,不能脱碳保铌;加入造渣剂时,造渣剂的碱度越低,铁水中的硅氧化量越低,碳氧化量越高,碳质量分数最低下降到0.032%,铌质量分数最低值从0.09%下降到0.082%;碱度越高,铁水中硅氧化量越高,铌的氧化量也越高;真空氧化冶炼能够促进碳氧化,减少硅的氧化,抑止铌氧化。在50 kg级真空感应电炉内成功进行了回收铁水中铌直接冶炼为含铌钢试验,为回收含铌铁水中的铌提供新方法,也为工业化直接冶炼含铌钢提供试验依据。     

铁水预处理时氧化脱磷和预脱硅间的热力学分析

从热力学角度分析了铁水预处理时预脱硅和脱磷之间的关系,经理论推导后得到了终点[P]含量和[Si]含量之间关系计算公式。计算发现,一定温度下氧化法脱磷时,终点硅含量越低,其终点磷含量也越低,并提出了铁水预处理脱磷的措施：首先脱硅要脱到较低含量;渣要有较高CaO含量来固定脱磷产物P2O5;脱磷结束后,要尽量扒除冶炼渣,防止温度升高时回磷。     

Role of Ti on the Growth of Coarse Columnar Austenite Grain During Nb-Bearing Peritectic Steel Solidification

The role of Ti on the growth behavior of the as-cast austenite grains of the Nb-bearing peritectic steel with different Nb contents during solidification was investigated by fast-directional solidification experiments. The results show that the austenite grains of the Nb-bearing peritectic steel were almost of coarse columnar austenite grains (CCGs) with different Nb contents. As the content of Nb increased from 0.02 to 0.08 wt pct, the number of Nb(C, N) particles increased from 876 to 3140/mm² at a distance of 10 mm from the surface. Accordingly, the short-axis diameters of the CCGs decreased from 1.71 to 1.14 mm as the pinning pressure provided by carbonitride increased from 0.36 to 0.62 kJ·m⁻³. The addition of Ti to the Nb-bearing peritectic steel greatly promoted the precipitation of carbonitride in the form of (Nb, Ti)(C, N) composite particles during solidification. As a result, the number of (Ti, Nb)(C, N) particles at a 10 mm distance from the surface increased significantly from 12,210 to 14,324/mm² as the content of Nb increased from 0.02 to 0.08 wt pct with 0.02 wt pct Ti addition compared to that without Ti addition. The substantial increase in the pinning pressure provided by the (Nb, Ti)(C, N) composite particles from 5.1 to 8.4 kJ·m⁻³ reduced the short-axis diameters of the γ grains from 1.32 mm to less than 0.2 mm. Meanwhile, the growth of CCGs was gradually inhibited. When the Nb content reached 0.08 with 0.02 wt pct Ti addition, the growth of CCGs was completely inhibited.

     

Practice of Hot Metal Full Pretreatment and Less-slag Steelmaking in ShouGangJingTang

The hot metal full pretreatment and less-slag steelmaking process constituted a platform to produce clean steel with low cost and rapid pace and also realized a professional production line. The w_[P] can be less than 0.030% at the end of De-P converter and 0.006% at the end of De-C converter. The w_[N] in steel can be less than 15×10⁻⁶ at the stirring station. This production line can make clean steel steadily used for auto sheet or pipeline, for example X65MS. The De-C slag was left in the converter for the next heat and recycled to De-P converter to reduce lime consumption, which has a great benefit for the cost saving.     

含铌铁水中碳和硅的氧化规律

 为了研究铌在铁水吹氧冶炼过程中的氧化规律，在中频炉内进行了加入碱度分别为0.538和1.5的CaO-SiO2-Al2O3系造渣剂和不加渣的含铌铁水底吹氧气的冶炼试验。铁水温度为1 550 ℃时，研究了含铌铁水中硅、碳和铌的氧化规律，并利用FactSage软件进行了不同温度与不同碱度的造渣剂和无渣氧化铁水中各元素的热力学平衡计算。结果表明，高温吹炼使铁水中的碳优先于铁水中的硅氧化，而低温吹炼则促进铁水中硅优先于碳氧化；降低造渣剂碱度促进铁水中碳氧化、抑制硅氧化，碳和硅的氧化转化温度为1 490 ℃；在吹氧冶炼终点，加入碱度为1.5的造渣剂，铁水中硅质量分数下降到0.138%时，铌开始氧化减少，而加入碱度为0.538的造渣剂，铁水中碳质量分数下降到0.61%，硅质量分数升高到0.56%，铌质量分数不变，因此含铌铁水可通过加入低碱度造渣剂高温吹氧冶炼为含铌钢水。     

Dynamics of the hot metal dephosphorization with Na2O slags

Dephosphorization reaction of hot metal by Na₂CO₃ has been studied experimentally to determine the reaction mechanism and thermodynamics. Most of the experiments were carried out at 1300 °C using Fe-C_sat.-Si-P-S alloys. The results indicate that the CO₂ gas released from Na₂CO₃ is important in the dephosphorization reaction as an oxidizer and increasing mass transfer by stirring the slag and metal. As the initial Si content in hot metal is increased, the degree of dephosphorization decreases significantly and the rephosphorization takes place earlier. The primary reason for the rephosphorization is that the activity of PO_2.5 increases in the slag because of the evaporation of Na₂O from the slag. The loss of Na₂O increases the activity coefficient of PO_2.5 and decreases the slag volume. At the later stage of Na₂CO₃ treatment, the reactions reach equilibrium with respect to phosphorus and sulfur, and the oxygen potential,P _o2, at the slag-metal interface is determined by the C-CO equilibrium (a _c=1 and 1 atm CO). The presence of sulfur in the metal increases the rate of the dephosphorization because of the electrochemical nature of the reaction; sulfur transfer to the slag accepts the electrons from phosphorus transfer.     

转炉大补炉后第一炉钢的脱磷探讨

转炉大补炉后冶炼第一炉钢时钢中磷含量容易偏高,有时甚至超出钢种要求的磷含量上限.结合某厂90t转炉大补炉后冶炼第一炉钢时的生产情况,分析了入炉铁水硅含量、脱磷剂加入量、碱度、渣中FetO、MgO和Al2O3含量对转炉大补炉前后钢水脱磷的影响,对改进脱磷效果提出了建议.     

Effect of ferrosilicon addition on the composition of inclusions in 16Cr-14Ni-Si stainless steel melts

The silicon deoxidation equilibrium between the 16Cr-14Ni-1.5Mn-Si melts and the CaO-SiO₂-8MgO-5CaF₂ (basicity=1.8) slag at 1743 K was investigated to understand the effect of aluminum and silicon contents on the composition of inclusions. Therefore, the ferrosilicon alloys with different aluminum content were chosen based on the preceding objective. In addition, the phase stability diagram of the inclusions was computed using commercial thermodynamic software based on the Gibbs energy minimization principles. The content of MnO in the inclusions sharply decreases with increasing silicon content when the steel melts were deoxidized by the ferrosilicon alloys containing high aluminum (FeSi-H). The content of SiO₂ in the inclusions slightly increases with increasing silicon content when the FeSi-L is used, while a maximum value is shown at [Si]=1.5 pct when the FeSi-H is used. The content of MgO in the inclusions increases by increasing the content of silicon, regardless of the kinds of ferrosilicon alloys. The use of the FeSi-L as a deoxidizer could suppress the formation of Al₂O₃ in the inclusions, while the content of Al₂O₃ increases with increasing silicon content when the FeSi-H is used. When the FeSi-H is used as a deoxidizer, the inclusions are the glassy type with the composition of Mn-silicates at [Si]≤1.3 pct, while the Mg(Ca)-silicates with the composition of the forsterite phase are observed in the steel composition of [Si]=3.3 pct. When the steel melts were deoxidized by the FeSi-L alloys, the inclusions are the glassy-type Mn-silicates at [Si]=0.8 pct, while the Mn-silicates containing the cristobalite phase are observed at [Si]=1.5 to 2.4 pct. In the composition of [Si]=3.3 pct, the Mg-silicates with the composition of the rhodonite phase are observed. The log(X _SiO2/X _MnO) of the inclusions linearly increases by increasing the log [a _Si · a _O / a _Mn] with the slope close to unity when the FeSi-L is used as a deoxidizer, while the slope of the line is about 2 times greater than that of the expected value when FeSi-H is used. The log (X _MgO/X _MnO) of the inclusions linearly increases by increasing the log [a _Mg/a _Mn] with slopes greater than the expected value of unity.     

高级别管线钢中碳磷硫控制工艺研究与应用

分析了高级别管线钢中碳磷硫对钢材质量的影响,通过对钢液中[C]、[P]和[Fe]选择性氧化的热力学理论分析,计算出转炉终点温度在1 640℃时,当碳低于0.06%时,继续供氧,氧气将优先与[P]反应生成(P2O5),能够实现熔池的深脱磷;但当碳低于0.04%时,继续供氧,氧气将直接与[Fe]反应为主,造成钢水过氧化,甚至发生回磷现象。通过优化拉碳工艺、优化铁水预处理脱硫工艺、控制转炉回硫、LF渣系等,实现了高级别管线钢成品w[C]≤0.05%,w[P]≤0.012%,w[S]≤0.001 5%的稳定生产工艺。     

转炉预直炼法最佳分界点的理论研究

通过对预直炼法前后期总物料平衡计算,得出总石灰耗量、总渣量、总氧气消耗量和渣中铁吹损量。计算结果发现,总石灰消耗、总渣量、铁吹损量随半钢中磷的增加存在最小值,且随中间倒渣量的增加而减小。总耗氧量则随半钢磷的增大有减小趋势。中磷铁水最佳倒渣点应控制前期脱磷率为87％～91％。     

转炉预直炼法最佳分界点的理论研究

通过对预直炼法前后期总物料平衡计算,得出总石灰耗量、总渣量、总氧气消耗量和渣中铁吹损量。计算结果发现,总石灰消耗、总渣量、铁吹损量随半钢中磷的增加存在最小值,且随中间倒渣量的增加而减小。总耗氧量则随半钢磷的增大有减小趋势。中磷铁水最佳倒渣点应控制前期脱磷率为87％～91％。     

120 t顶底复吹转炉双渣脱磷一次倒渣的工艺实践

通过对转炉脱磷和碳-磷选择性氧化转变温度的理论分析和计算,在铁水未经脱磷预处理的条件下,进行120 t顶底复吹转炉双渣脱磷生产实践。当铁水平均成分为(/%):4.81C、0.49Si、0.32Mn、0.127P、0.019S的情况下,在转炉冶炼前期(0~360 s),采用低温(1 330~1 350℃),较强底吹搅拌[0.030~0.040 m~3/(t·min)],中等炉渣碱度(2.0~3.0)和高氧化铁(20%~25%)工艺措施,实现一次倒渣的半钢(3.8%C)平均磷含量0.048%和平均脱磷率62.2%的脱磷效果。     

100t转炉用含钛铁水冶炼高碳钢的留渣+单渣操作实践

针对100t转炉用含钛铁水冶炼高碳钢的前期成渣难于熔化、脱磷率低的问题,分析了含钛铁水转炉炼钢的成渣过程和炉渣的物理特性,开发了留渣+单渣工艺技术。循环利用终点炉渣,充分发挥渣中10%～13%FeO高（FeO）含量的特点,快速把含钛铁水冶炼前期的CaO-TiO₂-SiO₂三元渣系转变为CaO-TiO₂-SiO₂-FeO四元渣系,脱除钢中大部分磷。控制终渣碱度大于3.2、（TiO₂）含量小于5%,使转炉出钢[C]≥0.20%、[P]≤0.014%,转炉炼钢脱磷率达到88%～92%,石灰消耗下降到28 kg/t钢。     

Fast diffusion of cobalt along stationary and moving grain boundaries in niobium

⁵⁷Co diffusion along grain boundaries (GBs) in high-purity Nb has been studied in the temperature range 823–1471 K by the serial sectioning technique. As it was not possible to fully stabilize the grain size by any pre-diffusion annealing, part of the GBs could migrate during the diffusion anneals. Using the earlier proposed method [Z. Metallk. 84, 584 (1993)], the product P = sD_GBδ [s being the 7GB-segregation factor, D_GB the GB-diffusion (GBD) coefficient, δ the GB width] for stationary GBs and the velocity V of moving GBs were deduced from the diffusion profiles. The P-values follow an Arrhenius dependence P = (4.84_−2.68^5.99) × 10⁻¹³ exp[-(14.5 +- 7.2) kJ mol⁻¹/RT] m³ s⁻¹ and are 4–2 orders of magnitude higher in the measured temperature range than the expected P-values for GB self-diffusion in Nb. This observation is well consistent with the known fact of fast lattice diffusion of Co in Nb and provides evidence for a combined vacancy-interstitial GBD mechanism. From the temperature dependence of V an activation enthalpy of GB motion in Nb H_m ≅ 182 kJ mol⁻¹ is estimated.