Inclusion variations and calcium treatment optimization in pipeline steel production

SiCa line and SiCaBaFe alloy were injected into liquid pipeline steel at the end of LF refining as calcium treatment,and samples were taken from the ladles,mould,and slabs.Analysis of Ca content and inclusions shows that Ca content in steel decreases obviously in the following process after calcium treatment;the compositions,morphology,and sizes of inclusions also vary much in the production;primary inclusions in the ladles prior to calcium treatment are mainly Al2O3 inclusions,but they turn to fine irregular CaS-CaO-Al2O3 compound inclusions after the treatment,then become fine globular CaO-Al2O3 inclusions in the mould,and finally change to a few larger irregular CaS-CaO-Al2O3 complex inclusions in the slabs.Thermodynamic study reveals that inclusion variations are related with the preferential reactions among Ca,Al2O3,and S and the precipitation of S in CaO-Al2O3 inclusions with high sulfur capacity.New evaluation standards for calcium treatment in high-grade pipeline steel were put forward according to the inclusion variations and requirements of pipeline steel on inclusion controlling,and the calcium process was studied and optimized.

Novel mechanism for the modification of Al_2O_3-based inclusions in ultra-low carbon Al-killed steel considering the effects of magnesium and calcium

Many researchers have explored the inclusion modification mechanism to improve non-metallic inclusion modifications in steelmaking. In this study, two types of industrial trials on inclusion modifications in liquid steel were conducted using ultra-low-carbon Al-killed steel with different Mg and Ca contents to verify the effects of Ca and Mg contents on the modification mechanism of Al_2O_3-based inclusions during secondary refining. The results showed that Al_2O_3-based inclusions can be modified into liquid calcium aluminate or a multi-component inclusion with the addition of a suitable amount of Ca. In addition, [Mg] in liquid steel can further reduce CaO in liquid calcium aluminate to drive its evolution into CaO–MgO–Al_2O_3 multi-component inclusions. Thermodynamic analysis confirmed that the reaction between [Mg] and CaO in liquid calcium aluminate occurs when the MgO content of liquid calcium aluminate is less than 3 wt% and the temperature is higher than 1843 K.

Influence of calcium content on solid ratio of inclusions in Ca-treated liquid steel

It has been found that Ca-treated liquid steel can be cast at a lower superheat. To ascertain the reason for the improved castability of Ca-treated liquid steel and to find the optimal range of calcium content, the behavior of calcium in liquid steel was studied in terms of the relationship between the calcium content and solid ratio of inclusions. The relationship between the calcium content and solid ratio of inclusions was obtained by means of the classification of nonmetallic inclusions in solid and liquid steels at casting temperature according to the Al2O3-CaO-SiO2 phase diagram. The optimum calcium content should be 17-23 ppm.

Effects of calcium treatment on non-metallic inclusions and magnetic properties of non-oriented silicon steel sheets

Based on the industrial production of non-oriented silicon steel,calcium treatment by CaSi wire feeding during the RH refining process was studied. The thermodynamics of CaS inclusion formation was analyzed, and the morphology and the size distribution were observed. Furthermore, the change in inclusion characteristics after calcium treatment and the effect of calcium treatment on magnetic properties were discussed. The results show that the formation of MnS and A1N inclusions were restrained, and the aggregating, floating and removing of microinclusions after calcium treatment were effectively promoted. The cleanliness of liquid steel was obviously increased. The main type of inclusions was single phase of CaO, with some complex inclusions composed of CaO, SiO2 and MgO. No CaS inclusion was observed after an appropriate calcium treatment. The size of all inclusions was distributed in the range of 2 - 20 μm, and the number was about 1.8 × 10^5/mm3. In addition, as an increasing amount of calcium was added,the core loss gradually decreased to a stable level, and the magnetic induction decreased quickly after a slow increase. The optimal calcium treatment mode depends on the chemical composition of steel.

Effect of calcium content on inclusions during the ladle furnace refining process of AISI 321 stainless steel

The effect of three heat processes with different calcium contents on the evolution of inclusions during the ladle furnace refining process of AISI 321 stainless steel was investigated.The size,morphology,and composition of the inclusions were analyzed by scanning electron microscopy and energy-dispersive X-ray spectroscopy.After the addition of aluminum and titanium,the primary oxide in the AISI 321 stainless steel was an AbOs—MgO—TiOx complex oxide,in which the mass ratio of AbOs/MgO was highly consistent with spinel(MgO・AbO3).After calcium treatment,the calcium content in the oxide increased significantly.Thermodynamic calculations show that when the Ti content was 0.2wt%,the Al and Ca contents were less than 0.10wt%and 0.0005wt%,respectively,which was beneficial for the formation of liquid inclusions in molten steel.Moreover,the modification mechanism of calcium on TiN-wrapped oxides in combination with temperature changes was discussed.

Synthesis of Calcium Silicate Hydrate based on Steel Slag with Various Alkalinities

This study aimed to improve the hydraulic potential properties of the slag. Therefore, a method of dynamic hydrothermal synthesis was applied to synthesize calcium silicate hydrate. The phases and nanostructures were characterized by XRD, FTIR, TEM, and BET nitrogen adsorption. The infl uence of alkalinity of steel slag on its structures and properties was discussed. The experimental results show that, the main product is amorphous calcium silicate hydrate gel with fl occulent or fi brous pattern with a BET specifi c surface area up to 77 m2/g and pore volume of 0.34 mL/g. Compared with low alkalinity steel slag, calcium silicate hydrate synthesized from higher alkalinity steel slag is prone to transform to tobermorite structure.

Functional Acrylic Polymer as Corrosion Inhibitor of Carbon Steel in Autoclaved Air-Foamed Sodium Silicate-Activated Calcium Aluminate/Class F Fly Ash Cement

The study focused on investigating the effectiveness of functional acrylic polymer (AP) in improving the ability of airfoamed sodium silicate-activated calcium aluminate/Class F fly ash cement (slurry density of ￡1.3 g/cm3) to mitigate the corrosion of carbon steel (CS) after exposure to hydrothermal environment at 200?C or 300?C. Hydrothermally-initiated interactions between the AP and cement generated the formation of Ca-, Al-, or Na-complexed carboxylate derivatives that improved the AP’s hydrothermal stability. A porous microstructure comprising numerous defect-free, evenly distributed, discrete voids formed in the presence of this hydrothermally stable AP, resulting in the increase in compresive strength of cement. The foamed cement with advanced properties conferred by AP greatly protected the CS against brine-caused corrosion. Four major factors governed this protection by AP-incorporated foamed cements: 1) Reducing the extents of infiltration and transportation of corrosive electrolytes through the cement layer deposited on the underlying CS surface;2) Inhibiting the cathodic reactions at the corrosion site of CS;3) Extending the coverage of CS by the cement;and 4) Improving the adherence of the cement to CS surface.

Effect of Ca2+ and Mg2+ on CO2 Corrosion Behavior of Tube Steel

Effects of Ca2+ and Mg2+ on the CO2 corrosion behaviors of tube steel were studied in simulated oil-field environment.The influence of Ca2+and Mg2+ on the corrosion rate and morphologies of corrosion product layer was determined by scanning electron microscope and measuring mass loss.Potentiodynamic polarization and impedance spectroscopy were used to investigate the change of electrochemical characteristic parameters of corrosion product layer and corrosion dynamic process.The results show that with Ca2+ and Mg2+ in electrolyte,the morphologies and microstructures of corrosion product layer changed obviously,thus affecting the corrosion process.

Evaluation and modification of inclusion characteristics in HK40 heatresistant cast steel

Specifications of inclusions such as the type, morphology, number, composition, size, and place of inclusions in HK40 heat-resistant casting steel were studied by optical microscopy and scanning electron microscopy equipped with an energy-dispersive spectroscopy system. The effects of calcium silicide （CaSi） addition on these characteristics were evaluated at two pouring temperatures of 1420℃ and 1470℃. It was found that most of the appeared inclusions were in the type of chromium oxide. CaSi addition had a significant effect on the morphological modification, size and distribution of inclusions as well as changing the composition to oxide-sulfide compounds.

Control of Al_2O_3 inclusions in austenite stainless steel

In the present study, samples were extensively collected throughout the stainless steel manufacturing process. The three-dimensional morphology of inclusions was revealed by non-aqueous solution electrolysis. The high concentration of aluminum in ferrosilicon caused the increment of [Al]s in steel and Al2 O3 in inclusions, which led to the higher melting temperature of inclusions. It was concluded that the application of low Al ferrosilicon and calcium treatment could prevent the formation of Al2 O3-rich inclusions.

Evolution of Nonmetallic Inclusion during Steelmaking Process of Cold Heading Steel SWRCH35K

In order to analyze the evolution of the inclusions in the cold heading steel SWRCH35K during the steelmaking process, a systematic sampling of the steelmaking processes in a steel plant was carried out. Both SEM-EDS and the image processing software Image-Pro-Plus6.0 were employed to analyze the chemical composition, morphology, quantity and size of non-metal inclusions in the steel samples. The results show that from BOF tapping to continuous casting tundish, the composition of inclusions in SWRCH35K steel changes from Al2O3 →MgO·Al2O3 →CaO-MgO-Al2O3-CaS, and the typical morphology of the inclusions in the steel gradually changes from irregular blocks and clusters to spherical. The number of inclusions in the BOF argon blowing station is the largest, 213#/mm2, while the number of inclusions at the end of LF refining is the least, about 12#/mm2, and there are basically no inclusions above 5 μm. In addition, LF calcium treatment will adversely affect the size and quantity control of inclusions in steel. In order to effectively reduce the large-size calcium-containing spherical oxide inclusions in cold heading steel, it is necessary to find a technical method that can replace LF calcium treatment to solve the problem of molten steel continuous casting.

Carbon monoxide production using a steel mill gas in a combined chemical looping process

Up to 9% of the global CO_(2) emissions come from the iron and steel industry. Here, a combined chemical looping process to produce CO, a building block for the chemical industry, from the CO_(2) -rich blast furnace gas of a steel mill is proposed. This cyclic process can make use of abundant Fe_(3)O_(4) and CaO as solid oxygen and CO_(2) carriers at atmospheric pressure. A proof of concept was obtained in a laboratory-scale fixed bed reactor with synthetic blast furnace gas and Fe_(3)O_(4) /CaO = 0.6 kg/kg. CO production from the proposed process was investigated at both isothermal conditions(1023 K) and upon imposing a temperature program from 1023 to 1148 K. The experimental results were compared using performance indicators such as CO yield, CO space time yield, carbon recovery of the process, fuel utilisation, and solids’ utilisation.The temperature-programmed CO production resulted in a CO yield of 0.056 ± 0.002 mol per mol of synthetic blast furnace gas at an average CO space time yield of 7.6 mmol kgFe^(-1) s^(-1) over 10 cycles, carbon recovery of 48% ± 1%, fuel utilisation of 23% ± 2%, and an average calcium oxide and iron oxide utilisation of 22% ± 1% and 11% ± 1%. These experimental performance indicators for the temperature-programmed CO production were consistently better than those of the isothermal implementation mode by 20% to 35%. Over 10 consecutive process cycles, no significant losses in CO yield were observed in either implementation mode. Process simulation was carried out for 1 million metric tonnes per year of equivalent CO_(2) emissions from the blast furnace gas of a steel mill to analyse the exergy losses in both modes of operation. Comparison of the exergy efficiency of the temperature-programmed process to the isothermal process showed that the former is more efficient because of the higher CO concentration achievable,despite 20% higher exergy losses caused by heat transfer required to change temperature.

Study on rapid stabilization of steel slag powder

Dry ball milling and wet ball milling were used to treat converter slag with particle size < 10 mm and the converter slag powder was stabilized by H_2O only and H_2O coupled with CO_2.respectively.Results showed that when CO_2 &H_2O was used,the free-calcium oxide(f-CaO) content in converter slag decreased significantly and after an-hour treatment the f-CaO content was reduced to 3%;however,when only treated by H_2O without CO_2, f-CaO needed 3-hour stabilization to decrease its content to 3%.When f-CaO in converter slag powder was treated by CO_2 &H_2O,its main reaction products were CaCO_3 and then Ca(OH)_2;however,when only H_2O was used, the f-CaO content decreased gently and the main products were Ca(OH)_2.

钢渣粉低液固比固碳工艺及固碳钢渣粉对水泥基材料性能的影响

矿物固碳进行CO_(2)捕集是减少温室效应的重要途径,钢铁生产企业利用钢渣与带有余热和CO_(2)的废气反应可以达到协同处置的效果。本工作研究了低液固比(润湿状态)条件下钢渣固碳的最佳工艺,确定出最佳固碳反应参数为反应温度100℃、液固比9%、反应时间60 min、CO_(2)压力0.4 MPa。该工艺条件下,钢渣粉固碳率可达119.1 g CO_(2)/kg,固碳产物主要为方解石型碳酸钙。在此基础上,研究了掺入固碳钢渣粉对水泥净浆体积安定性、标准稠度需水量、凝结时间、胶砂强度和水化热的影响。结果表明:钢渣粉固碳后,体积安定性明显改善;固碳钢渣粉对水泥净浆标准稠度需水量无不利影响;与未固碳钢渣相比,固碳钢渣对水泥凝结硬化的延缓作用有所减弱,且随固碳率增大减弱效果增强;固碳钢渣粉在低掺量(10%)时,能提高水泥胶砂的3 d、7 d和28 d抗压强度,但掺量过高(>30%)时,会显著降低水泥胶砂的3 d、7 d和28 d抗压强度。XRD测试表明CaCO_(3)能够水化生成单碳型水化碳铝酸钙(C_(3)A·CaCO_(3)·11H_(2)O)和半碳型水化碳铝酸钙(C_(3)A·0.5CaCO_(3)·0.5Ca(OH)_(2)·11.5H_(2)O)。低液固比固碳有助于钢铁企业实现碳中和,也可以改善钢渣体积安定性,使钢渣粉得到更有效的利用。

管线钢X65连铸过程絮流原因分析

通过对低碳低硫低氧铝镇静钢X65连铸过程絮流原因的分析,得出引起塞棒絮流的原因是高Ca的钙铝酸盐粘附在塞棒头部。浇注初期,塞棒头部吸热使周围钢液温度急剧下降,析出高熔点钙铝酸盐被粘附在塞棒头部,引起塞棒曲线上行。另外,通过热力学计算,在低碳低硫低氧铝镇静钢X65中,1 540℃时,形成12CaO·7Al_(2)O_(3)需要的w[Ca]为16×10^(-6),过量的Ca进一步反应形成高熔点钙铝酸盐。在中间包工作层、塞棒、水口、碗口等与钢水接触部位全部使用镁质耐材的条件下,在低碳低硫低氧的铝镇静钢生产时,向钢液中喂入的Ca含量越多,塞棒上行程度越严重。采用高碱度渣系和Al降低钢中的O和S,将Ca喂入量控制在0.065 0~0.071 5 kg/t,中间包w[Ca]控制在(10~15)×10^(-6),可以有效控制塞棒絮流。

45钢水口结瘤原因及控制

研究了45钢生产过程中中间包水口结瘤问题的原因并提出了改进措施。利用高速数据采集系统及EDX荧光分析技术监测了钢液波动情况及水口结瘤物的成分。结果表明:高熔点Al_(2)O_(3)非金属夹杂物和钙处理过程形成的CaS在中间包浸入式水口内壁聚集是水口结瘤的原因。减少Al_(2)O_(3)的产生量,同时防止过量的[Ca]与[S]形成CaS是解决水口结瘤的根本措施。通过将钢水成品钙含量控制在6×10^(-6)~10×10^(-6);LF过程渣料配比二元碱度控制在3.5~5范围,做到硫含量可控,同时硫合金化前置到VD真空前;将LF离站铝含量控制在≤0.015%;VD真空后减少合金化种类,铝合金化后进行钙处理,间隔时间设定为3~5 min;钢水过热度控制在25~35℃等工艺措施改善了45钢的可浇性,实现了整浇次稳定生产,中间包水口结瘤问题随之解决。

低碳铝镇静钢精炼渣理化性能研究及动态调控

为提升低碳铝镇静钢水的可浇性,基于低碳铝镇静钢精炼渣的热力学计算,研究典型组分CaO/Al2O3(C/A)、SiO_(2)、FeO对精炼渣液相线温度、1650℃黏度和表面张力的影响规律,结合精炼渣理化性能(熔点和黏度-温度曲线)测试结果,建立吹氩直上精炼渣动态调控模型,并投入生产实践应用。结果表明:随着C/A增加,精炼渣熔点在渣中SiO_(2)质量分数为5%时单调升高,在渣中SiO_(2)质量分数为10%时先降后升,另随C/A的增加精炼渣黏度及黏度-温度曲线的转折温度升高;精炼渣组分范围为C/A 0.75~1.50、SiO_(2)质量分数0~10%、FeO质量分数2%~6%时,可获得较低的液相线温度、较高的黏度和表面张力。生产实践中应用建立的模型可实现造渣物料的动态加入,精炼渣理化性能的稳定性得到显著提升,精炼渣的C/A和全铁(TFe)质量分数标准差明显降低;液相线温度、1650℃时的黏度和表面张力平均值分别降低6.9℃、增加0.0206 Pa·s和0.0109 N/m;全氧(TO)质量分数均值由2.78×10(-3)%下降为2.25×10(-3)%,改进了19.1%,钢水的可浇性得到显著改善。

钢渣尾渣中游离氧化钙水浸消解实验研究

随着冶金行业技术高速发展,钢铁产量逐年递增,钢渣作为其副产物,产量快速增长,钢渣中游离氧化钙(f-CaO)对环境的影响较大。为探究影响钢渣水浸过程中f-CaO消解的因素,设计了不同液固比、钢渣粒径、换水次数、搅拌时间等因素对钢渣中游离氧化钙消解影响的实验。实验结果表明,钢渣粒径加上适当的搅拌时间,对游离氧化钙消解效果影响最大,实验原渣中游离氧化钙的含量为7.17%,当钢渣粒径从1 mm减小至0.15 mm时,游离氧化钙含量从5.21%减少至4.92%,同时增加搅拌时间5 min,粒径为0.15 mm时,游离氧化钙的含量进一步降低至2.45%,此条件下从节能角度考虑较为合理。

钢液钙处理过程有效钙硫比对303 t超大钢锭中硫化物形貌的影响

通过工业实验研究了钙处理对303 t的16Mn重型管板铸锭中硫化物形貌的控制.未钙处理的锻件缺陷主要分布在轴向上靠近顶部、径向上在距中心1/2以内位置,缺陷主要为大尺寸Ⅱ类MnS夹杂物.采用Micro-CT检测了铸锭顶部中心位置MnS夹杂物三维分布,夹杂物为长条状和片状,数密度为0.77 mm^(-3),最大直径为1370μm.在真空脱气后对钢液进行钙处理,钙处理不仅将钢液中原生Al_(2)O_(3)夹杂物改性为液态钙铝酸盐,并且钙会在钢液凝固和冷却过程中优于锰先与硫结合生成CaS.通过FactSage热力学计算得到,钙处理将MnS夹杂物的析出温度由1244.7℃降低至1227.9℃,同时减少了MnS夹杂物析出量.钙在改性硫化物之前先改性了钢中氧化物,因此提出了有效钙硫比Ca/Seff.用来表征钙处理对硫化物形貌的影响,Ca/Seff.的含义为改性硫化物的有效钙和钢中硫的原子浓度比,可以直接根据钢液的总氧T.O含量、总硫T.S含量和总钙T.Ca含量计算得到,此公式适用于硫质量分数小于30×10^(-6)的低硫钢.随着钢中Ca/Seff.增加,铸锭顶部硫化物长宽比逐渐减小.钙处理后钢中有效钙硫比Ca/Seff.应大于0.8,铸锭顶部硫化物平均长宽比小于1.2,CaS和MnS复合硫化物以钙铝酸盐夹杂物为核心析出,硫化物为球形且尺寸显著减小,此时钙处理改性铸锭中硫化物效果较好.

木质素磺酸钙对模拟混凝土孔隙腐蚀液中碳钢阻锈作用

钢筋混凝土结构常因钢筋锈蚀而导致过早破坏,加入阻锈剂可以有效抑制钢筋锈蚀,提高钢筋混凝土结构耐久性。在模拟混凝土孔隙腐蚀液中加入不同浓度的木质素磺酸钙,通过开路电位、交流阻抗谱和动电位极化曲线研究其对碳钢的阻锈作用与机理。结果表明:在3.5%Na Cl、p H为12.5的腐蚀液中,木质素磺酸钙可提高开路电位、增大电荷转移电阻以及减小腐蚀电流密度,从而起到阻锈作用。同时,木质素磺酸钙在碳钢表面能够与氯离子竞争吸附,保护钝化膜,抑制腐蚀发展。