Analysis of various versions of the deoxidation of rail steel at OAO NTMK

The deoxidation of steel melted using various types of deoxidizers during out-of-furnace treatment is studied. The total oxygen and nitrogen content and the oxygen contents in the main types of oxide nonmetallic inclusions are determined by fractional gas analysis of steel samples taken from heats performed by various schedules. The main types of nonmetallic inclusions and their size distributions are found with qualitative and quantitative metallography. The oxygen content in the rail steel is minimal (5 ppm) when calcium carbide CaC₂ is introduced into the metal in tapping of a converter. When the metal is deoxidized using a steel wire filled with calcium or a steel wire filled with silicocalcium, the oxygen content in rail steel is ≈8 and ≈11 ppm, respectively. A comparison of various processes of rail steel deoxidation under the OAO NTMK conditions shows that the limitation of the aluminum content (no more than 30 ppm) or the use of a wire with a calcium or calcium carbide filler is more effective than the use of a wire filled with silicocalcium.     

履带链轨节用钢的研制

莱钢特钢厂采用电炉短流程工艺开发生产了35MnBM履带链轨节用钢。通过采用电炉冶炼过程的高比例热装铁水工艺、LF精炼、VD真空脱气、连铸全程保护浇注和其它防止钢液二次氧化等诸多措施,有效地控制了钢中的残余元素、气体含量和非金属夹杂物,钢材各项技术指标处于国内领先水平。     

Effect of Top Slag Composition on Inclusion Characteristics during Vacuum Degassing of Tool Steel

The focus of the study was to investigate the effect of the chemical composition of the top slag on the inclusion chemical composition during vacuum treatment of a plastic mould tool steel. Sampling was done before and after vacuum degassing. The chemical composition of the inclusions was determined by using SEM combined with EDX. The results showed that several inclusion compositions were found before vacuum degassing, while only one main composition of inclusions was present after vacuum degassing. Furthermore, the composition of the top slag was found to have a great influence on the composition of the inclusions found in samples taken after vacuum degassing. The present study also shows that the vacuum degassing effectively reduces the number of inclusions in steel. Finally, the thermodynamic calculations of the activities using Wagner's equation were found to predict a lower oxygen activity value than the calculations made using the Thermo‐Calc software.     

Change of Inclusion Characteristics during Vacuum Degassing of Tool Steel

The inclusion characteristics were studied during vacuum degassing by interrupting the operation at five different times after the start of operation. Slag and steel samples were collected and thereafter assessed with respect to steel and slag composition, total oxygen content, size distribution of inclusions and chemical composition of inclusions. The main conclusion is that the number of inclusions in the different size classes as well as the total oxygen content seem to reach a minimum value after around ten minutes of vacuum degassing. Furthermore, it seems to be a consistent trend that, during vacuum degassing, the top slag influences the inclusion composition.     

钙处理对20CrMnTiH齿轮钢中非金属夹杂物的影响

铝脱氧齿轮钢中易生成大量的高熔点Al₂O₃类夹杂物,容易导致水口结瘤及钢材性能恶化,目前较常采用钙处理将钢中高熔点的Al₂O₃类夹杂物改性为低熔点的钙铝酸盐类夹杂物。合理的钙处理可以减轻水口结瘤并提高连铸过程钢液的可浇性,工业试验研究了喂钙前钢液中T.Ca含量、喂钙速度、喂钙量、净空高度及渣厚等参数对齿轮钢中钙收得率的影响,并在1.5 m·s?1的喂钙速度条件下研究了不同喂钙量对钙处理过程中齿轮钢中非金属夹杂物改性的影响。研究结果表明,当喂钙前钢液中T.Ca的质量分数小于10×10?6,喂钙速度为1.5 m·s?1,适当降低喂钙量和净空高度和渣厚,钢液中钙收得率均高于20%。当钢液中T.Ca的质量分数高于17×10?6时,钢中生成大量高熔点CaS型夹杂物,三元相图中夹杂物的平均质量分数远离液相区。随着齿轮钢中T.Ca含量的增加,夹杂物的平均尺寸和数密度逐渐增加。热力学计算结果与工业试验钙处理对钢中非金属夹杂物改性效果具有较好的一致性。      

Nonmetallic inclusions in vacuum-treated austenitic stainless steel

The nonmetallic phase in 08X18H10T and 03X18H10 vacuum-treated austenitic stainless steel is investigated by means of a scanning electron microscope. The composition of the nonmetallic inclusions in cast samples of metal from the casting ladle, the vacuum unit, and the continuous-casting machine and samples of cold-rolled sheet (thickness 1.2 mm) is studied. In 08X18H10T steel samples from the tundish of the continuous-casting machine, the nonmetallic phase consists mainly of titanium-nitride aggregations, the crystals of which contain oxides of aluminum and titanium; a few of the nonmetallic inclusions are small globules with a titanium-oxide shell. In cold-rolled sheet, the nonmetallic inclusions are distributed over the whole cross section and consist of small (5–6 μm) crystals of titanium nitrides. Cast samples of 03X18H10 austenitic titanium-free steel are relatively free of nonmetallic inclusions. The nonmetallic phase consists mainly of small inclusions of alumocalcium silicate. In cold-rolled sheet (thickness 1.2 mm), the nonmetallic phase consists of a few very small globules (2–3 μm). The results are compared with the composition of the nonmetallic phase in analogous steel with no vacuum treatment.     

连铸过程中夹杂物去除数值模拟研究现状

摘要：随着钢材质量要求的提高,连铸过程中夹杂物的控制已经成为了钢铁企业的重要课题。受限于现实条件及连铸过程的复杂性,数值模拟技术成为了研究连铸过程夹杂物行为的重要手段之一。结合数值模拟研究现状介绍了中间包内电磁技术、流动控制元件和底吹氩技术对夹杂物上浮去除的积极作用,发现夹杂物性质及非等温条件对夹杂物行为的影响还较少被研究;探讨了优化浸入式水口（SEN）和合理应用电磁技术对结晶器内夹杂物去除的重要影响,当前结晶器内的夹杂物模拟研究正在向微观层面进行过渡。连铸过程中夹杂物行为的数值模拟研究随着计算机技术的发展和数学模型的完善也在不断进步。     

Q345R 抗酸钢 120 t BOF-LF-RH-260 mm x 2 70 mm CC冶炼工艺实践

分析了"BOF-LF-RH-连铸"生产Q345R抗酸钢的工艺和不同的钙处理方式对钢Ca/S、夹杂物的影响,以及低过热度结合动态轻压下浇铸对铸坯低倍质量的影响。研究表明:采用"LF+RH+钙处理"工艺冶炼,可提高钢中Ca/S,降低钢中A类和B类夹杂物尺寸。RH真空后进行钙处理,成品钢板中出现2.0级的Ds类夹杂,延长钙处理后软吹时间,可减少该类夹杂的尺寸和数量。采用LF/RH双步钙处理工艺,RH钙处理后软吹时间16～20 min,可达到钢板B类、Ds和D类夹杂尺寸控制在≤1.0级,A类和C类夹杂尺寸控制在≤0.5级。利用5～12℃过热度结合动态轻压下技术浇铸,铸坯低倍评级中心偏析达到C类1.0级,各元素偏析度较低。采用该工艺,可实现Q345R抗酸钢成分、夹杂物、低倍质量满足标准要求。     

Effect of the conditions of REM microalloying of steel on the corrosion activity of nonmetallic inclusions

Experimental heats of low-alloy steel are performed under various conditions of rare-earth metal microalloying and aluminum and calcium deoxidation. Electron-probe microanalysis of nonmetallic inclusions and a metallographic investigation of a metal are used to show that, when interacting with water, nonmetallic cerium oxide inclusions do not form hydrates and, correspondingly, are not aggressive. When aluminum, calcium, and cerium additions are sequentially introduced into a melt, a continuous cerium oxide shell forms on calcium aluminates, protects corrosive nonmetallic inclusions against interaction with water, and weakens local metal corrosion.     

20CrMo合金钢生产过程中非金属夹杂物的演变

为了进一步研究20CrMo合金钢在生产过程中夹杂物的演变机理,实现对钢中非金属夹杂物的合理控制,保证生产顺行,提高产品力学性能,针对“BOF→LF→RH→钙处理→连铸→热轧”工序生产20CrMo合金钢全流程中非金属夹杂物的演变规律进行了研究。在LF精炼及RH精炼加钙前钢中非金属夹杂物含有70%以上的Al₂O₃。钙处理后,由于过量的钙加入到钢液中,夹杂物中CaS质量分数迅速增加至59%,Al₂O₃质量分数降低至21%。在连铸过程中由于二次氧化的发生,夹杂物转变为CaO?Al₂O₃,其中含有50%的Al₂O₃、39%的CaO和10%的CaS,并且夹杂物平均尺寸增加。在钢的冷却和凝固过程中,CaO质量分数降低至5%,CaS质量分数增加至57%,钢中夹杂物转变为Al₂O₃?CaO?CaS的复合夹杂物,同时含有少量大尺寸的CaO?Al₂O₃夹杂物。在钢的轧制过程中,夹杂物中CaO含量进一步降低,CaS含量增加,夹杂物平均尺寸增加,形成了CaO?Al₂O₃与CaS黏结型的复合夹杂物与Al₂O₃?CaS复合夹杂物。对CaO-Al₂O₃与CaS黏结型的复合夹杂物的形成原因进行了讨论。      

Origins of Non‐metallic Inclusions and their Chemical Development during Ladle Treatment

In the present work, steel, slag and refractory samples were taken from the ladle at OVAKO Steel in Hofors, Sweden. The steel samples were analysed in LOM, SEM and OES PDA. The chemical compositions of the inclusions were determined by EDS. According to the morphologies and compositions, the inclusions were classified into 5 different types, namely, (1) type‐1, alumina inclusions, (2) type‐2, calcium aluminate, (3) type‐3, spinel+calcium aluminate, (4) type‐4, calcium aluminate surrounded by a CaS shell, and (5) spinel+calcium aluminate surrounded by a CaS shell. Ladle glaze was found to be a major supplier of the inclusions, while the inclusions brought over from EAF could be another important source. The results of OES PDA showed that removal of inclusions took place mostly during the vacuum degassing period.     

Q345D钢精炼过程夹杂物生成及演变行为

冶炼Q345D钢时由于夹杂物导致的探伤不合格情况时有发生,为了进一步去除和控制钢中非金属夹杂物,通过工业试验研究了"LF精炼→RH真空精炼→钙处理→软吹→连铸"工艺中的夹杂物生成及演变规律,并通过热力学计算优化钙处理工艺.结果 表明,转炉炉后及LF进站时采用铝强脱氧,夹杂物主要为Al2O3,LF精炼过程采用高碱度、强还...     

低碳铝脱氧20钢钢水洁净度控制研究

为了研究120 t BOF-LF-RH-160 mm×160 mm坯CC工艺生产的铝脱氧20钢（/%:0.13～0.23C,0.17～0.37Si,0.35～0.65Mn,≤0.035P,≤0.035S,0.020～0.050Al）中非金属夹杂物的控制技术,对LF精炼过程中脱氧剂加入时机进行调整,并对精炼过程中非金属夹杂物类型与夹杂物数量进行分析。结果表明,转炉出钢后采用铝块脱氧,LF精炼进站非金属夹杂物主要为Al₂O₃,精炼结束前部分夹杂物由Al₂O₃转变为Al₂O₃·CaO,RH结束后非金属夹杂物密度3～4个/mm²,铸坯氧含量（7.48～8.18）×10^-6;而转炉出钢后采用硅锰进行脱氧,精炼结束前采用铝线,精炼过程中夹杂物主要为MnO·SiO₂,CaO含量小于5%,精炼结束非金属夹杂物控制为Al₂O₃,RH真空处理后,非金属夹杂物密度小于1.5个/mm²,铸坯氧含量（4.94～5.53）×10^-6。因此,针对采用“BOF-LFRH-CC”工艺流程生产的含铝钢,提出精炼结束前将非金属夹杂物控制为Al₂O₃,同时运用RH真空高效去除夹杂物,以提高钢水的洁净度。     

Effect of a pipe-steel killing technology on the composition and number of nonmetallic inclusions

Pipes made from steels 19G, 17GS, 17G1S, 10G2FBYu, 13G1S-U, and 20KT of various manufacturers and technologies are studied. Electron microprobe and fractional gas analyses are used to determine the main types and number of nonmetallic inclusions (NIs). The effect of a modification procedure on the oxidic cleanness of steel 20KT (produced at JSC “Volzhskii Pipe Works”) is studied. The use of a silicocalcium-filled wire is shown to increase the total contamination of the steel by nonmetallic, in particular, calcium aluminate and magnesium spinel inclusions, which are conditionally related to corrosion-active nonmetallic inclusions (CANIs). Fractional gas analysis is shown to allow the number of oxide inclusions of various types to be accurately determined in pipe steels. No correlation is found between the volume fraction of oxide inclusions determined by fractional gas analysis and the number of CANIs determined by a metallo-graphic method.     

Innovative smelting of IIIX15CΓ-B electrosteel

A new smelting technology for IIIX15CΓ-B electrosteel is described. In this technology, the steel undergoes treatment in a ladle-furnace unit and a vacuum system. The output of bar batches of all five size groups is analyzed for the content of nonmetallic inclusions according to State Standard GOST 801-78 and the ASTM E-45 standard (method A). The phase-mineral composition of furnace slag on smelting steel in a DSP-60 arc furnace is studied by X-ray microstructural analysis. The change in chemical composition of oxide-fluoride slag when the steel passes through the ladle-furnace unit and the vacuum system is analyzed, along with the influence of CaF₂ on the activity of FeO in oxide-fluoride slag and on the durability of the ladle lining. In conclusion, the need for environmental improvements is noted, in the light of the use of fluorspar; research into means of reducing fluorspar consumption must be activated.     

Influence of calcium carbide slag additions on inclusion characteristics in steel

Abstract

An investigation into the cleanness of steel manufactured by a major Scandinavian producer of steel for railway wheels has been carried out. Samples taken before and after secondary refining in the ladle and after degassing were compared with samples taken similarly from a heat including the addition of a calcium carbide (CaC₂ ) slag modifier. The amount, size distribution, and composition of non-metallic inclusions, as well as the slag compositions of both heats, were determined. With the addition of CaC₂ , the total number of inclusions in the sample taken before casting was found to decrease, and the size distribution revealed the presence of mostly small inclusions (between 2·8 and 5·6 μm). The assessment of railway wheel specimens revealed that the inclusion content in CaC₂ treated steel was lower than that for standard steel.     

大型客机用300M钢疲劳破坏行为

 结合显微组织观察和力学性能测试,对国产大型客机用300M钢应力比[R＝－1]的轴向光滑疲劳性能进行了研究,分析了大型客机用300M钢的高周轴向疲劳断口形貌及起裂原因,重点研究了非金属夹杂物裂纹源的特性。结果表明,国产大型客机用300M钢冶炼纯净度较高,最终热处理后具有良好的综合力学性能,其应力集中系数[Kt＝1,]应力比[R＝－1]的高周轴向疲劳极限[σ－1]为907 MPa;通过断口SEM观察发现非金属夹杂物引起的应力集中是导致高周轴向疲劳开裂的主要原因,该类起裂源为复杂氧化物和硫化钙的复合非金属夹杂物,尺寸在5.5～20.5 μm之间,主要成分为铝、钙、硅、氧和硫等。     

Transient Evolution of Nonmetallic Inclusions During Calcium Treatment of Molten Steel

Metallurgical and Materials Transactions B - The transient evolution of nonmetallic inclusions after calcium addition in pipeline steels was investigated with a vacuum induction furnace. Samples...