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.     

Improvement of the technology of the out-of-furnace treatment of wheel steel

Various versions of the deoxidation and out-of-furnace treatment of wheel steel under the OAO VMZ conditions are analyzed. The effective partial pressure of carbon monoxide over a melt in a 130-t ladle degasser is found to be 54 ± 9 kPa. Thermodynamic analysis of the deoxidation demonstrates that low oxygen concentrations in the melt of wheel steel can be achieved when it is deoxidized by aluminum, silicocalcium, aluminocalcium, or carbon in vacuum. Experiments and a thermodynamic calculation show that the vacuum-carbon deoxidation of a high-strength wheel steel provides oxygen concentrations in the metal that are comparable with the concentrations obtained by silicocalcium deoxidation (0.0023 ± 0.0005 wt %) and ensures the optimum morphology and concentration of oxide inclusions. The causes of the formation of the defects revealed by ultrasonic inspection in railway wheel templates are studied. The level of rejection controlled by these defects depends on the deoxidation method and is related to the number and morphology of the oxide inclusions that form during secondary oxidation.     

Removing oxide and sulfide inclusions from molten steel by filtration

On the basis of thermodynamic calculations indicating that rare-earth sulfide inclusions may form in molten nonalloyed structural steel, the influence of filtration on the content of sulfur, oxygen, and nonmetallic inclusions in the steel is investigated. It is found that filtration removes the oxide phase and oxygen from 30Л steel. There is no change in the content of sulfide inclusions and sulfur. Filtration of steel preliminarily treated with 0.05–0.30% rare-earth metals removes 10–60% of the sulfur. Metallographic data show that the content of both oxide and sulfide inclusions is reduced here. Gray impressions of filter templates show that the sulfur-bearing phase is removed by an adhesive mechanism: this phase adheres to the filter surface, forming continuous borders around it.     

Ce-La合金化处理对取向硅钢夹杂物特征的影响

 为了研究稀土处理对取向硅钢中夹杂物特征的影响,借助FE-SEM/EDS和图像分析软件分析了稀土处理前后热轧取向硅钢夹杂物的成分、形貌、尺寸和数量并解明了影响机理。研究结果表明,未添加稀土的试验钢中,典型的夹杂物为形貌不规则的MnS-AlN复合夹杂物以及片状或条状的AlN夹杂物;添加稀土后,夹杂物则以球状或椭球状的CeS-LaS、CeS-LaS-AlN、Ce₂O₂S-La₂O₂S复合夹杂物和AlN夹杂物为主。稀土处理有效改善了夹杂物形貌,特别是大尺寸氮硫化物的形貌特征,未检测到MnS类夹杂物。尽管加入较多的稀土后夹杂物数量增加,大于5 μm夹杂物的平均尺寸增大量明显(增大0.89 μm),但整体夹杂物的平均尺寸仅增大了0.40 μm。由于稀土的脱硫作用,且稀土硫化物与AlN晶格常数差异大,钢中氮硫化物的数量密度和面积分数降低。稀土降低了AlN在钢中的平衡溶度积,使AlN夹杂物提前析出,导致AlN夹杂物数量增多,且先析出的AlN出现一定程度的长大。稀土对MnS在凝固前沿的析出有抑制作用,有利于热轧和常化过程析出更多用作抑制剂的MnS和AlN。在充分脱氧的取向硅钢中适当降低钢中酸溶铝含量,调整稀土在钢中的用量,在不增加钢中大尺寸夹杂物含量的前提下,发挥MnS、AlN抑制剂作用和Ce-La合金化作用。此外,通过稀土处理控制钢中夹杂物形貌特征,将有望达到改善钢的热轧组织和轧制加工性能的目的。     

高速重轨钢中尖晶石夹杂物的形成及控制

 高速重轨钢采用无铝脱氧工艺,但是钢中常发现大颗粒纯的MgO-Al₂O₃夹杂物,严重影响产品质量。为了明确高速重轨钢中尖晶石夹杂物的来源,进一步控制重轨钢中夹杂物,通过对重轨钢拉伸断口进行分析,结合水口结瘤物分析、热力学计算及典型夹杂物分析,系统研究了高速重轨钢中尖晶石夹杂物的形成机理。结果表明,重轨钢中的尖晶石夹杂物分为单独存在的尖晶石和钙铝酸盐包裹的尖晶石两类。其中钙铝酸盐包裹的尖晶石为CaO-SiO₂-Al₂O₃-MgO复合夹杂物在降温冷却过程中析出,析出温度与夹杂物中Al₂O₃和MgO质量分数有关;单独存在的小尺寸尖晶石夹杂物为钢液凝固冷却过程中析出,与钢液成分有关。此外,研究还表明,水口结瘤也是重轨钢中出现大颗粒镁铝尖晶石夹杂物的重要原因之一。因此,严格控制合金辅料中Mg、Al_s等杂质元素质量分数,防止钢液发生二次氧化、降低耐火材料侵蚀等,尽可能降低夹杂物中的Al₂O₃和MgO质量分数,对控制重轨钢中尖晶石夹杂物,提高产品质量至关重要。     

150 t BOF-LF-VD-CC流程无铝脱氧工艺高速轨钢冶炼过程的夹杂物行为

时速350 km高速钢轨要求钢中全氧含量T[O]≤20×10^-6,非金属夹杂物B、C、D类≤1.0级。国内在重轨钢冶炼中,通常采用无铝脱氧工艺,即采用SiCaBa合金强化脱氧,形成了低熔点的Mn-Al-Si-Ba-Ca多元型氧化物夹杂,该类夹杂物在精炼中全部排出钢液。研究了铁水预处理脱硫-150 t顶底复吹转炉-LF-VD-280 mm ×380 mm连铸流程冶炼钢轨钢U71MnG时的夹杂物行为,包括无铝脱氧工艺钢轨钢中氧化物夹杂的组成及特征,转炉终点[C]对钢水氧活度的影响以及LF精炼渣碱度和VD后期软吹氩搅拌对钢氧含量和夹杂物的影响。结果得出,钢轨头部的≤20μm氧化物夹杂为精炼时二次脱氧产物,通过控制转炉终点[C]＞0.15%,控制精炼渣碱度(CaO)/(SiO₂)=2.5~3,∑(FeO+MnO)≤1.0%可有效降低钢轨钢中氧化物的数量和尺寸。     

The development of new metallurgical materials and technologies. Part 1

Work by researchers at the Russian Academy of Sciences on new materials (metals and ceramics) and new technologies is reviewed. The topics include new high-strength corrosion-resistant nitrogen steels; high-temperature light alloys and composites based on intermetallics; modifiers for wheel steels; complex ferroalloys containing V, Cr, and Ni; anticorrosive protective coatings based on ultrafine Zn powders; catalytic converters for vehicle exhaust gases; magnetically hard materials with high temperature–time stability and excellent mechanical characteristics; nanostructured stents for endovascular operations; and corrosionand wear-resistant coatings and corresponding methods of plasma application. Methods have been developed for longitudinal rolling with shear deformation to improve the properties of the rolled product; recycling of oily scale; monitoring of the wear of the refractory lining at any point of the blast-furnace hearth; and monitoring of the content of inclusions in rail steel. Technologies have been developed for special electroproduction of steel for the power industry; synthesis of massive monocrystalline samples of transition-metal nitrides and nanopowders of W, Pt, and Ti and their carbides and nitrides; the processing of leucoxene concentrates from the Yareg Basin; the production of titanium implants with porous coatings; ferrous and nonferrous metal shot and powder; ultrafine Zn powder; recycling of metallurgical wastes with the extraction of Zn, Sb, Sn, and Fe; the production of sintered nanocrystalline Ta powder for capacitors; the processing of molybdenum-bearing sulfide material to obtain rare-earth metals, MoO₃, and CaMoO₄; and the utilization of sulfur dioxide. Injection units and technologies for their use have been developed, as well as high-speed systems for the plasma application of metals on surfaces including paint coatings, plastics, and cardboard. Data have been obtained regarding the thermodynamic functions of the solution of oxygen in Fe-based melts and the reactions of elements dissolved in such melts (Cr, Mn, Nb, V, Si, B, C, Ti, Zr, Al) with oxygen.     

Research on determination of the rare-earth content in metal phases of steel

The behavior of the rare-earth dissolved in a-Fe, of the iron-cerium intermetallic compounds and of the rare-earth inclusions in electrolytic separation process has been studied by means of counting measurements of radioactivity, the electron probe, and X-ray analysis. The experimental results show that the rare-earth sulfide and the rare-earth oxide are stable completely in the electrolytic separation process, when the composition of the electrolytic solution is 1 pct 4-methyl ammonium chloride, 5 pct triethanolamine, 5 pct glycerin, and 89 pct methyl alcohol, and the controlling anode current density is ≤100 mA/cm². But Fe-Ce intermetallic compounds and the rare-earth dissolved in a-Fe enter into electrolytic solution as ions. When the cerium ion concentration in electrolytic solution is >7.87 X 10^-5 mol/liter electrolyte, precipitates of cerium hydroxide will be formed. When the inclusions are separated quantitatively, the electrolytic solution must be filtered by using a funnel with filter paper pulp thick up to 6 mm, and not be filtered directly with single filter paper. Samples without rare-earth were remelted and a radioactive isotope¹⁴¹Ce was added to the steel. Inclusions were separated by the electrolytic method in the nonaqueous solution. The counting of 14lCe in the electrolytic solution was measured. Thus the rare-earth content in the metal phases can be calculated. Experimental results show that the rare-earth content in the metal phases increases with the total rare-earth content in steel. The rare-earth content in the metal phases of the steel was also found to increase as the aluminum content in steel was increased. This method for determining the rare-earth content in the metal phases of steel is very sensitive. The sensitivity is 10^-6 pct.     

基于激光诱导击穿光谱技术的重轨钢中铝系夹杂物含量分析方法研究

钢中夹杂物对钢铁材料的性能存在着重要的影响,钢水中凝固的夹杂物会降低钢的物理性能。为排除钢中夹杂物的影响,需要建立检测夹杂物的方法。基于重轨钢样品中铝夹杂物的异常信号响应及阈值选择,实验研究了一种新的钢中铝系夹杂物含量的激光诱导击穿光谱分析(LIBS)检测方法。由于钢材中夹杂铝大多以酸不溶铝的形式存在,故研究中采取的计算模型中夹杂铝的含量默认与酸不溶铝含量相同。实验中由于检测的中低合金钢中夹杂铝含量过低,故随机选择9块重轨钢待测样中5块作为标准样品,通过结合LIBS结果中异常信号的筛选和已发表文献的模型进行计算,发现在置信区间阈值K=2.6时,激光诱导击穿光谱法得到的结果中夹杂物计算值与真实值基本符合,由此确立了激光诱导击穿光谱对铝夹杂分析的计算数学模型。将所建立的夹杂物检测方法模型实际应用于剩余4块重轨钢样品的检测,并将测定结果与化学湿法进行结果比对,结果显示二者基本一致。     

硫含量对重轨钢中非金属夹杂物的影响

摘要：实际生产过程中由于原料和操作控制不精确,钢中硫含量和非金属夹杂物波动较大,严重影响钢的洁净度。为了准确控制重轨钢中硫化锰等非金属夹杂物的尺寸、形态和数量,在实验室开展了硫含量对重轨钢中非金属夹杂物的影响研究。钢中硫质量分数增至70×10-6、110×10-6、140×10-6后随炉冷却,采用全自动夹杂物分析仪对钢中非金属夹杂物进行统计,获得了硫含量与钢中非金属夹杂物成分、尺寸、形态和数量的关系。结果表明,钢中夹杂物大部分为以氧化物为形核核心的复合型MnS;随着硫含量的升高,复合型MnS、MnO-SiO2和MgO-Al2O3-SiO2-CaO型夹杂增多,CaO-SiO2和MgO-CaO-SiO2夹杂减少;夹杂物平均尺寸随硫含量的升高而增大,且不同尺寸的夹杂物均有所增加,尺寸为2~10μm增多最明显;硫质量分数为(70~140)×10-6的钢液凝固过程液相中都能单独析出MnS,且硫含量越高,MnS析出越早,含量越多。     

加热保温处理对重轨钢中MnS夹杂的影响

 以U75V高速重轨钢为例,研究了加热保温处理对MnS夹杂的影响。采用高温共聚焦激光显微镜分别对铸坯和钢轨中MnS夹杂在连续升温过程中的行为进行了动态原位观察,结果表明MnS夹杂在600~870℃发生球化,在1180℃左右时, MnS夹杂开始发生固溶。根据原位观察结果,在电阻炉中进行了加热保温处理实验。试验结果表明,830℃保温后,MnS夹杂尺寸只是略有减少,长宽比降低。在1180℃保温后,大型MnS夹杂数量明显减少,小尺寸MnS数量增多,且随保温时间的延长,夹杂物数量减少,长宽比进一步降低。通过加热保温处理可以改善重轨钢中长条状大型MnS夹杂。     

Effect of sulfur content on non metallic inclusions of heavy rail steel

Due to the inaccurate control of raw materials and operation in the actual production process, the sulfur content and non-metallic inclusions in the steel fluctuate greatly, which seriously affects the cleanliness of steel. To accurately control the size, shape and quantity of non-metallic inclusions such as manganese sulfide in heavy rail steel, the effect of sulfur content on non-metallic inclusions in heavy rail steel was studied in the laboratory. To investigate the changes of the number and morphology of non-metallic inclusions in steel under different sulfur contents, the sulfur content of test steel was increased to 70×10-6, 110×10-6 and 140×10-6, respectively. During the experiment, the test steel was heated and melted in a tubular furnace according to a certain heating rule, and then cooled naturally in the furnace. Subsequently, the non metallic inclusions in steel were scanned by automatic inclusions analyzer, and the relationship between sulfur content and the composition, size, form and quantity of non-metallic inclusions in steel was obtained. The results indicate that most of the inclusions in the steel are composite MnS with oxides as nucleating cores. With the increase of sulfur content, the quantity density of composite MnS, MnO-SiO2 and MgO-Al2O3-SiO2-CaO inclusions increase, while the CaO-SiO2 and MgO-CaO-SiO2 inclusions decrease. The average size of inclusions increases with the increase of sulfur content, and the number of inclusions with different sizes also increases, especially for inclusions with sizes of 2-10μm which increase obviously. During solidification, MnS can be separated from molten steel with sulfur content of (70-140)×10-6. In addition, the higher the sulfur content is, the earlier MnS inclusions precipitate and the more the MnS content is.     

车轮钢摩擦热影响区的相变及其损伤机理

将有限元热力耦合一温度场分析与材料相变特征的实验研究相结合，研究了高速度(200kin／h)、大载荷(10^5N)条件下车轮摩擦热影响区的相变过程，探讨了材料对该过程的影响。结果表明，轮一轨摩擦导致的车轮踏面局部升温可超过材料的奥氏体相变的临界点，碳含量为0．5％时，完全奥氏体化层的深度可达0．6mm；过冷奥氏体高速冷却，几乎全部形成脆硬的马氏体薄层，造成踏面剥离。通过降碳来降低车轮钢奥氏体相变的临界点，可以显著抑制踏面马氏体层的形成。随着碳含量从0．7％降至0．4％，材料的Ae3提高45℃，马氏体层的厚度减小30％，有助于减少车轮踏面的热疲劳损伤。     

稀土元素在洁净重轨钢中存在状态的热力学模型研究

建立了可以定量描述洁净稀土重轨钢凝固过程中成分偏析与夹杂物析出的耦合热力学模型,经文献验证,模型具有较高精度。通过模型分析了稀土加入量对洁净钢中夹杂物的析出规律与稀土存在状态的影响。得出在洁净重轨钢中加入稀土可以变质钢中MnS、Al₂O₃夹杂;钢中首先析出稀土氧硫化物(或稀土铝酸盐),其次是稀土硫化物,最后是稀土氮化物;在同一稀土加入量条件下,固溶La的量要大于固溶Ce的量。     

Precipitation behaviour and control of TiN inclusions in rail steels

This paper studied the precipitation behaviour and the control of TiN inclusions in rail steels by thermodynamic calculation and industrial experiments. The results showed that TiN inclusions could not precipitate in molten steel at present condition owing to low [Ti] and [N] content in rail steels; but when solid fraction exceeded 0.87 in mushy zone during solidification process, TiN inclusions could precipitate because of the separation–crystallisation of [Ti] and [N], and even long strip inclusions were formed around grain boundaries. Two types of TiN inclusions, including long strip type with size ranging 20–30?μm and block type with size below 10?μm, could be found in rail steels. The formation of TiN inclusions could be affected by the content of [Ti] and [N], the superheat of liquid steel, secondary cooling intensity and the intensity of strand electromagnetic stirring. The metallurgical process III was conducive to the control of TiN inclusions precipitated and grown up. The results of thermodynamic analysis were consistent with those of the metallurgical process tests.     

钢轨钢生产中硫的控制

 钢轨钢对钢水洁净度和非金属夹杂物控制均有较高要求。针对高硫铁水冶炼现状,为实现钢轨钢的洁净生产,攀钢在铁水预处理、转炉冶炼、钢水精炼方面进行了硫控制技术的开发与应用,形成了提高钢的洁净度和控制钢中非金属夹杂物的数量和形态的洁净钢生产工艺技术,实现了350km/h高速铁路用钢轨的生产。高速轨成品w(［S］)≤0.008%的合格率达到95%以上,钢轨w(T［O］)降至0.001 5%以下,夹杂物的分布形态得到有效控制。     

Effect of magnesium addition on microstructure and mechanical properties in wheel steel

In order to reveal the effect of Mg in low carbon microalloy steel, low carbon microalloy steel of HR60 wheel steel was smelted in vacuum induction furnace and industrial field respectively. The characteristics of typical non- metallic inclusions and microstructure of experimental steels were both compared by OM, SEM- EDS and INCA Feature with automatically scanning inclusions function. The mechanical properties of the experimental steels were also measured. The results show that alumina inclusions are modified to spinel inclusions with small size after Mg addition. Furthermore, acicular ferrite can be induced effectively by inclusions containing magnesium. The microstructures of experimental steels are changed from ??polygonal ferrite(PF) + pearlite(P)??to ??polygonal ferrite(PF) + degenerate pearlite(DP) + acicular ferrite(AF)?? and refined by Mg treatment. The strength of experimental steels is improved with Mg addition. In industrial experiments, the fatigue limit of Mg- treated steels is greater than 460MPa, while the fatigue limit of Ca- treated steels is about 450MPa. In addition, the fatigue life of Mg- treated steels is generally higher than that of Ca- treated steels under the condition that the stress is greater than the fatigue limit. In laboratory experiments, the contents of Nb and Ti are reduced while Mg content in steel is 18??10-6, the strength of the wheel steel is close to the reference steel. Therefore, the project to reducing production cost by taking advantage of the microalloy role of Mg is feasible.     

120t BOF-LF-VD-CC流程高品质重轨钢U75V的生产实践

通过对重轨钢U75V的生产过程进行取样分析,研究了实际冶炼过程中重轨钢夹杂物的演变规律和大型夹杂物的控制。研究结果表明:控制铝含量≤20×10^-6,精炼渣二元碱度1.8～2.2,白渣保持时间≥15min,RH真空度在100Pa以下保持高真空时间≥15 min,可使钢液中全氧含量降至10×10^-6以下,且铝含量不超过20×10^-6,轧材中基本消除B类和D类粗系夹杂,C类夹杂完全塑性化;中间包钢水过热度按25～35℃控制,中间包钢水平均停留时间（750±30）s、水口插入深度控制在90～110 mm,结晶器液面波动≤±3 mm等措施,可去除钢水中的夹杂物。     

提高PD3钢轨力学性能的实践

针对鞍钢模铸生产的PD3钢轨较U7lMn钢力学性能合格串偏低的情况，对可能影响钢轨力学性能的化学成分、钢轨氢含量、金相组织、非金属夹杂物等方面进行综合分析，认为控制非金属夹杂物的种类和数量是提高力学性能的主要手段，并通过调整生产工艺达到了这一目的。     

重轨钢中MnS析出热力学和动力学分析

 采用无水有机溶液电解法分离提取重轨钢中的MnS夹杂物,采用扫描电镜观察铸坯内和钢轨中MnS夹杂物的三维形貌,并结合能谱仪分析其成分。铸坯被轧制成钢轨后,相应的MnS夹杂物都沿着轧制方向被轧制成长条状。基于热力学和动力学模型,分析重轨钢中MnS夹杂物析出行为以及在钢液凝固过程中锰元素和硫元素偏析的程度。热力学分析表明,MnS夹杂物在凝固末期凝固分数为0.94时开始析出,其析出量由初始[w([Mn])]和初始[w([S])]决定,且在凝固过程受到冷却速率的影响,对比发现,热力学的计算析出结果与Thermo-Calc和FactSage6.4的计算结果有较好的一致性;动力学分析表明,在钢液凝固过程增加冷却速率,凝固析出的MnS颗粒尺寸将减小。通过调整钢中[w([Mn])]和[w([S])]以及改变冷却速率,可以控制MnS的析出时机和形态,减小其对钢性能的有害影响。