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.     

Corrosive Damage Close to Nonmetallic Inclusions in Bearing Steels

The development of corrosive damage in bearing steels close to nonmetallic inclusions is analyzed. The influence of the chemical and mineralogical composition of the inclusions on their activity in corrosive media is studied.     

Optimizing the production of steel with reduction by aluminum,in casting and rolling systems

Data on the metallurgical defects in pipe show that they may be due to nonmetallic oxide inclusions. Analysis of the formation of oxide inclusions from smelting to the continuous casting of steel shows that, in order to reduce the incidence of such defects, additional measures must be taken in the smelting and ladle treatment of the steel. Such measures reduce the content of oxide inclusions in the steel by half. The benefits of this approach are confirmed by the reduced rejection rate of the pipe on account of defects associated with the presence of nonmetallic inclusions.     

Nonmetallic Inclusions in Low-Alloy Tube Steel

Study of the nonmetallic phase of unalloyed tube steel 10G2FB has shown that the steel contains four types of nonmetallic inclusions. Relatively fine (no coarser than 12 µm) calcium aluminates of variable composition are the main type of nonmetallic inclusion (NI) in such steel. It was established that a decrease in the point rating for NI contamination of the steel from 3.5 to 1.5 leads to an increase in the steel’s impact toughness from 235 to 318 J/cm².__________Translated from Metallurg, No. 4, pp. 67–72, April, 2005.     

Possibilities for controlling the characteristics of nitride and carbonitirde inclusions in a low-carbon austenitic steel

The mechanisms of formation of nonmetallic inclusions in a stabilized low-carbon austenitic steel Ch-68id are studied. Technologies for controlling the sizes and distribution of the nonmetallic inclusions are suggested.     

Cyclic Tests of Stress-corrosion Cracks in Steel Gas Pipelines with No Corrosive Fluid

Stress-corrosion defects in the output pipeline of a compressor station are subjected to metallographic analysis and mechanical tests. The pipeline consists of pipe imported in the 1980s. Diagnostic data obtained in nondestructive monitoring of such pipelines are analyzed, and the effectiveness of various diagnostic methods in detecting stress-corrosion defects in large-diameter pipe is assessed. The grade of steel in the pipeline is identified. The cracks are identified by type and morphology, and their development is determined. Nonmetallic sulfide inclusions have no influence on pipeline failure in the stress-corrosion conditions considered. The sulfur content in the corrosion products is no more than the sulfur content in the metallic sample. In some samples, the sulfur content may be decreased except for local sections with nonmetallic sulfide inclusions. Electron-microscope images show that such nonmetallic inclusions do not promote failure. The results of cyclic tests of cracked samples cut from the pipeline are presented. The test conditions are selected in accordance with recent operating conditions of the compressor station. According to the results, pipe with defects at the initial stage of development exhibits considerable durability in the tests. In fact, the cracked samples withstand (1.6–7.5) × 10⁶ cycles under transverse cyclic flexure in a single plane, in the absence of corrosive fluid. In practice, the number of such cycles is no more than 120–200 per year, in normal pipeline operation. Hence, a pipeline with stress-corrosion defects in their initial stage of development will last a long time if its metal wall is protected from the action of corrosive fluid.     

合成渣精炼法控制帘线钢中的非金属夹杂物

主要论述了帘线钢中非金属夹杂物的控制方法.根据帘线钢对非金属夹杂物的要求和夹杂物对帘线钢性能的影响,利用CaO-SiO2-A12O3三元相图确定合成精炼渣的成分,优化设计帘线钢的冶炼工艺,使钢中夹杂物的尺寸变小,满足了帘线钢性能的要求.     

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。      

Nature and diagnostics of nonmetallic inclusions in steels

The chemicomineralogical nature of nonmetallic inclusions (NIs) in a number of steel grades prepared by traditional melting, elecroslag refining, and casting has been studied. Suboxides and phases having variable nonstoichiometric compositions are found to comprise nonmetallic inclusions. Their role in the formation of the properties of steel is demonstrated.     

自蔓延-离心不锈钢内衬钢管应力及裂纹研究

通过热应力计算及不锈钢层组织分析，研究了SHS－离心法制备的不锈钢内衬复合钢管不锈钢层中裂纹产生的原因以及消除裂纹的措施，研究表明，内衬层开裂是钢中的夹杂使钢变脆以及冷却过程中热应力共同作用的结果，通过加速相分离过程、减少内衬层中的夹杂、提高塑性以及提高钢中奥氏体含量等措施，可消除不锈钢层中的裂纹。     

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.     

Modern trends in the development of ladle metallurgy and the problem of nonmetallic inclusions in steel

The main trends in the development of the ladle treatment of steel have been analyzed. The most complex problem is shown to be the formation of nonmetallic inclusions having a certain type and a low concentration. The main parameters of the ladle treatment of steel that control the type and amount of nonmentallic inclusions in ready products are analyzed using the data of industrial heats, laboratory experiments, and physicochemical simulation and computation. The principles of control of steel purity in nonmetallic inclusions are formulated, and the main trends in the development of the concepts of nonmetallic inclusions are determined.     

Effects of test temperature on internal fatigue crack generation associated with nonmetallic particles in austenitic steels

Internal crack generation associated with nonmetallic inclusions or precipitates has been investigated on high-cycle fatigue at 4 K, 77 K, and 293 k of 25Mn-5Cr high-manganese austenitic steel and nitrogen-strengthened 25Cr-13Ni austenitic stainless steel. In both steels, the internal crack initiation typically occurred at 4 K or in long-life range over 10⁶ cycles at 77 K. Particles such as inclusions and precipitates were responsible for the internal crack-generation behavior, and the origins were identified as mainly Al₂O₃ inclusions in 25Mn-5Cr steel and AIN precipitates in 25Cr-13Ni steel, respectively. We discuss the crack-generation stage I mechanism and the relationship between stress range and size of crack-initiation site. The generation of fatigue cracks associated with the nonmetallic particles in the specimen interior involved a stage I crack. A threshold condition assumption was proposed, that the crack propagation occurred at any stress level when the local stress intensity factor range reached over a constant at or around the initiation crack associated with defects.     

Prevention of overgrowth on submerged nozzles during casting of steel deoxidized by aluminum

An initial reaction layer forms on the submerged entry nozzles; this layer is followed by bulk deposits that primarily contain endogenous alumina and steel inclusions. It would therefore be of some interest to prevent the formation of this initial layer opposite the refractory wall of the submerged nozzle. The presence of carbon and SiO₂ on the surface of the nozzle facilitates formation of a loose layer of alumina deposits. Refractories with various coatings were tested in contact with nonmetallic inclusions, liquid steel, and synthetic slag. It was found that a coating of pure alumina or ZrO₂ reduces overgrowth on the submerged nozzles and shows high chemical resistance to liquid steel.     

Nonmetallic inclusions in important steels

The contamination of 30Cr2Ni4MoV rotor steel with exogenous nonmetallic inclusions is studied. Technological measures intended to decrease the level of contamination of the steel with nonmetallic inclusions and to enhance its quality are recommended.     

Fracture toughness of calcium-modified ultrahigh-strength 4340 steel

Commercial and low-sulfur 4340 steels have been studied to determine the effect of calcium treatment on modifying the morphology of nonmetallic inclusions and plane-strain fracture toughness (K _IC ) of the ultrahigh-strength, low-alloy steels at commercial heat level. The significant conclusions are as follows: (1) for the low-sulfur 4340 steel, the addition of calcium in the molten steel gave rise to the formation of finely distributed, spherical, calcium-sulfide (CaS) inclusions with a mean diameter of 1.3 μm; (2) in comparing the calcium-modified 4340 steel with commercial 4340 steel, the calcium-modified steel not only had an improvedK _IC by about 25 MPa•m^1/2 in the longitudinal (L) orientation and by about 30 MPa • m^1/2 in the transverse (T) orientation, but also had increased fracture ductility and Charpy impact energy at similar strength levels; and (3) for the commercial 4340 steel, the calcium treatment was not very effective in modifying the morphology of the inclusions on improving the mechanical properties of the steel. The beneficial effect of calcium modification coupled with low sulfur content on theK _Ic is briefly discussed in terms of a crack extension model involving the formation of voids at the inclusion sites and their growth and eventual linking-up through the rupture of the intervening ligaments by localized shear.     

氧化物冶金技术应用及进展

氧化物冶金是利用钢中细小非金属夹杂物诱导晶内铁素体形核细化晶粒的新技术。应用氧化物冶金技术已成功开发出了高强度高韧性的非调质钢和低碳钢。文章讨论了氧化物冶金类型钢的显微组织特征,分析了钢中非金属夹杂物的性质和晶内铁素体的形核机理,简述了氧化物冶金技术的应用前景。利用钢中细小的氧化物,通过促进晶内针状铁素体形核明显改善焊接热影响区的组织,成为大线能量焊接用钢有效的技术途径。     

钢中液态夹杂物聚并行为的数学物理模拟

基于相似原理,采用水模拟钢液,用有机试剂模拟钢液中液态非金属夹杂物,同时采用数值仿真方法共同研究了夹杂物种类、两相间界面张力及黏度对于液滴聚并过程的影响规律.结果表明,夹杂物液滴间的聚合趋势与其自身的物理性质有紧密联系,其中液滴相与连续相之间的界面张力会促进其相互聚并,而液滴相的黏度则正相反,在液滴聚并过程中起抑制作用.因此,通过改变液态夹杂物与高温钢液之间的界面参数以及黏度参数,有望达到聚合或分散的控制目标,进而实现夹杂物尺寸的灵活控制.      

Study of the Effect of Process Parameters in Steel Production on the Content of Corrosion-Active Nonmetallic Inclusions in Corrosion-Resistant Pipes

The main reason for the accelerated local corrosion of tubes is contamination of the steel by corrosion-active nonmetallic inclusions (CANI), which determine the metallurgical properties of tube steel in terms of their corrosion resistance. Studies have shown that there are two main types of corrosion-active nonmetallic inclusions: CANI₁ — inclusions based on calcium aluminates; CANI₂ — complex inclusions that contain calcium sulfide. In order to master to production of tubes of steel 20-PKS at the Volga Pipe Plant (VTZ), a study was made of the effect of the parameters of out-of-furnace treatments on the contamination of steel by CANI. 1. The mechanisms and main sources of formation of CANI in tube steels made by the VTZ were determined. The main reasons for the formation of CANI₁ in furnace slag containing thermodynamically active CaO are mixing of the metallic and slag phases during the argon blow and the simultaneous introduction of additions to correct the chemical composition of the steel. Inclusions of the CANI₂ type may be formed by deoxidation operations carried out with suboptimal proportions of added aluminum and calcium (lime). 2. The following measures are recommended to ensure that steel 20-PKS made by the VTZ is clean with respect to both types of CANI: • optimize the composition of the ladle slag (increase the average content of Al₂O₃, increase the average content of SiO₂ as much as possible, and in any case decrease the average concentration of CaO); • keep the mass ratio of added CaO to added Al within the range 1.5–2; • continue the argon blow done after addition of the last batch of ferroalloys for at least 15–20 min; • ensure that the intensity of the blow is at least 0.5–1.5 m³/min. 3. Vacuum-degassing steel in the ladle after treatment on a ladle-furnace unit makes it possible to distribute the CANI more uniformly over the volume of the steel. __________ Translated from Metallurg, No. 7, pp. 38–42, July, 2005.     

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。