Interaction of metal matrix with nonmetallic inclusions in rail steel

The stress at the boundary between nonmetallic oxide inclusions and the matrix may be calculated, for different loads, by simulation of the system consisting of the matrix and inclusions. On that basis, the nonmetallic inclusions may be ranked in terms of the risk of contact-fatigue defects. The phase composition and geometry of the nonmetallic inclusions in rail steel are determined by the reduction of the rail steel and are extremely important for high rail performance.     

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.     

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。     

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。     

大型转炉过程精确控氧技术

转炉冶炼中的氧是产生钢中夹杂物的根源,对钢的洁净度有着不利的影响。为了加强转炉氧含量的控制,提高产品的内在质量,通过对宣钢转炉冶炼特殊钢现场试验研究,分析了转炉氧含量的分布状态,研究了氧活度、氧电势、炉渣厚度等因素对氧含量的影响规律,并提出了降低转炉氧含量的措施。     

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.      

37Mn5钢管内壁鳞片状缺陷原因分析及改进措施

针对37Mn5钢管生产过程中,管坯穿管后钢管内壁出现大量鳞片状缺陷的情况,采用宏观观察、化学分析、微观分析等方法对鳞片状缺陷产生的原因进行研究。结果表明,37Mn5钢管内壁存在多种大型夹杂物,管坯在进行穿管时,随着管壁厚度的减小,夹杂物会导致钢管内壁产生鳞片状缺陷。采取减少钢中大型夹杂物含量等改进措施后,钢管内壁鳞片状缺陷明显减少。     

非铝脱氧GCr15轴承钢的夹杂物演变和控制

铝脱氧轴承钢中常含有较多的D类、Ds类夹杂物,对轴承钢的疲劳性能影响较大.为了减少这类夹杂物,国内某钢厂采用低碱度渣、非铝脱氧的新冶炼思路冶炼轴承钢.对冶炼流程进行了过程取样,使用电镜、夹杂物自动分析系统等方法对夹杂物进行了表征,并研究了夹杂物的演变机理.研究表明,这种轴承钢中的全氧质量分数达到0.000 6％?0.0...     

电渣重熔钢中非金属夹杂物含量及成分的控制

在电渣重熔过程中，控制自耗电极冶炼的脱氧制度并配合电渣重熔渣系的选择，可以有目的地控制电渣重熔钢中非金属夹杂物的含量和成分。对于滚珠轴承钢ＺＧＣｒ１５，当自耗电极用钢采用Ｓｉ－Ｆｅ、Ｓｉ－Ｃａ脱氧并用酸性渣重熔可以获得最佳精炼效果，使钢中夹杂物转变为硅酸盐类塑性夹杂物。上述结论在工业生产中已得到验证。     

Effect of liquid–solid pouring on the as-cast structure and the distribution of nonmetallic inclusions in a 24.2-t steel 38KhN3MFA ingot

The primary dendrite structure and the distribution of nonmetallic inclusions in large-scale 24.2-t forging ingots of 38KhN3MFA steel cast by a standard technology and with the inoculation of a metallic stream are studied. The dendrite parameter in the inoculated ingot is found to be significantly smaller than that in the usual ingot. Therefore, the solidification process in the inoculated ingot should be faster than that in the usual ingot. This is confirmed by a more homogeneous dendrite structure of the inoculated ingot. The estimation of contamination with nonmetallic inclusions shows that nonmetallic inclusions in the ingots under comparison are of the same type, and among them are oxides, sulfides and oxysulfides. The study of the distribution of nonmetallic inclusions shows that the ingots to be compared are mainly contaminated with oxysulfide nonmetallic inclusions, and the contents of oxide and sulfide nonmetallic inclusions are minimal. The experimental ingot has lower total contamination with nonmetallic inclusions than that of the reference ingot. In this case, the inoculators having formed from a metallic melt stream do not favor an increase in the contamination of steel with nonmetallic (among them are oxide) inclusions. The study of the structure of large metal volumes shows that the inoculation of the stream is accompanied by an increase in the number of metallic droplets, which transform into solid particles in flight and increase the solidification rate when reach a solidifying ingot. This process suppresses the development of segregation phenomena in the cast metal and decreases the chemical and physical heterogeneities.     

Improving the production of pipe steel

Melts of pipe steel (strength class K52) obtained at the casting and rolling complex of AO OMK (a branch of AO OMK-Stal’) are analyzed. The initial data correspond to a set of 30 melts. The production system includes batch preparation, steel production in an arc furnace, treatment in a ladle–furnace unit, vacuum treatment (with microalloying and modification), hot rolling, and cutting of the rolled steel into sheet and strip. The basic factors affecting steel quality are identified. The rejection of the steel produced is mainly due to brittle and undeformable nonmetallic silicate inclusions. Changes in the process so as to reduce the content of nonmetallic silicate inclusions are recommended.     

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.     

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.     

Eliminating corrosive nonmetallic inclusions from pipe steel

Measures to optimize the production of corrosion-resistant steel have been introduced at OAO Severskii Trubnyi Zavod. They ensure that the steel’s content of corrosive nonmetallic inclusions of the first and second type is no more than 2 mm^?2. The measures were developed on the basis of research on the morphology and composition of nonmetallic inclusions and their formation and also current concepts regarding the formation and removal of corrosive nonmetallic inclusions.     

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。      

国内外气门弹簧钢54SiCr6中氧化物夹杂控制分析

通过对国内外钢厂生产的气门弹簧钢54SiCr6中氧化物夹杂的尺寸和成分的对比分析,发现国内A厂在氧化物夹杂尺寸上控制得较好,但塑性与国外钢厂相比,存在一定的差距。其主要原因是氧化物夹杂中Al2O3含量过高,在冶炼过程中采取以一些措施,降低钢水中的AlS含量,可以提高氧化物夹杂的塑性。     

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.     

Development of a slag system for the assimilation of titanium nitrides in casting austenitic stainless steel. Part 3

The variation in nitrogen content in austenitic stainless steel during smelting is investigated. A slag composition is proposed for the assimilation of titanium inclusions from the stainless steel. Experiments show that slag in the CaO-SiO₂-MgO-Al₂O₃-TiO₂ system is able to absorb up to 14.1% of the titanium oxides in the tundish, with corresponding decrease in the content of nonmetallic inclusions in the steel.     

用酸溶法研究钢中超细氧化物夹杂的三维形貌

 钢中超细氧化物夹杂对提高钢材性能有重大意义。介绍了用稀盐酸溶解铁基体后，利用配有特殊滤膜的专用溶剂过滤器，将钢中某些非金属夹杂物与溶液分离的方法。利用带有EDS(Energy Dispersive Spectrometer)的扫描电镜(SEM)对夹杂物形貌进行了观察。结果表明，该方法可以把耐酸的超细氧化物夹杂从钢基体中提取出来，同时可以得到夹杂物的三维形貌、尺寸、化学成分等详细信息，是一种研究钢中超细氧化物夹杂的有效方法。     

Technology for out-of-furnace treatment of steel with the use of a new deoxidizer

A technology has been proposed for obtaining rolled plates with the use of calcium carbide instead of vacuum degassing. The technology makes it possible to obtain steel that is equivalent to vacuum-degassed steel with respect to the composition and quantity of nonmetallic inclusions and the quality of the finished plates. It is shown that the use of calcium carbide reduces the content of nonmetallic inclusions by a factor of roughly 1.5 compared to use of the standard technology without vacuum degassing. The percentage of hot-rolled plates rejected for defects detected in ultrasonic tests is also decreased.