316L and DSS 2205 suffer from pitting corrosion in a denitrification agent, NaClO2 solution, despite their excellent corrosion resistance and widespread utilization in plants. Herein, nitric acid passivation was successfully employed to enhance the corrosion resistance of 316L and DSS 2205 in 3% NaClO2 solution. The 3% NaClO2 solution, in which 316L and DSS showed the lowest corrosion rate, was chosen by electrochemically studying the effect of NaClO2 concentration on the steel's corrosion from a series of solutions containing 1%, 3%, 6%, and 10% NaClO2. The passive films with and without nitric passivation were investigated by chemical composition, electrochemical property, semiconductor behavior, and morphology observation analyses. The enhanced corrosion resistance of both 316L and DSS 2205 after nitric passivation was attributed to the Cr enrichment and decreased active area on the steel surface. The semiconductor property test and point defect model showed that both the reduced doping density and the decreased diffusivity contributed better resistance against ClO2- and Cl-. The passivated 316L showed better corrosion resistance according to electrochemical tests and potentially is an option to replace high-cost DSS 2205.

Rare earth La was introduced into 40Cr steel in industrial experiments to achieve the purpose of modifying inclusions. The impact of La on the inclusion modification was studied, and its influence on the solidification structure was further investigated. With adding 0.0023

Corrosion is an unavoidable issue that steel encounters during service; however, the generic methods employed for corrosion prevention often need high cost or preparation conditions. In this study, a facile chemical replacement deposition method was proposed to realize an anticorrosion superhydrophobic coating on a X80 steel surface. The growth mechanism of the rough structure and its impact on the wettability of the superhydrophobic coating were analyzed. The superhydrophobic coating, deposited for 50 s and modified for 30 min, achieved optimal electrochemical properties and a maximum water contact angle. The immersion test, in the saturated CO2 oilfield produced water, demonstrated the better corrosion resistance of superhydrophobic coating than X80 steel. Correspondingly, a kinetic corrosion model was established to analyze the anticorrosion mechanism. In summary, this method significantly improves the corrosion resistance of X80 steel and is attractive for other industrial fields.

Nb-microalloyed steels are widely used in construction engineering fields due to their excellent mechanical properties, but they face serious corrosion problems in service environments. Pitting corrosion is the severest form of corrosion, and the types of inclusions are the leading cause to induce pitting corrosion. A new strategy is proposed to enhance the corrosion resistance of steels by achieving a beneficial transformation of inclusions with Ce treatment. In this paper, two types of Nb-microalloyed steels (0% Ce and 0.0058% Ce steel) were prepared to study the modification effect on inclusions in industrial production. The spherical CaS center dot C(12)A(7) inclusions were modified to smaller ellipsoidal Ce2O2S inclusions, and the proportion of inclusions (0-2 mu m) increased significantly from 27 to 66%, while large inclusions (>6 mu m) disappeared. A kinetic model of inclusion evolution was established. The results of electrochemical tests indicated that the corrosion potential was positively shifted, and the corrosion current was reduced after Ce treatment. Additionally, the number of defects in the passivation film was decreased, and the corrosion resistance of the steel was significantly improved. The addition of Ce changed the types of inclusions and reduced the number of pitting nucleation points, which led to a remarkable reduction in the number and size of pitting pits. The mechanism of pitting corrosion induced by different types of inclusions was further investigated, and a pitting corrosion model was modeled based on the immersion experiments. Research results provide theoretical support for enhancing the corrosion resistance of steel.

Industrialized tests are conducted to produce 20MnTiB cold heading steel with varying Ce contents.A Vickers hardness tester,tensile tester,impact tester,optical microscope,and scanning electron microscope are used to study the deterioration of inclusions in the steel and observe the changes in microstructure and mechanical properties of the hot-rolled wire rod after Ce addition.The application mechanism of Ce is also analyzed.The results show that the S content in the molten steel decreases,and the cleanliness is significantly improved after the addition of 0.0025％Ce.The inclusions in the wire rod transform from large-sized and elongated Al2O3·MgO·CaO·CaS composite inclusions to small-sized and spherical CeAlO3·MgO·CaO·CaS composite inclusions.Concurrently,the long strips of MnS inclusions disappear.Thermodynamic calculations indicate that at 1839 K,the order of precipitation of different Ce inclusions is as follows:CeAlO3＞Ce2O3＞Ce2O2S＞CeO2＞Ce3S4＞Ce2S3＞CeS.This suggests that with a Ce mass fraction of 0.0025％,the most probable inclusions are CeAlO3.Considering that 20MnTiB cold heading steel contains B,Ti,and other hardenability elements,improper process control during hot rolling can easily lead to the formation of a bainite structure in the wire rod.This causes the mechanical strength of the wire rod to be higher than desired,leading to occasional cracking during late cold heading and significant wear on the cold heading mold.After the addition of Ce,the microstructure of the wire rod is refined,with an increased proportion of ferrite and a reduction in both the presence and size of granular bainite.Ferrite is a soft and tough phase,while bainite is a reinforcing phase.The reduction in granular bainite and the increase in ferrite contribute to a decrease in strength and hardness.Lower hardness and strength are beneficial for improving the cold heading performance of the wire rod.After Ce addition,the cold heading performance of the wire rod is improved to a certain extent.Additionally,the ambient-temperature impact toughness of the wire rod significantly increases from 31.7 to 52.3 J with the addition of Ce,an increase of 65.0％.This substantial increase in impact performance further enhances the cold heading performance of the wire rod.The reduction in hardness and mechanical strength,combined with the significant increase in impact properties,makes the rare-earth microalloyed hot-rolled wire rod more suitable for cold heading applications.These research results provide technical and theoretical support for the further development of new rare-earth microalloyed cold heading steels.

Magnesium-based biodegradable metal bone implants exhibit superior mechanical properties compared to biodegradable polymers for orthopedic and cardiovascular stents. In this study, MgZZC-x (x = 1, 1.2) alloys were screened by in vitro biocompatibility tests in three simulated body fluids under nontoxic conditions. The MgZZC-1 alloys with better biocompatibility were selected to predict the days required for complete degradation. The evolution of degradation products was analyzed, and the mechanism of formation of the product film was inferred. A degradation kinetic model was established to investigate the effect of MEM components on the degradation of the alloys. The results demonstrate that the proteins in MEM can greatly retard the degradation progress by attaching to the surface of MgZZC-1 alloys, which are predicted to degrade completely within 341 days. The carbonate and phosphate buffers were adjusted to pH in MEM solution, delaying the degradation of magnesium alloys. This process in MEM more accurately reflects the actual degradation in the body and is superior to that in Hanks and SBF solutions. This study will promote the application of biodegradable materials in clinical medicine.

To optimize the economic advantages and corrosion-resisting property of A572 Gr.65 steels, the inhibition effect of water-soluble imidazoline on the sample surface with rare earth was explored in a 3.5 wt % NaCl solution. In this paper, the mechanism of corrosion and the adsorptive behavior of water-soluble imidazoline inhibitors on A572 Gr.65 steels with 47 ppm of rare earth in saltwater solution were discussed, along with the establishment of the adsorption model. Achievements proposed that the inhibition efficiency of water-soluble imidazoline was as high as 95.73% at 80 mg L-1 dosage following an anodic-dominated mixed-type inhibition mechanism. Besides, the scanning electron microscopy and X-ray diffraction analysis revealed that the corrosion inhibitor resulted in a smoother and more stable rust layer with a significant reduction of the γ-FeOOH. Theoretical calculations confirmed that imidazoline formed a unimolecular layer adsorption film on the steel surface, exhibiting adherence to both Langmuir and Frumkin adsorption isotherms, involving physical and chemical adsorption.

The corrosion behavior of rare earth (RE) low-alloy steel in soil simulation solution was investigated by immersion test, electrochemical experiment, scanning electron microscopy, and X-ray diffraction, compared with Q450 weathering steel. The kinetics model of all steels in soil simulation solution was established. The pitting corrosion mechanism of nonmetallic and RE inclusions was discussed. The results revealed that the RE improved the corrosion resistance of low-alloy steel by modifying inclusions and promoting the formation of a dense protective film. The steel containing 0.0047% RE achieved the best corrosion resistance. The corrosion product layers were mainly composed of gamma-FeOOH, alpha-FeOOH, Fe3O4, and Fe(OH)(3). The results of the kinetic model showed that the dissolution of the anode was the restricted link of the whole process. The lowest apparent corrosion rate constant k of the sample containing 0.0047% RE was 2.359 x 10(-4) mu m/h in the soil simulation solution. The kinetic model could serve as a method to predict the service life of steel parts.

通过金相显微镜、扫描电子显微镜、拉伸和冲击试验等分析测试手段,研究了稀土Ce含量对SUS444 铁素体不锈钢夹杂物及室温力学性能的影响.结果表明,添加 0.008wt%～0.015wt%Ce可改变夹杂物的种类、形态和尺寸,可将大尺寸、不规则形状的SiO2 变质为小尺寸球形的Ce2O3 夹杂物,添加 0.008%Ce不足以使SiO2 完全变质,但添加0.015%Ce可实现夹杂物的完全变质.稀土Ce可细化不锈钢的显微组织,随Ce含量增加,不锈钢的抗拉强度提升,拉伸断口由韧-脆结合断裂完全转变成韧性断裂;冲击韧性显著提升,最高可提升至未添加Ce的 4.9 倍,冲击断口由脆性断裂向韧性断裂转变.综合考虑夹杂物和力学性能,不锈钢中Ce最优含量为 0.015wt%.

采用电化学工作站、SEM、XRD等技术研究了A572Gr.65钢在pH4～10之间的土壤模拟液中的腐蚀行为,探讨了酸性和碱性溶液对A572Gr.65钢耐蚀性能的影响.结果 表明:随着pH增大,A572Gr.65钢的极化电阻随之增加,且自腐蚀电位正移,自腐蚀电流密度减小,在碱性溶液中A572Gr.65钢表现出最佳的耐蚀性能.当溶液为酸性时,腐蚀产物主要为γ-FeOOH.高浓度的H+会促进感抗弧的产生,使A572Gr.65钢表面的钝化膜遭到破坏,并且H+在反应过程中会生成氢气,造成腐蚀产物的疏松,在此过程中阴极的析氢反应为整个过程的限制性环节;当pH为中性或碱性时,OH-会促进γ-FeOOH向更加致密的Fe3O4和α-FeOOH转化,致密的腐蚀产物会阻碍侵蚀性离子和溶解氧的扩散,从而保护基体.此时金属表面腐蚀活性点的形成以及阳极的溶解速度为整个过程的限制性环节.

为研究稀土(RE)对HRB500E高强抗震钢筋点蚀行为和耐腐蚀性能的影响,通过浸泡腐蚀和电化学腐蚀的方法探究了稀土对夹杂物溶解及基体电位的作用,通过扫描电镜和能谱仪对腐蚀前后的夹杂物进行表征和分析,并观察浸泡72 h后腐蚀产物的微观形貌.研究结果表明:未添加RE试样发生点蚀的原因是MnS夹杂物的溶解以及Al2O3-MnO-CaO复合夹杂物周围基体的溶解;添加RE试样发生点蚀的原因是REAlO3和REAlO3-MnS夹杂物的溶解,且REAlO3夹杂物可以延缓点蚀坑的形成;添加RE的试样浸泡72 h后,其形成的腐蚀产物更加致密;添加RE后基体腐蚀电位正移,腐蚀电流减小,试验钢的耐腐蚀性能增强.

工业化试验冶炼不同稀土含量的HRB500E抗震钢筋,采用光学显微镜(OM),扫描电镜(SEM)和能谱仪(EDS)等手段研究稀土对HRB500E抗震钢筋夹杂物、显微组织和力学性能的影响,并探究稀土对夹杂物变质和低温冲击韧性的作用机制.结果表明:添加0.0066％稀土可以有效降低钢中的S含量,钢中单独的长条状的MnS和大尺寸不规则形状的Al-Mn-O夹杂物消失,变质为小尺寸球状的REAlO3-MnS的复合夹杂物.抗震钢筋的显微组织细化,在保证拉伸性能的基础上,低温冲击韧性显著提升,-40℃冲击功由7.55 J提升至10.7 J,-60℃冲击功由5.60 J升至8.00 J,分别提高41.72％,42.86％.

研究了时效处理对含Gd的AZ31镁合金显微组织和力学性能的影响,通过SEM,EDS对合金的显微结构进行了表征.结果 表明,AZ31镁合金中添加Gd后,优先形成了高熔点的A12Gd相,抑制了Mg17Al12相的生成;且随Gd含量的增加铸态合金的显微硬度呈现先增加后减小的趋势.对AZ31-xGd合金进行时效硬度分析,由时效硬化曲线确定了最佳T6处理工艺(500℃,16 h)+(200℃,32 h).在时效过程中,A12Gd相从颗粒状变为针状,再转变为短杆状最后团聚变成块状.铸态和时效态合金的力学性能随Gd含量的增加呈先增加后减小的趋势,这是由于时效析出的Al2Gd相具有弥散强化和析出强化的作用.

In this study, the nucleation and growth kinetics behavior of aluminum (Al) were investigated in the Choline-chloride (ChCl)-urea deep eutectic solvent (DES) ionic liquids. The studies of cyclic voltammetric and chronoamperometry demonstrated that the electrodeposition process of Al was controlled by three-dimensional progressive nucleation and instantaneous nucleation. And the growth of nuclei is a diffusion-controlled process. The diffusion coefficient of Al ions was calculated at 343 K, that is, 1.773 × 10−10 cm2/s. The Al coating was obtained on the surface of the AZ31 magnesium alloy electrode under appropriate conditions. According to the surface morphology of the Al film, it could be inferred that the theoretical deposit thickness is similar to the actual thickness, and the apparent diffusion rate of Al ions is slower than the diffusion coefficient in the electrolytes. So, in the later deposition, lamellar Al along the diffusion direction were formed, and lamellar depleted Al zones existed around the big grain Al-rich region.

The effect of rare earth (RE) on inclusion in HRB500E steel was studied based on plant trials. The results showed that S decreased by 47.6% after 0.0059% RE treatment. In samples without RE treatment, the inclusions change from Al2O3-MnO to ellipsoidal Al2O3-MnO-CaO complex inclusion, and the size of such inclusions is ≤ 2 µm and isolated strip MnS inclusion with the size of ≥ 2 µm. With RE treatment, Al2O3-MnO-CaO inclusions are transformed into spherical or ellipsoidal REAlO3 and REAlO3-MnS. The size of such inclusions is ≈ 1.5 µm and single MnS inclusions were not found. The number density and size of inclusions changed significantly after RE treatment. Thermodynamic calculations show that the Gibbs free energy of RE inclusions is more negative and more stable. The transformation model of inclusions is established to illustrate the modification of inclusions during the smelting process.

The improvement of mixing conditions in vacuum refining unit plays an important role in enhancing the purity and decarburization of molten steel. A numerical simulation is established to calculate the transport and mixing process of tracers in a water model of Single‐Snorkel Refining Furnace. The results show that the transport process of tracer in water model consists of one main circulation stream (inside the ladle and the vacuum chamber) and two side circulation streams (inside the ladle). The injection of KCl tracer can enhance the downward stream velocity and the stream deviates to the axial center of the ladle. After a while (about 30 s), the downward stream gradually returns to the state when the tracer is not injected. The difference between the transport process of pure water tracer and KCl solution tracer is that the KCl solution tracer flows downward at a higher pace from the vacuum chamber to the bottom of the ladle and later disperses rapidly from the bottom to the nozzle‐located side wall of the ladle. The upward transport process of KCl tracer is slowed down due to the existence of “dead zone” at the bottom of the nozzle‐located side wall of the ladle.

以钢包水模型为研究对象,用数值模拟方法研究了两类三种示踪剂(数学示踪剂:被动标量,物理示踪剂:纯水和 KCl 溶液)在流场中的传输过程.结果表明,被动标量和纯水示踪剂的传输规律基本相同;相比前两者,密度大于水的示踪剂(KCl 溶液)较快地沿水模型中主循环流向水模型底部传输,并沿水模型底部向气柱和偏心侧区域运动,随后沿偏心侧壁面向上传输至小循环流,但由于偏心侧底部"死区"的存在,示踪剂在此区域停留时间较长,沿偏心侧壁面向上传输过程有所延缓;最终,从水模型中示踪剂质量分数纵截面图和监测点得到的混匀时间均表明,KCl 溶液示踪剂较快完成混匀过程.

采用光学显微镜、扫描电镜和显微硬度仪等研究了T4和T6热处理对Mg-2.5Zn-1.5Ca-0.22Zr镁合金显微组织及硬度的影响.结果 表明:Mg-2.5Zn-1.5Ca-0.22Zr镁合金经T4热处理之后,网状结构的β-Ca2Mg6Zn3相逐渐分解并转变为不规则的团聚的块状结构,MgZn2相逐渐溶解于α-Mg基体中,硬度比铸态时显著提高,达到63.87 HV;经过不同时间的T6热处理之后,MgZn2相从α-Mg基体中重新析出,球状的Mg2Ca中间化合物均匀的分布于晶粒内且发生明显长大.随着时效时间的延长,MgZn2相增多,对位错的钉扎增强,合金的硬度提高,在“峰时效”时的硬度达到64.97 HV.410 cc×24 h固溶处理后150℃×8h时效处理为Mg-2.5Zn-1.5Ca-0.22Zr镁合金的最佳热处理工艺.

Two aspects of ladle shroud design in tundish are studied. The two strand tundish is a long and bare tundish i.e. without flow control devices but stopper rods to control flowrate. The 3D CAD geometry, turbulence models, discretisation of governing equations, numerical solution and post processing are performed in a commercial software Siemens STAR CCM+. Compared to the typical pipe ladle shroud, the velocity of impinging stream from the ladle shroud is lower for the trumpet ladle shroud. As a result, the flow stream in the whole tundish shows a contradictory tendency, i.e. the upward stream is more obvious than the downward stream for trumpet shroud and vice visa for pipe shrouds. In industrial production, the ladle shroud often canted to the front wall due to machinery reasons. Therefore, two cases that the misalignment degree of the ladle shroud are 5 and 10 degrees are studied. The results show that the impinging stream flow towards the front side of walls and the flow towards the outlets near the bottom wall and front wall. The horse like vortex that is typically observed in bare tundishes is destroyed. The non-symmetric flow pattern is formed for the severely biased cases which should be paid more attentions from industrial practice.