Characterization of Iron Grains near the P/T Boundary in the Meishan Section of China

The Meishan section of China has been confirmed as the ＂Global Stratotype Section and Point＂ of the P/T boundary. In the section, the authors found several types of iron grains, including pyrite, pure iron grains and goethite. From the research of macro minerals, it is easy to find that the grains rich in iron appear from the bottom of the event layer of the section. In other words, it is probably residue of the geochemical catastrophe of that time. Therefore, it is important to trace the source of these iron grains and their relationships, which probably provides evidence for volcanic eruption or impact-volcanoes and has directive significance to the crisis during the P/T transitional period. Through the study of the characterization and relationships of these iron grains, the authors make a preliminary discussion on the P/T mass extinction.

Formation and characterization of metallic iron grains in coal-based reduction of oolitic iron ore

To reveal the formation and characteristics of metallic iron grains in coal-based reduction, oolitic iron ore was isothermally re- duced in various reduction times at various reduction temperatures. The microstructure and size of the metallic iron phase were investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and a Bgrimm process mineralogy analyzer. In the results, the re- duced Fe separates from the ore and forms metallic iron protuberances, and then the subsequent reduced Fe diffuses to the protuberances and grows into metallic iron grains. Most of the metallic iron grains exist in the quasi-spherical shape and inlaid in the slag matrix. The cumula- tive frequency of metallic iron grain size is markedly influenced by both reduction time and temperature. With increasing reduction temperature and time, the grain size of metallic iron obviously increases. According to the classical grain growth equation, the growth kinetic parameters, i.e., time exponent, growth activation energy, and pre-exponential constant, are estimated to be 1.3759 ± 0.0374, 103.18 kJ·mol^-1, and 922.05, respec- tively. Using these calculated parameters, a growth model is established to describe the growth behavior of metallic iron grains.

Shock-induced migration of asymmetry tilt grain boundary in iron bicrystal: A case study of Σ3 [110]

Many of our previous studies have discussed the shock response of symmetrical grain boundaries in iron bicrystals.In this paper, the molecular dynamics simulation of an iron bicrystal containing Σ3 [110] asymmetry tilt grain boundary(ATGB) under shock-loading is performed. We find that the shock response of asymmetric grain boundaries is quite different from that of symmetric grain boundaries. Especially, our simulation proves that shock can induce migration of asymmetric grain boundary in iron. We also find that the shape and local structure of grain boundary(GB) would not be changed during shock-induced migration of Σ3 [110] ATGB, while the phase transformation near the GB could affect migration of GB. The most important discovery is that the shock-induced shear stress difference between two sides of GB is the key factor leading to GB migration. Our simulation involves a variety of piston velocities, and the migration of GB seems to be less sensitive to the piston velocity. Finally, the kinetics of GB migration at lattice level is discussed. Our work firstly reports the simulation of shock-induced grain boundary migration in iron. It is of great significance to the theory of GB migration and material engineering.

Grain Coarsening of Hematite in the Gushan Iron Deposit,Anhui Province,China

The iron ores of the Gushan mine occur in the contact zone of a Mesozoic dioriteintrusion and are composed primarily of hematite microcrystallites and chalcedony. Thehematite microcrystallites have undergone post-mineralization recrystallization and coarseningwith resultant formation of lath-shaped hematite porphyroblasts. Microscopic investigation reveals that recrystallization and coarsening of the hematite ores of the Gushan mine took placewithout the formation of new nuclei, due to the coalescence of the microcrystallites. The wholeprocess could have begun with the mutual approach of the microcrystallites, followed by grainrotation to realize parallelism and ending by the welding of these grains to form optically homogeneous porphyroblastic hematite.

Reconstruction of three-dimensional grain structure in polycrystalline iron via an interactive segmentation method

Using a total of 297 segmented sections,we reconstructed the three-dimensional(3D) structure of pure iron and obtained the largest dataset of 16254 3D complete grains reported to date.The mean values of equivalent sphere radius and face number of pure iron were observed to be consistent with those of Monte Carlo simulated grains,phase-field simulated grains,Ti-alloy grains,and Ni-based super alloy grains.In this work,by finding a balance between automatic methods and manual refinement,we developed an interactive segmentation method to segment serial sections accurately in the reconstruction of the 3D microstructure;this approach can save time as well as substantially eliminate errors.The segmentation process comprises four operations:image preprocessing,breakpoint detection based on mathematical morphology analysis,optimized automatic connection of the breakpoints,and manual refinement by artificial evaluation.

Effect of Metallic, Nonmetallic, Water Cooled and Cryogenic Chills on Pearlite Content (PC), Eutectic Cell Count (ECC) and Grain Size (GS) of Hypo Eutectic Nickel Alloyed Cast Iron

This paper presents the results obtained, deductions made from solidification behaviour and a series of micro structural studies such as pearlite content, eu-tectic cell count and grain size of hypoeutectic gray cast iron which was sand cast (CO2 moulding) using metallic, nonmetallic, water cooled and subzero (cryogenic) end chills. Hypo-eutectic cast irons containing C 3.42, Si 2.4 and Ni 1.5 with impurity contents (S, P, Mn etc.) were solidified unidirectionally in an American Foundrymen Society (AFS) standard mould, the end of which was provided with different end chills to study the effect of chilling during solidifi-cation. The melts were inoculated with 0.3% Fe-Si to promote graphitization. It was observed that the transition from one structure to another is more gradual than normally obtained in the structure of cast irons solidified mul-ti-directionally in a sand mould at room temperature. Austenite dendrite interactions were shown to be a major factor in determining the microstructure, in which the higher dendrite reaction leads to changes in DAS, ECC and GS. It is observed that, the number of eutectic cells is an index of graphite nucleation and the effect of these on structure, since the eutectic cells are developed on the graphite nuclei during solidification.

脱碳退火温度对晶粒取向纯铁组织、织构及磁性能的影响

为促进晶粒纯铁制造过程获得更高的磁性能,以实验室自制晶粒取向纯铁冷轧板为研究对象,对其进行脱碳退火实验,利用金相显微镜、电子背散射衍射扫描电子显微镜、磁性能测量仪测试表征其组织性能,研究脱碳退火温度对晶粒取向纯铁初次再结晶组织、织构及高温退火样品磁性能的影响。结果表明:脱碳退火板中仍存在部分聚集分布的细小晶粒,多数集中在样品中心位置附近;脱碳退火2 min、退火温度为775,800℃时,部分聚集的细小晶粒导致平均晶粒尺寸分别为6.12,6.39μm,825℃时平均晶粒尺寸为6.85μm;不同温度脱碳退火板的主要织构类型基本相同,α取向线上主要织构分布在{112~223}<110>附近,γ取向线上主要织构分布在{111}<112>和{111}<110>附近,其中{111}<112>织构强度始终最高,其余织构强度随脱碳退火温度升高变化不大;825℃×2 min脱碳退火时,成品板表现出最佳的磁感应强度,其中B_(800)为2.00 T,B_(10000)为2.13 T;成品中存在“孤岛”,织构类型为{110}<112>~<115>,“孤岛”的产生与均热温度较低有关,铸锭中的抑制剂质点没有完全固溶,抑制能力不足,在高温退火过程中导致{110}<112>~<115>位向的晶粒不同程度长大。“孤岛”的存在侧面表明晶粒取向纯铁的磁感应强度有进一步提升的空间。

自蔓延燃烧合成高氮氮化钒铌铁合金的工艺

自蔓延燃烧合成技术是依靠反应自身放热来合成材料的新技术,不需外加热源,设备简单,工序简洁。承德锦科科技股份有限公司利用此技术成功开发了氮化钒铁、氮化钒硅铁、氮化铌铁等专利产品。本文在常规自蔓延燃烧合成技术基础上,通过优化原料配比、原料粒度级配、氮气压力和稀释剂配加量等关键技术,成功开发出了高氮氮化钒铌铁新型合金FeV_(30)Nb_(4)N_(14)。该合金N/(V+Nb)比值达到0.4以上,微合金化过程能充分发挥钒的析出强化和铌的细晶强化作用。使用该合金制备的微合金化钢筋HRB600E的抗拉强度800~855MPa、延伸率16%~18%、正反弯性能均合格,力学性能符合抗震要求;晶粒度等级达到10.5级以上;V平均含量为0.105%,比常规钒氮合金+铌铁复合微合金化工艺的0.140%降低了0.035个百分点,节约钒消耗25%,吨钢成本降低50.5元,为钢企创造了显著的经济效益。

激光刻痕降低取向硅钢铁损的研究现状

激光刻痕是降低取向硅钢铁损的有效手段,也是目前唯一在工业生产中得到广泛应用的刻痕技术。本文列举了细化取向硅钢磁畴的各种技术及其优缺点,综述了激光刻痕系统的种类和特点及其研究现状,并对激光刻痕技术的发展进行了展望。

微细粒金银铁难处理多金属氧化矿工艺流程改造及生产实践分析

微细粒金银铁矿物是一种重要的贵金属材料,广泛应用于冶金、化工、石油等领域。难处理多金属氧化矿的制备一直是困扰微细粒金银铁回收工艺发展的主要问题之一。目前国内外对微细粒金银铁复杂难选矿石进行了大量研究,并取得一定进展。本文主要对微细粒金银铁难处理多金属氧化矿工艺流程改造及生产实践进行研究,以供参考。

施用铁基生物炭后镉污染稻田土壤有效镉及有机碳的变化

为了实现镉污染稻田减污固碳的现实需求,以铁基生物炭为研究对象,通过大田试验,采集了土壤和水稻子粒样品,分析了土壤有效镉含量、有机碳含量与子粒镉含量及其相关性。结果表明,与对照相比,铁基生物炭降低了稻田土壤有效镉含量,降幅为11.98%~28.71%;铁基生物炭提高了土壤有机碳含量,增幅为3.66%~12.88%;铁基生物炭降低了水稻子粒镉含量,降幅为4.16%~63.58%。土壤有效镉含量与土壤有机碳含量呈极显著负相关(P<0.01),与水稻子粒镉含量呈极显著正相关(P<0.01)。因此,铁基生物炭有利于实现镉污染稻田降镉固碳。

MODELING OF FERRITE GRAIN GROWTH OF LOW CARBON STEELS DURING HOT ROLLING

For most commercial steels the prediction of the final properties depends on accurately calculating the room temperature ferrite grain size. A grain growth model is proposed for low carbon steels Q235B during hot rolling. By using this model, the initial ferrite grain size after continuous cooling and ferrite grain growing in coiling procedure can be predicted. In-plant trials were performed in the hot strip mill of Ansteel. The calculated final ferrite grain sizes are in good agreement with the experimental ones. It is helpful both for simulation of microstructure evolution and prediction of mechanical properties.

Development of top high-grade non-grain-oriented silicon steels at Baosteel

The development, production and application of top high-grade non-grain-oriented （NGO） silicon steels at Baosteel were introduced in this paper. Top high grades refer to the highest grades in the intemational silicon steel product standard and above. B35A230 and B50A250 were developed at Baosteel in 2009 and have been used in inverter compressors for air-conditioners, small transformers and big hydropower generators in the Three Gorges project. Small- batch production of B35A210 and B50A230, which exceed the highest grades listed in the intemational silicon steel product standard,began in 2010. That was a breakthrough in the silicon steel making history in China. Presently,Baosteel＇ s high- grade NGO products have passed the strict qualifications of the three major electric power equipment manufacturers in China and the leading international power equipment suppliers like ALSTOM, GE, SIEMENS, VESTAS, etc. These products are characterized by low iron loss, low anisotropy, good punchability and a high lamination factor. They have been used in the 770 MW hydropower generator at Xiluodu Power Station in the three gorges area, 1 000 MW thermal power generators and 2.5 MW wind power generators.

Laser Surface Remelting of Medium Ni-Cr Infinite Chilling Cast Iron Roll

Laser surface remelting of medium Ni-Cr infinite chilling cast iron was performed with a continuous wave COa laser beam with the power of 7 KW under the argon shielding. The microstructural analysis of the laser remelted layer by optical microscope shows that the laser remelted layer consists of three zones, which is the melting zone, the transition zone and the heat affected zone. The size of the dendrite of the melting zone is only in the 1/10 to 1/30 range of that of the substrate. The distribution of the hardness of the laser remelted layer was detected, and the carrying capacity of rolling steel was also field-tested. The results show that both the hardness of the remelted layer and the carrying capacity all increase, especially, the carrying capacity was 50% increased compared with the substrate.

Enhancement of ductility and improvement of abnormal Goss grain growth of magnetostrictive Fe–Ga rolled alloys

The influences of initial microstructures on the mechanical properties and the recrystallization texture of magnetostrictive 0.1 at% Nb C-doped Fe83 Ga17 alloys were investigated. The directionally solidified columnar-grained structure substantially enhanced the tensile elongation at intermediate temperatures by suppressing fracture along the transverse boundaries. Compared with tensile elongations of 1.0% at 300℃ and 12.0% at 500℃ of the hot-forged equiaxed-grained alloys, the columnar-grained alloys exhibited substantially increased tensile elongations of 21.6% at 300℃ and 46.6% at 500℃. In the slabs for rolling, the introduction of 〈001〉-oriented columnar grains also promotes the secondary recrystallization of Goss grains in the finally annealed sheets, resulting in an improvement of the saturation magnetostriction. For the columnar-grained specimens, the inhomogeneous microstructure and disadvantage in number and size of Goss grains are improved in the primarily annealed sheets, which is beneficial to the abnormal growth of Goss grains during the final annealing process.

高性能钕铁硼永磁晶界扩散技术最新进展与未来展望

钕铁硼永磁在新能源等战略新兴领域有着广阔的发展前景。应用端的发展对钕铁硼磁体的高温性能和矫顽力提出了更高的要求。晶界扩散技术是烧结钕铁硼磁体的一项重大进展。它主要将重稀土元素或稀土合金以晶界扩散的方式渗透入磁体内部,通过强化硬磁相晶粒表面的薄弱区域,在有效提高磁体矫顽力的同时,大大减少了重稀土的用量,减小了重稀土对剩磁和磁能积的不利影响,显著降低了材料成本。自本世纪初发展至今,晶界扩散技术已迅速实现了工业化。最近几年,晶界扩散在理论和技术层面都有了较大的发展和创新。目前通过晶界扩散技术,烧结磁体的最大磁能积(MGOe)+内禀矫顽力(kOe)已达75以上。基于近期国内外的产业现状和研究前沿,总结了近年来扩散剂、扩散剂包覆技术、扩散方法、选区扩散和扩散基材的最新进展,并对晶界扩散的未来发展进行展望,为高性能钕铁硼永磁体的研发提供参考。

Effect of ball milling time on microstructures and mechanical properties of mechanically-alloyed iron-based materials

The microstructures and mechanical properties of an iron-based alloy (Fe-13Cr-3W-0.4Ti-0.25Y-0.30O) prepared by mechanical alloying were investigated with scanning electron microscope,optical microscope,X-ray diffractometer and hardness tester.The results show that the particle size does not decrease with milling time because serious welding occurs at 144 h.The density of the alloy sintered at 1 523 K is affected by the particle size of the powder.Finer particles lead to a high sintered density,while the bulk density by using particles milled for 144 h is as low as 70%.In the microstructures of the annealed alloy,large elongated particles and fine equiaxed grains can be detected.The elongated particle zone has a higher microhardness than the equiaxed grain area in the annealed alloys due to the larger residual strain and higher density of the precipitated phase.

京唐1号高炉风口熔损机理解析

对京唐1号高炉下线风口的不同熔损部位进行取样分析,重点探讨了风口熔损机理。利用光学显微镜对风口熔坑进行了三维形貌重建,发现风口表面的熔损区面积大,深度深,表明熔损对风口具有巨大的破坏作用。通过对下线风口铜的导电导热性能测试和金相分析,以及对风口熔损区进行微观分析,揭示了风口熔损机理,即:使用后的风口导热性变差,熔损部位的铜晶粒粗大且不均匀,在冷却不足前提下,风口表面受到热冲击形成导热性更差的铜-铁合金,并与渣铁不断黏结,铜-铁结合处熔化脱落时,造成铜的损失同时暴露出内部的新铜,如此往复直至风口熔穿。

某多金属选矿厂选锡工艺优化

某矿山锌、铜、锡、铁、硫多金属选矿厂开展锡石选别工艺优化,在优先回收70%的铜金属,90%的锌金属,在除铁硫后,原矿含锡品位为0.21%,铜、锌、铁、硫中锡已经带走20%的前提下,锡指标提升5个百分点,经济效益显著。

响应曲面法优化细粒铁尾矿浆絮凝沉降试验研究

针对细粒铁尾矿浆难以沉降的特点,采用响应曲面法优化细粒铁尾矿浆絮凝沉降条件。根据Design-Expert 8.0软件中的Box-Behnken试验方法设计三因素三水平试验,得到细粒铁尾矿浆絮凝沉降浊度模型的回归方程,结果表明,适宜的絮凝沉降条件为:无机絮凝剂FeCl3用量113.44 mg/L、有机絮凝剂PAM用量0.61 mg/L、搅拌速度440.57 r/min,在该条件下进行絮凝沉降,预测矿浆浊度11.45NTU,实测矿浆浊度12.38NTU,结果误差较小,模型准确度较好。结合模型方差分析、可信度分析、因素相互作用分析,证实采用响应曲面法优化细粒铁尾矿浆絮凝沉降条件合理可行,可为细粒铁尾矿浆的高效处理提供理论依据。