Effect of Rare Earth on Microstructures and Properties of High Speed Steel With High Carbon Content

The effects of rare earth （RE） on the microstructures and properties of high carbon high speed steel （HCHSS） were investigated. The results show that when suitable RE is added to the HCHSS, the effect of RE on the austenite and eutectic carbides is obvious. The austenite grain and coarse eutectic structure are refined, and flake carbides in the eutectic structures become short and fine. After heat treatment, most of the eutectic carbides are spheroidized and distributed in a uniform manner. The hardness and red hardness of modified HCHSS are slightly increased; impact toughness is greatly increased by 37.81% and reaches 10.17 J/cm^2. The mechanism by which RE improves the structures and properties of HCHSS is also analyzed.     

Effect of RE-Modifier on Microstructure and Mechanical Property of High-Carbon Medium-Manganese Steel

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Influence of rare earth nanoparticles and inoculants on performance and microstructure of high chromium cast iron

The high chromium cast irons (HCCIs) with rare earth (RE) nanoparticles or inoculants were fabricated in the casting process. The phase compositions and microstructure were analyzed by X-ray diffraction (XRD) and optical microscopy (OM), respectively. The hardness and impact toughness were tested by Rockwel-hardmeter and impacting test enginery. And then, the morphology of fracture was researched by scanning electron microscopy (SEM). The results demonstrated that the phase compositions of HCCIs with addition of RE nanoparticles or inoculants which were M7C3 carbides + α-Fe did not change obviously. However, the prime M7C3 carbides morphology had great changes with the increase of RE nanoparticles, which changed from long lath to granular or island shape. When the content of RE nanoparticles was 0.4 wt.%, the microstructure of high chromium cast iron was refined greatly. The microstructure of carbides was coarser when the addition of RE nanoparticles was higher than 0.4 wt.%. The hardness and impact toughness of HCCIs were improved by addition of RE nanoparticles or inoculants. The impact toughness of HCCIs was increased 36.4% with RE nanoparticles of 0.4 wt.%, but the hardness changed slightly. In addition, the adding of RE nanoparticles or inoculants could reduce the degree of the brittle fracture. Fracture never seemed regular, instead, containing lots of laminates and dimples with the increase of the RE nanoparticles. The results also indicated that the optimal addition amount of the RE nanoparticles was 0.4%, under this composition, the microstructure and mechanical property achieved the best cooperation. In addition, through the study of erosion wear rate, when adding 0.4% RE nanoparticles into the HCCIs, the erosion wear rate got the minimum 0.32×10-3 g/mm2, which could increase 51.5% compared with that without any RE nanoparticles.     

电解过程中非稀土杂质的行为

研究了氟化物体系熔盐电解制备电池用稀土金属时非稀土杂质的行为,并进行了理论分析。结果表明,杂质离子的放电行为受其在电解质熔盐中的结合状态影响：电位较ＲＥ３＋ 正的杂质离子优先放电进入金属中,这些离子在电解质中的含量较低;电位较ＲＥ３＋ 负的杂质离子难于放电析出,主要积累于熔盐中;Ｃ通过形成碳化稀土和物理溶解两种方式进入稀土金属,选择合理的工艺条件可获得Ｃ含量较低的稀土金属。     

Effect of Rare Earth Element on Formation and Propagation of Thermal Fatigue Crack in Low-Chromium Semi-Steel

The formation and growth of thermal fatigue crack in low chromium semi steel were investigated by means of optical microscope and scanning electron microscope, and the function of RE in low-chromium semi steel was analyzed. The results show that the thermal fatigue cracks are mainly generated at eutectic carbides, and the cracks not only grow and spread but also join each other. RE can improve the eutectic carbide‘s morphology, inhibit the generation and propagation of thermal fatigue cracks, and therefore promote the activation energy for the crack‘s propagation, which is especially more noticeable in case of the RE modification in combination with heat treatment. The mathematical model of the crack propagation is put forward.     

On the Spheroidized Carbide Dissolution and Elemental Partitioning in High Carbon Bearing Steel 100Cr6

We report on the characterization of high carbon bearing steel 100Cr6 using electron microscopy and atom probe tomography in combination with multi-component diffusion simulations. Scanning electron micrographs show that around 14 vol pct spheroidized carbides are formed during soft annealing and only 3 vol pct remain after dissolution into the austenitic matrix through austenitization at 1123 K (850 °C) for 300 seconds. The spheroidized particles are identified as (Fe, Cr)₃C by transmission electron microscopy. Atom probe analysis reveals the redistribution and partitioning of the elements involved, i.e., C, Si, Mn, Cr, Fe, in both, the spheroidized carbides and the bainitic matrix in the sample isothermally heat-treated at 773 K (500 °C) after austenitization. Homogeneous distribution of C and a Cr gradient were detected within the spheroidized carbides. Due to its limited diffusivity in (Fe, Cr)₃C, Cr exhibits a maximum concentration at the surface of spheroidized carbides (16 at. pct) and decreases gradually from the surface towards the core down to about 2 at. pct. The atom probe results also indicate that the partially dissolved spheroidized carbides during austenitization may serve as nucleation sites for intermediate temperature cementite within bainite, which results in a relatively softer surface and harder core in spheroidized particles. This microstructure may contribute to the good wear resistance and fatigue properties of the steel. Good agreement between DICTRA simulations and experimental composition profiles is obtained by an increase of mobility of the substitutional elements in cementite by a factor of five, compared to the mobility in the database MOBFE2.     

钢中稀土微合金化作用与应用前景

低氧硫钢中室温下稀土固溶量达10-5～10-4,MnS夹杂完全变质后,稀土固溶量显著增加,酸溶铝,Nb,Ti均有利于提高钢中稀土固溶量.固溶稀土偏聚在晶界,减少硫、磷在晶界的偏析,渗碳体中固溶稀土多于铁素体.稀土和碳相互作用,减少珠光体数量、珠光体片间距和渗碳体厚度,细化珠光体组织,提高硬度.稀土对钢的强度影响具有两面性,稀土能提高锰碳钢的屈强比和有利于改善低合金高强度钢的强韧性.稀土在低合金高强度钢中有广泛的应用前景,发展具有中国资源优势的稀土微合金钢有重要的意义.     

稀土在BNbRE重轨钢中的作用机制

通过化学分析、金相观察和理论分析,研究了稀土在BNbRE重轨钢中的存在状态和含量的变化规律,以及它对钢的硫化物夹杂、微观组织和性能的影响机制。研究发现,对于BNbRE重轨钢,加入大量的稀土并不能增加钢中固溶稀土的含量,固溶稀土的含量均保持在0．0012％以下。少量的固溶稀土可以细化BNbRE重轨钢的奥氏体晶粒和珠光体片层结构。在本实验条件下,BNbRE重轨钢的最佳稀土加入量约为0．02％,此时BNbRE重轨钢的塑性和冲击韧性得到显著提高。     

发展稀土钢提高包钢油井管竞争力

参考资料回顾了稀土在钢中应用的发展历史,总结了稀土在钢中的作用,阐述了区分“稀土处理钢”与“稀土钢”的概念对于更加强调微合金化作用的稀土钢开发具有方向性的意义。探讨性地提出了包钢发展稀土钢油井管的思路及前景。     

稀土对低碳钢耐工业大气腐蚀性的影响

研究了在江津地区暴晒2年低碳钢和稀土钢的大气腐蚀行为。结果表明:稀土可以有效提高低碳钢耐工业大气腐蚀性,试验钢的腐蚀数据符合动力学模型D=Atn。采用扫描电镜、极化曲线、XRD及Fourier变换红外光谱等手段对腐蚀产物进行研究。发现稀土能促进稳定的保护性腐蚀产物α-FeOOH生成,降低锈层中具有反应活性的Fe3O4含量;并可以增加锈层致密性。从锈层反应的角度阐述了稀土提高低碳钢耐蚀性的机理。     

Carbon Redistribution and Carbide Precipitation in a High-Strength Low-Carbon HSLA-115 Steel Studied on a Nanoscale by Atom Probe Tomography

HSLA-115 is a newly developed Cu-bearing high-strength low-carbon martensitic steel for use in Naval structural applications. This research provides, for the first time, a comprehensive compositional analysis of carbon redistribution and associated complex phase transformations in an isothermal aging study of HSLA-115 at 823 K (550 °C). Specifically, we characterize carbon segregation at lath boundaries, grain-refining niobium carbonitrides, cementite, and secondary hardening M₂C carbides, in addition to copper precipitation, by 3D atom probe tomography (APT). Segregation of carbon (3 to 6 at. pct C) is observed at martensitic lath boundaries in the as-quenched and 0.12-hour aged microstructures. On further aging, carbon redistributes itself forming cementite and M₂C carbides. Niobium carbonitride precipitates do not dissolve during the austenitizing treatment and are inherited in the as-quenched and aged microstructures; these are characterized along with cementite by synchrotron X-ray diffraction and APT. Sub-nanometer-sized M₂C carbide precipitates are observed after the formation of Cu precipitates, co-located with the latter, indicating heterogeneous nucleation of M₂C. The temporal evolution of the composition and morphology of M₂C carbides at 823 K (550 °C) is described using APT; their precipitation kinetics is intertwined with Cu precipitates, affecting the bulk mechanical properties of HSLA-115. Phase compositions determined by APT are compared with computed compositions at thermodynamic equilibrium using ThermoCalc.     

Behaviors of Lanthanum and Cerium on Grain Boundaries in Carbon Manganese Clean Steel

The behaviors of La and Ce on gram boundaries in carbon manganese clean steel were investigated by high-reso- lution transmission elecetron microscope （HRTEM）, scanning elecetron microscopy（SEM ）, energy dispersive spectrometer （EDS） and X-ray diffraction（XRD） analysis. The existing forms of rare earths （RE） in clean steel were as follows： dissolved in sohd solution, forming inclusion or second phase containing RE （RE-Fe-P, La-P, Fe-La eutectic and Fe-Ce phase）. The dissolved La or Ce segregated at grain boundaries. The segregation of both S and P at gram boundaries was reduced with suitable RE content. The impact toughness of the steel was improved obviously. La and Ce had effecets on purifying molten steel and modifying inclusions in clean steel, whereas with excessive La or Ce, La-Fe-P, La-P and Fe-La eutecetic phase or Ce-Fe-P and Fe-Ce intermetallic compound would form along grain boundaries, causing the impact energy to decrease significantly.     

四川稀土精矿与包头稀土精矿在冶炼稀土硅铁合金过程中的差异性

本文着重介绍了在冶炼稀土合金时 ,使用四川冕宁矿与包头稀土精矿在实际生产中的差异性 ,并分析了原因 ,从经济效益角度粗略探讨它们使用的合理性。     

标准加入原子吸收分光光度法测定高纯稀土产品中的微量钙

针对高纯稀土产品中微量钙的测定进行了试验。通过试验,确定了仪器最佳工作条件,用盐酸和硝酸分解试样,并采用标准加入原子吸收分光光度测定,满足了产品分析质量要求。     

Effect of rare earth addition on continuous heating transformation of a high speed steel for rolls

The effect of rare earth(RE) on continuous heating transformation of a high speed steel for rolls was investigated by using differ-ential scanning calorimetry(DSC) with combination of microstructure analysis.Determination of the Ac1 and Ac3,the starting temperature of carbide dissolution and melting upon heating,the enthalpy change for the α→γ transformation and overall carbide dissolution were also es-tablished.It was found that RE could reduce the volume fraction of large eutectic carbides and the chrysanthemum-like eutectic colonies but could not change the phase composition.RE made a little change to Ac1,but the variation in Ac3 and enthalpy for the α→γ followed an in-creasing pattern as the RE addition increased.The start temperatures of carbides dissolution increased with increase of RE addition,which may be associated with the influences of RE on the morphology of carbides,but the overall enthalpy change of carbides dissolution decreases as the RE addition increased.Moreover,the start temperature of melting also increased with increasing RE addition.     

合金元素钒对高碳钢丝组织与性能的影响

 钒对高碳钢丝的微观组织、力学性能及热稳定性具有显著的影响。钒元素在高碳钢中主要存在于渗碳体中,可以起到强化渗碳体的作用。添加钒元素有利于珠光体片层间距的细化,还可以增加渗碳体的热稳定性,从而抑制钢丝拉拔过程中渗碳体的分解。但在拉拔应变量较大时,富含钒的渗碳体片碎化严重,会加重钢丝在镀锌过程中的球化现象,而导致钒合金化钢丝与未添加钒元素的钢丝相比,无论镀锌与否,其扭转性能均明显下降。     

Crystallography and Morphology of Carbides in a Low-Cycle Fatigued 1Cr-1Mo-0.25V Steel

The carbide precipitation in 1Cr-1Mo-0.25V steel subjected to low-cycle fatigue (LCF) deformation at room and elevated temperatures was investigated by means of transmission electron microscopy. Based on the electron diffraction analyses, three types of carbides, M₃C-type cementite, M₂C, and MC, were identified in normalized and subsequently tempered specimen. The cyclic deformation at high temperature led to the following changes in morphology and composition of carbides: the spheroidization of cementite, the enhanced precipitation of H-carbide, the formation of M₂C and M₂₃C₆ at lath or prior-austenite grain boundaries, and the enrichment of Mo in most of carbides. Particular attention has been paid to the crystallographic orientation relationship (OR) between the cementite and the ferrite (α) matrix. The combined analyses based on the simulation of diffraction patterns and the trace analyses of habit plane on stereographic projection have shown that most cementite was related to the α matrix in accordance with Bagaryatskii OR, but in some cases, the Isaichev OR also was observed in the lath interior after LCF deformation at elevated temperature. In addition, M₂C obeyed the Burgers–Jack OR, and MC was related to the α by the Baker–Nutting OR.     

晶型碳酸稀土与稀土配分

用质量分析，Ｘ射线衍射图谱，红外光谱，电镜照片及分析等分析手段，研究了从不同类型风化壳淋积型稀土矿中得到的晶型碳酸稀土与稀土配分的关系，研究结果表明，晶型碳酸稀土的质量普遍优于草酸稀土；晶型碳酸稀土实际上就是简单稀土酸盐的水合结晶体；不同配分的晶型碳酸稀土其结构和晶型较大差异。     

The tempering of low carbon steels containing tungsten

The tempering behavior of three steels each containing 0.20 pct C and having tungsten contents of 2.1, 3.9 and 5.9 pct has been followed by thermomagnetic analysis and electron microscopy. Using a Sucksmith Balance, the proportions of autotempered carbide and retained austenite in as-quenched specimens were estimated, and the amount of cementite precipitated upon subsequent tempering measured accurately. Solution of tungsten in cementite during tempering was monitored by observing changes in Curie temperature. The magnetic nature of alloy carbides precipitating at high temperatures allowed tentative identification and this directed and assisted the electron microscopy study which provided new information on the morphology of tungsten carbides. J. B. LUPTON, formerly Research Student, Metallurgy Department, University of Sheffield, England, S. MURPHY, formerly Research Fellow, Metallurgy Department, University of Sheffield,     

Investigation on microstructure and properties of a combined precipitation hardening ultrahigh strength steel

The microstructure and properties of a combined precipitation hardening ultrahigh strength steel with nano-sized carbides and intermetallics were studied systematically.The results show that after tempering at 300℃lots ofε-carbides are precipitated in the martensite,the strength rises and the toughness falls slightly.After tempering at 430℃,much coarser cementite lamina are precipitated in martensitic laths,which causes the impact toughness falls to the minimum value.With temperature further increasing the cementites are dissolved and M₂C carbides,β-NiAl intermetallics and reverse austenite begin to precipitate.The tensile strength and yield strength achieve the peak value at 470℃,490℃respectively.The tested steel achieve a tensile strength of 2 120 MPa,a yield strength of 1 950 MPa and impact energy of 54 J/cm² after optimum tempering at 510℃.When tempering temperature is above 530℃the M₂C carbides and reverse austenite is coarsening.After tempering at 560℃the reverse austenite reaches the maximum volume fraction in present work.