Cerium Distribution in Spheroidal Graphite of Cast Iron

Six thin sections of spheroidal graphites in cast iron have been investigated by TEM and SEM.Thespheroidal graphites consist of two or three layers and have nuclei which are composed of Ce_2O_2S and Ce_2O_3.Cerium is existed ont only in nuclei,but also in central layer and middle layer of graphite.     

稀土变质铸铁中石墨—奥氏体共晶的生长方式

用Ｂｒｉｄｇｍ ａｎ 定向凝固技术制取了稀土变质共晶铸铁不同石墨形态时的液－固平界面试样。观察结果表明,稀土变质铸铁共晶凝固过程中,石墨相不论形态如何均为领先相;石墨与奥氏体共晶有共生生长和离异生长两种生长方式。在共生生长情况下,奥氏体紧贴石墨片两侧协同生长,形成锯齿状的液－固界面结构;在离异生长情况下,石墨相单独在液相中析出并充分长大,随后被奥氏体包围,液－固界面形态主要取决于奥氏体－液相界面的稳定性。分析表明,稀土在石墨－液相界面的富集是导致石墨－奥氏体共晶离异生长的主要原因。     

Wear Behavior and Mechanism of Spheroidal Graphite Cast Iron

Wear behavior and mechanism of spheroidal graphite cast iron were studied on a pin-on-disk elevated temperature wear tester. The phase and morphology of worn surfaces were examined by X-ray diffraction and scanning electron microscopy. Results show that with an increase of load, wear rate of spheroidal graphite cast iron gradually increases under low loads, rapidly increases or potentially increases under high loads; wear rate increases with increasing ambient temperature. At 25–200 °C, adhesive wear prevails; oxidative wear and adhesive wear coexist at 100 °C. As load surpasses 150 N at 100 °C, extrusive wear appears. The elevated-temperature wear of spheroidal graphite cast iron is a physical and chemical process including the following reactions: xFe + y/2O₂?Fe_xO_y, 2C + O₂?2CO and Fe_xOy + yCO?xFe+yCO₂. Hence, at 400 °C, the amount of graphite and tribo-oxides are substantially reduced because of reductive function of graphite. It can be suggested that wear-reduced effect of graphite and tribo-oxides is impaired.     

钒钛球铁齿轮的基础性能

作者对等温淬火的钒钛球铁齿轮进行了7种基础性能试验。结果表明:这种齿轮的接触疲劳极限σ_Hum值、抗磨损能力、结构阻尼比和降低噪声等方面具有优良的性能,而弯曲疲劳强度较低。用这种钒钛球铁制造QJ系列减速器齿轮,其承载能力可提高50%。     

球墨铸铁微观组织形成的数值模拟

基于结晶动力学理论,建立了球墨铸铁凝固过程各阶段微观组织形成形核和长大的数学模型;根据该结晶动力学模型,编制了球铁微观组织形成模拟软件FTStructure．该软件可以预测球铁凝固过程中各相的形成以及固态转变中铁素体和珠光体的形成,并进而预测铸态力学性能．模拟了阶梯形试块的冷却曲线、微观组织和布氏硬度．模拟与实测结果符合较好．     

球墨铸铁轧辊保温冒口研究

球墨铸铁轧辊的补缩,一般是采用砂型明冒口和浇注后每隔20-25分钟用过热铁水点冒口1-2次的办法解决,这样的工艺使冒口金属消耗量占轧辊毛重的15%左右。为了节约金属和提高轧辊上辊颈质量,本研究工作是采用铝型膨胀发热剂单独使用或与绝热套组合成的保温冒口,以取代原工艺以稻草灰覆盖的干砂型冒口。经过实验室及现场对此实验表明:采用保温冒口以后,球墨铸铁共晶凝固时间延长了33-62%,缩孔形状由倒锥形变为盆形,轧辊冒口的致密段高度增加,省去了用过热铁水点冒口的工序。冒口高度可以降低25~50%,节约冒口金属量20~50%。研究工作表明:采用保温冒口是解决球铁轧辊补缩的最合理、经济而简便的措施。     

Role of RE and Mg on Graphitization of Spheroidal Graphite Malleable Cast Iron

ＲｏｌｅｏｆＲＥａｎｄＭｇｏｎＧｒａｐｈｉｔｉｚａｔｉｏｎｏｆＳｐｈｅｒｏｉｄａｌＧｒａｐｈｉｔｅＭａｌｌｅａｂｌｅＣａｓｔＩｒｏｎ￥ＬｉｕＪｉｎ－Ｈａｉ（ＨｅｂｅｉＩｎｓｔｉｔｕｔｅｏｆＴｅｃｈｎｏｔｏｇｙ，Ｍｉａｎｊｉｎ３００１３０，Ｃｈｉｎａ）...     

球墨铸铁液压件发热冒口的研究

耐高压的液压件采用球墨铸铁（简称“球铁”）材质是一项先进技术。但是球铁的补缩困难,特别是对薄壁、复杂的液压件,热节处易产生缩松而导致铸件的渗漏,这是采用球铁生产液压件的关键问题。我们采用发热冒口解决球铁液压件的补缩问题。研究结果表明:发热冒口套热损失率比普通砂型冒口降低53%,等效模数约为几何模数（砂型冒口的模数）的两倍。节约冒口金属的50～80%,解决了普通砂型冒口解决不了的球铁液压件的补缩问题。     

Role of Sulfur on the Transition from Graphite to Cementite Eutectic in Cast Iron

In the current study, an analytic solution is considered to explain the influence of sulfur on the transition from graphite to cementite eutectic in cast iron. The outcome from the current study indicates that this transition can be related to (a) the graphite nucleation potential (directly characterized by the cell count and indirectly by the nucleation coefficients; (b) the eutectic graphite growth rate coefficient; (c) the temperature range between the equilibrium temperature for graphite eutectic and the formation temperature for cementite eutectic; and (d) the liquid volume fraction, after pre-eutectic austenite solidification. In addition, the absolute and the relative chilling tendencies, as well as critical cooling rates including the chill width of the cast iron can be predicted from the current study. The analytic model was experimentally verified for castings with various sulfur contents. It is found that the main role of sulfur on the transition from graphite to cementite eutectic is through its effect on lowering the growth coefficient, and hence, the graphite eutectic growth rate. In addition, it is found that with the increasing sulfur content, the critical cooling rate is significantly reduced, thus increasing the absolute and the relative chilling tendency values, including the chill width.     

Unidirectional Solidification of Eutectic Cast Iron

Abstract

High intrinsic damping in alloys finds many applications in the elimination of unwanted vibrations and reduction of acoustic noise. The increasing interest in these materials has resulted in the development of a new class of engineering alloys, the HIDAMETS (high-damping metals), specifically tailored for use in vibration-resistant structures. Numerous different physical mechanisms (usually controlled by the alloy microstructure) can be responsible for the level of internal friction or damping in a candidate alloy for a particular application. Consequently, alloy selection depends mainly upon the conditions to be encountered in service, i.e. temperature, frequency of vibration, amplitude of vibration, magnetic field, etc. Characterization of the internal friction in high damping alloys is described and some of the mechanisms involved are discussed. Results obtained for two different alloys are presented. The first is a commercial Mn-Cu alloy used for marine propellers and the second is a die-cast Zn-Al alloy with possible application in the automotive industry.     

The Effect of Carbon on the Transition from Graphite to Cementite Eutectic in Cast Iron

In this work, an analytical solution is proposed to explain the influence of carbon on the transition from graphite to cementite eutectic in cast iron. The outcome from this work indicates that this transition can be related to (a) the graphite nucleation potential (directly characterized by the cell count, N and indirectly by the nucleation coefficients N _s and b), (b) the eutectic graphite growth rate coefficient, μ, (c) the temperature range, ?T _sc = T _s  ? T _c (where T _s and T _c are the equilibrium temperature for graphite eutectic and the formation temperature for cementite eutectic, respectively), and (d) the liquid volume fraction, f, after pre-eutectic austenite solidification. In addition, the absolute and the relative chilling tendencies, CT and CT_r, respectively, as well as the critical cooling rate, Q _cr, and the chill width, w, can be predicted from this work. The analytical model was experimentally verified for castings with various carbon contents. It was found that the carbon content increases the eutectic cell count, N while reducing the maximum degree of undercooling at the onset of graphite eutectic solidification, ?T _m. From this work it is evident that the main role of carbon on the transition from graphite to cementite eutectic is through its effect on increasing the growth coefficient and hence, the graphite eutectic growth rate, u. Moreover, at increasing carbon contents the absolute and the relative chilling tendencies including the chill width, all are significantly reduced. Finally, the equations derived using theoretical arguments for the chill width are rather similar to expressions based on a statistical analysis of the experimental outcome.     

Fracture Characteristics of Austempered Spheroidal Graphite Aluminum Cast Irons

The fracture characteristics of austempered spheroidal graphite aluminum cast iron had been investigated. The chemical content of the alloy was C 3.2, Al 2.2, Ni 0.8 and Mg 0.05 (in mass percent, %). Impact test samples were produced from keel blocks cast in CO2 molding process. The oversized impact samples were austenitized at 850 and 950 ℃ for 2 h followed by austempering at 300 and 400 ℃ for 30, 60, 120 and 180 min. The austempered samples were machined and tested at room temperature. The impact strength values for those samples austempered at 400 ℃ varied between 90 and 110 J. Lower bainitic structures showed impact strength values of 22 to 50 J. The fractures of the samples were examined using SEM. The results showed that the upper bainitic fracture revealed a honey Comb-like topography, which confirmed the ductile fracture behavior. The lower bainitic fractures of those samples austempered for short times revealed brittle fracture.     

球墨铸管退火炉设备的改进

对球墨铸管退火炉加热段改造,采用平焰烧嘴和两区控温,降低了炉膛高度并采用耐火纤维模块替代浇注料,使温度调节灵活,提高了产品质量和降低能耗。     

稀土对球墨铸铁中共存As、Sn、Pb、Ti的中和作用

全部采用龙岩生铁，制取球墨铸铁。球化剂为镁硅铁合金，同时分别添加０．００％、０．０１％、０．０２％、０．０３％、０．０４％、０．０５％、０．０７％稀土硅铁合金进行球化处理。结果表明，稀土不能完全消除与中和高含量微量元素共存对石墨球化的干扰作用。但适量稀土可部分中和微量元素、促进形核、改善球状石墨的表面形貌。削弱微量元素的有害作用。     

Relationship Between the Trace Elements and Graphite Growth Morphologies in Cast Iron

The graphite morphology transition was studied using various techniques and additives in ultra-pure binary and ternary alloys with hypo- and hypereutectic compositions. Some of the trace elements were observed to stabilize the flake growth morphology of graphite, while others did not. The distance between the graphite basal planes of spheroidal, flake, and undercooled fine graphite was measured and the lattice fringes were studied using high resolution transmission electron microscope, after preparing a thin lamella of graphite using focused ion beam. Latent heat measurement was performed using differential scanning calorimeter on the pure binary alloy with and without sulfur and oxygen additions. The substitution of various elements under study in a monolayer of graphene was analyzed by considering the binding energies of the elements with C and their bonding nature. Simulations were performed using a molecule editor program and visualizer (Avogadro software), which considers various types of interatomic forces to optimize a monolayer of graphene to a minimum energy. The effect of the type of cyclic C-ring structure and energy of the basal plane of graphite with a connection to the addition of trace elements individually in the monolayer of graphene was studied and simulated to understand the resulting bulk graphite growth morphology.     

Mechanism for the Role of Silicon on the Transition from Graphite to Cementite Eutectic in Cast Iron

In this work, an analytical solution is proposed to explain the influence of silicon on the transition from graphite to cementite eutectic in cast iron. It is found that this transition can be related to (1) the graphite nucleation potential (directly characterized by the cell count N and indirectly by the nucleation coefficients N _s and b), (2) the growth rate coefficient of graphite eutectic cells ??, (3) the temperature range ??T _sc?=?T _s ?C T _c (where T _s and T _c are the equilibrium temperature for graphite eutectic and the formation temperature for cementite eutectic, respectively), and (4) the liquid volume fraction f _l after preeutectic austenite solidification. Analytical equations were derived that describe the absolute and the relative chilling tendencies (CT and CT_r, respectively) as well as the critical cooling rate Q _cr and, hence, the chill w of the cast iron. Theoretical arguments are experimentally verified for castings with various silicon contents. This work also describes the methods used in the determination of N _s, b, and ?? values. It is found that the main role of silicon on the transition from graphite to cementite eutectic is to raise the density of the graphite nuclei N and temperature range ??T _sc. In addition, it is shown that increasing the silicon content of cast iron leads to an increasing value of Q _cr and decreasing values of CT and CT_r, and of the chill width w. In particular, this work shows that the chilling tendency indexes and, hence, the chill all can be estimated from a simple thermal analysis using reference castings.     

Nucleation of Bainite in Bainite Ductile Cast Iron

The bainite ductile cast iron with given comppasition was quenched to get bainite strueture. The nucleating position of bainite and the distrihution of alloying elements in the matrix were measured. The results show thai the bainite nucleates at the interface between graphite and austenite during quenching. Based on the experimental results and thermodynamics, the nucleating tnechanism of bainite in ductile iron was analyzed.