Hybrid control of graphite cast iron structure by partial melt treatment process

The Modified Inmould Process, which forms a cast iron-graphite hybrid alloy with a spheroidal/flake graphite structure (SG/FG), has been developed by the author.^1-3 Though this process can easily control the transitional structure of SG/FG, there are some mild restrictions caused by rapid collision during the mixing of molten metals in the mould on pouring. In this study, a new experimental process was designed to solve this difficulty. The plate-like mould cavity was separated into a reaction chamber (RC) and a product cavity by a thin dam. An alloy of FeSiMg for spheroidization of base molten metal was prepared in the reaction chamber. Molten metal was poured up from the bottom of the product cavity and a part of it flowed over the dam into the reaction chamber. After being spheroidized in the reaction chamber, spheroidal graphite (SG) iron melt flowed backward into the product cavity. The density of SG molten iron with a higher carbon equivalent value is generally lower than that of flake graphite (FG) molten metal. Thus SG molten metal moved into the upper end of the product cavity by replacement of the base metal, while the base metal remained stationary at the lower end of the cavity. As a result of the phenomena of flow, movement and replacement between mutual melts, a SG/FG transitional layer structure was formed, downward, throughout the cast product.     

球墨铸铁件表面片状石墨层的应用

球墨铸铁具有较佳的高温强度,灰口铸中片状石墨对铝合人具有抗蚀性;利用片状石墨可防止铝液侵蚀金属基体的特性,设计制作表面为灰口铸件材质的热电偶保护,使控温热电偶不因熔液溶穿保护管而损坏。     

石墨形态和基体组织对铸铁断裂过程的影响

研究了石墨片混乱度Ｓ＝０的Ｆｅ－Ｃ合金和球墨铸铁在不同受力状态下的裂纹扩展现象，以及基体组织对断裂形貌的影响，试验发现：当裂纹遇到与其平行的片状石墨时，裂纹将在石墨内部以（０００１）面之间的解理而扩展；当裂纹遇到与其垂直的片状石墨时，裂纹将沿石墨／基体界面处扩展，也即界面的脱粘；当裂纹遇到球状石墨时，裂纹主要的二次石墨中前进，裂纹在铁素体－下贝氏体中以在铁素体中的扩展为主。     

生长条件对灰口铸铁共晶凝固过程石墨形态的作用

灰铸铁、蠕铁、球铁被统称为灰口铸铁,在现代工业中应用广泛.在主要成分相近情况下,由于微量元素等条件的不同引起石墨生长形态各异,从而同属灰口铸铁的三类铸铁性能迥异.懂得其基本规律及相关原理,有益于铸造工程技术人员在灰铁、蠕铁、球铁的生产实际中理性而有效地控制产品质量.本文基于灰口铸铁的奥氏体-石墨共晶凝固方式,从基本概念及原理、G形成过程、实际组织观察与分析的全新视角,主要针对灰铁和球铁概述了石墨形态的形成规律和机理.文中诸多图片等实例是以往国内教科书及专业书籍中未见的,文章内容也体现了对相关现象描述及观点上新的发展,有助于读者对该方面有关问题获得更为清晰的理解和认识.     

High Temperature Oxidation Behavior of Flake and Spheroidal Graphite Cast Irons

Flake and spheroidal graphite cast irons with similar composition were subjected to high temperature oxidation to investigate graphite morphology and distribution effects on the oxidation behavior. High temperature oxidation tests were conducted between 400 and 750 °C in air. For comparison low carbon steel was also tested.Graphite morphology obviously affected high-temperature oxidation resistance. The flake graphite cast iron exhibited the worst high-temperature oxidation resistance compared with spheroidal graphite cast iron. Since graphite flakes provide suitable sites for the iron oxide growth and are almost interconnected, the iron oxide grows faster and penetrates along the graphite flakes boundaries resulting in the subsurface oxidation. Due to the severe subsurface oxidation flake graphite cast iron parabolic rate constants are five times higher than that of the spheroidal graphite cast iron. However, spheroidal graphite cast iron parabolic rate constants and oxide layer thickness are similar to those of the low carbon steel. Therefore, graphite flakes have negative effect on the cast iron high temperature oxidation resistance.     

石墨形态对铸铁气割特性的影响

讨论了石墨的物理性能,分析了片状和球状石墨聚集状态对铸铁气割性的影响。发现,愈是细小、圆整石墨形态愈有利于气割。     

同质焊缝球墨铸铁焊条的研制

研制了一种适合于球墨铸铁与球墨铸铁以及球墨铸铁与结构钢焊接的专用球墨铸铁焊条，通过试验确定了球墨铸铁焊条的合金成分并给出了比较合理的焊芯和焊条药皮化学成分。采用该焊条对球墨铸铁焊接时，可以达到同质焊缝要求。测试结果表明，焊缝金属的化学成分、金相组织均满足焊接球墨铸铁的要求，焊缝的硬度在190～230HB之间，焊缝中石墨球化稳定，焊条具有良好的焊接工艺性能。     

Eutectic solidification mode of spheroidal graphite cast iron and graphitization

The shrinkage and chilling tendency of spheroidal graphite (abbreviated SG) cast iron is much greater than that of the flake graphite cast iron in spite of its higher amount of C and Si contents. Why? The main reason should be the difference in their graphitization during the eutectic solidification. In this paper, we discuss the difference in the solidification mechanism of both cast irons for solving these problems using unidirectional solidification and the cooling curves of the spheroidal graphite cast iron. The eutectic solidification rate of the SG cast iron is controlled by the diffusion of carbon through the austenite shell, and the final thickness is 1.4 times the radius of the SG, therefore, the reduction of the SG size, namely, the increase in the number, is the main solution of these problems.     

灰铸铁中石墨形态分级及其特点

文章就美国标准ASTMA-247与GB7216-1987对铸铁的石墨形态分级作了详细介绍。美国材料与实验学会ASTMA-247中将铸铁中可能出现的石墨形态分成7类,其中对灰铸铁的石墨形状分为5种,从A型到E型,而GB7216—1987把灰铸铁的石墨形状分为6种,即A型到F型。同时将石墨片长又分成8级。     

球铁铝锭模材料热疲劳性能的研究

模拟铝锭模的使用条件,研究了不同基体组织球墨铸铁的热疲劳性能.结果表明,退火铁素体铝铸锭模使用寿命最长.该铝锭模安装在包头铝业公司的2台铝锭连续铸造机上使用,平均每天铸锭48t/台,连续使用410天.而普通材质的球铁铝锭模使用寿命仅为120到150天左右.     

Colour Metallography of Cast Iron Chapter 4 Vermicular Graphite Cast Iron(Ⅰ)

Note:This book consists of five sections: Chapter 1 Introduction, Chapter 2 Grey Iron,Chapter 3 Spheroidal GraphiteCast Iron,Chapter 4 Vermicular Graphite Cast Iron,and Chapter 5 White Cast Iron.CHINA FOUNDRY publishes thisbook in several parts serially,starting from the first issue of 2009.     

表层石墨球化的灰铸铁件外表层片状石墨的防止

利用含有稀土的涂料实现了表层石墨球化的灰铸铁件,其组织形态由外到内依次为球化区、过渡区和灰铸铁本体。生产中发现,在某些条件下,已经实现了表层石墨球化的灰铸铁件的外表层又出现片状石墨。为防止这种现象发生,进行了研究。     

On the mechanism of the formation of widmanstätten graphite in flake graphite cast irons

The mechanism whereby Widmanstätten graphite develops during the solidification of flake graphite cast irons has been found to involve the preferential segregation and a complex interaction of specific elements at the surface of the graphite flake during solidification and the development of the plate like appendages in the solid austenite adjacent to the graphite flake. The literature has suggested that lead, calcium and hydrogen may be causal to the formation of Widmanstätten graphite, but has the interaction of these elements has not been effectively documented. While the formation of this degraded graphite is often attributed to the presence of a sufficient amount of lead alone, it has been observed that Widmanstätten graphite develops only in conjunction with a combination of factors operative at the graphite-austenite interface. Commercial flake graphite cast irons may exhibit Widmanstätten graphite as a function of lead and calcium content in the iron, moisture content in the molding media, solidification cooling rate and the rate of cooling immediately after solidification, etc. Lead contamination of cast irons was also observed to increase the chilling tendency of the iron. The detrimental effects of lead can be counteracted by the presence of rare earths in the iron, where rare earth elements react with lead to form stable, high melting point compounds.     

Colour Metallography of Cast Iron

Chapter 3 Spheroidal Graphite Cast Iron（I） Spheroidal Graphite Cast Iron, SG iron in short, refers to the cast iron in which graphite precipitates as spheroidal shape during solidification of liquid iron. The graphite in common commercial cast iron can only be changed from flake to spheroidal shape by spheroidising treatment. Since spheroidal graphite reduces the cutting effect of stress concentration, the metal matrix strength of SG iron can be applied around 70%-90%, thus the mechanical property of SG iron is significantly superior to other cast irons;even the tensile strength of SG iron is higher than that carbon steel.     

Isothermal and thermal cycling oxidation of hot-dip aluminide coating on flake/spheroidal graphite cast iron

Two types of cast iron, flake graphite and spheroidal graphite cast iron, with ferrite matrix and similar composition, were aluminized by hot-dipping. As-coated aluminide layer consists of the outer Al topcoat, inner Fe–Al intermetallic layer and dispersed graphite. Isothermal and thermal cycling oxidation tests of aluminized specimens have been conducted. Cast irons with aluminide coating exhibit higher oxidation resistance than without the coating. However, different graphite structure results in diverse quality of aluminide coatings. Aluminide coating on flake graphite cast iron exhibits less oxidation resistance and adhesion to the substrate.     

Numerical simulation of microstructure evolution on near eutectic spheroidal graphite cast iron

A multiphase cellular automaton model was developed to simulate microstructure evolution of near eutectic spheroidal graphite cast iron (SGI) during its solidification process, and both dendritic austenite and spheroidal graphite growth models were adopted. To deduce the mesh anisotropy of cellular automaton method, the composition averaging and geometrical parameter were introduced to simulate the spheroidal graphite growth. Solute balance method and decentered square algorithms were employed to simulate austenite dendrites growth with different crystallographic orientations. The simulated results indicate that the graphite nodule grows in a spherical morphology when the surrounding environment of a single graphite nodule is same. However, for two adjacent graphite nodules, the environment is different. The higher the carbon concentration, the faster the growth of graphite. By comparison with experimental results, it is found that the microstructure evolution of near eutectic spheroidal graphite cast iron during solidification process can be reproduced quantitatively by numerical simulation with this model.     

风力发电机组球墨铸铁件的超声波检测

风力发电机组中球墨铸铁得到大量的使用。球墨铸铁的无损检测一般采用超声波检测和磁粉检测,国外风电企业都有严格的球墨铸铁检测规程,随着国内对球墨铸铁检测的重视程度不断提高,球墨铸铁检测的风力发电行业规范也颁布实施。介绍了球墨铸铁的超声波检测特点,以及国外风电企业对球墨铸铁超声波检测的规程,最后介绍风电典型球墨铸铁结构的超声波检测方法。     

国外新版球墨铸铁标准

欧洲标准EN1563：1997在大量实验数据基础上,大幅度扩充和改进了球铁铸件标准,更加适应巨型重要球铁铸件的生产和技术发展需要。已为英法德意丹麦等27个欧洲国家等效采用作为国家标准。新版国际标准ISO1083：2004《球墨铸铁-分级》,也等效采用了欧洲标准EN1563：1997。     

用低碳当量球墨铸铁铸造黄麻织机伸缩杆

本文阐述了低碳当量球铁的特点及其生产工艺;论述了用低碳当量球铁铸造仲缩杆的可行性。     

超高碳球墨铸钢热疲劳性能研究

研究了新型耐磨耐热材料——球墨铸钢。通过对钢液进行适当的球化处理，铸态组织直接获得一定数量的球状石墨、碳化物和珠光体，并有效地降低了有害杂质的含量。重点研究了球墨铸钢的热疲劳性能。研究表明：球墨铸钢的耐热性能优于传统铸钢与锻钢40Cr。