Identification and evaluation of modification level for compacted graphite cast iron

The shape of the freezing zone of a thermal analysis cooling curve not only contains the information about the modification level of compacted graphite cast iron (CGI) right after vermicularizing treatment, but also reflects the following fading process during holding. When the freezing zones of two cooling curves are approximately the same, graphite morphologies of the samples cast from the two corresponding melts right after vermicularizing treatment are similar, and those of the two corresponding samples cast after holding for the same period are similar too. Based on the pattern recognition method and database established from a large amount of experimental results, the shape of the freezing zone of a cooling curve can be used to identify the modification level of CGI melt and on-line prediction of a CGI melt quality has been realized.     

蠕墨铸铁加工研究现状

蠕墨铸铁因为其优秀的力学性能越来越多地被应用在工业当中,特别是在汽车工业中制造高性能和轻质量的柴油发动机方面,已经成为替代灰铸铁的理想材料。然而,蠕墨铸铁优秀的力学性能,使得蠕墨铸铁加工成为一个难题,加工过程存在速度过快刀具过早失效或速度过慢表面质量不达标等问题。基于存在的问题和目前的研究进展,综述了蠕墨铸铁切削机制、内部成分、切削刀具等对加工蠕墨铸铁的影响,并进一步对刀具角度、表面涂层、切削参数、冷却方法等研究进行了介绍,指出了蠕墨铸铁的未来研究方向和发展趋势。     

Experimental and numerical analysis of effect of cooling rate on thermal–microstructural response of spheroidal graphite cast iron solidification

This work presents an experimental and numerical study of the solidification process of an eutectic spheroidal graphite cast iron (SGI). The effect of the cooling rate on the thermal–microstructural response is particularly analysed. To this end, experiments as well as numerical simulations were carried out. The experiments consisted in a solidification test in a wedge-like casting such that different cooling rates were measured at specific positions along the part. A metallographic analysis was also performed in five locations of the sample with the aim of obtaining the number and size of graphite nodules at the end of the process. The numerical simulations were made using multinodular based and uninodular based models. These two models predicted similar results in terms of cooling curves and nodule counts. Besides, good experimental–numerical agreements were obtained for both the cooling curves and the graphite nodule counts.     

Understanding compacted graphite iron solidification through interrupted solidification experiments

While the manufacture of compacted graphite (CG) iron castings has seen significant expansion over the recent years, the growth of CG during iron solidification is still not fully understood. In this work, effort was expanded to experimentally reveal the evolution of graphite shape during early solidification and its relationship to the solid fraction. To this purpose, interrupted solidification experiments were carried out on hypereutectic irons with three magnesium levels. The graphite shape factors were measured and analysed as a function of chemical composition and solid fraction. Scanning electron microscopy was carried out to establish the fraction of solid at which the transition from spheroidal graphite (SG) to CG occurs. It was confirmed that solidification started with the development of SG for all CG irons. The SG-to-CG transition was considered to occur when the SG developed a tail (tadpole graphite). The findings were integrated in previous knowledge to attempt an understanding of the solidification of CG iron.     

蠕墨铸铁CA6110柴油机缸体的试验研究

在现有汽缸体高压造型生产线上进行大马力柴油机蠕墨铸铁缸体的试验,试验铁液化学成分w为3.6%~3.9%C;2.2%~2.4%Si;0.2%~0.5%Mn;P≤0.06%;S≤0.03%,采用自行研制的成分为8%~10%Mg,2%~3%RE的蠕化剂进行冲入法蠕化处理,同时加入0.8%~1.0%Cu和0.03%~0.05%Sn,成功的铸造出蠕墨铸铁CA6110柴油机缸体。对附铸试样和铸件本体进行了金相组织和力学性能检测,结果表明,试样的的蠕化率可达80%~85%,珠光体含量达80%~85%,力学性能σb>480 MPa,δ=1.0%~1.5%,180~200 HBS;缸体铸件本体的蠕化率同样为80%~85%,硬度可达197~214 HBS。试验结果表明:采用的铸造工艺方案是合理的,在铁液中加入的Cu和Sn可明显增加蠕墨铸铁的珠光体数量,提高抗拉强度和硬度,满足大马力柴油机对性能的要求。     

微合金化蠕墨铸铁玻璃模具材质的研究

介绍了微合金化蠕墨铸铁玻璃模具材质的组织、力学性能及热物性，探讨了影响其性能的诸多因素。结果表明：这种材质具有较高的综合性能指标，具有良好的使用性能和显著的经济价值和社会效益。不仅适于与玻璃模具，还可广泛地应用于冶金、塑料和橡胶行业。     

含磷蠕墨铸铁闸瓦的研制

本文研制了一种新型材质的闸瓦—含磷蠕墨铸铁闸瓦。试验结果证明,一定量的磷加入蠕墨铸铁中,其硬度、抗拉强度均满足闸瓦的使用要求而耐磨性可达到中磷灰铸铁闸瓦的2倍以上。磷加入蠕墨铸铁中使得蠕墨铸铁的磷共晶数量增加而石墨数量减小,因此使得其强度降低,硬度升高,闸瓦的耐磨性提高。     

Using PCD for machining CGI with a CO2 coolant system

Polycrystalline diamond is widely used as a economic cutting material for machining non-ferrous materials such as aluminum. It is perceived that diamond cannot be used for cutting ferrous materials due to the high affinity of carbon to iron. Nevertheless, under certain conditions it is possible to use diamond materials for cutting ferrous metals. In order to avoid graphitization of the diamond matrix, it is necessary to keep the cutting temperature below the critical level of diamond graphitization. This paper presents the influence of a cryogenic CO₂ coolant strategy on the cutting process using PCD tools for cutting high strength compacted graphite iron (CGI). Investigations show, that tool wear behavior strongly correlates with the cutting speed, the cutting forces, cutting temperatures, and surface roughness of the workpiece. The test results show, that the tool life of PCD for cutting cast iron is dependent on the diamond grain size, the binder material, and the cutting parameters.     

Investigation of the wear mechanism of cubic boron nitride tools used for the machining of compacted graphite iron and grey cast iron

Various experiments were performed to investigate the wear mechanism of cubic boron nitride (cBN) tools used for the machining of compacted graphite iron (CGI). Comparative studies for tools used to machine grey cast iron (CI) were also performed in order to find out why in this case the tool lifetime is significantly higher. Two main effects were found that are responsible for tool wear, namely: (1) oxidation of the tool, and (2) interdiffusion of constituting elements between tool and CGI. These wear mechanisms are more or less the same for the machining of CGI and grey CI. The difference in tool lifetime can be explained by the formation of a MnS layer on the tool surface in the case of grey CI. This layer is missing in the case of CGI. The MnS layer acts as a lubricant and as a diffusion barrier and is the reason for the reduced wear in the case of grey CI.     

蠕墨铸铁在铁道车辆制动系统中的应用研究

在分析车辆制动器摩擦温度场的基础上 ,研究蠕墨铸铁在铁道车辆制动系统中的使用性能 ;研究结果表明 ,在车辆制动器服役条件下 ,摩擦速度与接触压力的提高 ,摩擦副的摩擦系数显著降低 ,磨损率显著增加 ;在所研究的不同石墨形态的铸铁中 ,蠕墨铸铁不但具有低而稳定的磨损率 ,而且具有高而稳定的制动性能 ,是制造车辆制动器部件的合理选材。     

Effects of Mo and Ni on the thermal conductivity of compacted graphite iron at elevated temperature

ABSTRACT

The effects of Mo and Ni on the microstructure and properties of compacted graphite iron were investigated experimentally, especially with regard to the thermal conductivity at elevated temperature. It was found that the ferrite fraction is weakly affected by Mo content but significantly reduced by Ni addition. Moderate content of Mo is beneficial to the tensile strength and the elongation, but it is detrimental for the thermal conductivity, which is more obvious than Ni. The phenomenon that thermal conductivity increases and then decreases at elevated temperature, which is named temperature dependence, could be connected with the lattice distortion of the matrix caused by solute atoms. With the addition of Mo or Ni, the rising amplitude of thermal conductivity increases as well as the temperature corresponding to the maximal of thermal conductivity. Besides, the effects of Mo on the temperature dependence of thermal conductivity are higher when compared with Ni.     

铸型冷却速度对半固态镁合金浆料凝固组织的影响

采用不同直径型腔的铜质和铁质两种金属型,研究了铸型冷却速度对双螺杆机械搅拌法制备的半固态镁合金浆料凝固组织的影响.结果表明,随着铸型冷却速度的降低,半固态浆料的固相率升高,初生α-Mg相晶粒平均尺寸增大.采用铁质重力金属型不能制备直径大于φ25mm的半固态镁合金坯料,半固态浆料必须采用压铸或挤压成形的方法才能为触变成形工艺提供优质的半固态坯料.     

Modelling and simulation of local mechanical properties of high silicon solution-strengthened ferritic compacted graphite iron

This study focuses on the modelling and simulation of local mechanical properties of compacted graphite iron cast at different section thicknesses and three different levels of silicon, ranging from about 3.6% up to 4.6%. The relationship between tensile properties and microstructure is investigated using microstructural analysis and statistical evaluation. Models are generated using response surface methodology, which reveal that silicon level and nodularity mainly affect tensile strength and 0.2% offset yield strength, while Young′s modulus is primarily affected by nodularity. Increase in Si content improves both the yield and tensile strength, while reduces elongation to failure. Furthermore, mechanical properties enhance substantially in thinner section due to the high nodularity. The obtained models have been implemented into a casting process simulation, which enables prediction of local mechanical properties of castings with complex geometries. Very good agreement is observed between the measured and predicted microstructures and mechanical properties, particularly for thinner sections.     

基体组织对球铁抗热疲劳性能的影响

研究了不同基体组织对球墨铸铁抗热疲劳性能的影响.结果表明:铁素体基体球铁的抗热疲劳性能最好,复相基体组织不利于提高球铁的抗热疲劳性能.