原铁液硅含量对厚大断面球墨铸铁件石墨形态与力学性能的影响

为研究原铁液硅含量对厚大断面球墨铸铁件凝固组织石墨形态和力学性能的影响,使用高精度热模拟系统,考察了不同硅含量的原铁液经过相同球化孕育工艺处理后在相同凝固条件下获得的厚大断面球墨铸铁件试样的凝固组织石墨形态和力学性能。结果表明,球化孕育工艺相同时,随着原铁液硅含量提高,厚大断面球墨铸铁件石墨形态恶化,力学性能下降。当钇基重稀土球化剂和含Ba孕育剂加入量分别为1.8%和0.4%时,原铁液硅含量控制在1.2%以内,有利于防止厚大断面球墨铸铁件石墨畸变,提高铸件力学性能。     

数字化热分析铸铁熔体质量表征与测评技术

介绍了用热分析方法测评液态金属质量的技术进展以及计算机和人工智能在热分析液态金属质量测评中的应用情况.指出基于冷却曲线特征值的热分析技术存在的不足,提出一种基于冷却曲线模式识别技术的液态金属熔体质量测评方法,实现了铸铁熔体质量的综合测评、蠕铁铁液蠕化效果的炉前定量测评和厚大断面球墨铸铁件石墨畸变的在线预测.     

球墨铸铁铁液熔体状态评估

研究了球化孕育效果、浇注温度等因素对球墨铸铁铁液冷却曲线特征值的影响。采用冷却曲线的初晶石墨析出温度TGL或大量共晶形核温度TEU到共晶凝固结束温度TS这一凝固段的整体形状表征球墨铸铁铁液的熔体质量,通过冷却曲线计算机模式识别结合数据库的方式实现了对球墨铸铁铁液的综合评估。当表征冷却曲线相似性的综合偏差值向0收敛时,球墨铸铁铁液对应的凝固组织和力学性能各指标间的差均向0收敛。     

厚大断面球墨铸铁件生产中若干问题的探讨(1)

介绍了厚大断面球墨铸铁的凝固时间长、共晶结晶平台长、石墨球数少、易畸变、基体组织异常等凝固特性,通过理论与生产实例相结合的方法,阐述了碎块状石墨问题,石墨球数少与石墨畸变的关系,球化剂、w(Mg残)量、RE与石墨畸变的关系,CE及化学成分的选择问题,厚大断面球墨铸铁件若干问题的措施,球化剂中RE问题以及如何增加石墨球数问题。最后指出:要保证厚大断面球墨铸铁正常生产,除上述问题外,还有浇注系统优化和浇注时间控制的问题,生产过程质量控制以及生产组织等问题,这些都需要注意和严格控制。     

厚断面球墨铸铁件组织与性能分析

浇注了厚大断面球墨铸铁试块,借助光学显微镜、扫描电子显微镜、能谱仪及拉伸试验机分析了厚断面球墨铸铁件表面及心部的微观组织和力学性能,探讨了其形成机理。结果表明,现有试验条件下近表层区域凝固速度快,石墨球数量较多、球径较小,中心或热节部位石墨畸变严重,为减少或抑制石墨畸变,微合金化的同时还应强化冷却;Mg、Sb、S及RE等的化合物是球状石墨核心的主要组成物,这些元素在石墨球周围的富集使各个面或方向的生长趋于球形;凝固速度对试块中各位置的抗拉强度和屈服强度影响不同,其断裂为石墨与基体处形成裂纹不断扩展所致。     

Y和Sb对厚大断面球墨铸铁石墨形态的影响

通过采用重稀土钇基稀土镁球化剂处理铁液,浇注厚大断面球铁试块,研究了重稀土Y和微量Sb对厚大断面球铁的石墨形态的影响,分析了石墨结晶的核心,并探讨了石墨畸变的原因。试验结果表明,重稀土Y在铁液中形成高熔点氧化物,残存时间长,作为石墨核心,有利于提高抗衰退性能;Sb具有细化石墨球、增加石墨球数、提高石墨圆整度的作用;在厚大断面球铁中,晶界上Ti的偏析和球化元素Mg或稀土等氧化形成的氧化夹杂,破坏了奥氏体壳的稳定性,造成石墨畸变。     

孕育处理对厚大断面球铁组织和性能的影响

为研究孕育处理对铸件组织和性能的影响情况,采用不同孕育处理方式制备厚大断面球墨铸铁试样.结果表明,多次孕育处理有助于改善厚大断面球墨铸铁的石墨形态、提高铸件力学性能.     

厚大断面珠铁生产中的几个主要问题

本文结合国 内外厚大断面珠铁的生产和应用现状,介绍了厚大断面珠铁中非球形石墨的形态及形成原因;基本化学成分和微量元素对厚大断面珠铁中石墨形态的影响;珠化剂及球化方法、孕育剂及孕育方法对厚大断面珠铁组织和性能的影响。     

大型风电球墨铸铁轮毂的质量控制

大型风电大断面球墨铸铁轮毂易产生石墨球粗大、石墨球数量减少、石墨漂浮、石墨球畸变、缩孔、缩松、浮渣等缺陷,结合国内外大断面球墨铸铁件生产情况,总结出了一系列大型风电球墨铸铁轮毂生产过程中的质量控制措施,并从原辅材料的选择,铁液化学成分的控制,合适的球化和孕育处理以及微量合金元素适当的添加等方面论述了厚大断面球墨铸铁轮毂生产中应采取的质量控制措施及工艺参数。应用这些措施,生产出了各项性能指标合格的风电轮毂。两年内生产4种共400件风电轮毂,轮毂合格率达96%以上。     

热分析技术在铁液质量控制中的应用

阐述了热分析测量技术的原理及功能,对热分析技术在灰铁、球铁和蠕铁铁液质量控制中的具体应用方法进行了详细介绍,认为热分析技术可以将铸件的凝固组织、石墨形态、白口倾向、缩松缩孔倾向、反白门倾向、石墨飘浮等问题提前加以控制,是稳定生产高质量铸件的必要工具之一.     

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.     

冷却曲线识别与亚共晶Al-Si合金熔体状态测评

研究了B，Sr含量以及保温时间对Al-7Si合金熔体冷却曲线与凝固组织的影响。利用数字化测温技术、模式识别技术和数字图像分析技术分别进行了冷却曲线和凝固组织的测量与比较，基于大量试验结果积累的数据库，实现了Al-7Si合金熔体组织细化及变质效果的测评。研究结果显示，随着表征曲线相似程度的综合偏差值趋近于0，相应的晶粒尺寸及变质级别差值均向0收敛。冷却曲线的整体形状可以表征包括熔体细化及变质效果在内的Al-Si合金熔体状态。     

蠕墨铸铁铁液状态的定量化测评

高质量蠕墨铸铁的最佳生产方式是在炉前预处理(蠕化和孕育)后,对铁液状态进行快速准确测评,并根据测评结果进行快速调整,实现铁液状态的闭环控制。在本研究中,用热分析曲线整体形状表征蠕墨铸铁铁液状态,当热分析曲线之间的差别很小时,相同凝固条件下试样组织的蠕化率差别可忽略。热分析曲线整体形状法与定量金相、模式识别和数据库技术相结合,能够实现蠕墨铸铁铁液状态的定量化预测,为铁液状态的闭环控制奠定基础。     

Effects of transition from lamellar to compacted graphite on thermal conductivity of cast iron

Abstract

Different levels of magnesium were added to a standard grey iron alloy in order to obtain a range of graphite morphologies from lamellar to compacted graphite. The thermal conductivity/diffusivity of samples, solidified at different cooling rates, was investigated by means of the laser flash technique. There is a significant decrease in the thermal conductivity as the morphology transits from lamellar to compacted graphite. The thermal conductivity of grey iron decreases considerably at elevated temperatures, whereas the thermal conductivity of compacted graphite iron is less sensitive to changes in temperature. At increased nodularities, compacted graphite irons exhibit a maximum thermal conductivity at ～400°C. The influence from the cooling conditions on the thermal conductivity decreases as the morphology alters from lamellar graphite to compacted graphite. The effective thermal conductivity of cast iron is modelled by means of existing models for composites.     

Modelling of compacted graphite cast iron solidification-Discussion of microstructure parameters

A melt maintained for hours in a press pour unit allowed the following changes over time from spheroidal graphite to compacted graphite iron by casting thermal cups at regular time intervals.This provided extensive experimental information for checking the possibility of simulating solidification of compacted graphite irons by means of a microstructure modelling approach.During solidification,compacted graphite develops very much as lamellar graphite but with much less branching.On this basis,a simulation of the thermal analysis records was developed which considers solidification proceeding in a pseudo binary Fe-C system.The simulated curves were compared with the experimental ones obtained from three representative alloys that cover the whole microstructure change during the holding of the melt.The most relevant result is that the parameter describing branching capability of graphite is the most important for reproducing the minimum eutectic temperature and the recalescence which are so characteristic of the solidification of compacted graphite cast irons.     

脉冲电场对Al-5wt%Cu合金熔体的孕育形核作用

对Al-5wt%Cu合金熔体进行了电脉冲处理,采用热分析方法研究了脉冲电场对该合金凝固冷却曲线的影响.结果表明,电脉冲可显著细化Al-5wt%Cu合金的凝固组织,进而改善其热裂倾向.凝固冷却曲线和温变速率曲线揭示了脉冲电场对合金熔体的孕育形核作用.     

Assessment of modification level of hypoeu- tectic Al-Si alloys by pattern recognition of cooling curves

1 Introduction Due to their excellent castability and good mechanical properties, Al-Si alloys are the most important and most widely used casting aluminum alloys. A further increase in mechanical properties can be achieved by means of a modification treatment with Na or Sr. Without this treatment, the eutectic silicon crystallises into an acicular or lamellar morphology with poor properties; when a modifying element is added, it becomes a very fine and fibrous silicon network resulting in a…     

Influence of graphite morphology on dry sliding wear of flake graphite cast irons

Abstract

Four flaky graphite cast irons of different graphite structures with a pearlitic matrix were prepared to clarify the graphite structure's influence on the dry sliding wear property. Two melts of cast iron with different carbon contents were solidified at two different cooling rates. The four resultant samples had type A flaky graphite or type D eutectic graphite structure with different graphite volume fractions and fully pearlitic matrixes. A pin on the disc type wear test evaluated the four samples' dry sliding wear properties. Results showed that the type D graphite structure wore down faster than the type A graphite structure did. The type of graphite morphology influenced the specimen wear rate as strongly as the graphite volume fraction did in flaky graphite cast irons of this experimental range.