PIXE ANALYSIS OF GRAPHITE PHASE IN NODULAR CAST IRON

The graphite phase has been extracted from the nodular cast iron to measure the concentration of trace element in it. The impurity phase was removed from the extracted matter by dissolving it with HCl and HCl+H2O2 to get the pure graphite phase. PIXE measurements were performed with thick targets of the pure graphite phase. Differences in the trace element concentrations between the graphite phase and the matrix have been observed. The effect of Ti and As in graphite phase on the nodularization rate and the mechanical properties have been studied.

Study on numerical simulation of nodular graphite iron microstructure formation

In this paper, the mathematical and physical model was developed based on thermodynamics and solidification theory before the eutectoid transformation of nodular graphite iron occurred. The Local Element Substitute and Magnification Method was brought forward and 3-dimensional numerical simulation program based on the model and the new assistant algorithm was developed and used to calculate the samples. Results of calculation have good agreement with experimental data. To display the microstructure formation during solidification of nodular graphite iron, a 2-dimensional numerical simulation program combined with the result of the 3-dimensional numerical simulation of experimental samples was compiled.

A reliable and consistent production technology for high volume compacted graphite iron castings

The demands for improved engine performance,fuel economy,durability,and lower emissions provide a continual challenge for engine designers.The use of Compacted Graphite Iron(CGI)has been established for successful high volume series production in the passenger vehicle,commercial vehicle and industrial power sectors over the last decade.The increased demand for CGI engine components provides new opportunities for the cast iron foundry industry to establish efficient and robust CGI volume production processes,in China and globally.The production window range for stable CGI is narrow and constantly moving.Therefore,any one step single addition of magnesium alloy and the inoculant cannot ensure a reliable and consistent production process for complicated CGI engine castings.The present paper introduces the SinterCast thermal analysis process control system that provides for the consistent production of CGI with low nodularity and reduced porosity,without risking the formation of flake graphite.The technology is currently being used in high volume Chinese foundry production.The Chinese foundry industry can develop complicated high demand CGI engine castings with the proper process control technology.

Strength Characteristics of Inoculated and Nodularised Thin Wall Ductile Iron Castings

Carbide precipitates in Thin Wall Ductile Iron (TWDI) used for automotive applications needs to be eliminated or reduced for improved strength, ductility, crack propagation resistance and good machinability. Ductile iron thin section profiles (≤3 mm) present danger of massive carbide precipitations in the as-cast sample. Precipitated carbide phase is brittle and negatively affects the mechanical properties of the iron matrix. The suppression of carbide formation is associated with the nucleating properties of the nodularizer and innoculant alloys. This treatment is vital in ensuring that carbide precipitation, flake graphite structure and non-nodular graphite phases are reduced or completely eliminated in the TWDI castings. Therefore, the temperature and technique of treatment would influence the yield of the process, and ultimately the mechanical properties. In this study, the effect of nodularization and inoculation treatment temperature on the microstructure and mechanical properties of TWDI castings is examined. The results indicate that good nodularity and nodule count with better percent elongations are achieved using low treatment temperatures in descending order of 1490°C, 1470°C and 1450°C, but have negative effect at lower treatment temperature of 1430°C. However, TWDI castings have superior properties in terms of nodule counts and nodularity at 1450°C. Treatment temperature does not produce significant influence on ultimate tensile strength (UTS) and hardness of TWDI castings. TWDI castings show poor nodularity, nodule count and ductility at higher inoculation treatment temperatures of 1550°C, 1530°C and 1510°C.

随流孕育对高镍奥氏体球墨铸铁的影响

介绍了高镍奥氏体球墨铸铁排气歧管铸件的结构及首次交付的样件在试验中的断裂问题,通过生产试验,验证了排气歧管断裂的原因是在浇注过程中不进行随流孕育,导致铸件金相中产生碎块状石墨,使铸件力学性能下降,加速了铸件开裂失效的风险。最后指出:(1)高镍奥氏体球墨铸铁件在生产过程中,除了保证球化处理严格按照工艺要求外,在浇注过程中还必须进行随流孕育;(2)在保证球化处理过程符合工艺要求的前提下,随流孕育会进一步增加铁液在凝固过程中石墨结晶的核心,增加共晶团数,避免碎块石墨的产生。

高镍奥氏体球墨铸铁涡壳的铸造工艺优化

介绍了高镍奥氏体球墨铸铁涡壳铸件的结构及铸造工艺,针对试制过程中出现的表面缩孔、缩松、显微缩松以及组织中的碎块状石墨、表面恶化层、碳化物等问题进行了工艺优化,最后指出:(1)高镍奥氏体球墨铸铁液态收缩量大、石墨化膨胀弱,冒口设计遵循顺序凝固原则是防止涡壳产生缩孔、缩松缺陷的有效措施;(2)涡壳厚处和舌尖易形成碎块状石墨,强化孕育可防止缺陷的产生;(3)表面恶化层超标,可通过较高的残余镁量和砂芯刷涂料进行防止;(4)由于冷却速度较慢,舌尖部位碳化物析出数量较多,良好的孕育可减少碳化物析出量,热处理也可改变碳化物体积分数及其形态。

采用硅氧化预处理工艺生产球墨铸铁

介绍了球墨铸铁的石墨形核,详细阐述了硅氧化预处理工艺,并与不采用硅氧化预处理工艺的传统球化孕育处理工艺生产的球墨铸铁组织、力学性能及生产成本进行对比分析,最后指出:利用75SiFe脱氧生成的氧化物(SiO_(2))作为球墨铸铁石墨球生长的过渡层,与球状石墨的生长有着良好的匹配度,为球状石墨的生长提供了充分的条件,该工艺降低了生产成本,简化了操作过程,可稳定生产球化率≥90%的球墨铸铁。

QT500-7球墨铸铁汽车制动钳与支架反白口产生原因

某QT500-7球墨铸铁汽车制动钳与支架日常检验中出现两种不同特征的反白口缺陷,采用宏观观察、化学成分分析、金相检验、显微硬度测试、扫描电镜与能谱分析等方法对反白口缺陷的产生原因进行分析。结果表明:成分偏析是制动钳试样反白口缺陷形成的主要原因,而成分偏析和孕育衰退是支架试样反白口缺陷形成的主要原因;制动钳试样存在反石墨化元素的偏析,增大了铁水的过冷倾向,从而形成反白口缺陷;支架试样中心区域存在孕育衰退,加上反石墨化元素的偏析,使试样形成反白口缺陷。

Thermal conductivity of cast iron-A review

This paper gives a brief introduction to the four research methods for the study on thermal conductivity of cast irons,including experimental measurement,statistical analysis,effective medium theory and numerical simulation.Recent studies on the thermal conductivity of various cast irons are reviewed through the influence of alloying elements,structural constituents,and temperature.The addition of alloying elements is the main reason that restricts the thermal conductivity of cast irons,especially spheroidal graphite cast iron.The connectivity of graphite has a significant effect on the thermal conductivity of flake and compacted graphite cast irons,semiquantitative and quantitative analysis of this factor is a key and difficult point in the study of thermal conductivity of cast irons.The thermal conductivities of different types of cast irons show varying degrees of dependence on temperature.This phenomenon is the combination of graphite and matrix,rather than just depending on graphite morphology.The study of the relationship between individual phase and temperature is the focus of future research.These summaries and discussions may provide reference and guidance for the future research and development of high thermal conductivity cast irons.

DISTRIBUTION AND EFFECT OF Ce IN RE BEARING DUCTILE IRON

The dependence of nodularization of graphite upon Ce content in RE bearing nodular cast iron,prepared by directional solidification,has been investigated by electrolytic extraction-radioisotope assay analysis of Ce in each phase of the iron together with measurement of nodulized graphite.Results show that the Ce occurs mainly as alloyed form. In the graphite phase,the Ce content is believed to be characterization of nodularization.The graphite would completely nodulized only the Ce is over a certain content in graphite phase.

“ISO 17804:2020 奥铁体球墨铸铁-分类”标准解读

奥铁体球墨铸铁具有优异的综合力学性能,在工程机械、矿山机械、交通运输车辆等领域广泛应用。随着对奥铁体球墨铸铁特性的认识提高和不断发展的应用需求,国际标准化组织修订了“ISO 17804奥铁体球墨铸铁-分类”,并于2020年颁布。分析解读了新修订标准的技术条款,新标准的牌号和技术指标与2005版标准的差异;新标准增加了技术术语,提高了球化率要求,修改了试块和试样制备技术要求,增加了材料检验批次的规定。笔者汇总了2020版标准与2005版标准的主要技术差异以及存在的问题,以便于理解掌握新修订的“ISO 17804:2020奥铁体球墨铸铁-分类”。

超声波声速仪在铸铁材料检测中的问题探讨

利用测量系统分析(MSA)这一质量工具,证实了超声波声速仪检测铸铁球化率与蠕化率是一种可靠的手段,分析了声速控制标准不同的原因可能是输入厚度的不准确、工件表面粗糙度的差异、声速仪品牌的不同。最后指出:超声波声速值与蠕化率/球化率的对应关系不是一个固定值。划定各种材料的声速控制范围时,一定要阐述清楚检测条件,如铸件表面状态、输入厚度的误差范围、声速仪型号等,控制这些变量后,对应声速值与金相,形成适应各厂家状况的管控范围。

石墨漂浮对球铁机械性能的影响

研究了石墨漂浮对球铁机械性能的影响规律．结果表明：石墨漂浮的出现使球铁的抗拉强度降为非漂浮区的８０％；延伸率为非漂浮区的７５％；断面收缩率为非漂浮区的６０％；冲击韧性平均降低为非漂浮区的２０％；残余屈服强度略有降低，对布氏硬度影响不大．石墨漂浮对球铁机械性能的影响不取决于铸件漂浮层深度，而取决于漂浮的有无．

Mn、Cu对球墨铸铁组织性能的影响

为获得高强度高塑性的球墨铸铁,通过加入微量合金元素Mn和Cu,研究Mn和Cu对球墨铸铁微观组织和力学特性的影响。结果表明:Mn的加入提高了球墨铸铁中珠光体含量、球墨铸铁的抗拉强度和硬度,但塑性下降;在Mn含量一定时,添加适量的Cu后,球墨铸铁的性能进一步提高。研究发现,添加适量的合金元素Mn和Cu可生产高强度的球墨铸铁,且塑性值比对应的国家标准大幅度提高。

过共晶球墨铸铁中石墨球周围奥氏体壳的形成机制

采用着色腐蚀技术 ,可清晰地显示出过共晶球墨铸铁中的高温凝固组织 ,观察分析了石墨球周围奥氏体壳 (奥氏体壳是奥氏体枝晶的一部分 )的形成机制。结果表明 ,初生枝晶和晕圈枝晶交替生长 ,促成石墨球周围奥氏体壳的形成 ;奥氏体以石墨生长面 (0 0 0 1)为衬底形核、生长 ,在初生石墨球周围形成环状封闭奥氏体壳 ;共晶前期石墨球在枝晶臂间或框架中形核、生长 ,尔后为枝晶高次臂所包围 ,形成封闭或不封闭的框架奥氏体壳。共晶后期石墨球不形成奥氏体壳。

激光表面处理对球墨铸铁冲蚀性能的影响

研究了激光表面熔化处理的球墨铸铁试样在石英浆料中的冲刷腐蚀特性 .结果表明 ,经过激光表面处理的球墨铸铁与原球墨铸铁相比具有很高的硬度和较好的耐冲蚀磨损性能 ,当冲刷角度为 0°、冲刷速度在 0 .5 8～ 4.47m/ s范围内时 ,激光处理试样的耐磨性是球墨铸铁试样的 3倍以上 ;冲刷角度对激光处理球墨铸铁的冲蚀磨损性能有很大的影响 ,激光试样的磨损质量损失随着冲刷角度的增大而增加 ,当冲刷角度为 45°时 ,激光试样与球墨铸铁试样的单位磨损质量损失已很接近 ;在 p H值处于 4～ 7的范围内 ,激光处理试样的耐腐蚀磨损性能为球墨铸铁的 2～

炉前快速评价球墨铸铁球化质量的新方法

介绍一种球铁球化质量炉前快速检测新技术。在理论分析与实验研究的基础上 ,提出了一种快速测定液态合金表面张力的新方法——气泡幅频当量法。通过毛细管向被测液体吹气 ,利用高精度数据采集与处理系统快速测得规定时间内所形成气泡的个数 (频 )以及气泡内微压差变化 (幅 ) ,以此两参数作变量 ,经适当运算后形成的当量来表征液体表面张力的变化。铁水表面张力与其石墨形态之间有密切关系 ,因此 ,应用气泡幅频当量法 ,可以实现球铁球化质量的炉前快速检测。

碳当量对球墨铸铁石墨漂浮的影响

采用金相现察法研究了碳当量w_（ＣＥ）对球墨铸铁石墨漂浮程度及漂浮区内石墨形态的影响规律．结果表明：w_（ＣＥ）高是引起石墨漂浮的主要原因，石墨漂浮的出现有一个临界w_（ＣＥ）值，但这个临界值不是固定的，它还与铸件厚度和浇注温度有关；w_（ＣＥ）增加石墨漂浮带深度增大；w_（ＣＥ）增加漂浮区内石墨变坏的程度加剧，严重时出现爆炸石墨；w_（ＣＥ）对石墨漂浮的影响对壁厚的敏感性较大，铸件壁厚越大，随w_（ＣＥ）值增加石墨漂浮增加的幅度越大．

改性纳米SiC粉体强化球墨铸铁的耐磨损性能

采用改性纳米SiC粉体对球墨铸铁进行了强韧化处理,研究了不同的纳米SiC粉体加入量对球墨铸铁的微观组织、力学性能以及耐磨损性能的影响。结果表明,经改性纳米SiC粉体强韧化处理后,球墨铸铁中的石墨球尺寸减小,圆整度提高,铁素体含量增多,球墨铸铁的韧性和耐磨损性能提高。当粉体加入量为0.1%(质量分数)时,其延伸率和冲击功分别增加了19%和194%。耐磨损性能提高的原因是石墨球形态的改善和基体组织韧性的提高。

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。