RE多元复合孕育剂强化机理的研究

通过金相分析方法对RE多元复合孕育剂的孕育强化机理进行研究。分析发现,经0.5%RE多元复合孕育剂孕育的CE4.0%～4.1%铁液的铸铁件石墨形态明显改善,基体组织中珠光体晶粒细化且层片间距减小,初生奥氏体枝晶细化明显,所形成的共晶组织中共晶团数量显著增加,从而使铸件的抗拉强度从200MPa稳定地提高到250MPa,且综合工艺性能保持良好。     

灰铸铁和球墨铸铁凝固过程中的几个问题

详细介绍了灰铸铁和球墨铸铁的凝固过程,包括生核过程、初生奥氏体枝晶的析出过程以及亚共晶铸铁、过共晶铸铁、共晶铸铁的形成过程。阐述了初生奥氏体枝晶的形态和初生奥氏体枝晶对铸铁性能的影响以及对初生奥氏体枝晶的控制。分析了灰铸铁和球墨铸铁的共晶转变过程以及石墨的晶核。最终得出:(1)对于灰铸铁,组织中枝晶所占的体积分数提高,铸铁的强度随之提高;(2)对于球墨铸铁,初生奥氏体枝晶的数量和枝晶间距,对石墨球的形态、尺寸和分布状况有重要的影响;(3)将w(Al)量控制在0.005%~0.01%,既促进灰铸铁石墨生核,又不会诱发针孔缺陷;(4)采用含S、O的孕育剂可以使球化率提高、石墨球数增多、石墨球尺寸减小,从而提高球墨铸铁质量。     

强化高碳当量灰铸铁组织初探

对高碳当量铁水、应用Ti、Mn复合添加,利用Ti细化石墨,增加组织中奥氏体枝晶数量、细化奥氏体枝晶及影响奥氏体枝晶分布的作用和Mn消除基体中铁素体的作用,有效地克服了高碳当量灰铸铁石墨易粗大,奥氏体枝晶数量少及基体中易产生铁素体等不利因素的影响,使其强度有较大的提高.在实验条件下,碳当量4.0~4.2%时,组织为D型石墨、20%以上奥氏体枝晶和珠光体加索氏体基体的灰铸铁,强度均在HT300牌号以上.     

过共晶球墨铸铁中石墨球周围奥氏体壳的形成机制

有用着色腐蚀技术，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（0001）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。     

过共晶球铁凝固过程中奥氏体的生长方式与形貌特征

采用着色腐蚀技术显示出过共晶球铁中的高温凝固组织，观察分析过共晶球铁凝固过程中奥氏体的生长方式与形持征。结果表明：在非平衡凝固条件下，过共晶球铁凝固时通常会析出初生枝晶和晕圈枝晶，其形成条件主要与冷却速率和熔体的过冷有关。随铸件模数Mc增大，枝晶数量减少，二次臂间距显著增大，形态趋于不发达，由初生枝晶向晕圈枝晶过渡。当Mc≤0.3cm时，二次臂间距的实测值与理论预测值基本吻合。初生石墨球周围往往形成环状封闭奥氏体壳；共晶前期石墨球周围形成封闭或不封闭的框架奥氏体壳；共晶后期石墨球往往被周边生长着的共晶奥氏体所包覆，最终成为共晶奥氏体的一部分。     

复合变质剂对高铬白口铸伯组织与性能的影响

用定向凝固方法系统地测定了复合变质剂高铬白口铸铁基体组织数量，奥氏体树枝状晶二次枝晶臂间距、共晶区域中心碳化物间距和边界碳化物间距的影响，同时测定了力学性能。如果表明，加入复合变质剂使合金基体组织数量增加，二次枝晶臂间距ｄ减小，共晶区域中心碳化物间和边界碳化物间距减小，均匀度提高，碳化物长条状变为团块状。     

图外铸造文摘

90401 亚共晶铸铁的初奥氏体形状与强度的关系(日)/米田博幸/铸锻造热处理 1,1990 15—22 作者长期研究亚共晶铸铁的初晶奥氏体枝晶的形状与强度的关系,在成分、石墨的形状、数量以及基体组织一定的前提下,调整冷却速度,从而改变初生晶的形状。进而定量地研究初生枝晶形状、数量与机械性能的关系,结果表明:(1)随着初生枝晶的两次臂的间隔的减小,抗拉强度增加,而这种倾向随碳当量的增加而减少。当碳当量达4.0时,这种倾向几乎     

复合变质和电磁搅拌对过共晶铝合金组织的影响

采用L9(3^3)正交试验，通过OM、XRD等分析方法研究了三元复合变质剂与旋转磁场对A1-13Si合金晶粒的影响。结果表明：当变质剂为0．8％Cu-10P，0．35%RE，0．02％A1-10Sr组合时，变质效果好，初生硅尺寸减小到25～30μm。在三元复合变质基础上，施加旋转磁场可以进一步增强变质效果并能有效细化α-A1枝晶尺寸。     

Yb和Al-Ti-B复合变质对过共晶Al-Si铸造合金组织和性能的影响

采用光学显微镜、扫描电子显微镜、电子探针,研究了不同比例的稀土Yb和Al-5Ti-B复合变质剂对过共晶Al-20Si合金显微组织与性能的影响。结果表明,Al-20Si合金中添加0.5% Yb和0.3% Al-5Ti-1B复合变质剂使得粗大的多边形状、块状和五瓣星状初生Si变质为细小块状,共晶Si由粗大的片状或针状结构变质为细小颗粒或者纤维结构,而且粗大的α-Al枝晶被细化为等轴枝晶。然而,当Al-5Ti-B变质剂含量达到0.4%时,初生Si和共晶Si出现粗化现象。力学性能测试结果表明,合金的抗拉强度和延伸率分别增加了83.7%和92.1%。     

高碳当量灰铸铁用稳定化孕育剂的研究

采用微分热分析法、着色腐蚀技术及自动图象分析仪对比研究了１＃ＲＥ，６８Ｍｎ－Ｆｅ，６３Ｃｒ－Ｆｅ，３０Ｔｉ－Ｆｅ，纯Ｓｂ等稳定化孕育剂对高碳当量灰铸铁的过冷度，初生奥氏体枝晶粒量，共晶团数，石墨组织等的影响，研究了高碳当量灰铸铁的凝固组织及稳定化孕育剂的孕育机理，试验结果表明，稳定化孕育剂均能增大高碳当量灰铸铁的过冷度，增加初生奥氏体枝晶数量，共晶团数量，且随加入量的增加而增大，孕育作用的强弱按稳     

Preparation of in situ-formed WC/Fe composite on gray cast iron substrate by a centrifugal casting process

An iron-based composite reinforced by in situ-formed tungsten carbide particles was fabricated on gray cast iron substrate by a centrifugal casting process. The as-prepared composite was characterized by X-ray diffraction, scanning electron microscopy, and microhardness and wear testers. An appropriate pouring temperature (1300 °C) of the gray cast iron melt was chosen considering the dissolution temperature of the tungsten wires determined by differential scanning calorimetry. The experimental results showed that the tungsten wires were dissolved partially by the cast iron melt. As a result, primary and secondary tungsten carbide particles and pearlite with a negligible amount of graphite flakes were formed as the reinforcing phase and the matrix, respectively. The composite with a thickness of about 3 mm was dense and metallurgically bonded to the gray cast iron substrate. Wear resistance was determined by a pin-on-disc wear test technique, indicating that the composite containing high volume fraction of hard tungsten carbides presented higher wear resistance compared with the unreinforced gray cast iron.     

不同孕育剂处理的高强度灰铸铁加工性能研究

为研究不同孕育剂对灰铸铁切削加工性能的影响,制备了高强度HT350材质的试样.对比研究了孕育剂75SiFe、SrSi、BaSi、SiSr(80％)+75FeSi(20％)处理的高强度灰铸铁的力学性能和切削加工性能.结果表明,SiSr(80％)+75FeSi(20％)复合孕育处理的灰铸铁较单一孕育处理的灰铸铁石墨细小弯曲,基体组织均匀性好,具有较高的硬度以及较小的切削抗力,但其断面敏感性较大.单一孕育剂中75SiFe孕育处理的灰铸铁具有较高的抗拉强度、较小的硬度以及较低的断面敏感性.灰铸铁中A型石墨越细小,基体组织越均匀,灰铸铁的加工性能越好,说明显微组织的均匀性对灰铸铁的加工性能具有较大影响.     

Volume change during the solidification of grey cast iron: its relation with the microstructural variation,comparison between experimental and theoretical analysis

The expansion/contraction during the solidification of grey cast iron was studied using Linear Variable Differential Transformer (LVDT). The experiments were conducted with and without melt treatment. Two types of inoculant used for melt treatment: ASSC (Si, Ca, Sr & Al) and MBZCAS (Si, Ca, Zr, Ba, Mn & Al). Microstructural investigations carried out to quantify the eutectic cells, undercooled graphite, primary austenite and secondary dendritic arm spacing (SDAS). It was found that the casting shows hardly any shrinkage during early solidification but in the eutectic region, the casting expands until the end of solidification. The measured and the calculated volume changes are close to one another, but the former shows more expansion. The addition of MBZCAS promotes more flake graphite, and ASSC does not increase eutectic cells much. In addition to that, it lowers the primary austenite fraction, promotes more eutectic growth, decreases undercooled graphite and SDAS. As a result, the volume expansion changes in the eutectic region.     

Improving chill control in iron powder treated slightly hypereutectic grey cast irons

Recent studies revealed that in eutectic to slightly hypereutectic grey irons (CE = 4.3%-4.5%) the presence of austenite dendrites provides an opportunity to improve the cast iron properties, as a high number of eutectic cells are "reinforced" by austenite dendrites. An iron powder addition proved to be important by promoting dendritic austenite in hypereutectic irons, but was accompanied by adverse effect on the characteristics of potential nuclei for graphite. The purpose of the present paper is to investigate the solidification pattern of these irons. Chill wedges with different cooling moduli (CM = 0.11 - 0.43 cm) were poured in resin bonded sand and metal moulds.Relative clear / mottled / total chill measurement criteria were applied. Iron powder additions led to a higher chill tendency, while single inoculation showed the strongest graphitizing effect. The various double treatments show an intermediate position, but the inoculant added after iron powder appears to be the most effective in reducing base iron chill tendency, for all cooling moduli and chill evaluation parameters. This performance reflects the improved properties of (Mn,X)S polygonal compounds as nucleation sites for graphite, especially in resin bonded sand mould castings. Both austenite and graphite nucleation benefit from a double addition of iron powder + inoculant,with positive effect on the final structure and chill tendency.     

机车用灰铸铁件组织中E型石墨的消除

在灰铸铁产品金相组织中经常会出现E型石墨,E型石墨的存在严重影响了灰铸铁的性能,遗传因素是E型石墨产生的主要原因。在铁水孕育处理过程中加入增碳剂和加入硅钡复合孕育剂,能够有效抑制E型石墨的产生。     

半固态灰铸铁的制备与显微组织

建立了一种不需搅拌和其它附加处理的半固态灰铸铁制备技术 ,用浇注前合理调整熔体温度或调温 适当快冷的铸造方法 ,并配以合适的凝固冷却速度 ,成功地制备了球状初生奥氏体圆整、尺寸细小、分布均匀的半固态亚共晶灰铸铁 ,得到了最佳工艺条件 ,并用铸铁金相计算机辅助检测系统 ,对初生奥氏体的形状系数和等效直径进行了测量与统计分析 ,定量描述了半固态组织的特性     

球墨铸铁中的奥氏体枝晶及球墨铸铁的偏析--球墨铸铁基础理论的最新发展(三)

介绍了球墨铸铁中奥氏体枝晶的形成，分类及影响因素，指出奥氏体枝晶排列方向的控制对进一步挖掘球铁力学性能潜力的意义，同时阐述了溶质元素，凝固速度等因素对球铁偏析的影响规律。     

Fuzzy neural network analysis on gray cast iron with high tensile strength and thermal conductivity

To develop a high performance gray cast iron with high tensile strength and thermal conductivity,multivariable analysis of microstructural effects on properties of gray cast iron was performed. The concerned parameters consisted of graphite content,maximum graphite length,primary dendrite percentage and microhardness of the matrix. Under the superposed influence of various parameters,the relationships between thermal conductivity and structural characteristics become irregular,as well as the effects of graphite length on the strength. An adaptive neuro-fuzzy inference system was built to link the parameters and properties. A sensitivity test was then performed to rank the relative impact of parameters. It was found that the dominant parameter for tensile strength is graphite content,while the most relative parameter for thermal conductivity is maximum graphite length. The most effective method to simultaneously improve the tensile and thermal conductivity of gray cast iron is to reduce the carbon equivalent and increase the length of graphite flakes.