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。     

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。     

大断面球铁件电炉熔炼工艺及石墨畸变机理研究

探讨了大断面QT600-3球铁件电炉熔炼生产工艺的技术要点,检测了试生产条件下球铁单铸试块与本体试块的化学成分、金相组织与力学性能,基于石墨结晶核心和石墨形态的分析,探讨了石墨畸变机理。生产试验结果表明:炉外增Si预处理增加铁液成核,轻、重稀土混合使用作为球化剂,侧重后期孕育,适当降低浇注温度,合理使用Cu元素,是电炉熔炼工艺生产大断面球铁件的重要环节;采用电炉熔炼工艺生产大断面球铁件,球化等级与化学成分稳定控制有关,抗拉强度、伸长率等力学性能与化学成分、基体组织有关;Y在铁液中形成高熔点Y2O3作为石墨析出的核心,可获得良好石墨形态;大断面球铁件中,Ti、Cu元素的偏析和球化元素Mg或稀土(Y、La、Ce)的氧化,破坏了奥氏体壳的稳定性,是造成石墨畸变的主要原因。     

球墨外围奥氏体壳的形成过程与对石墨畸变的影响

本文用彩色金相法研究了球墨外围奥氏体壳的生长过程及奥氏体对石墨畸变的影响。结果表明,球墨外围的奥氏体壳不是连续的奥氏体层,而是由若干个楔形晶体组成。由于球墨外围奥氏体成核的有利条件不同;故在不同位置先后成核并生长。之后,互相接触形成一个壳。 经电子探针分析,沟槽中正偏析元素及低熔点金属含量高,因而沟槽液体的熔点低、凝固慢。根据沟槽的凝固速度,奥氏体壳可分成快封闭、慢封闭及不封闭三种类型,与石墨球的畸变有密切关系。     

硅对铸态厚断面高韧性球墨铸铁组织及性能的影响

研究了硅对铸态厚断面高韧性球墨铸铁组织及性能的影响。试验结果表明,硅主要分布于基体中,富集于奥氏体壳局部区域时,降低奥氏体壳的熔点,延长石墨自由生长的时间,造成石墨畸变。在铸件壁厚为100mm,树脂砂工艺条件下,硅含量为2．0％～2．5％时,石墨球化等级2～3级,球径等级6-7级,基体为铁素体。抗拉强度大于400MPa,伸长率大于20％,-20℃时的冲击韧度在16J／cm^2以上。硅含量达到2．9％时,易产生开花状石墨和碎块状石墨,铸件的性能严重下降。     

石墨的球状生长--球墨铸铁基础理论的最新发展(二)

球形晶体的结晶学条件要求雏晶必须有大量辐射对称的小角分枝;此外,这些小角度分枝应具备“规则分枝”特征（即相同的生长习性与生长速度）。在众多球化理论中,缺陷生长理论较符合球形晶结晶学原理,而石墨的缺陷生长与溶液结晶时的过冷有密切关系,化学成分、冷却速度等工艺因素都通过动力过冷、成分过冷、热学过冷影响石墨螺型缺陷决定最终生长成的石墨形状。对石墨球在奥氏体晕圈（壳）包围下生长过程进行了研究。用彩色金相方法揭示出奥氏体壳的形成过程并将奥氏体壳分为快封闭、慢封闭、不封闭三种类型,讨论了它们与石墨畸变的关系。快封闭的奥氏体壳保证得到圆整的石墨球,慢封闭与不封闭都使石墨形成畸形。     

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。     

QT900-2高强韧厚大断面球墨铸铁的研究

研究了Sb和热处理工艺对厚大断面球墨铸铁组织和性能的影响,试验结果表明:(1)合理的RE加入量可以中和Sb的反球化作用,改善石墨形态,增加石墨球数量;(2)Sb强烈细化珠光体,但是含量太高会影响球化和导致碳化物的生成;(3)采用940℃(3 h)正火+460℃(4 h)回火的热处理工艺,合金元素含量为w(Cu)1.0%、w(Sn)0.15%、w(Sb)0.025%时,厚度为70 mm的附铸试块性能达到了QT900-2的要求,尺寸为500 mm×500 mm×700 mm的方形试块布氏硬度达到了311 HB以上,并且硬度偏差只有17 HB。     

球铁中干扰元素Sb和Mg、Ce的相互作用

本文用带能谱仪(EDAX9100)的扫描电镜(SEM505),对球铁中的微粒进行微区定量分析,以研究球铁中干扰元素Sb和Mg、Ce的相互作用。结果发现:Sb和Mg形成高熔点化合物Mg3Sb2,使铁水中游离Mg原子减少,因此引起球化衰退:Ce能和Sb形成熔点更高的化合物Cesb,从铁水中清除Sb原子,从而中和了Sb的有害影响。     

厚大断面球墨铸铁件的生产

大断面球铁件由于冷却缓慢,共晶凝固时间延长,引起了石墨畸变,石墨球数减少,共晶团粗大,元素偏析,使铸件易出现球化衰退,石墨过大,石墨漂浮、偏析、缩孔和缩松等缺陷产生,这是在铸造生产上值得研究的问题。我厂1985年接受了TTI-10型注塑机铸件的生     

Intergranular fracture caused by trace impurities in an Al–5.5 mol% Mg alloy

A coarse-grained Al–5% Mg alloy, which does not show high temperature embrittlement, is successfully prepared using high purity raw materials and a graphite crucible. By preventing the contamination of sodium and hydrogen, it becomes possible to examine separately the effects of various trace elements on hot ductility in the Al–5% Mg alloy. Sodium, calcium, or strontium of 2 mol ppm brings about the high temperature embrittlement based on intergranular fracture, while lithium of 4 mol ppm does not. Sodium is the most highly embrittling among such detrimental elements. The detrimental effect of such impurity is due to its segregation to grain boundaries. Further, the embrittlement caused by sodium or strontium of 2 mol ppm is greatly suppressed by an addition of more than 1000 mol ppm of silicon which scavenges those detrimental elements from grain boundaries.     

对球铁石墨畸变的认识

对球铁生产中经常爱生的各种畸形石墨的产生原因进行探讨。指出球状石墨畸变都是在石墨长大过程中，由于各种因素引起奥氏体壳破裂而造成的。提出防止球墨畸变的措施是：(1)严格控制球化剂的成分和加入量；(2)对微量元素的含量要严格控制；(3)球化处理温度不宜过高；处理后铁液停留时间不宜太长；孕育要适当；(4)浇注后应使铸件快速冷却。     

Trace Elements in Nodular and Compacted Graphite in Cast Iron

Abstract

Secondary Ion Mass Spectrometry (SIMS) was used to qualitatively analyse the distribution of trace solutes in nodules, compacted graphite (CG) particles, and the surrounding matrix in Mg-treated cast iron. In both nodular- and compacted-graphite cast iron, Mg was clearly observed to be present in the graphite particles. Ca and Ti were also observed in the particles at lower levels than Mg. The S was uniformly distributed at a low level throughout the cast iron, with higher concentrations in graphite particles containing Mg and Ca. The distribution of oxygen was also observed to be uniform throughout the graphite and matrix, with higher ion signals than S. The present results support the theory of nodule or compacted graphite growth in which the nodularising elements Mg or Rare Earths are incorporated into the graphite lattice during growth, or adsorbed onto the prismatic or pyramidal planes. The results do not support the theories which assume the nodularising elements react with Al and S, indirectly affecting nodular growth.     

钇基重REMg球化剂在风电铸件中的应用

介绍了QT400-18AL的主箱体和QT450-10的3 MW行星架铸件的要求和铸造工艺,以及生产厚大球铁铸件必须重视的问题,试验结果显示:应用Y基重REMg球化剂生产大断面风电球铁铸件,具有较强的抗球化衰退能力,铸件的各项力学性能指标完全符合材料要求。分析Y基重REMg球化剂抗球化衰退的原因为:①重RE元素沸点高;②不会发生因返S现象而导致的球化衰退;③具有较强的抗石墨畸变能力;④充分利用了RE元素间和Mg、Ba、Ca之间互为补充的叠加作用及复合作用。     

铸铁中微量元素分布规律的异化及应用

Pb、As、Sn等微量元素在不同形态的石墨区域中有不同的分布规律；在A型石墨区偏聚在基体中，在D型石墨区偏聚在石墨上。利用这两种分布规律，制取含Pb、As、Sn D型石墨铸铁，使Pb、As、Sn主要聚集在石墨上，微量残留在基体中，可以获得良好的力学性能。     

Magnesium Map of the Spheroidal-graphite Structure in Ductile Cast Irons

Abstract

In this paper, the author puts forward a new proposal relating to the nucleation and growth mechanism of spheroidal graphite in magnesium-treated cast irons. The Site Theory can not only explain the nucleation and growth mechanism for spheroidal graphite, but can be also applied to the understanding of all other forms of graphite in cast irons. A magnesium map of the microstructure was analysed using EPMA in conjunction with a coloured mapping display system. A Mg halo was found as a segregation around the spheroidal graphite nodules. Although inclusions were observed within some graphite nodules, these also had an Mg halo. These results were considered sufficient to prove the site theory.     

模拟软件参数选择对灰铸铁件缩松预测的影响

基于铸件缩松和补缩区的模拟计算,研究了40 mm×200 mm×1 00 mm试块在不同边界传热系数、型砂强度、石墨析出率条件下缩孔和缩松行为.模拟研究表明,石墨析出率变化对铸件缩孔形成有明显影响,应结合铸件的金相来选择MAGMA软件的石墨析出率；型砂强度改变对灰铸铁的补缩区的影响不大,在模拟计算时,可选取默认值stable;铸件与型砂的界面换热系数对铸件补缩区的影响也较小,可选取1 000作为默认值.     

Rapid solidification of steel droplets with different carbon contents in drop tube

Rapid solidification is regarded as being an effective method to refine the microstructure and reduce or eliminate the segregation of alloying elements.In this study the microstructures of rapid solidified carbon steel droplets (cooled in silicone oil) with different C contents by drop tube processing were observed.The volumes of droplets were set to be 2 mm×2 mm×2 mm (TM) and 5 mm×5 mm×5 mm (FM).For most samples,the microstructures are nearly the same from the surface to the center region.The microstructures of the FM samples with higher C content are much finer than those of the TM samples,which is the opposite of the situation with the lower C content samples.The distribution of C along the diameter of each sample was detected.The segregation of C was observed in TM samples with higher C contents while not in FM samples.This is regarded as relating to recalescence and the diffusion of C atoms during the solidification process.