共查询到19条相似文献,搜索用时 156 毫秒
1.
2.
3.
4.
《中国铸造装备与技术》2019,(2)
球墨铸铁中石墨绝大多数呈球团状,但随着球墨铸铁壁厚增加,凝固时间的延长,球化孕育的衰退,反球化微量元素的富集,石墨会出现:蠕虫状、开花状、碎块状、水草状等形态,铸件表层到心部石墨形态由球团状,逐渐变为团絮状、蠕虫状、开花状,碎块状等三明治现象。石墨的分布也会出现一些特殊规律,如:列队石墨球,偏聚石墨球,石墨球漂浮等。这些现象已严重影响了球墨铸铁厚大部位的球化率。我们采用合适的碳当量、铁水中加入0.005%的Sb,采用低稀土球化剂,使用高效、长效孕育等工艺方法,成功将500mm×500mm×500mm的试块心部球化率提高至Ⅵ+Ⅴ≥80%。 相似文献
5.
6.
为解决厚大断面球墨铸铁中心部位石墨衰退和碎块状石墨缺陷问题,采用250 mm×250 mm×260 mm试块,分别使用3种球化剂进行了现场试验,最后指出:(1)防止厚大断面球墨铸铁件石墨衰退和碎块块状石墨的形成,可将化学成分控制在:w(C)3.4%~3.7%,w(Si)2.0%~2.3%,w(Mn)<0.35%,w(S... 相似文献
7.
8.
介绍了最大壁厚为110 mm球墨铸铁前轴的铸件结构及生产情况,针对生产中出现的铸件断面石墨球数少以及碎块状石墨,通过增加冷铁强制冷却,球化时添加纯La低RE球化剂,热包时随流加入石墨型增碳剂以及采取包内孕育+型内孕育+随流孕育的3次孕育等措施,使铸件厚大位置的球化率≥85%、石墨球数达到130个/mm2,满足使用要求. 相似文献
9.
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。 相似文献
10.
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。 相似文献
11.
介绍了4种不同类型的二次孕育剂对模拟尺寸为φ590 mm×800 mm的大断面球墨铸铁的组织及性能的影响。结果表明,二次孕育工艺对球铁尤其是大断面球铁的石墨及力学性能均有良好的改善作用;利用Si-Ba-Ca孕育剂进行孕育处理后再添加0.15%的该孕育剂作为二次孕育处理,可改善铸件组织及提高铸件力学性能;S-O孕育剂和Si-Ba-Ca孕育剂的效果相对较好,模拟铸件中碎块状石墨区域明显减少、石墨球形态圆整、球化率较高,还可以有效避免孕育衰退,使铸件获得较好的微观组织和最佳的综合力学性能。 相似文献
12.
To improve the mechanical properties of heavy section ductile cast iron, bismuth (Bi) was introduced into the iron. Five castings with different Bi content from 0 to 0.014 wt.% were prepared; and four positions in the casting from the edge to the center, with different solidification cooling rates, were chosen for microstructure observation and mechanical properties test. The effect of the Bi content on the graphite morphology and mechanical properties of heavy section ductile cast iron were investigated. Results show that the tensile strength, elongation and impact toughness at different positions in the five castings decrease with a decrease in cooling rate. With an increase in Bi content, the graphite morphology and the mechanical properties at the same position are improved, and the improvement of mechanical properties is obvious when the Bi content is no higher than 0.011wt.%. But when the Bi content is further increased to 0.014wt.%, the improvement of mechanical properties is not obvious due to the increase of chunky graphite number and the aggregation of chunky graphite. With an increase in Bi content, the tensile fracture mechanism is changed from brittle to mixture ductile-brittle fracture. 相似文献
13.
本文通过研究硅对高炉冷却壁用铸态球铁的力学性能和导热性能的影响,确定了硅含量的最佳范围;讨论了硅对硅对孕育效果及碎块块状石墨形成的影响。生产实践表明,采用本研究设计的低硅随流孕育方案,成功地生产出铸态厚高性球铁冷却壁。 相似文献
14.
Liu Jin-hai Yan Jian-shuai Zhao Xue-bo Fu Bin-guo Xue Hai-tao Zhang Gui-xian Yang Peng-hui 《中国铸造》2020,17(4):260-271
The quantity and morphology of spheroidal graphite have an important effect on the properties of ductile iron,and the characteristics of spheroidal graphite are determined by the solidification process.The aim of this work is to explore the precipitation and evolution of graphite nodules in hypoeutectic,eutectic,and hypereutectic ductile irons by thermal analysis,liquid quenching and metallographic technique.Results show that hypoeutectic ductile iron has the longest solidification time and the lowest eutectic temperature;eutectic ductile iron has the shortest solidification time;hypereutectic ductile iron has the highest eutectic temperature.After solidification is completed,hypoeutectic ductile iron has the lowest nodule count,nodularity and graphite fraction;eutectic ductile iron has the highest nodule count,nodularity and the smallest nodule diameter;hypereutectic has the highest nodule diameter and graphite fraction.The nucleation and growth of graphite nodules in hypereutectic ductile iron starts before bulk eutectic crystallization stage,however,the precipitation and evolution of graphite nodules of hypoeutectic and eutectic ductile irons mainly occur in the eutectic crystallization stage.The graphite precipitated in eutectic crystallization of hypoeutectic,eutectic,and hypereutectic ductile irons,are 61%,68% and 43% of total graphite volume fraction,respectively.Simultaneously,there are plenty of austenite dendrites in hypoeutectic and hypereutectic ductile irons,which are prone to shrinkage defects.Therefore,the eutectic ductile iron has the smallest shrinkage tendency. 相似文献
15.
16.
《中国铸造》2018,(6)
Differential thermal analysis experiments have been performed on samples machined from Y2-blocks cast with different high-silicon spheroidal graphite irons. Depending on magnesium, silicon, cerium and antimony content, the as-cast microstructure showed various levels of chunky graphite in the central part of the blocks. In contrast, the microstructure of the materials after remelting and resolidification during differential thermal analysis consisted of lamellar or compacted graphite. The formation of chunky graphite in the as-cast microstructure is rationalized using an index or silicon equivalent that has been recently suggested. The differences in the microstructures after differential thermal analysis are discussed in terms of available free magnesium. Emphasis is finally put on the striking differences in characteristic size of the microstructures made of compacted graphite as compared to lamellar graphite and chunky graphite. This leads to tentative conclusions about growth of compacted and chunky graphite which would be worthy of further experimental investigations. 相似文献
17.
18.
介绍了近年来我国铸铁件的产量和新制订、修订的铸铁件国标:(1)灰铸铁的发展在产量增速上虽有所放缓,但质量上却有很大提高,体现在:新国标中牌号的细化,掌握了HT300和HT350的生产技术,专用灰铸铁的开发。(2)球墨铸铁不仅在产量上快速发展,而且更有质的飞跃,概括为:发展速度令人惊异,从无到有,从少量生产到占世界球铁产量的49.5%;球铁应用领域不断扩大;开发出各种球化处理方法;系列化生产了球化剂和孕育剂。重点介绍了Si固溶强化铁素体球铁、高强度高伸长率球铁、低温铁素体球铁、珠光体基体球铁、ADI、奥氏体球铁、高强韧TWIP铸铁,并指出了生产高端球铁件的关键点——优化石墨、净化晶界、强化基体。(3)蠕铁的进步体现在:新的国标替代了旧的部标,蠕铁缸体缸盖的生产渐入佳境,蠕铁制动盘的扩大应用正在稳妥推进。 相似文献