Fracture analysis of chilled cast iron camshaft

The fracture of a camshaft made of chilled cast iron, installed in a home-made Fukang car, happened only after running over a distance of 6,200 km. The fractured camshaft was received to conduct a series of failure analyses using visual inspection, SEM observation of fracture section, microstructure analysis, chemical composition analysis and hardness examination and so on, while those of CKD camshaft made by Citroen Company in France was also simultaneously analyzed to compare the difference between them. The results showed that the fracture of the camshaft mainly results from white section in macrostructure and Ledeburite in microstructure; the crack in the fractured camshaft should be recognized to initiate at the boundary of coarser needle-like carbide and matrix, and then propagate through the transverse section. At the same tide, the casting defects such as dendritic shrinkage, accumulated inclusion and initiated crack and abnormal external force might stimulate the fracture of camshaft as well. Based on failure analysis, some measures have been employed, and as a result, the fracture of home-made camshafts has been effectively prevented.

Effect of Nb on Structure and Mechanical Properties of Chilled Cast Iron at Room and Elevated Temperatures

Effect of Nb on microstructure and mechanical properties of chilled cast iron at room and elevated temperatures isstudied in this research. The results demonstrate that the cast structure and mechanical properties of chilled castiron at room and elevated temperatures are improved with the addition of trace amount of Nb. However, if Nb wasadded too much, the cast structure and mechanical properties of chilled cast iron would deteriorate. The suitablecontent of Nb in chilled cast iron is about 0.05% (mass fraction). Except the dissolution in the matrix of cast ironthe excessive Nb will form Nb-rich phases in three morphologies. Those are lumpy NbC, complicated strip-like phaseand compound with pearlite structure.

Effect of Lanthanun on micructure and properties of a chilled iron camshaft

Inoculation can reduce the chill depth of a chilled iron,and therefore influence the microstructure and properties of the iron.In this paper,the effect of rare earth Lanthanun (La) on the microstructure and properties of a chilled iron camshaft was studied.The results show that the La addition efficiently enhances the mechanical properties,yet with the unfavorable effect of decreasing the chilled depth and hardness.Moreover,La promotes graphite concentration and results in large graphite size,as well as A-type graphite.It is also found that excessive La destroys the interconnection and directivity of ledeburite.According to the experimental results,the optimum adding content of La should be no more than 0.02wt.%.

Application of Insert Chill Iron Melt in Investment Casting

The cast-steel creeper tread is a part with complex external surface and internal shape, having a hot spot cased by the uneven wall thickness. As the hot spot is far away from the gating system and the feeding channel is narrow, it is difficult to be fed by setting up a casting head, leading easily to shrinkage and causing great problems for investment casting. In this paper, the qualified castings can be successfully poured by feeding method of insert chill iron melt, smart design and placement process of chill, to realize simultaneous solidification of castings. The shrinkage of creeper tread is solved and the precision of castings is improved. This method exhibits easy operation, excellent feeding effect and simplified gating system to improve yield rate. Furthermore, it could save raw material, reduce waste product and lower product cost by using the insert chill iron melt in investment casting. The production practices showed that the qualified castings can be successfully poured by increasing feeding pressure, placing an internal chill to adjust the temperature of hot junction segments and realizing simultaneous solidification of castings.

Effect of Metallic, Nonmetallic, Water Cooled and Cryogenic Chills on Pearlite Content (PC), Eutectic Cell Count (ECC) and Grain Size (GS) of Hypo Eutectic Nickel Alloyed Cast Iron

This paper presents the results obtained, deductions made from solidification behaviour and a series of micro structural studies such as pearlite content, eu-tectic cell count and grain size of hypoeutectic gray cast iron which was sand cast (CO2 moulding) using metallic, nonmetallic, water cooled and subzero (cryogenic) end chills. Hypo-eutectic cast irons containing C 3.42, Si 2.4 and Ni 1.5 with impurity contents (S, P, Mn etc.) were solidified unidirectionally in an American Foundrymen Society (AFS) standard mould, the end of which was provided with different end chills to study the effect of chilling during solidifi-cation. The melts were inoculated with 0.3% Fe-Si to promote graphitization. It was observed that the transition from one structure to another is more gradual than normally obtained in the structure of cast irons solidified mul-ti-directionally in a sand mould at room temperature. Austenite dendrite interactions were shown to be a major factor in determining the microstructure, in which the higher dendrite reaction leads to changes in DAS, ECC and GS. It is observed that, the number of eutectic cells is an index of graphite nucleation and the effect of these on structure, since the eutectic cells are developed on the graphite nuclei during solidification.

中镍无限冷硬球墨铸铁轧辊辊颈缺陷原因分析及应用

分析了中镍无限冷硬球墨铸铁轧辊离心铸造时产生气孔、夹渣的工艺原因,采取了预脱氧处理、控制稀土镁球化剂使用率、提高浇注速度、提高型砂透气性、控制混合保护渣使用量、配箱时间控制在3 min以内等措施,辊颈气孔和夹渣产生的废品率从40%降低到6%以内,有效降低了废品率。

高镍铬无限冷硬球墨铸铁轧辊工作层离心铸造过程数值模拟

借助有限元模拟软件ProCAST对高镍铬无限冷硬球墨铸铁轧辊工作层离心铸造过程进行了分段建模,计算了铸件的温度场、流场。结果表明,铁液与离心铸型内壁接触后,受到自身重力、旋转铸型带来的离心力、摩擦力三个合力作用,以层状形式沿铸型内壁做圆周运动,沿着内壁同时向铸型两端运动,先到达离浇道距离较近的模具一端,沿轴向向另一端铺展。在有限元模拟辅助下生产出的高镍铬无限冷硬球墨铸铁离心复合轧辊,工作层为树枝状结晶组织,技术指标符合要求。

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。

铸造冷铁布置原则的研究及验证

借助铸造数值模拟技术对球墨铸铁件冷铁设置的部分原则及要求进行了研究及验证。研究了冷铁铺设厚度对铸件激冷效果的影响,验证了冷铁最大效用的“二分之一原则”;同时也研究了铸件的直角两侧面同时铺设冷铁的距离控制问题,确定直角两边同时铺设冷铁的最小控制距离,为今后的冷铁工艺设计提供指导。

Tappet Chill Depth Measuring by Magnetic Permeability and Inductance Displacement Meter

It is possible to measure different position along the axle direction of tappet.According to the maximum output of signal,the boundary of white iron structure and mottled iron structure can be deduced,and at the same time,it is possible to use inductance displacement meter to show the chill depth which is the distance from the boundary to the end.

钒添加量对冷硬铸铁组织及耐磨性的影响

采用金属型铸造制备了添加不同质量分数(0~2.0%)钒的冷硬铸铁,研究了钒含量对冷硬铸铁显微组织以及抗冲击磨粒磨损和摩擦磨损性能的影响。结果表明:随着钒质量分数的增加,冷硬铸铁的显微组织发生细化,碳化物分布更加均匀,碳化物由网状变为长条状,但当钒质量分数高于1.2%时碳化物长大聚集;随钒质量分数增加,冲击磨粒磨损试验后冷硬铸铁的磨损质量损失先下降后略微升高,当钒质量分数为1.2%时,抗冲击磨粒磨损性能最佳;添加质量分数0,1.2%钒的冷硬铸铁在1 J冲击功下的冲击磨粒磨损机理分别以微观切削和塑性疲劳为主;钒的添加降低了冷硬铸铁与45钢对磨时的摩擦因数,提高了冷硬铸铁的摩擦磨损性能;添加质量分数0,1.2%钒的冷硬铸铁在6.9 N载荷下的摩擦磨损机理分别为微观切削和疲劳磨损,9.8 N载荷下为磨粒磨损和疲劳磨损。

砂芯和冷铁的组合结构在中空曲轴的应用

介绍了一款主轴中空的4缸曲轴铸件,针对采用原设计工艺生产过程中在连杆轴颈部位出现的缩松问题进行了分析,通过在主轴中空的砂芯结构基础中增加冷铁,并把冷铁设计成为方形结构,与砂芯一起成型,芯头处直接为冷铁,所起到的激冷作用能减少曲轴连杆轴颈处产生缩松的概率。经过近10万件曲轴的生产验证,曲轴连杆处的缩松缺陷废品率由原来的20%以上降至1%,取得了明显改进效果。

含有激冷碳化物的球墨铸铁件的失效模式与预防

针对球墨铸铁件断裂问题,采用扫描电镜和金相显微镜分别进行断口形貌分析和金相组织检测,发现铸件中存在大量定向分布的激冷碳化物。这些碳化物虽然提高材料的抗拉强度和屈服强度,但大幅降低铸件的塑性,从而引起铸件断裂。通过研究球墨铸铁基体组织中激冷碳化物的形成机理,发现热处理手段可消除激冷碳化物,且使珠光体含量提高并均匀分布在基体中,同步提升材料强度和塑性。采用两阶段高温石墨化退火可有效消除球墨铸铁件中的激冷碳化物,且对于珠光体−铁素体型球墨铸铁,通过精确控制冷却速率和出炉温度,能使材料基体中珠光体含量可控且均匀分布。

冷铁对QT500-14试块理化性能的影响

在QT500-14材质砂模的基础上,探讨了冷铁激冷效果与实际性能之间的关系。针对250 mm×250 mm×250 mm试块(带有250 mm×120 mm×100 mm附铸试块)的不同冷铁进行试验,以获得不同冷铁条件下相关试块的理化性能。通过大量试验数据得出结论:在保持冷铁为单一变量的前提下,使用铸铁冷铁、石墨冷铁和不使用冷铁的抗拉强度、屈服强度、硬度、金相、-20℃低温冲击功等都有不同的变化,并且发现某组试验的性能与一风力发电机组前机架脚板面的套料性能几乎一致,即可通过该组试验条件反应产品某一特定厚度区域的力学性能。

华铸CAE软件在壳型铸造激冷铸铁凸轮轴工艺优化中的应用

介绍了壳型铸造激冷铸铁富康轿车凸轮轴批量生产初期存在的主要问题。采用华铸CAE软件 ,通过对凸轮轴充型过程流动场的模拟 ,揭示了卷气 (气孔 )、夹渣、冲砂的部位与形成原因 ;通过对流动场温度场的耦合计算 ,揭示了铸件产生冷隔浇不足、材质等缺陷的部位与形成原因。模拟结果表明 ,通过工艺优化后生产的凸轮轴有效地防止了铸件气孔、夹渣冲砂、冷隔浇不足、材质等缺陷 。

导卫板失效分析及表面喷涂层的耐磨性能

对受高温磨损破坏的导卫板进行了失效分析,认为导卫板主要受到了疲劳磨损和磨料磨损。为提高导卫板的耐磨性,采用氧-乙炔火焰喷涂的方法在其磨损表面喷熔钴基WC涂层。实际应用表明,该喷熔层具有良好的耐磨效果,显著提高了导卫板的高温耐磨性。

冷铁的失效原因分析

本文采用金相显微分析、电子探针微区成分分析等手段对铸铁材质冷铁的失效原因进行了研究，并在此基础上提出了本试验条件下铸铁氧化过程的机理。

冷硬铸铁中富Nb相形态及分布的研究

采用配有能谱和波谱的扫描电镜研究了冷硬铸铁中富Ｎｂ相的形态及分布，发现在冷硬铸铁中富Ｎｂ相有三种存在形态：块状ＮｂＣ、条状复杂铁碳铌相以及渗碳体型化合物。

原材料对冷激铸铁凸轮轴组织和性能的影响

详细地研究了主要原材料(生铁、废钢、增碳剂)对冷激灰铸铁神龙凸轮轴组织和性能的影响。试验表明:炉料质量的好坏是生产优质凸轮轴铸件的基础,生铁等炉料的“遗传性”是铸铁冶金学中需要注意的课题,试验确定的神龙凸轮轴生产用主要炉料有Q10生铁、汽车用碳素废钢、增碳剂等;要求生铁和废钢Ti等微量元素含量低,增碳剂固定碳含量高等;同时要求生铁、废钢必须经过抛丸处理,清除表面粘砂、锈蚀和油污。炉料配比对神龙凸轮轴的材质性能影响很显著,废钢的加入会改善凸轮轴的性能,但加入量大时,铁水的白口倾向增大,需加入大量增碳剂;增碳剂会显著降低铁液的白口化倾向,改善凸轮轴轴颈断口形貌和组织性能,对凸轮桃尖硬度影响很大,因此需控制好废钢和增碳剂的最佳配比,否则会引起较高的材质废品。生产中炉料配比应稳定,试验确定的适宜炉料配比为:生铁∶废钢∶回炉料=20%∶2.5%∶77.5%,各种炉料必须按工艺要求进行仔细称量。

石墨及碳化物对高镍铬无限冷硬铸铁轧辊耐磨性的影响

本文研究了具有不同石墨和碳化物含量的高镍铬无限冷硬铸铁轧辊材料在滚动摩擦和干滑动摩擦条件下的摩擦学特性,考察了高镍铬无限冷硬铸铁中石墨和碳化物数量、分布对其摩擦学特性的影响。研究结果表明,组织中的石墨和碳化物数量、形态和分布对材料的耐磨性有较大影响。石墨含量在低于9.21%时,增加石墨量并适当减少碳化物量可以提高材料的耐磨性;呈均匀分布的长片状石墨和连续网状分布的碳化物对提高高镍铬无限冷硬铸铁轧辊的耐磨性有显著意义。