Effect of scanning speed during PTA remelting treatment on the microstructure and wear resistance of nodular cast iron

The surface of nodular cast iron （NCI） with a ferrite substrate was rapidly remelted and solidified by plasma transferred arc （PTA） to induce a chilled structure with high hardness and favorable wear resistance. The effect of scanning speed on the microstructure, micro-hardness distribution, and wear properties of PTA-remelted specimens was systematically investigated. Microstructural characterization in-dicated that the PTA remelting treatment could dissolve most graphite nodules and that the crystallized primary austenite dendrites were transformed into cementite, martensite, an interdendritic network of ledeburite eutectic, and certain residual austenite during rapid solidifica-tion. The dimensions of the remelted zone and its dendrites increase with decreased scanning speed. The microhardness of the remelted zone varied in the range of 650 HV0.2 to 820 HV0.2, which is approximately 2.3-3.1 times higher than the hardness of the substrate. The wear re-sistance of NCI was also significantly improved after the PTA remelting treatment.

Effects of Light and Heavy Rare Earths on Anti-Degradation of Nodular Cast Iron

The effects of rare earths with different contents on anti-degradation of Y base heavy rare earths-magnesium and cerium base light rare earths-magnesium nodular cast iron were studied. Curves of the relationship between the spheroidization grade of liguid iron treated by different nodulizers and holding time were obtained. The results show that the more the remains of the rare earth, the longer the anti-degradation time, the liquid iron was treated either by Y-Mg-Si or by Ce-Mg-Si nodulizer. When the rare earth remains are above certain quantity, the spheroidization grade starts to decline. When liquid iron treated by either Y-Mg-Si or Ce-Mg-Si nodulizer with proper remains of rare earths about 0.04% 0.06%（mass fraction）, the anti-degradation is the best, and the remains of Mg being about 0.04% -0.07% （mass fraction）. Rare earths-Mg nodulizer with moderate RE remains is better than that of Mg-Si nodulizer in anti-degradation property. However, Y-Mg-Si nodulizer with moderate remins of Re is better than Ce-Mg-Si nodulizer. Sometimes Ce-Mg- Si nodulizer can be used for the production of heavy section nodular cast iron.

Centrifugal Casting of High Speed Steel/Nodular Cast Iron Compound Roll Collar

The centrifugal casting of compound HSS/nodular cast iron roll collar was studied,and the factors affecting transition zone quality were analyzed.The pouring temperature and interval in pouring are the main factors affecting transition zone quality.By controlling process parameter and flux adding during casting,high quality roll collar was obtained.The cause,why in the casting of HSS part,segregation appears easily,was analyzed and the countermeasure eliminating segregation was put forward,the measure eliminating heat treatment crackling was also put forward.

SIZE DISTRIBUTION AND BEHAVIOUR OF VC PARTICLES IN FERRITIC NODULAR CAST IRON

Size distribution and precipitation of VC particles in ferritic nodular cast iron have been examined by techniques of ultrasonic screening,small angle X-ray scattering and chemical dissolution.The VC particles are sized over a wide range.The superfine ones, dispersed in the ferritic matrix,are the majority.A saturated dispersion with ultrafine VC particles may be approached as the V content increasing in the iron.Thi5 seems to play an important role in the precipitation strengthening for ferritic nodular cast iron.

Strength distribution at interface of rotary-friction-welded aluminum to nodular cast iron

The morphology,size and composition of intermetallic compound at the interface of Al 1050 and nodular cast iron were studied by electron microprobe analysis(EMPA)and scan electron microscopy(SEM),respectively.The bond strength of the interface was measured by the tensile tests and the morphology of the fracture surface was observed by SEM.The observation of the interface reveals that there are two distinct morphologies:no intermetallic compound exists in the central area at the interface;while numbers of intermetallic compounds(FexAly)are formed in the peripheral area due to the overfull heat input.The tensile tests indicate that the distribution of strength in radial direction at the interface is inhomogeneous,and the central area of the interface performs greater bond strength than the peripheral area,which proves directly that the FexAly intermetallic compounds have a negative effect on the integration of interface.The morphology on the fracture surface shows that the facture in the central area at the interface has characteristic of the ductile micro-void facture.So it is important to restrain the form of the intermetallic compound to increase the bond strength of the Al 1050 and nodular cast iron by optimizing welding parameters and the geometry of components.

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.

Thermal Fatigue Behavior and Cracking Characteristics of High Si-Mo Nodular Cast Iron for Exhaust Manifolds

The thermal fatigue cracking behavior of high Si-Mo nodular cast iron （NCI） is investigated by means of optical microscope （OM）, scanning electron microscope （SEM） and energy dispersive spectroscope （EDS）, in order to find a new material used in exhaust manifolds in First Automotive Works （FAW） .Nodular cast irons with silicon content about 4.7% , in combination with up to 1.1% molybdenum , were produced by Jilin University and FAW. The repeated heating / cooling test was performed under cyclic heating at various maximum heating temperatures （Tmax） ranging from 800to 900℃.Experimental results indicate that the thermal fatigue cracking resistance of high Si-Mo NCI decreases with increasing the maximum heating temperature.The periods for crack initiation are 24-36 , 40-50and 70-90times associated with heating temperature of 900 , 850and 800℃ , respectively , when the holding time is about 10min at Tmax.When thermal fatigue cracking occurs , the cracking always initiates at the bigger surface of specimen.The major positions of cracks propagation are generally at the eutectic oxide boundary region and the region of the graphite disappearance.At the same time , the oxidation may accelerate crack initiation and propagation.On the other hand , micro-crack number varied from large to little because of shielding effect.As exhaust manifolds , the reasonable working temperature of high Si-Mo NCI is no more than 840℃ by test and analysis.

Microstructure and Mechanical Properties of Nodular Cast Iron Produced by Melted Metal Die Forging Process

The microstructure and mechanical properties of nodular cast iron produced by the melted metal die forging process （MMDF for short） were experimentally researched.The main obtained results are ： the nodular cast iron produced by this process can be machined as easy as traditional one only if holding at the remained temperature for 4 h ; its strength and plasticity are obviously higher than those of traditional ones ; the graphite size arrived at grade 8 , and the graphite spheroidizing arrived at grade 1 or 2 , but a streamline molded distribution of the graphite slightly appeared.Both of the strength and plasticity increased with the pressure when the pressure holding time was larger than its critical value.A new way to produce high properties nodular cast iron was provided.

LASER ALLOYING ON CHROMIUM-COATED SURFACE OF NODULAR CAST IRON

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MICROCOMPUTER PICTURE PROCESSING SYSTEM OF CAST-IRON METALLOGRAPHIC STRUCTURE

The development of computer picture processing technique in metallography analysis is dealed with and a picture processing procedure fit to metallography analysis is developed. The image processing of nodular cast iron is carried out with this system

Microstructure and properties of LZQT600-3 HCCDIBs for plunger pump cylinder

It is important to improve the comprehensive performance of the ductile iron bars(DIBs)for the cylinder block of the extra high pressure hydraulic plunger pump and accelerate the industrial application.In this work,the LZQT600-3 DIBs with the diameter of 145 mm were prepared by the horizontal continuous casting(HCC)process,that is,LZQT600-3 HCCDIBs.The microstructure and room temperature tensile properties of different sections[left-edge(surface layer),left-1/2R(left half of the radius),and the center of the HCCDIBs]were studied.The results show that the spheroidization of LZQT600-3 HCCDIBs matrix from the left-edge,left-1/2R to the center is at nodulizing grade II and above.As the cooling rate gradually decreases from surface to the center of the HCCIBs,the number of spheroidized graphite is gradually reduced,the size is gradually increased,the shape factor is decreased,and the pearlite content and lamellate spacing are increased.Along the horizontal direction of the section,the hardness of the material is distributed symmetrically around the center of the HCCDIBs.In the vertical direction,the hardness distribution in the center of the HCCDIBs is asymmetrical due to the gravity during the solidification process.Therefore,the microstructure in the lower part of the section solidifies relatively quickly.The left-edge has the best tensile mechanical properties,and the ultimate tensile strength,yield tensile strength and elongation are 597.3 MPa,418.5 MPa and 9.6%,respectively.The tensile fracture belongs to the ductile-brittle hybrid fracture.The comprehensive performances of LZQT600-3 HCCDIBs meet the actual application requirements of ultra-high pressure hydraulic plunger pump cylinder.

工艺参数对球墨铸铁和低碳钢激光焊接的影响

为了提高球墨铸铁和低碳钢焊接接头力学性能,解决容易开裂的问题,采用激光焊接的方法对球墨铸铁和低碳钢进行焊接,研究了工艺参数对其焊接接头的组织和性能影响。结果表明,随着激光功率逐渐增加或焊接速率的逐渐变缓,试验件抗拉强度呈现出先增大后减小的变化趋势;当焊接功率为4250 W和焊接速率为2.4 m/min时,试样件焊接接头的强度处于极值400 MPa;在球墨铸铁侧热影响区内形成3种壳体结构(双壳结构、单壳结构和无核结构);焊缝区组织主要由树枝晶组织、少量的马氏体和莱氏体组织构成;焊缝区存在微裂纹,通过添加镍基材料可获得无裂纹焊缝,并提升抗拉强度约40 MPa,达到母材的95%。该研究对后续球墨铸铁与低碳钢高功率激光焊接工艺优化是有帮助的。

球墨铸铁表面激光熔覆层的组织及耐腐蚀性能研究

目的解决用于乏燃料贮运的球墨铸铁筒体容器因内壁腐蚀导致服役寿命短的问题,提高球墨铸铁表面的硬度及耐腐蚀性能。方法利用送粉式激光熔覆技术在球墨铸铁表面制备4种不同组分的316L不锈钢、Ni625合金、410L不锈钢及NJ30合金熔覆层。采用金相显微镜、X射线衍射仪、扫描电子显微镜、能谱仪表征熔覆层的微观组织、物相组成、元素分布及腐蚀形貌。借助显微硬度计、电化学工作站测试熔覆层的显微硬度及耐腐蚀性能。结果4种合金熔覆层均成形质量良好,无裂纹及明显的气孔缺陷,并与基体形成了良好的冶金结合。熔覆层底部至顶部出现相似的组织形态,但晶粒尺寸存在较大的差异。316L、Ni625、410L及NJ30显微硬度显著高于基体,分别为基体的1.74、1.92、2.35及2.4倍,熔覆层内部固溶体及硬质相的生成是提高硬度的显著因素。在3.5%的NaCl溶液中,4种熔覆层的耐腐蚀性由好到差为316L、Ni625、410L、NJ30。腐蚀形貌显示,316L及Ni625熔覆层在电化学测试环境下具有良好的抗腐蚀性能。结论316L及Ni625合金熔覆层具有良好的综合性能,适用于提高大型球墨铸铁容器的表面改性。

基于ProCAST的熔胶座移动板浇注系统模拟优化

基于ProCAST仿真平台对QT500-7熔胶座移动板进行了充型与凝固模拟及浇注系统的优化设计。鉴于铸件在充型过程中的氧化夹渣与冒口对铸件质量影响很大,因此对铸造过程中的流动场和温度场进行了研究。结果表明,良好的流道可以保证低的氧化夹渣,同时合理的冒口可以降低铸件的缩孔与缩松。该结果对同类铸件工艺设计具有一定的参考价值和指导意义。

大型球墨铸铁蜗轮铸件的生产工艺

介绍了大型球墨铸铁蜗轮铸件的铸造工艺设计及生产过程,利用华铸CAE软件对球墨铸铁蜗轮铸件的两种工艺方案充型及凝固过程进行了数值模拟分析,经过对比,选择中心轴孔端面引入的工艺方案二进行进一步优化。为了满足力学性能要求,选用纯净的原材料、合理的化学成分,采用包内孕育与随流孕育相结合的处理方式。通过对生产的10件铸件进行表面质量及力学性能检测,结果显示:铸件加工后,中心轴孔、键槽、外圆齿圈位置未见缩孔、缩松、夹渣等铸造缺陷,铸件的金相组织和力学性能均符合技术要求。

盐浴氮化处理对球墨铸铁摩擦学行为的影响

针对轴向柱塞泵中柱塞副配对材料38CrMoAl/QT500在重载工况下表面承载能力低、耐磨性能差等问题,首次将盐浴氮化处理工艺运用于柱塞泵缸体材料QT500,将三种不同型号的球墨铸铁(QT450、QT500、QT550)作为试验材料,获得盐浴氮化表面改性层。根据实际应用工况,通过显微硬度仪和CFT-I往复式摩擦磨损仪,以及SEM和EDS分析渗氮后QT450、渗氮QT500、渗氮QT550和基体QT500在液体润滑状态下与38CrMoAl球体对磨的摩擦学行为,得到显微硬度、摩擦因数、磨损量、磨损形貌和磨损表面化学成分。结果表明在摩擦过程中,盐浴氮化处理后的球墨铸铁耐磨性能得到显著提升,达到减少磨损、提供连续且稳定的润滑效果,磨损机理主要是氧化磨损和疲劳磨损。

基于ProCAST的支架铸件熔模铸造工艺优化

分析了球墨铸铁支架铸件原工艺产生缩孔、缩松铸造缺陷的原因。通过ProCAST软件对工艺进行了分析和优化,对铸件浇注位置、排气位置等工艺参数进行了改进。结果表明:优化方案的铸件缩孔率总和为0.20%,缩松缩孔主要集中在直浇道和内浇道,并且缺陷明显减少。与原始方案相比,优化方案更合理。

基于ProCAST球墨铸铁支座的铸造工艺优化

以支座为研究对象,分析支座的工艺性和结构特点,制定初始铸造工艺方案,运用数值模拟软件ProCAST对初始铸造工艺方案进行模拟,根据结果对缺陷部位产生的原因进行分析并给出优化方案。优化后的模拟结果表明:支座铸件本身的缺陷基本消除且铸件表面无缩孔、缩松、夹砂等缺陷,满足铸件的技术要求。最后指出:运用ProCAST软件对支座的铸造工艺进行模拟,可以有效地分析和验证浇冒口系统设置的合理性以及方案的可行性,并改进优化铸造工艺方案不足之处,为工艺实践提供理论依据。

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。

某船用柴油机机架缺陷原因分析及修复方案

柴油机是现阶段船舶领域重要的动力和电力来源,而机架又是柴油机的基础,其他零部件均安装在机架上而形成一台完整可靠的柴油机。通常由于机架的腔道和结构的复杂性,进行铸造时难免会出现一些缺陷,在考虑到机架的时间和价值成本,选择对铸造缺陷进行修复,不失为一种经济可行的方法。文章就铸铁的材料特性及浇铸工艺,分析了中速水冷四冲程柴油机机架铸造缺陷的原因,提出了几种日常工作中铸件缺陷修复常用方法,并具体针对本文中机架凸轮轴孔的铸造缺陷问题,综合考虑确定最终采用镶套的修复方案,同时制订了详细修复工艺,并完成了机架缺陷修复。