Analysis of reasons causing riser feeding failure in nodular iron castings production

1 Introduction It is clarified by reference [1] that, in order to avoid shrinkage defects, a nodular iron casting must be fed from an outside feeding source in addition to use graphitization expansion to compensate it for its volumetric contraction. Because the feeding capacity of gating system is much lower than that of the riser, the mold conditions and other process condition requirements for riserless foundry method are more strict than that of the riser feeding method. Therefore, the rise…     

球墨铸铁件无冒口铸造可行性论证与实践--球墨铸铁缩孔、缩松问题探讨(一)

介绍球铁冷却、凝固过程中的体积变化以及型腔尺寸变化。分析、并用实例证明球铁件无冒口铸造的可行性及条件。指出无冒口铸造决不是无补缩铸造，强调采用高碳当量、高刚度铸型、同时凝固和强化铸型冷却以提高浇注系统补缩作用对实现无冒口铸造的重要性。、     

球墨铸铁件冒口补缩失败原因分析--球墨铸铁缩松、缩孔问题探讨(二)

除铸型刚度和铁液冶金质量外．球铁件冒口补缩失败的原因主要是：①采用冷冒口和明冒口；⑦冒口设置位置不当：③冒日直径或，和高度偏小；④内浇道不能在浇注结束时及时凝固；⑤铸件存在与冒口补缩通道不相通的孤立热节；⑥薄、小件补缩通道窄小．冒口补缩不进等。     

退火处理对金属型铸态奥-贝球铁组织和性能的影响

对金属型铸态生产的奥-贝球铁进行退火处理以改善力学性能,通过正交试验研究退火工艺对其组织和性能的影响.试验结果表明:退火处理对石墨形态无明显影响,但会改变基体中贝氏体的类型;低温退火可在硬度变化不大的情况下有效地提高金属型铸态奥-贝球铁的强度和塑性、韧性,抗拉强度可达到1080MPa.这表明了金属型铸造和退火处理相结合的方法可获得高性能铸态奥-贝球铁.     

球墨铸铁曲轴断裂失效分析

对柴油机早期断裂的球墨铸铁曲轴进行了分析研究。结果表明,轴颈圆角处的应力集中和表面加工缺陷容易使此处成为疲劳裂纹的起始源,断裂机制为准解理断裂,具有典型的脆性断裂特征。     

热疲劳作用下球墨铸铁组织变化规律

按球化率优化了球墨铸铁的化学成分,分析了热疲劳作用下球墨铸铁的组织变化.结果表明,球墨铸铁最佳热处理工艺为890℃淬火+400℃回火,可获得最佳的强韧性配比.890℃淬火次数对石墨级别基本没有影响.初次时,基体组织以马氏体为主;随淬火次数增加铁素体数量逐步增加,约25次左右铁素体量最多;随后铁素体数量减少,直至50次时组织几乎都是马氏体+石墨.     

离心铸造球铁芯复合轧辊辊颈缩松的控制

对球铁芯复合轧辊冒口端辊颈缩松原因进行了分析。介绍几种控制辊颈缩松的措施及效果，包括：提高冒口铁液温度；增加二次冒口，用高碳铁液补注冒口，提高冒口液位并吹氧；提高砂箱刚度和型壁冷却能力；减少吃砂量。     

Micromechanical modelling of nodular cast iron,a composite material

This article aims to show that the overall characteristics of nodular cast iron can be modelled with rather straight-forward micromechanical models. The mechanical and short crack properties of this composite are analysed using finite element models with symmetrical patterns of holes or voids, representing the graphite nodules. Closed form expressions for the elastic-plastic properties are also applied and compared. The mechanical properties are well described. An approximate expression for the stress intensity factor (K) is derived for a crack emanating from a nodule in a nodule pattern. Introducing a fatigue limit condition based on the assumption of the existence of a short crack fatigue threshold, simulations are performed with variations in crack size, nodule size and spacing. The fatigue results are essentially qualitative, but are considered capable of capturing some important trends since the qualitative agreement with experiments is good.     

球铁球化不良挽救措施的生产性研究

对球铁生产中出现的球化不良或球化不成现象，分析了产生的原因，借鉴日本铸造学者张博、明智清等在《球墨铸铁》中的防止球化衰退的“二次球化”，经过生产实践，摸索出了用“补充球化”法来挽救球化不良或球化不成的铁水，取得了较好的效果。     

Research on nodular iron joint welded with nickel-iron electrode by the moire fringe method

Nickel-iron type cast iron electrodes are widely used for weldingQT600-3 nodular iron.Nevertheless,the research work has demonstrated thatthe strength of these heterogeneous welded joints is low.In this paper,the uni-axial tension of the joints is studied by the Moire fringe method,and the dis-placement,strain and stress in the total fields are obtaind.Based on the unevendistribution of strain and stress,the reason of crack initiation and propagation isdiscussed.Through examining the appearance of the fracture by scanning elec-tron microscope,a lot of spherical substances distributed on the fracture surfaceare found,which may be another reason leading to cracking of the welded jointunder the lower tensile stress.These new findings will help to improve theproperties of nickel-iron type cast iron electrodes and the strength of the weldedjoint.     

Nodule influence on fatigue crack growth thresholds in nodular cast iron

The influence of microstructure i.e. nodules (voids) on the fatigue threshold value in nodular cast iron is numerically investigated. It is qualitatively shown that the fatigue threshold value is unaffected by the individual nodules and that the threshold value is proportional to the bulk Young's modulus. Furthermore it is shown that nodules (voids) do not influence the crack tip conditions (stress-intensity factor and crack tip opening displacement) if the voids do not lie very close to the tip for physically long cracks. It is concluded that linear elastic fracture mechanics is valid for these types of materials and no influence of the nodules need be taken into count for fatigue calculations when dealing with long cracks.     

Discussion on "proportional solidification technology" for nodular iron casting method

H ow should the graphitization expansion be reasonably utilized to feed nodular iron castings? H ow should the consideration be given to both feeding from feeders and self-feeding by expansion? These two problem s are the hot spotsofdiscussion on feeding m ethod ofnodulariron castings at present. In this regard, reference [1] published som e viewpointswhich cause differentcom m ents.W ith the wish to prom ote the discussion on shrinkage problem sofnodulariron castings and based on his investig…     

Modelling of microstructure and property distribution within industrial nodular graphite iron casting

A kinetic model that uses the internal state variable approach has been developed and implemented as a user-subroutine in a finite element model (FEM) program in order to relate the heat flow calculations to the micro-structure evolution within a complex shaped industrial nodular graphite iron casting. The model initially requires the input of the chemical composition and from there it is coupled with the heat flow calculations from which the evolution of the constituent phases are calculated utilising the constraint conditions imposed by the phase diagram and the kinetic equations. A further sophistication of the model involves the use of a separate set of response equations to relate the microstructure and the composition to the macro-mechanical properties, such as hardness, yield and tensile strength. In a calibrated form, the process model is capable of describing the microstructure evolution during primary and eutectic solidification as well as the subsequent solid-state transformations. IJCMR/368     

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 AI 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 interrnetallic 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 irdaomogeneous, 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 AI 1050 and nodular cast iron by optimizing welding parameters and the geometry of components.     

球墨铸铁行走轮的低温正火工艺

对一种Cu微合金化球墨铸铁行走轮进行了低温正火工艺试验,获得了850 ℃和860 ℃正火后行走轮轮缘和轮辐的显微组织和力学性能数据。分析了合金元素Cu对球墨铸铁组织和性能的影响,以及对奥氏体化及珠光体形成相变温度区间带来的变化。结果表明,试验含Cu的球墨铸铁行走轮850 ℃正火就可以获得95%珠光体,达到完全正火的状态,力学性能符合QT650-4牌号的要求。比较了850 ℃和860 ℃正火后组织和性能,虽然都能满足要求,但860 ℃正火后表面硬度较850 ℃正火的高,机械切削性能相对较差。说明试验行走轮正火工艺温度窗口较窄,因此,选择850 ℃正火工艺为佳。该热处理工艺已在工程上得到应用,生产的行走轮已批量出口。     

硅含量对耐热球墨铸铁显微组织和力学性能的影响

采用光学显微镜、扫描电镜、电子万能拉伸试验机测试分析手段,研究硅含量对耐热球墨铸铁显微组织和室温、高温力学性能的影响规律。试验结果表明,随着硅含量的增加,石墨圆整度逐渐下降,硅含量(质量分数,下同)达到3.8%时,基体中开始出现碎块状石墨,球化级别为3级。随着硅含量从2.8%增加至4.8%,珠光体含量从51.06%减少至8.65%。随着硅含量的增加,室温抗拉强度先上升后下降,伸长率逐渐下降,当硅含量为3.8%时,抗拉强度为726 MPa,伸长率为1.6%。随着硅含量的增加,高温抗拉强度逐渐上升,伸长率逐渐下降,当硅含量为4.8%时,抗拉强度为532 MPa,伸长率为6%。室温拉伸断口出现大量的解理面和河流花样,表现形式为脆性断裂。高温拉伸断口出现韧窝和撕裂棱,拉伸断口表现形式为韧-脆混合型断裂。     

球铁基体组织对QPQ盐浴渗氮层深度和耐磨性的影响

对不同铁素体含量基体组织的球墨铸铁进行了QPQ盐浴渗氮试验,对渗层进行了显微组织观察和物相分析.试验结果表明,渗层组织中主要为Fe_3O_4和Fe_2N相,且基体组织中铁素体含量越高,渗层越厚.通过对不同基体组织的球墨铸铁进行QPQ处理前后磨损速率的比较,结果表明经QPQ处理后的球墨铸铁试样磨损速率为QPQ处理前的4.3%～19%.     

Study on numerical simulation of nodular graphite iron microstructure formation

In this paper, the mathematical and physical model was developed based on thermodynamics and solidification theory before the eutectoid transformation of nodular graphite iron occurred. The Local Element Substitute and Magnification Method was brought forward and 3-dimensional numerical simulation program based on the model and the new assistant algorithm was developed and used to calculate the samples. Results of calculation have good agreement with experimental data. To display the microstructure formation during solidification of nodular graphite iron, a 2-dimensional numerical simulation program combined with the result of the 3-dimensional numerical simulation of experimental samples was compiled.     

高硅钼球铁排气歧管高温氧化开裂原因分析

通过电镜、金相、能谱分析等手段对高硅钼耐热球铁的排气歧管开裂进行综合分析.该耐热铸铁在高温条件下,氧化由外向内推进,由于材料表面不当的应力强度及分布在氧化区诱发了裂纹,同时,氧化层的破裂造成氧化呈管道向内突进;而排气歧管基体中局部区域石墨的非球形态促进了裂纹的萌生及扩展.因此该排气歧管的开裂为氧化腐蚀疲劳开裂.     

磨削用量对球墨铸铁QT400磨削淬硬层及其均匀性的影响

采用逆磨+顺磨的双程平面磨削方式对球墨铸铁QT400进行磨削淬硬试验,研究了磨削深度a_p和试样进给速度v_w对淬硬层及其均匀性的影响。结果表明,磨削后试样表层存在熔化、完全相变淬硬和未完全相变淬硬等3种情况,其中,熔化层组织为二次渗碳体、残留奥氏体和碳化物,完全相变淬硬层组织为针状马氏体、残留奥氏体和球状石墨,未完全淬硬层组织为针状马氏体、铁素体、残留奥氏体和球状石墨。显微硬度分布曲线中高硬度区的平均硬度值在850~950 HV0.2之间,与基体(190~230 HV0.2)相比,显微硬度提高近3倍。随着磨削深度a_p的增大或试样进给速度v_w的减小,试样表层呈现“完全未淬硬→未完全淬硬→完全淬硬→熔化”的变化规律,显微硬度分布曲线中高硬度区的范围也变宽,淬硬层的深度也增大且均匀性良好。