真空自耗熔炼工艺参数对齿轮钢凝固组织的影响

为进一步提高Cr-Co-Mo-Ni齿轮钢材料的均匀性和细晶化,建立了直径290 mm的齿轮钢钢锭真空自耗熔炼过程三维数学模型,研究了熔炼工艺参数对钢锭凝固组织分布及晶粒大小的影响规律。结果表明：在工艺参数可调范围内,冷却强度越大,晶粒尺寸越小、数目越多,二次枝晶间距越小;熔池温度越低,晶粒的细化效果越好,二次枝晶间距也越小;降低冶炼速率,形核数目增多,晶粒尺寸减小,但对二次枝晶间距的影响较小。对齿轮钢真空自耗熔炼工艺参数优化调整后,模拟结果显示,自耗锭内部等轴晶区域增大将近一倍,晶粒尺寸得到明显细化;最大二次枝晶间距减小了4.88%,合金元素分布实现均匀化。     

摩托车发动机连杆的锻造工艺设计

本文通过地摩托车发动机连杆的锻造工艺特点，连杆常用材料及其可锻性的分析，给出了确定全面模同，锻件公差，加工余量，模锻斜度和圆角尺寸的基本原则和方法，介绍了连杆锻造的典型工艺流程及注意事项。     

摩托车发动机连杆的锻造工艺设计

本文通过对摩托车发动机连杆的锻造工艺特点、连杆常用材料及其可锻性的分析,给出了确定分模面、锻件公差、加工余量、模锻钭度和圆角尺寸的基本原则和方法,介绍了连杆锻造的典型工艺流程及注意事项。     

等温模锻新技术中的节能

本文简要叙述了等温模锻的特点和适用范围，并详尽叙述和计算Ｔ２５ｔ·ｍ无砧座模锻锤上模锻和５０ＭＮ液压机上等温模锻Ｚ９飞机上２２１４铝合金起落架外筒锻件的电能消耗费用的数据，指出等温模锻技术是一项节能技术。     

浅谈模锻和精锻叶片的冷加工技术

本文通过例举模锻和精锻叶片在冷加工中几个难度较大的工序,阐明了这两种锻件在生产中的相互关系及它们不同的加工方法。最后,论证了在我国现有技术和设备能力下,大中型叶片的精锻件必将代替模锻件。     

1050mm汽轮机钛合金叶片的研制

采用优化的模锻工艺参数,完成了1050 mm汽轮机末级TC4钛合金叶片的锻造。锻件的机械性能及微观组织试验研究结果表明,锻件的性能满足技术要求,1050 mm汽轮机末级钛合金叶片的研制取得了成功。     

汽轮机高压整体转子锻件的重新热处理

1983年3月至5月,我们和日本制钢所、室兰制作所一起在室兰制作所对两根存在材料晶粒粗大问题的20万千瓦汽轮机高压整体转子锻件进行了重新热处理。重新热处理前锻件已达半精加工尺寸,单边最小尺寸仅余1.3毫米,这对重新热处理的具体实施造成了困难,本文就这两根汽轮机高压整体转子锻件重新热处理实施的工艺方案和结果     

A-100钢锻造工艺参数和大型模锻件应用研究

在变形温度为980、1 050、1 100和1 150℃,变形量为0%、10%、30%、50%的条件下,对23Co14Ni12Cr3MoE (A-100)钢晶粒度和显微组织演变规律进行了研究。同时在变形温度为1 050℃的条件下,对加热火次对A-100钢晶粒度和显微组织演变规律进行了研究。结果表明变形温度1 050℃、变形量30%～50%、一火次成形可以得到8级以上的晶粒度,为较优化的锻造工艺参数。最后采用该工艺参数试制了某型号A-100钢模锻件,首次在国内取得了σ_b>1 950MPa,K_IC>150MPa·m^-2综合性能优良的细晶化A-100钢大型模锻件。     

国产红套环锻件制造工艺与各项性能研究

阐述了超超临界汽轮机高压内缸红套环锻件的制造工艺,通过解剖试验,测定了锻件在不同部位的拉伸性能、冲击性能、晶粒度、夹杂物等各项性能。结果表明,锻件的制造工艺完整可靠,锻件的各项性能优异,尤其是均匀性非常好,实现了国产化目的。     

汽轮机叶片精密模锻件CAD软件系统研究

汽轮机叶片精密模锻件的设计,是叶片锻造模具和工艺设计的技术关键。结合无锡叶片厂叶片精密模锻件的设计过程,介绍了采用UG软件平台及其开发工具,研制出叶片精密模锻件的CAD系统。     

Prediction of Type IV creep failure of a seam-welded mod. 9Cr-1Mo elbow based on microscopic damage simulation

Utilising the random-fracture-resistance model of grain boundaries, micro-macro combined creep damage simulation was applied to the prediction of the distribution of small defects in the FGHAZ (fine-grained heat-affected zone) of longitudinal welds in an actual-size elbow of modified 9Cr-1Mo (9Cr-1MoVNb) steel subject to internal pressure at 923 K. Based on the simulation results, a prediction scheme for the final rupture life of welds was considered using the damage mechanics concept together with effective stress. The applicability of nonlinear fracture mechanics was also discussed, assuming the initial crack length determined from the microscopic simulation results. The results thus obtained are summarized as follows: As the simulation results showed, the peaks of small defect density in the subsurface could be predicted, corresponding well with the observed results. Final failure life prediction based on the damage mechanics concept was found to be applicable, by considering both the final failure surface connecting the weakest grain boundaries and the effective stress against this surface. The fracture mechanics approach was also found applicable when assuming the initial crack length from the high peaks of the simulated small defects in the last stage of creep life.     

Modelling the nucleation process in alumina lamellae deposited on a steel substrate

A one-dimensional model has been developed to address the non-equilibrium heat transfer between an alumina lamella deposited by plasma spraying, and a steel or alumina substrate. The model includes under-cooling phenomenon, heterogeneous nucleation and crystal growth kinetics, allowing for the prediction of the temperature evolution in the lamella and substrate and of the nucleation temperature, grain density and size distribution. The effect on the nucleation process of the contact angle between the nucleus and substrate surface and of the quality of the contact at the splat–substrate interface is emphasized. The influence of the splat thickness, substrate material and substrate oxidation on the grain size distribution is also discussed.     

Effect of ultrafine grain refinement on hydrogen embrittlement of metastable austenitic stainless steel

Micro-tensile tests were performed on high-pressure-torsion-processed specimens of type 304 steel with grain sizes in the range of 0.1–0.5 μm to clarify the effect of ultrafine grain refinement on the hydrogen embrittlement (HE) of metastable austenitic steel. The ultrafine-grained (UFG) specimens with average grain sizes < ～0.4 μm exhibited a limited uniform elongation followed by a steady-stress regime in the stress–strain curves, which was attributed to a martensitic transformation. A high yield stress and a moderate elongation to failure were attained for the UFG specimens with an average grain size of ～0.5 μm in the uncharged state. Hall–Petch relationships well hold between the yield stress and the average grain size for each uncharged and hydrogen-charged specimen. Hydrogen charging increased the friction stress by 40% but did not change the Hall–Petch coefficient. Hydrogen-induced ductility loss was mitigated by ultrafine grain refinement. Ductility loss due to hydrogen charging manifested in the local deformation after a martensitic transformation. This indicates that hydrogen does not significantly affect the martensitic transformation, but shortens the subsequent local deformation process.     

On the development of creep damage constitutive equations: a modified hyperbolic sine law for minimum creep strain rate and stress and creep fracture criteria based on cavity area fraction along grain boundaries

This paper reports (1) the latest development and application of a modified hyperbolic sine law for minimum creep strain rate and stress for both low Cr and high Cr steels, and (2) the development of a creep fracture criterion based on cavity area fraction along grain boundaries for high Cr steel. This work is part of the fundamental development of creep damage constitutive equations which were identified through a critical literature review. In the former the application of the new law results in an improved fitting; in the latter, a new creep fracture criterion based on cavity area fraction along grain boundaries was derived and quantitatively calibrated using the latest detailed cavity nucleation and growth kinetics models for high Cr steel. Furthermore, this paper revealed the trend of nucleation rate coefficient with stress, and the trend of creep life time coefficient with stress, which provide reliable and universal prediction capabilities. This paper contributes to the specific knowledge on the minimum creep strain rate and stress function, the development of a scientifically sound and novel creep rupture criterion based on the cavity area fraction along grain boundaries for high Cr steel, and the provision of creep damage/life prediction tools.     

Grain boundary control for improved intergranular stress corrosion cracking resistance in austenitic stainless steels: new approach

Abstract

The present paper provides an overview of a new approach which has focused on the behaviour of special grain boundaries in sensitised austenitic stainless steel. The aim of the work was to develop a general model for stress corrosion cracking, which would ultimately be capable of predicting the effects of the degree of sensitisation, the connectivity of special boundaries and the influence of stress gradients, such as those developed from surface preparation (machining or peening) or due to the stress concentration effect of pit formation. Experimental work using electron backscatter diffraction analysis and in situ high resolution computed X-ray tomography has correlated cracking with the microstructure in a type 304 austenitic stainless steel. In situ three-dimensional observations demonstrated that annealing twins cause local crack arrest and diversion, leaving non-fractured ligaments in the wake of the cracking path. The mechanical effects of the deformation and failure of these bridges have been modelled, demonstrating that special grain boundaries cause crack tip shielding. Increasing the fraction of special boundaries and decreasing grain size are both predicted to increase stress corrosion cracking resistance. Experimental observations using room temperature intergranular stress corrosion tests and high temperature autoclave tests confirm these predictions for thermomechanically processed microstructures. The effects of applied stress and stress gradients are also predicted by the model, which may be extended to include the kinetics of crack growth, clustering of grain boundary types and variation of the degree of sensitisation.     

Effects of grain size and dislocation density on the susceptibility to high-pressure hydrogen environment embrittlement of high-strength low-alloy steels

The tensile properties of several high-strength low-alloy steels in a 45 MPa hydrogen atmosphere at ambient temperature were examined with respect to the effects of grain size and dislocation density on hydrogen environment embrittlement. Grain size was measured using an optical microscope and dislocation density was determined by X-ray diffractometry. Both grain refinement and a reduction in dislocation density are effective in reducing the susceptibility to embrittlement. The steel that has high dislocation density or large grain size inclines to show a smooth intergranular fracture surface. Given only the grain size and dislocation density, a simple approximation of the embrittlement property of high-strength steel could be obtained. This method could be useful in selecting candidate materials in advance of the mechanical tests in high-pressure hydrogen gas.     

Thermoelastic Deformation of Three-Layer Combined Die with Non-Uniform Temperature Distribution

During precision forging processes, the elastic and thermal deformations always take place simultaneously on the forging dies, which will affect the dimension accuracy of the final forging components. According to the classic Lamé formulas and thermoelastic mechanics theories, the thermoelastic deformation of a combined die was investigated. Directly related to geometric parameters, material properties, external stresses, and temperature distribution, the expressions of die deformation and contact normal stresses were derived. A three-layer combined die with three different temperature distributions was studied as a specific example. The thermoelastic deformations of each layer, as well as the contact normal stresses between them, were both calculated by the derived expressions and by finite element simulation. There was good agreement between the calculated values and simulated results, which demonstrated the effectiveness and accuracy of the theoretical derivation. Based on this, the total deformation on the inner surface of the combined die and the contact stress between contact layers under non-uniform temperature distribution that would influence the practical die initial design were discussed further.     

Modelling and experimental characterisation of a residual stress field in a ferritic compact tension specimen

The aim of the work is to elucidate the influence of plasticity behaviour on the residual stress field in a ferritic reactor pressure vessel steel. To this end, we investigate two compressively pre-loaded compact tension (CT) specimens to generate a mechanical residual stress field. One specimen was subsequently pre-cracked by fatigue before both specimens were measured using high-energy synchrotron X-ray diffraction. A fine grain size microstructure (∼5–10 μm grain size) allowed a small X-ray beam slit size and therefore gauge volume. The results provide an excellent data set for validation of finite element (FE) modelling predictions against which they have been compared. The results of both mechanical testing and modelling suggest that the use of a combined hardening model is needed to accurately predict the residual stress field present in the specimen after pre-loading. Some discrepancy between the modelled crack tip stress values and those found by X-ray diffraction remain which can be partly explained by volume averaging effects in the presence of very high stress/strain gradients.     

考虑齿圈柔性的风电行星轮系动态啮合特性研究

针对集中参数法难以考虑齿圈柔性而有限元法计算量大的问题,以风电行星轮系为研究对象在集中参数/有限元混合法基础上提出一种揭示内啮合齿轮副延长啮合现象的分析方法。首先采用集中参数法建立风电行星轮系的动力学模型,并求解获得动态啮合力;随后,运用有限元法建立行星轮系内啮合齿轮副的有限元模型,并开展静态接触分析从而获得内啮合齿轮副各啮合位置发生多齿啮合时的变形阈值;最后,将集中参数模型获得的动态啮合力施加在内齿圈有限元模型上计算出内齿圈的动态响应,并结合发生多齿啮合时的变形阈值,从而揭示在不同负载和支撑数量下内齿圈上多齿啮合的分布区域,获得接触应力和齿根应力,分析啮合齿对数量改变前后对应力的影响。结果表明：考虑齿轮柔性后,内啮合齿轮副会出现除理论啮合齿对外其他齿对相接触的现象;随着负载扭矩的增大,内齿圈上三齿啮合首先发生在支撑两侧,随后三齿啮合发生区域不断增加;当行星轮与内齿圈间的啮合由理论两齿啮合变为三齿啮合时,其齿面接触应力和齿根应力小于其在相同时刻只计入两齿啮合时的应力值。