连续炉中稀土渗碳数值模拟

本文研究了20CrMoH钢在连续炉中稀土渗碳动力学,编制了相应的数值模拟软件,实现了稀土渗碳过程可视化数值模拟.结果表明稀土元素添加加快了渗碳速度,使20CrMoH钢在880～920℃相同推料周期条件下的渗碳层厚度提高17～35%,并且低温渗碳稀土催渗效果较高温明显. 880、900和920℃时稀土渗碳碳的扩散系数,分别为D880RE=1.84D880、DRE900=1.53D900和D920RE=1.40D920.(对20CrMoH钢在880～920℃稀土渗碳过程碳浓度分布和渗碳层增厚进行了数值模拟,模拟结果与实测值基本吻合.     

渗碳对后续淬火过程影响的数值模拟与分析

通过将渗碳模拟结果作为后续淬火模拟的初始条件,并根据碳浓度变化修正淬火模拟的材料参数,可实现渗碳-淬火连续热处理过程的数值模拟.研究中采用这种方法模拟了端淬试样的渗碳-淬火连续热处理过程,并据此分析了渗碳过程对后续淬火过程的影响.     

齿轮钢渗碳过程数学模型及计算机仿真

本文结合已有的气体渗碳和离子渗碳过程的数学模型,对齿轮钢渗碳的过程进行模拟,并在这些基础上利用有限差分法求解渗碳方程。分析有限差分法与传统数学方程各自的优缺点,根据数学模型设计了用于预测渗碳过程的图形用户界面程序。对于温度,时间,初始碳浓度等变量的影响均能给出准确预测。     

淬火温度对20CrMnTiH钢渗碳淬火后组织与残留应力的影响

根据过冷奥氏体等温转变曲线,建立了20CrMnTiH钢的组织转变模型;利用有限元软件中的热处理模块,对20CrMnTiH钢的渗碳淬火过程进行了有限元数值模拟;分析了不同淬火温度对渗碳淬火后的组织和残留应力的影响;并对渗碳淬火后的组织进行了金相试验分析。结果表明:模拟结果与试验结果相吻合,证明了20CrMnTiH钢相变模型的正确性;同时提出淬火温度在Ac_3温度以上时对组织转变的影响不大,降低淬火温度可以显著降低零件淬火后的残留应力。     

Cr25Ni35Nb和Cr35Ni45Nb合金高温渗碳浓度场的数值模拟

以Cr25Ni35Nb和Cr35Ni45Nb炉管钢为研究对象,以菲克第二定律和"平衡常数法"为理论基础,采用有限差分数值方法,实现了这两种高Cr-Ni裂解炉管材料高温渗碳时碳的扩散和碳化物析出的模拟,给出了渗层的总碳含量、基体中的碳含量、基体中合金元素含量在不同渗碳时间沿壁厚的分布.在1000℃对两种材料进行了固体渗碳实验,分析比较了高温下两种材料的渗碳动力学规律.结果表明,浓度场模拟结果与实验测量值吻合较好.从渗碳增重曲线和浓度场模拟结果可以看出,Cr35Ni45Nb钢的抗渗碳能力强于Cr25Ni35Nb钢.     

BH复合催渗程控系统的构建及数值模拟

通过对可控气氛多用炉设备进行改造,将闲置不用的氨气管道改为BH催渗用滴注管道并设计了催渗剂滴注控制系统,实现了BH渗碳工艺的自动化控制。研究了20Cr2Ni4A钢930 ℃超级渗碳和BH渗碳两种工艺的渗碳动力学,并模拟了渗层深度与碳浓度分布曲线。结果表明: BH渗碳时碳扩散系数要大于超级渗碳,BH渗碳的扩散系数为2.084×10^-9 mm²·s^-1,超级渗碳为1.667×10^-9 mm²·s^-1。本文模拟的20Cr2Ni4A钢在930 ℃进行BH渗碳及超级渗碳时的碳浓度分布和渗层厚度变化与实际验证情况相符。实际渗碳后要达到相同渗层厚度,采用超级渗碳所需的时间要高于BH渗碳,BH渗碳的渗碳速率提高了22.6%。     

气体渗碳温度分布不均匀对碳浓度场的影响

采用有限差分方法,利用Matlab脚本编写程序,针对不同温度分布条件下气体渗碳的碳浓度场进行数值计算,分析温度分布对碳浓度场的影响。结果表明,温度值的高低对碳浓度场有比较大的影响,在气体渗碳数值计算过程中将温度场简化为均匀温度场是有一定条件的,当工件表面温度差别超过4 ℃,工件内部相应位置碳浓度的最大差值即达到0.01%以上。但是温度梯度对碳浓度场的影响可以忽略不计,因此在气体渗碳的碳浓度场数值计算过程中可以按照工件表面当地温度计算碳浓度场的分布。     

稀土高浓度渗碳在推土机齿轮上的应用

模数m为7，渗碳层深度δ为1．3～1．8mm和m为5，δ为1．0～1．5mm的两种推土机变速箱齿轮，一般均用920℃气体渗碳。由于温度高，能耗大，齿轮变形较严重，金相组织偏上限，炉丝及挂具等使用寿命较短。采用稀土和高浓度渗碳的方法，将渗碳温度降至860℃，取得了令人满意的结果。1试验方法用20CrMnTi钢在配有KH－02A型红外线CO。碳势控制仪的R刀一90－gT井式气体渗碳炉内进行试验。所用渗剂为甲醇稀土混合渗剂和煤油。试验工艺如图1所示。在排气和强渗1、！阶段，分别滴入不同量的甲醇稀土混合渗剂和煤油，在扩散阶段仅滴入甲醇稀土混合…     

热处理数值模拟与远程服务

扼要归纳了上海交通大学在热处理计算机模拟研究中的一些体会。数值模拟技术在渗碳（或渗氮）中的应用，已能处理将工艺参数（温度、气体成分、传递系数、扩散系数等）作为时间函数的复杂的非线性问题，更加接近生产实际情况，同时考虑了形状因素的影响。以其为核心开发气体渗碳CAD软件，并与实时控制直接结合形成的智能化渗碳技术，已取得良好实用效果；淬冷过程的数值模拟应用瞬态温度场－相变－应力场相互耦合的非线性三维有限元模型，实现了复杂形状工件、复杂淬冷操作的模拟，并完成了生产试验验证，初步应用于生产。在总结过去的工作和结合国内外相关工作的基础上，本文指出，目前热处理模拟技术正逐步进入实用化阶段，并使热处理远程服务成为可能。热处理远程服务是借助因特网将服务中心与用户连接起来的不受地域限制的技术服务方式，可以进行即时的自助的技术服务，它将改变热处理传统技术服务方式，优化热处理技术资源配置，改变热处理技术人员的工作方法，使其能更多地在服务中心提供的虚拟环境中进行创造性思维和工作。     

稀土快速渗碳在Fe-2.5V合金中的应用

在920℃、1.20%C碳势条件下,对Fe-2.5V合金进行了稀土渗碳和常规渗碳。结果表明,两种渗碳方法均可使Fe-2.5V合金得到组织为马氏体加V4C3碳化物的渗层,碳化物尺寸均为200～300 nm;稀土渗碳比常规渗碳的渗速提高了38%左右,经920℃×9 h稀土渗碳的渗层比常规渗碳的深0.3 mm。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

新型的治疗阿尔茨海默氏症药物(1-二甲基磷酰基-2,2,2-三氯)-乙基-1-醇烟酸醋对体外神经细胞的作用

目的: 观察本实验室合成的一种治疗阿尔茨海默氏症(AD)的药物(1-二甲基磷酰基-2, 2, 2 -三氯)-乙基^-1-醇烟酸醋(NMF),对体外培养的皮层神经细胞活性的影响以及对海人藻酸(KA)所致的神经损伤的保护作用。方法: 采用体外培养皮层神经元的方法,解剖分离 15 d胚胎小鼠皮层神经细胞, 接种于 96孔板,48 h 后加药并培养 72 h,以 MIT 法 观察 NMF 对小鼠皮层神经细胞活性的影响;同时将接种于 24 孔板的细胞预先给予 NMF,d 3 时加或不加KA处理后,以台盼蓝染色鉴别并计数死、活细胞,可得出细胞的存活率。结果: NMF 明显促进胎鼠皮层神经元活性,其中 NMF1、0. 1、10nmol·L^-1促进神经元活性增殖率分别高达 34.7%、37.4%、36. 7%, NMF 明显促进正常胎鼠皮层神经元存活卒,与对照组比较,10nmol·L^-1 NMF 对皮层神经元的存活率分别提高 39.3%、73.5%。 NMF能显著 对抗 KA 所致的神经元损伤,与 KA 损伤组相比, NMF0.1、10、10nmol·L^-1对损伤皮层神经元的保护率分别为 77.30%、80.10%、84.15%。结论: NMF 明 显促进胎鼠皮层神经元的洁性、提高正常皮层神经元,的存活卒,并能有效地保护KA所致的神经元损伤,提示 NMF 是一种很有潜力的治疗 AD 的药物。     

THERMODYNAMICS STUDY ON THE DECOMPOSITION OF CHROMITE WITH KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

INFLUENCE OF HEAT TREATMENT ON DAMPING BEHAVIOUR OF THE MAGNESIUM WROUGHT ALLOY AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Three-Dimensional Growth of Coherent Ferrite in Austenite: A Molecular Dynamics Study

Coherent second phase often exhibits anisotropic morphology with specifi c orientations with respect to both the second and the matrix phases. As a key feature of microstructure, the morphology of the coherent particles is essential for understanding the second-phase strengthening eff ect in various industrial alloys. This letter reports anisotropic growth of coherent ferrite from austenite matrix in pure iron based on molecular dynamics simulation. We found that the ferrite grain tends to grow into an elongated plate-like shape, independent of its initial confi guration. The fi nal shape of the ferrite is closely related to the misfi t between the two phases, with the longest direction and the broad facet of the plate being, respectively, consistent with the best matching direction and the best matching plane calculated via the Burgers vector content(BVC) method. The strain energy calculation in the framework of Eshelby's inclusion theory verifi es that the simulated orientation of the coherent ferrite is energetically favorable. It is anticipated that the BVC method will be applicable in analysis of anisotropic growth and morphology of coherent second phase in other phase transformation systems.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.