热变形工艺对SAE8620H齿轮钢带状组织的影响

对比研究了截面规格为300 mm×340 mmSAE8620H齿轮钢连铸坯不同部位、变形量、变形方向、变形终了温度、变形后冷却方式等参数对其带状组织的影响。结果表明,连铸坯心部热变形试棒带状明显,带较宽;热变形后冷速对带状组织影响最为关键,适当快冷可抑制碳元素的偏析,掩盖合金元素的带状偏析而得到较轻的带状组织;提高热变形终了温度,铁素体-珠光体晶粒尺寸增大,带状组织有增强的趋势;变形量小于27%时,变形组织不形成交替的元素偏析带,即使完全退火缓慢冷却也不形成带状组织;带状组织形成与铸坯的拉坯方向无关,无论沿拉坯方向变形还是垂直拉坯方向变形,带状组织均沿变形方向形成。     

25CrMo钢中带状组织及其对冲击性能的影响研究

对25CrMo车轴钢中带状组织形成及其对横向/纵向冲击性能的影响进行研究.研究表明,钢中带状组织主要源于成分偏析,轧制过程中使铸锭中合金元素C、Cr、Mn等偏析区域沿轧制方向被拉长形成明显条带;在随后热处理过程中,元素偏析区与基体将出现明显组织差异,钢中组织上的方向性导致出现性能上的各向异性;缓解元素偏析的工艺措施有利于减轻带状组织.     

17CrNiMo6齿轮钢的组织均匀化

以17CrNiMo6齿轮钢为研究对象,通过对其锻态试样进行不同温度和不同时间的退火处理,采用光学显微镜(OM)、扫描电镜(SEM)、能谱仪(EDS)组织分析手段和Origin数据处理软件,对其带状组织形成原因以及均匀化行为进行了研究与定量分析。结果表明,C、Cr、Ni、Mn和Mo元素在珠光体+贝氏体区域的富集是17CrNiMo6齿轮钢带状组织产生的根本原因,当加热温度为1100 ℃、保温时间为11 h和加热温度为1250 ℃、保温时间为2 h以上时,带状组织已消除,但合金元素不均匀程度仍较高。当加热温度为1250 ℃、保温时间为4 h时,C、Cr、Mn、Ni、P、S、Mo的偏析系数K分别为1.02、0.98、1.02、1.02、1.01、0.98、0.98,元素分布也达到均匀。     

脱碳层对GCr15轴承钢带状组织的影响

对GCr15轴承钢进行退火处理,并用显微硬度法测量了脱碳层的深度,进而对表层脱碳层和心部非脱碳层进行带状组织评级。试验结果得出,随着保温时间的延长,脱碳层厚度增加,但表层脱碳层和心部非脱碳层的带状组织级别相当。扫描电镜成分分析发现,表层脱碳层与心部非脱碳层带状组织形成的主要原因均为铬、锰等元素的偏析。     

加热工艺对SUP6弹簧钢连铸坯成分偏析影响的研究

以SUP6弹簧钢为研究对象,评定了热轧带钢的带状偏析级别,对比分析了现场加热前后的连铸坯偏析情况,研究了不同加热温度和保温时间对连铸坯偏析的影响。结果表明,SUP6弹簧钢连铸坯的中心部位存在成分偏析,并遗传到热轧带钢中,形成带状组织。热轧前的加热工艺有利于偏析情况的减轻。综合考虑,SUP6弹簧钢较合适的轧前加热制度为温度是1000℃,保温30 min。     

低碳合金钢中带状组织的成因、危害和消除

研究了低碳合金钢中带状组织和混晶组织形成的原因、对钢材质量的影响和消除方法。结果表明,这两种组织主要是钢中的成分偏析引起的,而且常成因果关系。带状组织会降低钢的力学性能,切削加工性能和逆性成形性能,带状组织中的合金元素偏析,在常规退火、正火、淬火、渗碳加热条件下难以消除。采用电渣重熔、快速结晶、增大锻造比和扩散退火等技术,可以减轻或避免钢材带状组织的形成。     

ZL205A合金大型铸件带状偏析组织对力学性能的影响

介绍了ZL205A合金大型铸件中的一种宏观带状偏析缺陷的形貌,分析了带状偏析最严重区域的组织对力学性能的影响,观察了试棒断口形貌,并分析了断口处偏析组织的化学成分。研究发现,ZL205A合金带状偏析组织使该区域力学性能降低,造成力学性能低的原因是带状偏析组织中Cu量偏高且聚集在晶界位置,形成了晶间脆性相。     

Q345R钢热成型封头带状组织的成因和消除

Q345R钢封头由于热冲压成型后产生较严重的带状组织,导致冲击吸收能量、屈服强度、抗拉强度等指标不合格。经分析,Q345R钢带状组织是由于合金元素偏析和成型后冷却速度较小造成的,通过适当提高热成型后正火加热温度和冷却速度消除了带状组织,恢复了力学性能,满足设计要求。     

Microscopic Characterization of Semi-Solid Ti14 Alloy

采用热模拟系统研究半固态变形参数对合金微观组织演变和元素分布的影响,并讨论变形过程中的Ti2Cu析出行为。结果表明:微观组织,特别是Ti2Cu析出过程受变形参数影响较大;温度的增加,应变速率和变形量的降低将促进Ti2Cu在晶界的偏析,最终形成了网状晶界结构。分析认为:半固态晶界的析出过程主要受控于包晶反应,升温或降低其他变形参数将有利于液相在晶界的析出,形成晶界Cu元素富集区。液相的偏析和Cu元素的富集增加了该区域的包晶反应,最终在冷却过程中形成了粗大的网状晶界结构。     

保温工艺对G20CrNi2Mo轴承钢带状组织的影响

G20CrNi2Mo轴承钢工件易出现带状组织，降低其疲劳性能和服役寿命。为掌握带状组织的形成原因和消除方法，采用光学显微镜(OM)、扫描电镜(SEM)、电子探针(EPMA)和电子背散射衍射(EBSD)等表征分析了保温工艺对G20CrNi2Mo轴承钢带状组织成分和结构的影响。结果表明：G20CrNi2Mo轴承钢形成带状组织的原因是C元素的偏析，部分区域贫C导致其马氏体相变所需的临界冷却速率增加，随后在锻造冷却时此区域先共析形成了铁素体带；通过高温长时保温可以促进C元素的扩散，进而消除带状组织。对于渗碳/氮热处理过程，当处理温度≥820℃时，带状组织可完全消除。而当处理温度≤820℃时，可通过940℃保温3 h的正火预处理将带状组织提前消除，其在后续的渗碳/氮热处理过程中不再出现。     

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.     

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.     

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。     

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).     

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.     

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.