氢对灰口铸铁焊接接头裂纹影响的研究

采用排液测氢法和插销试验法较系统地研究了氢对钢芯石墨化铸铁焊条施焊的灰口铸铁焊接接头冷裂倾向的作用；将试验结果与高强钢综合比较，得出灰口铸铁对氢致裂纹不甚敏感的结论。在微观上应用显微镜下录象测氢试验法观测焊接接头中氢的动态行为，明确了氢的微观扩散行为及逸出过程。对此问题的研究不仅对工程实践具有较高的指导意义，更为进一步探讨灰口铸铁焊接接头裂纹产生原因提供了实验与理论依据。     

螺杆泵泵体焊接修复

某石化公司原油卸车场的螺杆泵的底座加热套严重冻裂,其泵体材质为灰口铸铁（HT-250）。根据灰口铸铁的焊接特点和多年实践经验,选用碱性低氢型结构钢焊条（E4315）和EMCrMo-3焊条进行焊补施工,焊补施工严格执行焊接工艺,抓好全方位的过程控制,取得了良好的焊接效果。经过几个月的质量跟踪验证,产品各项技术指标均满足要求,设备运行良好,为使用碱性低氢型结构钢焊条和镍合金焊条焊补灰口铸铁机泵提供了依据。     

灰口铸铁抗拉强度值的Weibull统计分析

制备了HT200和HT150两种牌号灰口铸铁抗拉试样并进行了拉伸试验.通过对强度值进行Weibull统计分析以及对试样的石墨形态的观察分析,认为灰口铸铁的脆性表现主要在于片状石墨的切割作用;片状石墨的不均匀分布是造成灰口铸铁抗拉强度值分散的主要原因.     

温度对柴油机缸盖用HT325力学性能的影响

随着国家排放要求不断提高,实现碳中和,发动机厂不断研究提升满足耐高温、高爆压、高性能、高功率柴油发动机缸盖材料,以便达到耐高温高压的稳定性能要求。本文以灰口铸铁HT325为研究对象,通过变温拉伸和压缩实验并结合化学成分和金相组织分析,研究了温度对HT325铸件力学性能的影响规律。在25℃～450℃温度范围设立10个温度点,保温30 min.研究结果表明：1)HT325材料的热膨胀系数随温度的升高而单调增加;2)HT325弹性模量随温度的升高而单调呈下降趋势;3)HT325材料拉伸应力应变曲线表现出明显的非单调变化;4)HT325的抗拉强度整体上随温度的升高而降低,但在250℃和350℃附近出现反常的回升现象;5)HT325的抗压强度在200℃～300℃温度区间内无明显波动,这将具有广阔的应用前景;6）温度对灰口铸铁HT325抗拉和抗压强度的影响有显著差异。本研究结果为优化气缸盖材料性能、改良铸造工艺、提高产品安全性和节约成本提供了理论与试验依据。     

焊接工艺对数控机床床身用材料焊缝机械性能的影响

分别采用传统CO2气体保护、新型CO2气体保护和激光CO2气体保护复合焊接工艺进行了数控数控机床车身结构灰口铸铁HT250的焊接试验,并进行了接头的X光无损检测、表面硬度和力学性能测试与分析。结果表明,与传统CO2气体保护焊接相比,焊前进行预热处理的新型CO2气体保护焊接获得的接头抗拉强度增加19MPa、接头系数增加8%;而激光CO2气体保护复合焊接获得接头的抗拉强度增加32 MPa、接头系数增加17%。     

灰口铸铁焊接区氢的微观分布及逸出特点

采用显微镜下摄影测氢法,从微观上研究了灰口铸铁母材同质焊缝及异质焊缝焊接区扩散氢的分布及其逸出动态过程,说明了由于石墨的储氢及阻碍氢向前扩散的作用,使进入灰口铸铁焊接接头热影响区的扩散氢很少,因此,氢对灰口铸铁热影响区的冷裂纹倾向影响也小。     

冷焊修复剪板机机架横粱

介绍材质为灰口铸铁的横梁断裂修复焊接工艺，采用冷焊补焊灰口铸铁，综合使用镍基焊条、普通碳钢焊条、常用奥氏体不锈钢焊条进行交叉过渡焊，提高焊接质量，简化修补工艺，降低修补成本。     

铸铁同质焊缝组织判据研究

本文通过实测多种条件下补焊灰口铸铁的热循环曲线,系统分析了各种焊接工艺条件采用同质铸铁焊条所焊铸铁焊缝及其半熔化区的白口组织的形成和分布的影响规律,首次提出了判断白口形成的冷速判据－ｔ和ｔ８／５,为实际焊接灰口铸铁防止白组织提供了简便可行的方法。     

退火温度对HT250焊接残余应力的影响

以未进行退火处理试件为对比，研究了三种不同的退火温度（500℃、600℃、650℃）对HT250焊接残余应力的影响：对四块试件分别测试了各自的焊接应力，并将测试数据输入计算机得到了不同退火温度下的试件的焊接应力曲线；结果表明：此试验的最佳退火温度为650℃。     

焊接温度对铸铁件焊补区组织和性能的影响

在生产条件下使用多元微合金化铸铁同质电弧冷焊焊条对HT250板材进行不同温度下的焊接试验,结果表明,200℃大电流连续焊可获无白口的焊补区,焊缝由珠光体,少量铁素体加细小的片墨构成,焊缝与熔合区硬度分别为176HB和198HB,机加工性能良好,抗裂性好。熔敷金属强度高,能够满足缸体类铸铁件焊补需要。     

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.     

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).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.     

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.