ZA27合金金属型铸造时的凝固特性,伴生缺陷和壁厚效应

金属型铸造是ZA27的主要铸造方法之一。本文试验研究了ZA27合金金属型铸造时的凝固特性、伴生缺陷和壁厚效应。结果表明,ZA27合金在金属型中以糊状方式凝固,铸件易于产生缩松和比重偏析,铸件的力学性能对于壁厚有明显的敏感性。     

压力管道焊缝含环向表面裂纹J积分估算方法

基于SC .ENG(表面裂纹工程估算 )方法的基本原理 ,建立了弯矩作用下压力管道焊接接头含有内表面、等深度及有限长度环向表面裂纹的J积分近似估算公式 ,在计算公式中考虑了焊缝非匹配因素的影响。与SC .ENG1和SC .ENG2方法相对应 ,在此分别称所推导的J积分估算方法为SC .ENG3和SC .ENG4方法。该方法建立在塑性形变理论、Ramberg -osgood本构关系和等效原则基础上 ,通过使裂纹存在时的结构柔度与壁厚局部减薄时模拟结构的柔度相等的方式建立J积分的估算公式。有限元数值解验证了上述J积分估算公式的有效性     

10CrMo910钢焊接工艺探讨

通过对大庆２００ＭＷ机组主蒸管道１０ＣｒＭｏ９１０钢的焊接性能分析,提出了一整套行之有效的焊接工艺,并在施工现场检修焊接中进行了实践,为焊接同类钢材提供了可借鉴的经验和工艺参数。     

钢结构制造中焊接变形的控制方法

着重介绍了桥梁、建筑、船舶、压力容器等钢结构制造中经常遇到的一个比较棘手的问题--焊接变形的控制方法和解决方案.     

活性剂对镁合金交流A-TIG焊的影响

分别以单质Te,Ti和Si,氧化物SiO2,TiO2和V2O5,卤化物MnCl2,CdCl2和ZnF2作为表面活性剂进行了镁合金交流A-TIG焊,研究了活性剂对焊缝成形和组织的影响规律.Te粉,ZnF2和CdCl2都能明显增加熔深,其中Te粉使熔深达到传统TIG焊的1.6倍,焊缝深宽比达到0.43.Ti粉对焊缝熔深熔宽几乎没有影响.V2O5,SiO2,TiO2,MnCl2和Si粉都使得焊缝熔深熔宽减小.在三种明显增加熔深的活性剂中,Te粉和ZnF2都使得焊缝组织晶粒细化,而CdCl2使得焊缝组织晶粒略有粗化.结果表明,活性剂增加镁合金ATIG焊熔深主要与活性剂粒子和电子复合导致电弧收缩有关.     

含钪与不含钪铝镁钪合金焊接接头的组织与性能

分别采用Al-Mg-Zr和Al-Mg-Zr-Sc合金焊丝为填充材料,对2 mm厚的Al-Mg-Sc合金薄板进行惰性气体保护焊接,然后对两种焊接接头的显微组织和力学性能进行对比研究。结果表明:采用两种焊丝焊接的Al-Mg-Sc合金薄板的焊接接头强度系数均大于0.9。但采用Al-Mg-Zr-Sc合金焊丝为填充材料时,焊缝晶粒组织明显细化,熔合区形成的细小等轴晶层提高了基材与焊缝填充材料的结合力,焊接接头的屈服强度比采用Al-Mg-Zr合金焊丝为填充材料时提高了100 MPa,显著提高了Al-Mg-Sc合金焊接构件的许用强度,因此焊接Al-Mg-Sc板材更宜采用Al-Mg-Sc-Zr焊丝。     

2205双相不锈钢管焊缝韧度分析

2205双相不锈钢具有优异的力学性能和耐腐蚀性能,广泛用于运输、石油、天然气、海洋和化工等行业.与普通奥氏体不锈钢相比,双相不锈钢焊接有许多特点,被公认为是一种较难焊接的材料.某天然气集输管道最高操作压力13.3 MPa,最低操作温度-30℃,对韧度提出了较高的要求.对该高压天然气管道钢管纵、环焊缝的冲击韧度和断裂韧度(CTOD)进行了试验、分析.结果表明,纵焊缝(SAW焊接方法)的冲击韧度和断裂韧度比环焊缝(TIG SMAW焊接方法)明显好.其主要原因是采用的填充金属不同,以及因热输入量差异、焊后固溶处理与否而引起显微组织中两相比例的差异造成的.     

SAF2205双相不锈钢焊接热影响区在尿素介质中的腐蚀研究

研究了SAF2205双相不锈钢和尿素级316不锈钢对接焊热影响区在工业尿素合成介质中的耐蚀性.实验结果表明,焊接线能量对热影响区的耐蚀性有重要影响,腐蚀最重处是在距离熔合线3-6mm区域,局部腐蚀深度随线能量的增加而增大.SAF2205不锈钢焊接线能量对热影响区腐蚀的敏感程度比316L不锈钢大.     

Defect structure and chemical diffusion in nickel sulfide β-Ni3S2

The chemical composition, defect structure, and diffusion in nickel sulfide -Ni₃S₂ have been investigated in H₂S-H₂ mixtures containing between 1 and 65% H₂S between 560 and 700°C. Gravimetric, density, and X-ray studies were carried out. In the thermodynamically stable compound the ratio of Ni/S varied between 1.3 and 1.75. The X-ray examination showed a step change in the lattice parameter at the Ni/S ratio 1.4. A linear dependence of the density values (between 5.5 and 6.2 g/cm³) on the composition was observed. On the basis of the chemical composition and density measurements the number of nickel and sulfur atoms in 1 cm³ were determined. It has been shown that the Ni₃S₂ phase is defected in both anion and cation sublattices and that its chemical formula may be described as follows: Ni_3±yS_2x, where y 2x. It has been found that in the mixture containing 10% H₂S the process of defect formation is determined by their diffusion in the sulfide. The temperature dependence of the diffusion coefficient is described by the equation D = 13.15 exp(-30,000/RT) cm²/sec. No dependence of D on the sulfur partial pressure was observed, but this may be due to the relatively large uncertainties in the measurement of the diffusion coefficients.     

Kinetics and mechanism of iodide-film growth on lead-effect of short-circuiting and higher-valent dopant

The effect of a higher-valent dopant like Sb on the iodination rate of lead under normal and short-circuit conditions in iodine pressure of 0.615–6.578 kPa and in the temperature range of 423–523 K has been investigated. Like pure Pb, Sb-doped Pb also follows the parabolic law of film growth. The isothermal parabolic rate constants are found to be enhanced due to the presence of Sb. The iodine-vapor-pressure dependence of the isothermal parabolic rate constant has been observed to be k_ppI ₂ ^1/2 . This has been explained on the consideration of electron-hole migration across the film as the rate-limiting step. The activation energy for iodination of Sb-doped Pb under normal condition is estimated to be 64 kJ · mol^–1 in an iodine pressure of 0.615 kPa. The rate of iodide-film growth has been found to increase considerably under a short-circuit mode of experiments. Such observations have been explained with the concept of ion migration as the rate-limiting step for the film-growth process. The iodine pressure dependence of rate constants under short-circuit conditions is observed to be k_pI ₂ ^1/3 , associated with an activation energy value of 51 kJ mol^–1. The effect of putting additional resistances in series to the short-circuit Pt path during iodination of Sb-doped Pb is found to be similar to that observed for pure Pb. Results of the present study have been explained considering the prevalence of Schottky-Wagner type of point defects in the lead-iodide film. Wagner's electrochemical potential gradient has been confirmed to be the main driving force for the film-growth process. Iodide films have been characterized by SEM, EDS, EPMA, XRD, and AES analyses to substantiate the kinetics results.