Effect of strong carbide forming elements in hardfacing weld metal

To achieve high carbon hard-facing weld metals with both high hardness and crack resistance, strong carbide forming elements Ti, Nb and V were alloyed into the weld metals, and their effect on the formation of carbides and the matrix microstructure were studied. Electron Probe Microanalysis (EPMA), Energy Dispersive Spectroscopy(EDS) and Transmission Electron Microscopy (TEM) were adopted to investigate the microstructure, then thermodynamics of the formation of carbides was calculated and their effect on the matrix was further discussed. It is revealed that Nb, Ti and V influence strongly the distribution and existing state of carbon, inducing precipitation of carbides accompanying with the depletion of carbon in matrix. But when only V are alloyed as carbide forming element, the carbides are scarce and distributed along grain boundaries, and the hard-facing alloy is too hard, while the using of only Nb or Ti could not reinforce the weld metals effectively. The hard-facing alloy reinforced with Nb, V a     

A study on keyhole evolution and weld ripple formation in dissimilar welding under pulsed laser

A three-transient multiphase model is developed to study the dissimilar metal welding of pure niobium plate to titanium alloy Ti–6Al–4V sheet under pulsed laser. The physical process of dissimilar metal welding involves melting, resolidification, mass transfer, self-consistent keyhole, and weld bead formation. The major physical factors, such as recoil pressure induced by vapourisation, surface tension, heat transfer, fluid flow, Marangoni shear stress, buoyancy force, and their coupling are considered. The results show that the keyhole mainly occurs on the Ti–6Al–4V side due to the differences in physical properties of the materials. The effects of pulse overlapping factor on the weld bead are studied. It is found that the pulsed laser has a significant influence on the weld bead formation. The mixing of materials mostly occurred in the upper part of the molten pool. The simulated weld bead profile and the phase distribution agree well with the experimental results.     

V、N共存埋弧焊焊缝中V的析出相行为的研究

已有的15MnVN钢工字梁大线能量理弧焊研究结果表明,焊缝的强度总是过高而韧性偏低。本文利用透射扫描电镜和能谱仪研究了Mn-V-N和Mn-Mo-V-N系焊缝中V的析出相行为和V、N的存在形式及其对焊缝强韧性的影响。试验表明,在焊态或SR态下,由于焊缝冷速大,或因重复加热温度不够高,V、N均不能以非共格形式析出。V的共格析出是使焊缝强度过高和韧性偏低的重要原因。     

00Cr16Sn超纯铁素体不锈钢焊接接头腐蚀性能

采用脉冲钨极氩弧焊工艺,对含锡超纯铁素体不锈钢母材和焊缝的腐蚀性能进行研究.结果表明,焊缝能够获得与母材相当的耐腐蚀性能.含锡超纯铁素体不锈钢通过添加双稳定元素Ti和Nb,形成第二相Ti(C,N)和Nb(C,N),即使在焊接热循环的作用下,未熔解的Ti(C,N)和Nb(C,N)仍然起到细化铁素体晶粒和第二相强化的作用;添加微合金元素Sn,使得冷轧态的母材和焊接接头的耐腐蚀性能均得以提高,并且在焊接接头组织中的锡与Ti(C,N)和Nb(C,N)在晶界形成偏聚的竞争机制,从而得到耐腐蚀性能与母材相当的焊缝组织.     

Influence of filler wire composition on weld microstructures of a 444 ferritic stainless steel grade

Seven compositions of metal cored filler wires for gas metal arc welding (GMAW), containing the same weight percent of chromium (Cr) and molybdenum (Mo) as 444 steel, but with different titanium (Ti) and niobium (Nb) contents were investigated. Experimental results pointed out that the filler wire Ti content required to be twice time more than the amount expected in the deposited metal. This was due to the low Ti transfer ratio during arc welding. Moreover, Ti increased the wetting angle and promoted penetration. It was supposed that Ti affected the weld pool surface tension what led to inward Marangoni convection.Columnar to equiaxed grain transition (CET) was also promoted thanks to the precipitation in the weld pool of Ti rich refractory compounds which act as heterogeneous nucleation sites for equiaxed grains. A minimum 0.3% Ti was required in the filler wire to form a completely equiaxed grain structure in the fusion zone. Niobium in the filler wire did not seem to have any effect on penetration, wetting and grain structure of the fusion zone.     

Effect of Ti on the microstructure and mechanical properties of MAG multipass weld metal

Metal active gas (MAG)welding has been carried out on microalloy controlled rolling steel (S355J2W)by two kinds of welding wires with different Ti content.The mechanical tests have been carried out on the welded joint.The optical microscope and scanning electron microscope (SEM)observations have been performed to investigate the effect of microalloy element Ti on the microstructure of weld metal and impact fracture,respectively.The microstructure of the MAG multipass weld metal includes the columnar grain zone (CGZ)consisting of primary ferrite (PF),ferrite with second phase (FS)and acicular ferrite (AF),and the fine grain zone (FGZ)consisting of polygonal ferrite due to the heat effect of subsequent welding pass.It has been found that the small amount of Ti can significantly increase the impact energy of the weld metal at low temperature and weakly affect tensile strength of welded joint.By adding small amount of Ti,the inclusions have changed from Mn-Si-O inclusions to Ti-bearing inclusions,which causes the Mn-depleted zones (MDZs)much larger and is beneficial to the impact energy by promoting the AF formation,refining the PF and pinning the austenite grain boundary during the subsequent transformation process.     

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.     

Effect of welding processes on joint characteristics of Ti–6Al–4V alloy

Abstract

Although Ti–6Al–4V alloys show reasonable weldability characteristics, the joint properties are greatly influenced by the welding processes. Microstructures and tensile and impact properties of welded Ti–6Al–4V alloy were evaluated for high vacuum electron beam welding, CO₂ laser beam welding and gas tungsten arc welding. The resultant tensile and impact properties of the welded joints are correlated with the weld metal microstructure and hardness. The results indicate that the electron beam welding is more suitable for Ti–6Al–4V sheet welding and the welding seam without defects can be obtained. The full penetration butt welds are obtained by gas tungsten arc welding process, but they have many drawbacks such as wide weld seam, big deformation and coarse grains. Laser beam welding has many advantages such as the narrowest weld seam, the least deformation and the finest grains, but it should be studied again for the reasons of unstable welding technologies and strict condition.     

一种核电核岛主设备用镍基焊丝的研制

通过试验分析了核电核岛主设备用镍基焊丝中各元素对焊丝和焊缝熔敷金属性能的影响.结果表明,随着焊丝中Al,Ti,Mn,Nb元素含量的增加,焊丝的强度、硬度及焊缝金属的抗拉强度增加;随着焊丝中Al,Ti,Nb元素含量的增加,室温焊缝熔敷金属的冲击吸收功增加;随着焊丝中Mn元素含量的增加,焊缝熔敷金属的冲击吸收功降低.通过调整焊丝成分得到了符合核电核岛主设备使用要求的焊缝熔敷金属.     

复合孕育剂Ti、Zr对2519铝铜合金焊缝组织及性能的影响

采用3种焊丝对2519铝铜合金进行MIG焊,研究了孕育剂Ti、Zr对焊缝组织和性能的影响。结果表明:Ti和Zr的细化作用是相容的,当焊丝中单独添加孕育剂Ti或Zr时,焊缝几乎由粗大的柱状晶组成;焊丝中复合添加少量的孕育剂Ti和Zr时,Ti和Zr在熔池中分别形成Al3Ti和Al3Zr,促进了α(Al)非均质形核;随着焊丝中Ti和Zr含量的增加,焊缝组织逐步细化,当焊丝中Ti和Zr含量较高时,Ti和Zr还在熔池中形成大量的Al3(Ti,Zr)质点,促进α(Al)非均质形核;焊缝组织由细小均匀的等轴晶组成,显著提高了接头强度和塑性。