平面应力状态“铁素体-奥氏体-铁素体”异质接头疲劳特性

针对10Ni5Cr Mo V钢采用0Cr18Ni24Mo6N奥氏体焊条焊接形成的"铁素体-奥氏体-铁素体"异质接头,采用薄片试样疲劳试验研究了无加强高和带加强高两种情况下平面应力状态接头的疲劳行为,并建立了带加强高接头S-N疲劳曲线。结果表明,无加强高情况下疲劳裂纹在焊缝金属内启裂并扩展;带加强高情况下疲劳裂纹在焊趾处启裂、并近似垂直载荷方向在母材内扩展至断裂,寿命较无加强高情况大幅降低,且启裂寿命占疲劳总寿命的比例较高,达到70%—80%。     

船用10Ni5CrMoV高强钢的疲劳性能

通过对三轴疲劳加载试验后带有裂纹的10Ni5CrMoV钢T型焊接节点试样进行金相、硬度、断口试验,利用光学显微镜、扫描电镜对低合金高强钢10Ni5CrMoV的焊接接头的组织、结构和性能进行分析,并结合有限元方法研究其对疲劳特性的影响。分析结果表明:10Ni5CrMoV钢的组织主要为回火索氏体,焊接接头有明显的分区界限,各区的硬度不同,断口呈现韧性断裂的形貌。进一步研究表明,热影响区硬度高于母材区和焊缝区,断口含有孔洞、夹杂等缺陷,裂纹扩展路径受组织和外力影响较大,疲劳寿命对应力集中比较敏感。利用有限元模拟方法计算得到焊趾根部弯曲疲劳寿命,分析结果与试验有较好的吻合程度。因此,改善热处理工艺,改进结构设计,可以提高低合金高强钢10Ni5CrMoV的疲劳特性。     

10Ni2CrMoV钢焊接接头腐蚀特性研究

通过室内挂片和电化学测试试验,结合微观分析,比较了手工焊和埋弧焊工艺制备的10N i2CrMoV钢焊接接头的腐蚀特征,讨论了相关因素的影响。结果表明:两种工艺的焊接接头均以焊缝金属的耐蚀性最差,热影响区的耐蚀性最好;接头各区中的化学成分和微观组织的差别,是导致接头各区耐蚀性差异的主要因素;埋弧焊接头的耐蚀性优于手工焊接头的,焊接过程中输入的线能量较高是主要原因。     

不同焊接方法对铁路桥梁用321-Q370qE复合板焊接接头疲劳性能的影响

桥面结构焊接的方法主要是埋弧自动焊和焊条电弧焊,为了比较采用不同的焊接方法对321-Q370qE复合板焊接接头疲劳性能的影响,对这两种焊接方法形成的焊接接头进行了疲劳试验.试验结果表明,采用焊条电弧焊形成的焊接接头的抗疲劳性能优于埋弧焊形成的焊接接头.     

超声冲击对高速列车转向架焊接十字接头超高周疲劳性能的影响

针对高速列车转向架在实际运用中出现的疲劳问题,利用HJ-Ⅲ型超声冲击处理装置,对高速列车转向架用SAM490BW钢十字接头焊趾进行超声冲击处理,并对处理后接头的超高周疲劳性能进行研究。结果表明,原始焊态试样和超声冲击态试样的S-N曲线均出现了传统意义上的水平段。超声冲击处理试样的疲劳强度相比于未处理试样提高了25%。经过超声冲击处理后,疲劳裂纹源的数量由多个变为单个,焊接接头焊趾处的应力集中系数下降了32.4%,降低了裂纹萌生概率;超声冲击降低了焊趾区域的残余拉应力,并诱发产生残余压应力,高达-255.5 MPa;焊趾表层晶粒得到细化,晶粒平均尺寸小于100nm;裂纹在塑性变形区扩展路径变长。     

15CrMoR(H)+SUS321不锈复合钢板的焊接

对15CrMoR(H)+SUS321不锈复合钢板的基层和堆焊层焊接性进行了分析,选择手工电弧焊+埋弧焊的方法,制定合理的焊接工艺,对焊前预热、层间温度、焊后消氢进行控制,完成了15CrMoR(H)+SUS321的焊接。     

压力容器焊接技术研究

针对压力容器焊接的特点及存在的问题,介绍了手工电弧焊、埋弧焊、钨极气体保护焊、熔化极气体保护焊、等离子弧焊、电渣焊、激光焊、激光-电弧复合焊等焊接方法,并对压力容器焊接技术的发展进行了展望。     

铜-钢电子束焊接材料的疲劳特性EI北大核心

异种金属焊接构件的疲劳性能对于航天器的服役可靠性具有重要影响。探索了Cr0.8铜合金和1Cr21Ni5Ti不锈钢异种金属焊接接头的疲劳寿命和疲劳断裂机制,采用合理的电子束焊接工艺制备得到铜-钢复合板。利用金相显微镜表征和分析焊缝处的组织与成分,使用电子拉伸试验机和疲劳试验机对焊接接头进行力学性能测试,利用扫描电镜观察不同周次断裂下的疲劳断口。结果显示:两种金属整体冶金结合情况良好,但是钢侧局部熔合区面积较大且由钢基体伸入到焊缝中;铜-钢电子束焊接接头的拉伸试样均断裂于焊缝最小截面处,疲劳试样的平均疲劳极限值为48.04 MPa,且均起裂于焊缝最小截面处;高周疲劳试样在焊缝上表面端点处观察到单一裂纹源,低周疲劳试样观察到较多裂纹源分布于焊缝上下表面及内部,两者的最终断裂区均位于铜合金基体。可见在疲劳断裂过程中,焊接试样在高周和低周断裂下的裂纹源数量存在差异,但是裂纹均易萌生于焊缝最小截面处,且向铜合金基体进行扩展。     

800MPa级低合金高强钢焊接工艺试验

本文针对乌东德水电站压力钢管制造,分别采用手工电弧焊、埋弧自动焊、富氩气体保护焊进行现场焊接工艺试验,通过分析研究焊接工艺试板力学性能,确定了合理的焊接工艺（埋弧自动焊）参数,为800MPa级低合金高强钢超大型压力钢管制造提供了经验借鉴。     

超声捶击提高超细晶粒钢焊接接头的疲劳性能

焊接接头疲劳强度是其最重要的服役性能，由于焊接残余应力的作用和焊接接头处的几何不连续性，焊接接头的疲劳强度一般大大低于母材，采用超声捶击方法提高超细晶粒钢焊接接头的疲劳强度，通过对对接接头焊践处进行超声波冲击处理，对比超声波冲击处理后焊接接头的疲劳强度，实验结果表明：超声捶击使得S-N曲线右移，FAT（循环寿命为10^6时的疲劳强度）提高幅度达到66%，在应力范围为200MPa的疲劳寿命提高58倍，研究表明，经超声捶击处理，焊趾处的应力集中系数相应减小，焊接残余应力由拉应力转换为压应力，这是超声捶击提高焊接接头疲劳强度的主要机制。     

焊接方法对X90管线钢焊接接头性能的影响

目前,关于焊接方法对X90管线钢焊接接头组织性能的影响相关报道较少。采用手工电弧焊(SMAW)、熔化极气体保护焊(GMAW)、埋弧焊(SAW)3种焊接方法对X90管线钢进行对接焊。利用金相显微镜(OM)、扫描电镜(SEM)及能谱仪(EDS)对焊接接头及冲击断口进行显微组织及成分分析,分析了焊接方法对X90管线钢焊接接头组织性能的影响规律。结果表明:焊缝区组织主要为粒状贝氏体和针状铁素体;SMAW粗晶区组织主要为多边形铁素体、粒状贝氏体及M/A组织,GMAW和SAW粗晶区组织主要为粗大的铁素体、粒状贝氏体及板条贝氏体;3种焊接接头硬度分布趋势一致,盖面层硬度最高;SMAW、GMAW和SAW焊接接头抗拉强度依次为714,771,790 MPa,断后伸长率依次为23.3%,22.9%,20.0%;SAW与GMAW熔合线处20℃冲击吸收功比SMAW高约40 J,断裂机制为微孔聚集型,在韧窝底部有金属碳化物粒子析出。     

Effect of welding processes on fatigue crack growth behaviour of AISI 409M ferritic stainless steel joints fabricated using duplex stainless steel fillers

The present investigation aims to study the effect of welding processes such as shielded metal arc welding (SMAW), gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW) on fatigue crack growth behaviour of the ferritic stainless steel (FSS) conforming to AISI 409M grade. Rolled plates of 4 mm thickness were used as the base material and AISI 2209 grade duplex stainless steel (DSS) was used as filler metal, for preparing single pass butt welded joints. Centre cracked tensile (CCT) specimens were used to evaluate the fatigue crack growth behaviour. From this investigation, it is found that the GTAW joints showed superior fatigue crack growth resistance compared with SMAW and GMAW joints. The reasons for the superior performance were discussed in detail.     

高强船体钢双丝埋弧焊焊接接头CTOD试验研究

根据GB／T2358—1994标准,对16ram厚的高强船体钢焊接接头的焊缝中心-40℃的裂纹尖端张开位移（CTOD）进行测试,绝大部分试样的断裂韧性值是有效合格的,其CTOD值大于0．15mm,符合DNV验收标准。试验结果表明,在给定的双丝埋弧焊接工艺下,该钢种焊缝低温韧性好。该钢种中等厚度双丝埋弧焊焊接接头可以在不进行焊后热处理的情况下使用。     

Effect of Notch Location on Fatigue Life Prediction of Strength Mismatched HSLA Steel Weldments

Welding of high strength low alloy steels (HSLA) involves usage of low, even and high strength filler materials (electrodes) than the parent material depending on the application of the welded structures and the availability of the filler material. In the present investigation, the fatigue crack growth behaviour of weld metal (WM) and heat affected zone (HAZ) regions of under matched (UM), equal matched (EM) and over matched (OM) joints has been studied. The base material used in this investigation is HSLA-80 steel of weldable grade. Shielded metal arc welding (SMAW) process has been used to fabricate the butt joints. Centre cracked tension (CCT) specimen has been used to evaluate the fatigue crack growth behaviour of the welded joints. Fatigue crack growth experiments have been conducted using servo hydraulic controlled fatigue testing machine at constant amplitude loading (R=0). A method has been proposed to predict the fatigue life of HSLA steel welds using fracture mechanics approach by incorporatin     

10Ni5CrMoV钢双轴弯曲应力下表面裂纹疲劳扩展特性研究

以10Ni5CrMoV钢为研究对象,在加载条件与构件使用环境相近条件下,在原板厚大尺寸试样表面引入人工缺口模拟实际构件中存在的类表面裂纹缺陷,采用双轴弯曲疲劳试验方法,开展原板厚大尺寸试样双轴弯曲应力下的表面裂纹疲劳扩展特性试验研究。结果表明,裂纹半长c和裂纹深度a都随循环次数N单调递增,且曲线a-N满足一定的线性关系。建立表面裂纹半长c与深度a之间的定量关系式预测模型,从而定量解决裂纹深度尺寸不好直接测量的难题。     

Role of butter layer in low-cycle fatigue behavior of modified 9Cr and CrMoV dissimilar rotor welded joint

The present work aims at studying the role of butter layer (BL) in low-cycle fatigue (LCF) behavior of modified 9Cr steel and CrMoV steel dissimilar welded joint. The significant difference of the chemical composition of base metals (BMs) makes it a challenge to achieve sound welded joint. Therefore, buttering was considered to obtain a transition layer between the dissimilar steels. The LCF tests of two kinds of specimens without and with butter layer were performed applying strain-controlled cyclic load with different axial strain amplitudes. The test results indicated that the number of cycles at higher strain amplitudes of welded joint without butter layer was greatly higher than that of the joint with butter layer, while the fatigue lifetime to crack initiation (2N_f) became closer to each other at low and middle strain amplitudes. The failure was in the tempered heat affected zone (HAZ) at the CrMoV side for specimens without BL, while the fracture occurred at the tempered HAZ in the BL for specimens with BL. The microstructure details of BM, BL, HAZ and weld metals (WMs) were revealed by optical microscopy (OM). It was found that the tempered martensite was major microstructure for welded joint and much more carbides were observed in tempered HAZ than other parts due to the repeated tempering. Microhardness test indicated a softest zone existing tempered HAZ of BL and also there was a softer zone in tempered HAZ at the CrMoV side due to repeated tempering during welding and post weld heat treatment (PWHT). And scanning electron microscopy (SEM) was applied to observe the fractography. It was indicated that the fatigue crack initiation occurred from the specimen surface and all specimens were ductile–brittle mixed fractures. It is deemed that the softening behavior in BL caused by twice tempering correspondingly decreased the LCF lifetime at higher strain amplitudes. So suitable welding parameters and heat treatment processes became a key measure to ensure LCF property without losing other properties for welded joint with BL.     

A study on mechanical and microstructure characteristics of the STS304L butt joints using hybrid CO2 laser-gas metal arc welding

In order to examine mechanical characteristics of the stainless steel (STS304L) hybrid welded butt joints, two-dimensional thermal elasto-plastic analysis has been carried out. To this end, a 2D simulation model has been developed considering hybrid welding features. Based on thermal history data obtained from this heat source model, the residual stress distribution in weld metal (WM), heat affected zone (HAZ) and base metal (BM) characteristics have been calculated and found to be in reasonable agreement with the experimentally measured values. In order to investigate the effect of welding process, thermal elasto-plastic behaviour of the hybrid welded joints was compared with a welded joints obtained by conventional submerged arc welding (SAW) process. The results show that the longitudinal residual stress in the hybrid welded joints is less (13–15%) than that of the SA welded joints. Weld metal formed in both welding processes shows very fine dendritic structure. Due to higher heat input in SAW, the HAZ size of the SA welded joints is more than twice that of the hybrid welded joints. Therefore, from mechanical and metallurgical point of view, it could be confirmed that it makes a good sense to use SAW instead of hybrid CO₂ laser-gas metal arc welding (GMAW) for butt joint of the STS304L thick steel.     

Influence of post weld treatments on the fatigue behaviour of Al-alloy welded joints

In this paper the influence of different post welding treatments, such as ageing or shot peening, on the fatigue behaviour of Al-alloy welded joints was investigated. The analysed joints were candidates for car structural applications. Several four point bending fatigue tests were conducted on GMAW specimens subjected to different post weld treatments. The residual stress field acting on specimens was measured by the X-ray diffraction (XRD) technique. The results of tests were discussed with the aid of a finite element model of the specimen aimed to calculate the actual fatigue cycle, also taking account of residual stresses and of their redistribution during the test. This allowed to characterize the fatigue resistance of the joints, taking account of the effective stress acting in the region of crack initiation.     

Influence of the submerged arc welding in the mechanical behaviour of the P355NL1 steel—part II: analysis of the low/high cycle fatigue behaviours

A normalized fine grain carbon low alloy steel, P355NL1 (EN10028-3), intended for service in welded pressure vessels, where notch toughness is of high importance, has been investigated. Applications with this steel usually require the intensive use of welds. One of the most common welding processes that are used in the manufacturing of pressure vessels is the submerged arc welding. This welding process is often automated in order to perform the main seam welds of the body of the vessels. The influence of the automated submerged arc welding, in the mechanical performance, is investigated. In this paper (Part II) the low and high cycle fatigue and crack propagation behaviours are compared between the base and welded materials. Several series of small and smooth specimens as well as cracked specimens made of base, welded and heat affected materials, respectively, were fatigue tested. Strain, stress and energy based relations for fatigue life assessment, until crack initiation, are evaluated based on experimental results and compared between the base and welded materials. Finally, the fatigue crack propagation behaviours are compared between the base, welded and heat affected materials.     

Establishing criteria for root and toe cracking of load carrying cruciform joints of pressure vessel grade steel

In this investigation an attempt has been made to establish a criterion to forecast the possible crack initiation region (toe or root) in double fillet welded load carrying cruciform joints and also to know the probable failure mode. Cruciform joints were fabricated from pressure vessel grade (ASTM 517 ‘F’ grade) steel using shielded metal arc welding (SMAW) and flux cored arc welding (FCAW) processes. Fatigue crack growth experiments were carried out in a mechanical resonance vertical pulsator (SCHENCK 200 kN capacity) with a frequency of 30 Hz under constant amplitude loading (R=0). It was found that the fatigue crack initiation lives (root crack or toe crack) were relatively lower in the joints fabricated by FCAW process than the joints fabricated by SMAW process.