Fatigue strength improvement of stainless steel using weld toes dressing with low transformation temperature welding wire

In the present study, low transformation temperature welding wire (LTTW), which can induce residual compressive stress around 304L welded joints, has been developed to improve the fatigue performance of welded joints. Procedure of design and chemical composition of weld metal and deposited metal of LTTW are introduced. The microstructure of weld metal of LTTW is composed of low carbon martensite and residual austenite. The residual stress distribution of a single welding bead of LTTW was measured and the result shows that compressive residual stress is generated. In addition, fatigue test was also carried out on no-load cruciform welded joints of 304L stainless steel under three conditions: as welded, 308L dressing and LTTW dressing. The result shows that the fatigue life of LTTW dressing joints (2×10⁶ cycles) is improved by 14–23 times and 3–6 times compared with that of as welded joints and 308L dressing joints.     

Numerical and experimental study of the microstructural evolution and the properties of joints welded on rebars using the GMAW process

This paper is a study of CA-50 rebars from SAE steel grade 1026. This study was carried out in order to improve the control of the mechanical properties of welded joints. Knowing certain variables are very important when it comes to finding the ideal welding parameters and the respective microstructural results, and consequently for the mechanical properties of welded joints. In order to carry out this study, a study of the material as received was carried out in order to establish a solid basis for comparison. The material was welded using argon as the shielding gas with 20% carbon dioxide. The wire used was copper-covered ER70S-6, and the welded joints were lap joints. The temperature was monitored using thermocouples for two different heat inputs. A numerical computer code was developed to simulate the phenomena that occur during the process (temperature gradient, phase transformations and heat transfer). The welded joints did not introduce martensite as a brittle phase, the weld metal had a dendritic structure, the heat-affected zone (HAZ) had two different zones with different grain sizes. All of this was due to the temperature gradient, which also led to different characteristics in the weld bead, HAZ, phases formed and different grain sizes.     

Fatigue life prediction using two stage model for AISI 304L cruciform joints,with different fillet geometry,failing at toe

Abstract

Reports in the literature indicate that the fillet geometry affects the fatigue properties of cruciform welded joints in structural steels. In an attempt to study the above effect with respect to stainless steel sheet metal welded joints, load carrying transverse fillet welded cruciform joints having a two fillet geometry were fabricated from AISI 304L stainless steel using gas tungsten arc welding and gas metal arc welding with 308L electrodes. The objective of the present work is to predict the fatigue life of AISI 304L cruciform joints failing at the weld toe using a two stage model. The local stress life method was applied to calculate the fatigue crack initiation life, whereas the fatigue crack propagation life was estimated using fracture mechanics concepts. Constant amplitude fatigue tests with stress ratio R ~ 0 were carried out using a 100 kN servohydraulic Dartec universal testing machine at a frequency of 30 Hz. An automatic crack monitoring system based on crack propagation gauges was used to obtain the propagation data during the fatigue process. The predicted lives were compared with the experimental values.     

Mechanical and fatigue properties of stress relieved type 302 stainless steel wire

Type 302 stainless steel wire is manufactured using a cold extrusion process. The cold working increases the ultimate strength of the wire from approximately 690 MPa to 2070 MPa. However, the cold working process creates residual stresses and surface microcracks in the wire. The residual stresses and microcracks reduce the fatigue life of the wire considerably. Elimination or minimization of residual stresses and microcracks is necessary if longer fatigue life is required. Residual stresses or microcracks in a wire can be minimized by a heat treatment process, which could improve both its mechanical properties and fatigue properties. Experimental evidence shows that the stress relieving process yields maximum mechanical properties between 316 and 482 ° (600 and 900 °F). The fatigue properties of the wire are optimum at a stress relieving temperature of 649 ° (1200 °F). However, the mechanical properties such as yield strength, modulus of resilience, modulus of toughness, and ultimate strength, etc., are reduced by as much as 30% if compared to the similar properties of 316 ° (600 °F) stress relieved wire.     

超长寿命区间16Mn钢焊接接头疲劳性能

使用自行研制的TJU-HJ-Ⅰ型超声疲劳试验系统装置进行了16 Mn钢母材和焊接接头试件的超声疲劳性能试验,以探索其在超长疲劳寿命区间的疲劳行为.结果表明,无论母材还是焊接接头,其S-N曲线都是一条连续下降的曲线;在106～107循环周次范围内焊接接头不存在传统概念上的疲劳极限,载荷循环周次超过107甚至109以后,试件依然发生疲劳断裂.在超长寿命区间,焊接接头疲劳强度远低于母材的疲劳强度.使用现有疲劳极限数据去设计工作在超长寿命区间的焊接结构件是很危险的.     

深水钢悬链立管焊接工艺及焊缝性能试验研究

深水钢悬链立管(Steel Catenary Riser,SCR)是浮式平台的主要部件,在服役条件下由于受到海洋特殊的海浪、潮汐、台风等各种环境因素的影响,极其容易发生疲劳破坏.为解决钢悬链立管在深水服役环境中受循环载荷的作用容易产生疲劳失效的问题,采用冷金属过渡(Cold Metal Transition,CMT)打...     

Influence of oxides on cold lap formation in tandem GMAW

Abstract

The connection between the formation of cold laps and the presence of Mn–Si oxides was studied. The underlying purpose is to understand the fundamental mechanisms of cold lap formation and to avoid it. Tandem gas metal arc welding (GMAW) was used to produce welded specimens in two different shielding gases (pure Ar and pure CO₂) with base metal S355 MC (EN-10149-2) and wire G3Si1 (EN ISO 14341-A). Cross-sections of welds in the cold lap location were evaluated by light optical microscopy and scanning electron microscopy combined with energy dispersive spectroscopy. The results showed that the Mn–Si oxides significantly enhanced cold laps formation, especially the overlap type cold lap formation. The Mn–Si oxides originated from oxidation of the droplets. These oxides transfers to the surface of the weld pool at the weld toe, where they contributed to the formation of the cold laps.     

异种先进高强度钢搭接接头熔化极气体保护焊焊接工艺参数优化

以2 mm板厚无涂层DP780与MS1180钢为母材的异型搭接接头为研究对象,运用正交试验方法优化其熔化极气体保护焊工艺参数. 主要研究了送丝速度、焊接速度、电弧电压、焊接倾角4个影响接头上下板热输入分配的因素对异种材料搭接接头抗拉强度的影响规律. 对正交试验及结果进行直观分析和方差分析,找到了影响接头抗拉强度的主要因子为送丝速度、焊接速度和焊接侧面倾角,同时通过回归分析得到了控制接头抗拉强度的近似二阶数学模型和最优工艺参数组,揭示了主要工艺参数对异种高强度钢搭接接头抗拉强度的影响规律.     

Microstructure and high temperature properties of the dissimilar weld between ferritic stainless steel and carbon steel

Dissimilar joints between STS441, a ferritic stainless steel, and SS400, a carbon steel, were welded by GMAW (Gas Metal Arc Welding) using STS430LNb as a welding wire. The fracture behavior of the dissimilar weld was analyzed by a microstructural observation and thermo-mechanical tests. Martensite was formed at the region between SS400 and the weld metal because the Cr and Nb content in this region decreased due to the dilution of SS400 carbon steel during welding. According to results from a high temperature tensile test with a specimen aged at 900 °C, it was found that the tensile strength of the dissimilar weld at high temperature was equal to that of STS441 base metal and the formation of martensite had little influence on tensile strength of the dissimilar weld at high temperature. However, in the case of thermal fatigue resistance, the dissimilar weld had an inferior thermal fatigue life to STS441 because of the presence of martensite and the softened region around the interface between the dissimilar weld metal and SS400.     

Fatigue life of multilayer hard-faced specimens

Specimens and the method for experimental evaluation of the fatigue life of multilayer hard-faced metal subjected to cyclic mechanical loading are described. The tests were carried out by three-point bending with cyclic non-zero loading in the centre of the specimen, which reproduces, with certain assumptions, the force loading characteristics of rolling rolls, the rolls of continuous casting installations and other tools and equipment for deformation of metals and alloys which are subjected in service to the simultaneous effect of cyclic mechanical and thermal loads. The proposed method is then used to investigate the durability of the specimens of 40Kh steel, hard faced with PP-Np-25Kh5FMS flux-cored wire with and without a ductile sublayer. The sublayer was deposited using Sv-08A solid wire or the PP-Np-25Kh5MF flux-cored wire. The experimental results show that the deposition of the ductile sublayer with Sv-08A and PP-Np-25Kh5MF wires increases the fatigue life of the deposited specimens 1.3 and 1.6 times, respectively. PP-Np-123Kh1MF wire, which produces a deposited metal with higher mechanical properties in comparison with the Sv-08A wire, results in a higher fatigue life of multilayer hard-faced specimens.     

镍基高温合金电子束焊接接头疲劳性能

对GH4169高温合金板材电子束焊接试样进行了金相分析和高、低周疲劳试验,分析GH4169合金的高、低周疲劳性能及疲劳断口形貌.结果表明,GH4169合金电子束焊接接头焊缝区的特点是树枝晶比较明显,为比较发达的树枝晶和明显的二次枝晶.在较高放大倍数下发现,母材和热影响区也为树枝晶结构.接头低周疲劳性能不低于母材,随应变幅降低,相同应变幅下焊接接头疲劳寿命变得略高于母材.接头高周中值疲劳强度比母材高约80 MPa.     

Residual stresses in cold-wire gas metal arc welding

This work compares the welding residual stresses of the cold-wire gas metal arc welding and conventional gas metal arc welding processes. Two techniques were used to measure the residual stresses: X-ray diffraction and acoustic birefringence. The base metal used was carbon manganese steel plates of 9.5-?mm thickness. The results showed that the introduction of the cold-wire tends to decrease the residual stresses, suggesting that the introduction of the cold wire decreases the amount of heat given to the base metal, and consequently lowers residual stresses.     

Microstructure and fatigue resistance of high strength dual phase steel welded with gas metal arc welding and plasma arc welding processes

This study presents the microstructure and high cycle fatigue performance of lap shear joints of dual phase steel (DP590) welded using gas metal arc welding (GMAW) and plasma arc welding (PAW) processes. High cycle fatigue tests were conducted on single and double lap joints under a load ratio of 0.1 and a frequency of 20 Hz. In order to establish a basis for comparison, both weldments were fabricated to have the same weld depth in the plate thickness. The PAW specimens exhibited a higher fatigue life, a gentle S-N slope, and a higher fatigue limit than the GMAW specimens. The improvement in the fatigue life of the PAW specimens was primarily attributed to the geometry effect that exhibited lower and wider beads resulting in a lower stress concentration at the weld toe where cracks initiate and propagate. Furthermore, the microstructural constituents in the heat-affected zone (HAZ) of the PAW specimens contributed to the improvement. The higher volume fraction of acicular ferrite in the HAZ beneath the weld toe enhanced the PAW specimen’s resistance to fatigue crack growth. The double lap joints displayed a higher fatigue life than the single lap joints without changing the S-N slope.     

马氏体时效钢金属粉芯焊丝堆焊层的性能

采用脉冲TIG焊马氏体时效钢金属粉芯焊丝堆焊铝合金压铸模表面来提高模具表面性能.利用SEM、TEM和XRD对堆焊层的微观组织和相特点进行分析.结果表明,堆焊层金属在时效处理后利用低碳马氏体基体上沉淀析出的金属间化合物(Ni3Ti、Ni3(Al,Ti))强化,得到较高硬度和强度,兼具一定韧性的耐疲劳堆焊层,发现还析出(Ni2.9Fe0.1)Ti、(Ni0.7Fe0.3)Al相.与18Ni马氏体时效钢和H13钢实心焊丝进行抗热疲劳试验对比,测试热循环作用下的硬度变化、产生热疲劳裂纹的热循环次数及热裂纹扩展速率,结果显示金属粉芯焊丝堆焊层具有较高的抗热疲劳性能.     

焊丝中Si元素含量对铝合金接头裂纹敏感性的影响规律及机理

使用扫描电镜、能谱、温度场实时采集等测试方法,研究了焊丝中Si含量对AA6063铝合金GMAW焊接头热裂纹敏感性的影响规律及机理. 结果表明,当焊丝为纯铝时,鱼骨试样的焊缝中心会出现细长的焊接裂纹;当焊丝中的Si含量为4.5% ~ 6%时,裂纹的长度变短,但是开裂距离明显增加;当焊丝中的Si含量达到11% ~ 13%时,试样焊缝无裂纹出现. 随着Si含量的不断提高,合金易出现裂纹的凝固温度区间先增大后减小;焊丝中Si含量的不同还会影响凝固后期金属液的流动性,使得焊缝晶界处的物相成分和形态都有明显的区别;同时,Si含量的提高会使得接头的冷却速度先增加后减小,从而导致应力状态改变,热裂纹敏感性先升高后降低.     

Influence of weld geometry and process on fatigue crack growth characteristics of AISI 304L cruciform joints containing lack of penetration defects

Abstract

The influence of weld geometry in conjunction with the gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) processes on fatigue properties of AISI 304L load carrying transverse fillet welded cruciform joints, containing lack of penetration (LOP) defects, has been studied. The fatigue lives of the joints were evaluated using conventional S -N (stress - number of cycles to failure) and fracture mechanics methods. The fatigue lives were calculated according to the two stage approach in which both the fatigue crack initiation and the crack propagation phases were considered. Constant amplitude fatigue experiments with stress ratio R=0 were carried out using a 100 kN servohydraulic Dartec universal testing machine at a frequency of 30 Hz. An automatic crack monitoring system based on crack propagation gauges was used to obtain the crack initiation and propagation data during the fatigue process. The predicted life was compared with the experimental values. It was found that the fatigue lives of the joints fabricated via GTAW were longer than those of the corresponding GMAW joints. It was also observed that the fillet geometry plays a major role in determining the failure mode and life. Test results have been compared with the BS 5400 design curve.     

6005A铝合金激光-MIG复合焊接接头超高周疲劳性能试验研究

对18 mm 6005A铝合金厚板进行多层多道激光-MIG复合焊接,采用超声疲劳试验技术对板状焊接接头与母材的超高周疲劳性能进行试验研究。结果表明,焊接接头和母材在10~9循环周次后均会发生疲劳断裂。焊接接头的高周疲劳数据点分散性较大,母材和焊接接头的S-N曲线均呈连续下降趋势,在10~6~10~9周次范围内焊接接头的疲劳强度为母材的50%~80%。对比IIW标准疲劳曲线发现,焊接接头的疲劳性能在N=10~4循环周次下与IIW标准基本一致,在高周范围内表现优于IIW标准。经扫描电镜微观分析发现,焊接接头的裂纹通常萌生在表面气孔处,疲劳裂纹断裂形式为穿晶断裂,主要表现为准解理断裂特征。     

Analysis of martensite transformation behaviour in welded joint using low transformation temperature welding wire

Abstract

Low transformation temperature welding (LTTW) wire has been found to improve the fatigue strength in welded joints. In the present study, the temperature dependence of the mechanical properties in a dual phase microstructure of austenite and martensite was estimated using the properties of full austenite and full martensite in numerical analyses. A welding method effective for residual stress reduction and fatigue strength improvement was shown by applying a calculation method under transformation superplasticity and transformation induced plasticity in high strength steel welded joints. With this method, the influence of the welding pass sequence on the residual stress distribution and fatigue strength was examined in a boxing fillet welded joint using LTTW. The transformation tensile residual stress in the weld toe was decreased by sectioned welding, and the fatigue limit by sectioned welding with LTTW improved in comparison with the fatigue limit of a joint welded with conventional wire in the same process.     

随焊冲击碾压整形新方法及等承载接头拉伸与疲劳性能

提出了随焊冲击碾压整形方法（weld shaping with trailing impact rolling,,WSTIR）,并研制了一套随焊冲击碾压整形装置．对随焊整形后低匹配等承载接头（equal load-carrying capacity,ELCC）进行了拉伸试验和疲劳试验．结果表明,随焊整形后接头拉伸均断裂在近焊趾的母材处,断裂应力均达到母材的抗拉强度;随焊整形后接头的疲劳寿命明显大于原始焊态接头,由于随焊整形接头焊趾处圆弧过渡降低了应力集中,进而提高了随焊整形接头的疲劳承载能力．拉伸与疲劳试验说明随焊冲击碾压整形后的平余高低匹配接头达到了等承载的要求．这种随焊整形方法将有力地推动低匹配等承载接头设计方法在工程实际的应用．     

共渗对大丝径65Mn金属橡胶疲劳性能影响

研究了稀土硼碳氮共渗对大丝径65Mn金属橡胶疲劳性能的影响.结果表明:以静态损耗因子作为金属橡胶疲劳的判定指标比较合理;经过共渗处理.金属橡胶的疲劳寿命提高28.6%.