X90钢级管线钢预精焊接头的性能研究

为综合研究X90管线钢的焊接性,选用国内某钢厂轧制的X90管线钢卷板,利用预精焊工艺制备试验钢管4根,采用金相分析、扫描电镜(SEM)断口分析、夏比V型缺口冲击试验、拉伸、弯曲、硬度等试验,研究了焊接接头各个区域的组织和性能.试验结果表明:内外焊缝区组织均为针状铁素体,热影响区(HAZ)粗晶区晶粒粗化严重,主要组织为粒状贝氏体和贝氏体铁素体,在原奥氏体晶界和贝氏体板条内部存在块状或条状的(马氏体-奥氏体)M-A组元;HAZ冲击功离散性较大,出现了单值较低(45 J)的试样,SEM断口分析呈现典型的解理断裂特征;焊接接头抗拉强度805~815 MPa,断裂位置均在HAZ;焊接接头反弯试样易在HAZ出现裂纹和脆断现象;HAZ硬度在220~250 HV之间,较母材下降30 HV左右.HAZ是X90预精焊钢管焊接接头的薄弱环节,为提高X90管线钢的焊接稳定性,应重点研究精焊内外热循环双热影响亚区的组织转变和脆化机理.     

焊接电流对X80钢低温焊接接头组织与性能的影响

通过显微组织分析、硬度测试、拉伸试验、冲击试验、腐蚀试验,利用扫描电子显微镜(SEM)、能谱仪(EDS)和X射线衍射(XRD)等实验手段,研究了焊条电弧焊(SMAW)不同焊接电流对X80钢低温焊接接头组织与性能的影响。结果表明:随着焊接电流增加,热影响区(HAZ)晶粒粗化,并且软化现象更加明显;焊接电流在180~190A的接头综合力学性能最佳,但当电流增加到190~200A时,接头的综合力学性能显著降低;各组接头腐蚀速率相差不大,范围在0.14~0.19g/(m2·h),腐蚀膜具有较好的致密性,能够阻止腐蚀介质对基体继续进行腐蚀,从而达到较好的耐腐蚀效果。     

Microstructure and toughness of coarse grain heat-affected zone of domestic X70 pipeline steel during in-service welding

The microstructures and mechanical properties of coarse grain heat-affected zone (CGHAZ) of domestic X70 pipeline were investigated. The weld CGHAZ thermal cycles having different cooling time Δt _8/5 were simulated with the Gleeble-1500 thermal/mechanical simulator. The Charpy impact absorbed energy for toughness was measured, and the corresponding fractographs, optical micrographs, and electron micrographs were systematically investigated to study the effect of cooling time on microstructure, impact toughness, and fracture morphology in the CGHAZ of domestic X70 pipeline steel during in-service welding. The results of simulated experiment show that the microstructure of CGHAZ of domestic X70 pipeline steel during in-service welding mainly consists of granular bainite and lath bainite. Martensite–austenite (M–A) constituents are observed at the lath boundaries. With increase in cooling time, the M–A constituents change from elongated shape to massive shape. The reduction of toughness may be affected by not only the M–A constituents but also the coarse bainite sheaves. Accelerating cooling with cooling time Δt _8/5 of 8 s can be chosen in the field in-service welding X70 pipeline to control microstructures and improve toughness.     

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。     

不锈钢激光点焊接头组织和力学性能研究

目的 改善SUS301L–HT不锈钢激光点焊焊接性能。方法 以2 mm SUS301L–HT不锈钢为母材进行激光点焊试验,并分析焊接接头的金相组织、硬度、拉伸性能以及断口形貌等。结果 焊点表面无损坏、压痕均匀、无较大焊接变形,表面无飞溅、母材颜色无明显变化。焊核区的微观组织主要是柱状晶,柱状晶依附于未熔化母材晶粒向焊核中心生长。母材硬度最高,约为309HV;焊核中心附近区域硬度适中,约为255HV,热影响区硬度最小,不到220HV。点焊接头断裂形式多为纽扣式断裂且发生在热影响区。结论 不锈钢激光点焊整体质量较好,可用于轨道列车车体加工。     

Refill friction stir spot welding of 5083-O aluminum alloy

In this work,refill friction stir spot welding(RFSSW) was used to weld 2 mm-thick 5083-O alloy.The Box–Behnken experimental design was used to investigate the effect of welding parameters on the joint lap shear property.Results showed that a surface indentation of 0.3 mm effectively eliminated the welding defects.Microhardness of the stir zone(SZ) was higher than that of the base material(BM) and the hardness decreased with increasing the heat input during welding.The optimum failure load of 7.72 k N was obtained when using rotating speed of 2300 rpm,plunge depth of 2.4 mm and refilling time of 3.5 s.Three fracture modes were obtained during the lap shear test and all were affected by the hook defect.     

Evaluation of fatigue fracture mechanism in a flash butt welding joint of a U75V type steel for railroad applications

Nowadays, U75V steel is widely used in high speed railway construction, and commonly jointed by means of flash butt welding procedure. Considering the fact that fatigue failure is the main failure mode of railways, to ensure an adequate service life of railways, especially railways in coastal areas, this work mainly investigated the fatigue fracture mechanism of flash butt welding joints of U75V rail steel. First, the flash butt welding joints were prepared under two sets of process parameters and certain welding joints were corroded beforehand. Then, the microstructure, hardness, S–N curve and fatigue fracture of welding joints were analyzed in detail. Finally, the fracture mechanism was comprehensively discussed by considering the effect of welding parameters. It was concluded that the fatigue performance of flash welding joint is mainly determined by the upset pressure. Higher upset pressure is conducive to improve the fatigue strength. The fatigue crack source of fractured specimens under the condition of corrosion environment is at interface area and at the subsurface of sample. Meanwhile, the corrosion fatigue life obviously reduces.     

316L/X65复合管弧焊工艺研究

采用手工钨极氩弧焊和电弧焊实现了316L/X65双合金复合管的对接焊接。为了研究复合管的焊接工艺,对焊接接头进行了硬度、拉伸和冲击测试,利用光学显微镜、扫描电镜和能谱仪分析了接头的微观结构和成分特点,并对接头进行了电化学实验。结果表明:复合管焊缝由碳钢层、扩散层、过渡层和不锈钢层组成,碳钢层主要为针状铁素体,扩散层出现了马氏体组织,过渡层和不锈钢层焊缝中铁素体呈骨架或蠕虫状分布在奥氏体晶界;本实验焊接工艺下,覆层未受到碳钢层的稀释,化学成分与母材基本一致,但耐蚀性略有降低;焊接接头各项力学性能良好。     

Local mechanical properties of radial friction welded supermartensitic stainless steel pipes

In this work, supermartensitic stainless steel pipes were radial friction (RF) welded and their microstructures and local mechanical properties (hardness, fracture toughness and micro-tensile strength) were characterized in the as-welded condition. Defect-free RF welds were produced with a matching consumable ring (CR) under optimized welding conditions. The formation of a fine structure consisting of a mixture of virgin martensite and some stable austenite retained in the CR region was observed. On the other hand, the presence of virgin martensite plus δ-ferrite was found in the microstructures of the heat affected zone (HAZ) and thermo-mechanically affected zone (TMAZ). A ductile fracture was detected in the CR and weld interface regions at −40 °C. Moreover, both the CR and weld interface regions showed higher hardness and strength values than those of the base material (overmatching), without presenting significant losses in ductility and fracture toughness, which was attributed directly to the fine transformed microstructure of the weld region.     

Laser welding and weld hardness analysis of thick section S355 structural steel

Laser welding is becoming increasingly common and has been found to be of particular interest in the welding of various steel structures. A new generation of high power lasers has entered the market during recent years. These lasers have thus far mostly been used for welding of thin sheet. However, with the availability of higher power, such lasers have possible application to thick section welding. This study investigates the performance and potential of deep penetration laser welding of S355 EN 10025 structural steel of 20 and 25 mm thickness with a high power fiber laser at power levels of 12–30 kW. Visual examinations of the macrographs and hardness tests of all welded specimens were made. Quality windows were drawn based on the results of the experiments. Preferable welding parameters are formed based on the experimental study. The results of the hardness test show that surface hardness level of the weld is up to 2.5 times higher than the surface hardness of the base material.     

Welding current influences on Inconel 625/X65 cladding interface

The pulsed gas tungsten arc welding with hot wire was used to clad Inconel 625 on the surface of X65 steel. The influences of welding current in horizontal welding position on the dilution, in further the composition, microstructure, and property of the Inconel 625/X65 cladding interface were investigated. Experimental results show that with the increase in welding current, namely, in heat input and arc force, dilution rate increased; the composition transition region in the cladding layer close to the fusion line, controlled by the cladding temperature, would be widen; in further, the microstructure would be different due to the heat transfer and composition change; the precipitates were niobium-rich MC carbide with a low welding current, but tended to be the intermetallic compounds, Laves phase, with a high welding current; the highest and lowest hardness values appeared on the heat-affected zone and cladding layer next to the bonding interface, respectively.     

Influence of peak temperature during in-service welding of API X70 pipeline steels on microstructure and fracture energy of the reheated coarse grain heat-affected zones

In this investigation, thermal simulated specimens were used to investigate the effect of second peak temperature during in-service welding on characteristic fracture energy and microstructure feature of the subcritically (SC), intercritically (IC), supercritically (SCR), and unaltered (UA) reheated coarse grain heat-affected zones (CGHAZs). The API X70 high-strength pipeline micro-alloyed steel was subjected to processing during in-service welding by applying double thermal cycle shielded metal arc welding process with heat input of 9.3 kJ/cm and thermal cycles to simulate microstructure of reheated CGHAZs. This consisted of first thermal cycle with a peak temperature of 1350 °C, then reheating to different second peak temperatures of 600, 800, 1000, and 1200 °C with a constant cooling rate of 60 °C/s. Toughness of the simulated reheated CGHAZs were assessed using Charpy impact testing at −20 °C, and the corresponding fractographs, optical micrographs, and electron micrographs have been examined. It is found that accelerating cooling rate during in-service welding has an improving effect on the microstructure of CGHAZs. Owing to small heat-input and accelerating cooling, the grain size in reheated CGHAZs is relatively small and the brittle microphases are eliminated or minimized. The Charpy impact results show that the CGHAZ fracture energy is improved after the second thermal cycle. The SC CGHAZ showed higher absorbed impact energy and the IR CGHAZ had less absorbed energy, but the phenomenon of embrittlement in IR CGHAZ is not serious. Therefore, it can be concluded that the fracture energy of CGHAZ and IR CGHAZ can be improved by accelerating cooling with appropriate cooling rate.     

Precipitation,microstructure and mechanical properties of low nickel maraging steel

Abstract

A maraging steel with a composition of Fe–12·94Ni–1·61Al–1·01Mo–0·23Nb (wt-%) was investigated. Optical, scanning electron and transmission electron microscopy and X-ray diffraction analysis were employed to study the microstructure of the steel after different aging periods at temperatures of 450–600°C. Hardness and Charpy impact toughness of the steel were measured. The study of microstructure and mechanical properties showed that nanosized precipitates were formed homogeneously during the aging process, which resulted in high hardness. As the aging time is prolonged, precipitates grow and hardness increases. Fractography of the as forged steel has shown mixed ductile and brittle fracture and has indicated that the steel has good toughness. Relationships among heat treatment, microstructure and mechanical properties are discussed. Further experiments using tensile testing and impact testing for aged steel were carried out.     

Microstructural evolution of tool steels after Nd-YAG laser repair welding

The present paper is aimed at investigating the microstructural behaviour of tool steels after repair welding or refurbishing by a pulsed Nd-YAG precision laser. The 1.2311 (40CrMnMo7), 1.2083 (X42Cr13) and 1.2343 (X38CrMoV5-1) steels were selected for experimental investigations to cover a wide range of steel grades, commonly used in tooling industry.Laser repair welding condition was simulated by preparing small deposits in one or more passes on steel samples having several reference geometries. Investigations on microstructural properties, microhardness evolution and on defect formation were carried out. The effects of different laser welding parameters were also considered.The study allowed to state several fundamental information on tool behaviour during repair welding in order to gain a deeper insight into this process, routinely considered in industrial practice but often neglected in scientific research works on welding metallurgy.     

Joining of CP-Ti to 304 stainless steel using friction stir welding technique

Friction stir welding parameters were adjusted in order to achieve defect-free dissimilar lap joint of CP-Ti to 304 stainless steel. Titanium as a softer material was selected to be on the lap top side. The joint stir zone was found to be consisted of two main regions; the dominant fine dynamically re-crystallized titanium grains at the upper region and a minor composite-type microstructure of fragments of 304 stainless steel in a matrix of fine dynamically re-crystallized titanium grains in the lower region. The stir zone was separated from the 304 stainless steel side by an interface layer of TiFe-based crystal structure. Joint shear strength was measured; a maximum failure load of ∼73% of that of CP-Ti was achieved. This was associated with the occurrence of fracture at the joint intermetallic-based interface. The failure load value of the fabricated joints is related to the thickness of the intermetallic interface.     

X70大变形管环焊接头及断裂机制研究

目的基于应变设计大变形管线环焊接头热影响区的软化问题,解决制约管线安装质量和服役寿命等难题。方法通过显微硬度测试、微观组织分析,研究了X70大变形管接头热影响区的软化原因,并利用数字相关法研究了焊接接头拉伸过程中的断裂机制,还对焊接接头热影响区进行了激光增强探索。结果 X70焊接接头热影响区粗晶区的最大硬度损失达HV0.239;软化区最大应变达到37%以上;经过热影响区激光重熔后,X70钢焊接接头抗拉强度可提高10%以上,断裂位置均位于母材。结论 X70焊接接头热影响区粗晶区存在明显的软化;拉伸过程中在软化区出现了明显的应变集中,是X70焊接接头断裂于近缝区的主要原因;焊接接头热影响区粗晶区粗大的粒状贝氏体和铁素体导致了焊接接头热影响区的软化。     

Characteristics of the reverse dual-rotation friction stir welding conducted on 2219-T6 aluminum alloy

Reverse dual-rotation friction stir welding (RDR-FSW) has great potential to obtain appropriate welding conditions through adjusting the independently rotating tool pin and surrounding shoulder. The welding torque exerted on the workpiece by the reversely rotating shoulder also cancels off a part of the welding torque exerted by the rotating tool pin, thus the clamping requirement for the workpiece is also reduced. In the present paper, a tool system for the RDR-FSW was designed and successfully applied to weld high strength aluminum alloy 2219-T6, and then microstructures and mechanical properties of the optimized joint were investigated to demonstrate the RDR-FSW characteristics. The weld nugget zone was characterized by the homogeneity of refined grain structures, but there was a three-phase confluction on the advancing side formed by different grain structures from three different zones. The tensile strength of the optimized joint was 328 MPa (73.7% of the base material), showing an obvious improvement when compared with the optimized joint welded by the FSW without the reversely rotating assisted shoulder. The tensile fracture occurred in the ductile fracture mode and the fracture path propagated in the weakest region where the Vickers hardness is the minimum.     

Q&P980镀锌高强钢电阻点焊工艺及液态金属脆化裂纹分布EI北大核心

通过设计电阻点焊工艺的正交实验,确定了Q&P980镀锌高强钢的点焊工艺参数范围,并对其焊接接头进行显微组织表征和力学性能分析。结果表明:熔核区组织以交错分布的板条马氏体为主;热影响区组织由板条马氏体、残余奥氏体和铁素体组成,马氏体板条平均宽度在不完全淬火区最大为4.86μm。显微硬度测试发现,焊接接头硬度值呈“W”形对称分布,硬度峰值出现在细晶区,达到559HV,硬度最低值出现在不完全淬火区,为338HV,呈现明显的软化现象。对焊接接头进行室温拉伸,最大拉剪载荷的峰值为27.92 kN,其断口形貌呈现典型的韧窝状,属于韧性断裂。由于Zn的熔点较钢基体低,镀锌高强钢点焊时易发生Zn层优先熔化并沿晶界向基体渗透,在焊接接头处可观察到明显的液态金属脆化裂纹。     

焊接参数对铁素体不锈钢搅拌摩擦焊接头组织及性能的影响

对4mm厚T4003铁素体不锈钢进行搅拌摩擦焊接工艺实验,研究焊接参数对接头组织特征、硬度分布及常温和低温冲击韧性的影响。结果表明:接头搅拌区和热力影响区由铁素体和马氏体双相组织构成;接头搅拌区组织沿试样厚度方向存在非均质性,且随转速的降低及焊接速率的增加越发显著;转速从150r/min增加至250r/min,前进侧热力影响区组织呈现小梯度过渡趋势,无明显变形拉长特征。焊缝硬度分布相对均匀,其最高硬度为290HV,约为母材的1.87倍。焊接参数和温度对接头的冲击吸收功有较大影响:常温(20℃)下,热影响区为母材的90%～92%,搅拌区为母材的85%～103%;低温(-20℃)下,热影响区为母材的87%～97%,搅拌区为母材的82%～95%,表明焊缝区仍具有较好强韧匹配。     

Influences of flux-cored arc welding consumables on dynamic fracture toughness (J1d) of armour grade Q&T steel joints

Quenched and tempered (Q&T) steels are prone to hydrogen-induced cracking in the HAZ after welding. Austenitic stainless steel (ASS) welding consumables are traditionally used for welding of high hardness Q&T steels as they have higher solubility for hydrogen. The use of stainless steel consumables for a non-stainless steel base metal is not economical. In recent years, the developments of low hydrogen ferritic steel (LHF) consumables that contain no hygroscopic compounds are utilized for welding of Q&T steels The use of ASS and LHF consumables for armour grade Q&T steel will lead to formation of distinct microstructures in their respective welds. This microstructural heterogeneity will have a drastic influence in the dynamic fracture toughness of the armour grade Q&T steel welds. Hence, an attempt was made in this paper to study the influence of flux-cored arc welding consumables on dynamic fracture toughness ( J _1d) of armour grade Q&T steel joints. The flux-cored arc welding consumables have a significant effect on the dynamic fracture toughness of the armour grade Q&T steel welds. The joints fabricated using ASS flux-cored wires showed superior J _1d values than the joints fabricated using LHF consumables and the base metal.