Interactive effect of thermal aging and proton irradiation on microstructural evolution and hardening ofδ-ferrite in 308L stainless steel weld metal

In the harsh service environment of high temperature and intense neutron irradiation in water-cooled nuclear reactors,the austenitic stainless steel weld overlay cladding on the inner surface of the reactor pressure vessel suffers from thermal aging and irradiation damage simultaneously,which can induce microstructural evolution and hardening of the material.Since it is quite difficult to achieve this simul-taneous process out of the pile,two kinds of combined experiments,i.e.,post-irradiation thermal aging and post-aging irradiation were performed on 308 L stainless steel weld metals in this work.The interactive effect of thermal aging and proton irradiation on microstructural evolution and hardening ofδ-ferrite in 308 L weld metal was investigated by combining atom probe tomography,transmission elec-tron microscopy and nanoindentation tests.The results revealed that thermal aging could eliminate the dislocation loops induced by irradiation and affect the phase transition process by accelerating spinodal decomposition and G-phase precipitation,thus enhancing hardening of irradiatedδ-ferrite.For the effect of irradiation on the microstructure and hardening of thermally agedδ-ferrite,however,intensive collision cascades can intensify G-phase precipitation and dislocation loop formation but decrease spinodal decomposition,leading to a limited effect on hardening of thermally agedδ-ferrite.Furthermore,the interaction of thermal aging and irradiation can promote G-phase precipitation.Meanwhile,the interaction can causeδ-ferrite hardening,which is mainly influenced by spinodal decomposition,followed by G-phase and dislocation loops,where spinodal decomposition and G-phase cause hardening by inducing strain fields.

Effects of Aging at 550℃ on α'-Martensitic Transformation of High Si-Bearing Metastable Austenitic Stainless Steel Weld Metal

The high Si-bearing 15Cr-9Ni-Nb metastable austenitic stainless steel weld metal was prepared via gas tungsten arc welding and then processed by stabilized heat treatment(SHT)at 850℃ for 3 h.The effects of 550℃ aging on the α'-martensitic transformation of the as-welded and the SHT weld metals were investigated.The results showed that the weld metal had poor thermal stability of austenite.The precipitation of NbC during the 850℃ SHT made the thermal stability of the local matrix decrease and led to the formation of a large amount of C-depleted α'-martensite.The precipitation of coarse σ-phase at the δ-ferrite led to the Cr-depleted zone and the formation of Cr-depleted α'-martensite at the early stage of 550℃ aging.The homogenized diffusion of C and Cr in the matrix during 550℃ aging led to the restoration of austenitic thermal stability and the decrease of α'-martensite content.The C-depleted α'-martensite content in the SHT weld metal decreased rapidly at the early stage of aging due to the fast diffusion rate of the C atom in the matrix,while the Cr-depleted α'-martensite decreased at the later stage of aging due to the decreased diffusion rate of the Cr.

Deformation and cracking behaviors of proton-irradiated 308L stainless steel weld metal strained in simulated PWR primary water

The proton-irradiated 308L stainless steel weld metal was strained by using constant extension rate tensile testing in simulated PWR primary water, and its deformation microstructures and irradiation assisted stress corrosion cracking(IASCC) behavior were investigated. The results suggest that the irradiation significantly increases the SCC susceptibility of 308L weld metal and causes various deformation microstructures including lathy faulted planes, dislocation channels and deformation twins in austenite and atomic plane rotation in δ-ferrite. The propagation of intergranular IASCC cracks is closely related to the location of the crack tip. For the crack tip in the specimen matrix interior, localized deformation is likely the key factor responsible for the crack growth. For the crack tip close to the specimen surface, however, localized corrosion along the grain boundary rather than the localized deformation appears to dominate the crack propagation. Unlike the intergranular cracks, the IASCC cracks along the δ-ferrite/austenite phase boundary can initiate either by crack initiation at the phase boundary or by crack propagation from the grain boundary. In both cases, the cracked phase boundaries contain a large number of carbides and are severely corroded, but no deformation microstructures are observed, which implies that the localized corrosion may play an important role in the IASCC along the phase boundary. In addition, δ-ferrite can retard the IASCC crack propagation along the grain boundary, which is probably related to the reduction of localized deformation by δ-ferrite.

Effect of thermal ageing and dissolved gas on corrosion of 308L stainless steel weld metal in simulated PWR primary water

The corrosion of unaged and 7000-h thermally aged 308 L stainless steel weld metals in simulated PWR primary water under aerated and deaerated conditions was investigated,involving the corrosion of austenite,δ-ferrite andδ-ferrite/austenite phase boundary.The results revealed that thermal ageing for 7000 h had a limited effect on the corrosion behavior of 308 L weld metal as it only increased the inner oxide thickness ofδ-ferrite slightly under the deaerated condition.No obvious corrosion enhancement of 308 L weld metal under the aerated condition was found compared to the deaerated condition regardless of the thermal ageing.Nevertheless,Cr-enrichment on the surface of oxide particles,dissolved regions at the metal/oxide interface and localized corrosion along theδ-ferrite/austenite phase boundary occurred under the aerated condition.

Tensile and Impact Properties of Shielded Metal Arc Welded AISI 409M Ferritic Stainless Steel Joints

The present study is concerned with the effect of filler metals such as austenitic stainless steel, ferritic stainless steel and duplex stainless steel on tensile and impact properties of the ferritic stainless steel conforming to AISI 409M grade. Rolled plates of 4 mm thickness were used as the base material for preparing single pass butt welded joints. Tensile and impact properties, microhardness, microstructure and fracture surface morphology of the joints fabricated by austenitic stainless steel, ferritic stainless steel and duplex stainless steel filler metals were evaluated and the results were reported. From this investigation, it is found that the joints fabricated by duplex stainless steel filler metal showed higher tensile strength and hardness compared to the joints fabricated by austenitic and ferritic stainless steel filler metals. Joints fabricated by austenitic stainless steel filler metal exhibited higher ductility and impact toughness compared with the joints fabricated by ferritic stainless steel and duplex stainless steel filler metals.

Microstructure and pitting corrosion of shielded metal arc welded high nitrogen stainless steel

The present work is aimed at studying the microstructure and pitting corrosion behaviour of shielded metal arc welded high nitrogen steel made of Cromang-N electrode. Basis for selecting this electrode is to increase the solubility of nitrogen in weld metal due to high chromium and manganese content. Microscopic studies were carried out using optical microscopy(OM) and field emission scanning electron microscopy(FESEM). Energy back scattered diffraction(EBSD) method was used to determine the phase analysis, grain size and orientation image mapping. Potentio-dynamic polarization testing was carried out to study the pitting corrosion resistance in aerated 3.5% NaCl environment using a GillAC electrochemical system. The investigation results showed that the selected Cr-Mn-N type electrode resulted in a maximum reduction in delta-ferrite and improvement in pitting corrosion resistance of the weld zone was attributed to the coarse austenite grains owing to the reduction in active sites of the austenite/delta ferrite interface and the decrease in galvanic interaction between austenite and delta-ferrite.

EFFECT OF TRANSITION METAL Ni ON WELDING PROPERTIES OF TITANIUM ALLOY STAINLESS STEEL

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Gas metal arc welding of duplex stainless clad steel plates

The 2205 duplex stainless ＋ DH36 clad steel plate was welded by gas metal arc welding（GMAW）, and the welding performance of the clad steel plate was investigated. The results show that the adaptability of the welding procedure for the base metal of carbon steel, the transition layer, and the cladding material is excellent. The test results indicate that the phase proportion and component dilution of the GMAW-welded joints of clad steel plate can be effectively controlled to yield joints with good mechanical properties and corrosion resistance.

Effect of welding process on the microstructure and properties of dissimilar weld joints between low alloy steel and duplex stainless steel

To obtain high-quality dissimilar weld joints, the processes of metal inert gas （MIG） welding and tungsten inert gas （TIG） welding for duplex stainless steel （DSS） and low alloy steel were compared in this paper. The microstructure and corrosion morphology of dissimilar weld joints were observed by scanning electron microscopy （SEM）; the chemical compositions in different zones were detected by en- ergy-dispersive spectroscopy （EDS）; the mechanical properties were measured by microhardness test, tensile test, and impact test; the corro- sion behavior was evaluated by polarization curves. Obvious concentration gradients of Ni and Cr exist between the fusion boundary and the type II boundary, where the hardness is much higher. The impact toughness of weld metal by MIG welding is higher than that by TIG weld- ing. The corrosion current density of TIG weld metal is higher than that of MIG weld metal in a 3.5wt% NaC1 solution. Galvanic corrosion happens between low alloy steel and weld metal, revealing the weakness of low alloy steel in industrial service. The quality of joints pro- duced by MIG welding is better than that by TIG welding in mechanical performance and corrosion resistance. MIG welding with the filler metal ER2009 is the suitable welding process for dissimilar metals jointing between UNS $31803 duplex stainless steel and low alloy steel in practical application.

Welding of nickel free high nitrogen stainless steel: Microstructure and mechanical properties

High nitrogen stainless steel(HNS) is a nickel free austenitic stainless steel that is used as a structural component in defence applications for manufacturing battle tanks as a replacement of the existing armour grade steel owing to its low cost, excellent mechanical properties and better corrosion resistance.Conventional fusion welding causes problems like nitrogen desorption, solidification cracking in weld zone, liquation cracking in heat affected zone, nitrogen induced porosity and poor mechanical properties.The above problems can be overcome by proper selection and procedure of joining process. In the present work, an attempt has been made to correlate the microstructural changes with mechanical properties of fusion and solid state welds of high nitrogen steel. Shielded metal arc welding(SMAW), gas tungsten arc welding(GTAW), electron beam welding(EBW) and friction stir welding(FSW) processes were used in the present work. Optical microscopy, scanning electron microscopy and electron backscatter diffraction were used to characterize microstructural changes. Hardness, tensile and bend tests were performed to evaluate the mechanical properties of welds. The results of the present investigation established that fully austenitic dendritic structure was found in welds of SMAW. Reverted austenite pools in the martensite matrix in weld zone and unmixed zones near the fusion boundary were observed in GTA welds. Discontinuous ferrite network in austenite matrix was observed in electron beam welds.Fine recrystallized austenite grain structure was observed in the nugget zone of friction stir welds.Improved mechanical properties are obtained in friction stir welds when compared to fusion welds. This is attributed to the refined microstructure consisting of equiaxed and homogenous austenite grains.

Arc characteristics of submerged arc welding with stainless steel wire

The arc characteristics of submerged arc welding （SAW） with stainless steel wire were studied by using Analysator Hannover （AH）. The tests were carded out under the same preset arc voltage combined with different welding currents. By comparing the probability density distribution （PDD） curves of arc voltage and welding current, the changes were analyzed, the metal transfer mode in SAW was deduced, and the characteristics of a stable arc were summarized. The analysis results show that, with an increase of welding parameters, the short-circuiting peak in the PDD curves of arc voltage decreases gradually until it disappears, and the dominant metal transfer mode changes from flux-wall guided transfer to projected transfer and then to streaming transfer. Moreover, when the PDD curves of arc voltage are both unimodal and generally symmetrical, the greater the peak probability and the smaller the peak span, the more stable the arc becomes.

A PROBABILISTIC ASSESSMENT OF TEMPERATURE EFFECTSON THE LOW CYCLE FATIGUE BEHAVIOUR OF 1Cr_(18)Ni_9Ti STEEL WELD METAL

Based on the test results obtained from the single-step test and the incremental-step test at room temperature and 240℃, a probabilistic assessment of temperature effects on the cyclic stress-strum response and the fatigue life of 1Cr18Ni9Ti steel weld metal is performed. In orber to assess the temperature effect on cyclic stress amplitude where there is a scatter of the material cyclic constitution, a probabilistic assessment approach on the basis of probabilistic modified Ramberg-Osgood relations is introduced.The investigation shows that the cyclic stress amplitude and the scatter of cyclic stress amplitude data are decreased at 240℃. Similarly, from the consideration of the fatigue life scatter a probabilistic assessment of temperature effect on the fatigue life is suggested on the basis of probabilistic Langer S-N relations. The investigation shows that the crack initiation life is increased and the scatter of crack initiation life data is decreased at 240℃.

The effect of solidification behaviour of austenitic stainless steel on the solidification cracking susceptibility

On the basis of quantitative evaluation of susceptibility to solidification cracking with Trans-Varestraint-Test, the microstructures of two stainless steels of 316L and alloy 800H with different Creq/Nieq ratios during solidification process were analyzed with several methods. It is concluded that the susceptibility to solidification cracking of 316L-stainless steel is much lower than that of alloy 800H due to different solidification behaviors of the weld metal of the two materials. The weld metal of alloy 800H solidifies in the form of primary austenite whose boundaries are straight and smooth and easily wetted by low melting-point liquid phases, which increases the susceptibility to solidification cracking; while the 316L weld metal solidifies into primary austenite/ferrite. Owing to a series of dynamic microstructure changes during solidification such as peritectic reactions, migration of austenitic boundaries and nailing of δ-ferrite to the boundaries, the grains become finer, the orientations of columnar grains get disordered and the boundaries are curved and complex. Also high temperature δ-ferrite exists, segregation of impurities at boundaries decreases and the boundaries are hard to be wetted by liquid films, which reduces the cracking susceptibility.

Effect of welding processes and consumables on fatigue crack growth behaviour of armour grade quenched and tempered steel joints

Quenched and Tempered(Q&T) steels are widely used in the construction of military vehicles due to its high strength to weight ratio and high hardness. These steels are prone to hydrogen induced cracking(HIC) in the heat affected zone(HAZ) after welding. The use of austenitic stainless steel(ASS) consumables to weld the above steel was the only available remedy because of higher solubility for hydrogen in austenitic phase. The use of stainless steel consumables for a non-stainless steel base metal is not economical. Hence, alternate consumables for welding Q&T steels and their vulnerability to HIC need to be explored. Recent studies proved that low hydrogen ferritic steel(LHF) consumables can be used to weld Q&T steels, which can give very low hydrogen levels in the weld deposits. The use of ASS and LHF consumables will lead to distinct microstructures in their respective welds. This microstructural heterogeneity will have a drastic influence in the fatigue crack growth resistance of armour grade Q&T steel welds. Hence, in this investigation an attempt has been made to study the influence of welding consumables and welding processes on fatigue crack growth behaviour of armour grade Q&T Steel joints. Shielded metal arc welding(SMAW) and Flux cored arc welding(FCAW) were used for fabrication of joints using ASS and LHF consumables. The joints fabricated by SMAW process using LHF consumable exhibited superior fatigue crack growth resistance than all other joints.

EVALUATION OF CREEP PROPERTIES FOR 316FR STEEL THICK PLATE WELDMENT USING MINIATURE CREEP SPECIMEN

Evaluation of creep properties of the welded joint through taking local fluctuation of the mechanical properties into consideration is experimentally or analytically seldom carried out. The purposes of the present study are to examine the surface strain distribution in the weld metal of a full thickness welded joint specimen and subsequently to investigate the local variation in the properties of the all-weld metal part of the joint using miniature specimens. A welded joint was prepared for 316FR steel plates by gas tungsten arc welding process using Mod. 316L filler wire. Creep tests were conducted at 823K in air using full thickness large welded joint specimens, HAZ and all-weld metal miniature specimens. From the results obtained, it is concluded that the creep properties of multi-layer welded joints strongly depend on the location of specimen sampling.

316H不锈钢母材与焊缝在模拟沿海大气中的高温腐蚀行为

采用高温腐蚀试验,研究了316H不锈钢母材与焊缝在520℃模拟沿海大气环境中长达3000 h的高温腐蚀行为。采用扫描电镜、能谱仪和X射线衍射仪对腐蚀产物形貌和成分进行了观察和分析,并探讨了其腐蚀机理。结果表明:焊缝与母材的腐蚀质量增加曲线均符合抛物线规律;高温腐蚀3000 h后,母材和焊缝试样的腐蚀均轻微,氧化层致密且无剥落,主要成分为(Cr,Fe)_(2)O_(3),其腐蚀速率分别为0.44,0.61μm/a,均小于0.001 mm/a,均属于完全耐蚀级别;焊缝试样的腐蚀速率略大于母材,原因是母材中的Cr与Mo含量较高。

19Cr-17 Ni-5Mn-4Mo奥氏体不锈钢焊缝金属超低温断裂韧性试验研究

为了解决托克马克核聚变装置D型线圈盒19Cr-17 Ni-5Mn-4Mo奥氏体不锈钢焊缝金属4.2 K超低温断裂韧性值偏低和不稳定的问题,通过使用不同的焊接线能量、焊道布置、道间温度和清洁度控制等条件下进行焊接试验,探索了这些焊接变数对焊缝金属超低温断裂韧性的影响规律;并采用金相分析、EBSD和断口电镜扫描等表征方法研究了微观组织与超低温断裂韧性内在关系,为优化焊接工艺提供了理论基础。研究结果表明:通过降低焊接线能量和层间温度来细化晶粒和减少析出相,及通过提高氩弧焊气保护质量、加强道间清理和优化焊道布置等措施来提高焊缝纯净度和均匀性等措施可以有效提高焊缝的低温断裂韧性。

铜与不锈钢焊接技术与工艺研究现状

铜与不锈钢的合金结构件广泛应用于石油化学、空调冷凝、航空航天和汽车零部件等中高端工业领域,存在着广阔地展现出极高的实用价值和应用潜力。由于铜与不锈钢物理化学性质差异较大,使得两者之间的焊接相当困难,文章通过分析铜与不锈钢的焊接性,综述了各种焊接方法及其原理,分析了各种焊接缺陷以及解决办法,并指出当前领域内的研究热点与难点。同时,文章还将展望铜与不锈钢异种金属焊接技术的未来发展趋势,以期推动该领域的持续进步。

不锈钢与钛合金电子束熔覆增材焊接工艺分析

不锈钢与钛合金的双金属结构已在化工、航天、航空等领域得到了广泛的应用。基于对异种金属构件焊接技术的研究,分析了异种金属焊接在熔点、膨胀系数、热导率、比热容等方面的性能特点。基于电子束异种金属的焊接工艺及特点,进一步讨论了不锈钢-钛合金电子束熔覆增材焊接技术。采用电子束熔覆增材焊接技术对不锈钢和钛合金进行焊接时,需要考虑过渡层的设置、焊接的强度与耐腐蚀性工艺、气体环境保护等重要的环节。

CMT焊接S32101双相不锈钢焊缝成形研究

研究了S32101双相不锈钢CMT焊接参数(焊接电流、送丝速度、焊接速度)对焊缝成形特性的影响,结果表明:熔宽随着送丝速度增大而增大,随着焊接速度和保护气体流量的增大而减小;熔深随着送丝速度的增大先减小后增大,随着焊接速度和保护气体流量的增大而减小;余高随着送丝速度增大而不断增大,随着焊接速度的增大而减小,随着保护气体流量的增大先增大后减少。这些研究结果对优化双相不锈钢的CMT焊接技术,促进海洋工程、核电设施等领域的发展具有十分重要的意义。