X70管线钢焊接接头组织及其海水腐蚀规律

对X70管线钢现场实际焊接工艺下的焊接接头,采用显微镜、电化学方法及失重法等方法和手段对母材、焊缝、热影响区进行了显微组织分析和在海水中的极化曲线、腐蚀速率的测试,研究焊接接头在模拟海水环境中的腐蚀性能。研究表明,X70管线钢焊接接头各区域组织不均匀,实验室模拟海水环境下的电化学行为、腐蚀速率存在明显差异;在海水腐蚀过程中腐蚀电位和腐蚀速率会发生变化,热影响区（HAZ）与母材及焊缝形成电偶腐蚀,接头腐蚀以点蚀为主。     

X80管线钢焊接接头重构及其在NACE溶液中的腐蚀行为

借助模块化的阵列电极制备技术对X80管线钢焊接接头进行模拟重构,并采用经典电化学测试技术与微电极阵列测试技术研究X80钢模拟焊接接头在CO_2饱和的NACE溶液中的腐蚀行为。结果表明,孤立的母材区开路电位最正,热影响区次之,焊缝金属的开路电位最负;腐蚀电流密度表现为焊缝母材热影响区;在NACE溶液的浸泡过程中,焊缝区始终作为腐蚀电偶对的的主阳极,腐蚀加速;热影响区始终作为主阴极,腐蚀减缓,母材微电极随着与焊缝区距离不同,其电流极性不一、交替出现。在本文实验条件下,焊缝区是X80钢模拟焊接接头的薄弱环节。     

双相不锈钢与微合金钢异金属焊接接头的组织及性能

采用ER2209焊丝对双相不锈钢SAF2205与微合金管线钢X65进行熔化极气体保护焊接,获得了具有良好力学性能的异种钢焊接接头.焊接接头不同区域显微组织观察和成分分析表明,微合金钢与不锈钢焊缝间存在异金属熔合区和第二类边界线,熔合区存在Ni、Cr的浓度梯度分布,且硬度高于两侧的焊缝和母材.通过宏观拉伸、缺口拉伸和低温冲击实验测试了焊接接头的力学性能,并获得了接头不同部位在1mol.L-1NaCl溶液中的极化曲线.拉伸试样断裂发生于强度相对较低的微合金钢母材.焊缝金属的缺口拉伸强度和冲击韧性均略低于双相不锈钢母材,但腐蚀电位略高于母材.微合金钢热影响区与母材力学性能相当,腐蚀电位略高于母材.     

带堆焊层钢管焊接接头耐蚀性的电化学评定

采用电化学测试技术评价了低碳钢管管端内壁不锈钢焊条堆焊后再用相同焊条进行打底焊所得焊接接头（特别是焊接热影响区）的耐蚀性，选用两种高合金焊条M2、M6，并对堆焊金属进行热模拟试验，测定了模拟热影响区不同部位在3％NaCl介质中的阳极极化行为．结果表明，按新工艺焊接的接头代替普通碳钢焊接接头可有效地提高管道接头的使用寿命．两种焊条中，含Nb的M2耐蚀性比M6好，铌能够有效提高接头的耐均匀腐蚀、晶间腐蚀和点蚀能力，热影响区600～1000℃是高合金接头耐蚀性最薄弱的区域，建议采用超低碳含铌高合金焊条，以解决热影响区的腐蚀问题．     

2507双相不锈钢在SO2污染模拟海水中的腐蚀行为

采用开路电位、电化学阻抗谱(EIS)、Mott-Schottky曲线和浸泡腐蚀实验研究了2507双相不锈钢在含不同浓度(0,0.001和0.01 mol·L-1)NaHSO3模拟海水中的腐蚀行为.研究表明:开路电位随NaHSO3浓度的增加而负移,腐蚀倾向增大;电荷转移电阻Rt随浓度的增加而减小,耐蚀性降低;2507不锈钢的腐蚀形态为局部腐蚀,点蚀程度随浓度升高有所加剧,腐蚀速率随浓度的增加而增大;Mott-Schottky曲线和成膜后电化学阻抗谱测试表明,NaHSO3的加入增加了2507不锈钢表面钝化膜的点缺陷浓度,降低了钝化膜的稳定性,电荷转移阻力减小,腐蚀更容易发生.这可能归因于NaHSO3的加入增加了模拟海水的酸度,并随NaHSO3浓度的增加促进了不锈钢表面钝化膜的破坏.     

A710高强耐候钢焊接接头耐蚀性分析

通过干、湿交替周期浸润试验和浸泡试验,结合腐蚀形貌观察和电化学测试,对A710高强耐候钢母材和焊接接头在模拟海洋大气环境(3.5%NaCl溶液)中的耐蚀性能差异进行了研究。结果表明,A710钢焊接接头不同区域的显微组织存在明显差异,即母材主要为铁素体,热影响区主要由铁素体和贝氏体组成,还有大量M-A岛,焊缝区则主要为贝氏体及少量针状铁素体,这种组织的不均匀性使得A710钢的焊接接头区域在3.5%NaCl溶液中形成了众多微电偶腐蚀电池,而多个微电偶腐蚀电池耦合会导致焊接接头发生宏观电偶腐蚀,焊缝和热影响区为阳极,母材为阴极;电偶腐蚀的存在则导致A710钢焊接接头在模拟海洋大气环境中的平均腐蚀速率高于母材。     

409L铁素体不锈钢热轧板材焊接接头的电化学腐蚀行为

采用电子探针(EPMA)和金相显微镜对409L铁素体不锈钢热轧板材焊接接头的3个区域(母材区(BM)、热影响区(HAZ)和焊缝区(WM))的成分和组织进行分析,并且运用电化学的方法测试其3个区域在10％ H2SO4溶液中的极化曲线特征参数,并对其进行室温(25℃)、24 h的浸泡腐蚀试验.结果表明:409L铁素体不锈钢...     

不同种不锈钢电化学腐蚀性能的对比

采用CHI660D电化学工作站研究304、316L、2205、2507不锈钢在模拟塔里木油田复杂腐蚀介质中的电化学腐蚀性能,并通过扫描电子显微镜(SEM)对其表面的腐蚀产物膜进行对比分析.结果表明:2种复杂腐蚀介质条件下,随温度升高,4种不锈钢的耐蚀性和抗点蚀能力都会降低.CO2的通入对不锈钢的腐蚀过程影响较为复杂.20℃时,4种不锈钢的耐蚀性和抗点蚀能力随CO2的加入均降低;而50、80℃时,4种不锈钢的耐蚀性和抗点蚀能力则会增强.相同腐蚀条件下,4种不锈钢的耐腐蚀能力由强到弱的顺序为:2507、2205、316L、304.     

AF1410钢电子束焊接件在模拟海洋环境中的腐蚀行为

采用中性盐雾试验模拟海洋环境,研究了AF1410钢电子束焊接接头不同位置、不同暴露时间的腐蚀电化学阻抗谱特征,并结合电子束焊接接头组织结构分析评价了焊缝熔合区及母材的耐腐蚀性能及电化学行为.开路电位及阻抗谱研究表明,焊缝熔合区的粗大回火马氏体和析出碳化物易构成腐蚀电池,比基材腐蚀反应阻力小,易引起电化学腐蚀.建立了不同腐蚀阶段的阻抗谱等效电路,并对其进行了拟合.     

AF1410钢电子束焊接件在模拟海洋环境中的腐蚀行为

采用中性盐雾试验模拟海洋环境,研究了 AF1410钢电子束焊接接头不同位置、不同暴露时间的腐蚀电化学阻抗谱特征,并结合电子束焊接接头组织结构分析评价了焊缝熔合区及母材的耐腐蚀性能及电化学行为。开路电位及阻抗谱研究表明,焊缝熔合区的粗大回火马氏体和析出碳化物易构成腐蚀电池,比基材腐蚀反应阻力小,易引起电化学腐蚀。建立了不同腐蚀阶段的阻抗谱等效电路,并对其进行了拟合。     

3Cr低合金管线钢及焊接接头的CO_2腐蚀行为

采用高温、高压反应釜和电化学技术对3Cr低合金管线钢及焊接接头的CO2腐蚀行为进行研究.结果表明,3Cr低合金管线钢在高温、高压CO2腐蚀环境中表面生成致密的富Cr腐蚀产物膜,这是其抗CO2腐蚀性能优于X65钢的主要原因.3Cr低合金管线钢焊接接头中母材、热影响区和焊缝的腐蚀产物膜特征相似,结构致密,均存在Cr元素的富集.与X65钢相比,3Cr低合金管线钢的自腐蚀电位较正,自腐蚀电流密度较低.在CO2腐蚀介质中,3Cr低合金管线钢焊接接头的母材区域作为阳极首先发生腐蚀,焊缝和热影响区作为阴极受到保护.     

Characterizations of dissimilar S32205/316L welds using austenitic,super-austenitic and super-duplex filler metals

UNS S32205 duplex stainless steel plates were welded to AISI 316L stainless steel using the pulsed gas tungsten arc welding process with three different filler metals: ER2594, ER312, and ER385. The microstructures of the welds were characterized using optical and scanning electron microscopy, and all of the specimens were evaluated by ferrite measurements. The mechanical properties were studied through hardness, tensile, and impact tests. In addition, the pitting resistance equivalent number was calculated and cyclic polarization tests were performed to evaluate the corrosion resistance of the weld metal. The results showed that chromium nitride was formed in the heat-affected zone of the duplex side, whereas no sigma phase was detected in any of the specimens. The ferrite number increased from the root pass to the final pass. The absorbed energies of the impact test decreased with increasing ferrite number, whereas the tensile strength was enhanced. The fully austenitic microstructure of the specimen welded with ER385 exhibited the highest resistance to pitting corrosion at 25°C, and the super-duplex weld metal presented superior corrosion resistance at 50°C.     

AISI316L奥氏体不锈钢在摸拟人体组织液中腐蚀疲劳裂纹萌生的初步研究

AISI316L奥氏体不锈钢是较常用的金属植入材料之一.但在临床应用中,由它制成的植入物特别是全髋关节,常因腐蚀疲劳破断而失效.本文对316L不锈钢在Hank’s溶液中的腐蚀疲劳裂纹萌生机理进行了初步研究.结果发现,在Hank’s溶液中,自然钝化的316L不锈钢在稳定钝化态下,裂纹的萌生是由交变应力引起的微观塑性变形和Hank’s溶液交互作用的结果;在有点蚀产生的非钝化态下,裂纹的萌生是点蚀和腐蚀疲劳相叠加的结果.316L不锈钢经离子氮化表面处理后,提高了在Hank’s溶液中的抗点蚀能力,但在外加腐蚀电位的苛刻条件下,困氮化层发生晶间腐蚀和脱落而加速了裂纹的萌生     

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 energy-dispersive spectroscopy (EDS); the mechanical properties were measured by microhardness test, tensile test, and impact test; the corrosion 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 welding. The corrosion current density of TIG weld metal is higher than that of MIG weld metal in a 3.5wt% NaCl 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 produced 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 S31803 duplex stainless steel and low alloy steel in practical application.     

Acoustic emission detection of 316L stainless steel welded joints during intergranular corrosion

This study analyzes acoustic emission (AE) signals during the intergranular corrosion (IGC) process of 316L stainless steel welded joints under different welding currents in boiling nitric acid. IGC generates several AE signals with high AE activity. The AE technique could hardly distinguish IGC in stainless steel welded joints with different welding heat inputs. However, AE signals can effectively distinguish IGC characteristics in different corrosion stages. The IGC resistance of a heat-affected zone is lower than that of a weld zone. The initiation and rapid corrosion stages can be distinguished using AE results and microstructural analysis. Moreover, energy count rate and amplitude are considered to be ideal parameters for characterizing different IGC processes. Two types of signals are detected in the rapid corrosion stage. It can be concluded that grain boundary corrosion and grain separation are the AE sources of type 1 and type 2, respectively.     

Pitting corrosion and crevice corrosion behaviors of high nitrogen austenitic stainless steels

Pitting corrosion and crevice corrosion behaviors of high nitrogen austenitic stainless steels (HNSS) were investigated by electrochemical and immersion testing methods in chloride solution, respectively. The chemical constitution and composition in the depth of passive films formed on HNSS were analyzed by X-ray photoelectron spectrum (XPS). HNSS has excellent pitting and crevice corrosion resistance compared to 316L stainless steel. With increasing the nitrogen content in steels, pitting potentials and critical pitting temperature (CPT) increase, and the maximum, average pit depths and average weight loss decrease. The CPT of HNSS is correlated with the alloying element content through the measure of alloying for resistance to corrosion (MARC). The MARC can be expressed as an equation of CPT=2.55MARC-29. XPS results show that HNSS exhibiting excellent corrosion resistance is attributed to the enrichment of nitrogen on the surface of passive films, which forms ammonium ions increasing the local pH value and facilitating repassivation, and the synergistic effects of molybdenum and nitrogen.     

Corrosion behavior of ferritic stainless steel with 15wt% chromium for the automobile exhaust system

The effect of chloride ion concentration, pH value, and grain size on the pitting corrosion resistance of a new ferritic stainless steel with 15wt% Cr was investigated using the anodic polarization method. The semiconducting properties of passive films with different chloride ion concentrations were performed using capacitance measurement and Mott-Schottky analysis methods. The aging precipitation and intergranular corrosion behavior were evaluated at 400–900℃. It is found that the pitting potential decreases when the grain size increases. With the increase in chloride ion concentration, the doping density and the flat-bland potential increase but the thickness of the space charge layer decreases. The pitting corrosion resistance increases rapidly with the decrease in pH value. Precipitants is identified as Nb(C,N) and NbC, rather than Cr-carbide. The intergranular corrosion is attributed to the synergistic effects of Nb(C,N) and NbC precipitates and Cr segregation adjacent to the precipitates.     

X80管线钢在近中性pH溶液中的应力腐蚀开裂

采用电化学动电位扫描技术、慢应变速率拉伸(SSRT)试验和扫描电镜观察研究了X80管线钢及焊接接头在NS4溶液中的应力腐蚀行为.电化学实验结果显示,X80管线钢及焊接接头在NS4溶液中的极化曲线具有典型的活性溶解特征.SSRT试验结果表明,随着外加电位的负移,断裂时间、断面收缩率、应变量都明显变小,X80管线钢及焊接接头的应力腐蚀开裂敏感性增加,应力腐蚀断口呈现穿晶准解理特征.施加相同外加电位时,焊接接头较母材的应力腐蚀敏感性增加,其断裂位置全部落在焊缝或HAZ处.     

Microstructures and mechanical properties of dissimilar Nd:YAG laser weldments of AISI4340 and AISI316L steels

This paper presents studies on the microstructure and mechanical properties of AISI 316L stainless steel and AISI 4340 low-alloy steel joints formed by the Nd:YAG laser welding process. The weld microstructures and heat affected zones (HAZs) were investigated. Austenitic microstructures were observed in all of the samples. The sizes of the HAZs changed when the heat input was varied, and the 316L sides exhibited a larger HAZ. The cooling rates were calculated by measuring the solidification dendrite arm spacing. It is shown that high cooling rates lead to an austenitic microstructure. Tensile tests were carried out, and the results revealed the tensile properties of both the base metals and the weldments. The hardness test results agreed well with the tensile test results.