Intergranular corrosion susceptibility in supermartensitic stainless steel weldments

The intergranular corrosion susceptibility in supermartensitic stainless steel (SMSS) weldments was investigated by the double loop – electrochemical potentiokinetic reactivation (DL-EPR) technique through the degree of sensitization (DOS). The results showed that the DOS decreased from the base metal (BM) to the weld metal (WM). The heat affected zone (HAZ) presented lower levels of DOS, despite of its complex precipitation mechanism along the HAZ length. Chromium carbide precipitate redissolution is likely to occur due to the attained temperature at certain regions of the HAZ during the electron beam welding (EBW). Scanning electron microscopy (SEM) images showed preferential oxidation sites in the BM microstructure.     

SPV50Q钢焊接接头腐蚀和氢渗透性能分析

具有不同组织结构的焊接接头是腐蚀环境中服役焊接设备或管道的薄弱环节,这与焊接接头处发生的非均匀腐蚀密切相关.利用动电位极化、交流阻抗技术和氢渗透技术,研究了液化石油气（LPG,liquefied petroleum gas）球罐用SPV50Q钢焊接接头在含H2S溶液中的腐蚀和氢渗透特性.结果表明,具有不同组织结构的SPV50Q钢焊接接头各区金属（母材、热影响区和焊缝）,在含H2S溶液中的耐腐蚀性和氢渗透性能都具有一定的差异性,母材的耐蚀性最好,热影响区次之,焊缝金属的最差;对氢渗透性能而言,焊缝金属的氢扩散速度和扩散系数最大,热影响区的次之,母材的最小.     

核电汽轮机焊接转子接头在氯离子环境中的电偶腐蚀行为

为了研究焊接接头的尺寸效应对焊接接头的电偶腐蚀行为的影响,采用宏观电化学、微区电化学（SVET）、浸泡试验等试验研究了25Cr2Ni2MoV转子钢焊接接头在氯离子溶液中的电偶腐蚀行为.结果表明,焊缝的腐蚀电位最低,腐蚀电流密度最大,焊缝区作为阳极优先发生腐蚀,而母材和热影响区作为阴极区被保护.进一步运用三维形貌仪（IFM）和扫描电镜（SEM）观察腐蚀表面形貌,发现随着焊接接头尺寸的增加电偶腐蚀效应更显著,但是当接头尺寸增大到一定程度后,电偶腐蚀效应又有所减弱.     

Corrosion behavior of Ti–6Al–4V alloy weldment in hydrochloric acid

The corrosion behavior of a thin sheet of Ti–6Al–4V alloy was investigated in hydrochloric acid solution after welding by gas tungsten arc welding. The resulting microstructure of the weld metal (WM) consisted of coarse prior β grains containing fine acicular α platelets. It was found that both base metal (BM) and WM exhibited active–passive behavior after surface activation in open circuit potential experiments. The corrosion resistance of the BM and WM was found to decrease with increasing the temperature and acid concentration. However, the WM exhibited higher corrosion rate than the BM in all examined conditions. These results were also corroborated by electrochemical impedance spectroscopy measurements. Furthermore, it was revealed that the activation energy of the corrosion process for the WM was lower as compared to the BM, which confirmed the inferior corrosion behavior of the WM.     

Galvanic corrosion of gas tungsten arc repair welds in 17-4PH stainless steel in 3·5% NaCl solution

Abstract

In this paper, the galvanic corrosion of individual components of a 17-4PH repair welded stainless steel in 3·5% NaCl solution was investigated using various dc electrochemical measurements and microscopy. Open circuit potential measurement of the regions in the vicinity of a repair weld [i.e. parent metal, weld metal and heat affected zone (HAZ)] in 17-4PH stainless steel in 3·5% NaCl solution indicated that the most likely galvanic couple was between HAZ and weld with the HAZ acting as the anode and weld metal as the cathode. Slow scan rate potentiodynamic polarisation measurement of pitting potentials revealed a lower passive current density and a higher pitting potential in the weld region, while the HAZ showed the highest passive current density and the lowest pitting potential. Observation of the material after applying an anodic potential close to the pitting potential of the individual weld parts also confirmed the formation of several stable pits in the HAZ but only a few metastable pits in the weld and parent metal zones. Galvanic coupling using a zero resistance ammeter also showed a higher current density in the weld metal/HAZ as compared with the parent metal/HAZ and parent metal/weld galvanic couples. Although, the current densities in all measurements were in the range of a few to tenths of nanoampere per square centimetre, it can still be concluded that the weld metal/HAZ couple has the highest risk of galvanic corrosion among the three individual galvanic couples.     

核电汽轮机转子堆焊焊接接头的电偶腐蚀行为及有限元仿真

采用宏观电化学试验和浸泡试验研究25Cr2Ni2MoV汽轮机转子堆焊焊接接头在80 ℃,3.5% Cl?环境下的电偶腐蚀行为. 电化学试验结果表明,焊缝为腐蚀薄弱区,腐蚀电位从高到低依次为热影响区、母材、焊缝. 浸泡试验结果表明,随着母材面积的增大,焊缝平均腐蚀厚度逐渐加深. 进一步利用宏观电化学测试所获的电化学参量建立焊接接头电偶腐蚀有限元模型对比浸泡试验结果. 结果表明,有限元仿真结果能有效模拟堆焊焊接接头的电偶腐蚀行为,为实际生产提供电偶腐蚀速率预测.     

Laboratory Studies of Galvanic Corrosion – II. Three-metal Couples

Electrochemical and weight loss measurements have been used to study galvanic corrosion of three-metal couples extending earlier studies of the galvanic interaction of two dissimilar metals. Materials studied include Zn, Cd, Cu, Ni, the Al alloys 2024, 6061 and 7075, 4130 steel, stainless steel 304, Ti-6Al-4V, Inconel 718 and Haynes 188 in 3.5% NaCl at 21°C. Different electrical arrangements for galvanic current measurements using the zero resistance ammeters (ZRA) are discussed. With the use of two ZRA's the current flowing on each of three metals can be continuously monitored. Weight loss data are used to obtain additional information concerning accelerated corrosion or protection of the individual metals in galvanic couples. Such measurements can be used to evaluate the corrosion behavior of metal combinations such as encountered in a porous Cd coating on a steel fastener installed on an Al structure.     

Impact property analysis of weld metal and heat-affected zone for low-alloy carbon steel multi-pass welded joint

Welded joint impact performances of low-alloy carbon steel plates welded by full-automatic gas metal arc welding (GMAW) were evaluated. To clarity the effect of impact temperature on impact properties of weld metal (WM) and heat-affected zone (HAZ), Charpy V impact tests at different temperatures and fracture surface analysis were carried out. The Charpy V impact energy decreases with the decreasing test temperature both for the WM and HAZ, while the proportion of crystal zone on WM and HAZ impact fracture surface increases with the decreasing test temperature. Research results indicate that the welding defects (void and slag) make the impact energy of WM more scattered and lower than that of HAZ.     

Corrosion Behavior of Metal Active Gas Welded Joints of a High-Strength Steel for Automotive Application

In this work, the corrosion behavior of metal active gas-welded joints of a high-strength steel with tensile yield strength of 900 MPa was investigated. The welded joints were obtained using two different heat inputs. The corrosion behavior has been studied in a 3.5 wt.% NaCl aqueous solution using electrochemical impedance spectroscopy and potentiodynamic polarization tests. Optical microscopy images, scanning electron microscopy and transmission electron microscopy with energy-dispersive x-ray revealed different microstructural features in the heat-affected zone (HAZ) and the weld metal (WM). Before and after the corrosion process, the sample was evaluated by confocal laser scanning microscopy to measure the depth difference between HAZ and WM. The results showed that the heat input did not play an important role on corrosion behavior of HSLA steel. The anodic and cathodic areas of the welded joints could be associated with depth differences. The HAZ was found to be the anodic area, while the WM was cathodic with respect to the HAZ. The corrosion behavior was related to the amount and orientation nature of carbides in the HAZ. The microstructure of the HAZ consisted of martensite and bainite, whereas acicular ferrite was observed in the weld metal.     

130mm铝合金扫描激光填丝焊接头微区组织和性能

针对船用130 mm 5A06铝合金厚壁结构件的扫描激光填丝焊接头,对其焊缝（weld metal,WM）、热影响区（heat affected zone,HAZ）及母材（base metal,BM）的显微组织进行研究,并通过维氏硬度和微型剪切试验研究了接头各区力学性能差异.结果表明,5A06铝合金单激光焊缝以等轴晶为主,填丝焊焊缝以柱状晶为主,HAZ和BM晶粒比WM粗,母材及热影响区为轧制的纤维状组织;由于焊接热循环作用,接头热影响区硬度略高于母材,抗剪强度二者差别不大,单激光焊缝硬度和抗剪强度略高于填丝层.总体而言,焊缝区强度低塑性好,母材及热影响区强度高塑性低.     

Determination of threshold stress intensity factor for stress corrosion cracking (KISCC) of steel heat affected zone

Threshold stress intensity factor for stress corrosion cracking of heat affected zone (HAZ) of mild steel in caustic solution has been determined using circumferential notch tensile (CNT) technique. HAZ microstructure produced during manual metal arc welding of grade 250 steel was simulated over a length of 35 mm of CNT specimens, using a thermo-mechanical simulator. Inter-granular stress corrosion cracking has been confirmed with scanning electron microscope. The results presented here validate the ability of CNT technique for determination of K_ISCC of HAZ and base metal.     

Study on microtexture of laser welded 5A90 aluminium–lithium alloys using electron backscattered diffraction

Abstract

The microtexture features of Nd:YAG laser welded joints in 5A90 aluminium–lithium (Al–Li) alloys were examined using electron back scattered diffraction (EBSD). Microtexture was determined by means of the grain orientation image maps (OIM), pole figures (PF), misorientation angles and orientation distribution function (ODF) of the weld metal (WM), heat affected zone (HAZ) and unaffected base metal (BM) of the welded joint. The results show that there is a change of microtexture in the WM and HAZ of the welded joint in terms of the component and intensity of the texture. The HAZ of the welded joint inherits the texture characteristics of the BM, whereas the welding heat input has an important influence on the component C {112}<111>. The WM of the welded joint is composed of predominantly equiaxed grains with a random microtexture.     

Analysis of the Creep Behavior of P92 Steel Welded Joint

Different regions of heat-affected zone (HAZ) were simulated by heat treatment to investigate the mechanisms of the Type IV fracture of P92 (9Cr-2W) steel weldments. Creep deformation of simulated HAZ specimens with uniform microstructures was investigated and compared with those of the base metal (BM) and the weld metal (WM) specimens. The results show that the creep strain rate of the fine-grained HAZ (FGHAZ) is much higher than that of the BM, WM, the coarse-grained HAZ (CGHAZ), and the inter-critical HAZ (ICHAZ). According to the metallurgical investigation of stress-rupture, the FGHAZ and the ICHAZ have the most severely cavitated zones. During creep process, carbides become coarser, and form on grain boundaries again, leading to the deterioration of creep property and the decline of creep strength. In addition, the crack grows along the FGHAZ adjacent to the BM in the creep crack growth test (CCG) of HAZ.     

Mechanical and corrosion properties of 445J2 ultra pure ferritic stainless steel joint

The microstructure, mechanical and corrosion resistance properties of 445J2 ultra pure ferritic stainless steel thin plate joints conducted by the pulsed current gas tungsten arc welding (PCGTAW) were discussed in this paper. In order to avoid weld defects, the appropriate welding process was adjusted. The joints were subjected to optical microscopy, transverse static tensile, plastic deformation, intergranular corrosion and electrochemistry corrosion tests. The results indicated that the weld zone (WZ) is characterized with columnar grains and equiaxed grains and the heat-affected zone (HAZ) shows coarse ferrite grains due to the rapid solidification of thin plate welding. The PCGTAW joint exhibited acceptable mechanical properties and equivalent corrosion resistance properties as the base metal.     

Behaviour on corrosion of API X70 steel welded using the process of double submerged arc welding immersed in corrosive media

ABSTRACT

API X70 steels are used for manufacturing and constructing pipes for transporting hydrocarbons; however, they deteriorate over time due to the environment to which they are exposed; influencing the rate and type of corrosion on the surfaces of the base metal (BM), heat-affected zone (HAZ) and fusion zone (FZ). In order to find out and evaluate the susceptibility to corrosion in joints made from API X70 steel subjected to different corrosive media, various tests were carried out using the process of double submerged arc welding, which were immersed in different electrolytes: sodium chloride (3.5% NaCl) and water (H₂O) at ambient temperature in order to find out about behaviour. Electrochemical noise techniques and cyclic polarization curves were used to obtain the rate and type of corrosion produced in each of the analysed samples, including the three zones: BM, HAZ and FZ. In addition, characterization techniques such as optical microscopy and scanning electron microscopy were used for surface analysis. Most welds show mixed corrosion, with higher corrosion rates in 3.5% NaCl.     

ADB610钢焊接接头概率疲劳裂纹扩展分析

采用焊条电弧焊方法对ADB610钢进行焊接,对焊接接头进行疲劳裂纹扩展试验,研究其概率疲劳裂纹扩展规律.采用两步七点递增多项式拟合方法,计算了一系列相同裂纹长度下母材区、热影响区和焊缝区的对数裂纹扩展速率方差和存活率分别为50%,90%,95%,99%,99.9%的裂纹扩展速率.结果表明,总体上母材区的裂纹扩展分散性最小,热影响区其次,焊缝区分散性最大;而且总体上存活率相同时,在裂纹扩展的初期,母材区的裂纹扩展速率最快,焊缝区的裂纹扩展速率最慢;在裂纹扩展末期,三区域的裂纹扩展快慢相当;随着存活率增大,三区域裂纹扩展快慢差别不大时所对应的裂纹长度减小.     

Responsive behaviour of galvanic anodes in concrete and the basis for its utilisation

In this study, a unique concrete specimen was used to analyse the response of embedded sacrificial zinc and steel anodes to rainfall and fluctuations in temperature. Current from the zinc and steel anodes increased when the environment was aggressive, showing that the required protection current depends on the present level of corrosion risk. A basis for using the ‘responsive behaviour’ of galvanic anodes is provided by the protective effects of pit re-alkalisation and pH maintenance. By contrast, protection based on achieving adequate polarisation inhibits the use of responsive behaviour and galvanic anodes might only deliver adequate polarisation in aggressive environments.     

Microstructure and properties of as welded duplex stainless steel

Abstract

Butt welds of duplex stainless steel plate (grade 2205) have been produced using grade 2209 consumables for a variety of welding processes employed in the shipbuilding industry. The welding processes were used initially with interpass temperatures in the range 250–350°C. When the interpass temperature was controlled to below 150°C, the average ferrite content increased in the weld metal and in the heat affected zone (HAZ). Controlling the interpass temperature did not dramatically affect the properties in the mechanical tests performed. Heat inputs were in some instances higher than those used previously, but this did not adversely affect weld metal and HAZ properties. No evidence of intermetallic phase precipitation was found, by TEM of thin foils, in any of the weld metal in the processes used. There was evidence of fine particle precipitation of M₂₃C₆ in the HAZ regions. The level of precipitation observed is acceptable for the final application as all the mechanical test and corrosion test requirements were comfortably met. There was evidence that the HAZ was an area of higher strain: dislocation density was high and deformation bands, twinning, and stacking faults were present.     

Effect of magnetic field applied during gas metal arc welding on the resistance to localised corrosion of the heat affected zone in AISI 304 stainless steel

Resistance to localised corrosion at the heat affected zone (HAZ) of AISI 304 stainless steel gas metal arc welded (GMAW) in presence of magnetic fields of different intensity was studied. Samples of HAZ, 8 mm away from the weld centre, were subjected to electrochemical potentiokinetic reactivation to assess the degree of sensitisation (DOS). The application of magnetic field during welding induced lower DOS and better resistance to pitting corrosion in 3.5% NaCl solution than samples welded without it. Experimental findings suggest that magnetic fields enable Cr redistribution in the austenitic base metal during the welding thermal cycle reducing Cr depletion.     

Weldability and toughness evaluation of pressure vessel quality steel using the shielded metal arc welding (SMAW) process

The present study was carried out to assess the weldability properties of ASTM A 537 Cl. 1 pressure-vessel quality steel using the shielded metal arc welding (SMAW) process. Implant and elastic restraint cracking (ERC) tests were conducted under different welding conditions to determine the cold cracking susceptibility of the steel. The static fatigue limit values determined for the implant test indicate adequate resistance to cold cracking even with unbaked electrodes. The ERC test, however, established the necessity to rebake the electrodes before use. Lamellar tearing tests carried out using full-thickness plates under three welding conditions showed no incidence of lamellar tearing upon visual examination, ultrasonic inspection, and four-section macroexamination. Lamellar tearing tests were repeated using machined plates, such that the central segregated band located at the midthickness of the plate corresponded to the heat-affected zone (HAZ) of the weld. Only in one (no rebake, heat input: 14.2 kj cm^-1, weld restraint load: 42 kg mm^-2) of the eight samples tested was lamellar tearing observed. This was probably accentuated due to the combined effects of the presence of localized pockets of a hard phase (bainite) and a high hydrogen level (unbaked electrodes) in the weld joint. Optimal welding conditions were formulated based on the above tests. The weld joint was subjected to extensive tests and found to exhibit excellent strength (tensile strength: 56.8 kg mm^-2, or 557 MPa), and low temperature impact toughness (7.4 and 4.5 kg-m at-20 °C for weld metal, WM, and HAZ) properties. Crack tip opening displacement tests carried out for the WM and HAZ resulted in δ_m values 0.36 and 0.27 mm, respectively, which indicates adequate resistance to brittle fracture.