Hot-rolled backup rolls are widely used in steel rolling and usually need to be repaired by arc hardfacing after becoming worn. However, a corrugated-groove defect commonly occurs on the roll surface ...due to the uneven hardness distribution in the hardfacing layers, affecting the proper usage of the roll. Accordingly, a new swing-arc submerged arc welding (SA-SAW) process is proposed to attempt to solve this drawback. The microstructure and hardness are then investigated experimentally for both SAW and SA-SAW hardfacing layers. It is revealed that a self-tempering effect occurs in the welding pass bottom and the welding pass side neighboring the former pass for both processes, refining the grain in the two areas. In all the zones, including the self-tempering zone (STZ), heat-affected zone (HAZ), and not-heat-affected zone in the welding pass, both SAW and SA-SAW passes crystallize in a type of columnar grain, where the grains are the finest in STZ and the coarsest in HAZ. In addition, the arc swing improves the microstructure homogeneity of the hardfacing layers by obviously lowering the tempering degree in HAZ while promoting the even distribution of the arc heat. Accordingly, the hardness of the SA-SAW bead overall increases and distributes more uniformly with a maximum difference of < 80 HV
along the horizontal direction of the bead. This hardness difference in SA-SAW is accordingly decreased by ~38.5% compared to that of the SAW bead, further indicating the practicability of the new process.
Dikey karıştırıcılı öğütücüler, çeşitli maden cevherinin ekonomik olarak öğütülmesinde kullanılırlar. Karıştırma vidası öğütme haznesinin üstüne dik eksenli çalışacak şekilde yataklanması yapılır. ...Öğütücü karıştırma sırasında oluşan zorlanmalara karşı mukavim olması ve rijitliğini koruması istenir. Bu nedenle parçalar birleştirilirken en iyi kaynak yöntemi seçilmelidir. Kaynaklı birleştirmelerde tüm kaynak işlemleri, istenen kaynak dikişi parametreleri, minimum bozulma ile mükemmel mekanik özellikler ile kaynaklı bir bağlantı elde etmek amacıyla kullanılır. Tozaltı Ark Kaynağı (SAW) işlemi, kolay uygulanabilirliği, yüksek akım yoğunluğu ve aynı anda birden fazla tel kullanarak büyük miktarda kaynak metali biriktirme kabiliyeti nedeniyle geniş endüstriyel uygulama alanı bulmaktadır. Özellikle aşınmış parçaları onarabilme özelliğinden dolayı imalatta çokça uygulanmaktadır. Kaliteli bir bağlantı elde etmek için, SAW’ın çeşitli proses parametrelerinin incelenmesi ve kaynak kalitesini iyileştirmek için hassas bir şekilde seçilmesi gerekir. SAW, daha sonra kaynak kalitesini etkileyen biriktirme hızı, seyreltme ve sertlik gibi performans çıktılarını etkileyen çok sayıda proses parametresi ile karakterize edilir. . Bu nedenle vida yapraklarının mile kaynağı SAW yöntemi ile yapılmıştır. SAW makinesi ile kaynak yapılmış deney numuneleri Taguchi'nin deney tasarımına göre veriler toplanmış ve sürecin girdi-çıktı ilişkilerini kurmak için varyans (ANOVA) ve regrasyon analizi yapılmıştır. Optimum kaynak parametrelerini belirlemek için ANN modellerine dayalı optimizasyon prosedürlerini kullanan iyi bir dikiş geometrisi elde edilmesi amaçlanmıştır. Bu tekniklerden elde edilen optimize edilmiş değerler deneysel sonuçlarla karşılaştırılmış ve sunulmuştur.
Display omitted
•Organic adhesive assisted underwater submerged-arc welding was first time proposed.•The epoxy resin successfully isolated the welding process from surrounding water.•The application ...of mixture optimized the microstructure and mechanical properties of the welded joints.
Underwater welding technology has become indispensable to the construction, maintenance, and repair of many offshore structures in oceanographic engineering industry. However, the existing disadvantages of current underwater welding technologies make them be unpopular and limited. An innovative organic adhesive assisted underwater submerge-arc welding was proposed to avoid the water disturbances to the maximum extent in wet condition. The mixture composed of bisphenol-A epoxy resin (EP) and welding flux in a weight ratio of 4:6 was placed on the metal surface before welding. Welding arc totally submerged in the mixture and maintained stable burning between the wire and base metal. The coverage effectively isolated the serious direct disturbances from surrounding water and greatly reduced the cooling rate of the welded joints to 19.57 °C/s. High-performance and defect-free welded joints were achieved with fine microstructures. The average tensile strength and maximum bending angle of the welded joints obtained by underwater submerged arc welding reached 463 MPA and 180°, respectively. Especially, low temperature impact toughness still keep 63 J/cm2 in 0 °C, which means far better mechanical properties compared with underwater wet welding. For the wet condition, this provides a possibility to acquire high-quality underwater welded joints comparable to that in air.
For the application in heavy wall pressure vessels such as hydrocracking reactors in the petrochemical industry, creep-resistant 2.25Cr–1Mo-0.25V steel is usually joined via submerged-arc welding. To ...ensure a long service lifetime at elevated temperatures and high pressures, the steel plates and weldments must maintain a beneficial combination of toughness and creep strength for several years. One approach to adjust the weldments' mechanical properties is to perform a post-weld heat treatment (PWHT).
This study is dedicated to the impact of the PWHT-temperature and -time on the complex interplay of microstructure, precipitates and mechanical properties of 2.25Cr–1Mo-0.25V weld metal. The mechanical testing showed that a higher PWHT-temperature increases the weld metal's impact toughness and ductility while simultaneously decreasing its strength and creep resistance. The high-resolution investigation with transmission electron microscopy and high-energy X-ray diffraction demonstrated that this is linked to accelerated recovery processes and severe coarsening of fine MX carbonitrides. At lower PHWT-temperatures, the absolute increase of the MX phase fraction during PWHT and the MX coarsening is less pronounced, allowing the MX carbonitrides to effectively contribute to precipitation hardening by maintaining their fine size. Besides MX carbonitrides, the weld metal consists of Cr-rich M7C3 and M23C6 as well as a substantial amount of Mo- and V-rich M2C carbides. The precipitate transformation sequence during PWHT was found to be M3C→M3C + MX + M7C3→M3C + MX + M7C3+M23C6+M2C→MX + M7C3+M23C6+M2C, whereas prolonged annealing times at higher PWHT-temperatures again lead to the dissolution of M7C3 in favor of MX.
Display omitted
•Besides M7C3, M23C6 and MX, heat-treated 2.25Cr–1Mo-0.25V weld metal also possesses a substantial amount of M2C carbides.•The heat treatment temperature is decisive for the MX and M2C fraction, as well as the MX/M2C-ratio.•The carbide transformation sequence in 2.25Cr–1Mo-0.25V weld metal at 690–720 °C is M3C .→ M3C + MX + M7C3 → M3C + MX + M7C3+M23C6+M2C → MX + M7C3+M23C6+M2C.•Prolonged PWHT at 705 and 720 °C causes dissolution of M7C3, which is related to an increase of the MX fraction.
Welding processes are the most common manufacturing solution that frequently complete the final steps of an industrial production. Their large use makes these techniques worth of attention of the ...scientific community, so that several efforts are spent for optimising and improving the way the processes are executed.
Submerged Arc Welding is widely used in the industrial scenario being semi-automatic but it cannot be ignored that this joining technique is far from the full automatization and is still dependent by the operator expertise.
In this study, an experimental investigation has been performed to build a robust data set for the subsequent application of seven machine learning classifier. The aim of the work is the definition of a suitable classifier able to detect and predict invalid process conditions which could lead to failed joint.
Crystallization behaviors of CaF2-TiO2 fluxes with varying TiO2 contents from 10 to 40 wt.% for high heat input submerged arc welding application have been systematically investigated by using single ...hot thermocouple technique (SHTT), field emission scanning electron microscopy (SEM), and X-ray diffraction (XRD). It is demonstrated that, as a function of the TiO2 content, the crystallization temperature initially decreases (from 10 to 30 wt.%) but increases afterwards (>30 wt.%), while the incubation time follows an opposite trend. It has been confirmed that CaTiO3 and CaF2 are the two dominant precipitated phases. It is further shown that the growth of CaTiO3 crystals follows a three-dimensional pattern while that of CaF2 a two-dimensional one. The effective activation energy is the highest when the TiO2 content is 30 wt.%, indicating the greatest barrier to crystallize and the highest capability to achieve the most desired production of amorphous welding fluxes for high heat input applications.
In submerged arc welding (SAW) process, t8/5 is critical in determining the microstructure, dimensions and mechanical properties of weld metal (WM) and heat affected zone (HAZ) and it depends on the ...heat input developed depending on the welding parameters and the temperature of the base metal (BM) and is extremely sensitive to any change therein.
When t8/5 values are identical in the case of identical welding heat inputs gained, although all the welding parameters are different, the notch impact toughness and hardness values of the welded construction are very approximate to each other. Although all welding parameters are identical, t8/5 and consequently the notch impact toughness and hardness values are different from each other because of the difference of interpass temperature between internal and external welding. The interpass temperature of weld area can be changed by stopping the welding machine for a while after the internal welding or by shifting the external weld head from internal welding. While the improvement of notch impact toughness at −20°C is 24.5% by stopping the welding machine after the internal welding, this value is 17.7% by shifting the external weld point. This work shows the importance of the interpass temperature and cooling rate being defined with t8/5 in order to improve the mechanical properties of steel welds.
Display omitted
•The underwater submerged-arc welding (USAW) process was innovatively developed.•A mixture of epoxy resin and submerged-arc flux was employed.•The process stability and weld formation ...was enhanced.•Weld metal microstructure consists of pro-eutectoid ferrite and acicular ferrite.•The comprehensive mechanical properties of joints were greatly improved.
The serious interferences from the surrounding water severely limit the process stability and joint quality of the current underwater welding technologies. To effectively isolate the welding area, a mixture of epoxy resin and submerged-arc flux was innovatively prepositioned in the welding area during underwater welding process. Butt welding experiments of a typical high strength marine steel were conducted to verify the advantages of this technique. Compared with the traditional underwater wet welding, underwater submerged-arc welding significantly optimized the arc burning environment due to the covering and isolation, which effectively improved the stability of welding process. Defectless joints with microstructure that full of fine acicular ferrite and high-quality mechanical properties, especially, outstanding performance of ultimate strength and plasticity were obtained. The results are expected to positively widen the practical application of underwater welding in many water related industries.
