Abstract: This work aims to analyze the influence of low temperature on the toughness of a high-strength steel HARDOX 450® joints welded by the Metal Core Arc Welding (MCAW) process. Impact toughness tests (Charpy V-notch test) were performed on the 10 mm base metal (BM), weld metal (WM), and heat-affected-zone (HAZ) at temperatures of -100 °C, -80 °C, -60 °C, -20 °C, 0 °C, and 25 °C to obtain the ductile-brittle transition curve for each of these regions. Additionally, the tensile test and metallographic characterization were performed in order to complement the evaluation of the welded joint. The results of the impact tests showed higher toughness values of the base metal compared to the other two regions of the weld joint analyzed (WM and HAZ). The low toughness present in the HAZ is related to its microstructure composed of Widmanstätten ferrite and coarse grain. However, temperatures of -100 °C and -80 °C show the absorbed energy values in the three regions remarkably close to each other (between 11 J and 20 J).

Resumo: O presente trabalho visa analisar a influência da temperatura baixa na tenacidade ao impacto de juntas de aço de alta resistência HARDOX 450® soldadas através do processo Metal Core Arc Welding (MCAW). Para tanto foram realizados ensaios de tenacidade ao impacto (ensaio de Charpy com entalhe em V) no metal base de 10 mm (MB), no metal de solda (MS) e na zona termicamente afetada (ZTA) nas temperaturas de -100 °C, -80 °C, -60 °C, -20 °C, 0 °C e 25 °C com o objetivo de levantar a curva de transição dúctil-frágil para cada uma dessas regiões. Adicionalmente, foi realizado ensaio de tração e caracterização metalográfica a fim de complementar a avaliação da junta soldada. Os resultados dos ensaios de impacto mostraram maiores valores de tenacidade do metal base em relação às outras duas regiões da junta solda analisada (MS e ZTA). A baixa tenacidade apresentada na ZTA está relacionada à sua microestrutura composta por ferrita de Widmanstätten e grão grosseiro. Contudo, as temperaturas de -100 °C e -80 °C apresentam os valores de energia absorvida nas três regiões bem próximos entre si (de 11 J a 20 J).

Abstract The demand for light weight and small components has increased tremendously over the years. The present work describes the plasma micro welding of SS304 alloy. Plasma arc micro welding is carried out on thin sheet to characterize the effect of welding parameters. The proper ranges of welding current at constant welding speed for two different plasma gas flow rates are evaluated to obtain better quality of weld at butt joint configuration. Distortion is a major problem for welded structures especially for the thinner materials. Hence, the variation of process parameters viz. welding current and plasma gas flow rate are studied on weld-induced distortion. Distortion analysis both longitudinal shrinkage and transverse shrinkage are done for six different welding conditions. It is predicted that both longitudinal shrinkage and transverse shrinkage increases with increase in plasma gas flow rate and current. The tensile strength and microstructure are also determined at different gas flow rates and welding currents. This may be due to the application of more heat at higher values.

Abstract The in-service welding of natural gas distribution pipes is a critical operation. The shield metal arc welding (SMAW) process has low cost and is very simple, but it has limitations in the minimum pipe thickness. Gas tungsten inert arc welding (GTAW) employs more qualified operators and expensive welding machines and accessories. However, it can weld thinner pipes. In this work, both processes were tested and compared for the welding of an API 5L grade B pipe, often used in the distribution lines of Rio de Janeiro State. The results obtained showed that both processes gave satisfactory results. The minimum tensile strength was 430 MPa for both methods, under the standard range of 415 to 760 MPa. The impact toughness was 50 and 48 J for GTAW and SMAW, respectively. The GTAW showed more fine grains than the SMAW process. The hardness values in the SMAW HAZ was around 220 HV, while the GTAW HAZ was slightly lower, at 180 HV. For both processes, the hardness measured in the heat affected zone (HAZ) was superior to the base metal (BM), but much lower than the limit of 350 HV considered critical for hydrogen induced cold cracking.

Resumo A soldagem em operação de um duto de distribuição de gás natural é uma operação crítica. O processo de soldagem com eletrodo revestido, embora simples e barato, encontra limitações quanto à espessura do duto. O processo TIG exige soldadores mais treinados e equipamentos de maior custo, mas o controle do aporte de calor permite soldar menores espessuras. Neste trabalho, os dois processos foram comparados para a soldagem de um tubo de aço API 5L grau B frequentemente utilizado nas linhas de distribuição. Os resultados mostraram que os dois processos forneceram resultados satisfatórios de propriedades mecânicas, a resistência à tração mínima foi de 430 MPa em ambos os processos, dentro do intervalo esperado de 415 a 760 MPa. A tenacidade também ao impacto foi de 50 e 48 J para as juntas por TIG e eletrodo revestido, respectivamente. Comparativamente, a solda pelo processo TIG apresentou mais regiões de grãos refinados. A dureza da ZTA com eletrodo revestido foi em torno de 220 HV, quanto para o TIG o valor foi ligeiramente menor, 180 HV. Nos dois processos, foi superior ao metal base, porém muito abaixo do valor limite de 350 HV considerado crítico para fissuração por hidrogênio (trinca a frio).

Abstract Advanced materials and automated processes in manufacturing pose a challenge in terms of adaptability. Introduction of 3rd-generation advanced high strength (3rd-gen AHSS) steels aimed for weight reduction in the automotive without compromising its strength and efficient fuel consumption. Nevertheless, welding 3rd-gen AHSS using resistance spot welding (RSW) is often affected by liquid metal embrittlement (LME) or other quality matters. Identifying the process window to control and produce defect-free welds, requires huge experimental work with an enormous time. Therefore, this paper aimed to use machine learning (ML) to identify the process window by computing the relationship between the input parameters and output weld defect categories like 'Splash', 'LME', 'Insufficient nugget size' and 'Good weld'. Classification-based algorithms, K-nearest-neighbour (KNN) and Naive Bayes algorithms were used. Among these, Naive Bayes exhibits better prediction efficiency of 71% and KNN has 63%. Using these models, predicting the incidence of weld spot defects with the fore-mentioned predictability is possible. Therefore, this work supports the industry experts and researchers to study and predict the process window for the welding process to produce defect-free welds and this idea could implement in different manufacturing processes.

Abstract Overlay welding with stainless steels has gained attention in several sectors of industry by increasing the mechanical and electrochemical properties of surfaces, in order to obtain them using lower cost substrates. However, the control of welding parameters can become complex due to the multiple control variables, being of interest to obtain deposits with greater productivity. In this context, the objective of this paper is to analyze the effect of the heat input on weld overlays of austenitic stainless steel 316L-Si obtained by the GMAW process, to determine the best welding conditions. For this, a Design of Experiments was implemented to analyze the response variables, which include heat input, reinforcement, width, dilution and hardness of the weld metal. The models were considered significant, presenting R2>0.9 for all responses, based on a 95% confidence limit. Surface graphs indicated influence of welding speed or/and voltage for all responses, in addition to the results demonstrating optimal parameters for overlays such as high ratio between reinforcement and width (0.631), and low dilution values (8.81%). The microstructural analysis indicated the presence of residual γ-austenite and δ-ferrite in all samples, and also the formation of peninsulas and islands, added to defects such as voids, for some weld deposits.

Abstract This paper shows results of an investigation on the behavior of assemblies produced with welded fillet joints subjected to eccentric, quasi-static and “out-of-plane” structural impact loads. Therefore, weldments were manufactured, with one of the elements in “balance”, using ASTM A-36 and ASTM A-572 grade 50 structural steels, joined by the process of gas metal arc welding (GMAW or MAG). For the purpose of comparison, all weld beads were made with parameters kept constant and classes AWS ER70S-6 and AWS ER120S-G electrodes. Among the main results, it was observed that in tests with quasi-static loading, for both base metals, the parallel weld beads welded with AWS ER120S-G preheated to 150 °C withstood greater loads for shorter times, and the transverse weld beads withstand smaller loads for longer periods of time. Related to structural impact tests of ASTM A572 grade 50 base metal weldments, the parallel weld beads welded with electrode AWS ER70S-6, preheated to 150 °C, withstood near to 50% of the designed load. Fracture surfaces produced by structural impact loading of the weld beads with the AWS ER120S-G electrode were analyzed by scanning electron microscopy. Parallel weld beads produced fractures witch ductile characteristics, and perpendicular weld beads produced ductile fractures with cleavage planes.

Resumo Este artigo mostra resultados de uma investigação sobre o comportamento de conjuntos produzidos com juntas soldadas de filete, submetidos a carregamentos excêntricos, quase estáticos e de impacto estrutural “fora do plano”. Sendo assim, os conjuntos soldados foram fabricados, com um dos elementos em “balanço”, utilizando-se aços estruturais ASTM A-36 e ASTM A-572 grau 50, unidos pelo processo de soldagem a arco com proteção gasosa (MAG). Para fins de comparação, todas as soldagens foram realizadas com os parâmetros mantidos constantes e eletrodos classes AWS ER70S-6 e AWS ER120S-G. Dentre os principais resultados foi observado que nos ensaios com carregamento quase estático, para ambos os metais base, os cordões paralelos soldados com AWS ER120S-G pré-aquecidos a 150 °C suportaram maiores carregamentos por tempos menores, e os cordões transversais suportaram menores carregamentos por tempos maiores. Nos ensaios de impacto estrutural dos conjuntos soldados com metal base ASTM A572 grau 50, cordões paralelos soldados com eletrodo AWS ER70S-6, pré-aquecidos a 150 °C resistiram cerca de 50% da carga projetada. Superfícies de fratura produzidas pelo carregamento por impacto estrutural dos cordões soldados com eletrodo AWS ER120S-G foram analisadas por microscopia eletrônica de varredura. Cordões de solda paralelos produziram fraturas com características dúcteis e cordões perpendiculares fraturas dúcteis com planos de clivagem.

Abstract In this study, the influence of heat input on the mechanical properties and microstructure of welded joints in ASTM A572 grade 50 steel using the GMAW process and 90Ar-10CO2 shielding gas was investigated. Process parameters were varied between 20-30 V and 230-250 A, which were adjusted aiming to obtain spray transfer together producing two heat inputs with a 10% difference between them. Visual inspection, tensile tests, microhardness scans, measurements of the width of the heat-affected zone (HAZ), and metallography were performed. The experimental measurements were complemented by calculating the continuous cooling transformation (CCT) diagram of the steel from its chemical composition. The results showed that discontinuity-free and visually acceptable welded joints were obtained. The microstructure of the fusion zone was primarily composed of acicular ferrite, and the HAZ contained a mixture of bainite, pearlite, and ferrite as calculated by the CCT diagram. No statistically significant variations were observed in the microhardness measurements, with the highest value (240 MHV) obtained in the fusion zone. The width of the HAZ varied proportionally with the heat input, while no significant differences were found in the stress results as a function of the heat input.

Abstract Friction stir welding (FSW) is considered one of the most prominent methods for joining ductile materials. In this process, joining occurs in a plastic state without melting the base metals. Therefore, there is a lack of solidification cracking and shrinking of friction stir weld joints. Although, the improper stirring action of the FSW tool reduces the frictional heat input and flow of plasticized material, which deteriorates the weld joint quality. Insufficient and excessive heat input both results in the formation of weld flaws. The FSW is assisted with various new supporting tools to reduce weld flaws. The main objective of this paper is to provide collective information regarding supportive tool systems employed with FSW for the mitigation or elimination of weld flaws. FSW tool systems such as non-rotational shoulder assisted FSW, counter-rotating twin tool, reverse dual rotation, self-reacting tool, and in-situ rolling tool, and their impact on the weld joint formation is presented in this article. This paper also presented an overview of the remarkable effect of optimizing the FSW process parameters and the influence of tool pin profiles on weld joint quality. From this review, it is concluded that various FSW supporting tool systems significantly reduce the weld flaws.

Abstract Numerical simulations are commonly employed for comprehending and prognosticating welding procedures. However, repair often requires supplementary actions such as gouging for defect removal. Thermal cycles and non-uniform expansion and contraction of the base metal can engender internal and residual stresses in the gouged region. Residual stresses can wield influence over mechanical properties, thereby underscoring the necessity for their investigation. This study endeavors to establish a numerical method to simulate gouging while devising a rationale for thermal cutting processes. The model was validated by comparing computational and experimental results, which showed good agreement. Mechanical simulation unveiled residual stresses characterized by modest magnitude. This methodology can prevent mechanical failures in repaired components by providing valuable insights into the effects of the gouging process. procedures However removal nonuniform non uniform region properties investigation processes results agreement magnitude process