Austenitic stainless steel and nickel-base alloys welds are widely used in nuclear reactor components, plants of energy generation, chemical, and petrochemical industries, due to their high corrosion resistance. The post weld heat treatments (PWHT) are generally applied to welding in order to relieve the welding residual stress. The aim of this work was to evaluate the influence of different PWHT on corrosion behavior of a dissimilar weld joint of two AISI 316L austenitic stainless steel plates with a nickel-base alloy as filler material in saline environments. The material was submitted to heat treatments for three hours at 600, 700 and 800 °C. The weld joint was examined by optical microscopy to determine the effects of PWHT in the microstructure. The corrosion behavior of the samples before and after heat treatment was evaluated using cyclic potentiodynamic polarization (CPP) in sodium chloride solutions (19% v/v) and pH 4.0 at room temperature. Metallographic analyses showed that delta ferrite dissolute as PWHT temperature increased. CPP curves demonstrated an increase of pitting corrosion resistance as the PWHT temperature rises, although the pit size has been increased. The heat treated weld joint at 600 °C showed a similar corrosion resistance compared to as-welded material.
Resumo Esse trabalho visa estudar, pela análise de imagens do arco, os mecanismos propostos para explicar o aumento de penetração na soldagem TIG quando é utilizado fluxo ativo na superfície (A-TIG). Foram realizados testes com fluxos de Cr 2 O 3 , SiO 2 e TiO 2 para avaliação da ocorrência de alterações na forma do arco que indiquem, por exemplo, a ocorrência de sua constrição. Para tal, foi feita a aquisição de dados de corrente e tensão, bem como fotografias do arco durante a soldagem com uma câmera semiprofissional e uma lente de macrografia, para que fosse possível uma melhor avaliação de quaisquer variações no arco no decorrer do teste. Foi notado um aumento da tensão quando utilizados Cr 2 O 3 e SiO 2 como fluxo, entretanto não foi observada variações consideráveis na largura do arco de soldagem, o que seria uma indicação de constrição elétrica do arco. Palavras-chave:Soldagem A-TIG; Constrição do arco;Fotografia do arco; Sinais elétricos.
The overwhelming bulk of oil and gas in pipeline construction is done by welding the individual joints of pipe together. In a broad sense, welding is a metal-joining process wherein coalescence is produced by heating to a suitable temperature. In pipeline construction, this temperature has to be sufficient to render fusion of the joint. The mechanical and metallurgical properties and distortions usually present in weld structures are strongly influenced by preheating and interpass temperatures that are applied during the welding process. Basically, interpass temperatures depend on two factors: composition of the material and cooling rate. It is very important to choose the correct interpass temperatures, however, this is not a completely dominating matter. The objective of this paper is to present a study on the effect of different interpass temperatures on morphology, microstructure and consequently on microhardness of welded API 5L X65 steel. The welds were deposited by a Flux Cored Arc Welding Process and the heat input was held constant during all welding production. The interpass temperatures were calculated by different methods. Such temperatures were later verified experimentally. Temperature data were collected via a data acquisition system. The geometry and microstructure characterizations were performed via light optical microscopy and image analysis. These data were related to the different thermal cycles obtained. The results showed that the morphology, the microstructure and the microhardness of welded API 5L X65 steel were strongly influenced by the interpass temperature, revealing how important it is to choose the appropriate value.
The results of the corrosion tests, in chloride environment, of lean duplex stainless steel UNS S32304 welded by submerged arc welding (SAW) process variant with cold wire, indicated that the sample with higher heat input heat input (HI) (2.7 kJ/mm) had higher corrosion resistance, which can be explained by higher amount of austenite and lower amount of precipitates. Therefore, the results indicate that the use of HI above the limit recommended by literature (2.5 kJ/mm) may produce welds with adequate corrosion resistance with SAW with cold wire addition, because this technique has the potential to deliver higher productivity still controlling the process HI.
Resumo Os aços inoxidáveis ferríticos apresentam vantagens econômicas e técnicas apreciados por diversos setores industriais e dentro desta classe, o AISI 430 é o mais utilizados por ser resistente ao calor e à corrosão e esteticamente atraente e, em algumas aplicações, adequado para substituir os inoxidáveis austeníticos. Para suprir algumas exigências que o tipo AISI 430 não possuía, surgiram os aços estabilizados, sendo o Ti e Nb os elementos mais comumente utilizados.O aço AISI 430E, estabilizado com Nb, possui menor susceptibilidade a sensitização além de melhores propriedades mecânicas. Este trabalho consiste em analisar a influência da adição de Nb no AISI 430 tratado termicamente. As implicações da adição de Nb na microestrutura e dureza foram avaliadas por meio de microdureza vickers, microscopia óptica e eletrônica de varredura. Os resultados mostram que o AISI 430A apresentou uma estrutura ferrita e martensita, após tratamento em temperaturas elevadas, enquanto o aço AISI 430E, apresentou crescimento heterogêneo de grão. Notou-se um aumento da dureza no aço AISI 430 A após tratamento térmico em elevadas temperaturas (1000 °C) devido à presença da martensita, enquanto no aço estabilizado, o valor de dureza diminuiu devido ao coalescimento de precipitados de Nb.
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