When a variable magnetic field is applied to a ferromagnetic material, it has been observed that, next to the coercive field (Hc), rise in induction (B) takes place through abrupt jumps known as Barkhausen jumps. In this research, the microstructure variation in carbon steel welded joints was monitored by the Magnetic Barkhausen Noise (MBN). The samples were welded by SMAW process, in which both one-pass and two-pass were applied. Microhardness and microstructure were also characterized. The MBN signal was measured and analysed by means of several frequency and time domain parameters. Furthermore, maps of the welded steel surfaces were plotted. The variation of the MBN parameters was correlated to those of the microhardness and microstructure. The results allowed identifying a heat-affected zone (HAZ) of the welded joint using the MBN signals.

Cuando un campo magnético variable se aplica a un material ferromagnético, se ha observado que cerca al campo coercitivo (Hc) ocurre un aumento en la inducción (B) de forma abrupta a manera de saltos conocidos como saltos de Barhausen. En esta investigación la variación de la microestructura en uniones soldadas de aceros al carbono fue monitoreada usando el Ruido Magnético de Barkhausen (RMB). Las muestras fueron soldadas por el proceso SMAW, con aplicación de uno y dos pases de soldadura. Se caracterizaron la microdureza y la microestructura y se hicieron mediciones de RMB. Esta señal de RMB fue analizada utilizando varios parámetros en los dominios del tiempo y de la frecuencia, y fueron levantados mapas superficiales de los aceros soldados. La variación de los parámetros de RMB fue correlacionada con los cambios en la microestructura y la microdureza. Los resultados permitieron identificar la zona afectada térmicamente de la unión soldada usando las señales de RMB.

Este trabalho apresenta resultados de avaliação de juntas soldadas de aço estrutural ASTM A36 por meio do Ruído Magnético de Barkhausen (RMB). A soldagem foi feita em chapas de 6 mm de espessura com preparação de chanfro em V, com um e dois passes. Foram feitas a caracterização de microestructuras e microdurezas através da junta soldada, e na superfície foram feitas medições de RMB. Os sinais de RMB foram analisados com o valor máximo, uma média de valores acima de 80% do pico máximo, o rms e o rms do envelope, dos quais foram obtidas curvas da variação com respeito ao centro do cordão e também foram obtidos mapas superficiais. Na caracterização microestructural obteve-se que as amostras de um e dois passes apresentaram tamanhos da zona afetada pelo calor (ZAC) diferente. As microdurezas mostraram que no limite de fusão tem-se a maior dureza enquanto que no fim da ZAC tem-se a menor dureza. O RMB mostrou que no limite de fusão tem o menor valor, enquanto que no fim da ZAC tem o maior valor. Este estúdio mostrou que as mudanças na microestrutura influenciam em todos os parâmetros analisados, sendo que a junta soldada ficou melhor representada pelo valor rms e rms do envelope do RMB.

This paper shows results for the evaluation of ASTM A36 carbon steel welded joints by Magnetic Barkhausen Noise (MBN). V-groove shape welded samples were made in a 6 mm thickness plates, with one-pass and two-pass. Microstructural and microhardness characterization were made on a transversal section of welds. In the surface was made measurement of MBN. The signal of MBN were analyzed with the maximum value, threshold of 80% above of maximum, the root mean square (rms), the root mean square of the profile, and these parameters were plotted in function of the distance to center bead. Surface maps were obtained, too. The microstructural characterization identified different heat affected zone (HAZ) sizes for one-pass and two-pass. In addition, changes on microhardness showed which higger hardness was happened in the fusion boundary whereas lower microhardness happened in the HAZ end. With MBN monitoring were verified that the lower value happened in the fusion boundary, whereas the MBN higher value happened in the HAZ end. The study showed that changes in the microstructure influence all analyzed parameters. The welded joint are best represented by the root mean square (rms), the root mean square of the profile.