Autores:
GALEAZZI, Daniel - M. Eng
SILVA, Régis Henrique Gonçalves e - Prof. Dr. Eng.
ROCHA, Pedro Correa Jaeger - B. E. Materials Engineer
SILVA, Rafael Gomes Nunes - B. E. Materials Engineer
SCHWEDERSKY, Mateus Barancelli - Prof. Dr. Eng.
Abstract
This work focused on developing a methodology for welding joints made of AISI 410 stainless steel, applied in environments requiring high pressure and temperature resistance. The difficulty found in the welding of martensitic steels is its high hardenability, susceptibility to cracking, among others, being necessary a posteriori thermal treatment for hardness control and stress relief. To identify the problems concerning this material, initial tests were performed. A groove was defined to facilitate the preparation, in this case a V-type groove with 30° bevel, nose of 1.5 mm and gap of 1.5 mm, machined in sheets of 12.5 mm thickness. For these tests, the SMAW process was used due to the equipment's flexibility in terms of consumables. The consumable adopted was the 309L stainless steel covering electrode, due to its mechanical properties that are equivalent to the base metal, i.e. 750 MPa, in addition to the resulting alloy carrying a nickel and chromium equivalent of 12.50% and 13.32%, which according to Schaeffler's diagram may present an austenitic and martensitic phase that tends to generate cold cracking. Among the evaluated consumables these were the ones that best fit within the proposed scope. Taking into account the cold cracking of this alloy, preheating of 315°C and to interpass 250°C was also adopted. The current and welding speed were 90A and 18 cm/min. Using the methodology mentioned above, the bead appearance was verified with total root penetration, low convexity, but with superficial defects, such as porosity and cracks, in small quantities, but sufficient to fail the joint according to the standard (AWS D1.1). In this sense, observing the mechanism of formation of these defects, it was verified that generating a disturbance on the melting pool could facilitate the escape of internally trapped gases, therefore, using the same parameters, the tests were repeated, however using an axial oscillation of the electrode from 0.5 Hz to 2.0 Hz, with amplitude of 3 mm. With this, the aim was to increase the diffusion of gases to decrease porosity and cracks. It was verified with these tests that for values of 0.8 Hz to 1.3 Hz there is a significant decrease in the incidence of pores. The value of 1.2 Hz being the best value within the range, decreasing about 90% the incidence of pores in relation to the process without oscillation. After welding and visual inspection, quenching and tempering heat treatments were performed to achieve the expected mechanical characteristics of tensile strength and toughness. It was verified that the tensile strengths of the joints with oscillation between 0.8 Hz to 1.2 Hz presented values higher than the nominal of 750 MPa, where they presented values between 755 to 760 MPa. For frequencies out of operating range, the benefits of porosity reduction were not evident. Moreover, the tensile strength test resulted in values lower than the nominal. Therefore, the axial oscillation of the electrode is a practice that can be adopted to decrease the incidence of porosity.
Key-words: Pool Oscillation; SMAW; Stainless Steel; Welding
Resumo publicado nos Anais do 2º Congresso online de Engenharia de Materiais – EngMatCon - 2020