Manufatura aditiva por deposição a arco de paredes finas de aço inoxidável super duplex com resfriamento ativo por quase-imersão

Abstract

Within the processes used for additive manufacturing of metals, Wire Arc Additive Manufacturing (WAAM), which employs processes traditionally applied for welding, stands out due to the lower costs and higher deposition rates achieved. Strategies to manufacture super duplex stainless steels (SDSS) parts through WAAM should focus on guaranteeing a deposit with proper geometry, free from defects, proper phase balance (ferrite and austenite) and minimize the occurrence of deleterious phases. Given the importance of controlling cooling rates in WAAM, different thermal management methods have been studied aiming at mitigating problems related to heat accumulation, resultant from the energy input throughout the deposition process. Thus, this work aims at assessing the use of Near-Immersion Active Cooling (NIAC) in the deposition of SDSS thin walls in terms of geometry, microstructure and deposition time. The operational modes CMT and Pulsed GMA were explored throughout the work, with different travel speeds. During the first step clues that a higher tendency to form porosity was caused by the shielding gas composition Ar + 2 % CO2. This was confirmed by the fact that when Ar + 25% He was applied no indication of porosity was found in the walls. In terms of cooling conditions, it was found that it is possible to achieve acceptable fractions of austenite and ferrite with natural cooling (NC) with dwell times long enough so the wall reached 100 °C. With short dwell times and NC, heat accumulation resulted in a progressive increase in width, unacceptable phase balance and indications of sigma phase presence. By using NIAC it was possible to manufacture walls with no indications of defects, acceptable phase balance and dwell times up to 89% shorter, compared to the NC condition. For a same wire feed speed, when a travel speed two times higher was employed in relation to CMT, similar widths were achieved. Comparing these two conditions, Pulsed mode resulted in better surface finish. However, to reach the same wall height, the number of layers was twice greater with Pulsed mode. Clues were found that a more pronounced nitogren loss occurs during the deposition onvi Pulsed mode, resulting in ferrite contents higher than expected, but still within the limits. Except in the conditions where heat accumulation occurred (NC with short times), secondary austenite (γ2), which is considered also a deleterious phase although less critic than sigma, was commonly observed. In general, the use of NIAC in WAAM of SDSS thin walls showed itself promising with the potential of reducing the overall deposition time significantly, without causing defects or metallurgical problems.