Soldagem do aço SA 517 gr. B para aplicações em vasos de pressão sem pré-aquecimento

Abstract

There is a continuous development of materials with better mechanical properties. Following this same line, the industry has been developing and applying materials with better mechanical properties in the construction of pressure vessels. Currently, SA 517 Gr. B steel has been used in the construction of this equipment for the storage of liquefied petroleum gas. The production flow of a pressure vessel with SA 517 Gr B steel, on the production line commonly has 10 steps. Among them are the preheating of the vessel, welding of the joint with the submerged arc process in three passes and post-welding heat treatment for stress relief. The electrode and flux used are the tubular wire F11A8-ECF6-F6 and the flux OK Flux 10.61 B, recommended for welds that require high resistance. This work was carried out with the purpose of reducing the number of passes to two, reducing the welding time and the volume of deposited material, and not preheating. For this, welding was carried out to define a new chamfer profile in double "V", with an opening angle of 90o. Simulations with the JMatPro® program were performed to determine cooling curves; phase diagram and properties of SA 517 Gr B steel when welded. The data obtained from these simulations in the JMatPro® program were used as a reference in the experimental and numerical welding simulation studies, using the ANSYS® program. The part of the experimental study consisted of exploratory welding by simple deposition on plates to determine current, voltage ranges, welding speeds and their effects on the weld bead geometry. Exploratory welds were also carried out to fill the chamfer and measure the dimensional characteristics of the welded joint. With the aid of the STATISTICA® software, applied to the measured dimensions of the weld beads, an optimized experimental condition for welding the joint was determined (I = 505 A, U = 32.3 V and Vs = 40 cm / min). The numerical simulation of the joint welding was carried out using a program developed in ANSYS®. This program is fed with information from simulations with JMatPro® and with the current welding parameters, voltage and welding speed, raised in the experimental studies. This simulation generated an optimized combination of parameters: current 500 A, voltage 31 V and welding speed 31.6 cm / min for the study. Finally, welding with the optimized parameters from the experimental study and the simulation with ANSYS® was performed. Samples of the two welded conditions were taken to perform microstructural characterization using optical microscopy (OM). The welded joint with the conditions obtained experimentally with the help of STATISTICA®, presented a bainitic microstructure in the base metal, ferrite and perlite in the ZAC GF, bainite in the ZAC GG and acicular ferrite in the molten zone, which was already expected and desired according to the diagram CCT of steel 517 Gr. B. The welded joint with the conditions obtained from ANSYS®, presented a bainitic microstructure in the base metal, ferrite and perlite in the ZAC GF, bainite in the ZAC GG and acicular ferrite in the molten zone. In both conditions there was no lack of penetration or other discontinuity. The microhardness profiles of the welded joints in the three conditions showed similar behavior. For the optimized welding conditions of the experimental and simulation study, there was a small reduction in hardness in the regions of ZAC and MS, in comparison with the welded joint with the current manufacturing conditions of pressure vessels. In view of these results, there are real possibilities of carrying out the welding of these pressure vessels, without the use of preheating. However, mechanical tests of traction, folding and Charpy, required in norm, must be carried out on welded joints to confirm the procedures developed.