Abstract
Grade P91 is a relatively new class of steel, which has received special attention from designers because it presents extremely interesting characteristics for specific applications. This steel exhibits ideal properties for demanding applications, especially involving high temperature and pressure, being employed in facilities such as power plants and other equipment, such as heat exchangers. P91 welds usually need heat treatments, which are already parameterized in the codes. However, standardized treatments are time-consuming and harmful to the environment, as they massively consume energy. Some attempts have been made in the past to reduce the time and energy spent on these treatments. This work aims to extend this study, now presenting better solutions than those obtained previously. This work presents four new conditions for the heat treatment of joints carried out on P91 steel, with a view to reducing processing time, reducing energy consumption, and an even better balance between mechanical strength and elongation after failure. Heat treatment conditions were established in which there was a loss of about 14% in Ultimate Tensile Strength (UTS), but in which a gain of about 50% in elongation was obtained, compared to welding without any treatment, but also with 10% losses in the UTS and 30% gains in elongation when compared to the solution recommended as more correct in the codes, saving a lot of time and energy in the treatment process. Thus, these solutions may be adopted in the future with gains in terms of productivity and economic and environmental sustainability.
Highlights
Welding continues to be one of the most studied manufacturing techniques within the metalworking field
These hardness tests allowed for the assessment of hardness values of the profile across the joint, from the base material 1 (BM 1) to the base material 2 (BM 2), passing through both the heat-affected zones 1 and 2 (HAZ 1 and HAZ 2) and the melted zone (MZ)
It can be observed that the hardness values in the HAZ and MZ were higher before Post Weld Heat Treatment (PWHT), as the martensite was not yet tempered, being extremely hard and brittle in that state
Summary
Welding continues to be one of the most studied manufacturing techniques within the metalworking field. Due the diversity of materials that can be joined by this technique, the multiplicity of existing processes, the high range of parameters involved, and the high number of defects whose can be generated, this process requires proper planning and execution [1,2] These studies assume particular relevance whenever a new welding process is developed, such as in the case of the Friction Stir Welding process [3], or some variant of them is explored, or even when any material assumes special importance in applications where welding becomes unavoidable. The first steels with 12% Cr date from the 1960s in the 20th century These steels have traditionally presented creep problems when used under hard work conditions, which prevented their use in certain more demanding applications, such as power plants boiler construction, main steam pipelines, heat furnace piping in petrochemical industry and heat exchangers. The loss of mechanical properties was essentially associated with the formation of modified Z-phase, due to the formation of nitrides of Cr (V, Nb) in steels with
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