Austenitic stainless steels specimens were deformed by tension in temperatures in the range of −50 • C to 20 • C and 0.03 to 0.12 true strain, in order to obtain different volumetric fractions of ε (hexagonal close packed) and α (body centered cubic) strain induced martensites. The morphology, distribution and volumetric fractions of the martensites were characterized by metallography and dilatometry analysis and quantified by ferrite detector measurements. The damping behavior of specimens with different volumetric fractions of martensites was studied in an inverted torsion pendulum in the 40 • C to 400 • C range. The εand α -martensites reversion was observed in the temperature range of 50 • C-200 • C and 500 • C-800 • C, respectively, by dilatometry. Internal friction curves in function of temperature of the deformed samples presented internal friction peaks. The first internal friction peak is related to sum of the amount of εand α -martensites. For low deformations it aligns around 130 • C and it is related only to the ε → γ reverse transformation. The peak situated around 350 • C increases with the specimen degree of deformation and is, probably, related to the presence of α /γ interfaces, and deformed austenite.

RESUMOAços inoxidáveis austeníticos da classe ABNT 304, quando deformados, sofrem transformações de fase, gerando as fases martensíticas epsilon, de estrutura hexagonal compacta, e alfa-linha, tetragonal de corpo centrado. As propriedades mecânicas, assim como a conformabilidade desse aço, dependem da morfologia, distribuição e fração volumétrica das martensitas. Ensaios de tração foram realizados nas temperaturas de -50ºC a 20ºC, com deformação verdadeira de 0,03 a 0,12, com o intuito de obter diferentes quantidades de martensitas. Determinou-se a fração volumétrica de martensita alfa-linha através de um ferritoscópio, indicando a diminuição da martensita alfa-linha, com a elevação da temperatura de deformação. Ensaios dilatométricos foram conduzidos na faixa de temperaturas de 50 a 1000ºC a 1ºC/s e mostraram duas transformações de fase, nas faixas de temperaturas de 50 a 200ºC e 500 a 800ºC, que foram relacionadas às transformações reversas epsilon→gama e alfa-linha→gama. A quantidade transformada de epsilon cresce até um máximo, enquanto que a quantidade transformada de alfa-linha aumenta, continuamente, com a deformação. A formação de epsilon precede o aparecimento de alfa-linha e diminui sua quantidade à custa do aumento de martensita alfa-linha.Palavras-chaves: martensita induzida por deformação, aço inoxidável austenítico, dilatometria. Dilatometric evaluation of strain-induced martensite reversion in type AISI 304 austenitic stainless steel ABSTRACTAustenitic stainless steels can form strain-induced martensites when deformed. The mechanical properties, as the formability, depend on morphology, distribution and volumetric fractions of phases generated, epsilon-martensite, with a close-packed hexagonal structure, and alpha-prime martensite, which possesses a body-centered cubic structure. Tensile tests were carried out in temperatures in the range of -50 to 20ºC with true strains ranging from 0.03 to 0.12, in order to obtain different volumetric fractions of epsilon and alpha-prime martensites. The amount of alpha-prime martensite was measured by using a ferritoscope indicating that the alpha-prime martensite fraction increases with strain for a constant temperature and decreases with the temperature for a constant strain. The epsilon and alpha-prime martensites reversion was observed in the temperature range of 50 to 200ºC and 500 to 800ºC, respectively, by dilatometer tests. The epsilon martensite volumetric fraction first rises with the strain and, at higher deformations, drops from a maximum value, which depends on the deformation temperature. The epsilon martensite occurs before alphaprime martensite and its amount decreases with the increase on the volumetric fraction of alpha-prime martensite.

In the laser cladding process, control of the process parameters and knowledge of the characteristics of the materials used are essential for obtaining depositions with excellent metallurgical union, satisfactory dilution values, absence of defects, and acceptable geometric characteristics. Without such precautions, depositions can exhibit low or excess dilution, low wettability, and the presence of pores, consequently reducing the performance of the materials. The aim of the present work was to evaluate the effects of the laser beam power, with maximum power of 4000 W and continuous wave mode, and scanning speed in laser cladding processes employing the AISI 316L austenitic stainless steel and the AISI 431 martensitic stainless steel, considering the geometric characteristics, dilution, and structural defects of the depositions. It was found that the laser power had a greater effect on the width and dilution of the depositions, while the scanning speed influenced the deposition height. The depositions of AISI 431 steel presented dilution values between 9 and 25%, using power settings between 1400 and 1600 W. The depositions of AISI 316L steel required higher power values between 1900 and 2600 W to achieve dilution values between 15 and 41%. The existence of pores and satisfactory hardness values were observed for both materials, with the average of microhardness of 522 HV0.5/15 and 356 HV0.5/15 on the AISI 431 and AISI 316L depositions. It was also found that the different characteristics of the addition metals, considering their morphology, particle size distribution, and flow rate, led to significant changes in the geometric features of the depositions.

Hybrid Laser-Arc Welding (HLAW) is a relatively new joining technique that combines advantages from both laser beam welding and arc welding. The interaction between laser beam and arc welding provides advantageous synergic effects, especially for thick joints. On the other hand, this interaction brings extra complexity to HLAW, limiting its acceptance in industry. Therefore, it is still necessary to elucidate some features of HLAW, such as the influence of parameters and consumables on the characteristics of the resulting joints. In the present study, the effects of welding gases (Ar + CO2 in different proportions) and filler metals (solid and flux-cored wires) on thick S355 structural steel joints are assessed. The best welds in terms of geometric characteristics, microstructures, and mechanical behavior were fabricated with high CO2 content welding gases and flux-cored welding wires. The use of flux-cored wires promoted higher penetration, lower hardness, and formation of acicular ferrite, avoiding the formation of martensite encountered in joints welded with solid wires. Moreover, the application of flux-cored wires could lead to cost savings in future applications, by reducing the laser power required to produce sound joints.