Marcelo José Gomes da Silva

Texture analysis of deformation induced martensite in an AISI 301L stainless steel: microtexture and macrotexture aspects.

Experiments have been conducted to study the strain induced transformation from austenite to martensite in a metastable AISI 301LN austenitic stainless steel, deformed by uniaxial tension applied along rolling direction. Samples deformed 10 and 20% have shown the presence of α´ martensite phase. Measured pole figures of martensite phase were compared to calculated ones, assuming no variant selection and selection of variants where interaction between stress and the plate of martensite adds to the driving force transformation variants. EBSD (electron back scatter diffraction) microtexture experiments and macrotexture X-ray diffraction were performed. The orientation distribution functions (ODFs) from measured pole figure data were calculated. The measured results were compared with calculated results in both polycrystalline and single crystal samples of austenite. The results showed that the calculated textures based in a process of variant selection consistent with Patel and Cohens theory, which emphasizes a mechanical component of free energy, were in good agreement with measured texture.

Microstructural and electrochemical characterization of the low temperature sensitization of AISI 321stainless steel tube used in petroleum refining plants

This work describes the behavior of ASTM A312 TP321 tubes heat treated at 600°C for periods of 1, 3, 10, 30, 40, 50, 60, 70, 80, 90, and 100 hours. The degree of sensitization that had occurred was assessed by Scanning Electron Microscopy (SEM) and by the Double Loop Electrochemical Potentiodynamic Reactivation test (DLEPR). The results showed that exposure at 600°C for 80 hours or longer caused severe precipitation of chromium carbides along the grain boundaries characterizing the sensitization of the material despite it being titanium stabilized. In order to minimize the sensitization process, solution annealing in the temperature range of 900–1100°C was studied. Solution annealing at 900°C was the best heat treatment in order to prevent sensitization at 600°C. The solution annealing at 900°C was also effective for samples from tubes that were sensitized after one year of operation in a refining plant.

CARACTERIZAÇÃO MICROESTRUTURAL DO AÇO SAE 1080 APÓS DIFERENTES TRATAMENTOS TÉRMICOS

Acos com teores eutetoides, tratados termicamente sao usualmente utilizados em trilhos metroviarios, parafusos, engrenagens para caminhoes, virabrequins, etc. A fim de que sejam atingidas as propriedades mecânicas almejadas para as devidas aplicacoes, o material deve ser submetido a alguns tratamentos termicos, como, por exemplo, Recozimento Pleno (aquecimento ao forno e resfriamento ao forno), Normalizacao (aquecimento ao forno e resfriamento ao ar) e Tempera (aquecimento ao forno e resfriamento em agua). Os tratamentos termicos sao de extrema importância no processo de fabricacao dos materiais, pois nao ha uma variacao em grande escala das dimensoes fisicas da peca, apenas as propriedades metal mecânicas sao alteradas. Neste estudo, as amostras utilizadas para o procedimento experimental sao provenientes de um trilho metroviario e foram fornecidas pelo Laboratorio de Pesquisa e Tecnologia em Soldagem. Foram feitas analises metalograficas (preparacao da superficie e analise microscopica), no laboratorio de Caracterizacao dos Materiais, apos os tratamentos termicos nas pecas de Aco SAE 1080 Fe-C, com o intuito de verificar os aspectos da microestrutura das amostras e a alteracao nas propriedades mecânicas, como, por exemplo, dureza, ocasionada pelos tratamentos realizados. Pelo fato do material estudado ter uma matriz com composicao perlitica de, aproximadamente, 100%, sao mostradas as consequencias devido a mudanca nos espacamentos interlamelares perliticos provocadas pela movimentacao atomica difusional e a influencia da estrutura martensitica nas propriedades mecânicas da peca.

ESTUDO DA RESISTÊNCIA À CORROSÃO ENTRE VERGALHÕES COM DIFERENTES MICROESTRUTURAS FRENTE AOS ÍONS CLORETOS

The rebar are produced by hot rolling process. In the process studied here there are two distinct production routes. Prior to the hot rolling process, one route uses the reheat step through the furnace, and the other uses the semi-finished steel product directly from the solidification process. When establishing a comparison between the routes, the obtained microstructures show some differences. The objective of this work is to evaluate how the differences between the microstructures influence in the resistance to corrosion by chlorides. For this, anodic potentiodynamic polarization and electrochemical impedance spectroscopy tests were performed in NaCl solution, simulating the effects of Cl ion present in the marine atmosphere. From the curves obtained in the electrochemical tests, it was possible to observe that the corrosion properties are similar for both process.