RESUMO Nos últimos anos, vários estudos foram realizados buscando reduzir o peso de veículos automotores, a fim de diminuir as emissões de poluentes. Neste cenário os aços de baixa densidade do sistema Fe-Mn-Al-C podem ser considerados uma alternativa promissora para suprir essas exigências da indústria automotiva. Geralmente, nos aços de baixa densidade, uma quantidade considerável de alumínio é adicionada a fim de reduzir a densidade geral do aço. No entanto, altos teores de alumínio promovem características distintas na microestrutura, destes aços quando comparados aos aços convencionais, como a presença do carboneto k ((Fe, Mn)3AlC), além da necessidade de se entender a combinação deste elemento com outros elementos de liga que podem ser adicionados. Neste contexto, este trabalho tem como objetivo avaliar a microestrutura, a dureza e a densidade resultantes em função da influência do Al e do Nb em uma nova composição química pertencente ao sistema Fe-Mn-Al-C, na condição trabalhada a quente, a partir de análises de difração de raios X, microscopia eletrônica, medidas de dureza e densidade por princípio de Arquimedes. Os resultados permitiram indicar que o alto teor de Al adicionado promoveu uma redução de cerca de 13% na densidade, em relação aos aços estruturais tradicionais, e a estabilidade da ferrita δ até a temperatura ambiente. A condição avaliada apresentou a temperatura ambiente uma microestrutura formada por uma matriz de ferrita δ e α, juntamente com precipitados de carboneto k (AlFe3C) e carboneto de nióbio (NbC), estes dois últimos devido as adições de Al e Nb, resultando em uma dureza de 59,4 ± 1 HRA e uma estimativa do limite de resistência a tração de próximo a 800 MPa – dentro da faixa dos aços avançados de alta resistência (Advanced High Strenght Steels – AHSS).

ABSTRACT In recent years, several studies have been carried out seeking to reduce the weight of motor vehicles to reduce pollutant emissions. In this scenario, low-density steels from the Fe-Mn-Al-C system can be considered a promising alternative to meet these requirements of the automotive industry. Generally, in low-density steel, a considerable aluminum amount is added in order to reduce the overall density of the steel. However, high aluminum contents promote distinct characteristics in the microstructure of these steels when compared to conventional steels, such as the k carbide presence ((Fe,Mn)3AlC), in addition to the need to understand the combination of this element with other alloying elements that can be added. In this context, this paper aims to evaluate the resulting microstructure, hardness and density as a function of the Al and Nb influence in a new chemical composition belonging to the Fe-Mn-Al-C system, in hot worked condition from X-ray diffraction and eletron microscopy analyses, hardness, and density measurements by Archimedes’ principle. The results indicated that the high added Al promoted a reduction of about 13% in density, in relation to typical structural steels, and the δ ferrite stability up to room temperature. The condition evaluated at room temperature presented a microstructure formed by a matrix with δ and α ferrite, together with k-carbide (AlFe3C) and niobium carbide (NbC) precipitates, the latter two due to the Al and Nb additions, resulting in 59.4 ± 1 HRA hardness and an estimated tensile strength limit close to 800 MPa – within the range of the Advanced High Strength Steels (AHSS).

ABSTRACT During production and heat treatments of aluminum alloys, numerous second phase particles form, which maximizes their mechanical properties. This work aimed to perform a correlation between Vickers hardness and X-ray diffraction results, when 7475-T7351 aluminum alloy processed by the cross rolling is subjected to annealing heat treatments (AHT) at 500 °C for different soaking times (15, 30 and 60 minutes) and for a soaking time of 15 minutes at different temperatures (200, 300 and 400 °C). The influence of the AHT (500 °C / 15 minutes) on the microstructure, via scanning and transmission electron microscopy, and tensile tests properties was also investigated. The results show evidence that the Vickers hardness decreased for AHT performed at 200 and 300 °C / 15 minutes and increase for greater temperatures and times. This behavior is probably due to modifications in the constituent/dispersoid particles and aluminum matrix observed from the X-ray analysis. Partial recrystallization and a coarsening of the precipitates was observed after the AHT at 500 °C / 60 minutes, whose brought harmful effects on the tensile mechanical properties.

Abstract In this work, the residual stress study by XRD was carried out after martensitic transformation of a 304L steel subjected to plastic strain by rolling and tensile test, at room and cryogenic temperatures. This article intents to contribute with the understanding of residual stresses generated by martensitic transformation induced by plastic deformation due to its complexity. From the experimental conditions employed, it was possible to obtain high martensite volumetric fraction and it was possible to observe the influence of existing phases on the performance of residual stress measurements. In general, compressive residual stress was observed for both austenite and martensite phases. The samples rolled at cryogenic temperature showed higher magnitudes of compressive stresses, between -123 and -231 MPa, for martensite volumes between 98 and 100%. It was also clearly displacement and widening of diffraction line due to the presence of residual macro and microstresses when compared to the as-received material.

RESUMO O aço inoxidável austenítico 304L é suscetível à transformação martensítica induzida por deformação. Esta transformação de fases depende da temperatura, assim como do modo, taxa e nível de deformação. Neste trabalho as fases e tensões residuais de um aço TRIP 304L, em que a transformação martensítica foi induzida por laminação a frio, foram investigadas por difração de raios-X (DRX). As análises foram realizadas em diferentes espessuras das amostras. Os resultados mostraram que a composição de fases e as tensões residuais são fortemente dependentes da espessura das amostras. Todas as amostras apresentaram tensão residual compressiva.

ABSTRACT The 304L austenitic stainless steel is susceptible to deformation induced martensitic transformation. This phase transformation depends on the temperature as well as on the mode, rate and level of deformation. In this work the phases and residual stresses of a 304L TRIP steel where martensitic transformation was induced by cold rolling were investigated by X-ray diffraction XRD. The analyses were performed for different sample thicknesses. The results showed that the phase composition and the residual stresses are strongly dependent on sample thickness. All samples showed a compressive residual stress.

The 304L austenitic stainless steel is susceptible to mechanically induced martensitic transformation from slightly above room temperature down to cryogenic temperatures. In this work, austenitic 304L steel produced by two different thermomechanical processes, hot rolling (HR) and cold rolling and annealing (CR/A), were subjected to martensitic transformation by rolling and by tensile tests at 298 K and 155 K and the volume fraction of martensite was determined by X-ray diffraction and ferritescope measurements. The results showed that the martensitic transformation was complete for CR/A samples rolled at 155 K and that the volume fraction of martensite was larger in CR/A samples than in HR samples in all cases.

ABSTRACT Samples of the Al 7075 naturally and artificially aged were processed by conventional and asymmetrical rolling with 5% of thickness reduction. The rolling processes were evaluated under room temperature and under warm condition (130°C). Mechanical properties were evaluated by uniaxial tensile and Vickers microhardness tests. Microstructure evolutions were followed by optical microscopy analysis. Naturally aged samples showed better yield strengthening under warm processing. Greater ultimate stress and ductility under room temperature processing was also noticed in naturally aged specimens. Artificially aged samples showed better mechanical properties under room temperature, softening under warm processing due to grain recovery process. Microhardness tests showed expected results for both rolling types, especially on asymmetrical rolling with the higher predictions were observed. Micrographs have shown no expressive grain changes or refinement although its flattening was observed. Precipitates were analyzed by EDS/SEM revealing the presence of MgZn2 and CuMgAl along the matrix that provides plastic strengthening.

In the present study, poly (ethylene terephthalate)-based composites were produced and characterized. These composites were composed by poly (ethylene terephthalate) (PET) reinforced with geopolymer concrete waste (GCW). Both untreated (U-GCW) and treated with oleic acid (OA) geopolymer concrete waste (T-GCW) were used in the production of the composites. The PET/GCW ratios used for either treated or untreated GCW bodies were 80/20 (wt%), 60/40 (wt%) and 50/50 (wt%). Chemical compositions were assessed by X-ray fluorescence spectroscopy (XRF), crystallinity by differential scanning calorimetry (DSC), thermal stability by thermogravimetry (TGA), microstructure by field emission gun scanning electron microscopy (FEG-SEM) with energy dispersive X-ray spectroscopy (EDS), and mechanical properties were assessed by compression tests. Fourier transform infrared spectroscopy (FT-IR) was used to check the efficiency of the treatment with OA, as well as the interaction between PET and GCW. The T-GCW PET composites showed better thermal, physical, and mechanical properties, for non-structural applications, when compared to U-GCW.

Two distinct AISI type 316 stainless steels, of Brazilian and Swedish origins, were compared regarding their creep fracture mechanisms at 600, 700 and 800°C. The possible mechanisms associated with the creep fracture strength were identified by means of fracture maps proposed either by Ashby and collaborators or by Miller and Langdon. Experimental creep results were consistent with the general Ashby and collaborators map for face centered cubic alloys. By contrast, the two different 316 steel displayed significant differences in the model-based map of Miller and Langdon. In the present work, changes in the maps frontier are proposed as well as the introduction of a new field in the map related to grain boundary precipitation. These propositions allowed the Miller and Langdon map to be coherent with the experimental creep fracture results of both 316 stainless steels.

Abstract The crystallographic texture developed during cold rolling and subsequent annealing of interstitial free sheet steels aims to increase conformability. For this, it is necessary to obtain partial α-fiber and continuous and homogeneous γ-fiber texture components. In this work, the influence of symmetric (SR) and asymmetric (AR) cold rolling on crystallographic texture and mechanical properties of an interstitial free steel (IF) was investigated. Symmetric cold rolling yields α- and γ-fibers, which are enhanced as deformation increases. Moreover, α-fiber weakening occurs due to recrystallizations, improving formability. The same fibers are produced by asymmetric cold rolling, but in this case, the γ-fiber is slightly shifted in psi, which is one of Euler angles second ROE's notation1,2, and more homogeneous than in symmetric rolling. The best mechanical properties were achieved by asymmetric cold rolling/annealed with about 80% deformation.

The metastable 304L austenitic stainless steels are susceptible to phase transformation induced by plastic deformation. The traditional metallographic preparation, via mechanical methods, introduces superficial plastic deformation from grinding and polishing. It is important to evaluate this effect on the results of quantitative analysis of martensite formed in 304L steels and similar alloys. In this work, phase transformation was induced by a tensile test at room temperature with two different plastic deformation rates in order to provide distinct structural conditions for the proposed analysis. X-ray Diffraction (XRD) and Ferritescopy were used to determine the volume fraction of martensite in samples with and without metallographic preparation. The results show that the analyses quantitative were not affected by metallographic preparation.