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 High Strength Low Alloy steels (HSLA) for oil and gas pipelines should display high mechanical strength, toughness, ductility and weldability. In this work we studied the influence of quenching and tempering temperature on the yield strength, ultimate tensile strength, percent elongation and hardness of API 5L steel pipes in order to optimize heat treatments to be performed after hot induction bending of the material. The thermal cycles involved soaking temperatures of 880, 920 and 960 °C, cooling water at 15, 23 and 31 °C and tempering at 530, 600 and 670 °C. From this, experimental design techniques were used to reduce the number of experiments. The results from contour maps suggest that soaking temperatures of 910 and 950 °C and tempering between 540 and 610 °C were the most suitable for treatment, regarding mechanical strength. The variation of the water temperature was not significant for the assumed cooling conditions. The prediction regression models of the mechanical properties from the variables involved in the heat treatments showed a good fit between the experimental and predicted results, with correlation coefficient between 0.89 and 0.94.

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 API 5L X70 steel is used in high-pressure gas transmission pipelines. Because of this, knowledge of presence of residual stress and their magnitude is important to assess the material integrity in service. For the pipeline manufacturing, tubes need to be curved which is often made using the hot induction bending process. This process can introduce different residual stress depending of tube position. For this research, in order to evaluate the residual stress, was used an API 5L X70 tube that was previously curved by hot induction process. Samples were taken from the extrados, intrados, neutral line and straight section of the curved tube. Residual stresses were studied by two conventional methods: X-Ray Diffraction (XRD) and Hole-Drilling, which are destructive and non-destructive methods, respectively, in order to assess their qualitative responses. Each of these methods presents particular methodologies in sample preparation and material analysis, but also they differ in factors such time consumption and cost of the analysis. The qualitative responses obtained by the two different methods were comparable and satisfactory and pointed out the existence of a compressive residual stress state in steel pipe.

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 effects of asymmetric and conventional deformations and annealing on the microstructure of non-grain-oriented (NGO) 3 wt% silicon steel were analyzed by x-ray diffraction, optical microscopy and magnetometry. The results suggest that pure asymmetric rolling tends to lessen magnetic losses. However, intermediate annealing resulted in lower planar anisotropy, which could be estimated from the magnetic anisotropy theory. In this work, it was shown that this theory is able to predict the J50 magnetic polarization values using crystallographic texture.

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.

Dislocations are responsible for most aspects of plastic deformation in metals. In this work, the dislocation density, ρ, in brass was estimated after different deformation processes via line broadening of X-ray diffractograms using the Convolutional Multiple Whole Profile Program (CMWP) and by Transmission Electron Microscopy (TEM). In addition, we attempted to evaluate, on a global basis, the influence of crystallographic texture in ρ analysis, making sure that the results obtained by XRD could be trusted even in samples with moderate levels of texture. For this, we compared the ρ values for α brass samples (66% Cu and 34% Zn) with different levels of texture, one deformed by cold rolling and the other by equal channel angular extrusion (ECAE).The results suggest that using CMWP program it was possible to satisfactorily estimate the dislocation density in α brass. It also the was shown that the results by XRD and by TEM were self-consistent in two samples texturized to different degrees.

The influence of hot-band grain size and additions of aluminum and manganese on the magnetic properties of non-oriented grain (NOG) low-carbon electrical steel with about 3 wt. (%) Si were investigated using optical microscopy and X ray diffraction. The addition of manganese resulted in larger grains after final annealing. Coarse grains in the hot-band and addition of Mn led to a Goss orientation component after final annealing, which resulted in an increase in the magnetic permeability.