Effect of volume fraction of phases and precipitates on the mechanical behavior of UNS S31803 duplex stainless steel.

Mechanical properties of a grade UNS S31803 duplex stainless steel were studied. Samples were annealed at three different temperatures, 1060 C, 1200 C, and 1300 C, to change the a/c proportion, to precipitate undesirable phases (for example, a0 , r and chromium nitrides), and to study the effect of the microstructure on the mechanical behavior. Specimens with a thickness of 1.8 mm were prepared according to ASTM standards and tested at room temperature. Tensile tests were conducted using displacement control at a rate of 5 mm/min. Force-controlled constant amplitude axial fatigue tests were conducted at a frequency of 30 Hz and an R stress ratio of 0.1. Microstructural analyses, performed by optical microscopy and scanning electron microscopy, showed the following modifications to the microstructure: changes in the phase volume fractions, the phase grain growths, and the morphology of the c-phase and the precipitation of chromium nitrides in the a-phase. The mechanical properties of the steel were significantly changed due to the changed microstructure. The results demonstrate the sensitivity of the steel to the annealing temperature

Corrosion behavior of UNS S31803 steel with changes in the volume fraction of ferrite and the presence of chromium nitride.

The goal of this study was to examine the changes caused in stress corrosion cracking and the critical pitting temperature behavior of a UNSS31803 duplex stain less steel due to variations in the ferrite fraction and the presence of chromium nitride in their microstructure. The steel plates were cold rolled and annealed at 1060 °C. Microstructural variations in the plates were produced by thermal annealing treatments a t1200 °C and 1300 °C. Steel annealed at 1060 °C showed greater resistance to stress corrosion cracking than steel annealed at 1300 °C. Steel annealed at 1300 °C had the lowest critical pitting temperature

Inspection of steel bridge railway verification of carrying capacity of the “Bridge of Barra” in Ouro Preto/MG.

Esse trabalho procurou diagnosticar os fenômenos patológicos apresentados pela “Ponte da Barra” (ponte metálica restaurada e reforçada para implantação da Ferrovia Turística Cultural entre Ouro Preto e Mariana/MG) e apresentar soluções para o combate a tais fenômenos. Para o cadastro da ponte, foram identificadas, por inspeção visual e registros fotográficos, as patologias presentes. Também foi realizada a modelagem numérica através de elementos finitos (elemento de barra com seis graus de liberdade por nó), visando a analisar o comportamento estrutural da ponte antes e após reforço estrutural. Dessa maneira foi possível fazer a avaliação da estabilidade da mesma e, também, a avaliação da eficiência do reforço estrutural proposto. A análise numérica foi viabilizada através de parâmetros levantados in loco, como geometria, propriedades mecânicas e fatores patológicos. Os estudos laboratoriais, como caracterização química, ensaio de tração, análise metalográfica e dos produtos de corrosão, foram determinadas através de amostras do aço de elementos estruturais da própria ponte. Observou-se que o sistema de curva tensionada utilizado para reforço estrutural agravou, sistematicamente, a estabilidade global da ponte, introduzindo acréscimo de carga aos elementos estruturais mais críticos.This work sought to diagnose and propose solutions for the pathological phenomena occurring on the bridge “Ponte da Barra” (a metallic bridge that was restored and reinforced for use by the Tourist- Culture Railroad between Ouro Preto and Mariana/MG). To obtain the bridge profile, a visual inspection and photographic registers were performed to evaluate existing pathologies. Numerical modeling was also performed, using finite elements (bar elements with six degrees of freedom per node), aiming to analyze the bridge’s structural behavior before and after reinforcement. This permitted evaluation of the bridge’s stability as well as the efficiency of the structural reinforcement proposed. The numerical analysis proved feasible when parameters measured in situ, such as geometry, mechanical properties and pathological factors were implemented. The laboratory studies, such as: chemical characterization, stress tests, metalographic analysis, and corrosion, were performed using steel samples from the bridge’s structural elements. The conclusion reached was that the Rigid Tension Curve System used for structural reinforcement systematically diminished the overall stability of the bridge, introducing a load increase on the most critical structural elements

Microstructure and mechanical properties of two Api steels for iron ore pipelines

This research compares the mechanical behavior of two API steels (X60 and X70) used in the longest pipeline in the world for the conveyance of iron ore. Tensile tests, Charpy impact tests, CTOD tests and fatigue crack growth tests are performed at ambient temperature. Metallographic examination showed a banded microstructure consisting of polygonal ferrite and pearlite in both steels, with smaller grain size and the presence of a small quantity of bainite in the X70 steel. All the mechanical tests revealed a ductile behavior for the two steels. The X70 steel is preferable for the pipeline project, due its better mechanical resistance, with no significant loss of fracture toughness and fatigue resistance. Its performance could be even better, if an appropriate combination of thermomechanical processing parameters were able to produce a microstructure with minor amount of pearlite, where acicular ferrite/bainite are present