Abstract The microstructure of the main structural elements (Phoenix columns, transversal beams and tie-rods) of the Simón Bolivar iron bridge, located in Arequipa (Peru), was investigated. The bridge was supposedly designed by Gustave Eiffel and opened to the public in 1882. The characterisation revealed that the columns, beams and tie-rods are made of puddled iron (ferritic matrix of equiaxial grains and numerous slag inclusions). The tensile properties were estimated by hardness and nanohardness measurements, and the tensile strength varied between 285 and 390 MPa and the Young's modulus from 187 to 198 GPa. The components of puddled iron with the same provenance, Phoenix Iron Company, showed typical variations in the chemical composition and microstructure of the slag inclusions. The microanalysis results of the slag inclusions indicated that the wüstite phase presented qualitatively the same composition with pronounced variations in the ratio between V2O5 and TiO2 contents, confirming that a single parameter cannot be used to determine the provenance of iron artefacts. The intense presence of slag inclusions in the puddled iron components (~ 10% in volume fraction) heterogeneously distributed in the iron illustrates the technological limits of the iron refining technique of the time.

Abstract The paper reviews the events that led to the understanding of the recrystallisation of metals throughout history, covering the timeline from 3500 BC until the 1950s and dealing mainly with the misconceptions related to the “recrystallisation” and “amorphisation”. This history begins with the thermomechanical processing of native metals in pre-Columbian America (3,000 BC), and the production of brass coins in Rome (100 BC). The analysis of the fracture surfaces of metals, commonly used between the 16th and 18th centuries in Europe for the quality control of metallic products, is briefly discussed. The observation of crystalline and fibrous fractures lead to the common misconception of the 19th century that “recrystallisation” takes place during the heating of “amorphous” cold-worked metals. The use of reflecting optical microscopy in the late 19th century indicated, however, that the plastic deformation only promotes a morphological change in the microstructure of the metals without any “amorphisation”. In the early 20th century, the plastic deformation of metals by crystal plane slipping and twinning was well documented by metallographic observation during tensile testing. Nevertheless, in 1915, Prof. Rosenhain advocated that the “crystal” inside the slip bands of a plastically deformed metal was “amorphous” and responsible for the work hardening. The discovery of the X-ray diffraction technique, in 1913, allowed to resolve the ongoing dispute of the “amorphisation” of metals during plastic deformation. Between the 1920s and 1950s, X-ray diffraction was practically the only means of studying the internal structure of metals to explain the nature of their plasticity, confirming many aspects of the dislocation theory. This technique was crucially important to understand the atomic crystal structure of metals in the annealed and cold-work states. Our history finishes in the 1950s when the transmission electron microscopy finally revealed the first images of dislocation in metals. Up to that date, most of the understanding of the dislocations’ distribution and organisation in cold-work and annealed states had already been derived from X-ray diffractograms, which gave birth to the modern physical metallurgy.

Abstract Stress corrosion cracking (SCC) of UNS S31603 austenitic stainless steel (ASS), UNS S32205 duplex stainless steel (DSS) and UNS S32750 super duplex stainless steel (SDSS) was investigated. SCC tests were carried out at 110 ºC for 500 h under drops of synthetic seawater (DET, drop evaporation test). Two loading conditions were investigated: 50 % and 100 % of the experimental yield strength of each steel. DSS and SDSS specimens showed no susceptibility to SCC under loading of 50 % of their yield strength, contrary to ASS, but all steels fractured at the highest load. SCC nucleated under the salt deposit formed on the surface of all specimens. SCC propagation was mainly transgranular, but SCC propagation of DSS also featured crack ramification in the austenite phase. In addition, SDSS also presented crack propagation along the ferrite/austenite interfaces. Transgranular cleavage fracture was also observed in all fractured specimens, but DSS also presented ferrite/austenite interfacial brittle fracture, while SDSS also featured intergranular brittle fracture.

This paper studied the effect of the austenite grain refinement on the tensile and impact properties of a cast Hadfield steel (12 % Mn, 1.2 %C and 0.65 % Si). The austenite grain refinement was obtained by hafnium inoculation. Microstructural characterization showed that the Hf-refined cast Hadfield steel featured a grain size of 600 µm, while the non-refined condition presented a grain size of 3000 µm. Mechanical test results indicated that the austenite grain refinement promoted an increase in the values of the yield stress (6%), the ultimate tensile strength (37%), the toughness (88%), the work-hardening coefficient (50%) and the Charpy absorbed energy (15%). Microscopic characterization of the fractured test-pieces indicated that the grain refinement increased the proportion of plastic deformation by the twinning mechanism and furthermore improved the values of the mechanical properties of the cast Hadfield steel considerably.

Abstract The thermodynamic optimization of Ti-X-Si systems requires that their respective binary systems be constantly updated. The most recent assessments of the Ti-Si phase diagrams used three sublattices to describe the Ti5Si3 phase. The stable version of this phase diagram indicated the presence of Ti(β)+Ti5Si3→Ti3Si and Ti(β)→Ti(α)+Ti3Si reactions in the Ti-rich corner, while the metastable version featured the presence of a Ti(β)→Ti(α)+Ti5Si3 reaction. The present investigation assessed these phase diagrams using two sublattices to describe the Ti5Si3 phase in order to simplify the optimization of Ti-X-Si systems.

Microstructural characterization techniques, including EDX (Energy Dispersive X-ray Analysis) microanalyses, were used to investigate the slag inclusions in the microstructure of ferrous artifacts of the Royal Iron Factory of São João de Ipanema (first steel plant of Brazil, XIX century), the D. Pedro II Bridge (located in Bahia, assembled in XIX century and produced in Scotland) and the archaeological sites of São Miguel de Missões (Rio Grande do Sul, Brazil, production site of iron artifacts, the XVIII century) and Afonso Sardinha (São Paulo, Brazil production site of iron artifacts, XVI century). The microanalyses results of the main microconstituents of the microstructure of the slag inclusions were investigated by hierarchical cluster analysis and the dendrogram with the microanalyses results of the wüstite phase (using as critical variables the contents of MnO, MgO, Al2O3, V2O5 and TiO2) allowed the identification of four clusters, which successfully represented the samples of the four investigated sites (Ipanema, Sardinha, Missões and Bahia). Finally, the comparatively low volumetric fraction of slag inclusions in the samples of Ipanema (~1%) suggested the existence of technological expertise at the ironmaking processing in the Royal Iron Factory of São João de Ipanema.

Abstract The thermodynamic optimization of Ti-Si-X systems requires that their respective binary systems are constantly updated. The Ti-Si system has been experimentally investigated since the 1950s and these critical experimental data can be employed to calculate the Ti-Si phase diagram using thermodynamic modeling. The most recent assessment of the Ti-Si system was performed in 1998, showing the presence of stoichiometric Ti3Si as stable phase. In the light of the dispute over the stability of Ti3Si phase in the eutectoid reaction of the Ti-Si and Ti-X-Si systems, the present work assessed the Ti-rich corner of the "stable" (featuring Ti3Si phase) and "metastable" (featuring Ti5Si3 phase) Ti-Si phase diagrams. The phase boundaries, the values of the error of the least-square method of the optimization procedure and the relative standard deviation of the calculated variables of the assessed diagrams; and previous investigations were discussed in order to inspire further experimental work on the eutectoid reaction of the Ti-Si phase diagram.

Microstructural characterization is an important tool to optimize the properties of engineering materials. Metallography is a common technique, but it provides two-dimensional images from (sometimes complex) three-dimensional microstructures. Three-dimensional reconstruction of microstructures provides more precise informa tion on the morphologies of the material microconstituents, providing more accurate control over their physical and mechanical properties. The main barrier for the dis semination of this technique is the extensive time dispended to obtain a record of in numerous metallographic polished planes and the 3D image reconstruction procedure. The present work shows a practical example of three-dimensional reconstruction of the graphite phase in a compacted graphite cast iron executed by "manual" technique and using optical microscopy.

ResumoA presente investigação analisou artefatos de ferro coletados em dois sítios arqueológicos na Montanha de Araçoaiaba. Uma metodologia conhecida foi adaptada para investigar várias amostras coletadas na Real Fábrica de Ferro de São João do Ipanema e no sítio de Sardinha. Resultados de microanálise EDX de inclusões não metálicas foram inseridos em gráficos bivariantes. Regressão linear (com e sem a restrição de intersecção pela origem) e testes de significância do intercepto da reta foram usados para interpretar esses resultados. Essa análise não permitiu identificar a assinatura dos sistemas produtivos de Sardinha e Ipanema. A presença de inclusões ricas em Ti foi uma característica típica dos artefatos coletados no sítio de Sardinha.

AbstractThe present investigation analysed iron artefacts collected in two sites around Araçoaiaba Hill. A known methodology was adapted to investigate several samples collected at the Royal Iron Factory of São João do Ipanema and Sardinha sites. EDX microanalysis results of non-metallic inclusions were plotted in bivariate graphs. Linear regression (with and without the zero-intercept constraint) and line intercept significance tests were applied to interpret these results. The analysis did not allow the identification of the provenance of the production systems of Sardinha and Ipanema sites. The presence of Ti-rich inclusions was an unambiguous attribute of the samples collected at the Sardinha site.

O efeito do tratamento térmico de solubilização sobre a resistência à corrosão por pite do aço inoxidável austenítico 17Cr-6Mn-5Ni-1,5Cu foi avaliado em solução de 0,6M NaCl. O aço UNS S30403 (304L) foi usado como referência. Foram realizados tratamentos térmicos de solubilização (TTS) a 1010°C, 1040°C, 1070°C e 1100°C. A caracterização microestrutural revelou a presença de ferrita δ, especialmente na condição tal como recebida (TCR), observou-se que os TTS diminuíram a quantidade de ferrita. Também foram observados precipitados ricos em Mn na condição TCR do aço 17Cr-6Mn-5Ni-1,5Cu, os quais foram dissolvidos pelos TTS, causando o enriquecimento localizado da austenita em Mn. Os testes potenciodinâmicos mostraram que o potencial de pite (Ep) do aço 304L não foi alterado significativamente após TTS. Por outro lado, o valor de Ep do aço 17Cr-6Mn-5Ni-1,5Cu diminuiu após os TTS. Esse efeito detrimental foi explicado pelo enriquecimento em Mn das áreas ao redor dos precipitados dissolvidos, o que promoveu a adsorção mais intensa de Cl- nessas regiões.

The effect of solution heat treatment on the pitting corrosion resistance of 17Cr-6Mn-5Ni-1.5Cu austenitic stainless steel in 0.6M NaCl aqueous solution was evaluated. UNS S30403 (304L) steel was used as benchmark material. Solution heat treatments (SHT) were conducted at 1010°C, 1040°C, 1070°C and 1100°C. The microstructural characterization revealed the presence of δ-ferrite, especially in the asreceived condition (AR). The SHT decreased the proportion of the ferrite phase. Mnrich precipitates were observed in the as-received condition of 17Cr-6Mn-5Ni-1.5Cu steel, but they were dissolved after the SHT, causing localized Mn enrichment in the austenite. Potentiodynamic tests showed that the pitting potential (Ep) in the 304L steel was not altered significantly after SHT. On the other hand, the value of Ep of the 17Cr-6Mn-5Ni-1.5Cu steel decreased after SHT. This detrimental effect was explained by the formation of Mn enrichment areas due to the solubilization of Mn-rich precipitates, which promoted preferential Cl- adsorption in these regions.