Rodrigo Rangel Porcaro

Envelhecimento por Deformação em Juntas Soldadas de Tubos de Aço API5L X65Q sem Costura

In this work was investigated the influence of the strain ageing on joints obtained by gas-metal arc welding (GMAW) of API 5L X65Q seamless pipes. Specimens were machined from the welded joints, plastically strained to 3% and aged at 250°C for 1h posteriorly, in order to characterize effects of static strain ageing. For the dynamic strain ageing characterization, the specimens were simultaneously strained and aged. Then, the aged specimens were submitted to tensile tests and representative samples were analyzed at a light optical microscope and a scanning electron microscope (SEM). From the results, it was observed that the strain ageing phenomenon changed the volumetric fraction of secondary constituents in the weld metal and in the heat-affected zone, increasing the proportion of ferrite-carbide aggregates. Regarding the mechanical properties, it was noticed that the phenomenon led to higher tensile mechanical properties such as ultimate tensile strength and total elongation and lower elastic ratio, and, therefore, not impaired the mechanical properties under tensile of the welded joints. Comparing the static strain ageing with dynamic strain ageing it was observed that the effect on the plastic straining ability of welds was higher after static strain ageing.

Evaluation of the influence of post welding heat treatments on microstructure and mechanical properties of API 5L X70Q weld joints

Abstract Steels that meet the API 5L standard are employed in pipeline construction, and there is considerable interest in those of higher strength, such as grade API 5L X70Q. There have nevertheless been few studies relating to seamless pipes. During installation, the pipes may be welded with covered electrodes (SMAW) and may optionally undergo inductive heating for adjustment to the topography of the terrain, processes that may alter the microstructure of the joints. In this work, welded joints were obtained by the SMAW process, from seamless pipe of grade API 5L X70Q. The joints were submitted to post-weld heat treatments at temperatures of 920 and 600 °C. Tensile, Charpy impact and microhardness tests were carried out, besides metallographic characterization in specimens of base metal and in the joints, as-welded and after the heat treatments. Heat treatment at 920 °C promoted formation of a ferrite/pearlite structure, with consequent reduction in the mechanical strength of the joints to values below those specified for grade X70Q. However, heat treatment at 600 °C proved to be beneficial owing to the reduction of the volume fraction of the martensite/austenite and martensite-austenite-bainite constituents, without significantly reducing the mechanical strength and with a relative gain in impact toughness in the heat-affected zone and in the fusion zone (FZ).

Strain ageing in welded joints of API5L X65Q seamless pipes

Abstract In this work, we investigated the effects of the phenomenon of strain ageing in joints obtained by gas-shielded arc welding (gas metal arc welding, GMAW), of seamless pipes of API5L X65Q steel. Test specimens obtained from the welded joints were submitted to cold plastic strain of 3% and then aged for 1 h at 250 °C, so as to induce static ageing. For evaluating dynamic ageing, the test specimens were strained to 3% and loading was maintained for 1 h at 250 °C. The aged specimens were submitted to tensile testing and representative samples were examined in the light microscope and the scanning electron microscope. It was observed that the phenomenon altered the volume fraction of secondary constituents in the weld metal and in the HAZ, with increase in the proportion of ferrite–carbide aggregates. Regarding the mechanical properties, it was found that the phenomenon reduced the elastic ratio of the welded joints due to an increase in the ultimate strength, besides increasing the total elongation, but without impairing the tensile properties of the welded joints. On comparing static ageing with dynamic ageing, it was observed that the increase in the capacity for plastic strain of the welded joints was greater after static strain ageing.

DESENVOLVIMENTO DE DISPOSITIVO PARA SOLDAGEM COM ELETRODOS REVESTIDOS POR GRAVIDADE E APLICAÇÃO EM ESTUDO DE METALURGIA DA SOLDAGEM DE AÇO API X65Q

* Contribuição técnica ao 72o Congresso Anual da ABM – Internacional e ao 17o ENEMET Encontro Nacional de Estudantes de Engenharia Metalúrgica, de Materiais e de Minas, parte integrante da ABM Week, realizada de 02 a 06 de outubro de 2017, São Paulo, SP, Brasil. DESENVOLVIMENTO DE DISPOSITIVO PARA SOLDAGEM COM ELETRODOS REVESTIDOS POR GRAVIDADE E APLICAÇÃO EM ESTUDO DE METALURGIA DA SOLDAGEM DE AÇO API X65Q *

ESTUDO CINÉTICO DA LIXIVIAÇÃO DE CALCOPIRITA POR SULFATO FÉRRICO E CLORETO DE SÓDIO

This work aimed at investigating the kinetics of chalcopyrite leaching by ferric sulphate in the presence of chloride ions. That was accomplished through batch tests performed with 0.5mol/L Fe3+ solutions, in which the temperature varied from 60oC to 90oC, whereas the NaCl concentration was increased up to 2mol/L. Chloride ions improved copper extractions, which increased from 16.4% in the absence to 29.4% with 1mol/L NaCl. The experimental data were fitted to the shrinking core model for constant particle size. The leaching kinetics was controlled by chemical reaction on the particle surface with activation energy of 55.6kJ/mol. Chloride ions also increased the reaction rate constant, which was about 1.5 to 2 times that in the absence of chloride and the reaction order was 0.24 with respect to NaCl.

APLICAÇÃO DO MODELO DO NÚCLEO NÃO REAGIDO À LIXIVIAÇÃO DA CALCOPIRITA PELO ÍON Fe+3

Chalcopyrite leaching by ferric iron is considered a slow process with low copper recovery; a phenomenon ascribed to the passivation of the mineral surface during leaching. Thus, the current study investigated the leaching kinetics of a high purity chalcopyrite sample in the presence of ferric sulfate as oxidant. The effects of the stirring rate, temperature, Eh and Fe3+ concentration on copper extraction were assessed. The leaching data could be described by the shirking core model (SCM) for particles of unchanging size and indicated diffusion in the ash layer as the rate-controlling step with a high activation energy (103.9±6.5kJ/mol); likely an outcome of neglecting the effect of particle size distribution (PSD) on the kinetics equations. Both the application of the quasi-steady-state assumption to solid-liquid systems and the effect of the particle size distribution on the interpretation of kinetics data are also discussed.