Luiz Cláudio Cândido

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.

Avaliação da Influência de Tratamentos Térmicos Pós-Soldagem Sobre a Microestrutura e Propriedades Mecânicas de Juntas de um Aço API 5L X70Q

Pipelines for oil and gas conduction are manufactured of steel tubes that meet the API 5L requirements. Currently, much of the research related to the materials used in this industry is target to steels with higher tensile strength such as API 5L X70Q. But studies related to seamless pipes remains rare. During the manufacture of the pipelines, the pipes are usually welded by the SMAW process and may be heated by the inducted bending process to fit the topography of the land, processes that can change the proportion or morphology of the constituents in the heat affected zone (HAZ) and in the fused metal. The present study used an API 5L X70Q seamless steel manufactured by the Mannesmann Process to produce weld joints by the SMAW process. The joints were subjected to post weld heat treatments in the temperatures of 920 °C and 600 °C. Mechanical tests which included tensile test, Charpy impact and microhardness were applied, in addition to microstructure evaluation in the joints as welded and after heat treatments. The results showed that the first heat treatment (920 °C) promoted the formation of structure ferrite/pearlite, which reduced the mechanical properties to values under the specified for materials API grade X70Q. The second heat treatment (600 °C) was feasible in reducing the volume fraction of the Martensite-Austenite and Martensite-Austenite-Bainite constituents, without significant reduction in mechanical strength of the welded joints and with significant gain in impact toughness in the HAZ and in the weld metal.

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 *

Avaliação da integridade estrutural do quartzito Itacolomi empregado em monumentos históricos de Ouro Preto sem e com colagem usando diferentes resinas

The art of carving stone using itacolomi quartzite was employed in the monuments of Ouro Preto city in Minas Gerais. More than 350 years after being built, some of these monuments are in an advanced stage of deterioration. In the restoration of these buildings, some restaurateurs employ orthophthalic polyester resin. In the present study, both non-glued and glued (using different types of resins) itacolomi quartzite were submitted to a flexion strength test. After some trials, it was verified that the resins supported greater loads than the quartzite. All specimens broke outside the resins application area, thus confirming the effectiveness of resin adherence to rock.

Avaliação da integridade estrutural da Ponte Marechal Hermes - rio São Francisco/MG

Its known that the degradation, which occurs in steel bridge structures, is a worldwide problem. This happens for several reasons such as the bridges advanced age, the increase of the traffic weight, environmental attacks and, sometimes, because of designs, inadequate detailment and construction of structures. In order to solve these problems, different procedures in inspection of bridges have been used in different countries. In Brazil, however, it seems there is not any concern about keeping the integrity of the structures, not being commonly used proper procedures such as inspections and maintenance of the structures that can affect its safety, causing the need of more severe and expensive repairs. This research intends to make a diagnosis and propose solutions, which aim for the least occurrence of the corrosion developed by Marechal Hermes Bridge (Sao Francisco River). Therefore visits were made in locus, in which visual inspection, screen and photo registers, the information necessary for the analysis, were collected. Some samples were also collected and than, chemical, mechanical and metalographic characterizations were made on the steel used on the bridge, besides the analysis of the corrosion. The numerical modeling was made by using the finite element method, which aimed to analyze the structural behavior of the bridge with or without damages made by corrosion in these areas. There were made tests with salt spray in different systems of painting which aims to identify the best procedure of covering in order to protect the bridge. It was verified that the use of etil silicate of zinc, with primer epoxy-amide, rich in zinc and aliphatic varnish polyurethane was the one which presented the best performance.

Tenacidade à fratura e crescimento de trinca por fadiga de dois aços bifásicos de emprego automotivo

Fracture toughness J Q and fatigue crack growth da/dN x ∆K have been studied in two dual-phase steels used in the automotive industry, with 8.8% to 12.5% of martensite volumetric fraction. The main difference between the steels is the chemical composition: one of the steels had chromium additions while the other had silicon as an alloy element. Silicon steel presents higher fracture toughness than chromium steel. It was not noticed significant effect of anisotropy in both steels, while an increase of side grooves decreased the value of J Q of the materials. The two steels present a similar behavior in fatigue crack growth resistance with no significant effect of anisotropy. An increase of R ratio increased the crack growth rates and decreased the value of ∆K th of the materials.