Célio de Jesus Marcelo

Estudo Numérico e Experimental da Evolução Microestrutural e das Propriedades de Juntas Soldadas de Vergalhões pelo Processo GMAW

This work is a study of rebar CA-50 class of steels SAE 1026. To better control the mechanical properties of the weld was carried out this study, knowledge of certain variables is very important to find the optimal parameters of welding, and the results microstructure and therefore on the mechanical properties of the welded joint. For this study was conducted a study of the material as received for establishing a solid basis for comparison. Welding the material using argon as protective gas of 20% carbon dioxide was performed, the wire used was ER70S-6 coppered, welded joints were of the type with crossover temperature monitoring thermocouple through two distinct thermal contributions. A computational numerical code was developed to simulate the phenomena occurring in the process (temperature gradient, phase transformations, heat transfer). Welded joints did not show how fragile martensite phase, the weld metal showed dendritic structure, the ZTA presented two distinct regions with different grain sizes all this due to the temperature gradient, which also originated distinct characteristics of the weld bead, ZTA, stages formed and different grain sizes.

Numerical and experimental study of the microstructural evolution and the properties of joints welded on rebars using the GMAW process

Abstract This paper is a study of CA-50 rebars from SAE steel grade 1026. This study was carried out in order to improve the control of the mechanical properties of welded joints. Knowing certain variables are very important when it comes to finding the ideal welding parameters and the respective microstructural results, and consequently for the mechanical properties of welded joints. In order to carry out this study, a study of the material as received was carried out in order to establish a solid basis for comparison. The material was welded using argon as the shielding gas with 20% carbon dioxide. The wire used was copper-covered ER70S-6, and the welded joints were lap joints. The temperature was monitored using thermocouples for two different heat inputs. A numerical computer code was developed to simulate the phenomena that occur during the process (temperature gradient, phase transformations and heat transfer). The welded joints did not introduce martensite as a brittle phase, the weld metal had a dendritic structure, the heat-affected zone (HAZ) had two different zones with different grain sizes. All of this was due to the temperature gradient, which also led to different characteristics in the weld bead, HAZ, phases formed and different grain sizes.

Evaluation of Residual Stresses in Welded ASTM A36 Structural Steel by Metal Active Gas (MAG) Welding Process

The use of structural steel in the industry is increasing every day, and the study of stress state after welding has been shown to be of great importance. Nondestructive techniques become quite appropriate to be performed before and during the service component of welded, and thus ensure its integrity. The magnetic technique to be nondestructive, and easy to apply in the field, has potential to be an inspection tool for measuring residual stresses and other microstructural parameters. In this work it was possible to analyze the state of residual stresses through nondestructive techniques, Magnetic Barkhausen Noise and X-ray Diffraction, as well as the semi-destructive technique, high speed hole drilling method, and thereby determine the residual stresses in ASTM A36 steel plate welded by MAG (Metal Active Gas) process.

Characterization of Residual Stresses and Microstructural by Technique of Magnetic Barkhausen Noise of API 5L X80 Steel Heat Treatment

Residual stresses typically are generated during the manufacturing process of mechanical components. The non-destructive techniques are quite sensitive to these residual stresses, and to microstructural changes resulting from thermal cycling. In this work, samples of API 5L X80 steel were exposed to several conditions of cooling, under water, air and oil, thus obtaining different microstructures and different levels of residual stresses. The residual stress measurements were made using the methods of Magnetic Barkhausen Noise and X-ray diffraction.

Secondary Austenite Precipitation during the Welding of Duplex Stainless Steels

In this work a multipass welding procedure was carried out on a 2205 Duplex stainless steels (DDS) plate. Due to the reheating cycle caused by the adopted procedure, it has favored the precipitation of secondary austenite at the weldment microstructure, besides of encouraging the grain growth at the heat affected zone (HAZ).

Grain Growth Kinetics of (NdPr)2Fe14B Magnets

Two different effects need to be considered in the sintering: (i) The densification should be maximum, to optimize the energy product BHmax and the remanence, however, (ii) the .grain size should be small, in order to maximize the coercivity. Grain growth takes place during the sintering step of the magnets, usually performed at the range 1000-1100°C. In this study, the grain growth kinetics is investigated. Samples of NdPrFeB magnets (proportion 3 Nd : 1 Pr) were heat treated at the temperature of 1050 °C, for times between 1 to 12 hours. The knowledge of the grain growth and coarsening kinetics allows extrapolation to other temperatures, and this information is helpful to maximize coercivity and remanence at the same time.