Showing papers by "Paulo José Modenesi published in 2015"

Effect of flux density and the presence of additives in ATIG welding of austenitic stainless steel

Abstract: Active flux TIG (ATIG) welding is a simple variant of the conventional TIG process that allows increased penetration of the weld and enables welding in one pass, with total penetration and without chamfer opening, for joints with thicknesses of 5 mm or more. Different mechanisms have been proposed to explain this effect, with emphasis on contraction of the arc due to the presence of negative ions and alteration in the movement of liquid metal in the weld pool, associated with variations of surface tension as a function of temperature. This study evaluates the effect of the amount of one flux of one component (Cr2O3) placed on the surface of the work piece, and the additions of KClO4 and Al2O3, on the shape of the weld bead. Three sets of bead-on-plate weld tests were performed on 5-mm-thick ABNT 304 stainless steel plates. In the first set, the amount of flux used varied; in the second set, the effect of the additions of KClO4 was studied; and in the third, Al2O3. Electric current and voltage were measure...

Microstructure characterization of a duplex stainless steel weld by electron backscattering diffraction and orientation imaging microscopy techniques

Abstract: This paper describes the electron backscatter diffraction (EBSD) technique used to characterize the microstructure (especially the morphology and constitution) of the base metal (BM), the heat-affected zone (HAZ) and the fusion zone (FZ) on a lean duplex stainless steel (LDX). This technique provides advantages due to its simplicity of use and greater depth of information, thereby increasing the amount of information obtained by traditional characterization techniques such as optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The use of EBSD together with orientation imaging microscopy (OIM) as a tool to understand phase transformation paths and ferrite-austenite variant selection was discussed. Vickers microhardness measurements were performed and no significance difference between the different zones was found. Orientation distribution function (ODF) results show that there are no significant changes on the crystallographic texture of the samples after welding. The advantages of using SEM together with EBSD for microstructure analyzing and texture development were also discussed.

The chemistry of TIG weld bead formation

Abstract: TIG welding has high levels of stability and permits more refined control than the majority of other arc welding processes. However, it is well known that small changes in the chemical composition of the base metal and arc operating region can have a pronounced effect on the resulting weld bead shape, which reduces the ability to control and predict the process. Obviously, this reduces the reliability and controllability of TIG welding. This study reviews the variability of weld beads obtained in the TIG process, with small changes in chemical composition of the base metal, and A-TIG and TIG weldings with active gas. Aspects that are similar and unique to each case are highlighted and discussed. The mechanisms of weld bead shape presented in the literature are also presented and compared.

An investigation of bending fatigue crack propagation in structural steel by the measurement of indirect parameters

Abstract: This work analyzes procedures to monitor fatigue crack propagation in smooth specimens made of high-strength structural steel based on the measurement of variations in the induced moment at the fixed support. Bending fatigue tests were performed with strain control for eight different levels of strain amplitude. The moment at the support was recorded during each test and the number of cycles to fracture determined. For each strain amplitude, the average moment at the support was plotted against the time and the point where a significant decrease occurred in the specimen flexibility was identified. From these results, a curve indicating the initial crack detection was built. To verify in each curve the relationship between the crack size and corresponding number of cycles, a set of interrupted fatigue tests was performed. Crack size and position were marked by specimen heating and oxidation followed by cycling to final fracture and fracture surface analyses. The initial results indicate that this methodology can identify the transition from the fatigue crack initiation to the propagation phase.