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American Society for Testing and Materials

Twenty-five years of ultrafine-grained materials: achieving exceptional properties through grain refinement

http://doras.dcu.ie/17608/1/Final_Version%2C_Review_paper.pdf

Optimization of different welding processes using statistical and numerical approaches - A reference guide

Finite element modeling was used to examine the flow processes in high-pressure torsion (HPT) when using quasi-constrained conditions where disks are contained within depressions on the inner surfaces of the upper and lower anvils. Separate simulations were performed using applied pressures from 0.5 to 2.0 GPa, rotations up to 1.5 turns and friction coefficients from 0 to 1.0 outside of the depressions. The simulations demonstrate the distribution of effective strain within the depressions is comparable to the prediction by ideal torsion, and the applied pressure and the friction coefficient outside the depressions play only a minor role in the distribution of effective strain. The mean stresses during processing vary linearly with the distance from the center of the disk such that there are higher compressive stresses in the disk centers and lower stresses at the edges. The torque required for rotation of the anvil is strongly dependent upon the friction coefficient between the sample and the anvil outside the depressions.

Using finite element modeling to examine the flow processes in quasi-constrained high-pressure torsion

Twelve commercially available WC–Co powders with different average WC grain sizes (0.2, 2, and 6 μm) and cobalt contents (8, 12, 17 and 25 wt.%) were sprayed on carbon steel substrates using High Velocity Oxy-Fuel (HVOF) spraying process. Hardness, Young's modulus, and fracture toughness of the coatings were measured. While the hardness and Young's modulus decreased with increasing cobalt content from 1600 to 1100 Hv and from 400 to 300 GPa respectively, the fracture toughness remained in the range from 4 to 6 MPam 1/2 . The coatings with 2 μm carbide showed lower hardness than those deposited from 0.2 and 6 μm carbide. These measured mechanical properties were discussed with the help of microstructures of the coatings investigated by scanning electron microscopy, X-ray diffraction and chemical analysis. Finally, the hardness of the binder phase in these coatings was estimated to range from 1000 to 1300 Hv by applying the mixture rule for composites to the experimental data, demonstrating that such hardening of the binder phase is a key factor affecting the mechanical properties of the coatings.

Effects of carbide size and Co content on the microstructure and mechanical properties of HVOF-sprayed WC–Co coatings

Welding thermal cycles may severely impair duplex stainless steel (DSS) performance, especially local pitting resistance and toughness. The restricted welding energy between 0.5 and 2.5 kJ mm−1 represents a limiting factor for productivity increase in DSS welding, and the addition of cold wire is an interesting alternative to increase the welding deposition rate without adding extra heat. The aim of this work is to evaluate the influence of the cold wire feeding rate (CW) and heat input (HI) on pitting corrosion behavior of DSS UNS S32304 bead-on-plate welds obtained by submerged arc welding (SAW). Cyclic potentiodynamic polarization was carried out in transverse weld sections using 1 mol L−1 NaCl solution at room temperature. Most pitting corrosion spots were located on the heat-affected zone (HAZ), and the pitting potentials were lower than the base metal due to higher ferrite fractions and the presence of chromium nitrides. Considering the same CW, the HI increasing reduced Epit for 1.6, 1.9, 2.2 kJ mm−1, but increased Epit for 2.7 kJ mm−1, due to a balance between the HAZ width and the austenite fraction.

Influence of Heat Input and Cold Wire Feeding Rate on Pitting Corrosion Resistance of Submerged Arc Welding Duplex Stainless Steel Welds

GMA welding is characterized by a strong dependence between its operational parameters and a high sensitivity to small variations of those. These characteristics tend to make it harder to replicate welding conditions. It is also a barrier to welding automation and makes it necessary to perform a number of real welding tests before determining operational conditions for a given application. In order to contribute to reduce these limitations of GMA welding, the authors of the present work have been working on the development of a mathematical model to simulate the variation of operational and electrical parameters during welding. This paper aims to evaluate methodologies to determine two key variables of this model (the electrode electrical resistivity and the sum of the voltage drops in the arc anode and cathode regions)in short-circuit welding. Experimental trials were performed in a mechanized jig by depositing bead-on- plate welds on low-carbon steel bars. Methodologies to evaluate those variables were developed based in proposals from the literature. Experimental details of these methodologies are analyzed and their results are compared to results from the literature. These procedures are evaluated, compared with data from the literature and new procedures are proposed to estimate those parameters and the contact resistance between the contact tip and the electrode. Results suggest values between 6 and 9 W for this last parameter.

/pdf/estudo-de-alguns-parametros-basicos-da-soldagem-gmaw-com-1xgsfp8uum.pdf

Estudo de alguns parâmetros básicos da soldagem GMAW com transferência por curto-circuito (Evaluation of Basic Parameters of Short-Circuit GMA Welding)

O processo de soldagem GMAW e caracterizado por uma forte interdependencia de seus parâmetros operacionais e uma grande sensibilidade a variacoes destes. Estas caracteristicas podem causar variacoes nas condicoes operacionais, dificultando o estabelecimento e a reproducao destas condicoes que, usualmente precisam ser verificadas pela realizacao de testes. Como uma forma de minimizar esta dificuldade e facilitar o entendimento da relacao entre as variaveis deste processo, tem-se trabalhado no desenvolvimento de um modelo matematico capaz de simular aspectos eletricos e operacionais da soldagem GMAW. O objetivo do presente trabalho foi estudar procedimentos de determinacao e fatores que afetam duas variaveis fundamentais para o desenvolvimento deste modelo (a resistividade eletrica do arame durante a soldagem e a soma das quedas de tensao anodica e catodica no arco, UAC) na soldagem com transferencia por curto-circuito. Os testes experimentais envolveram a deposicao mecanizada de cordoes emaco de baixo carbono usando arames do mesmo material com diferentes gases de protecao. Metodologias para a determinacao dos parâmetros citados foram desenvolvidas com base em procedimentos similares indicados na literatura. Os detalhes destes procedimentos sao avaliados, os resultados obtidos sao comparados com dados da literatura e metodos para estimar a resistencia eletrica entre o bico de contato e o eletrodo sao apresentados. Os resultados sugerem valores para esta resistencia entre 6 e 9 mΩ.

/pdf/estudo-de-alguns-parametros-basicos-da-soldagem-gmaw-com-3kjskpqf6t.pdf

Estudo de alguns parâmetros básicos da soldagem GMAW com transferência por curto-circuito

This work aimed to study the effect of some operational conditions on the characteristics of beads produced by a Brazilian-made basic tubular wire (ASME SFA-5.20: E71T-5/E71T-5M), 1.2 mm in diameter, intended for welding common structural carbon steels with low and medium levels of carbon. Welding tests were carried out, in a flat position, on thick plates (12 mm thick) of common low-carbon steel using a source operating in constant voltage mode and with continuous monitoring of the arc current, arc voltage, and feed speed (fusion) values for the wire. The composition of the shielding gas (75%Ar–25%CO2 and 100%CO2), the electrode polarity (positive and negative), and the wire feed speed (7 and 9 m/min) were varied. The other welding parameters were kept fixed, including the energized lengths of the electrode (16 mm) and the arc (3.5 mm). The effects of the operational conditions on the main characteristics of the bead were evaluated including its geometry (penetration, reinforcement, width, welded area, d...

Bead characterization on FCAW welding of a basic tubular wire

The aim of this work was to make a comparative study of the characteristics of the weld bead produced by nationally manufactured tubular wires; all rutilic (ASME SFA-5.20: E71T-1/E71T-9/E71T-9M), basic (ASME SFA-5.20: E71T-5/E71T-5M) and ‘metal cored’ (ASME SFA-5.18: E70C-3M), 1.2 mm in diameter, intended for the welding of structural steels with low and medium levels of carbon. Welding tests were carried out, in the flat position, on thick plates (with a thickness of 12 mm) of common low-carbon steel using a source operating in ‘constant voltage’ mode, with monitoring of the current and voltage signals of the arc and feed speed (fusion) of the wire. The following were varied in welding with each type of tubular wire: the composition of the shielding gas (75%Ar–25%CO2 and 100%CO2) and the feed speed of the wire (7 and 9 m/min). The other parameters were kept fixed, including the polarity of the electrode (DC+) and the energized lengths of the electrode (16 mm) and of the arcs (3.5 mm). For the different t...

Paulo José Modenesi

Papers

Influence of Heat Input and Cold Wire Feeding Rate on Pitting Corrosion Resistance of Submerged Arc Welding Duplex Stainless Steel Welds

Estudo de alguns parâmetros básicos da soldagem GMAW com transferência por curto-circuito (Evaluation of Basic Parameters of Short-Circuit GMA Welding)

Estudo de alguns parâmetros básicos da soldagem GMAW com transferência por curto-circuito

Bead characterization on FCAW welding of a basic tubular wire

Comparison of operational performance and bead characteristics when welding with different tubular wires