Edmilson Otoni Correa

Microstructure and mechanical properties of WC-Ni-Al based cemented carbides developed for engineering applications

Abstract In this paper the influence of the Ni binder metal and Al as an additional alloying element on the microstructure and mechanical properties of WC-based cemented carbides processed by conventional powder metallurgy was studied. Microstructural examinations of the cemented carbides with 3 and 5 wt.% of Al in the binder metal indicated the presence of a very low and evenly distributed porosity as well as the presence of islands of metal binder in the microstructure. With the cemented carbide with 7 wt.% of Al in the metal binder, the presence of brittle needle-like regions was observed. The WC particles inside these regions were rounded and had a larger mean free path. Vickers hardness and flexural strength tests indicated that the cemented carbide WC-Ni-Al with addition of 5 wt.% of Al in the binder metal presented bulk hardness similar to the conventional WC-Co cemented carbides as well as superior flexure strength and fracture toughness.

Mechanical and Microstrutural Characterization of Weldments of Ferritic Stainless Steel AISI 444 Using Austenitic Stainless Steels Filler Metals

The objective of this study was to investigate the influence of the filler metal on the microstructure and mechanical properties of ferritic stainless steel AISI 444 welded using two types of filler metal of austenitic stainless steel. Microstructure examinations showed that in both welded joints grain growth occurred in the heat affected zone (HAZ). The results also showed that the fusion zone of the weld joints using E309L filler metal presented a discontinuous network of delta ferrite unlike the fusion zone of the weld joint using E316L. Tensile tests showed that the failures of specimens always occurred in the HAZ and that the weldments using E316L filler metal presented tensile strength lower than that of the weldment using E309L filler metal. In the fusion zone of the weldments using E316L filler metal, values for hardness were found to be higher than those found in the fusion zone of the E309L filler metal.

Finite element reduction strategy for composite sandwich plates with viscoelastic layers

Composite materials have been regarded as a convenient strategy in various types of engineering systems such as aeronautical and space structures, as well as architecture and light industry products due to their advantages over the traditional engineering materials, such as their high strength/stiffness relation characteristics and their anti-corrosion properties. This paper is devoted to the finite element modeling of composite laminated structures incorporating viscoelastic materials to the problem of vibration attenuation. However, the typically high dimension of large finite element models of composite structures incorporating viscoelastic materials makes the numerical processes sometimes unfeasible. Within this context, emphasis is placed on a general condensation strategy specially adapted for the case of viscoelastically damped structures, in which a constant (frequency- and temperature-independent) reduction basis to be enriched by static residues associated to the applied loads and the viscoelastic forces is used. After presenting the theoretical foundations, the numerical applications of composite plates treated by viscoelastic materials are addressed, and the main features of the methodology are discussed.

Thermodynamic simulation as an assistant tool in the development of iron based hardfacing materials

A thermodynamic model was used to investigate the solidification of a hardfacing material in Fe-Cr-C-Nb system designated CNO, and developed for cladding components subjected to severe abrasive wear by welding. Microstructural characterization of the alloy showed that the theoretical simulations carried out to predict the amount and volume fraction of the phases using the module Scheil of MT-DATA Software gave very realistic results in the case of the rapid solidification of the hardfacing alloy CNO. The results obtained in this study indicate that the utilization of this tool may provide a good understanding of alloys solidification. As a consequence, it is possible to enable the refinement of alloy composition during the early stages of hardfacing materials development, leading to a decreasing of overall cost and time of manufacturing of hardfacing electrodes.

Susceptibility to stress corrosion cracking of stainless steel dissimilar joint AISI 316 and AISI 310 and 2304 duplex stainless steel with addition of E2209 metal.

In this work we investigated the influence of metal addition duplex 2209 on the susceptibility to stress corrosion cracking by (CST) of welded joints of austenitic stainless steel AISI 310 and AISI 316 stainless steel with duplex UNS S2304, aiming to study the steel austenitic stainless with better resistance to cracking from stress corrosion. For this study, the microstructure of welded joints will be analyzed was used an optical microscope. The mechanical properties of the welded joint with the duplex filler metal were analyzed by tensile and Vickers hardness. To evaluate the susceptibility of welded joints to stress corrosion cracking by, we used the test method under constant load followed by microstructural characterization of the tested specimens CST. The susceptibility to SCC was assessed in terms of time to fracture. The under stress corrosion tests indicate that the HAZ metal base 316 is the most likely region CST.

Effect of Solubilization Temperature on the Sigma Phase Precipitation of a Superduplex Stainless Steel

Superduplex stainless steel is an important class of stainless steels because it combines the benefits of ferrite and austenite phases, resulting in steels with better mechanical properties and corrosion resistance. However, a significant problem of this steel is the precipitation of deleterious phases during heat treatment. Among these precipitated phases, the most relevant is the sigma phase, because it causes higher loss of properties. The objective of this work therefore is to study the sigma phase precipitation in the superduplex stainless steel UNS S32520 when submitted to heat treatment of solubilization in three different temperatures (1050 C, 1150o C and 1250° C) and subsequently aged in the temperature of 850oC during 10 minutes, 30 minutes, 60 minutes, 3 hours and 10 hours, followed by water quenching. The results showed that as the solubilization temperature increases, there is a significant grain growth and an increase of the ferrite volumetric fraction, which delays the sigma phase precipitation in this superduplex stainless steel. Moreover, it can be verified that the hardness of the material is directly related to volumetric fraction of sigma present in the steel.

Influência do tratamento térmico de envelhecimento a 850ºC na microestrutura e nas propriedades mecânicas e magnéticas do aço Duplex UNS S31803

Duplex stainless steels are those that have a microstructure constituted by two phases, ferromagnetic ferrite (α) and paramagnetic austenite (γ), which are present in approximately equal volumetric fraction. In this work, the microstructure of duplex steel UNS S31803 was modified by a thermal solubility treatment at temperature of 1050 °C for 30 minutes, followed by water cooling. Next, specimens were aged for 5, 15, 30, 60 and 180 minutes at temperature of 850°C. This treatment promoted the formation of a deleterious phase, the sigma phase, which is formed by the decomposition of ferrite, rich in the elements Cr and Mo. The formation of this phase changes the mechanical and chemical properties of the duplex and super duplex steels. The magnetic and mechanical properties were evaluated in each of the conditions mentioned and a correlation with the microstructure was made. The magnetic properties of the specimens were obtained in a Vibrating Sample Magnetometer (VSM), where the material hysteresis curves were obtained. The mechanical properties of the samples were characterized by Vickers micro-hardness measurements performed with a load of 0.2 kgf. Microstructural characterization was carried out by using an optical microscope. VSM tests results showed that as the aging time increased, the volume fraction of sigma phase also increased, causing a diminution of the steel duplex magnetic properties. The diminution of the magnetic properties of the duplex steel with the aging time is attributed to the lower fraction of ferrite as more sigma phase is formed by the decomposition of ferrite. The hardness results showed an increasing of the hardness of the material as the aging temperature increased, which confirms the higher brittleness of the steel due to the higher amount of sigma phase.