This article demonstrates the importance of stress concentrations on the life of industrial components. The design review and analysis of maintenance tasks (repair) can foresee and avoid such harmful design defects and/or bad habits that can reduce component life in service. Three steel shop examples are mentioned and details of these selected situations are analysed using metallurgy and finite element tools.
We have studied the effect of a post-weld heat treatment on plasma arc welds on Zircaloy 4 plates. The samples consist of two 100 mm long, 50 mm wide, and 6.25 mm thick plates, welded along the rolling (longitudinal) direction. The heat-treatment consisted of a steady increase in temperature from room temperature to 450oC over a period of 4.5 hours; followed by cooling with an equivalent cooling rate. Residual strains and stresses along the longitudinal, transverse and normal directions on an as-welded and a heat-treated specimen were measured by neutron diffraction on the ENGIN-X beamline at the Isis Facility, Rutherford Laboratory, UK. Peak tensile stresses of (105±25) MPa were found in the as-welded specimen, which were reduced to (70±20) MPa after the heat-treatment. Thermal compressive stresses of (-80±20) MPa were found along the normal direction, which were not affected by the heat treatment. The use of a full-pattern Rietveld refinement for the determination of bulk strains in Zircaloy specimens is also discussed.
Este es un artículo publicado en acceso (Open Access) abierto bajo la licencia Creative Commons Attribution Non-Commercial, que permite su uso, distribución y reproducción en cualquier medio, sin restricciones siempre que sin fines comerciales y que el trabajo original sea debidamente citado. Resumen: Actualmente, los aceros microaleados son ampliamente utilizados en reemplazo de los aceros al C y C-Mn por sus ventajas en cuanto a propiedades mecánicas, resistencia a la corrosión y soldabilidad, permitiendo una reducción de peso de los vehículos y estructuras sin detrimento de su resistencia. Cuando estos aceros son soldados, el ciclo térmico de la soldadura provoca cambios microestructurales que modifican sus propiedades originales. El calor aportado (HI: heat input) es una de las principales variables a tener en cuenta cuando se evalúan estas modificaciones. Las propiedades finales de la unión soldada también se definen por el tipo de consumible utilizado. El objetivo de este trabajo es analizar las propiedades mecánicas y la microestructura de juntas soldadas a tope de un acero microaleado con dos grados de metal de aporte y diferentes HI. Como resultado del trabajo se observó un aumento considerable de tamaño de grano en la ZAC adyacente a la línea de fusión para todas las condiciones, siendo este efecto más marcado cuando se soldó con alto HI; y un ablandamiento en la ZAC de grano fino. Prácticamente se mantuvieron los valores de resistencia a la tracción al soldar con ambos consumibles, con un mejor desempeño cuando se soldó con bajo HI. La tenacidad en la ZAC mejoró con la disminución del HI.Palabras clave: Aceros microaleados; Propiedades mecânicas; Microestructura; Junta soldada; Alambres tubulares. Influence of Heat Input and Filler Metal on Mechanical Properties and Microstructure of Microalloyed High Strength Steel Welded by FCAWAbstract: Currently, microalloyed high strength steels are being widely used to replace C and C-Mn steels for their advantages in terms of mechanical properties, corrosion resistance and weldability, allowing weight reduction of vehicles and structures without impairing their strength. When these steels are welded, the welding heat cycle causes microstructural changes that alter their original properties. The heat input (HI: heat input) is one of the main variables to consider when these modifications are evaluated. The final properties of the welded joint are also defined by the type of consumable used. The aim of this paper is to analyze the mechanical properties and microstructure of a butt welded microalloyed steel with two filler metal grades and different HI. A considerable increase grain size in the heat affected coarse grain zone, especially for high HI; and a softening in fine grain zone were observed. The values of tensile strength at both welding consumables remained basically unaltered, with better performance when welded with low HI. The toughness in the HAZ was improved when the HI decreased.
The cavitation erosion of various hardfacing coatings was investigated by using a vibratory cavitation apparatus according to ASTM G 32. Coatings of austenitic stainless steel containing 10 % cobalt were applied by arc welding. High velocity oxy-fuel spraying (HVOF) was employed to produce coatings of various kinds of cermets and metallic alloys. For each coating, the steady state erosion rate was determined and the effect of process parameters and alloy composition on the microstructure and erosion rate was investigated. The morphology and microstructure of the coatings before and after cavitation testing were analysed by metallographic methods in order to study the erosion mechanism. It is demonstrated that the high resistance to cavitation erosion of the cobalt-alloyed steel can even further increase when the fluxed core arc welding process and an improved pulsed power source are used to produce the coatings. The erosion resistance of the HVOF coatings, however, was limited by pores, microcracks and oxides and did not significantly exceed the level typical for bulk stainless steel 316 L.
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