Effect of the Aging Treatment in Micro-Alloyed Steel
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Effect of the Aging Treatment in Micro-Alloyed Steel M. A. Doñu Ruiz1*, J. A. Ortega Herrara1, N. López Perrusquia1, V. J. Cortés Suárez2, L. D. Rosado Cruz3 1
Instituto Politécnico Nacional, Grupo e Ingenieria Mecánica Computacional, SEPI-ESIME, Adolfo López Mateos, Zacatenco, México D.F., 07738, México. 2 Universidad Autónoma Metropolitana UAM unidad Azcapotzalco, Departamento de Materiales, Av. San Pablo 180 Azcapotzalco, Mexico .DF, 02200; 3 Universidad Politécnica del Valle de México UPVM. Av. Mexiquense s/n esquina Av universidad politécnica, Col villa esmeralda, 54910, Tultitlan. Edo de México. * E-mail: [email protected] ABSTRACT This work study the effect on aging thermal treatment on micro-alloyed steels API X70 pipe, microstructure and mechanical properties such a yield strength (Y), hardness (Hv) and Young´s modulus (E) are presented in this work. Thermal treatment consists of two phases: i) The solution treatment introducing samples in a electric induction furnace at 1100 °C for 30 min under argon atmosphere and water quenching, ii) aging process for five temperature in the range between 204 to 650 °C for 30 min of time exposition and water quenching, respectively. The microstructural characterization was examined by optical microscopy and matrix samples aging showed microstructures like acicular ferritic, polygonal ferritic and bainitic-ferritic, and the secondary phases were examined by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) obtained by SEM evidencing the presence of precipitates composed of vanadium (V), niobium (Nb) and titanium (Ti). The mechanical properties were evaluated by depth sensitive indentation test at the samples aging, the results showed increase of the (Hv) and (E) to the conditions of low temperature aging. Keywords: microstructural, hardness, second phases, nano-indentation, scanning electron microscopy (SEM). INTRODUCTION High strength low alloy (HSLA) steels or microalloyed steels are a technologically important structural materials in application included pipelines (of crude oil or natural gas transport), body parts in automotive industry and pressure vessels [1]. A lot of researches have dealt with the acicular ferrite dominated microstructure and its properties [2,3]. These steels contained small amounts of alloying elements, such as titanium, niobium and vanadium, which enhance the strength through the formation of stable carbides, nitrided or carbonitrides are important in the control of austenite recrystallization. The mechanical characterization of the materials is represented by hardness and is defined as the resistance of permanent deformation. In depth sensing indentation, hardness H is defined as the mean contact pressure Pm under the loaded indenter, H=P/A= Pm and is calculate as the indenter load P divided by the projects contact area A. Yield strength Y can, be calculate from the mean contact pressure Pm (or hardness). For soft metal with low hardness compared to elastic modulus, yield stress is usually calculated according to Tab
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