Sensitivity to hydrogen induced cracking, and corrosion performance of an API X65 pipeline steel in H2S containing environment: influence of heat treatment and its subsequent microstructural changes

In this investigation, the effect of microstructural changes and phase equilibria on corrosion behavior and hydrogen induced cracking (HIC) sensitivity of an API X65 pipeline steel was studied. For this purpose, heat treatment was performed at 850 °C, 950 °C, 1050 °C and 1150 °C to engineer the desired microstructure of this pipeline steel. Then, the microstructural evolution was performed by optical microscopy, and Field Emission Scanning Electron Microscopy (FE-SEM) equipped with Energy Dispersive X-Ray Spectroscopy (EDS). Corrosion properties were evaluated in H2S environment by open circuit potential (OCP), Potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS). As well, HIC sensitivity of the API X65 pipeline steel was assessed by hydrogen charging of the cathode and immediately conducting the tensile test. Microscopy analyses showed that the microstructure of the steel is ferritic-pearlitic together with the islands of martensite/austenite constituents. Increasing the heat treatment temperature reduced the amount of pearlite and increased ferrite grain size. It also stabilized the ferrite content. Corrosion results indicated that no active layer was formed on the surface of this pipeline steel. Also, increasing the heat treatment temperature increased the corrosion resistance and reduced sensitivity to micro-galvanic localized corrosion. As well, results suggested that the sensitivity to HIC in the API X65 pipeline was substantially increased with increasing the amount of pearlite and reducing the amount of ferrite; i.e. at lower heat treatment temperature.publishedVersio

A new approach to incorporating the effect of nano-sized dispersoids on recrystallization inhibition into Monte Carlo simulation

In this research, a new approach to incorporating the effect of nano-sized dispersoids on recrystallization was developed as a combination of physical modeling and Monte Carlo simulation. The energy stored during preceding deformation and the nucleation rate at the onset and during recrystallization were calculated using a physical model and were incorporated into the Monte Carlo simulation. The conventional approach to incorporating the Zener drag effect was also considered for comparison with the new approach. Predictions were validated by comparing the microstructures obtained from the simulations with those from experimental results. It was found that the general Monte Carlo approach to incorporating the effect of second-phase particles on recrystallization inhibition was not suitable for nano-sized dispersoids being significantly smaller than the lattice size of the simulation. The effect of dispersoids could be incorporated into the simulation using a combination of analytical modeling and Monte Carlo approach. By using this approach, it was possible to differentiate between small variations in the volume fraction of dispersoids. (C) 2011 Elsevier BM. All rights reserved

Finite element simulation and experimental investigation of hot forming cold die quenching and equal channel angular pressing of AA2024 aluminum alloy

The present study investigates the variations in the microstructure and mechanical properties of AA2024 aluminum alloy as a consequence of thermal and strain gradient in combined hot forming cold die quenching (HFQ) and equal channel angular pressing (ECAP) method. Solution-treated AA2024 aluminum alloy was HFQ–ECAPed for five passes of deformation and 3D simulations plus microstructural evolutions, and mechanical properties over the thickness of the sample were investigated. Furthermore, after each ECAP pass, intermediate solution treatment was applied, and a group of specimens was subjected to aging treatment following the deformation. 3D simulations illustrated strain uniformity by increasing the number of deformation passes with its maximum uniformity after four passes. Microstructural observations demonstrated evident grain refinement in successive passes, which were higher in the central and top parts of the sample than in the lower area. Also, a high quantity of shear bands occurred in the workpiece after the first ECAP pass. However, shear banding was deducted in the consecutive passes of deformation and intermediate solutionizing. Preferable properties in central regions were seen comparing tensile properties in surface area and central parts. Besides, the microhardness test resulted in more uniform outcomes by enhancement in the number of ECAP passes. Hardness variations showed an increase in average hardness after the first pass of deformation (compared to the annealed condition (Baghbani Barenji et al. in J Mater Res Technol 9:1683–1697, 2020) and then a negligible decrease in the following two passes. The hardness quantities again increased in the fourth pass and then dramatically decreased after the fifth pass due to the partial decomposition of the solid solution. Besides, due to strain distribution, hardness values illustrate the maximum and minimum amount in the uppermost and lowermost areas, respectively. The overall conclusions of this article presented mechanical similarities in the surface and inner parts of the material

Studying the age hardening kinetics of A357 aluminum alloys through the Johnson–Mehl–Avrami theory

This paper demonstrates the application of the Johnson–Mehl–Avrami (JMA) theory to study the kinetics of the age hardening process in an A357 aluminum alloy. The precipitation hardening effect was studied at various times and temperatures. The outcomes show that the hardness can be improved via time and temperature changes.Itis thus concluded thattime and temperature are key variables in the precipitation hardening of the alloy. According to the results, solubilization at 823 K (550 8C) and then aging treatment at 453–463 K (180–190 8C) for 12–18 h is the optimum cycle to obtain the maximum hardness. The apparent activation energy of 40 kJ/mol was achieved through the kinetic studies. Based on the practical data, it is generally possible to estimate the hardness at a certain time and temperature by an appropriate equation. Furthermore, the maximum hardness and the time required to reach that maximum can be easily predicted through a suitable calculated relationship. Experiments by means of hardness measurement have been performed to provide the relevant information to validate the model. This paper aims to presentthe application ofthis simple modeling. The novelty ofthis paper is obtaining anequation that could be used to predict the hardness of an A357 alloy with a good agreement with the practical data

Modeling high temperature deformation characteristics of AA7020 aluminum alloy using substructure-based constitutive equations and mesh-free approximation method

This research was aimed to assess the potential of a radial basis function (RBF) approximation method against the dislocation substructure-based constitutive model in predicting high-temperature deformation behavior of the AA7020 aluminum alloy. Hot compression tests were performed over a range of strain rate of 0.1–100 s−1 and a range of temperature of 350–500 °C up to a strain of 0.6. The hot deformation behavior of the alloy was first described by a substructure kinetic-based constitutive equation, with the effects of strain, strain rate and temperature together with dynamic recovery parameters taken into consideration. A RBF approximation method was then developed to model the flow behavior of the material. The RBF model, as a kind of novel mesh-free function estimation approach, was trained and tested with the obtained datasets from the hot compression tests. The performance of the developed analytical and neural computational models was evaluated using statistical criteria. The results showed that the RBF model was more proficient and accurate in predicting the hot deformation behavior of this aluminum alloy than the substructure-based constitutive model.Accepted Author ManuscriptBiomaterials & Tissue Biomechanic

Sensitivity to hydrogen induced cracking, and corrosion performance of an API X65 pipeline steel in H2S containing environment: influence of heat treatment and its subsequent microstructural changes

In this investigation, the effect of microstructural changes and phase equilibria on corrosion behavior and hydrogen induced cracking (HIC) sensitivity of an API X65 pipeline steel was studied. For this purpose, heat treatment was performed at 850 °C, 950 °C, 1050 °C and 1150 °C to engineer the desired microstructure of this pipeline steel. Then, the microstructural evolution was performed by optical microscopy, and Field Emission Scanning Electron Microscopy (FE-SEM) equipped with Energy Dispersive X-Ray Spectroscopy (EDS). Corrosion properties were evaluated in H2S environment by open circuit potential (OCP), Potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS). As well, HIC sensitivity of the API X65 pipeline steel was assessed by hydrogen charging of the cathode and immediately conducting the tensile test. Microscopy analyses showed that the microstructure of the steel is ferritic-pearlitic together with the islands of martensite/austenite constituents. Increasing the heat treatment temperature reduced the amount of pearlite and increased ferrite grain size. It also stabilized the ferrite content. Corrosion results indicated that no active layer was formed on the surface of this pipeline steel. Also, increasing the heat treatment temperature increased the corrosion resistance and reduced sensitivity to micro-galvanic localized corrosion. As well, results suggested that the sensitivity to HIC in the API X65 pipeline was substantially increased with increasing the amount of pearlite and reducing the amount of ferrite; i.e. at lower heat treatment temperature