Influence des traitements thermiques à haute température sur l'évolution de la texture et de la microstructure des soudures d'acier inoxydable duplex 2205

This work deals with the study of the texture and microstructure evolution during welding and subsequent annealing treatment of 2205 duplex stainless steel. Microstructural examination showed the presence of higher ferrite amount in the heat affected zone (HAZ), while higher amount of austenite was recorded in the centre region of the weld metal. Annealing treatment at temperature range of 800-1000°C resulted in a precipitation of σ phase and M23C6 chromium carbides at the γ/δ interfaces that were found as preferential precipitation sites. Above 1050 °C, the volume fraction of δ ferrite increases with annealing temperature. Optimal mechanical properties and accepted γ/δ ratio throughout the weld regions corresponds to annealing at 1050 °C. Aging at 850 °C after solution treatment showed that increasing the solution treatment temperature from 1050 to 1250°C delays the σ phase formation and favours the precipitation of intragranular secondary austenite γ2. The simulation of the σ phase precipitation kinetic in the base metal, HAZ and weld metal indicates a good agreement between the experimental fitted data and the modified J.M.A model. The results indicate also a marked sensitivity of the σ phase precipitation kinetic to the solution treatment temperature. Texture analysis using EBSD technique led to determine the exact orientation relationship between austenite and ferrite in the weld metal as a 44.2 rotation around axis. While no major change was observed in the HAZ and base metal texture, some scatter of the orientation relationship determined in the base metal was registered after annealing at 1250°C because of the grain morphological change.Ce travail traite de l'évolution de la texture et de la microstructure dans les soudures d'acier inoxydable duplex 2205 traitées thermiquement. L'analyse microstructurale a montré que la ZAT est caractérisée par une forte teneur en ferrite alors que le centre du métal fondu contient plus d'austénite. Les traitements thermiques effectués dans le domaine 800-1000°C ont causé la précipitation de la phase σ et des carbures de chrome M23C6 aux interfaces γ / δ qui sont les sites privilégiés de germination. Au-delà de 1050°C la fraction volumique de la ferrite augmente avec la température. Les propriétés mécaniques optimales du joint soudé sont obtenues suite à un traitement d'hypertrempe à 1050 °C pendant 1h. Le passage de la température d'hypertrempe de 1050 à 1250 °C retarde la précipitation de la phase σ et favorise celle de l'austénite secondaire γ2. L'étude de la cinétique de précipitation de la phase σ dans les différentes zones de la soudure montre que celle-ci suit le modèle modifié de JMA. Les résultats obtenus montrent une dépendance significative de la précipitation de la phase σ par rapport à la température d'hypertrempe. L'analyse par EBSD de la texture cristallographique du métal fondu a permis de déterminer la relation d'orientation exacte entre l'austénite et la ferrite comme étant une rotation de 44.2° autour d'un axe . La texture du métal de base reste quasiment stable suite à l'opération de soudage et aux traitements thermiques effectués au moment où une petite dispersion vient perturber légèrement la relation d'orientation dans le métal fondu

Influence des traitements thermiques à haute température sur l'évolution de la texture et de la microstructure des soudures d'acier inoxydable duplex 2205

Ce travail traite de l évolution de la texture et de la microstructure dans les soudures d acier inoxydable duplex 2205 traitées thermiquement. L analyse microstructurale a montré que la ZAT est caractérisée par une forte teneur en ferrite alors que le centre du métal fondu contient plus d austénite. Les traitements thermiques effectués dans le domaine 800-1000C ont causé la précipitation de la phase et des carbures de chrome M23C6 aux interfaces g / qui sont les sites privilégiés de germination. Au-delà de 1050C la fraction volumique de la ferrite augmente avec la température. Les propriétés mécaniques optimales du joint soudé sont obtenues suite à un traitement d hypertrempe à 1050 C pendant 1h. Le passage de la température d hypertrempe de 1050 à 1250 C retarde la précipitation de la phase et favorise celle de l austénite secondaire g2. L étude de la cinétique de précipitation de la phase dans les différentes zones de la soudure montre que celle-ci suit le modèle modifié de JMA. Les résultats obtenus montrent une dépendance significative de la précipitation phase par rapport à la température d hypertrempe. L analyse par EBSD de la texture cristallographique du métal fondu a permis de déterminer la relation d orientation exacte entre l austénite et la ferrite comme étant une rotation de 44.2 autour d un axe . La texture du métal de base reste quasiment stable suite à l opération de soudage et aux traitements thermiques effectués au moment où une petite dispersion vient perturber légèrement la relation d orientation dans le métal fondu.This work deals with the study of the texture and microstructure evolution during welding and subsequent annealing treatment of 2205 duplex stainless steel. Microstructural examination showed the presence of higher ferrite amount in the heat affected zone (HAZ), while higher amount of austenite was recorded in the centre region of the weld metal. Annealing treatment at temperature range of 800-1000C resulted in a precipitation of phase and M23C6 chromium carbides at the g/ interfaces that were found as preferential precipitation sites. Above 1050 C, the volume fraction of ferrite increases with annealing temperature. Optimal mechanical properties and accepted g/ ratio throughout the weld regions corresponds to annealing at 1050 C. Aging at 850 C after solution treatment showed that increasing the solution treatment temperature from 1050 to 1250C delays the phase formation and favours the precipitation of intragranular secondary austenite g2. The simulation of the phase precipitation kinetic in the base metal, HAZ and weld metal indicates a good agreement between the experimental fitted data and the modified J.M.A model. The results indicate also a marked sensitivity of the phase precipitation kinetic to the solution treatment temperature. Texture analysis using EBSD technique led to determine the exact orientation relationship between austenite and ferrite in the weld metal as a 44.2 rotation around axis. While no major change was observed in the HAZ and base metal texture, some scatter of the orientation relationship determined in the base metal was registered after annealing at 1250C because of the grain morphological change.PARIS13-BU Sciences (930792102) / SudocSudocFranceF

Residual stresses of a magnesium alloy (AZ31) welded by the friction stir welding processes

The objective of this study was to evaluate the residual stresses of FSW welding magnesium alloys (AZ31). The results show that the FSW processes lead to the formation of several distinct zones with differing mechanical properties. The residual stresses evolution have been explained by the heterogeneous modifications of the microstructure particularly a marked decrease in the grain size, a high modification of the crystallographic texture and the different anisotropic properties resulting from plasticity induced by the FSW process

Parametric Investigation of Similar TiAl6V4 and AA2024 Rotary Friction Weld Joints Using Taguchi-L9 Array Method

The objective underlined in this work is to apply Rotary Friction Welding (RFW) process to joint similar AA2024 and TiAl6V4 welds. The experiment is conducted by varying the input parameters (rotational speed, friction pressure and friction time) using Taguchi’s L9 orthogonal array method. MINITAB software was used to plot the response chart. The output parameter considered in this approach is the Ultimate Tensile Strength (UTS) of the weld joint, where the optimum RFW condition for maximizing the UTS were determined. Besides, the most influential process parameter has been determined using statistical analysis of variance (ANOVA). Finally, the general regression equations of the UTS for both materials are formulated and confirmed by means of the experimental tests values

Residual stresses of a magnesium alloy (AZ31) welded by the friction stir welding processes

The objective of this study was to evaluate the residual stresses of FSW welding magnesium alloys (AZ31). The results show that the FSW processes lead to the formation of several distinct zones with differing mechanical properties. The residual stresses evolution have been explained by the heterogeneous modifications of the microstructure particularly a marked decrease in the grain size, a high modification of the crystallographic texture and the different anisotropic properties resulting from plasticity induced by the FSW process

Effect of Solution Treatment on the Microstructure, Micromechanical Properties, and Kinetic Parameters of the β → α Phase Transformation during Continuous Cooling of Ti-6Al-4V Titanium Alloy

International audienc

Multi-objective optimization and evolution of dissimilar welding process between Cr-Mo steel and austenitic stainless steel for power plant application

In this study, response surface methodology (RSM) was employed to optimize the welding parameters’ effects on mechanical properties of dissimilar welds between Cr-Mo steel grade (P11) and austenitic stainless steel (AISI 316LN). To determine the best welding parameters, variance analysis (ANOVA), desirability function, and perturbation analysis were used to create regression models and identify the significant parameters influencing tensile strength and hardness gaps in the weld joints. The results indicated that welding speed is the most significant parameter affecting both the austenitic hardness gap and tensile strength, while gas flow has the most significant impact on the hardness gap of Cr-Mo steel. Furthermore, welding speed positively influences the mechanical properties of dissimilar weld, whereas welding current has a slight negative effect on tensile strength. The optimum welding parameters were found to be 130 A for welding current, 70 mm min ^−1 for welding speed, and 13 l min ^−1 for welding gas flow, resulting in hardness gap values of 18.10 HV (Stainless steel side), 27.38 HV (Cr-Mo steel side), and a tensile strength of 453.90 MPa. The optimum parameter effect is concentrated at the weld interfaces between the fusion zone and the heat-affected zone. This effect led to limitations in grain coarsening, a reduction in the martensite and delta ferrite phase percentages, a slight increase in the bainite ratio, and a decrease in carbide precipitations. As a result, a homogenization of strain distribution in the optimum weld was achieved, leading to ductile fracture in Cr-Mo steel

Mechanical behavior and microstructure of dissimilar aluminium/titanium rotary friction weld joints

International audienceThe objective of this study is to employ the rotary friction welding (RFW) technique to join dissimilar materials AA2024/Ti6Al4V. The experimental design encompasses the manipulation of RFW process input parameters, using the Taguchi L9 array methodology. The collected data underwent thorough analysis, aimed at determining the ultimate tensile strength (UTS) of the resultant weld joint. The prime focus rested on ascertaining optimal RFW conditions that could effectively maximize the UTS. Through the use of statistical analysis of variance (ANOVA), the process parameter of utmost significance was identified. The outcomes of this investigation were harnessed to formulate regression model pertaining to the UTS of the RFW joint. Furthermore, fatigue tests were executed to exhibit the cyclic behavior of the dissimilar welds, yielding a comprehensive Wöhler curve that facilitated the estimation of specimen longevity under stress cycles. In addition, microscopic observations were carried out to discern the microstructural evolution and the quality of the weld joint. Finally, scanning electron microscopy (SEM) analysis was conducted to investigate damage micro-mechanisms specimens. The results show that using a rotational speed of 1290 rpm, friction pressure of 6 MPa for 6.3 s, and forging pressure of 6 MPa for 8 s leads to an improvement in the UTS value up to 424.31 MPa, corresponding to a joint efficiency of 90.46%

Gleeble-Assisted Investigation and Thermokinetics Simulation of <i>α</i> Phase Isothermal Precipitation during Short-Time Duplex Heat Treatment of Ti-6Al-4V Alloy

International audienceThe precipitation mechanism and kinetics of the secondary alpha phase during short-time duplex heat treatment of the Ti-6Al-4V alloy were investigated. The precipitation kinetics was determined by means of in situ isothermal electrical resistivity tests in a Gleeble thermomechanical testing machine in the temperature range of 600-700 degrees C. The results showed that the higher the aging temperature, the faster the secondary alpha phase precipitation, which obeys the Kolmogorov-Johnson-Mehl-Avrami (KJMA) equation with an Avrami parameter n = 1. The precipitation process was also investigated by simulation using the thermokinetic software MatCalc. Results of the simulation on MatCalc indicated that the secondary alpha phase nucleation ended at an earlier stage of the precipitation and that the latter is mainly controlled by the growth of secondary alpha phase precipitates. Increasing the aging temperature resulted in an increase of the precipitate's size with an activation energy of Q = 62 kJ/mol for the process. Evolution of the simulated elements contents showed that only the vanadium concentration in the beta phase changed significantly during the isothermal aging. Thus, the growth of the secondary alpha phase is governed by the vanadium diffusion into the beta phase

Beta to alpha transformation kinetics and microstructure of Ti-6Al-4V alloy during continuous cooling

International audienceIn the present paper, an approach based on the Kolmogorov-Johnson-Mehl-Avrami (KJMA) model has been developed and applied to study the transformation kinetics of the beta phase in Ti-6Al-4V titanium alloy during cooling. To this purpose, Differential Scanning Calorimetry (DSC) tests have been conducted using a set of cooling rates ranging from 10 to 50 degrees C/min. This approach allows the kinetics parameters, particularly the activation energy, to be calculated from a single DSC test using a simple linear regression. The microstructural analysis indicates that the microstructure is dominated by the alpha Widmanstatten morphology (alpha(W)). Microstructural observations along with the calculated values of the Avrami index and of the activation energy suggest that the growth of the alpha(W) platelets obeys a mixed mode combining the vanadium diffusion and a displacive mechanism. (C) 2016 Elsevier B.V. All rights reserved