The Influence of the Post-Weld Heat Treatment on the Microstructure of Inconel 625/Carbon Steel Bimetal Joint Obtained by Explosive Welding

Inconel 625 and steel P355NH were bonded by explosive welding in this study. Explosively welded bimetal clad-plate was subjected to the two separated post-weld heat treatment processes: stress relief annealing (at 620 °C for 90 min) and normalizing (at 910 °C for 30 min). Effect of heat treatments on the microstructure of the joint has been evaluated using light and scanning electron microscopy, EDS analysis techniques, and microhardness tests, respectively. It has been stated that stress relief annealing leads to partial recrystallization of steel P355NH microstructure in the joint zone. At the same time, normalizing caused not only the recrystallization of both materials, but also the formation of a diffusion zone and precipitates in Inconel 625. The precipitates in Inconel 625 have been identified as two types of carbides: chromium-rich M23C6 and molybdenum-rich M6C. It has been reported that diffusion of alloying elements into steel P355NH takes place along grain boundaries with additional formation of voids. Scanning transmission electron microscope observation of the grain microstructure in the diffusion zone shows that this area consists of equiaxed grains (at the side of Inconel 625 alloy) and columnar grains (at the side of steel P355NH).

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The Influence of the Post Weld Heat Treatment on the Microstructure of Inconel 625/Carbon Steel Bimetal Joint Obtained by Explosive Welding

10.20944/preprints201812.0252.v1 ◽

2018 ◽

Cited By ~ 1

Author(s):

Robert Kosturek ◽

Marcin Wachowski ◽

Lucjan Śnieżek ◽

Michał Gloc

Keyword(s):

Heat Treatment ◽

Electron Microscope ◽

Diffusion Zone ◽

Scanning Transmission Electron Microscope ◽

Post Weld Heat Treatment ◽

Inconel 625 ◽

Joint Zone ◽

Transmission Electron ◽

Scanning Transmission ◽

Weld Heat

In this investigation steel P355NH has been successfully cladded with Inconel 625 through the method of explosive welding. Explosively welded bimetal clad-plate was subjected to the two separated post weld heat treatment processes: stress relief annealing (at 620oC for 90 minutes) and normalizing (at 910oC for 30 minutes). In order to analyze the microstructure of the joint in the as-welded state and to investigate the influence of the post weld heat treatment on it, the light and scanning electron microscope observations and microhardness analysis have been performed. The examination of the diffusion zone microstructure has been performed by using the scanning transmission electron microscope. It was stated that obtained joint has characteristic wavy-shape geometry with the presence of the melted zones and severe deformed grains of both joined materials. Strain hardening of the materials in joint zone was established with microhardness analysis. In both of the heat treatments the changes in the grain structure have been observed. The normalizing heat treatment has the most significant impact on the microstructure of the joint as well as the concentration of the chemical elements in the joint zone. It was reported that due to normalizing the diffusion zone has been formed together with precipitates in the joint zone. The analysis of the diffusion zone images leads to the conclusion that the diffusion of alloying elements from Inconel 625 to steel P355NH takes place along the grain boundaries with additional formation of the voids in this area. The precipitates in Inconel 625 in the joint zone are two type of carbides – chromium-rich and molybdenum-rich. Scanning transmission electron microscope observation of the grain microstructure in the diffusion zone shows that this area consists of equiaxed grains (from the side of Inconel 625 alloy) and columnar grains (from the side of steel P355NH).

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The effects of the heat treatment on the microstructure of Inconel 625/steel bimetal joint obtained by explosive welding

MATEC Web of Conferences ◽

10.1051/matecconf/201824201007 ◽

2018 ◽

Vol 242 ◽

pp. 01007 ◽

Cited By ~ 2

Author(s):

R. Kosturek ◽

M. Wachowski ◽

L. Śnieżek ◽

M. Gloc ◽

U. Sobczak

Keyword(s):

Heat Treatment ◽

Electron Microscope ◽

Diffusion Zone ◽

Explosive Welding ◽

Chemical Elements ◽

Scanning Transmission Electron Microscope ◽

Grain Structure ◽

Inconel 625 ◽

Joint Zone ◽

Scanning Transmission

In this investigation steel P355NH was successfully clad with Inconel 625 through the method of explosive welding. Explosively welded bimetal was subjected to the two separated heat treatment processes: stress relief annealing (at 620oC for 90 minutes) and normalizing (at 910oC for 30 minutes). In order to identify the microstructure of the joint and to investigate the influence of the heat treatment on it, the light and scanning electron microscope observations and microhardness analysis have been performed. In order to investigate the diffusion zone microstructure the scanning transmission electron microscope observation have been performed. It was stated that obtained joint has characteristic wavy-shape geometry with the presence of the melted zones and severe deformed grains of both joined materials. Strengthening of materials in joint zone was established with microhardness analysis. In both of the heat treatments the changes in the grain structure have been observed. The normalizing heat treatment has the most significant impact on the microstructure of the joint as well as the concentration of the chemical elements in the joint zone. It was reported that due to normalizing the diffusion zone has been formed together with precipitates in the joint zone.

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Residual Stress Relaxation in a Tube Attachment Weld Inside a Pressure Vessel Forging During Post Weld Heat Treatment

Volume 6: Materials and Fabrication ◽

10.1115/pvp2007-26290 ◽

2007 ◽

Cited By ~ 1

Author(s):

P. R. Hurrell ◽

J. Davies ◽

N. A. Leggatt ◽

R. J. Dennis ◽

R. H. Leggatt

Keyword(s):

Heat Treatment ◽

Residual Stress ◽

Stress Relaxation ◽

Pressure Vessel ◽

Hold Time ◽

Stress Relief ◽

Post Weld Heat Treatment ◽

Secondary Creep ◽

Axial Tensile ◽

Weld Heat

This paper presents analyses done to determine residual stress relief achieved by post weld heat treatment (PWHT) of tube attachment welds inside a thick SA508 steel pressure vessel forging. Finite element (FE) analyses were performed modelling the manufacturing operations in detail including welding, machining and PWHT. The analyses demonstrate that PWHT at 600°C for 8 hours is effective in reducing as-welded residual stress levels from tensile yield magnitude (+500MPa approx) to <100MPa. The maximum residual stress was computed to be 90MPa sub-surface in a region of hydrostatic (tri-axial tensile) stress. Secondary creep was modelled using data from creep tests on SA508 steel uni-axial tensile specimens. Practically all of the stress relaxation is due to creep strain with minimal additional plastic strain. Most stress relief occurs during the first hour of soak, with diminishing benefit thereafter. Analysis results also indicate that PWHT effectiveness is more sensitive to soak temperature than hold time. These FE results are considered slightly pessimistic but are reasonably consistent with other analytical predictions. By comparison surface hole drilling stress measurements of <50MPa (10% yield strength) were recorded from a representative welded test block. Analysis pessimism was attributed to ignoring both primary creep and relaxation during the slow warm up phase of the heat treatment cycle.

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Finite Element Modelling of a Tube to Vessel Attachment Weld and Local Post-Weld Heat Treatment

ASME 2011 Pressure Vessels and Piping Conference: Volume 6, Parts A and B ◽

10.1115/pvp2011-57944 ◽

2011 ◽

Author(s):

Benjamin M. E. Pellereau ◽

Paul R. Hurrell ◽

Christopher M. Gill ◽

Sarah L. Allen

Keyword(s):

Heat Treatment ◽

Finite Element ◽

Pressure Vessel ◽

Hold Time ◽

Measurement Data ◽

Stress Relief ◽

Post Weld Heat Treatment ◽

Isotropic Hardening ◽

Fe Model ◽

Weld Heat

This paper describes Finite Element (FE) modelling of a weld between a tube and a machined feature on a curved pressure vessel surface. The components were manufactured from a ferritic steel with a matched weld metal deposited by a mechanised TIG process. The weld region then underwent a local Post-Weld Heat Treatment (PWHT) which used heating bands and cooling air flows to control the temperature distribution. The PWHT’s aim was to provide stress relief and HAZ tempering, while minimising the stresses due to thermal gradients in the component. Trial welds on representative test pieces had predicted significant welding-induced distortions. Therefore, during the weld and PWHT, restraints were applied to the tube to prevent excessive deformation. The material behaviour was represented using Abaqus’ built-in material options, with the same properties for both the base metal and the filler. Isotropic hardening was assumed and the stress relaxation during the PWHT was modelled by applying a Norton creep law only during the hold time. Phase transformation effects in the ferritic material were not included. Initial modelling used a 2D axisymmetric model to allow sensitivity studies to inform the development of the PWHT process. These showed that the degree of stress relief was much more sensitive to the soak temperature than the hold time. Subsequent runs analysed a 3D model using a segmented block-dumping technique, with the deposition modelled by introducing the weld elements in 90° segments. The 3D modelling was undertaken in order to more accurately model potentially asymmetric welding distortions and residual stresses. The torch was represented by a body flux into each segment after its introduction. This model was also run without restraint to provide validation by comparing the predicted distortion with measurements from the welding trials; a good match was demonstrated. Further comparisons were made between the predicted stresses and results of Incremental Centre Hole-Drilling (ICHD) stress measurements made on the trial specimens both in the as-welded condition and after PWHT. The measured stresses were close to those predicted by the FE analysis and the key features of the predicted stress field were apparent in the measurement data. Due to the location of the tube’s attachment to the pressure vessel, thermal expansion of the vessel during the PWHT caused the tube to bend. The induced bending stresses were then relaxed during the soak and re-introduced in the opposite sense as the system cooled. This effect was captured by running the analysis as a submodel of a global FE model with displacements read across at nodes in the pressure vessel shell immediately below the weld.

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The Effect of PWHT on the Material Properties and Micro Structure in Inconel 625 and Inconel 725 Buttered Joints

Volume 3: Materials Technology; Ocean Engineering; Polar and Arctic Sciences and Technology; Workshops ◽

10.1115/omae2003-37196 ◽

2003 ◽

Cited By ~ 10

Author(s):

Vigdis Olden ◽

Per Egil Kvaale ◽

Per Arne Simensen ◽

Synno̸ve Aaldstedt ◽

Jan Ketil Solberg

Keyword(s):

Heat Treatment ◽

Impact Toughness ◽

Post Weld Heat Treatment ◽

Fusion Line ◽

Coarse Grained ◽

Inconel 625 ◽

Micro Structure ◽

Mixed Zone ◽

Heat Treated ◽

Weld Heat

This report describes investigations performed on as welded and post weld heat treated samples of AISI 8630 steel, buttered with Inconel 625 and Inconel 725. The investigations have focused on the properties and microstructure in the partial mixed zone between the buttering and the steel before and after post weld heat treatment. The samples were heat treated for 4 1/2 hours at 640°C, 665° and 690°C and investigated with respect to mechanical properties and microstructure near the fusion line. A range of testing and analyses were performed including notch impact toughness testing, identification of fracture initiation and propagation in impact specimens, hydrogen measurements, examination of the micro structure in steel and Inconel using light microscope, hardness testing and electron micro-probe analysis of the alloying elements across the fusion line. Additional investigations in TEM on samples from an actual joint, post weld heat treated at 665°C were also performed. The results show that post weld heat treatment at 665°C and 690°C reduced the impact toughness in coarse grained heat affected zone, caused by decarburisation, ferrite formation and grain growth. The partially mixed zone (5–10μm) of the Inconel buttering, gained partly extremely high hardness caused by carbon enrichment, reaustenitization and formation of virgin martensite. As welded samples gave more favorable properties and microstructure than the post weld heat treated ones.

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Effect on Hardness and Microstructures of Rail Joint with Ultra-Narrow Gap Arc Welding by Post Weld Heat Treatment

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.737.90 ◽

2017 ◽

Vol 737 ◽

pp. 90-94 ◽

Cited By ~ 4

Author(s):

Lian Gong ◽

Liang Zhu ◽

Hong Xiang Zhou

Keyword(s):

Heat Treatment ◽

Arc Welding ◽

Weld Seam ◽

Stress Relief ◽

Post Weld Heat Treatment ◽

Test Results ◽

Narrow Gap ◽

Narrow Gap Welding ◽

Scanning Electron ◽

Weld Heat

U71Mn rails were welded by ultra-narrow gap welding with constrained arc by flux strips，then normalizing treatment and stress relief annealing were performed for the joints. Another sample with no heat treatment, was studied in comparison. The effect of post weld heat treatment on the hardness and microstructure of rail joint were studied by scanning electron microscope (SEM) and microhardness test. The test results showed that normalizing treatment can improve the hardness of weld seam and base metal, and stress relief annealing couldn’t improve the hardness of joints obviously.

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