Increasing the welding interpass temperature (IT) can reduce the welding time and cost of welding but may degrade the quality of the welded joint. The objective of the present study was to analyze ...the effects of the IT on microstructure and Charpy V-notch (CVN) impact energy of coarse-grain heat-affected zone (CGHAZ) of an AISI 4130 steel welded pipe. The welding was computationally simulated using finite element method. The CGHAZ was physically simulated and evaluated via optical and scanning electron microscopy, electron backscatter diffraction analysis, Vickers microhardness, and CVN impact. The numeric model had an accuracy of 97.5% (difference in the simulated and measured maximum temperatures), with a simulated cooling rate equal to the measured value. An increase in IT changed the microstructure from bainite (B) and martensite (IT 315 °C) to B, ferrite with aligned martensite–austenite–carbide (AC), and pro-eutectoid ferrite (FP) (IT 400 °C), followed by ferrite AC, FP, ferrite with non-aligned martensite-austenite-carbide, and ferrite–carbide aggregate (IT 475 and 550 °C). These changes in microstructure significantly impacted the effective grain size and grain boundary character distribution, which directly influenced CVN impact energy of the CGHAZ. IT = 315 °C exhibited the highest CVN impact energy (89 J), and ITs ≥ 400 °C did not satisfy the ASME 31.3 code. Therefore, indiscriminately increasing the IT is unsuitable method for reducing the welding cost for AISI 4130 steel pipes.
Welding costs associated with the laying of pipes for deepwater oil and gas extraction can be reduced using high interpass temperatures (ITs). However, a high IT can decrease the mechanical ...properties of the heat-affected zone (HAZ) of welded joints. With the use of high strength-toughness steels, this decrease may be an acceptable trade-off. Therefore, it is necessary to evaluate the influence of high ITs on the HAZ. The influence of the IT on the coarse-grain HAZ (CGHAZ) and intercritically reheated coarse-grain HAZ (ICCGHAZ) of an API 5L X70 pipe joint welded by gas metal arc welding was investigated. The welding was numerically simulated using finite element method software. The microstructure of the HAZ was predicted using thermodynamic simulation software. The CGHAZ and ICCGHAZ were also physically simulated and evaluated via optical microscopy and scanning electron microscopy, dilatometry, and Vickers microhardness and Charpy V-notch (CVN) impact tests. The increase in IT led to a decrease in CGHAZ microhardness but did not affect the ICCGHAZ. The CVN energies obtained for all ITs (CGHAZ and ICCGHAZ) were higher than that set by the DNVGL-ST-F101 standard (50 J). These results show that increasing the IT is an interesting and effective method to reduce welding costs. In addition, thermodynamic simulation proved to be a valid method for predicting the phases in the HAZ of API 5L X70 pipe welded joints.
With the aim of reducing pipe-laying costs through the application of more efficient welding techniques, this study evaluated the influence of an interpass temperature (IT) higher than 230 °C ...(Petrobras N-133 IT standard specific limit) on the microstructure, Vickers microhardness, and Charpy V-notch (CVN) impact energy of the simulated coarse-grained and intercritically reheated coarse-grained heat-affected zones (CGHAZ and ICCGHAZ, respectively) of a clad API 5L X65 pipe gas metal arc welded joint. The welding was computationally simulated using Sysweld®, a commercially finite element method (FEM) software. In response to an increase in the IT, the microstructure of the CGHAZ transformed from martensite to lath and granular bainite, which led to a decrease in the microhardness. Conversely, the microstructure of the ICCGHAZ transformed from needle-like to elongated grains of ferrite in response to an increased IT, but this change did not significantly influence the microhardness. The increase in the IT led to the formation of a dot-shape and necklace-type martensite-austenite (M-A) constituent (
IT
≥ 360 °C); however, it did not compromise the CVN impact energy of the CGHAZ because all ITs were higher than that set by the DNVGL-ST-F101 standard (45 J). For the ICCGHAZ, an increased IT led to the formation of block-like and massive M-A, which decreased the CVN impact energy and did not meet the DNVGL-ST-F101 standard at
IT
= 420 °C. Therefore, an increase in the IT up to 360 °C can serve as an alternative strategy to reduce the welding cost.
The present work characterized the 9 pct Ni steel heat-affected zone (HAZ). HAZ thermal cycles (peak temperatures—
T
p
—of 500 °C, 600 °C, 650 °C, 700 °C, 750 °C, 850 °C, 1100 °C, and 1370 °C) were ...numerically (FEM model) and physically (Gleeble machine) simulated. The simulated HAZ was evaluated through optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), dilatometry, and Vickers hardness.
T
p
≤ 650 °C had microstructure similar to base metal;
T
p
of 700 °C yielded the partial transformation (
A
c1
<
T
p
<
A
c3
) and presence of ferrite and martensite;
T
p
> 750 °C yielded martensite (majority) with maximum hardness (344 HV10) for
T
p
= 850 °C. The amount of austenite was maximum (3.1 pct) to
T
p
= 700 °C and decreased to
T
p
≥ 750 °C, becoming approximately zero for
T
p
≥ 1100 °C. Besides, the austenite quantification methodology (electrolytic polished and 4 pct Picral etching + SEM image analysis) was validated through XRD measurement and used to analyze the roundness and number of austenite particle size of the BM and HAZ subzones. Its roundness and amount remained are close to the BM for
T
p
≤ 650 °C, increase in the
T
p
= 700 °C, and decrease for
T
p
≥ 750 °C.
Increasing the welding interpass temperature (IT) reduces the welding time and cost, particularly for offshore welding pipeline construction. However, it may degrade the mechanical properties of the ...welded joint; therefore, it is necessary to evaluate the effect of high IT on the heat-affected zone (HAZ). The influence of IT as high as 400 °C on the coarse-grained and intercritically reheated coarse-grained HAZs (CGHAZ and ICCGHAZ, respectively) of a Ni-based superalloy 625 (corrosion-resistant alloy UNS N06625) clad API 5 L X65 pipe was investigated. The joints were welded using a mechanized gas metal arc. The base metal (BM) and HAZ of the joints were evaluated using optical and scanning electron microscopy, as well as Vickers hardness, tensile strength, Charpy V-notch (CVN) at −30 °C, and crack tip opening displacement (CTOD) fracture toughness (−20 °C) testing. The CVN energy decreased as the IT increased from 300 to 400 °C owing to the formation of a large martensite-austenite-carbide (MAC) in the CGHAZ; however, all tests performed on joints welded at ITs up to 360 °C were considered acceptable based on DNVGL-ST-F101 requirements. The toughness results of the joint welded at an IT of 400 °C were not satisfactory, which indicates potential risks for the welding procedure qualification in this temperature range. Based on these findings, an increase in the IT up to 360 °C during gas metal arc welding (GMAW) using the adopted heat input is feasible. Moreover, this IT may be adopted for cost reduction because it decreases the total welding time by approximately 3 min per joint in the offshore welding of nickel-based superalloy 625 clad API 5 L X65 pipes.
The microstructure, Vickers microhardness, and prior austenite grain size (PAGS) of the heat-affected zone (HAZ) in a circumferential welded joint of a 9% Ni steel pipe were compared with those of a ...physically simulated (Gleeble machine) HAZ to validate a developed methodology for evaluating the HAZ via finite element method simulation. The welding of the cap pass was computationally simulated; subsequently, the thermal cycles of the HAZ subzones were reproduced (thermomechanical simulator), and the HAZ (physically simulated and of the welded joint) microstructures were compared. The HAZs in these conditions showed similar microstructures, microhardnesses, and PAGSs, thereby validating the developed methodology. The subcritical (SCHAZ), intercritical (ICHAZ), fine-grain (FGHAZ), and coarse-grain HAZs (CGHAZ) exhibited base metal unaltered microstructure, dual-phase microstructures (martensite and ferrite), refined martensite, and coarse martensite with coalesced bainite, respectively. The physically simulated HAZ was investigated using X-ray diffraction spectroscopy and transmission electron microscopy, and it exhibited globular and thin-film austenite morphologies, with minimum and maximum contents in the CGHAZ and ICHAZ, respectively. The developed computational and physical simulation methodology can be reliably reproduced and can evaluate the HAZ microstructure of the 9% Ni steel welded joint.
A 9%Ni steel (ASTM A333 Gr. 8) was selected for the first time for use in CO2 injection units (CO2-IUs) in the Brazilian pre-salt; however, because of the presence of H2S, it is susceptible to ...sulfide stress cracking (SSC), especially in welded joints. In this regard, the susceptibility to SSC of the subzones of the heat-affected zone (HAZ) of a 9%Ni steel (BM) welded pipe joint was evaluated. The thermal cycles of the HAZ were simulated numerically and physically. HAZ subzones were evaluated through optical microscopy, scanning electron microscopy, X-ray diffraction, Vickers microhardness, and slow strain rate testing. The BM and subcritical HAZ showed similar microstructures (fine ferrite and carbide/retained austenite(γret) aggregates) and behaviors in aggressive environment, with plastic elongation ratios (REs) of 0.15 and 0.17, respectively. The intercritical HAZ (ICHAZ; fine ferrite and martensite) had the highest microhardness and γret content, with a decrease in RE(0.04); fine-grain HAZ (FGHAZ; martensite and bainite) showed the smallest RE(0.01) and brittle fracture. The coarse-grain HAZ (CGHAZ; coarse martensite and coalesced bainite) showed the lowest plastic region and brittle fracture, with RE of 0.05 and the highest time-to-failure ratio. The high microhardness of the ICHAZ, FGHAZ, and CGHAZ (>250HV, NACE 0175/ ISO15156) made them more susceptible to SSC than the BM. These results lead to the conclusion that both the 9%Ni steel and its welded joints are prone to SSC, and the use of this steel in CO2-IUs presents an operational failure risk.
Finite element method (FEM) simulations are a powerful tool for understanding the thermal–metallurgical–mechanical effects of wire arc additive manufacturing (WAAM). Nonetheless, owing to the ...multiphysical nonlinear nature of welding coupled with the longer deposition time of WAAM, FEM simulations can be laborious and time-consuming, which makes it difficult to simulate the numerous procedural parameters of WAAM. Therefore, the present work aimed to employ an FEM mode to analyze the influence of idle time (30–240 s) on the interpass temperature (IT) of 20-layer single-bead walls produced via WAAM and use the FEM results to develop a predictive model for the IT based on an artificial neural network (ANN). The FEM simulations were performed using a heat source and a 20-layer single-bead wall model that was experimentally calibrated and validated. The first layers exhibited similar energy accumulation; however, as the wall height increased, the IT rapidly increased under to low idle times (≤120 s). The ANN was trained using the FEM simulations results, validated with FEM results (not included in the training database), and used to establish a process map (including the idle time, number of layers, and IT). This can help the manufacturers to obtain a suitable balance between productivity (lower idle times) and part behavior (e.g., microstructure and mechanical properties).
•A FEM 20 single-bead layer wall WAAMed model was accurately calibrated and experimentally validated;•The influence of idle time (30–240 s) on interpass temperature (IT) was analyzed trough the FEM model;•FEM results were used as database to train an artificial neural network (ANN);•ANN was used to predict the process map considering the idle time, layer number, and IT.
This work aimed to develop a microstructure-predicting methodology (MPM) using coupled physical-FEM-thermodynamic simulation to predict the influence of cooling time from 800 to 500 °C (t8/5 – 15, ...30, 80, and 210 s) on the microstructure and mechanical behavior of the coarse grain heat-affected zone (CGHAZ) of a Cr-Mo low alloy steel welded joint. The MPM was experimentally validated. The MPM certainly predicted that the increase of t8/5 caused a remarkable change in CGHAZ microstructure (martensite and bainite to ferrite with aligned and non-aligned martensite-austenite-carbide M-A-C) and also decreases the Vickers microhardness. The MPM and experimental data show that the use of welding parameters that increases t8/5 (reducing the cooling rate) can jeopardize the welded joint behavior. Besides, the MPM proved to be a suitable tool for estimating the microstructure and microhardness of the CGHAZ.
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