Microstructure and microchemistry of laser welds of irradiated austenitic steels (original) (raw)
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Microstructure and microchemistry of laser welds of irradiated austenitic steels q
has been authored in part by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).
Materials, 2021
In this study, ultra-high-strength steels, namely, cold-hardened austenitic stainless steel AISI 301 and martensitic abrasion-resistant steel AR600, as base metals (BMs) were butt-welded using a disk laser to evaluate the microstructure, mechanical properties, and effect of post-weld heat treatment (PWHT) at 250 °C of the dissimilar joints. The welding processes were conducted at different energy inputs (EIs; 50–320 J/mm). The microstructural evolution of the fusion zones (FZ) in the welded joints was examined using electron backscattering diffraction (EBSD) and laser scanning confocal microscopy. The hardness profiles across the weldments and tensile properties of the as-welded joints and the corresponding PWHT joints were measured using a microhardness tester and universal material testing equipment. The EBSD results showed that the microstructures of the welded joints were relatively similar since the microstructure of the FZ was composed of a lath martensite matrix with a small ...
Influence of Irradiation and Laser Welding on Deformation Mechanisms in Austenitic Stainless Steels
2019
This dissertation describes the recent advancements in micromechanical testing that inform how deformation mechanisms in austenitic stainless steels (SS) are affected by the presence of irradiation-induced defects. Austenitic SS is one of the most widely utilized structural alloys in nuclear energy systems, but the role of irradiation on its underlying mechanisms of mechanical deformation remains poorly understood. Now, recent advancement of microscale mechanical testing in a scanning electron microscope (SEM), coupled with site-specific transmission electron microscopy (TEM), enables us to precisely determine deformation mechanisms as a function of plastic strain and grain orientation. We focus on AISI 304L SSs irradiated in EBR-II to ~1-28 displacements per atom (dpa) at ~415 °C and contains ~0.2-8 atomic parts per million (appm) He amounting to ~0.2-2.8% swelling. A portion of the specimen is laser welded in a hot cell; the laser weld heat affected zone (HAZ) is studied and consi...
Microstructural Changes During Laser Beam Welding of Austenitic Stainless Steel Sheets
Acta Materialia Transylvanica, 2020
The purpose of our study was to investigate the properties of welded joints formed by 1.5 mm thick plates with a diode laser beam equipment. The technological parameters influence the shape of the weld metal. In the heat affected zone no grain coarsening appeared. Increasing the welding speed, in case of similar laser power, the ferrite content of weld metal decreases. The hardness’ of the streams are higher than that of base metal, but the highest values were measured in heat affected zones.
Microstructure-property relationship for AISI 304/308L stainless steel laser weldment
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2018
Laser welding is attractive for numerous applications requiring materials joining, due to its low energy input. However, it is unknown how the laser welding process influences the microstructure-property relationship across the weldment. The objective of this study is to determine the strengthening mechanisms in the weld metal, base metal, and heat affected zone (HAZ) of an AISI 304/308L stainless steel (SS) laser weldment. Scanning electron microscopy (SEM) with electron backscattered diffraction (EBSD) scanning and transmission electron microscopy (TEM) was used to evaluate the microstructure, and static nanoindentation was used to evaluate strength across the weldment. Although the HAZ has a finer dendritic grain structure, its higher hardness compared to the base and weld metal cannot be explained by the Hall-Petch relationship. Therefore, a new strengthening model for weldments that considers the evolution in grain boundary size and orientation angle, as well as dislocation density, precipitation, and solid solution is proposed. Notably, core-shell TiC -N precipitation, which provides Orowan dislocation bypass strengthening, is found to be a major contributor to strengthening in the HAZ. The proposed model predictions fall within 10% of experimentally measured properties for all three regions of the analyzed weldment.
Microstructure and Mechanical Properties of Laser Beam Welds of 15CDV6 Steel
The present study is concerned with laser beam welding of 15CDV6 steel, that is in the hardened (quenched and tempered) condition before welding. Autogenously butt-welded joints are made using carbon dioxide laser with a maximum output of 3.5 kw in the continuous wave mode. Weld microstructure, microhardness measurement across the weldment, transverse tensile properties, and room temperature impact properties of the weldment have been evaluated. The fusion zone exhibits a epitaxial grain growth. The microstrutural features of heat-affected zone and fusion zone vary, due to different thermal cycles for which these were subjected during welding. The average weld metal hardness was 480 Hv. The observed hardness distribution across the welds were correlated with the micro structures. The welds exhibited lower toughness of 50 joules as compared to parent metal of 55 joules and the tensile strength values of the welded specimens are close to that obtained for sheet specimens.
ISIJ International, 2006
Microstructure and high temperature oxidation behaviour of laser weldments of 316L and 316LN steels have been found to influence by the variation in welding speed. Ferrite content and ferrite morphology change for both type 316L and 316LN laser weld with welding speed. Laser weldments consisting mainly of weld metal and base metal region of two austenitic stainless steels (ASS) were oxidized in dry air at 973 K for 240 h. Steel weldment was found to have a higher oxidation rate when joined with lower welding speed of 11.66 mm/s as compared to 25 mm/s speed. On the other hand, 316LN steel weldments have indicated much superior oxidation resistance property under similar condition. Oxidation behaviour of two ASS weldments has been correlated with microstructure and oxide scales formed over the different regions have been characterized by scanning electron microscopy (SEM/EDXA).
Laser Dissimilar Welding of AISI 430F and AISI 304 Stainless Steels
Materials, 2020
A dissimilar autogenous laser welded joint of AISI 430F (X12CrMoS17) martensitic stainless steel and AISI 304 (X5CrNi18-10) austenitic stainless steel was manufactured. The welded joint was examined by non-destructive visual testing and destructive testing by macro- and microscopic examination and hardness measurements. With reference to the ISO 13919-1 standard the welded joint was characterized by C level, due to the gas pores detected. Microscopic observations of AISI 430F steel revealed a mixture of ferrite and carbides with many type II sulfide inclusions. Detailed analysis showed that they were Cr-rich manganese sulfides. AISI 304 steel was characterized by the expected austenitic microstructure with banded δ-ferrite. Martensitic microstructure with fine, globular sulfide inclusions was observed in the weld metal. The hardness in the heat-affected zone was increased in the martensitic steel in relation to the base metal and decreased in the austenitic steel. The hardness range in the weld metal, caused by chemical inhomogeneity, was 184–416 HV0.3.
Development of Weld Metal Microstructures in Pulsed Laser Welding of Duplex Stainless Steel
Journal of Materials Engineering and Performance, 2012
The microstructure of the weld metal of a duplex stainless steel made with Nd:YAG pulsed laser is investigated at different travel speeds and pulse frequencies. In terms of the solidification pattern, the weld microstructure is shown to be composed of two distinct zones. The presence of two competing heat transfer channels to the relatively cooler base metal and the relatively hotter previous weld spot is proposed to develop two zones. At high overlapping factors, an array of continuous axial grains at the weld centerline is formed. At low overlapping factors, in the zone of higher cooling rate, a higher percentage of ferrite is transformed to austenite. This is shown to be because with extreme cooling rates involved in pulsed laser welding with low overlapping, the ferrite-to-austenite transformation can be limited only to the grain boundaries.
Materials & Design, 2013
Martensitic stainless steels are often used in cases where high strength and medium corrosion resistance are required. In this study, pulsed Nd:YAG laser welding of AISI 420 martensitic stainless steel is considered. Welding of samples were carried out autogenously. The spacing between samples was set to almost zero. All samples were butt welded. The effect of welding parameters such as voltage, laser beam diameter, frequency, pulse duration, and welding speed on the weld dimensions were investigated and the optimum values were obtained for the 450 V voltage, 0.6 mm focal diameter, 6 Hz frequency, 5 ms pulse duration and 1.5 mm/s welding speed. Microstructure of weld pool and heat affected zone (HAZ) were investigated by optical microscopy (OM) and scanning electron microscopy (SEM). Micro-hardness studies were also carried out. The results showed the presence of some remaining delta-ferrite in the martensitic weld structure and coarsening of M 23 C 6 carbides in HAZ. The magnitude of hardness in the HAZ was higher than that of the weld zone. To reduce the hardness of weld and HAZ and to increase the toughness in these regions, two types of post-weld heat treatments (PWHTs) were carried out. In type 1, samples tempered for 2 h. In type 2, samples austenitizied for 0.5 h at 1010°C and then tempered for 2 h. In order to achieve high strength and toughness, optimum temper temperatures for type 1 and 2 heat treatments were obtained for 595 and 537°C, respectively. The results showed higher toughness for type 2 than type 1.