Influence of Long-Term Subcritical Annealing on the Unalloyed Steel Welded Joint Microstructure (original) (raw)
Related papers
Annealing Heat Treatment Effects on Steel Welds
Journal of Minerals and Materials Characterization and Engineering, 2010
This paper reports investigations made on the annealing heat treatment effects on steel welds. The properties of the weld investigated were hardness value and toughness. Micro examination of the samples was also done with optical microscopy. Four (4) different grades of steel rods (10mm) in diameter were obtained. The range of the carbon contents of the steel rods was from 0.16 wt pct C to 0.33 wt pct C. From each grade of the steel materials, grooved specimen of about 150mm were prepared. The groves were then filled to create welds using arc welding. The resulting welds were then subjected to annealing heat treatment. The hardness values and toughness of the welds were determined. The microstructural analyses of the welds were carried out as well. The results show that hardness and toughness were dependent on the carbon content. There was also significant microstructural modification due to heat treatment.
IOP Conference Series: Materials Science and Engineering, 2010
The structural changes of three trial weld joints of creep resistant modified 9Cr-1Mo steels and low alloyed chromium steel after post-weld heat treatment and long-term creep tests were investigated. Smooth cross-weld specimens ruptured in different zones of the weld joints as a result of different structural changes taking place during creep exposures. The microstructure of the weld joint is heterogeneous and consequently microstructural development can be different in the weld metal, the heat affected zone, and the base material. Precipitation reactions, nucleation and growth of some particles and dissolution of others, affect the strengthening of the matrix, recovery at high temperatures, and the resulting creep resistance. Therefore, a detailed study of secondary phase's development in individual zones of weld joints can elucidate mechanism of cracks propagation in specific regions and the causes of creep failure. Type I and II fractures in the weld metal and Type IV fractures in the fine prior austenite grain heat affected zones occurred after creep tests at temperatures ranging from 525 to 625 °C and under stresses from 40 to 240 MPa. An extended metallographic study of the weld joints was carried out using scanning and transmission electron microscopy, energy-dispersive and wave-dispersive X-ray microanalysis. Carbon extraction replicas and thin foils were prepared from individual weld joint regions and quantitative evaluation of dislocation substructure and particles of secondary phases has been performed.
Advanced Technologies & Materials, 2019
The effect of Post Weld Heat Treatment (PWHT) on the microstructure, mechanical and corrosion properties of low carbon steel have been investigated. The welding process was conducted on butt joint using Manual Metal Arc Welding (MMAW) techniques at a welding voltage of 23 V and welding current of 110 A with the use of E6013 and 3.2 mm diameter as filler material. Heat treatment through full annealing was carried out on the welded low carbon steel. The mechanical properties (hardness, impact toughness and tensile properties) of the AW and PWHT samples were determined. The microstructure of the AW and PWHT samples was characterized by means of an optical microscopy. Corrosion behavior of the sample was studied in3.5 wt.% NaCl environment using potentiodynamic polarization method. The results showed that the AW samples has good combination of mechanical and corrosion properties. The microstructure revealed fine grains of pearlite randomly dispersed in the ferrite for the AW base metal (BM) sample while agglomerated and fine particle of epsilon carbide or cementite randomly dispersed on the ferritic phase of the heat affected zone (HAZ) and weld metal (WM), of the AW, respectively. The PWHT samples shows that the annealing process allow diffusion and growth of the fine grains into partial coarse grains of ferrite and pearlite which did not encourage improvement of the properties. Therefore, it was concluded that the welding parameters put in place during welding of the low carbon steel are optimum for quality weld.
Lecture Notes in Electrical Engineering, 2021
The present investigation analyzes the influence that a welding process has on the microstructure and hardness in the heat-affected zone, due to successive repairs in welded joints of low alloy and high resistance steel. AISI 4140 steel plates, with dimensions 200x75x40 mm were used to build the test assemblies. In particular, four assemblies were welded to perform the analysis. The welding procedure specifications were as follow: GMAW process for fabrication and SMAW process with low hydrogen electrodes for repairing. The welding procedure applied to the manufacturing and repairing of high-pressure pipes of hydroelectric plants was deployed. For the manufacturing and repair stages, the assemblies were labeled from 1 to 4 and distributed as: (1) production welding simulation, and (2), (3), and (4) for one, two, and three, repair processes simulation, respectively. The dimensions and thickness of the assemblies were determined according to the ASME BPVC Section IX code. To determine the changes in the metallographic structure of the base material after each repair process the following tests were executed: penetrant testing, micro hardness test, and metallurgical analysis. As a result, while the number of repairs increased, the formation of martensite in the metallographic structure and the formation of cracks in the thermally affected area at the root of the welded joint also increased.
Effect of post-welding heat treatments on mechanical
2013
The present study focuses on the effect of postwelding heat treatments on mechanical properties of double-lap Friction Stir Wel ded (FSW) joints in 2024T3 and 7075T6 aluminium alloys. Heat treatments were performed at aging and solution temperatures. Micro-hardness profiles measured on transversal sections of postwelded heat treated joints reveal conditions (temperature and time) of hardness homogeneity at top, bottom and central nugget zone along the whole measured profile. When hardness homogeneity is reached, fracture occurs in the nugget. The double lap FSW joints after post-welding heat treatments at low temperatures (200°and 300°C) have tensile properties comparable with the as-FSW joint and fracture occurs in 7075T6 Base Material. At higher temperatures, fracture strain is almost 50% of joints deformed after heat treatment at lower temperature and failure occurs inside the stir zone. Polarized Optical Microscopy (POM) and Scanning Electron Microscopy (SEM) analysis reveal a progressive change in grain size and morphology in high temperature post-welding heat treated joints, leading to Abnormal Grain Growth in the stir zone.
Materials Science, 2012
The article deals with the ageing and heat treatment influence on operational reliability of 5 % Cr-0.5 % Mo steel welded joints and pipeline elements. Separate components of the pipelines in the refineries are manufactured from chromemolybdenum 5 % Cr-0.5 % Mo alloy steel. Reduction of internal stresses in chrome-molybdenum steel welded joints can be provided only by thermal treatment. Other methods of stress relieving are not acceptable for these steels. Presented materials analyses the impact of heat treatment on the microstructure and operational reliability of this steel. The objects of research are heat-treated welded joints of piping elements operated at high temperature for an extensive period of time, where degradation of mechanical properties has been observed. When value of the heat treatment temperature or time are exceeded, the structure degradation process is taking place, carbides coagulate within the boundaries of ferrite grains, they form coarse carbide colonies combined into long chains. Mechanical properties-tensile strength and impact strength decrease. Detailed analysis of these objects and the interpretation of the received results allow to select the most appropriate heat treatment parameters for the investigated steel structures.
Today getting high thermal efficiency in thermal and nuclear power plant is a big challenge. Many new material are developed. SA 335 grade 91 steel is modified high chrome-moly martenstitic steel. This material is having excellent toughness and high temperature creep strength. During welding, this material is having tremendous change in its microstructure and hence mechanical property. Many research works were done in this area. This paper discusses weld ability of P91 material. Effect of different welding process, type of filler wire, its chemical composition and type of flux is discussed in this paper. PWHT is necessary after welding of P91 steel. PWHT temperature and its duration affects phase transformation and mechanical properties of weld metal, HAZ and parent metal. Major focus is given on hardness, creep resistance and notch toughness.
Materials
The purpose of the research was to obtain an arc welded joint of a preliminary quenched high-carbon wear resistant steel without losing the structure that is previously obtained by heat treatment. 120Mn3Si2 steel was chosen for experiments due to its good resistance to mechanical wear. The fast cooling of welding joints in water was carried out right after welding. The major conclusion is that the soft austenitic layer appears in the vicinity of the fusion line as a result of the fast cooling of the welding joint. The microstructure of the heat affected zone of quenched 120Mn3Si2 steel after welding with rapid cooling in water consists of several subzones. The first one is a purely austenitic subzone, followed by austenite + martensite microstructure, and finally, an almost fully martensitic subzone. The rest of the heat affected zone is tempered material that is heated during welding below A1 critical temperature. ISO 4136 tensile tests were carried out for the welded joints of 120...
The lean duplex stainless steel welded joint after isothermal aging heat treatment
The purpose of this paper is the microstructural evaluation of the lean duplex stainless steel UNS S32101 (EN 1.4162) welded joints after isothermal aging heat treatment at 650°C. The scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) was applied in the microstructural analysis. Design/methodology/approach: The welding joints were produced using the metal active gas (MAG) method where the filler metal was in wire form grade Avesta LDX 2101. During the process a shielding gas mixture of Ar + 2.5% CO 2 was applied and as a forming gas pure technical argon was used. Findings: The welded joint in the as-welded condition shows Cr 2 N nitride precipitation in the HAZ, while isothermal aging at 650°C for 15 min causes further precipitation of nitrides, both in the parent metal, as well as in the HAZ and the weld area. Increasing the aging time at this temperature to 90 min causes the formation of numerous nitrides at the grain boundaries of austenite and ferrite and nitride precipitation inside ferritic grains in each zone of the welded joint. Research limitations/implications: The electron backscatter diffraction of particular zones of the welded joints considered only austenite and ferrite and their character was evaluated, while small precipitates like chromium nitrides were omitted in this study and will be evaluated in the further work. Originality/value: Sometimes the production cycle involves the heat treatment of welded components made of lean duplex stainless steel. In such situations the additional heating of the welds and heat affected zone can produce carbides, nitrides or sigma phase precipitation-the extent of which depends on the temperature and time of heat treatment. These issues are widely reported in relation to the base material but not when considering welded joints, which may behave differently.
Archives of Metallurgy and Materials, 2013
This paper presents the studies of the microstructure and properties of the welded joints made of 15-7Mo precipitation hardened semi-austenitic stainless steel welded by Tungsten Inert Gas. Microstructural changes in the heat treated welded joints was assessed. It was found that the joints of 15-7Mo steel in as welded state contain martensite, austenite and δ-ferrite. Scanning electron microscope study of the joints was carried out. The sub-zero and destabilization heat treatment were found to decrease or completely eliminate the austenite in the microstructure and increase hardness of the welded joint.