The Microstructure of Dissimilar Chromium Steel Welds during PWHT and In-Service Exposure
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Welding residual stresses have consequences for the performance of welded components. The remaining stresses can be reduced by post-weld heat treatment (PWHT). In this study, A517-Gr.B steel specimens welded by shielded metal arc welding (SMAW) were subjected to PWHT at 450 °C, 500 °C, 550 °C, and 600 °C to study the effects of these temperatures on yield, tensile, bending, and impact strengths. The fracture surfaces of the specimens heat treated at different temperatures were studied using the scanning electron microscope (SEM). The results indicated that the optimum temperature for PWHT was below 500 °C. Higher PWHT temperatures increased yield strength, tensile strength, and ductility of the weld piece but greatly decreased its bending weld strength.
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Welded joints of high-Cr ferritic heat-resistant steel, ASTM A335 Gr. P91, were subjected to post weld heat treatment (PWHT) to improve mechanical properties and to reduce residual stress. We have measured the A c1 of weld metals for Gr. P91 steel, containing varying amounts of Mn+Ni, and have examined the effects of PWHT temperatures on the mechanical properties of each weld metal. The upper limits of the PWHT temperature for the respective weld metals are considered.
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Austenitic stainless steel and nickel-base alloys welds are widely used in nuclear reactor components, plants of energy generation, chemical, and petrochemical industries, due to their high corrosion resistance. The post weld heat treatments (PWHT) are generally applied to welding in order to relieve the welding residual stress. The aim of this work was to evaluate the influence of different PWHT on corrosion behavior of a dissimilar weld joint of two AISI 316L austenitic stainless steel plates with a nickel-base alloy as filler material in saline environments. The material was submitted to heat treatments for three hours at 600, 700 and 800 °C. The weld joint was examined by optical microscopy to determine the effects of PWHT in the microstructure. The corrosion behavior of the samples before and after heat treatment was evaluated using cyclic potentiodynamic polarization (CPP) in sodium chloride solutions (19% v/v) and pH 4.0 at room temperature. Metallographic analyses showed that delta ferrite dissolute as PWHT temperature increased. CPP curves demonstrated an increase of pitting corrosion resistance as the PWHT temperature rises, although the pit size has been increased. The heat treated weld joint at 600 °C showed a similar corrosion resistance compared to as-welded material.
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s. On construction sites many challenges and premature failures are being encountered in welded joints of creep strength-enhanced ferritic (CSEF) steels. The primary reason of these premature failures is found to be the dissimilar material joints, having strength mismatch, or improper heat treatment that is mandatorily carried out to achieve the required weld hardness. This study aims at determining the impact of post welding heat treatment (PWHT) on dissimilar alloy steels joints, between ASTM A335 Gr. P-22 and ASTM A335 Gr. P-91 steels, welded by gas tungsten arc welding (GTAW) using ER 90S-B9 filler wire. The PWHT, at 745°C for 1hr., was applied to attain the required hardness. The effect of PWHT was investigated on the weld metal and the heat affected zones (HAZ) by hardness testing. Due to the martensitic microstructure, the hardness values of HAZ of P91 steel are over 350 HV. However, the hardness value of the P22 HAZ less than 350 HV. P91 HAZ has a higher hardness value than P22 HAZ because of its higher hardenability and due to phase transformation from martensite to ferrite. The interaction between the too high hardness microstructure with hydrogen can result in the hydrogen induced cracking (HIC) initiation in the HAZ. Therefore, the PWHT is needed to reduce this high hardness HAZ.
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This paper reviews the results of investigations on how post-weld heat treatment (PWHT) influences the hardness and microstructures of welded joints in stainless steel X3Cr-NiMo 13-4. It is known that welding leads to high segregation of components in the solidification process, which has an influence on phase transitions in PWHT. The investigated steel has a very narrow PWHT range, about 600–620°C, which provides optimum levels of hardness and toughness. Excessive annealing temperature leads to decreased toughness, which in turn causes exceeding of the Ac1 temperature in the segregation range, which then leads to increased 'fresh' martensite content.
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CA6NM steel is widely used in the manufacture of hydraulic turbines metallic parts, due to its resistance to corrosion and cavitation damage, combined with good weldability and fatigue properties. However, welding of this type of steel is complex and to ensure a minimum residual stress after welding it is necessary perform a post welding heat treatment (PWHT) of the part. This study aims to analyze the effect of a PWHT on the microstructure and mechanical properties of CA6NM steel weld joint produced by the FCAW process and compare it with the characteristics of an as-welded joint. A martensitic microstructure has been present in both materials. However, the PWHT material has shown finely dispersed retained austenite, in an amount near 10 vol.%. Vickers microhardness values of all regions of PWHT welded joint present lower hardness values compared to those of the as-welded joint. Despite nearly identical toughness values of the weld metal from AW and PWHT samples, results of fracture analysis have shown distinct features in appearance of the fractures.
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