Microstructure Of Weld Heat-affected Zone Research Articles

Effect of Post-Weld Heat Treatment Temperature on the Mechanical Properties and Microstructure of Weld Heat-Affected Zone of 2.25Cr-1Mo Steel

The effect of post-weld heat treatment (PWHT) temperature on the mechanical properties of the heat-affected zone (HAZ) of 2.25Cr-1Mo steels was investigated. SA-387 Gr. 22 Cl. 2 steel was employed, and the specimens taken from the steel were thermally cycled using Gleeble to simulate the coarse-grained HAZ (CGHAZ), fine-grained HAZ (FGHAZ), and intercritical HAZ (ICHAZ). Before the PWHT, the simulated HAZs exhibited poor impact toughness as compared with the base metal. The base metal and simulated HAZ specimens were heat treated in a furnace at 610, 650, 690, and 730℃ for 8 h; their impact toughness improved significantly irrespective of the PWHT temperature. The microstructural changes owing to the PWHT were observed using scanning electron microscopy and correlated with the mechanical properties.

Effect of Post-Weld Heat Treatment Temperature on the Mechanical Properties and Microstructure of Weld Heat-Affected Zone of Low-Alloy Steel for Nuclear Reactor Pressure Vessel

The effect of post-weld heat treatment (PWHT) temperature on the mechanical properties of the heat-affected zone (HAZ) of P-No. 3 low-alloy steel was investigated by taking into account the changes in microstructure. SA-508 Gr. 3 Cl. 1 forged steel was employed, and the specimens taken from the steel were thermally cycled using a Gleeble simulator to simulate coarse-grained HAZ (CGHAZ), fine-grained HAZ (FGHAZ), intercritical HAZ (ICHAZ), and subcritical HAZ (SCHAZ). The respective base metal and simulated HAZ specimens were heat treated in a furnace at 610, 650, 690, and 730°C for 8 hours. Before the heat treatment, the ICHAZ, FGHAZ and CGHAZ exhibited high hardness and poor impact toughness. However, when the PWHT was applied, the hardness decreased and the impact toughness improved; the impact toughness was highly dependent on the PWHT temperature. The impact toughness of the ICHAZ and FGHAZ increased significantly when the PWHT temperature was 650°C or below, while that of CGHAZ improved significantly when the PWHT temperature was 650°C or higher. The microstructural changes due to the PWHT were observed by scanning electron microscopy and correlated with the mechanical properties.r composed of iron-based composition system had similar characteristics to the material to be repaired. Key words: Low-alloy steel, Heat-affected zone, Post-weld heat treatment, Impact toughness

Factors Affecting Impact Toughness in Stabilized Intermediate Purity 21Cr Ferritic Stainless Steels and Their Simulated Heat-Affected Zones

The correlation between simulated weld heat-affected zone microstructures and toughness parameters has been investigated in four intermediate purity 21Cr ferritic stainless steels stabilized with titanium and niobium either separately or in combination. Extensive Charpy V impact toughness testing was carried out followed by metallography including particle analysis using electron microscopy. The results confirmed that the grain size and the number density of particle clusters rich in titanium nitride and carbide with an equivalent circular diameter of 2 µm or more are statistically the most critical factors influencing the ductile-to-brittle transition temperature. Other inclusions and particle clusters, as well as grain boundary precipitates, are shown to be relatively harmless. Stabilization with niobium avoids large titanium-rich inclusions and also suppresses excessive grain growth in the heat-affected zone when reasonable heat inputs are used. Thus, in order to maximize the limited heat-affected zone impact toughness of 21Cr ferritic stainless steels containing 380 to 450 mass ppm of interstitials, the stabilization should be either titanium free or the levels of titanium and nitrogen should be moderated.

Effect of microstructure and grain size on the fracture toughness of a micro-alloyed steel

It has been reported that the high temperature austenitisation heat treatments have resulted in improving the fracture toughness of several structural steels. This is contrary to the conventional understanding of the relationship between larger prior austenite grain sizes, associated with high austenitising temperature, and fracture toughness. This anomalous increase in fracture toughness has some important practical significance to welded joints where the material adjacent to fusion zone experiences high austenitising temperatures resulting in a coarse grain zone. This investigation has been undertaken to verify the effects of microstructure and grain size on fracture toughness in a typical pressure vessel steel that is extensively welded during fabrications. A range of simulated weld heat affected zone microstructures were produced by austenitising the specimens at various temperatures followed by quenching at three different cooling rates. The trends of variations in properties, such as, fracture toughness are explained in terms of grain size, and microstructural analyses. It was observed that the specimens provided with low temperature austenitisation followed by air-quench possess a better fracture toughness than the base metal.

The relationship between atomic partitioning and corrosion resistance in the weld-heat affected zone microstructures of UNS S32304 duplex stainless steel

Wrought material as well as physically simulated welding heat affected zone (HAZ) samples of an UNS S32304 duplex stainless steel were subjected to electrochemical corrosion tests and electron microscopy characterization. An impaired corrosion resistance of the HAZ microstructures compared to the wrought material microstructure was observed. Calphad-based numerical simulation of phase transformations and solute redistribution taking place during welding provided an explanation of the observed corrosion behavior. The poor corrosion resistance of the HAZ microstructures studied was mainly attributed to a decrease in corrosion resistance of ferritic grains after welding, which exhibited lower chromium content than ferritic grains in the wrought material.

A toughness study of the weld heat-affected zone of a 9Cr–1Mo steel

The toughness of the weld heat-affected zone microstructures of a 9Cr–1Mo steel has been studied with simulated samples. From the Charpy impact test results, the highest toughness in terms of the highest upper-shelf energy and the lowest ductile-to-brittle transition temperature have been observed in the intercritical region. The lowest toughness was observed in the coarse prior-austenitic grained martensite region adjacent to the fusion line. The microstructural effect on the toughness has also been discussed.

Influence of phosphorus on weld heat affected zone toughness in niobium microalloyed steels

Weld heat affected zone microstructures have been simulated in a niobium microalloyed C–Mn steel. These structures have been Charpy impact tested and examined metallographically. Troughs were observed in the plots of Charpy energy against post-weld heat treatment time at 600°C. The explanation for this behaviour is shown to be associated with non-equilibrium segregation of phosphorus to lath boundaries in the steel. Mathematical modelling of non-equilibrium segregation, together with high spatial resolution analytical electron microscopy results, support this contention. Using the predictions of the model, several suggestions are made concerning the alleviation of phosphorus segregation to boundaries and hence the reduction of cracking susceptibility during post-weld heat treatment of the steel.MST/994

Microstructure of weld heat-affected zone of 12Cr–Mo steel

Detailed studies have been made of the transformations and microstructure of the weld heat-affected zone (HAZ) of a class 212Cr–Mo steel, particular attention being given to δ-ferrite. The investigation covered a wide range of welding heat inputs and involved real and simulated HAZ material. To obtain the phasetransformation data extensive use was made of a weld simulator and dilatometer. The weld H AZ consisted of three regions: secondary-hardened martensite, homogeneous martensite, and duplex δ-ferrite and martensite adjacent to the fusion line. The amount of δ-ferrite increased with increasing weld heat input. It was shown that δ-ferrite forms above 1320°–1360°C, depending on the heat rate and remains untransformed on cooling to room temperature for the normal range of weld cooling rates. Detailed metallography showed that δ-ferrite forms at austenite grain boundaries, involves redistribution of allo ying elements and is associated with interphase precipitation of carbides. However, in amounts up to 16·6% it does not affect the subsequent decomposition of austenite. From these findings a representative C–C–T diagram is produced to describe the transformation occurring in the HAZ of this 12Cr-Mo steel.

Diagram for the prediction of weld heat-affected zone microstructure

The performance of welded joints, both during fabrication and operation, can depend critically upon the microstructure ofthe heat-affected zone, which, in a steel of given composition, is a function of the welding procedure andjoint geometry. The selection of suitable welding conditions which avoid the formation of crack-sensitive structures is clearly desirable. Standard heat-flow equations have been used in conjunction with continuous cooling transformation diagrams, determined using a weld simulation and dilatometric technique, to predict as-welded heat-affected zone microstructures for a wide range ofwelding conditions. A novel microstructure-welding diagram is described in which the variation in heat-affected zone microstructure as a function of process heat input, joint thickness, and preheat temperature is presented in a readily comprehensible form. A 0.5Cr-Mo-V steam-pipe composition is used as a detailed example, but the method is, in principle, applicable to a wide range ofsteel compositions.

多重熱サイクル溶接熱影響部と多重焼入材の性質について

A atudy is made on structural features and mechanical properties, especially on notch toughness of duplicated weld heat-affected zone and multi-quenched steel similar to refined weld heat-affected zone for Si-Mn and Si-Mn-Cr-V steels by induction heating and tempering in furnace, based on the results of notch toughness surveys of welded joint for quenched and tempered steel.Refined microstructure in weld heat-affected zone is produced by rapid heating and cooling thermal cycles above Ac1 temperature, whose maximum heating temperature are presumed to be lower in later ones. Shift of Ac1 and Ac3 transformation temperature was little observed, as compared with that of slower rate of heating, however, tranformation products in cooling were much influenced by heating temperature of thermal cycles, being martensitic in higher heating temperature, whereas rather ferritic in lower temperature.Hardness in duplicated weld heat-affected zone initially heated to 1350°C was lower after subjecting to the thermal cycles of lower heating temperature. Carbide grains in those steels were rather globular than ordinarily quenched and tempered steels.Subjecting to singly quenched thermal cycle, steels had the best notch toughness, when heated to just above Ac3 temperature followed by tempering, and toughness of singly quenched steel was improved further by repeated heating between Ac3-Ac1 temperature range followed by tempering.Microstructure of those steels consists of extreamly refined ferrite and globular carbides in both Si-Mn and Si-Mn-Cr-V steels, thus suggesting superior impact properties of those steels and special heat treatment for such steels.Generally steels have the poor impact properties, when repeatedly heated between Ac3-Ac1 temperature, however, tempering treatment gives the favourable effect on the impact properties.