Post Weld Heat Treatment Specimen Research Articles

A Study on the Microstructure and Mechanical Properties of Electron Beam Welds of SA508 Gr.3 Cl.1 steel with Different Heat Treatment conditions for Small Modular Reactor

Electron beam welding was conducted on SA508 Gr.3 Cl.1 steel, which is being considered as a material used in the pressure vessel steel of small modular reactors. The characteristics of the welds were analyzed under various heat treatment conditions. The heat treatment conditions were categorized as as-welded, post weld heat treatment(PWHT), quality heat treatment(QHT), and their features were examined and compared through cross-sectional structure and composition analyses, as well as mechanical property tests. The electron beam welded joints displayed no defects, including pores or cracks. weld metal of the as-welded specimen revealed a needle-type martensite with high hardness, whereas the base metal was characterized by tempered bainite. The weld cross-section bead of the QHT specimen exhibited no significant difference in microstructure compared to the base metal. Tensile testing revealed that both the as-welded and PWHT specimens fractured at the base metal, whereas the QHT specimen fractured at the weld metal. The PWHT specimens showed enhanced impact values in the welds compared to the as-welded specimens. In the QHT specimens, both the base metal and the weld metal demonstrated similarly favorable impact values, approximately 200 Joules. It is evident that post-welding heat treatment improves the toughness value, and quality heat treatment can result in the weld metal being similar to the base metal.

Local microstructure evolution of a V-containing Fe–Cr–Ni–Mo weld metal subjected to post-weld heat treatment

The high-strength steels are widely used in modern shipbuilding and marine facilities. However, welding of >900 MPa grade steels is particularly challenging owing to the lack of understanding of fine microstructure for the weld metal (WM). The present investigation is mainly focused on a V-containing Fe–Cr–Ni–Mo WM fabricated by gas metal arc welding (GMAW) in aspects of localized microstructure evolution during post-weld heat treatment (PWHT). Microanalysis of the localized microstructure of inter-dendritic regions (IDRs) and dendrite core region (DCRs) for WMs was conducted by transmission electron microscopy (TEM), transmission kikuchi diffraction (TKD) and atom probe tomography (APT), complimented by nanoindentation hardness testing. It is found that the microstructure of WM in as-welded (AW) and PWHT condition was characterized by elongated martensitic laths with high-density dislocations in IDRs, while that in DCRs was coarse bainitic microstructure with relatively fewer dislocations. Most of retained austenite (RA) formed during cooling after welding was decorated martensite lath boundaries within IDRs owing to the segregation of austenite stabilizing elements after solidification. For PWHT condition, more numerous and smaller nano-scale MC carbides were observed in IDRs compared to DCRs. Furthermore, V atoms were mainly responsible for the nucleation of nano-scale MC carbides, and the growth and coarsening process of them were mainly controlled by diffusion of Mo atoms. Besides, the RA could also decompose into nano-scale MC carbides during PWHT. The IDRs of the PWHT specimens showed the average nanohardness value of 7.4 ± 2.3 GPa, which was higher than that of the DCRs (4.0 ± 0.2 GPa).

Interfacial microstructure and mechanical properties of rotary inertia friction welded dissimilar 422 martensitic stainless steel to 4140 low alloy steel joints

In this work, dissimilar rotary inertia friction welds between 422 martensitic stainless steel and 4140 martensitic low-alloy steel were made to fabricate prototype heavy-duty diesel engine pistons. The influence of the inertia friction welding process and post weld heat treatment (PWHT) temperature on the interfacial microstructure evolutions and corresponding effects on mechanical properties of the 422/4140 welds were evaluated in detail. Carbon diffused from the 4140 side to the 422 side during PWHT at 650 °C for 1.5 h, causing the formation of a hard carbide-rich layer on the 422 side, and a softer but discontinuous C-depleted layer the 4140 side. PWHT at 700 °C for 1.5 h greatly accelerated C diffusion across the interface relative to 650 °C, resulting in a thicker hard carbide-rich layer and a relatively thick and continuous layer of coarse C-depleted grains (ferrite) on the 4140 side. In addition, the PWHT temperature greatly influenced the tensile properties and fracture behavior of the welds, with the 650 °C PWHT-ed samples failing predominately in a ductile manner in the 4140 heat affected zone during tensile testing. Conversely, the 700 °C PWHT specimens exhibited a strength reduction compared with the 650 °C PWHT specimens because of additional coarsening of the interfacial ferrite layer and softening of the base materials during PWHT, with brittle fracture between the hard and soft layers the predominate failure mechanism. Based on the findings, a reduced PWHT temperature and/or time, minimizing the hardness differential of the base metals, and pre-heating the 422 steel prior to welding are the potential pathways to achieve a more optimal balance between desirable tempering and stress relief of the weld microstructure and undesirable C migration across the weld interface, and to reduce the strength mismatch across the weld.

Effects of TIG dressing, PWHT and temper bead techniques on microstructure and fatigue strength of fillet welded steel patch repairs: an experimental investigation

In-service patch welding is frequently used to repair corroded or damaged steel structures. However, the repair welding may adversely affect the long-term mechanical integrity of the structure. Fatigue treatment techniques could reduce such drawbacks. However, the effectiveness of treatment techniques in the case of in-service fillet welded steel patch repairs has not received due attention. This paper deals with the fatigue behavior of fillet welded patch repairs made on normalized A516 GR.70 carbon steel plates. The test specimens received different thermal treatments, including post-weld heat treatment (PWHT), TIG-dressing (TD), and temper bead (TB) welding. The pros and cons of these treatments were evaluated through quasi-static tensile tests, high-cycle constant amplitude fatigue testing, microstructural assessments, and hardness measurements. The TD treatment provided the most significant fatigue improvement, owing to beneficial changes it made to the geometry, microstructure and hardness of the weld toe area. The fatigue life and the fatigue-prone locations in the PWHT and TB specimens did not significantly vary from those in the untreated welded specimens. However, there was a reduction of the ultimate tensile strength in the PWHT specimens. The microstructure of the heat-affected zone plus the hardness of the weld toe areas significantly contributed to the fatigue performance. The fatigue lives of the fillet welded patch repairs were also interrelated to the geometrical changes caused in the weld toe by the treatment method.

Fatigue performance of rib-to-deck joints in orthotropic steel deck with PWHT

Post-weld heat treatment (PWHT) displays potential for enhancing the fatigue strength of rib-to-deck (RD) welded joints in orthotropic steel decks (OSDs) by mitigating welding residual stress. In this study, residual stress measurements, fatigue tests, and fracture analyses were performed to investigate the influence of PWHT on the welding residual stress and fatigue strength of RD joints. Eighteen full-scale specimens were fabricated, i.e. ten PWHT-processed specimens and eight as-welded specimens without additional treatment. Hole drill (HD) and X-ray diffraction (XRD) were used to measure the residual stress in four PWHT specimens and four as-welded specimens. The PWHT specimen showed a reduction in the peak residual stress by 76% and 78% in the HD and XRD results, respectively. Fatigue tests were carried out on the six PWHT specimens and four as-welded specimens. The comparison was made between the two specimen types using the mean value of equivalent fatigue strength derived at 2 million cycles. The results indicated that PWHT improved the mean equivalent fatigue strength of RD joints by 23% and 33% under nominal stress and hot-spot stress, respectively. Parametric investigations were carried out using finite element-based fracture analysis to elucidate the influence of residual stress mitigation on fatigue crack growth in RD joints. The result indicated a significant decrease in the crack growth rate owing to residual stress mitigation. Such a decrease enhances the fatigue strength of RD joints.

Nanoindentation Characterization of Creep-fatigue Interaction on Local Creep Behavior of P92 Steel Welded Joint

In modern fossil and nuclear power plants, the components are subjected to creep, fatigue, and creep-fatigue (CF) due to frequent start-up and shut-down operations at high temperatures. The CF interaction on the in-service P92 steel welded joint was investigated by strain-controlled CF tests with different dwell times of 30, 120, 300, 600 and 900 s at 650 °C. Based on the observations of the fracture surface by scanning electron microscope (SEM), the characteristic microstructure of fatigue-induced damage was found for the CF specimens with short dwell times (30 and 120 s). The hardness, elastic modulus and creep deformation near the fracture edges of four typical CF specimens with 30, 120, 600 and 900 s dwell times were measured by nanoindentation. Compared to specimens with post-weld heat treatment (PWHT), lower hardness and creep strength were found for all CF specimens. In addition, significant reductions in hardness, elastic modulus, and creep strength were measured near the fracture edges for the CF specimens with short dwell times compared to the PWHT specimens. Compared to PWHT specimens (0.007), the increased strain rate sensitivities (SRS) of 0.010 to 0.17 were estimated from secondary creep. The increased values of SRS indicate that the room temperature creeps behavior is strongly affected by the decrease in dislocation density after the CF tests.

Post-Weld Heat Treatment of API 5L X70 High Strength Low Alloy Steel Welds.

High Strength Low Alloy (HSLA) steels are the materials of choice in pipeline construction with the API X70 grade as the steel for the majority of pipeline networks constructed during the late 20th and early this century. This paper reports on the influence of Post-Weld Heat Treatment (PWHT) on the reduction of residual stresses, resulting changes in the microstructure, and mechanical properties of a multi-pass, X70 HSLA steel, weld joints made by a combined Modified Short Arc Welding (MSAW) and Flux Cored Arc Welding (FCAW) processes. Neutron diffraction results highlighted high magnitude of tensile residual stresses, in excess of yield strength of both parent and weld metal, in the as-welded specimen (650 MPa), which were decreased substantially as a result of applying PWHT (144 MPa). Detailed microstructural studies are reported to confirm the phase transformation during PWHT and its interrelationship with mechanical properties. Transmission Electron Microscopy (TEM) analysis showed polygonization and formation of sub-grains in the PWHT specimen which justifies the reduction of residual stress in the heat-treated weld joints. Furthermore, microstructural changes due to PWHT justify the improvement in ductility (increase in the elongations) with a slight reduction in yield and tensile strength for the PWHT weld joint.

Basic Microstructural Characterization of Second Phases in Homogeneous Weld Joint Made of X6CrNiNbN25-20 Steel After Long-Term Exposure Time at 973 K

Abstract New blocks of fossil fuel power plants designed for steam temperatures above 873 K require advanced stainless steels as material for superheater or reheater systems. Weld joints are critical parts in fossil power units. Great attention is paid to the exploitation of new steel grades with higher material properties. In the austenitic steels family, the superior grade is undoubtedly HR3C steel (X6CrNiNbN25-20). A detailed knowledge on stability and microstructure composition during thermal exposure of the weld joints made from HR3C is necessary in order to use them in fossil fuel power plants with ultrasupercritical (USC) and new advanced ultrasupercritical (A-USC) steam parameters. The aim of the paper is to identify critical minor phases in HR3C steel, which allow acceleration of creep damage. The σ-phase and rough carbides M23C6 type is considered as such a phases in this steel. In this study, the σ-phase is identified and studied in more detail in relation to the development of creep damage at 973 K. Experimental material of the homogeneous HR3C weld joints in two states: in the as-welded state (AW) and after the postweld heat treatment (PWHT). Weld joints were manufactured by orbital welding using the gas tungsten arc welding (GTAW) method, heat input Qs = 1600 J/mm, interpass 423 K, three beads. Nickel-base alloy UTP A6170 Co (equivalent to Thermanit 617) was used as a filler material. The PWHT was carried out at the temperature of 1503 K for 15 min. Stress rupture tests were performed on the cross-weld (CW) joints of tubes ø 38 × 6.3 mm at 973 K with times to rupture up to nearly 22,000 h. The polished surface of the longitudinal sections was subjected to color etching in Murakami (30 g K3(Fe(CN)6), 30 g KOH, 60 ml H2O) in order to highlight the σ-phase. Several microscopic techniques were used for the study. The results were supplemented by creep, grain size, and microhardness data hardness vickers (HV) 0.5. The PWHT specimens exhibited an average σ-phase size of approximately 5 μm as well as AW specimens in specimens with short time to rupture (tr). However, tr such as 20,000 h, the average σ-phase size already reached dangerous border 10 μm. The AW specimens as opposed to the PWHT specimens did not show a noticeable growth of austenitic grains in the heat-affected zone (HAZ). In specimens after PWHT, the average grain size in HAZ was more than twice that of the body material (BM). It is worth noting that creep ductility values of specimens in the state after PWHT are very low, which is the result of coarse-grained structure in the HAZ and accelerated precipitation of σ-phase particles along grain boundaries during creep at 973 K.

Microstructure and Charpy Impact Toughness of a 2.25Cr-1Mo-0.25V Steel Weld Metal.

The demand for heat-resistant steel has increased owing to its utility in numerous devices that must withstand high steam pressures and high temperatures, such as turbine rotors and blades in ultra-supercritical power plants. It is inevitable to join heat-resistance steel part by welding method, so it is important to maintain the toughness of the weld metals. In this study, the microstructure, low-temperature impact toughness, and fracture surface of as-welded and post-weld heat treatment (PWHT) of 2.25Cr-1Mo-0.25V weld metal were investigated. The microstructures of the as-welded and PWHT specimens are granular bainite and ferrite, respectively. This work revealed the relationship between effective microstructure nearby crack initiation origin and low temperature impact toughness for both the as-welded and PWHT specimens. The evolution of the microstructure and prior austenite was then investigated using confocal laser scanning microscopy (CLSM) to observe the formation of coarse ferrite grain structures. A suggestion for enhancing the low-temperature toughness was provided based on the effect of adjusting Mn content and forming acicular ferrite.

Effect of post-weld heat treatment on tensile strength and microstructure characteristics in dissimilar friction welded (AA6061–AA7075-T6) joints

Dissimilar AA6061 to AA7075-T6 joints fabricated by friction welding has been investigated to enhance the mechanical properties by post-weld heat treatment (PWHT) process. After fabrication, the welded samples are heat-treated by three different conditions namely, solution treatment, artificial aging and solution treatment followed by aging. Following this, the tensile properties and micro hardness of PWHT specimens were systematically investigated. Further, the influence of PWHT in fully deformed zone, partially deformed zone, heat affected zone, and parent metals were examined through the optical microscopy, scanning electron microscopy, transmission electron microscopy and energy dispersive spectrum. Finally, the results of PWHT specimens were discussed and compared with as-welded conditions.

Welding Cylinder Head: The Effect of Filler Variations and Post Weld Heat Treatment (PWHT) on Microstructure and Mechanical Properties on TIG Welded Cast Iron FC 250

Cylinder head made from grey cast iron, is one of critical engine part which work on high temperature and pressure. The condition which occurs continuously during engine operation causes wear which identified as a fretting failure. Therefore repairing process is needed by using Tungsten Inert Gas (TIG) welding. By considering the working condition and the materials, welding parameters are used 140A current, 100% Argon, DCEP and preheat at 250°C. The welding process is done on specimen sample of cylinder head which fretting failure by using Ni-CI, NiFe, NiFe-1 dan 308L filler variation for each specimen and done by PWHT at temperature 650°C which holding time 90 minutes. Visual test, macroscopic test, microscopic test and hardness test already done in this research. The results are there is no defect such as crack, porosity, undercut, and lack of fusion on the visual and macroscopic test. On microscopic test, there is the brittle phase (martensite) in HAZ at Non-PWHT specimen, but after PWHT the martensite transform became martempered phase. FC250 standard hardness value is about 170-235HB, and the result is the hardness value of non-PWHT specimen higher than the standard in HAZ, and the high hardness value of PWHT specimen on weld metal by using NiFe, NiFe-1 and 308L. So from the filler variation, Ni-CI filler with PWHT is on standard either on phase or on hardness value

Effect of post weld heat treatments on fracture frontier and type IV cracking nature of the crept P91 welded sample

The research work explores the microstructure evolution and creeps rupture behavior of the shielded metal arc welded joint of reduced activation ferritic/martensitic P91 steel plate in the as-welded and different states of post weld heat treatment (PWHT). Two types of heat treatments were employed including (i) post weld heat treatment (PWHT) at 760 °C for 2 h and finally air cooled and (ii) re-austenitizing at 1040 °C for 60 min and air-cooled and tempered at 760 °C for 2 h, followed by air cooling (PWNT). The P91 steel plates were received in the cast and forged condition having fully tempered lath martensite with lath blocks, packet boundaries and prior austenite grain boundaries (PAGBs). In this research, microstructural evolution at fracture frontier of crept P91 weld sample, creep rupture life and effect of creep exposure time on microstructure evolution in the fine-grained heat affected zone (FGHAZ) were studied. The results show a dominating effect of PWNT treatment on fracture behavior and creep rupture life of the P91 welded joints. PWNT treatment results in negligible hardness variation across the transverse section of the weld joint. The creep rupture life of PWNT specimen was 594.895% higher as compared to that of PWHT specimen and 142.7% higher than that of the as-welded specimen for the similar condition of creep exposure (620 °C/150 MPa). In PWHT condition, the most common type IV cracking was observed. However, it was eliminated in PWNT specimens and fracture occurred form the base zone. The fracture frontier of crept PWNT specimen showed a higher amount of creep cavities that can be attributed to the formation of Laves phase.

Effect of Post-weld Heat Treatment on the Fatigue and Fracture Mechanisms of Weld-Repaired Bisplate80 With or Without a Buffer Layer

In this work, weld-repaired Bisplate80 joints without or with a buffer layer (BL) were subjected to a post-weld heat treatment (PWHT) at 930 °C for 1 h followed by air cooling. The mechanical properties and fracture mechanism of the PWHT specimens were compared to those from corresponding as-welded specimens to study the influence of the PWHT and to compare them with as-received Bisplate80 specimens to inspect the welding quality of the joints. Fatigue crack growth curves and micro-hardness profiles across the welded joints for the as-weld or PWHT conditions were measured together with relevant scanning electron microscope observations along the crack growth path. Special attention was paid to the areas at and around the welded interfaces. The results showed that the incorporation of a BL with an appropriate thickness significantly improved the fatigue crack growth behavior of the welded joint for the PWHT condition, as the da/dN over the entire area of the welded joint was much lower than for both the as-welded and as-received Bisplate80 specimens, showing that the incorporated BL greatly improved the fracture mechanisms of the fatigue specimens.

Influence of Weld Defects and Postweld Heat Treatment of Gas Tungsten Arc-Welded AA-6061-T651 Aluminum Alloy

Welding defects and the reduction of mechanical performances are the foremost problems for fusion welded aluminum alloys joints. The influences of weld defects and postweld heat treatment (PWHT) on tensile properties of gas tungsten arc (GTA) welded aluminum alloy AA-6061-T651 joints are investigated in this current study. All welded specimens are nondestructively inspected with phased array ultrasonic testing (PAUT) to classify weld defect and measure the projected defects area-ratio (AR). Ultimate tensile strength (UTS) decreased linearly with the increase of the size of weld defect but tensile toughness behaved nonlinearly with defect size. Depending on defect size, defective samples' joint efficiency (JE) varied from 35% to 48% of base metal's (BM) UTS. Defect-free as-welded (AW) specimens observed to have 53% and 34% JE based on UTS and yield strength (YS) of BM, respectively. PWHT was applied on defect-free welded specimens to improve tensile properties by precipitation hardening, microstructures refining, and removal of postweld residual stresses. Solution treatment (ST) (at 540 °C) followed by varying levels of artificial age-hardening (AH) time was investigated to obtain optimum tensile properties. For GTA-welded AA-6061-T651, peak aging time was 5 hr at 180 °C. PWHT specimens showed 85% JE based on UTS and up to a 71% JE based on YS of BM. However, toughness values decreased about 29% due to the presence of precipitate-free fusion zones. The experimental investigations can be used to establish weld acceptance/rejection criteria and for the design of welded aluminum alloy structures.

THE EFFECT OF PWHT ON WELD PROPERTIES OF TITANIUM ALLOY FOR REFURBISHMENT OF AIRCRAFT ENGINE EXHAUST CONE

The mounting bolt hole of aircraft engine exhaust cone was found cracked in the weld area. Exhaust cone material is �. /�� titanium (Ti-6Al-4V) alloy. The cracked section will be repaired by welding to restore its function. The purpose of this research is to evaluate the effect of post weld heat treatment (PWHT) on ductility, grain size, and shear strength of Ti-6Al-4V plates (0.063 in. thickness) welded by gas tungsten arc welding (GTAW) using commercial purity (CP) titanium wire electrode (AMS 4951H). The weld quality was evaluated by non-destructive and destructive tests, using the acceptance criteria of AWS D17.1 and AWS B2.1 as references. The effect of PWHT was examined by preparing two weld specimens: with and without PWHT at 620 o C. Non-destructive inspection by dye penetrant and xray radiography tests revealed that the weld in these two specimens is free from surface and internal defects. Weld specimen without PWHT is brittle and failed during fillet break test, whereas PWHT specimen is ductile and pass the same test. Metallography observation was conducted to measured grain size of base metal and heat affected zone (HAZ). The average grain size of PWHT specimen is 18.40 o m on base metal and 36.80 o m on HAZ, and for nonPWHT specimen is 26.85 o m on base metal and 52.10 o m on HAZ. Using Hall-Petch approach, the yield strength is calculated about 920 MPa on the base metal of PWHT specimen, which result in the shear strength of about 531 MPa. Under static loading, the shear stress on the outer surface of exhaust cone due to exhaust gas is about 38 MPa, which is much lower than material shear strength.

Microstructure and Mechanical Properties Evaluations of Heat Treated Dissimilar Metal Joint Weldment between API 5CT C90 and ASTM A182 F22

In this research, post-weld heat treatment (PWHT) of dissimilar API 5CT C90 and ASTM A182 F22 welded pipe was carried out at temperatures of 500, 600, 700 and 800°C. The effects of PWHT on the microstructure and mechanical properties of the weldment were investigated. The mechanical tests and microstructure examinations were focused on the fusion line area of API 5CT C90 as this area is the most crucial part of the weldment. The main objective of this research is to assess the microstructure and mechanical properties of the dissimilar weldment. The results were then compared with NACE MR0175/ISO15156 code which requires hardness values below 275 Hv10 at a cap, below 250 Hv10 at a root and an average value 42 Joules at-20°C for charpy impact test [. The experimental results show that PWHT reduces the hardness value and increase the toughness of the weldment. Meanwhile, the optical microscopic examination shows that the higher the PWHT temperature, the coarser the grain size. The results showed that the 800°C PWHT specimen complied with the code.

Post-weld heat treatment cracking in autogenous GTA welded cast Inconel 738LC superalloy

The post-weld heat treatment (PWHT) cracking in autogenous gas tungsten arc (GTA) welded Inconel 738LC superalloy, which was given two different preweld heat treatments, was studied. One of the preweld heat treatments, designated as SHT, consisted of solution heat treatment at 1120°C for 2 h in vacuum followed by argon quenching. The second preweld heat treatment, designated as UMT, consisted of solution treatment at 1120°C for 2 h followed by air cooling and then aging at 1025°C for 16 h followed by water quenching. The welded specimens were given the same conventional PWHT, which consisted of SHT at 1120°C for 2 h in vacuum followed by argon quenching and subsequent aging at 845°C for 24 h in vacuum. Microstructural examination of the welded SHT and UMT treated material showed that intergranular microfissuring occurred during welding only in the heat affected zone (HAZ) with some cracks extending into the adjoining base metal (BM), whereas after the PWHT microfissures were observed in the fusion zone (FZ), HAZ and the BM far removed from the HAZ. The crack width ranged from 5 to 10 μm in the PWHT specimens as compared with 1–2 μm in the as welded sections. Although similar type of cracks was observed in samples given the two preweld heat treatments, the UMT preweld heat treatment was found to result in a significant reduction in average total crack length and average crack length, both during welding and during the subsequent PWHT. After PWHT, SHT samples had ∼43% more cracking than the UMT samples. It is suggested that a larger particle size of γ′ precipitates in the HAZ and a smaller size of HAZ in the as welded samples, combined with a softer BM of the UMT material (hardness 280 ± 12 HV10, as compared with 380 ± 10 HV10 of the SHT material) resulted in an improved capability of the material to absorb the strain–aging stresses, and hence a reduced incidence of cracking during PWHT.

Study on Evaluation of AE Signals at Weld Region of SA 516 Steel

The purpose of this study is to find out the method to detect AE signals at around the notch tip and to evaluate the AE signal characteristics for the basemetal, PWHT(post weld heat treatment) and weldment specimens of SA-516 steel during bend test. AE signals were produced in the process of plastic deformation. AE signal strength and amplitude of the weldment was the strongest, followed by PWHT specimen and basemetal. More AE signals were produced from the weldment because of the oxides, and discontinuous mechanical properties. The stronger AE signal strength, amplitude and more AE event counts for the weldment were shown.

Evaluation of fracture behavior of SA-516 steel welds using acoustic emission analysis

The purpose of this study is to evaluate the AE characteristics for the basemetal, PWHT (post-weld heat treatment) and weldment specimens of SA-516 steel during fracture testing. Four-point bending and AE tests were conducted simultaneously. AE signals were emitted in the process of plastic deformation. AE signal strength and amplitude of the weldment was the strongest, followed by PWHT specimen and basemetal. More AE signals were emitted from the weldment samples because of the oxides, and discontinuous mechanical properties. AE signal strength and amplitude for the basemetal or PWHT specimen decreased remarkably compared to the weldment because of lower strength. Pre-cracked specimens emitted even lower event counts than the corresponding blunt notched specimens. Dimple fracture from void coalescence mechanism is associated with low-level AE signal strength for the basemetal or PWHT. Tearing mode and dimple formation were shown on the fracture surfaces of the weldment, but only a small fraction produced detectable AE.

Study on corrosion characteristics and stress corrosion cracking of the weldment for HT-60 steel in synthetic seawater

The contents of this paper include the evaluation of corrosion characteristics and the behaviour of stress corrosion cracking (SCC) for the weldment and post weld heat treatment (PWHT) specimen and parent of HT-60 steel using a slow strain rate test (SSRT) in synthetic seawater. Corrosion characteristics were obtained from the polarization curves by potentiostat, and SCC phenomena were evaluated through the parameters such as reduction of area and time to failure by comparing the experimental results in corrosive environment with those obtained in air. Corrosion rate of the weldment was the fastest, followed by parent and PWHT specimen. SCC phenomena between the weldment of HT-60 steel and synthetic seawater were shown. Besides, SCC was dependent upon the pulling speed greatly. Maximum severity of SCC was obtained at a speed of 10−6 mm/min, whereas SCC could not be seen almost at 10−4 mm/min. The resistance to SCC for PWHT specimen was improved considerably compared that of the weldment at 10−6 mm/min. In case of SCC failure, it was verified from SEM examination that brittle mode and lots of pits could be seen at the fractured region near the surface of the specimen.