This paper investigated on microstructure and impact toughness of different zones in duplex stainless steel welding joint. High-temperature heat-affected zone (HTHAZ) contained coarse ferrite grains and secondary precipitates such as secondary austenite, Cr2N, and sigma. Intergranular secondary austenite was prone to precipitation in low-temperature heat-affected zone (LTHAZ). Both in weld metal (WM) and in HTHAZ, the austenite consisted of different primary and secondary austenite. The ferrite grains in base metal (BM) presented typical rolling texture, while the austenite grains showed random orientation. Both in the HTHAZ and in the LTHAZ, the ferrite grains maintained same texture as the ferrite in the BM. The secondary austenite had higher Ni but lower Cr and Mo than the primary austenite. Furthermore, the WM exhibited the highest toughness because of sufficient ductile austenite and unapparent ferrite texture. The HTHAZ had the lowest toughness because of insufficient austenite formation in addition to brittle sigma and Cr2N precipitation. The LTHAZ toughness was higher than the BM due to secondary austenite precipitation. In addition, the WM fracture was dominated by the dimple, while the cleavage was main fracture mode of the HTHAZ. Both BM and LTHAZ exhibited a mixed fracture mode of the dimple and quasi-cleavage.

To explore the high-temperature tensile behavior and fracture mechanism of a novel 9% chromium tempered martensitic steel, G115, a series of tensile tests were conducted at 625, 650, and 675 °C within the strain rate range of 5.2×10−5–5.2×10−3 s−1. The results demonstrated that the tensile strength decreased with increasing temperature and decreasing strain rate. However, the elongation to failure increased with increasing temperature. The ductility at 675 °C exhibited significant improvement. Furthermore, three typical constitutive equations were comparatively analyzed to accurately describe the tensile deformation behavior of G115 steel. A stress exponent of approximately 11.1 and an activation energy of approximately 639.865 kJ/mol were obtained via the hyperbolic sine law. To explain the actual deformation mechanism, the threshold stress concept was introduced. The modified hyperbolic sine constitutive equation was proposed to determine the threshold stress σth, the true stress exponent nt, and the true activation energy Qt of G115 steel. The Qt value increased with increasing temperature and strain rate. Dislocation climb was the dominant deformation mechanism under the tested conditions. In addition, fracture surface investigations revealed a typical ductile fracture mode with a dense array of dimples at 625 and 650 °C. However, transgranular facets with tear ridges were observed in the central region at 675 °C. In addition, the microstructures of the fracture frontier and longitudinal section away from the fracture surface were studied to further understand the fracture mechanism.

In this work creep-strain test ranging from 180 to 240 MPa at 973 K, 998 K, and 1023 K were conducted to investigate the high temperature deformation and fracture mechanisms for Sanicro 25 alloy. The relationship between minimum creep rate and applied stress followed Norton's law. Apparent stress exponent values of 8, 6.5, and 5 were obtained at 973 K, 998 K, and 1073 K, respectively, with an apparent creep activation energy value of 437.3–606.1 kJ/mole illustrating that the rate-controlled creep occur in Sanicro 25 during creep. The threshold stresses were 129.5, 111.5, and 82.0 MPa at 973 K, 998 K, and 1023 K, respectively. The true creep activation energy and the true stress exponent were found to be 271.6 kJ/mole and 3, respectively. The presence of nanoscale MX and Cu precipitates were observed and theoretical calculations of threshold stresses confirmed that shearing of the nano-Cu precipitates occurred at 973 K, while the dislocations climbed up MX precipitates at 973–1023 K. The apparent stress exponent obtained for creep rupture shows that similar mechanisms operate in creep deformation and rupture behavior for Sanicro 25. A damage tolerance factor of ~5 in the alloy indicates that the microstructural degradation such as coarsening of precipitate and subgrain structure is the dominant creep damaging mechanism in the alloy.

This paper exhibits a novel in situ remediation technique named friction tapered stud overlap welding (FTSOW) to repair a through crack in structures and components in extremely harsh environments. Furthermore, this paper presents variations in process data, including rotational speed, stud displacement, welding force, and torque for a typical FTSOW weld. In the present study, the effects of welding parameters on the microstructures and mechanical properties of the welding joints were investigated. Inapposite welding parameters consisted of low rotational speeds and welding forces, and when utilized, they increased the occurrence of a lack of bonding and unfilled defects within the weld. The microstructures with a welding zone and heat-affected zone mainly consisted of upper bainite. The hardness value was highest in the welding zone and lowest in the base material. During the pull-out tests, all the welds failed in the stud. Moreover, the defect-free welds broke at the interface of the lap plate and substrate during the cruciform uniaxial tensile test. The best tensile test results at different depths and shear tests were 721.6 MPa and 581.9 MPa, respectively. The favorable Charpy impact-absorbed energy was 68.64 J at 0 °C. The Charpy impact tests revealed a brittle fracture characteristic with a large area of cleavage.

In this work, the microstructure evolution and fracture mechanism of a novel 9% chromium tempered martensite ferritic steel G115 were investigated over the temperature range of 625–675 °C using uniaxial creep tests. The creep curves consist of a primary transient stage followed by an apparent secondary stage, and an accelerated tertiary creep regime. The relationship between the minimum creep rate and the applied stress followed Norton's power law. Based on the EBSD analysis, there were no obvious textural features formed after creep deformation, and with the increase in creep time, the number of subgrains slightly increased, and then sharply increased, indicating dynamic recrystallization (DRX) occurs after creep deformation. In addition, three types of precipitates can be observed after creep deformation: W-rich Laves phase, Nb-rich MX, and Cu-rich precipitates. The Nb-rich MX with a square shape and Cu-rich precipitates with an ellipsoidal shape remain very stable. However, the W-rich Laves phases distributed mainly on the grain boundaries have rod-like, chain-like, and bulky shape, which are coarsened significantly. Representative fractographs of the G115 steel after creep deformation exhibit significant necking with an elliptical shape. A dense array of deep and equiaxed dimples appear in the central region under the tested creep conditions. Ductile fracturing is the dominant fracture mechanism during short-term creep deformation.

•Multiscale precipitation behaviours of Sanicro 25 during long-term creep were revealed.•Fine-distributed nanoscale precipitates were found as the main strengthening phases of Sanicro 25 at elevated temperatures.•Preferred grain orientation of Sanicro 25 before and after creep under different conditions were investigated by electron back-scattered diffraction.In the present work, creep deformation and fracture behaviours of Sanicro 25 alloy were obtained based on long-term creep-strain tests. The multiscale precipitation behaviours were calculated thermodynamically and inspected by examination of the microstructure of the as-crept alloy. Creep cavitation nucleation near the M23C6 precipitates and an increase in amount of Laves phase with increased creep time were observed. The nanoscale MX-type and Cu-rich phases were found distributed evenly within the as-crept alloy, which leads to the high creep resistance of Sanicro 25 at elevated temperatures. The dislocation substructure evolution was surveyed, and dislocation cells were discovered in abundance of the alloy during creep. The grain orientation transformation of the alloy before and after creep were analysed, and 〈111〉//RD and 〈001〉//RD were detected as the preferred orientations during creep. The number of low-misorientation angles grain boundaries increased in as-crept alloy due to the presence of grain rotation and dislocation cells.

In this study, a series of uniaxial strain cycling and ratcheting tests were conducted on 304L stainless steel and weld metal made with ER308L stainless steel welding wire. The ratcheting strain and fatigue life of the materials were measured at different loading levels and their cyclic behaviours are discussed. Microstructural evolution during cyclic loading was investigated by electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The experimental results show that the cyclic behaviours of the base metal and the weld metal are different. The cyclic behaviour of the base metal includes primary hardening, slight softening, and significant secondary hardening, while the weld metal exhibits a short hardening stage for several early cycles and later exhibits cyclic softening until failure. The evolution of dislocations during strain cycling and ratcheting deformation is discussed and the cyclic and ratcheting behaviours of the two materials are explained qualitatively. The final ratcheting strain of the materials depends greatly on the mean stress and stress amplitude. However, the fatigue life variation in the two materials is different. The base metal exhibited minimum fatigue life when a mean stress of 30 MPa was loaded; at constant mean stress, the fatigue life decreases when the stress amplitude is increased. In the case of the weld metal, the fatigue life decreases with increasing mean stress and stress amplitude.

Dislocation structures and their evolution of 304L stainless steel and weld metal made with ER308L stainless steel welding wire subjected to uniaxial symmetric strain-controlled loading and stress-controlled ratcheting loading were observed by transmission electron microscopy (TEM). The correlation between the cyclic response and the dislocation structure has been studied. The experiment results show that the cyclic behaviour of base metal and weld metal are different. The cyclic behaviour of the base metal consists of primary hardening, slight softening and secondary hardening, while the weld metal shows a short hardening within several cycles followed by the cyclic softening behaviour. The microscopic observations indicate that in base metal, the dislocation structures evolve from low density patterns to those with higher dislocation density during both strain cycling and ratcheting deformation. However, the dislocation structures of weld metal change oppositely form initial complicated structures to simple patterns and the dislocation density gradually decrease. The dislocation evolution presented during the strain cycling and ratcheting deformation is summarized, which can qualitatively explain the cyclic behaviour and the uniaxial ratcheting behaviour of two materials. Moreover, the dislocation evolution in the two types of tests is compared, which shows that the mean stress has an effect on the rate of dislocation evolution during the cyclic loading.

•Apparent change in LTHAZ was the intergranular secondary austenite precipitation.•Ferrite in HAZ maintained same distribution as ferrite texture in base metal.•Different austenite in different zones showed different orientation with ferrite.•Ferrite and austenite grains exhibited different boundary characteristics.•Local deformations were generated in grain boundary and within deformed grain.The microstructural evolution, orientation relationships, boundary characteristics, grain type, local deformation, and microhardness across the welded interface of duplex stainless steel (DSS) were investigated. The DSS welded joint consisted of four typical zones: base metal (BM), low-temperature heat-affected zone (LTHAZ), high-temperature heat-affected zone (HTHAZ), and weld metal (WM). The apparent microstructural changes in the HTHAZ and LTHAZ were secondary austenite and Cr2N precipitation. A modified cooperative precipitation mechanism of secondary austenite and Cr2N at the interface was proposed. Furthermore, the ferrite in both the HTHAZ and LTHAZ maintained the same distribution as the ferrite texture in the BM, while this ferrite texture disappeared completely in the WM. Different austenite grains in the different zones exhibited different orientation relationships with the ferrite matrix. Special grain boundaries were mainly distributed between the austenite grains, while the ferrite grains primarily contained random grain boundaries. Austenite twins constituted the largest proportion of the special boundaries. The special austenite grain boundaries in the BM and LTHAZ were higher in relative frequency than those in the HTHAZ and WM. The ferrite grains in the HTHAZ and WM mainly consisted of substructured grains. In the BM, the recrystallization degree of ferrite was significantly lower than that of austenite grains. The local deformations were mainly generated in the grain boundaries and within the deformed grains. The HTHAZ exhibited the highest hardness, while the BM had the lowest hardness. The LTHAZ had a lower hardness than the HTHAZ and higher hardness than the BM.

•Electrochemical potentiokinetic reactivation was used to study selective corrosion.•Microstructure evolution affected corrosion behaviour in flux-cored arc welded DSS.•Secondary austenite was preferentially attacked over ferrite and primary austenite.•Localised corrosion occurred around Cr2N and sigma phase in heat-affected zone.•Flux-cored arc welded metal had the smallest susceptibility to localised corrosion.The influence of microstructural evolution on selective corrosion in duplex stainless steel flux-cored arc welding joint was investigated by the modified double loop electrochemical potentiokinetic reactivation in acidified chloride. Due to the lower pitting resistance equivalent number, the secondary austenite was preferentially attacked over the ferrite and primary austenite phases, and inclusions acted as nucleation sites for micro-pits in the weld metal. Localised corrosion was generated in the secondary austenite and Cr-depleted zone around the Cr2N and sigma phases in the heat-affected zone. The weld metal exhibited the smallest susceptibility to localised corrosion because of the least weak phases.

•A creep-fatigue damage evolution model is proposed.•A third term is used to consider the creep-fatigue interaction.•The model is proved to have the ability in predicting creep-fatigue crack growth.•The effects of initial crack depth, specimen dimension and hold time are studied.A creep-fatigue crack growth model considering creep-fatigue interactions based on continuum damage mechanics was proposed in this paper. Numerical analyses of creep-fatigue crack growth of P91 steel at 625 °C using compact specimens were conducted. The results agreed well with the experiment which indicated its good capability in predicting creep-fatigue crack growth behavior. The effects of initial crack depth, specimen dimension and hold time on crack growth behavior were investigated using the model. The results indicated that the increasing initial crack depth and specimen dimension promoted the crack growth rate, while the decreasing hold time accelerated the crack growth.

•LTJT with nanosilver paste realized stable connections in graded TE arms.•Harsh aging tests were carried out on the joints of graded TE arms.•316 stainless steel blocked the diffusion among TE materials effectively.•The interface evolution process in both p-type and n-type FGM was presented.•The joint strength of junctions in p-type and n-type graded arms were tested.Lead free solder Sn96.5Ag3.0Cu0.5 (SAC305) and nano-silver paste were used to connect graded thermoelectric (TE) arms, respectively. A series of harsh aging tests were carried out on joints of both p-type and n-type graded TE arms. The results showed that nano-silver paste printed by low-temperature joining technique was much more suitable for the stable connection of TE materials working in medium temperature range. 316 stainless steel and nickel were proved effectively as diffusion barrier layers in p-type junctions. While for n-type TE junctions, when aging at 300 °C, (Fe, Cr, Te) ternary alloy could be detected at Bi2Te2.7Se0.3/316 stainless steel interface. The formation of ternary compound realized fine metallurgical interconnection which was benefit for the improvement of joint strength. The average joint strength for p-type and n-type junctions in graded TE arms were above 20 MPa and 30 MPa, respectively.

•Corrosion current of 3Cr low-alloyed steel increases with the increasing temperature.•The Cr content of corrosion layer increases with the increase of temperature.•A double corrosion layer forms at low temperatures of 30–50 °C.•A single corrosion layer forms at high temperatures of 70–90 °C.The initial corrosion behavior of 3Cr low-alloyed steel in sodium chloride (NaCl) solution with 0.3 MPa CO2 was systematically investigated at various temperatures. Electrochemical measurement revealed that the corrosion potential of this alloy exhibits a negative shift with increasing temperature, resulting in an increase in corrosion current and decrease in linear polarization resistance (Rp) with increasing temperature. Subsequent electrochemical impedance spectroscopy analysis showed that the amount of adsorbed intermediate corrosion product and amorphous scale also decreased with increasing temperature, which was confirmed by a field emission scanning electron microscope (SEM), energy dispersive X-ray spectrometry (EDS) and X-ray photoelectron spectroscopy (XPS) analysis. Through comparison of electrochemical measurement results with thermodynamic calculation of the ionic concentration and equilibrium electrode potential, it was found that the anodic reaction of 3Cr low-alloyed steel in CO2 solution consists of three main reactions: the direct dissolution of Fe, and the formation of FeCO3 and Cr(OH)3. Analyzing the morphology, composition and structure of the initial corrosion product layer under various temperatures, it is believed that a double corrosion layer forms at low temperatures of 30–50 °C, but a single corrosion layer forms at high temperatures of 70–90 °C.

•SiGe solid solution with SiO2 as media forms more quickly during the MA process.•The density of media has effects on the peak position of the SiGe solid solutions.•The media density affects the average grain size of powders during MA process.•ZrO2 media causes serious segregation of P and Si in the sintering process.•The deviation above is good for the next machining while bad for the TE property.In this work, Si80Ge20P2 alloys were fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). SiO2 and ZrO2 were taken as milling media respectively to investigate the effect of milling media on the fabricating process and the thermoelectric properties of SiGe alloys. The results show that, compared with the zirconia ball, though the agate one contains less kinetic energy, the solid solution of SiGe taken it as the milling media forms more quickly and at the same time has smaller average grain size through the whole milling time. The solid solution of Ge to Si crystal of samples under ZrO2 media remains stably around 98% and is much higher than that of specimens with agate as the media. In the sintering process, the previous application of ZrO2 easily causes the enrichment of elementary P and the loss of Si and leads to serious deviation from the original stoichiometric proportion of the compounds which is beneficial to the following machining and finally does harm to the thermoelectric properties of the Si80Ge20P2 alloys.

•Pure Bi0.5Sb1.5Te3 alloys can achieve after ball milling for 12 h under certain way.•Negative Seebeck coefficient appeared in Bi0.5Sb1.5Te3 alloys in certain case.•Laminated structure is more familiar in HP sample compared with the SPS one.•HP temperature has important effects on the TE properties of Bi0.5Sb1.5Te3 alloys.In this study, bulk ternary alloy Bi0.5Sb1.5Te3 was fabricated by mechanical alloying combined with hot pressing (HP) and spark plasma sintering process (SPS), respectively. Differences in microstructure and thermoelectric properties between HP samples and SPS specimens with different ball milling parameters were investigated visually. The results showed that certain improvement in rotate speed of ball milling process can reduce the formation time of Bi0.5Sb1.5Te3 powders from 60 h to 12 h. Mechanical alloying process had an important effect on the Seebeck coefficient of Bi0.5Sb1.5Te3 alloy, negative Seebeck coefficient may even appear due to the deformation induced donor-like effect. The study also discovered that laminated structure was much more familiar in hot pressed Bi0.5Sb1.5Te3 alloy compared with that in the spark plasma sintering samples. The figure of merit of Bi0.5Sb1.5Te3 alloy was enhanced with the increasing hot pressing temperature and reached 0.0027 K−1 around room temperature. Spark plasma sintered samples with 450 rpm + 60 h + 20:1 ball milling parameters have the maximum figure of merit 0.0048 K−1 which is about 1.5 times higher than the maximum TE value of HP samples.

Varying weight fractions of graphene nanosheets were successfully incorporated into lead-free solder using the powder metallurgy route. The effects of graphene nanosheets on the physical, thermal, and mechanical properties of a SnAgCu solder alloy were investigated. With the increasing addition of graphene nanosheets, the nanocomposite solders showed a corresponding improvement in their wetting property but an insignificant change in their melting point. The thermomechanical analysis showed that the presence of graphene nanosheets can effectively decrease the coefficient of thermal expansion (CTE) of the nanocomposites. Furthermore, an improvement in UTS and a decrease in ductility were recorded with the addition of graphene nanosheets. The reinforcing mechanism of the graphene nanosheets on various properties obtained was also analyzed in this study.

In this study, the effect of microstructure at the base metal (BM), the fine grain heat affected zone (FGHAZ), the coarse grain HAZ (CGHAZ) and weld metal (WM) under different welding heat input on hydrogen permeation in X80 steel weldments have been investigated. Base metal showed the highest effective diffusivity. With each heat input, the effective hydrogen diffusivity in FGHAZ is comparable to that of the base metal. The effective hydrogen diffusivity in weld metal was lower than that in CGHAZ. With increasing the welding heat input, the effective diffusivity in different zones of the weldment decreased correspondingly. Non-metallic inclusions were not detected in each specimen. Constituents in microstructure under low heat input are likely to agglomerate during accelerated cooling. The retained hydrogen may create an unpredictable susceptibility to hydrogen cracking at the CGHAZ even existing during service.Highlights► The effect of microstructure on hydrogen permeation has been investigated. ► With increasing the welding heat input, the effective diffusivity decreased. ► Constituents under low heat input are likely to agglomerate during accelerated cooling.

High temperature creep crack growth tests were carried out on standard compact specimens machined from the welded joint of ASME P92 steel pipe. The creep crack growth behaviors of the distinct sub-regions of welded joint were investigated to clarify the ability of creep crack resistance under high temperature. In addition, good correlations between creep crack growth rate and C⁎ for different microzones of welded joint were obtained. The tested results revealed that the sub-regions of welded joint exhibited different creep crack behaviors and at the same value of C* the highest creep crack growth rate occurred in the fine grained heat affected zone (FGHAZ) which was known as Type IV cracking zone. Furthermore, finite element method analyses coupled with continuum damage mechanics were conducted to predict the creep crack growth behavior and to study the effect of multistress state on crack propagation.

Different regions of heat-affected zone (HAZ) were simulated by heat treatment to investigate the mechanisms of the Type IV fracture of P92 (9Cr-2W) steel weldments. Creep deformation of simulated HAZ specimens with uniform microstructures was investigated and compared with those of the base metal (BM) and the weld metal (WM) specimens. The results show that the creep strain rate of the fine-grained HAZ (FGHAZ) is much higher than that of the BM, WM, the coarse-grained HAZ (CGHAZ), and the inter-critical HAZ (ICHAZ). According to the metallurgical investigation of stress-rupture, the FGHAZ and the ICHAZ have the most severely cavitated zones. During creep process, carbides become coarser, and form on grain boundaries again, leading to the deterioration of creep property and the decline of creep strength. In addition, the crack grows along the FGHAZ adjacent to the BM in the creep crack growth test (CCG) of HAZ.

Eutectic 80Au/20Sn solder alloy is widely used in high power electronics and optoelectronics packaging in which the creep property of the solder joint is essential to meet the global demand for longer operating lifetime in their applications. In this study, the tensile creep behavior of bulk eutectic 80Au/20Sn solder alloy is reported and compared with 63Sn37Pb solder joint. The creep strain rate increases and creep lifetime decreases as the applied stress level and temperature increase. The 80Au/20Sn solder alloy shows a superior anti-creep performance over the 63Sn37Pb solder joint. The experimental data were successfully fit with Dorn model and Garofalo model. However, the application of Garofalo model resulted in a lower estimated variance of error terms as compared to the Dorn model. Grain boundary sliding is the possible creep mechanism within the given stress level and temperature. The nucleation, accumulation and further growth of microvoids lead to the creep rupture.

The fracture behavior of a ceramic reinforced metal-base coating prepared by high velocity arc spraying (HVAS) technology in three-point bending test was studied. Moreover, finite element analysis (FEA) was adopted to analyze the stress distribution in the crack front. It can be found that the crack normal to the interface in the coatings occurred at the location where a fixed moment of force was reached. So the critical moment can be taken as the coating cracking criterion, which was confirmed by FEA results. In addition, the stress levels at three different locations where cracks occurred near the interface are almost the same. The results will provide reference for the design of coatings and the structure integrity evaluation of coating/substrate systems.

•We propose a new parameter-the average equivalent stress.•The assessment function for creep crack initiation position is obtained.•The assessment function for creep crack incubation time is obtained.Creep crack initiation position and incubation time of P92 steel pipes with embedded spherical defects at 650 °C were investigated with finite element method. The function for the relationship between creep crack initiation position and the geometric parameters was obtained by fitting methods. The average equivalent stress was proposed to characterize the stress variation throughout the creep process and the mathematical relationships between it and the geometric parameters, internal pressures, creep crack incubation time were established through nonlinear regression. Finally, the proposed assessment function for creep crack incubation time was deduced from the above functions.

•We obtained the η factors for the SE(T) specimens with the undermatched weld mental.•Various factors affecting the η factors were investigated.•A set of equations for the η factors is proposed.At present, the growing demand for the subsea transport of the highly corrosive media has driven the oil and gas industries to use clad or lined pipes. In order to ensure the corrosion resistance performance of circumferential welds in clad or lined pipes, nickel based alloy consumables are routinely used, which indicates that the yield strength of the weld metal is lower than that of base metal. To measure the toughness of the undermatched weld metal, plastic eta factors for clamped-end and pin-loaded single-edge tension specimens with a wide range of configurations and different undermatched levels were obtained based on detailed plane strain finite element analysis. From this analysis, a set of equations for the plastic eta factor is proposed.

•Effect of constraint induced by specimen size on creep crack growth was performed.•Creep crack growth rate increased as specimen size increased at same C∗ values.•C∗–Q two parameter approach was proposed to correlate constraint effect.•Values of constraint level Q were increased with specimen size enlarging.•Two parameter approach provided more accurately predicted crack growth rates.Experimental and numerical investigations on the effect of constraint induced by different specimen sizes on creep crack growth had been conducted using compact tension specimen with P92 steel. The experimental results revealed that at the same C∗ values, creep crack growth rates increased as specimen size increased and the difference enlarged with increasing C∗ values. In addition, the variations of constraint level Q during creep were obtained and a modified C∗–Q approach incorporating constraint effect was proposed to predict creep crack growth. In comparison with conventional single C∗ parameter approach, two parameter approach could provide more accurate crack growth rates.

The microstructure degradation and creep damage evolution process of Type IV cracking in a 9Cr–0.5Mo–1.8 W–VNb steel (ASME P92) welded joint during creep were investigated. Creep tests were carried out at 923 K and 70 MPa, and terminated at specific times in order to analyze the microstructure change and the creep voids formation in the welded joint. The welded joint finally ruptured in the fine grained heat affected zone adjacent to the base metal, identified as Type IV cracking. It revealed that the creep strength in the fine grained heat affected zone was lower than other zones of the welded joint. Creep voids were likely to nucleate and grow in this zone. In addition, carbides played an important role as nucleating sites for creep voids. As the creep time increased, creep voids linked to each other and finally formed micro-cracks resulting in the fracture in the fine grained heat affected zone. On the basis of microstructure degradation and creep voids propagation, the creep damage evolution process was proposed.Highlights► Microstructure change in ASME P92 steel welded joint during creep is studied. ► Creep damage in the FGHAZ is the most severe in the welded joint during creep. ► Carbides play an important role as nucleating sites for creep voids. ► The creep damage evolution process in the FGHAZ is proposed.

•The solution of Kastner was modified based on von Mises criterion.•An empirical formula for γ was developed.•The formula for γ is verified to be valid for cracked pipes under pressure and axial strain.Owing to ground movement, in-service pipelines may be subjected to large scale axial plastic strain. Therefore, determining the fracture capacity of pipelines with crack-like defects is a key issue that needs to be addressed. In this study, to conduct an engineering critical assessment (ECA) for in-service pipelines, the limit load solution of Kastner for pipelines with circumferential surface cracks under tension was modified based on the von Mises yield criterion. Then, the limit load solution of Kastner was adapted to the situation under combined inner pressure and axial plastic strain. Furthermore, the optimised reference stress method was applied to improve the accuracy of the ECA for in-service pipelines. Finally, the formula for the non-dimensional parameter, γ, was developed.

•Ag-GNSs was added into 96.5Sn-3.0Ag-0.5Cu solder to synthesize composite solders.•The IMC thickness of Ag-GNSs solder joints was thinner than that of GNSs solder joints after soldering and isothermal aging.•The composite solder joints with Ag-GNSs exhibit lower diffusion coefficients than GNSs.•Ag-GNSs can effectively retard the growth of the IMC layer in this study.•Ball-milling method had the advantage than mechanical mixing method in synthesizing composite solders.In this study, varying amounts of Ag-modified graphene nanosheets (Ag-GNSs) were added to Sn–Ag–Cu (SAC) solders to synthesize composite solders. Then, the morphology and thickness of the intermetallic compound (IMC) layers were investigated during the liquid–solid reactions and isothermal aging. The test results revealed that the IMCs were scallop-shaped after soldering, but they changed from scallop-shaped to an irregular shape with increasing aging time. The IMC thickness and diffusion coefficients of the composite solders were both found to be lower than those of the plain solders. Moreover, it is worth noting that with the same amount of reinforcement, the composite solders reinforced with Ag-GNSs exhibited thinner IMC layers and lower diffusion coefficients than the solders reinforced with GNSs alone. Furthermore, Ag-GNSs prepared using ball milling yielded thinner IMC layers and lower diffusion coefficients than the same amount of Ag-GNSs prepared via mechanical mixing using a blender. Our results indicate that Ag-GNSs are more influential on delaying the growth of IMC layers than GNSs alone and that ball milling has advantages over mechanical mixing using a blender for the preparation of Ag-GNS composite solders.

The effects of nitrogen addition in shielding gas on microstructure evolution and localized corrosion behavior of duplex stainless steel (DSS) welds were studied. N2-supplemented shielding gas facilitated the primary austenite formation, suppressed the Cr2N precipitation in weld root, and increased the microhardnesses of weld metal. Furthermore, N2-supplemented shielding gas increased pitting resistance equivalent number (PREN) of austenite, but which decreased slightly PREN of ferrite. The modified double loop electrochemical potentiokinetic reactivation in 2 M H2SO4 + 1 M HCl was an effective method to study the localized corrosion of the different zones in the DSS welds. The adding 2% N2 to pure Ar shielding gas improved the localized corrosion resistance in the DSS welds, which was due to compensation for nitrogen loss and promoting nitrogen further solution in the austenite phases, suppression of the Cr2N precipitation in the weld root, and increase of primary austenite content with higher PREN than the ferrite and secondary austenite. Secondary austenite are prone to selective corrosion because of lower PREN compared with ferrite and primary austenite. Cr2N precipitation in the pure Ar shielding weld root and heat affected zone caused the pitting corrosion within the ferrite and the intergranular corrosion at the ferrite boundary. In addition, sigma and M23C6 precipitation resulted in the intergranular corrosion at the ferrite boundary.