Weld Metal Impact Research Articles

Study on the effect of microstructure on toughness dispersion of X70 steel girth weld

The girth weld metal impact toughness would affect the safe operation of long transmission oil and gas pipeline. In order to further clarify toughness law of pipeline steel girth weld, the Charpy impact toughness of X70 steel girth weld at −10 °C was studied by standard impact method, and the impact energy range was determined to be 18–95 J. The impact energy range of girth welds varied significantly, and the toughness was discrete. The impact toughness of the different microstructures in the girth weld at −158 °C was studied by the small specimen impact test. The root weld metal mainly consisted of ferrite and a small amount of pearlite, and its impact toughness was low. The large effective grain size and dislocation density difference between large lath bainite (LB) and coarse granular bainite (GB) increased the strain heterogeneity during impact deformation. In fine GB, effective grain size reduction and uniform distribution of Martensite austenite (M–A) components reduced the local strain, resulting in more uniform deformation. Therefore, the sample with the fine GB had higher impact the toughness and ductile fracture mode. For the standard Charpy impact samples, the main reason for toughness dispersion was change of fine GB proportion. The fine GB proportions of P6-2, P3-3 and P3-2 were 46.7 %, 40.8 %, and 29.5 %, respectively. Simultaneously, the influence of position change on the impact energy was considered.

P92 steel and inconel 617 alloy welds joint produced using ERNiCr-3 filler with GTAW process: Solidification mechanism, microstructure, mechanical properties and residual stresses

The objective of the current study was to analyse the microstructure, mechanical characteristics, and residual stresses of a dissimilar welded joint (DWJ) made of P92 steel and the Inconel alloy 617 (IN617) using the gas tungsten arc welding (GTAW) method. The ERNiCr-3 filler was selected to produce the conventional V groove (VG) and narrow V groove (NVG) butt joint. The filler deficient zones in the weldments, such as the filler deficient beach, i.e. unmixed zone (UZ), peninsula, and island, as well as the distinct heat-affected zone (HAZ), were visible near the interface of ERNiCr-3 filler weld and P92 steel due to the distinct differences in the chemical composition, microstructure, and mechanical properties between the filler and P92 base metal (BM). A very narrow partial melted zone (PMZ) and almost negligible UZ and HAZ were noticed at the interface of IN617 and ERNiCr-3 weld metal and it occurred mainly due to the similarity in microstructure and melting point. The austenitic microstructure of ERNiCr-3 filler weld was accompanied by precipitates enriched with Ti and Nb along with the inter-dendritic space. At room temperature, the mechanical properties of both the groove joints were evaluated, and the test results indicated that the welded joint satisfied the standard requirements for AUSC power plants' boiler applications. The tensile test results showed the failure from ERNiCr-3 filler weld with a tensile strength of 627 ± 2 MPa and 636 ± 3 MPa for VG and NVG welded joints, respectively. A poor weld metal impact toughness in comparison to the BMs was attributed to the presence of the brittle Ti(C, N) and Nb(C) particles in the interdendritic space. The impact toughness for the NVG weld joint was measured higher than for the VG weld joint. A significant hardness deviation was measured along the weldments that might be due to heterogeneous microstructure, i.e. UZ, HAZ, delta ferrite, and weld metal. To impart the ductility and temper the martensite in P92 HAZ, post-weld heat treatment (PWHT) was also performed, and a studied their effect on microstructure evolution across the weldments and mechanical properties. Groove design also showed a significant effect on residual stress variation. The work highlights the groove geometry, welding procedure, evolution of the microstructure along the weldments, mechanical characteristics, and residual stress variation of DWJ of P92 steel and IN617 alloy. In comparison to conventional VG joints, the NVG joints exhibited superior mechanical properties and lower residual stress values.

Effect of welding parameters on the mechanical and metallurgical properties of armor steel weldment

The effect of welding parameters on the mechanical and metallurgical properties of armor steel weldment was studied using gas tungsten arc welding process with two filler wires: carbon steel and austenitic stainless-steel filler wires (AWS A5.18 ER 70S-6 and AWS A5.9 ER 307, respectively). The joint configurations were mainly single V and single bevel grooves. Using both AWS A5.18 ER70S-6 carbon steel filler wire and AWS A5.9 ER307, austenitic filler wire for the two joints passed the required tensile strength by the military standard. The joints successfully regained the base metal hardness at a distance of less than 15 mm. The ultimate tensile strength of the joints welded in a single bevel groove is 906 MPa which is higher than the joints welded using a single V groove is 865 MPa. This could be attributed to the increase in dilution percentage with the single bevel joints. Both single V joint and single bevel joints passed the required Charpy V-notch impact test whether using both carbon and stainless-steel wires. The effect of heat input and cooling rate on the mechanical and microstructure of welded joints was studied. The reduction of heat input caused a narrow HAZ with a small reduction in its hardness values with much reduction in the width of softening microstructure zone. SEM observations show that the base metal has a martensitic structure, but the weld metal microstructures depend on the filler: carbon steel or austenitic steel types. Using a single bevel groove with an austenitic steel filler metal, the weld metal shows a martensitic/austenitic microstructure by SEM observation, and this was verified by the Schaeffler diagram which showed a high dilution percentage (about 35% dilution). This resulted in a significant increase in joint strength and a higher weld metal impact resistance.

Effect of post weld heat treatment on the interplay of microstructure, precipitates and properties of creep-resistant 2.25Cr-1Mo-0.25V weld metal

For the application in heavy wall pressure vessels such as hydrocracking reactors in the petrochemical industry, creep-resistant 2.25Cr–1Mo-0.25V steel is usually joined via submerged-arc welding. To ensure a long service lifetime at elevated temperatures and high pressures, the steel plates and weldments must maintain a beneficial combination of toughness and creep strength for several years. One approach to adjust the weldments' mechanical properties is to perform a post-weld heat treatment (PWHT).This study is dedicated to the impact of the PWHT-temperature and -time on the complex interplay of microstructure, precipitates and mechanical properties of 2.25Cr–1Mo-0.25V weld metal. The mechanical testing showed that a higher PWHT-temperature increases the weld metal's impact toughness and ductility while simultaneously decreasing its strength and creep resistance. The high-resolution investigation with transmission electron microscopy and high-energy X-ray diffraction demonstrated that this is linked to accelerated recovery processes and severe coarsening of fine MX carbonitrides. At lower PHWT-temperatures, the absolute increase of the MX phase fraction during PWHT and the MX coarsening is less pronounced, allowing the MX carbonitrides to effectively contribute to precipitation hardening by maintaining their fine size. Besides MX carbonitrides, the weld metal consists of Cr-rich M7C3 and M23C6 as well as a substantial amount of Mo- and V-rich M2C carbides. The precipitate transformation sequence during PWHT was found to be M3C→M3C + MX + M7C3→M3C + MX + M7C3+M23C6+M2C→MX + M7C3+M23C6+M2C, whereas prolonged annealing times at higher PWHT-temperatures again lead to the dissolution of M7C3 in favor of MX.

Filler Metal 16-8-2 for Structural Welds on 304H and 347H Stainless Steels for High-Temperature Service

The use of Type 16-8-2 filler metal was examined for application in structural welds on 304H and 347H stainless steels for high-temperature service applications and compared to welds with matching filler metals 308H and 347, respectively. Microstructural stability during elevated temperature expo-sure, weld metal impact properties, and susceptibility to stress-relief cracking were examined. It was found that the lean composition and low ferrite (~ 2 Ferrite Number [FN]) in 16-8-2 weld metal provide high resistance to intermetallic phase formation. No hot cracking was observed despite the low ferrite level. The 16-8-2 weld metals displayed superior toughness as compared to the matching filler metal welds, especially after longer elevated-temperature exposure. Experimental evidence for some martensite transformation in aged 16-8-2 weld metal upon cooling to ambient temperature was presented and explained an increase in magnetic response (as FN) after postweld heat treatment at 1300˚F (705˚C). None of the tested weld metals failed by stress-relief cracking mechanisms under the applied test conditions. The 16-8-2 filler metal welds exhibited significantly lower levels of stress relief during high-temperature exposure and significantly high-er tensile strength after high-temperature hold as compared to the matching filler metal welds.

Experimental investigation of structural integrity behavior of High strength low alloy steel – Study of mechanical, microstructural and corrosion behavior of Submerged arc welding weldments

The present study aims at investigating the effect of submerged arc welding fluxes for enhanced corrosion resistance of structural steel welds. By varying the basicity index of submerged arc welding fluxes the corrosion resistance and mechanical properties of weld metal such as tensile strength, impact strength, microhardness in submerged arc weldments were evaluated. The result shows that with the increase in bascity index tensile strength of weld specimen reduced while impact strength and microhardness value increased. Maximum microhardness (288 HV) was observed for flux 2 while base metal show minimum microhardness value (205 HV). Flux 5 gives maximum impact strength (94.17 J) as compared to the base metal (80 J). This is due to the reduced content of oxygen in weld metal which increases the weld metal impact toughness. Corrosion resistance of weld specimen increased as compared to the base metal. Ductile fracture mode and shear lip or tears were observed in the weld zone. Shear dimples and shear lips were more severe in base metal as well as weld metal impact specimens due to the rapid effect of external forces on the impact test. The banded microstructure of delta ferrite and austenite was observed in the base metal. Fine grains of ferrite and pearlite at the center and edges were present in the weld zone.

The Influence of Nanosized Particles Introduced into Molten-Pool Tail on the Impact Toughness of Weld Metal

This article discusses the possibility of introducing nanosized particles into a molten pool using a flux-cored wire. A flux-cored wire has been proposed with added composite granules obtained upon the combined treatment of nickel powder and nanosized particles. In order to avoid the overheating of particles, it has been proposed to add a flux-cored wire to a molten-pool tail using preheating. The following hardmelting particles have been tested: tungsten carbide (WC), titanium nitride (TiN), and aluminum oxide (Al2O3). It has been demonstrated that the addition of tungsten carbide to a molten pool improves the stability of weld-metal (WM) impact toughness while retaining its average value and the addition of aluminum oxide to a molten pool leads to increased average values of WM impact toughness while retaining its stability. Meanwhile, nanosized particles of titanium nitride in a molten pool are prone to dissociation, which leads to the formation of porosity, thus limiting the field of application of this modifier.

Welding behaviour of Duplex and Superduplex Stainless Steels using Laser and Plasma ARC Welding processes

1.4462 (UNS S31803) duplex stainless steel (DSS) and EN 1.4410 (UNS S32750) superduplex stainless steel (SDSS) have been welded by fibre laser welding and plasma arc welding (PAW) processes with-Cout filler metal. Impact toughness testing at various temperatures from 20 °C down to −60 °C was carried out. Microstructural examination included macro and microphotographs of the cross-sections, ferrite content measurements and hardness survey of the weld zones. Weld metal impact toughness results on the order of 100 J were obtained while values between 30 J and 60 J were measured respectively for plasma arc and laser welds of the duplex and superduplex grades even at −60 °C test temperature. Ferrite content of the welds varied generally in an acceptable range which affected the microstructure and the toughness properties. Better toughness results of plasma arc welds of both duplex and superduplex material compared to the laser welds are attributed to the balanced microstructure of the weld metal having ferrite- austenite ratio close to 50:50 % obtained by controlled heat input.

Effect of Vibratory Weld Conditioning on Weld Impact Toughness

With vibratory weld conditioning, the enhancement of weld metal microstructure can be achieved. The mechanical properties, level of residual stresses, and deformation can also be affected. This article provides the research results of the effect on weld metal impact toughness. Four different types of single welds were made; vibrated, tempered, and combinations of both conditions were compared to as-welded condition. Results were compared to and confirmed with multipass weld impact toughness measurements. The vibration during welding benefits energy absorbed in impact toughness test of weld metal and improves fracture behavior.

Effects of Nitrogen on Weld Metal Microstructure and Toughness in Submerged Arc Welding

The effects of nitrogen content on weld metal impact toughness in submerged arc welding were investigated and interpreted in terms of microstructural changes and solid solution hardening. The weld metal impact toughness in as-welded condition decreased with increasing nitrogen content from 110 to 200 ppm. The weld metal microstructure changed with increasing nitrogen content; ferrite with second phase increased at the expense of tough acicular ferrite. In addition to microstructural changes, the microhardness of acicular ferrite increased gradually with the nitrogen content. Therefore, the loss of impact toughness can be attributed to a combination of the effects of microstructural changes and solid solution hardening.

Prediction of Mechanical Properties in Submerged Arc Weld Metal of C–Mn Steel

The prediction model has been developed for steel weld metal mechanical properties as a function of flux ingredients such as CaO, MgO, CaF2 and Al2O3 in submerged arc welding carried out at fixed welding parameters. The results of quantitative measurements of mechanical properties on eighteen weld metal samples were utilized for developing the prediction equations of mechanical properties applying statistical design of experiment for mixtures. Among the flux ingredients, MgO appears to be important on its own in influencing the mechanical properties. The other ingredient CaO appears to be most important as it interacts with CaF2 and Al2O3 in influencing weld metal mechanical properties. The prediction equations have been checked for adequacy by performing tests on submerged arc welds using randomly designed flux and found satisfactory. The ISO-response curves were developed for weld metal impact toughness to show the output levels at different percentage of flux ingredients.

Weld metal hydrogen-assisted cracking in thick steel plate weldments

The transverse crack, a type of cold crack, occurs perpendicular to the welding direction. From experience, preheating and interpass temperature are important factors in cold crack occurrence. Transverse cracks were detected in the specimen welded with preheating and interpass temperatures below 30 °C, but cracks were not detected for the specimen welded with preheat and interpass temperatures of 100–120 °C. Hardness values of preheating and interpass temperatures below 30 °C were higher than preheating and interpass temperatures below 100–120 °C in deposited weld metal. The residual stress values for the specimen welded with a preheating and interpass temperature below 30 °C were higher than the specimen welded with a preheating and interpass temperature at 100–120 °C. The result of weld metal impact test shows higher impact values for the weld condition with preheating and interpass temperature at 100–120 °C, compared to the specimen welded with a preheating and interpass temperature below 30 °C.

Weld metal impact toughness of electron beam welded 9% Ni steel

9% Ni steel was electron beam welded and the impact toughness of its weld metal was investigated. The improvement of weld metal toughness was studied by an increase of Ni content in the weld metal and its mechanism was discussed. The weld metal impact toughness was as low as 25–55 J at −196°C. However, it increased remarkably by an increase of Ni and showed 118 J at the same temperature when Ni content was 16.6%. As Ni lowers the martensite start temperature, martensite formed in weld metal with a high Ni content has more chance of auto-tempering because of its slow cooling rate at a low temperature range. Therefore, the improvement is believed to be due to the formation of auto-tempered martensite and retained austenite during the cooling cycle after welding