Impact Toughness Of Weld Metal 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.

해양구조물용 YS 420MPa 강재 Flux Cored Arc 용접금속의 기계적 성질에 미치는 용접 자세의 영향

This study investigated the mechanical properties of flux-cored arc weld metal of 420-MPa yield-strength (YS) steels for offshore structures based on welding position. Results showed that the recovery rate of alloying elements in the horizontal-position weld metal was higher than that in the vertical-up-position weld metal, and the fraction of low-temperature transformation phases with high dislocation density in the horizontal-position weld metal was high. Consequently, the YS, tensile strength, and impact toughness of the horizontal-position weld metal were higher than those of the vertical-up-position weld metal. In addition, the impact toughness of the weld metal was affected to a greater extent by the microstructure and fraction of the weld metal itself than by the fraction of the martensite-austenite constituents.

Microstructure evolution and enhanced cryogenic toughness of laser welded dissimilar SA645/AISI304L joints via intercritical tempering

In this study, we explored the impact of intercritical tempering on the microstructural evolution and mechanical properties of dissimilar welds formed through laser welding between 5%Ni steel (SA645) and austenitic stainless steel (AISI304L). Upon tempering at 500 °C, reversed austenite manifested within the weld metal. The volume proportion of reversed austenite in weld metal at room temperature increased first, exhibiting a maximum (∼10%) at ∼600 °C, and then decreased with increasing tempering temperature, which was associated with the diminished stability of austenite. Due to the change in tempering temperatures, two distinct types of reversed austenite were present, with one being located at the high-angle grain boundaries and the other within the martensite blocks. As the tempering temperature increased, the weld metal hardness decreased, reaching a minimum of ∼306 HV at 600 °C, and then increased. The dislocation density within the martensite matrix and the quantity of reversed austenite are the crucial factors to determine the hardness of weld metal. The cryogenic impact toughness of weld metal increased at first and then decreased as the tempering temperature increased. The maximum of ∼40 J for the cryogenic impact toughness was obtained when tempering at 600 °C. The low-temperature impact toughness of the weld metal was determined by the synergy of the TRIP effect of reversed austenite, the compatible deformation capability of dual-phase structure, and the crack propagation behavior.

Study on impact toughness of TMCP and quenched and tempered high strength steels

In this study, the effect of steel rolling technique, temperature, yield strength and welding heat input on the impact toughness of high-strength steels is studied. The impact toughness of five kinds of high strength steels with yield strength of 550 MPa, 690 MPa and 890 MPa are experimentally studied. The standard Charpy V-notch test is carried out and the absorbed energy AKV of the test specimens is obtained. The test results show that the impact toughness of QT550 high-strength steel is not sensitive to temperature and it also has good impact performance at low temperature. For other high strength steels, with increase of steel strength, the impact toughness is severely degraded with decreasing temperature. For the effect of rolling technique on impact toughness, the QT type high-strength steel generally follows the law that the impact toughness deteriorates with the increase of the yield strength. QT process can produce better impact resistance than TMCP process for 690 grade steel. The effect of temperature on the impact toughness of WM is intensified at high heat input. The impact toughness of the base material (BM), heat-affected zone (HAZ) and weld metal (WM) deteriorates with the rise of the yield strength. QT550 and QT690 show different impact characteristics for HAZ and WM. The former HAZ has better impact performance under high heat input while WM is better under low heat input; both HAZ and WM of QT690 show higher impact toughness under low heat input.

Evolutions of Microstructure and Impact Toughness of Submerged Arc Weld Metal via Introducing Varied Si for Weathering Bridge Steel

In this paper, the influence of the silicon (Si) content on microstructure and impact property of submerged arc weld metals (WMs) for weathering bridge steel was clarified. Actual submerged arc welding (SAW) was carried out to produce WMs with 0.18 wt.%, 0.36 wt.%, 0.51 wt.%, and 0.60 wt.% of Si. The low temperature impact property of weld metal was detected, and the weld microstructures were characterized by optical microscopy (OM), scanning and transmission electron microscope (SEM and TEM), and electron backscatter diffraction (EBSD). The results indicate that WMs consist of polygon ferrite (PF), acicular ferrite (AF), granular bainitic ferrite (GBF), and martensite/austenite (M/A) constituents in each Si content. With increasing Si, the proportion of PF increased, while AF and GBF coarsened, the area fraction, fM/A, and the mean size, dM/A, of M/A constituents increased, the number of inclusions decreased, but the size increased. Further, the fraction of high-angle grain boundaries (HAGBs) with the misorientation tolerance angles (MTAs) greater than 15° reduced, while the mean equivalent diameter, MEDMTA≥15°, of ferrite grains with HAGBs increased. Accordingly, the impact toughness of WM was degraded from 108.1 J to 39.4 J with the increase in Si. The increase in M/A constituents and inclusions size reduced the critical fracture stress, thereby formation of larger microcracks and cleavage planes occurred. The reduced HAGBs exhibited a low hindering effect on crack propagation, and, consequently, the impact toughness decreased with increasing Si content.

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 shielding gas on MIG welding performance with austenitic wire

Two different shielding gases, Ar + CO2 and Ar + He + N2, were used for MIG welding of a 20 mm 10CrNi3MoV steel plate. The effects of shielding gases on the chemical composition, microstructure, purity, and low-temperature impact toughness of weld metal were studied in detail. N-containing shielding gas can increase the nitrogen content in the weld metal, change the solidification mode of deposited metal, reduce ferrite content in the weld metal, and significantly improve the low-temperature impact toughness of deposited metal. The purity of weld in the ternary inert gas atmosphere is high, which is beneficial to the improvement of low-temperature toughness. The ferrite content of the ternary joint is higher than that of the binary joint, and the strength of the ternary joint is much higher than that of the binary joint.

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.

Microstructure anomaly during welding and its influence on the mechanical properties of dissimilar weldments of P92 martensitic steel and AISI 304L austenitic stainless steel

In this investigation, microstructural characteristics, mechanical properties, and residual stress magnitude of dissimilar weld joints (DWJs) between creep strength enhanced ferritic-martensitic (CSEF) P92 steel and austenitic stainless steel (ASS) 304L has been investigated. The Thermanit MTS 616 (P92 filler) filler metal was employed to prepare P92/304L SS DWJs. The groove geometry also plays a crucial role in DWJs, so the conventional V-groove and narrow shape groove geometry was adopted for P92/304L SS DWJs. The microstructure characterization was performed using optical microscope (OM), scanning electron microscope (SEM), and filed emission SEM (FESEM). The microstructural examination showed the formation of the δ-ferrite grains and unmixed zone (UZ) at the weld interface. The martensitic microstructure produced after welding is brittle due to quenched martensite and the dissolution of precipitates. Thus, the post-weld heat treatment (PWHT) known as tempering was carried out at 760 °C for the period of 2 h to get tempered martensitic microstructure. The ultimate tensile strength (UTS) of the as-weld (AW) and PWHT tensile specimen of the P92/304L SS DWJs was 660 MPa and 643 MPa, respectively for V-groove geometry specimens and 640 MPa and 609 MPa, respectively for narrow groove geometry specimens. The tensile fracture was experienced at 304L base metal, and the UTS value of DWJs was very close to the UTS of the 304L SS. The average microhardness value of the martensitic weld metal (352HV0.5) and coarse-grain heat-affected zone (CGHAZ, 366HV0.5), fine grain HAZ (FGHAZ, 320HV0.5) in the AW state was beyond the maximum permissible hardness value of 265HV0.5, as per the A335/A335M − 15a standard. The hardness value beyond 265HV0.5 indicates the undesirable brittle martensitic microstructure. After PWHT, the micro-hardness value of the CGHAZ (235HV0.5), FGHAZ (215HV0.5), and inter-critical HAZ (ICHAZ, 201HV0.5) was below the maximum allowable value of 265HV0.5 for P92 material because of the tempering of the quenched martensite. However, the Charpy test result concluded that the problem associated with the martensitic P92 filler is to obtain an acceptable value of the impact toughness of weld metal in AW state. The Charpy impact toughness of weld metal for P92/304L SS DWJs in AW condition was 10 J (V-groove geometry) and 37 J (narrow groove geometry), while for PWHT condition, it was 188 J (V-groove geometry) and 150 J (narrow groove geometry). The impact toughness of the P92 filler weld was below the minimum requirement of 47 J (EN ISO 3580:2017) in AW state. However, the impact toughness of the welds made by using P92 filler metal met the minimum requirement of 47 J (EN ISO 3580:2017) after PWHT due to the tempering of the martensite. The residual stress analysis using deep hole drilling (DHD) technique revealed the existence of the compressive residual stresses in the weld metal and P92 HAZ in as-weld and PWHT condition. The compressive stress was dominant because of the martensitic phase transformation.

Lexicographic Multi-Objective Optimization Approach for Welding Flux System Design

Multiple response optimization of welding flux performance has been found to be cost effective and useful for the achievement of the best balance among conflicting welding flux quality attributes. Many multi-criteria optimization methods (MCOM) have been applied in flux formulation situations where flux quality attributes are of comparable importance. However, information on applications of MCOM to flux design situations where quality attributes are in hierarchical order of importance is scarce in the open literature. In this study, a Lexicographic Multi-objective Optimization (LMO) model was proposed for handling flux design situations in which the attributes are in hierarchical order of importance. The model was applied using data from literature. Two priority levels were used: acicular ferrite (AF) maximization was assigned first priority while the maximization of polygonal ferrite (PF) content and weld-metal impact toughness (WIT) were assigned second priority subject to oxygen content constraint of 250 – 350ppm. The respective solutions for AF, PF, WIT and oxygen content were 51.19%, 21.80%, 23.70J at -20oC and 315ppm. The corresponding flux formulation was CaO (25.90) MgO (15.00) CaF2 (31.10) and Al2O3 (8.00%). Various priority structures were used to explore trade-off options and to generate three more pareto efficient solutions from which the flux formulator can select the most preferred one. The proposed model has filled the existing gap in the literature being a pioneering work in the application of lexicographic multi-objective optimization method in welding flux design.

Effects of Long-Term Service on Microstructure and Impact Toughness of the Weld Metal and Heat-Affected Zone in CrMoV Steel Joints

The microstructure and impact toughness of weld metals (WMs) and heat-affected zones (HAZs) of a low-alloy CrMoV steel gas turbine rotor which had served for 14 years were investigated. The ex-service joints in the turbine part (serving at 500–540 °C) and the compressor part (serving below 300 °C) of the rotor were selected for comparative research. The microstructure of the WMs and HAZs between the turbine part and the compressor part was similar, indicating that there was no significant deterioration in microstructure of the turbine part during service. However, compared with the compressor part WM, the impact energy of the turbine part WM decreased significantly, and FATT50 increased greatly. The degraded toughness of turbine part WM was related to more serious intergranular cracking caused by higher segregation level of phosphorus (P) at prior austenite grain (PAG) boundaries. Welding and post-weld heat treatment led to obvious segregation of P at PAG boundaries in WMs, and the segregation of P in turbine part WM was further aggravated during serving at 500–540 °C. Additionally, the inhomogeneous microstructure of the WMs also aggravated the segregation of P. The toughness of the HAZs in both turbine part and compressor part was high, which was because of fine grains. Furthermore, due to there being more grain boundaries and low P content, the segregation of P in HAZs was slight and its adverse effect on the toughness could be ignored.

Investigation of the microstructure and mechanical properties of the laser welded joint of P22 and P91 steel

The present manuscript investigates the microstructural aspects and mechanical properties of laser beam welded ASTM A335 Grade P91 and P22 steel joint for power plant applications. Detailed microstructure characterization of the weld metal (WM) and heat-affected zone (HAZ) were carried out in as-welded and post-weld heat treatment (PWHT) conditions. A variation in microstructure was observed along the welded joint. This resulted in inhomogeneity in mechanical properties. The PWHT resulted in the formation of the stabilized microstructure in weldments and reduced heterogeneity in mechanical properties along the weldments. Tensile strength of weld joint in as-welded (AW) and PWHT condition was found slightly higher (617 MPa and 628 MPa, respectively) than the tensile strength of P22 steel (610 MPa). The fracture location for both AW and PWHT was observed in the P22 base region, which indicates that welded joint is stronger than the base material. Maximum tensile strength of the WZ was found 864 MPa in the as-welded condition. The hardness of WM, P91 CGHAZ and P22 CGHAZ were found 376 HV, 420 HV and 302 HV, respectively. After the PWHT, the hardness of the WM, P91 CGHAZ, P91 ICHAZ, P22 CGHAZ and P22 ICHAZ were measured 237 HV, 264 HV, 212 HV, 208 HV and 190 HV, respectively. The reduction in hardness is attributed to the tempering reaction, which results in the formation of the tempered martensite in WM and HAZ of P91 and tempered bainite in P22 HAZ. The impact toughness of the weld metal in as-welded condition was measured 85 J, which was lower than P22 and P91 steel. PWHT resulted in a drastic increase in impact toughness of WM and it was 145 J. The impact toughness of the P22 and P91 HAZ was measured 146 J and 92 J, respectively, for AW and 168 J and 140 J, respectively, after PWHT. The optimum microstructure and mechanical properties of the dissimilar welded joint were obtained after the PWHT.

Effect of Microstructure on Low-Temperature Impact Toughness of Multi-Pass Weld Metal of 1 GPa Class High Strength Steel

A 1 GPa class weld metal was prepared by multi-pass welding using a prototype flux-cored wire, and the correlation between microstructure and low-temperature impact toughness of the weld metal was investigated. The microstructure of the as-deposited columnar region and the equiaxed region reheated by subsequent welding passes was observed, and it was found that low-temperature transformation products such as bainite and martensite mainly developed in both regions. Since the prior austenite grains were coarse in the columnar region, the effective grain size of the final microstructure could be large; in this case, it was confirmed that the low-temperature impact toughness of the weld metal was very low. However, in the weld metal used in this study, acicular ferrite was formed inside the grains of the columnar region; the effective grain size and grain boundary misorientation distribution of the final microstructure were similar to those of the equiaxed region, and a good low-temperature impact toughness of the weld metal was obtained. Key words: High strength steel, Multi-pass weld metal, Acicular ferrite, Impact toughness

Effects of pre-tempering on the microstructure, hardness and impact toughness of the 2.25Cr–1Mo-0.25V heat-resistant steel weld metal

In this study, the effects of pre-tempering on microstructure, hardness, impact toughness and fracture modes of weld metals in 2.25Cr–1Mo-0.25 V heat-resistant steel were investigated. Four weld metals with as-welded, three different post welding heat treatments were chosen as the investigated materials. Optical Microscopy (OM), Scanning Electron Microscope (SEM) were used to evaluate the microstructures of the weld metals. The mechanical properties of the weld metals were examined by hardness, and impact toughness experiments. The fracture surfaces of the weld metals were observed and analyzed by SEM. Results indicated that the impact toughness of as-welded metal is only 6 J, Post welding heat treatment (PWHT) of 705 °C + 8 h can increase the impact toughness of the weld metals to 16,18 and 119 J; 44, 80, 100, 169 and 177 J, respectively. The pre-tempering process with 650 °C with the heating rate of 55 °C/h and holding 40 h before 705 °C+8 h tempering process can increase the impact toughness to 126, 135, 136, 136, 167 J. The change of the impact toughness is directly related to the change of the microstructure. The microstructure of as-welded weld metal is mainly composed of granular bainite, which determined the lower impact toughness. The improvement of impact toughness for the weld metals after post welding heat treatment is attributed to the decomposed degree from Martensite-Austenite constituent into carbides.

Study on toughening mechanism of Ti on weld metal of high strength steel

The effect of Ti element on acicular ferrite microstructure of high strength steel weld was studied by scanning electron microscope(SEM), Transmission electron microscopy(TEM) and EDX spectrum analysis. The results show that Ti element content in a certain range can promote the precipitation of acicular ferrite in high strength steel weld metal. The increase of Ti content in the weld makes the Ti-rich inclusions increase, which is conducive to the formation of acicular ferrite. Charpy impact test results show that with the increase of Ti content, the impact toughness of weld metal increases first and then decreases. The tensile test results show that the tensile strength of weld metal increases and the elongation decreases with the increase of Ti content. There are high density dislocations and M-A components in acicular ferrite. M-A elements hinder the crack growth and improve the impact toughness of weld metal. When the Ti content is 0.253%, the impact energy of the weld metal is 155 J at-60 °C, and the impact toughness is the best.

The effects of fusion ratio on microstructure and cryogenic toughness of dissimilar joint between SA553 and SUS304

The fusion ratio of base metal was adjusted by changing the welding conditions for dissimilar joint between SA553 and SUS304. Both the content and the size of retained austenite (RA) both at grain boundary and among martensite laths increased when the fusion ratio of SUS304 increased. The content, distribution and stability of RA were compared by SEM, TEM, XRD and EBSD before and after cryogenic treatment (−196 ℃, 100 h). After cryogenic treatment, the RA in weld metal of all specimens declined. The lower the austenite content, the more the decline ratio after low temperature immersion. The stress resulted from phase transformation played a vital role in the stability of RA according to EBSD analysis. With the decrease of RA content, the room temperature impact energy of weld metal increased, but the low temperature impact energy decreased. The difference between room temperature impact energy and low temperature impact energy is affected by the content of retained austenite. When the austenite content was higher than 30 %, the cryogenic impact toughness of weld metal met the application requirements. It is demonstrated that the dissimilar joint between SA553 and SUS304 made by autogenous laser welding is practical in the field of liquid natural gas (LNG).

Impact Toughness Characteristics of SM570-TMC Steel Joint Using Welding Wire Containing 0.4% Nickel at Different Level of Heat Input

The study was conducted to evaluate the impact toughness of flux-cored arc welded of SM570-TMC steel joint under different heat inputs, 0.9 kJ/mm (low heat input) and 1.6 kJ/mm (high heat input). Welding wire containing 0.4%Ni was selected on this experiment. Multi-pass welds were performed on SM570-TMC steel plate of 16 mm in thickness with a single V-groove butt joint on flat position (1G). The evaluation consists of observations on microstructure using an optical microscope and SEM-EDS, and mechanical properties including tensile, microhardness Vickers and Charpy V-notch (CVN) impact test at temperatures of 25, 0 and-20 °C. Results showed that the impact toughness of the base metal (BM) was higher than the weld metal (WM) at all test temperatures. Hardness and impact toughness of WM at low heat input was observed higher than when applied a high heat input. The welded samples at low and high heat inputs had high of tensile strength, and the fracture seemly occurs on the BM. Microstructure observation showed that at a high heat input, larger grains and microsegregation were observed. It might affect on decreasing their impact property.

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.

Sources of variability and improvement in impact toughness of a low Cr–Mo steel weld metal

For the heat resistance steel weld metal, special post-weld heat treatments need to be performed to maintain the creep resistance, improve the impact toughness, and relieve the welding residual stress. In this paper, firstly, the three factors affecting variability and lower values of toughness were revealed. Secondly, two different post-weld heat treatment (PWHT) methods have been used to improve the impact toughness of a heat resistance steel weld metal. Two PWHT methods include post-weld direct tempering (PWDT) process at 690 °C/26 h/air cooling and post-weld normalized tempering (PWNT) process with re-austenitization at 960 °C/1.5 h/air cooling + tempering at 690 °C/26 h/air cooling. For three type specimens with as-welded (AW), PWDT, PWNT processes, the impact toughness and the hardness were measured, and the fracture surface, microstructures were observed and analyzed by scanning electron microscope (SEM). Results indicated that PWDT heat treatment can improve the impact toughness of the weld metals from the original 79 J - 169 J to 82 J–290 J because the microstructure is changed from granular bainite to block ferrite and granular bainite. PWNT heat treatment can remarkably improve the impact toughness of the weld metals from the original 79 J- 169 J to 148 J–325 J. It is attributed to that PWNT heat treatment process can remove the boundaries of the columnar grain zone and reheated zone, make the difference of the microstructure between the columnar grain zone and reheated zone decrease, and improve the homogeneity of the microstructure.

Role of tempering cooling rate on impact toughness of 2CrMoV weld metal

Abstract