Effect Of Post-weld Heat Treatment Research Articles

Application of wire arc additive manufacturing for repair of Monel alloy components

ABSTRACT Monel alloys containing 63Ni-30Cu-2.0Mn-2.0Fe-AlTiC (wt. %) are often used for manufacturing of machine parts in marine, chemical, and oil extraction industries. Despite excellent corrosion resistance and mechanical properties, Monel components may fail via wear, which is enhanced in corrosive environment. Heavy components working under high loads may experience galling, which is welding followed by tearing of large pieces of material off the contacting surfaces. In addition to high cost of Ni-based alloys, heavy parts of machinery may not be easily replaced, and, thus, require repair being in partial assembly. In this paper, we introduce wire arc additive manufacturing (WAAM) technology as a repair method for Monel alloy components. The effect of post-weld heat treatment on microstructure and hardness of both the component body and the repair layer is investigated and discussed.

Effect of Post-Weld Heat Treatment Conditions on Mechanical Properties, Microstructures and Nonductile Fracture Behavior of SA508 Gr.1a Thick Weldments

This study analyzes the effects of post-weld heat treatment (PWHT) on the mechanical properties and microstructures of SA-508 Gr.1a welds and proposes a new PWHT exemption criterion based on nonductile fracture evaluation considering welding residual stress. The welding coupons were prepared with submerged-arc welding, gas-tungsten arc welding, and shielded-metal arc welding, using ferritic steel, SA-508 Gr.1a. The microstructure of the heat-affected zone (HAZ) was analyzed using optical microscopy, electron-back-scatter diffraction and Vickers hardness testing. The mechanical properties of the welds were evaluated by uniaxial tensile test, transverse side bend test, Charpy V-notch impact test and side bend test. Bainite and ferrite structures formed mainly in the HAZ, and the grain size became coarser with proximity to the surface and fusion line. The mechanical properties did not depend strongly on PWHT, weldment thickness or welding techniques, and they satisfied the welding procedure qualification test specified in the ASME Boiler & Pressure Vessel code. Welding residual stresses were considered in assessing structural integrity using nonductile fracture evaluation. A margin of safety against nonductile fracture with residual stress was calculated for Korean Standard Nuclear Power Plant steam-generator welds, using its design parameters and operating conditions, and this safety margin is suggested as an acceptance criterion for residual stress for exemption from PWHT.Graphic abstract

Effect of post-weld heat treatment on microstructure and corrosion properties of multi-layer super duplex stainless steel welds

Abstract To investigate the influence of post-weld heat treatment on the microstructure and corrosion properties of super duplex stainless steel welded joints, multi-layer multi-pass welding of 2507 super duplex stainless steel by tungsten argon arc welding was performed using an ER2594 welding wire. The microstructures of the welded joints before and after post-weld heat treatment at 1150 °C, 1170 °C and 1190 °C were observed, and the mechanical and corrosion properties were tested. The post-weld heat treatment changed the austenite content and morphology of the welded joint and improved the corrosion resistance of different parts of the weld metal. The choice of various solution heat treatment temperatures affected the change in austenite content in the weld zone and the degree of diffusion and homogenization of the alloy elements. After post-weld heat treatment at 1170 °C, the two-phase ratios in each area of the weld were the most suitable and uniform, and the overall mechanical and corrosion properties of the joint were more uniform.

Dissimilar Laser Beam Welding of AISI 420 Martensitic Stainless Steel to AISI 2205 Duplex Stainless Steel: Effect of Post-Weld Heat Treatment on Microstructure and Mechanical Properties

Dissimilar Laser Beam Welding of AISI 420 Martensitic Stainless Steel to AISI 2205 Duplex Stainless Steel: Effect of Post-Weld Heat Treatment on Microstructure and Mechanical Properties

Effect of PWHT on the Microstructure and Mechanical Properties of Friction Stir Welded DP780 Steel

In the present study, the effect of post-weld heat treatment (PWHT) on the microstructure and mechanical properties of friction stir welded (FSW) DP780 steel sheets was investigated. FSW was carried out at a constant tool rotation speed of 400 rpm and different welding speeds (200 mm/min and 400 min/min). A defect free weld was witnessed for both of the welding conditions. The mutual effect of severe plastic deformation and frictional heat generation by pin rotation during the FSW process resulted in grain refinement due to dynamic recrystallization in the stir zone (SZ) and thermo-mechanically affected zone (TMAZ). Lower tensile elongation and higher yield and ultimate tensile strengths were recorded for welded-samples as compared to the base material (BM) DP780 steel. The joints were subsequently annealed at various temperatures at 450–650 °C for 1 h. At higher annealing temperature, the work hardening rate of joints gradually decreased and subsequently failed in the softened heat-affected zone (HAZ) during the uniaxial tensile test. Reduction in yield strength and tensile strength was found in all PWHT conditions, though improvement in elongation was achieved by annealing at 550 °C. The digital image correlation analysis showed that an inhomogeneous strain distribution occurred in the FSWed samples, and the strain was particularly highly localized in the advancing side of interface zone. The nanoindentation measurements covering the FSWed joint were consistent with an increase of the annealing temperature. The various grains size in the BM, TMAZ, and SZ is the main factor monitoring the hardness distribution in these zones and the observed discrepancies in mechanical properties.

Effect of Post-Weld Heat Treatment on Microstructure and Properties of Al-Mg Alloy Welded Joints

Effect of Post-Weld Heat Treatment on Microstructure and Properties of Al-Mg Alloy Welded Joints

Effects of Post-Weld Heat Treatment on the Microstructure and Mecanical Properties of the AZ91 Laser Welded Joint

Effects of Post-Weld Heat Treatment on the Microstructure and Mecanical Properties of the AZ91 Laser Welded Joint

Effect of Postweld Heat Treatments on Type IV Creep Failure in the Intercritical Heat-Affected Zone of 10% Cr Martensitic Steel Welded with Haynes 282 Filler

This study investigated the effect of postweld heat treatment (PWHT) conditions on Type IV failure behavior of 10% Cr martensitic steel welds using Haynes 282 filler. The welded joints were subjected to PWHT at temperatures of 688, 738, and 788 °C for 4 and 8 h. Creep tests were carried out at 600 °C under a stress of 200 MPa. The as-welded joint without PWHT showed Type IV cracking due to growth of voids around Laves phase by localized creep deformation in the intercritical heat-affected zone (ICHAZ). The creep properties of the PWHTed joints at 688 °C were similar to those of the as-welded joints without PWHT. On the other hand, the PWHTed joints at 738 °C exhibited a significantly longer creep life by a lower amount of Laves phase in the ICHAZ than those at 688 °C; this could be a result of the homogenization of ICHAZ microstructure during PWHT at 738 °C. However, the PWHT at 688 and 738 °C showed the same Type IV creep failure mode. Meanwhile, the PWHTed joints at 788 °C exhibited the shortest creep life in this study. The failure location was shifted to the base metal away from the HAZ, and severe plastic deformation occurred due to the softened matrix by excessive tempering.

Effect of Post-weld Heat Treatment on the Cross Tensile Strength of Resistance Spot-Welded Medium Manganese Steel

The influence of the post-weld heat treatment (PWHT) on the cross tensile strength (CTS) of the resistance spot-welded medium manganese steel (MMS, 7Mn steel) is investigated in the present study. The results showed that the PWHT (tempering) could increase the CTS of the resistance spot-welded 7Mn steel to 5.4 kN, nearly 3 times compared with that for the as-welded specimen (~ 2.0 kN). The as-welded 7Mn steel contains fully dendritic martensite and revealed severe Mn segregation at the grain boundaries, leading to a weak zone adjacent to the centerline in the nugget. As a result, the fracture resulted in a complete intergranular fracture morphology, reflecting an interfacial fracture (IF) mode. On the other hand, the tempering of PWHT transformed the microstructure of 7Mn steel to tempered martensite. In addition, the PWHT introduced nano-sized Mn23C6-type carbides along the grain boundaries in the nugget, successfully relieved the Mn segregation and strengthened the grain boundaries. Consequently, the as-tempered 7Mn steel failed in partial interfacial fracture (PIF) mode with a large amount of dimples on the fracture surface. This experimental study shows the capability of PWHT to dramatically improve the CTS of 7Mn steel by microstructure manipulation.

A comprehensive review on pre- and post-forming evaluation of aluminum to steel blanks via friction stir welding

Tailored blanks of aluminum and steel have increasing applications in recent years. In less critical section of a parts where it is not necessary to use high strength steel but requires lightweight, aluminum provides a reliable substitute. As a promising alternative to join aluminum and steel, friction stir welding has been studied extensively. This review paper emphasizes on the evaluation of pre- and post-forming of friction stir welded blanks and manufacturability issues during metal forming. Upon selection of appropriate parameters to obtain a successful weld, quality and performance are reviewed. The necessity and effect of post-welding heat treatment on heat treatable and non-heat treatable weld joint are discussed. Following, evaluations of pre and post-forming are presented, including mechanical and microstructure characterization as well as formability of the joint using limiting dome height test and springback via v-bending and twist forming. This article concludes important aspects in heat treatment and forming of friction stir welded aluminum and steel blanks.

Evolution of Soft Zone in a Simulated 1.25Cr-0.5Mo Steel-Welded Joint During Post-weld Heat Treatment

In the present study, the effect of post-weld heat treatment on the soft zone of 1.25Cr-0.5Mo steel welded joint has been systematically studied. Outstanding features of the soft zone, including grain size, number density of carbides, volume fraction of carbides, and hardness distribution, are quantitatively analyzed by means of scanning electron microscopy and a microhardness testing. Results show that ferrite grain growth, carbide coarsening, and alloying element segregation are main factors accounting for hardness variations.

Temperature and time effects of post-weld heat treatments on tensile properties and microstructure of Zircaloy-4

Opportunities exist to expand the application of Zircaloy-4 (Zry-4) into lower-temperature (<100°C) applications. Welded areas within these structures are potential failure points and post-weld heat treatments (PWHTs) are not yet standardized for application in this temperature range. Zry-4 tungsten inert gas (TIG) welds were given PWHTs from 450-900°C with hold times from 0.5-48 hours to investigate changes to tensile properties and microstructure. Treatment of 800°C for 1 hour was found to produce the most ductile material, measured by total elongation of the tensile bar (16.5%). Both PWHT time and temperature were observed to increase total elongation, except in extreme (>800°C or >18hours) cases, but the effect of temperature was stronger. The second order cumulative annealing parameter shows a trend with tensile properties. Average grain sizes in the fusion zone and heat affected zone did not change under any of the PWHTs until the development of an undesirable blocky-alpha phase, which was only observed to form in the heat affected zones for hold times greater than 18hr at 800°C.

Effect of post-weld heat treatment and dissimilar filler metal composition on the microstructural developments, and mechanical properties of gas tungsten arc welded joint of P91 steel

In the present study, the Gas Tungsten Arc Weld (GTAW) joint of P91 steel was produced using the dissimilar IN617 grade filler wire. The welded joints have been subjected to different post-weld heat treatment (PWHT) to obtain the stable microstructure and mechanical properties for P91 heat-affected zone (HAZ). The PWHT was performed at 750 °C (less than Ac1) and 800 °C (close to Ac1). The welded joint was characterized for mechanical properties using tensile test, hardness test and Charpy impact toughness test. In order to understand the role of the dissimilar filler metal and PWHT on the Charpy impact toughness of the weld metal, Charpy impact toughness tests were conducted at room temperature. The Charpy impact toughness of the weld metal was measured 55 ± 4 J for the as-welded condition. The PWHT has observed almost a negligible effect on Charpy impact toughness value. The tensile strength was measured 638 MPa for the as-welded joint and improved significantly after the PWHT. The role of the filler metal and PWHT on heterogeneity in microstructure and hardness produced along the HAZ of P91 steel were investigated in detail. The microstructure features of HAZ (grain size, particle size, fraction area of the precipitates and particle to particle distance) were measured experimentally using the ImageJ software as a possible contributor to the hardening mechanism. The coarse-grained HAZ (CGHAZ) devoided from the carbide precipitates showed the peak hardness of about 395 HV in as-welded condition and the minimum of 189 HV was measured for inter-critical HAZ (ICHAZ). The PWHT at 800 °C produced the homogenous microstructure and a negligible hardness variation along the HAZ. The precipitate free δ-ferrite region was identified in the CGHAZ region near to fusion line for as-welded condition and remain unaffected during the PWHT.

Effects of post-weld heat treatment on microstructures and properties of laser welded joints of new high-strength Ti-55531 alloy

This study investigated the effects of post-weld heat treatment (PWHT) on microstructures and properties of a laser welded joint of high-strength and high-toughness titanium alloy, namely Ti-5Al-5V-5Mo-3Cr-1Zr (Ti-55531). The experimental results demonstrate that PWHT can improve the tensile strength of the joint by 47.8 %, which reaches 92.4 % of base metal (BM). Average microhardness of a weld metal (WM) of the joint increases from 309 HV in the as-welded state to 371 HV. The analysis shows that PWHT can significantly improve microstructures of the joint, which is an important reason for rising strength of the joint. The BM of the as-welded joint presents a typical duplex microstructure and 10∼20 % of equiaxed αp phases are inserted into fine transformed β microstructures. Equiaxed grains are retained in a heat affected zone (HAZ) and the WM is composed of coarse columnar grains. After PWHT, there is no obvious change in microstructures of the BM of the joint. While maintaining β phases in BM, the edge of equiaxed α phases in the HAZ gradually dissolves and change to the WM microstructure. In the WM, microstructures change the most significantly and a lot of acicular α phases appear.

Effects of post-weld heat treatment on dissimilar laser welded joints of austenitic stainless steel to low carbon steel

The dissimilar austenitic stainless steel (AISI316) and low carbon steel (AISI1018) have been welded without filler metal by CO2 4 kW laser welding. Then, the effect of Post Weld Heat-Treatment (PWHT) on the microstructure, tensile and yield strength, microhardness, phase composition in the weld zone and distribution of Ni and Cr of welded joints was investigated. As a result of remove chromium carbide formed during welding process and homogenizes the microstructure, heat treatment was carried out on the sample at 960 °C. The microstructural, fracture cross-section, phase composition and distribution of Ni and Cr of welded samples were investigated by OM, SEM and EDS. Tensile strength, yield strength and microhardness tests were employed to illustrate mechanical properties of the samples. The results designate that the welded joints had good mechanical properties after the heat treatment so that the best tensile and yield strength obtained at 960 °C. Because of reduce grain size, the heat-treatment samples show higher mechanical properties at 960 °C in comparison to as-welded.

Effect of post-weld heat treatment on the joint of friction-welded 1MnCrMoNi steel

The microstructural evolution, mechanical and electrochemical properties of the rotary friction welding joint of 1MnCrMoNi maraging steel were investigated after post-weld heat treatment (PWHT). The joint could be divided into two zones: weld zone and thermo-mechanically affected zone. After PWHT, the parallel alignment of the laths turned ‘blurred’; sub-grain and cell structure appeared; M23C6 and -Cu precipitated, respectively; the joint was softened. But the microhardness was still higher than that of base materials and distributed unevenly. The closer it was to the weld centre, the higher the microhardness was. No deformation occurred in the joints during tensile test, indicating the excellent bonding strength. PWHT process slightly reduced the impact toughness and corrosion resistance of the joint.

Effect of Post-Weld Heat Treatment on Microstructure and Hardness Evolution of Functionally Graded Materials Produced by Direct Energy Deposition

In this work, the effects of post weld heat treatment (PWHT) on the microstructure and mechanical properties of functionally gradient materials (FGM) was investigated. The FGM consisted of five different layers which were mixtures of austenitic stainless steel (type 316L) and ferritic steel (LAS). The ratio of type 316L and LAS powder in each deposition layer was 100:0, 75:25, 50:50, 25:75, and 0:100. FGM samples were successfully fabricated without cracks or delamination by a direct energy deposition process. The sensitization phenomenon of the FGM samples was investigated after PWHT. The PWHTs were conducted at 700&lt;sup&gt;o&lt;/sup&gt;C, 900&lt;sup&gt;o&lt;/sup&gt;C, and 1100&lt;sup&gt;o&lt;/sup&gt;C for 4 hours and the samples were then air-cooled. After PWHT, the annealed specimens were observed by optical and scanning electron microscopy to analyze their microstructure. The occurrence of sensitization was found in the specimen annealed at 700&lt;sup&gt;o&lt;/sup&gt;C. The contents of Cr and C increased substantially along grain boundaries. However, the sensitization did not occur in other samples annealed at 900&lt;sup&gt;o&lt;/sup&gt;C and 1100&lt;sup&gt;o&lt;/sup&gt;C. In the C and D layers of the 1100&lt;sup&gt;o&lt;/sup&gt;C annealed sample, micro-hardness was measured to be very high due to the formation of bainitic ferrite and a lath martensite structure. In addition, a reduction of the austenite fraction was confirmed by Electron Back Scatter Diffraction.

Effect of post-weld heat treatment on mechanical properties of local weld-affected zones in friction stir welded AZ31 plates

This study explored the mechanical, microstructural, and textural characteristics of friction stir welded (FSWed) AZ31 magnesium alloy plates. The joints were subsequently annealed at various temperatures in the range of 300–500 °C for 1 h. Reduction in yield strength was found, though simultaneous improvement in tensile strength and elongation was achieved by annealing at 300 °C and 400 °C. The digital image correlation (DIC) analysis clearly showed a gradual expansion of the strain localized area toward the base material (BM) zone with an increase of the annealing temperature. The texture-dependent Hall-Petch relationship was established and discussed together with the dislocation density. The nanoindentation maps in concert with the kernel average misorientation (KAM) reveal that the difference of dislocation density in stir zone (SZ), thermo-mechanically affected zone (TMAZ), and BM zone is responsible for different grain growth trends which links to the improvement in mechanical properties.

The Effect of Post Weld Heat Treatment (PWHT) on the Microstructure, Microhardness and Sulphide Stress Corrosion Cracking (SSCC) of Ni-Base Superalloy IN625 Hot Wire TIG Cladding on AISI 4130 Steel

This study aims to investigate the effect of post-weld heat treatment (PWHT) on the microstructure, microhardness, and sulfide stress corrosion cracking (SSCC) of IN625 weld overlay on AISI 4130. In this paper, cladding was conducted by TIG (tungsten inert gas arc welding) technique, then PWHT was carried out at 650, 750, and 850°C temperatures with the constant time of 1 h. Also, the SSCC test was performed for 720 h. According to the results, columnar dendrites with MC carbide in g solid solution matrix comprise the microstructure. Furthermore, there was not any crack in the Weld Overlay (WO), tempered martensite, bainite in the base metal (BM), coarse tempered martensite, and ferrite in the heat-affected zone (HAZ). The results demonstrate that as the temperature of PWHT rises, the hardness of BM and HAZ reduces while hardness in the WO increases; it can be seen that at 750°C γ'' phase rapidly emerged and changed to stable δ at 850°C by the shearing mechanism. Furthermore, the results of the magnetic test showed stress crack in samples that heat-treated at 850°C. SEM images reveal that stress cracks in BM continued along grain boundaries and reached the WO.

Effect of PWHT on the dissolution of δ-ferrite in the welded joint of 12Cr–1Mo steels for steam turbines

In this research work, the optimal parameters of post welding heat treatment (PWHT) for 12Cr–1Mo Steel in the welding condition are determined. The PWHT aims to decrease δ-ferrite percentage in the interface of the heat-affected zone (HAZ) and partially melted zone (PMZ). The parameters of post welding heat treatment (time, temperature, and cooling media) are determined through statistical analysis of a full factorial design. These considered δ-ferrite percentage in the HAZ-PMZ interface as the response variable, as well as microhardness in the critical welding regions. Subsequently, a predictive equation of δ-ferrite percentage in the HAZ-PMZ interface was obtained after the post welding heat treatment using non-linear regression coefficients given by full factorial design. The interaction between time and cooling media was essential to improve the PWHT. Also, a high temperature in the PWHT produced a total decrease of δ-ferrite. These mechanisms were associated with the dissolution of forming elements of the primary δ -ferrite, such as Cr and Mo. The PWHT optimal parameters to eliminate δ-ferrite were the temperature of 860 °C with the following combinations of treatment time and cooling media: 1 h-air and 2 h-oil.