Effect Of Post-weld Heat Treatment Research Articles

Effect of Post Weld Heat Treatment on the Microstructure and Electrochemical Characteristics of Dissimilar Material Welded by Butter Method.

In the present study, the effect of post weld heat treatment (PWHT) on the microstructure and corrosion kinetics of butter welded Nickel Alloy 617 and 12Cr steel was investigated. Buttering was carried out on the 12Cr side with the Thyssen 617 filler metal. Furthermore, post weld heat treatment (PWHT) was conducted at 730 °C with a holding time of 4 h followed by furnace cooling. Optical Microscopy (OM) was conducted to study the microstructural evolution in dissimilar material welding as a result of PWHT. Moreover, Scanning Electron Microscopy with energy dispersive spectroscopy (SEM-EDS) was employed to determine the elemental concentrations in all important regions of the butter weld before and after the PWHT. In addition, the effect of PWHT on the corrosion kinetics of the butter weld was also investigated by potentiodynamic polarization measurements in 5 wt.% NaCl + 0.5 wt.% CH3COOH electrolyte at room temperature, 30 °C, 50 °C and 70 °C. The corrosion activation parameters were also determined for both the samples by using Arrhenius plots. The results revealed the higher susceptibility of corrosion of the butter weld after PWHT, which was attributed to the reduced Cr content in the heat affected zone of the 12Cr region due to the sensitization effect of the heat treatment, resulting in higher corrosion rates.

Effect of Post-Weld Heat Treatment on Hardness in Superduplex Stainless Steel ASTM A890/A890M - Grade 6A

Superduplex stainless steel alloy exhibit high mechanical and corrosion resistance, which main industrial application is in the petrochemical industry. The manufacture and maintenance of such equipment usually involve welding processes, followed by post-welded heat treatment and it often becomes impossible to apply heat treatments. Thereby, the purpose of this work is to verify the effect of a post-welded heat treatment on shielded metal arc welding in steel grade ASTM A890/A890M - grade 6A. The microstructure in the as-welded condition consisted of austenite, secondary austenite, and ferrite phases and, the post-welded heat treatment condition exhibited only austenite and ferrite. The hardness in the melt zone reached values of 300 HV after welding and, the value was reduced to 260 HV in the post-welded heat treatment condition.

Effect of post-weld heat treatment on double-sided friction stir welded joint of 120 mm ultra-thick SiCp/Al composite plates

Friction stir welding (FSW) is a very promising and efficient technique in joining aluminum matrix composites (AMCs) without clear drawbacks, and post-weld heat treatment (PWHT) is a viable option to improve the mechanical properties of friction stir welded joint for heat treatable AMCs. In this work, 120 mm ultra-thick plates of 16 vol% SiCp/2014Al composites were successfully joined by double-sided FSW and subsequently friction stir welded joints were subjected to four different PWHTs (T6–25, T6–70, T4–25 and T4–70, denoting T6 or T4 heat treatment and being quenched in water at 25 °C or 70 °C after solution during heat treatment), respectively. The effect of PWHT on the distributions of microstructures and mechanical properties along the thickness direction in the nugget zone (NZ) of friction stir welded joint is investigated. For as-FSW joint, the tensile strength first decreases gradually along the thickness direction in the shoulder-affected and pin-affected regions, and then increases in the overlapping region. For T6–25 joint, the tensile strength does not vary a great deal in the shoulder-affected and pin-affected regions, and then increases slightly in the overlapping region. After T6–25 PWHT, the finer precipitates θ' are detected, aluminum grains grow up, and the tensile strength is obviously improved both in the NZ and base material attributing to the precipitation strengthening effect from finer precipitates θ'. The distributions of microstructures and mechanical properties along the thickness direction in the NZ are changed from heterogeneous distribution for as-FSW joint to nearly homogeneous distribution for T6–25 joint except in the overlapping region. After different PWHTs, the T6–25 joint shows the highest Vickers hardness in the NZ, followed by T6–70, T4–25 and T4–70 joints, and the as-FSW joint shows the lowest Vickers hardness. A comprehensive understanding can be provided for the effect of PWHT on the double-sided friction stir welded joint of thick or ultra-thick metal matrix composite plates.

The Effect of Post-weld Heat Treatment on the Corrosion Behavior of Different Weld Zones of Titanium Ti-6Al-4V Alloy by Friction Stir Welding

This study aims to investigate the effect of post-weld heat treatment on the corrosion behavior of different weld zones of titanium Ti-6Al-4V alloy by friction stir welding. Thus, the friction stir welding was used to join 3-mm-thick sheets of Ti-6Al-4V titanium alloy. Then, the welded sample from the optimal conditions underwent normalized heat treatment at 950 °C for 1 h in an argon inert gas environment. Next, the microstructures of different weld zones were examined using field emission scanning electron microscopy (FESEM), elemental analysis via EDS, phase analysis by XRD, and corrosion behavior through potentiostat equipment in HCl 5% solution. The results obtained from post-weld heat treatment also indicated that these operations significantly enhance the potential and converge the corrosion rate of different weld zones. Specifically, if the corrosion rate of the transition zone before heat operations is around 3.5 times that of the friction stir zone and 10 times that of the base metal, this difference will be less than 2.5 times that of the friction and 4 times that of the base metal following post-weld heat treatment. The post-weld heat treatment has reduced the difference in corrosion rate across various weld zones, but it has not made any changes in the corrosion rate of welds obtained at different traverse speeds.

Three-layered SS321/AA1050/AA5083 explosive welds: Effect of PWHT on the interface evolution and its mechanical strength

In this study, the effect of post-weld heat-treatment (PWHT) on the interface microstructure and its mechanical properties in the three-layered explosive welded (EXWed) SS321/AA1050/AA5083 joints fabricated with different stand-off distances were investigated. The welded specimens were heat-treated at 250 and 350 °C for 1000–10000 s. The microscopy studies exhibited that the AA5083/AA1050 interface was smooth and continuous in all conditions and was free of cracks since the SS321/AA1050 interface contained a reaction layer with variable thickness, having discontinuous and wavy morphology including some transverse and longitudinal cracks. As the stand-off distance increased, the SS321/AA1050 interface appearance altered from smooth to be wavier, and the average thickness of the developed reaction layer was enhanced from 4.95 to 6.7 μm. By PWHT, the thickness of the interfacial layer increased in proportion to the diffusion kinetics and reached a maximum of 18.56, and 15.02 μm for samples joined with a stand-off distance of 6.75 and 6 mm, respectively. For specimens with a stand-off of 6.75 and 6 mm, the diffusion driving energy values were 46.6 and 42.4 kJ mol−1, respectively, while the constant diffusion values were calculated to be 142.2 and 45.3 m2 s−1, respectively. For the samples with an applied distance of 6.75 mm, by increasing the treatment temperature and retention time, the average concentration of aluminum in the reaction layer increased since the concentration of iron decreased. Moreover, the compressive-shear strength was declined from 94.6 to 56.7 MPa. For the sample with a longer stand-off distance, lower shear strength reduction was examined after thermal treatment due to higher collision energy, the formation of wavy interface with larger amplitude, and greater plastic deformation, as well as, stronger mechanical interlocking.

Effects of Postweld Heat Treatment on the Phase Transformation and Mechanical Behavior of NiTi Ultrasonic Spot Welded Joints With Al Interlayer

Abstract The influence of postweld heat treatments (PWHTs) on the phase transformation characteristics, microstructural evolution, and mechanical properties of ultrasonic spot welded NiTi alloy with Al interlayer was investigated. At room temperature, the as-welded joints were fully austenitic, while the microstructure of welded joint after PWHT at 450 °C consisted of a mixture of martensite and austenite. The transformation temperatures were found to increase after the PWHT. Transmission electron microscope analysis shows that Al3Ti intermetallic compounds were formed on the Al side of the Al/NiTi interface after the PWHT at 450 °C for 90 min. Furthermore, finely dispersed nanoscale Ni4Ti3 precipitates were observed in the joint. These nanoscale precipitates resulted in an increase in the transformation temperatures and improved the mechanical properties of the PWHT material. During lap shear test, the as-welded samples failed in a brittle manner in the NiTi alloy, while the PWHT samples failed in the Al interlayer and exhibited ductile-like fracture characteristics.

A critical review on dissimilar welds joint between martensitic and austenitic steel for power plant application

Abstract In this review article, microstructure and mechanical behavior of the dissimilar welded joint (DWJ) between ferritic-martensitic steel and austenitic grade steel along with its application have been summarized in Ultra Super Critical (USC) power plant. Creep-strength enhanced ferritic-martensitic (CSEF/M) P91 steel was developed to sustain at extreme operating conditions of ultra-supercritical (USC) power plants, and later, P92 was developed to achieve better mechanical properties, higher creep-rupture strength and high operating temperature with the reduction in wall thickness as compared to P91 steel. The most common application of P91/P92 material in power plants includes high pressure and high-temperature steam piping, headers, super-heater tubing, and water-wall tubing. The other most commonly used material in the power plants is austenitic stainless steel, i.e., SS 304 L. The austenitic grade stainless steel offers high resistance to corrosion due to the high wt. % chromium and nickel content (18–20 and 8–12, respectively). Due to the low carbon content, the SS 304 L is less sensitive to the sensitization problem and offers excellent weldability. The joining of these dissimilar materials is frequently required in the power generation industry. The current review focuses on the main difficulty associated with dissimilar welding of martensitic P91/P92 and austenitic grade stainless steel. The different chemical composition, mechanical, physical and metallurgical properties of the martensitic P91/P92 and austenitic grade stainless steel leads to the problems such as hot cracking and carbon migration. The other weldability issues are the formation of a brittle intermetallic compound, the formation of soft transaction heat affected zone along with martensitic steel, δ ferrite formation in fusion zone, diffusion related problem, and residual stresses, which necessitates thorough study and qualification of welds. The effect of coarsening of various precipitates such as M23C6 carbides, MX carbonitrides, and effect of laves phase, z-phase, and sigma phase on mechanical property, and creep-rupture strength of DWJ are also discussed in detail. Based on the literature reviewed, it has been found that some of the above-stated problems can be solved by using nickel-based filler wire due to its intermediate physical and mechanical properties. The selection of the proper filler metal is another vital issue in dissimilar welds joint that is also covered in this review article. The reason behind the formation of the unmixed zone, filler deficient region, peninsula, island, beach, migrated grain boundaries, solidified grain boundaries, and solidified subgrain boundaries during DWJ of martensitic P91/P92 and austenitic grade stainless steel is also discussed. The heat treatment is required to eliminate the heterogeneous microstructure during the dissimilar welding. The effect of post-weld heat treatment (PWHT) on the microstructure and mechanical behavior of the DWJ also reviewed. The residual stress developed during the DWJ may cause the premature failure of the components under service, has also been discussed in detail. The effect associated with the residual stress deformation has been reviewed in the different conditions of the DWJ.

The effect of PWHT on the microstructural evolution, carbides formation and mechanical properties of a Nb containing martensitic heat resistance steel used in gas turbine

The purpose of this study was to investigate post weld heat treatment (PWHT) of a heat resistant alloy steel used in gas turbines, in terms of microstructural evaluation, carbide phases formation and mechanical properties. EN10302.2002.X10CrMoVNb9-1(DIN1.4903) plates were welded by shielded metal arc welding process using an AWS E9015-B9 electrode, which is a cellulosic coated electrode. PWHTs were conducted at 700 and 740 °C for 4 and 8 h. Optical microscopy, Field Emission Scanning Electron Microscopy (FE-SEM) equipped with Electron Diffraction Spectroscopy (EDS), and X-Ray Diffraction (XRD) analyses were used to study the microstructure of the samples and to perform a thorough analysis. Uniaxial tensile tests, Charpy impact tests and Vickers microhardness were used to assess the mechanical properties of the welded joints. To define the fracture mode, the surfaces of the fractured samples were analyzed by FESEM after tensile and Charpy impact tests. XRD results showed that, in the weld metal, the ferrite phase is formed together with the iron and chromium carbides in the post weld heat treated cases. Whereas mostly martensite is formed in the as-welded condition. It was observed that increasing the PWHT soaking time and temperature increased the amount of ferrite. Results of microstructural observations and phase analyses showed that the microstructure of the weld joints contain ferrite phase together with retained austenite and chromium carbides, as well as niobium carbides. With increasing the temperature and soaking time of the PWHT, the amount of ferrite was increased at the expense of martensite. Assessing the tensile tests and Charpy tests results showed that performing the PWHT decreased yield strength and increased elongation to fracture in the joints. Ductility increased from 10.5% in as-welded condition, to 15% after PWHT at 740 °C for 8h. As such, the yield strength decreased from 600 MPa to 540 MPa after this PWHT process. On the other hand, toughness was improved with increasing the temperature and soaking time of the heat treatment. As well, performing heat treatment removed hardness gradient in these welded joints. Finally, fracture mode analyses by FESEM showed that by performing this specific PWHT process, the fracture mode has changed from brittle to ductile one making it an attractive procedure to pursue industrially.

Effect of post-weld heat treatment (PWHT) on the intergranular corrosion of ENiCrFe-7 weld overlay cladding materials

Effect of post-weld heat treatment on the intergranular corrosion of ENiCrFe-7 weld overlay cladding materials was investigated. The results showed that Cr-rich precipitates occured in the dendrites and grain boundaries, and Cr-depletion areas appeared around Cr-rich precipitates. The degree of Cr-depletion in the dendrite was aggravated with the increase of PWHT time to 16 h, then it was gradually recovered with increasing PWHT time to 48 h. The results showed that as-weld Alloy ENiCrFe-7 was only susceptible to dendritic corrosion after EPR, the one heat treated after 615 ℃/16 h has more serious dendritic corrosion than that of as-weld Alloy, moreover, the less intergranular corrosion was also observed when the weld was heat treated at 615 ℃/16 h. Only the intergranular corrosion was exhibited in the one heat treated after 615 ℃/48 h. Howerver, Alloy ENiCrFe-7 has better corrosion resistant properties.

Effect of post-weld heat treatment on microstructure and mechanical properties of 7055 aluminum alloy electron beam welded joint

The spray forming 7055 aluminum alloy is welded by electron beam welding (EBW). After welding, the single solution treatments under different temperatures and then aging treatment (STA) and the stepped solution treatment and then aging treatment (SSTA) are carried out for the welded joints respectively. The effect of different post-weld heat treatment (PWHT) procedures on the microstructure and mechanical properties of welded joints is systematically investigated. Results show that, in as-welded condition, the fusion zone mainly consists of α-Al phase, and there are some precipitated phases such as Mg32(Al,Zn)49, Al7Cu2Fe, Al2CuMg, and a small amount of phase MgZn2 in weld metal. After PWHT, the continuous network structures at grain boundary disappear. There are only a few isolated particle phases at grain boundary, and many ellipsoidal η′ phases and rod-like η phases are precipitated within grains. The mechanical property of welded joint is improved after PWHT. Compared with that of in STA condition, the strengthening effect to welded joint is more obvious after SSTA. In SSTA condition, the hardness of weld zone is close to that of base metal (BM), and the tensile strength of welded joint reaches 486.2 MPa, which is 85.6% of that of BM. There are many equiaxed dimples on the tensile fracture surface, and the joint mainly presents the characteristic of ductile fracture.

Effect of post-weld heat treatment on microstructure and mechanical properties of deep penetration autogenous TIG-welded dissimilar joint between creep strength enhanced ferritic steel and austenitic stainless steel

The present study centres on the effect of post-weld heat treatment (PWHT) on microstructure and mechanical properties of the deep penetration keyhole Tungsten Inert Gas (K-TIG) welded dissimilar joint between creep strength enhanced ferritic (CSEF) steel and austenitic stainless steel (ASS). The as-received normalized and tempered CSEF steel was joined with ASS in a single pass without using any filler materials and edge preparation. Detailed characterization across the welded joint was conducted using stereomicroscope, electron microscopy, energy dispersive spectroscopy (EDS), electron backscattered diffraction (EBSD), hardness test, tensile test and Charpy impact test. Results showed that PWHT had significant effect on the microstructure and mechanical properties of both the weld metal and CSEF steel heat-affected zone (HAZ), while it had little influence on the ASS side. By using proper PWHT, the hardness gradient across the welded joint could be mitigated and toughness in both the weld metal and the CSEF steel HAZ could be restored. 760 °C was considered the most appropriate PWHT temperature for such dissimilar joint in terms of the overall mechanical properties. The tensile properties of K-TIG welded joint after PWHT were comparable to both friction stir welded joint and laser and/or electron beam welded joint, indicating that deep penetration TIG welding technology may provide a good alternative for the nuclear industry. The correlation among welding thermal cycle, various heat treatment, microstructure evolution and mechanical properties was also analysed in detail.

용접후열처리가 SM490A 용접부의 미세조직 및 피로강도에 미치는 영향

SM490A 강재는 용접구조용 강으로 자동차, 조선, 철도차량 등 여러 분야에서 많이 사용되고 있다. 주로 판재를 용접하여 구성품이나 구조물로 만들어 사용하는데 용접을 하면 구조물에는 국부적인 소성변형이 발생하게 되고 용접 후 구조물에는 잔류응력이 남는다. 잔류응력은 구조물의 정적 강도와 피로강도를 낮출 수 있으므로 이 잔류응력을 제거하기 위하여 용접 후 열처리를 하여 사용하는 것이 철도산업에서는 일반적이다. 본 연구에서는 모재 시편, 맞대기용접 시편 그리고 ㅗ형 필렛 용접을 제작하여 용접 후 열처리가 피로강도에 미치는 영향을 인장 피로시험을 통하여 조사하였다. 그리고 용접 후 열처리에 의한 인장강도, 경도 변화 및 미세조직의 변화를 조사하였다. 시험결과에 의하면 용접 후 열처리는 모재와 맞대기 용접의 경우 피로강도에 미치는 효과가 미미하였고, ㅗ형 시편의 경우는 열처리가 피로강도를 낮추는 효과가 있었다.

Effect of post-weld heat treatment on the residual stress and deformation of 20/0Cr18Ni9 dissimilar metal welded joint by experiments and simulations

It is known that some problems commonly arise when welding dissimilar metals, especially because it is more difficult to join dissimilar metals than similar metals. Therefore, to join 20/0Cr18Ni9 dissimilar plate with good quality, this paper based on the finite element simulation software Simufact Welding, the residual stress field and deformation results for 6-mm-thick 20/0Cr18Ni9 plates were examined by combining numerical simulation with experimental verification and performing an orthogonal experiment of post-weld heat treatment parameters. The experimental results show that the residual stress of each model is significantly reduced, the reduction of lateral residual stress is greater than that of longitudinal residual stress, the stress reduction of the 20 steel side is significantly larger than that of the 0Cr18Ni9 side, but the deformation of each model was small after heat treatment. It is found that the heat treatment temperature has the greatest effect on the reduction of residual stress and deformation, and the reduction of residual stress will also be affected by the plasticity of the material. Moreover, the material of the weld should be selected as far as possible from the properties of the base metal.

Dissolution of δ-ferrite and its effect on mechanical properties of P92 steel welds

This paper reports on the dissolution of δ-ferrite in the weld fusion zone using post-weld normalizing and tempering (PWNT) and its effect on mechanical properties. The autogenous gas tungsten arc welding (GTAW) was used to prepare double-sided welded joints of P92 steel. After welding, post-weld heat treatment (PWHT) at 760 °C for 2 h and post-weld normalizing at 1050 °C for 1 h followed by tempering at 760 °C for 2 h were performed. The morphology, composition, structure, and hardness of δ-ferrite are verified. The effect of PWHT and PWNT on mechanical properties is also observed. In as-welded and PWHT conditions, the retention of δ-ferrite was observed while the dissolution of δ-ferrite was confirmed after PWNT. In the PWNT condition, uniform microhardness across the welded joint, increased ductility, and increased Charpy toughness of weld fusion zone (almost equal to as received material) were achieved. Dissolution kinetics of δ-ferrite is quantified using Thermo-Calc for Scheil's solidification calculation and DICTRA for calculating diffusion coefficients of Cr and W at 1050 °C in austenite.

Effect of Post-Weld Heat Treatment Temperature on the Mechanical Properties and Microstructure of Weld Heat-Affected Zone of Low-Alloy Steel for Nuclear Reactor Pressure Vessel

The effect of post-weld heat treatment (PWHT) temperature on the mechanical properties of the heat-affected zone (HAZ) of P-No. 3 low-alloy steel was investigated by taking into account the changes in microstructure. SA-508 Gr. 3 Cl. 1 forged steel was employed, and the specimens taken from the steel were thermally cycled using a Gleeble simulator to simulate coarse-grained HAZ (CGHAZ), fine-grained HAZ (FGHAZ), intercritical HAZ (ICHAZ), and subcritical HAZ (SCHAZ). The respective base metal and simulated HAZ specimens were heat treated in a furnace at 610, 650, 690, and 730°C for 8 hours. Before the heat treatment, the ICHAZ, FGHAZ and CGHAZ exhibited high hardness and poor impact toughness. However, when the PWHT was applied, the hardness decreased and the impact toughness improved; the impact toughness was highly dependent on the PWHT temperature. The impact toughness of the ICHAZ and FGHAZ increased significantly when the PWHT temperature was 650°C or below, while that of CGHAZ improved significantly when the PWHT temperature was 650°C or higher. The microstructural changes due to the PWHT were observed by scanning electron microscopy and correlated with the mechanical properties.r composed of iron-based composition system had similar characteristics to the material to be repaired. Key words: Low-alloy steel, Heat-affected zone, Post-weld heat treatment, Impact toughness

Effect of post-weld heat treatment on microstructure and mechanical properties of DP800 and DP1200 high-strength steel butt-welded joints using diode laser beam welding

Among the available high-strength steels, there is growing demand for dual phase (DP) steels for wide application in the automotive industry owing to their good combination of high strength, ductility and formability. Also, the use of innovative welding technologies like laser beam welding (LBW) has growing importance in the field of high-strength steel because of its excellence in providing high-quality welds, high welding speed, high power density, low heat input, a narrow heat-affected zone and low heat distortions as compared to the conventional gas metal arc welding process. However, the hardening and softening in the heat-affected zone is a major issue when welding high-strength steel, i.e. DP steel grades, greatly affecting the strength, formability and plasticity of the whole-welded joint and thus affecting service performance and reliability. Based on preliminary experiments, the optimal welding condition was a nominal laser power of 1.0 kW and a welding speed of 8 mm/s. The aim of this work is to analyse and compare the weld and heat-affected zone characteristics, microstructure and mechanical properties of DP steels with 1-mm thick butt joints of DP800 and DP1200 high-strength steel (HSS) by diode laser beam welding. The effects of post-weld heat treatment (PWHT) on the strengthening of the laser-welded joints were evaluated by microstructural examinations under optical microscope and scanning electron microscope, and mechanical properties were examined by microhardness test, three-point bending tests and tensile tests.

Effect of post-weld heat treatment on mechanical properties and fatigue crack growth rate in welded AA-2024

In this study, effect of post weld heat-treatment (PWHT) at two different aged temperatures was investigated on the microstructure and the material properties of the aluminum alloy 2024. The plates of AA2024 were welded using friction stir welding process, followed by PWHT at different aged conditions: 190°C for 10 hrs and 200°C for 10 hrs. Both tensile and cyclic properties were investigated. PWHT at 200°C–10 h resulted in significant changes in the microstructure and improvement in the mechanical properties of the welded joint. PWHT resulted in re-precipitation of the precipitates, specifically in the thermo-mechanically affected zone (TMAZ) & nugget zone (NZ) but no significant abnormal grain growth was observed in the nugget zone. A significant improvement in the ductility and the hardness of welded joint was observed for PWHT at 200°C–10 h. Long crack growth tests were conducted using sinusoidal loading of 10 Hz frequency and at a stress ratio of 0.1. The PWHT joint at 200-10 h resulted in higher threshold stress intensity factor range (ΔKth) as compared to as-welded joint and the PWHT joint at 190°C–10 h. The observations are explained based on microstructural changes in the FSW joint and are discussed in this work.

Effect of Post-weld Heat Treatment on Microstructure and Mechanical Properties of Al-Zn-Mg-Cu Alloy Welded Joint

Metal inert-gas welding (MIG) test was carried out using ER5183 welding wire as filler metal and Al-4.8Zn-1.6Mg-0.16Cu alloy profile as base material. Different post-weld heat treatment processes were adopted for Al-4.8Zn-1.6Mg-0.16Cu alloy welded joints. The effects of different post-weld heat treatment processes on the microstructures and mechanical properties of welded joints were studied by means of hardness test, microstructure observation and scanning electron microscopy analysis. The results show that the mechanical properties of welded joints can be improved by artificial aging treatment after welding. At the same time, the comprehensive mechanical properties of re-solution and aging after welding will be significantly improved. The inhomogeneity of welded joints and the distribution of strengthening phases will also be improved, the softening of heat affected zone will almost disappear, and the strength of welded joints will be restored.

Effects of post-weld heat treatments on the microstructure, mechanical and corrosion properties of gas metal arc welded 304 stainless steel

PurposeThe purpose of this study is to determine the effects of post-annealing and post-tempering processes on the microstructure, mechanical properties and corrosion resistance of the AISI 304 stainless steel gas metal arc weldment.Design/methodology/approachGas metal arc welding of AISI 304 stainless steel was carried out at an optimized processing condition. Thereafter, post-annealing and post-tempering processes were performed on the weldment. The microstructure, mechanical and electrochemical corrosion properties of the post-weld heat treated samples, as compared with the as-welded, were investigated.FindingsThe as-welded joint was characterized with sub-granular grain structure, martensite formation and Cr-rich carbides precipitates. This made it harder than the post-annealed and post-tempered joints. Because of slower cooling in the furnace, the post-annealed joint contained Cr-rich carbides precipitates. However, the microstructure of the post-tempered joint is more refined and significantly devoid of the carbide precipitates. Post-tempering process improved the elongation (∼23%), tensile (∼10%) and impact (∼31%) strengths of the gas metal arc AISI 304 stainless steel weldment, while post-annealing process improved the elongation (∼20%) and impact strength (∼72%). Owing to the refined grain structure and significant elimination of the Cr-rich carbide precipitates at the joint, the post-tempered joint exhibited better corrosion resistance in 3.5 Wt.% NaCl solution than the post-annealed and the as-welded joints.Originality/valueThe appropriate post-weld heat treatment that enhances microstructural homogeneity and quality of the AISI 304 gas metal arc welded joint was determined.

Effect of post-weld heat treatment on the microstructure and hardness of P92 steel in IN740H/P92 dissimilar weld joints

The microstructural factors that contribute to hardening mechanisms were investigated to explain the effect of post-weld heat treatment (PWHT) on the hardness of P92 steel in IN740H/P92 dissimilar weld joints. This study presents experimental analysis of the distribution of microstructural factors such as precipitate size, precipitate fraction, grain size and dislocation density in the heat-affected zone (HAZ) and base metal (BM) of the martensitic heat-resistant steel. Although precipitates mainly decorated the prior-austenite grain boundaries (PAGBs), packet boundaries (PBs), and block boundaries (BBs), their spatial distribution strongly depended on the distance from fusion line and the PWHT conditions. The grain size and the densities of geometrically necessary dislocations (GNDs) also exhibited a non-uniform distribution. The individual contributions of the microstructural factors to hardness were explained by introducing a simple hardening equation that considers the independent effect of different hardening mechanisms.