Weld HAZ Research Articles

Influence of Residual Stress on the Corrosion Behaviors of Welded Structures in the Nature Seawater

The corrosion behaviors of X65 welded structures were investigated, aiming to achieve the influence of residual stress on the corrosion behaviors of welded structures in the nature seawater. Methods such as corrosion rate measurement and corrosion morphology observation were used in the research. The results indicated that high-level of residual stress could accelerate the corrosion damage of weld joint, HAZ, and parent metal of welded structures, but had little influence on the overall corrosion rate of welded structures. Under the influence of different level of residual stress, corrosion morphology evolution on the surface of weld joint, HAZ, and parent metal were different, and so did the corrosion characteristics of the different areas of welded structures. Compared to the weld joint and parent metal, area with the most serious corrosion damage generated in the HAZ at last. Therefore, the HAZ needs to be significant concerned while designing the corrosion failure prevention measures of the welded structures.

Structure and Crack Resistance of N-A-XTRA-70 Steel Joints Manufactured by Hybrid Laser-Arc Welding

Crack resistance of welded joints is one of the most important indices of service reliability of critical designation structures. The purpose of the research is the establishment of the influence of technological modes, hybrid laser-arc welding of high strength steel NA-XTRA-70 on the formation of structure in the metal welded joints, as well as analysis of the influence of this structure on their crack resistances. For the experiments the laboratory setup has been developed on which the experiments were carried out in the technological scheme that provides the location of the consumable electrode arc at a certain distance in front of the laser beam in the welding direction. Nd: YAG-laser DY 044 of company ROFIN (Germany) was a laser radiation source. Power for consumable electrode arc was carried out by welding generator PSG-500. Investigations of structural-phase changes in weld metal and HAZ were carried out by means of optical microscopy (optical microscope Versamet-2 and Neophot-32), microhardness was measured using M-400 gage of Leco company at 0.98N loading. Fractographic investigations were carried out by scanning electron microscopy (scanning electron microscope SEM-515 of PHILIPS company, Netherlands) on fractured specimens of welded joints, made as a result of impact bend tests. An analysis of crack resistance of the welded joints was carried out under different conditions of test temperatures. It was based on experimental data, received by a quantitative fractography method. It is shown that metal of a welded joint produced by hybrid laser-arc welding at Vw = 72m/h rate has mainly failure of ductile nature after external loading. This indicates sufficient level of crack resistance and further working capacity under operation conditions.

Comparison between GTA and laser beam welding of 9%Ni steel for critical cryogenic applications

In comparison with GTA welded joints, higher tensile strength comparable to that of the base metal was obtained for laser beam welded joints due to fine martensitic microstructure. Impact fracture toughness values with much lower mismatching were obtained for laser beam welded joints due to similarity in the microstructures of its weld metal and HAZ. In this case, the lower impact fracture toughness obtained (1.37 J/mm2) was much higher than that of the GTA welded joints (0.78 J/mm2), which was very close to the specified minimum value (≥0.75 J/mm2). In contrast to other research works, the overall tensile and impact properties are influenced not only by the fusion zone microstructure but also by the size of its hardened area as well as the degree of its mechanical mismatching, as a function of the welding process. A better combination of tensile strength and impact toughness of the concerned steel welded joints is assured by autogenous laser beam welding process.

An Investigation on the Causes of Failure in A210 Carbon Steel Boiler Tubes in an Oil Refinery

As boilers are subjected to corrosive streams and harsh operating conditions, their tubes are susceptible to corrosion and failure by different damage mechanisms. In the current study, the causes of cracking and failure of connection tubes of a boiler header are studied. These tubes were connected between the primary and secondary headers of the boiler and according to the design information were constructed of ASTM A210-A1 carbon steel. There were two cracked tubes wherein one of them had a crack in a weld HAZ region and another had a crack in the base material. To investigate the failure, different microscopical and analytical techniques such as SEM and mechanical tests were used. The results of analysis showed that the material of construction was in accordance with the design specification. Considering the cracks dagger-shaped appearance, it was concluded that thermal fatigue due to the operation conditions and utilization of water spray cooling technique was the main cause of the failure.

Ageing effect on the creep performance of simulated weld HAZ for the steels X20 and P91

Changes in size- and spatial distribution of precipitates and their effect on stationary creep rate of two grades of creep-resistant 9-12% Cr steels, X20 and P91, as a function of ageing at two different conditions were investigated. Ageing of both steels was performed at 650°C lasting up to 2 years and at 750°C lasting up to 6 months. Prior to the ageing, simulation of two weld heat-affected zone HAZ regions, i.e., coarsegrained microstructure (γ), and grain-refined microstructure (α+γ) was performed. Accelerated creep tests at 580°C and 170 MPa, lasting up to 100 hours were performed on the above microstructures prior to- and after the ageing. In addition, optical and SEM imaging were performed on metallographic specimens, followed by image analysis. Deterioration of the creep performance show a proportional behaviour with the precipitate coarsening, which is more pronounced after the ageing at 750°C. Comparatively, the increase of the stationary creep rate after the ageing at 650°C was more pronounced in the steel X20 than in the P91. In both steels and both tempering temperatures, the most troublesome region with respect to the creep behaviour was observed to be the simulated intercritical (α+γ) HAZ microstructure.

In-service operating conditions affecting on weld HAZ hardness for API5L Gr.B pipe steel maintenance.

This study aims to investigate the influences of in-service welding conditions on maximum HAZ hardness, namely heat input, pipe wall thickness, and medium flow rate. The research consists of two parts; computationally thermal analysis and actual welding experiments. In conclusion, it suggested that increasing heat input resulted in decreasing maximum HAZ hardness, as well as, the range of run pipe thickness in the experiment was insignificantly influenced on HAZ hardness. Additionally, the higher flow rate induced more HAZ hardness with a certain flow rate level. HAZ hardness between the sleeve plate and the run pipe was insignificantly different. Nevertheless, it indicated that HAZ hardness prediction via computational analysis was more conservative than experiments.

Prediction of steel weld HAZ Charpy impact property based on stochastic fracture model incorporating microstructural parameters

The present study proposed a model to predict Charpy impact absorbed energy for steel weld HAZ of predominantly upper bainite containing martensite-austenite constituent (MA) as a second phase. Probability distribution of local fracture stress for cleavage crack nucleation is calculated from microstructural parameters. On the other hand, local stress and strain are calculated from dynamic elastic-plastic finite-element analysis. Applying the weakest-link mechanism, probability of cleavage fracture is calculated. Charpy impact tests were conducted for steel simulated HAZ with various cooling rates. As a result, the predicted Charpy absorbed energy transition curves agreed well with the experiment and the model was validated.

THE RELATIONSHIP BETWEEN CONTINUOUS COOLING RATE AND MICROSTRUCTURE IN THE HEAT AFFECTED ZONE (HAZ) OF THE DISSIMILAR WELD BETWEEN CARBON STEEL AND AUSTENITIC STAINLESS STEEL

This paper investigates the changed in the microstructure in HAZ of the dissimilar weld between carbon steel and 304 austenitic stainless steel. Continuous cooling transformation diagrams (CCT), peak temperature profiles and cooling rates can be used to predict the change in the microstructure of the HAZ during the welding process. Optical microscopy, X – ray, SEM and TEM were used to determine the phases which formed in HAZ of carbon steel and austenitic stainless steel. The results of this study indicate that grain size in HAZ depended on the temperature at that point could be reached during the welding. Fully Martensitic layer observed at the interface in carbon side due to the combination of the rapid cooling subsequent to weld and local chemical composition. Cooling rate played the rule on forming Widmanstatten ferrite, Bainite and Pearlite. On the other hand, microstructures and grain size in HAZ of austenitic stainless steel were not affected by temperature and cooling rate. Carbides precipitation (M23C6, M7C3), however, were found in the boundary of grains.

Experimental investigation on the corrosion behavior of G20Mn5QT cast steel and butt weld with Q345D steel

The corrosion tests of G20Mn5QT cast steel and butt weld with Q345D steel in wt 3.5% NaCl solution are conducted. The corrosion morphology of the specimens is observed by SEM. It is mainly corrosion pitting for G20Mn5QT cast steel due to the casting defect and the erosion of chloride ions. The corrosion morphology of weld zone and HAZ tends to be uniform corrosion accompanied with pitting corrosion. Welding defect and erosion of chloride ions cause pitting corrosion for weld zone and HAZ. The largest circular radius of the divided circular pits is defined as the maximum radius of the irregular pit.

Effect of Welding Processes on the Microstructure, Mechanical Properties and Residual Stresses of Plain 9Cr-1Mo Steel Weld Joints

9Cr-1Mo steel designated as P9 is widely used in the construction of power plants and high-temperature applications. It is chosen for fabricating hexcan fuel subassembly wrapper components of fast breeder reactors. Arc welding processes are generally used for fabricating 9Cr-1Mo steel weld joints. A-TIG welding process is increasingly being adopted by the industries. In the present study, shielded metal arc (SMA), tungsten inert gas (TIG) and A-TIG welding processes are used for fabricating the 9Cr-1Mo steel weld joints of 10 mm thickness. Effect of the above welding processes on the microstructure evolution, mechanical properties and residual stresses of the weld joints has been studied in detail. All the three weld joints exhibited comparable strength and ductility values. 9Cr-1Mo steel weld joint fabricated by SMAW process exhibited lower impact toughness values caused by coarser grain size and inclusions. 9Cr-1Mo steel weld joint fabricated by TIG welding exhibited higher toughness due to finer grain size, while the weld joint fabricated by A-TIG welding process exhibited adequate toughness values. SMA steel weld joint exhibited compressive residual stresses in the weld metal and HAZ, while TIG and A-TIG weld joint exhibited tensile residual stresses in the weld metal and HAZ.

Laser Welding of New Grade of Advanced High Strength Steel STRENX 1100 MC

AbstractThe article presents results of investigations on autogenous laser welding of new grade STRENX 1100 MC steel. The modern Disk laser was applied for of 5.0 mm thick butt joints welding. The influence of laser welding parameters, mainly the energy input of laser welding on the penetration shape, weld quality, structure and mechanical performance was investigated. It was found that the investigated steel has surprisingly low carbon equivalent CET just 0.328, and also relatively high temperature of martensitic transformation Msat 430.6°C. Despite very rapid cooling times t8/5in a range from 0.6 to 1.3 s, thus rapid solidification there was no tendency to cracking of weld metal or HAZ. Significant drop of microhardness in the HAZ resulted in a decrease of tensile strength of joints, compared to the base metal. Impact toughness of test joints was at only 50÷60% of the base metal.

Investigation of physically simulated weld HAZ and CCT diagram of HSLA armour steel

The phase transformation under various cooling rates and in different HAZ regions for high-strength armour steel was analysed by dilatometry. To develop a continuous cooling transformation (CCT) diagram, the samples were heated up to a peak temperature of 1250 °C to achieve a coarse-grained microstructure and then cooled down with a cooling time t 8/5 varying from 3 to 240 s. Analysis of dilatation curves revealed the austenite decomposition process, during which transformation temperatures were determined. The results showed martensitic transformations for all welding-relevant cooling times. Furthermore, to analyse different heat-affected subzones of the weld, the peak temperature was varied between 550 and 1250 °C at a constant cooling time t 8/5 of 6 s. The simulated coarse-grained heat-affected zone (CGHAZ) and fine-grained-heat affected zone (FGHAZ) showed only martensitic transformations with transformation temperatures below 400 °C. The steel exhibited an inhomogeneous hardness with hardening in the CGHAZ and FGHAZ and softening in the intercritical and subcritical HAZ. The physically simulated microstructure was validated by a real hybrid laser-arc weld microstructure.

Effect of microstructure inhomogeneity on hydrogen embrittlement susceptibility of X80 welding HAZ under pressurized gaseous hydrogen

Hydrogen embrittlement (HE) of high-grade pipeline welded joint is a threat to hydrogen gas transport. In this research, slow strain rate tension (SSRT) tests in high-pressure hydrogen gas, combined with hydrogen permeation tests and microstructure analysis were conducted on X80 steel, intercritical heated-affected zone (ICHAZ), fine-grained heat-affected zone (FGHAZ) and coarse-grained heat-affected zone (CGHAZ). The change of HE susceptibility from high to low was CGHAZ, FGHAZ, ICHAZ, and base metal. Microstructure was the important factor influencing hydrogen permeation and susceptibility to HE. Susceptibility to HE was increased in the order of “fine-grained massive ferrite (MF) and acicular ferrite (AF)”, “fine-grained granular bainite (GB) and MF”, “coarse-grained GB and bainite ferrite (BF) embedded with martensite-austenite (M-A) constitute”. The fine-grained MF and AF in base metal with lower hydrogen diffusivity can impede the embrittlement behaviour, while the coarse-grained GB and BF with higher hydrogen diffusivity in CGHAZ increased its susceptibility to HE.

Study of MA Effect on Yield Strength and Ductility of X80 Linepipe Steels Weld

Multipass GMAW (Gas Metal Arc Welding) welding was used to join X80 linepipe materials using two weld metals of slightly different compositions. Welding wires with diameters of 0.984 and 0.909 mm were used while applying the same heat input in each pass. The slight difference in the wire diameters resulted in different HAZ microstructures. The microstructures in the doubly reheated HAZ of both welds were found to contain bainite-ferrite. However, etching also revealed a difference in martensite-austenite (MA) fraction in these reheated zones. The MA exhibited twice the hardness of ferrite when measured by nanoindentation. Tensile testing from the reheated zone of both welds revealed a difference in yield strength, tensile strength and elongation of the transverse weld specimens. In the reheated zone of weld A, (produced with a 0.984 mm wire) a higher fraction of MA was observed, which resulted in higher strength but lower elongation compared to weld B. The ductility of weld A was found severely impaired (to nearly half of weld B) due to formation of closely spaced voids around the MA, along with debonding of MA from the matrix, which occurs just above the yield stress.

Investigating the effects of welding process on residual stresses, microstructure and mechanical properties in HSLA steel welds

One of the important steps in the design and fabrication of welded structures is the selection of the welding process and the filler consumables. This is because these two factors control the mechanics of thermal distribution and the chemistry of the welded join, which in turn affect weld integrity through the resulting microstructure and residual stresses. The present study employed neutron diffraction to investigate the effects of welding process on the residual stresses in high-strength low-alloy steel weld joints made by SMAW (shielded metal arc welding) and combined MSAW (modified short arc welding) and FCAW (flux cored arc welding) processes. A significantly higher level of residual stress was found in the MASW+FCAW combination which was shown to be in line with the microstructural and mechanical properties. Higher levels of residual stresses may be related to the formation of bainite and Widmanstätten ferrite in the weld metal and HAZ of the combined MSAW and FCAW processes.

Microstructure and transverse shrinkage stress analysis in GTA welds of P91 steel pipe

In a steam power plant, several components such as boiler tube, condenser and steam lines are made of high creep resistant steel. The P91 steel pipes are generally used in steam power plant because of high creep strength at service temperature of approximately 600oC. In the present research work, the study about shrinkage stresses and their distribution in the four quadrants of P91 pipe weld of 11 mm thickness is reported. The conventional-V and narrow-groove welds were prepared by using the gas tungsten arc welding (GTAW) process. Welding current, arc voltage, groove design, and straining length were the main parameters that affect the transverse shrinkage stresses. In the present research work, the effect of groove design on transverse shrinkage stresses has been evaluated. It also describes the effect of the number of passes on shrinkage. It is concluded that, for a given heat input, the narrow groove pipe weld joint exhibits comparatively less transverse shrinkage stress. Scanning electron microscope (SEM) with field emission gun and optical microscope has been used to characterize the weld fusion zone and HAZs of P91 pipe weldments.

The effect of combined mechanical load/welding residual stress on mixed mode fracture parameters of a thin aluminum cracked cylinder

In this paper, the gas tungsten-arc welding (GTAW) process of a thin cylinder made of Al6061-T6 alloy was simulated using 3-D finite element model in the ABAQUS code and the induced distribution of residual stress was obtained. Temperature dependent thermo-mechanical properties were considered for the aluminum alloy and for simulating the heat source of tungsten arc welding; Goldak's double ellipsoid model was employed. The numerical simulation method employed for the GTAW process of investigated aluminum material was validated experimentally using the hole drilling method as well. High residual stresses were found around the weld line and HAZ area which can increase the risk of crack initiation and propagation in this region of welded aluminum cylinder. Hence in the second part of this research, a longitudinal semi-elliptical crack was considered in the wall of aluminum cylinder subjected to combined internal pressure and torsional loads and its mixed mode I/II fracture parameters (i.e. KI, KII and T) were determined numerically along the crack front and for different crack geometries. Finally the influence of obtained residual stress field on the computed fracture parameters was reanalyzed using the coupled residual stress/mechanical loading applied to the cylinder. The residual stress field had no effect on the mode II fracture component but the most influence of this factor was observed for mode I stress intensity factor (KI) and the deepest point of 3D elliptical crack.

Effect of Nb on Corrosion Behavior of Simulated Weld HAZs of X80 Pipeline Steel in Simulated Seawater Environments Correxxxxsponding to Shallow Sea and Deep Sea

Effect of Nb on Corrosion Behavior of Simulated Weld HAZs of X80 Pipeline Steel in Simulated Seawater Environments Correxxxxsponding to Shallow Sea and Deep Sea

Investigation of Nd:YAG pulsed laser dissimilar welding of AISI 4340 and AISI 316L stainless steels on weld geometry and mechanical properties

In this paper, laser welding of 316L and AISI 4340 steel is studied. Studies are focused on the effects of laser parameters on the depth and width of the welds. The results show that increasing in pulse energy and frequency will increase the weld depth and the weld width. The calculation of effective peak power density related to the welded joints results in optimum operating welding parameters with full penetration and proper dimensions and strengths. The tensile strength values of the full penetrated weldments are greater than the tensile strength values of AISI 316 base metal. The effects of laser parameters on weld grain size and HAZ size were investigated. The results show that the weld grain size and HAZ size increase with pulse energy and frequency.

Effect of HF Welding Process Parameters and Post Heat Treatment in the Development of Micro Alloyed HSLA Steel Tubes for Torsional Applications

The aim of the present study is to investigate the effect of High frequency (HF) Electric resistance welding process parameters and post heat treatment on the torsional fatigue life of micro alloyed HSLA steel tubes. Micro alloyed grades exhibit higher strength and formability owing to the presence of fine recrystallized ferritic grains due to thermo mechanical treatment and presence of alloying elements like Vanadium, Niobium and Titanium. Welded tubular components made of micro alloyed HSLA steel grades are highly emerging and manufacturing them remains quite challenging. Weld bond width, HAZ width and bond angle are the significant factors that directly influences the Weld quality and strength. The effect of key welding parameters like Heat input, welding temperature, squeeze roll pressure, Vee-angle, Vee-length and Impeder diameter on the above mentioned significant factors was analysed. Narrow bond, Minimum HAZ width with pronounced Hour glass pattern and optimum bond angle resulted in superior bond strength and formability of HSLA tubes. Microstructural characterization of the samples was carried out using Light optical microscopy and Scanning electron microscopy. Residual stress was determined using X-ray diffract meter and tube slitting method. Higher tensile residual stress of magnitude 200 MPa was observed in the weld region. Since such high magnitude of tensile residual stress is detrimental to torsional fatigue life, stress relieving of the tubes was carried out at different subcritical temperatures 650°C and 700°C with soaking time of 45 minutes. Without significant drop in the tensile properties, compressive residual stress of magnitude 129 MPa was observed at a particular stress relieving cycle. As an effect of stress relieving heat treatment below Ac1 temperature, there is a significant improvement in the Torsional fatigue life of the HSLA steel. Thus, High Frequency welded micro alloyed HSLA steel tubes with enhanced torsional fatigue performance were successfully developed.