Weld Metal Cracking Research Articles

Investigation on fracture resistance behaviour of dissimilar metal weld joint of modified 9Cr–1Mo steel and AISI 316LN SS

Fracture behavior of dissimilar metal weld joint consisting of mod. 9Cr–1Mo steel, AISI 316LN stainless steel, Inconel 82 butter layer and Inconel 182 weld has been investigated through experiments and FE simulations. The metallographic studies on weld joint and its interfaces have been carried out to determine the influence of microstructure on tensile and fracture properties. Tensile properties of different weld regions viz., weld metal, butter layer and HAZ have been evaluated using sub-size specimens. Fracture resistance behavior of weld joint has been studied through testing of compact type specimens with initial cracks machined at different locations. The plastic η factors for estimation of J-R curve have been obtained using FE analysis for crack in different regions viz., weld metal, butter layer and HAZ. Crack in weld metal exhibits lower fracture resistance as compared to butter layer and HAZ. Further, the constraint acting on crack and its susceptibility for deviation have been discussed in terms of stress triaxiality ahead of crack tip.

Microstructural evolution and stress relaxation cracking mechanism for Super304H austenitic stainless steel weld metal

• Stress relaxation cracking in Super304H austenitic stainless steel weld metal. • The pre-compressed CT technique combined with FEM analysis was successfully used. • The mechanism responsible for stress relaxation cracking formation was illustrated after short-term aging and long-term aging. The pre-compressed CT technique was used to quantitatively investigate the formation of stress relaxation cracks under different tensile residual stresses and aging time in Super304H austenitic stainless steel weld metal. The statistical results revealed that intergranular cracks could occur within 2000 h under 650 °C when the residual stress was applied with greater than 18 KN pre-compression force. Detailed grain interior and boundary analyses showed that the growth of intragranular Cu-rich particles could induce a strong grain interior, and the intergranular Nb(C, N) carbides were one of the causes to crack under short-term aging time. For long-term aging time conditions, the intergranular M 23 C 6 carbides were more susceptible to crack than intergranular Nb(C, N) carbides. Finally, the mechanism responsible for stress relaxation cracking formation was carefully illustrated for the weld metals after short-term aging and long-term aging, respectively.

Environment assisted cracking of 308L weld metal in high temperature water

• The environmental enhancement factor of 308 L weld metal reached a value of 50 when the frequency was decreased to 0.00001 Hz. • The 308 L weld metal showed excellent SCC resistance regardless of the thermal aging or water chemistry. • No preference of the γ/δ crack path and no elevated EAC either with thermal aging or in oxidizing water was attributed to the no sensitization of the γ/δ boundaries before and after thermal aging. The environment assisted cracking (EAC) behavior, including stress corrosion cracking (SCC) and corrosion fatigue (CF), of a low carbon 308 L stainless steel weld metal was evaluated in high temperature water. The effects of thermal aging (400 °C for 10,000 h) on the crack growth rate (CGR) are discussed. Experimental results reveal an environmental acceleration effect on CGRs with decreasing loading frequency, and the environmental enhancement factor reached a value of 50 when the frequency was decreased to 0.00001 Hz. The 308 L weld metal showed excellent SCC resistance regardless of the thermal aging or water chemistry, which is related to the low carbon content and well-controlled duplex microstructure. After thermal aging, the ferrite/austenite (γ/δ) phase boundaries show negligible sensitization, consistent with the low carbon concentration. No preference of the γ/δ crack path and no elevated EAC either with thermal aging or in oxidizing water was attributed to the no sensitization of the γ/δ boundaries before and after thermal aging.

Investigations on the weld metal composition and associated weld metal cracking in laser beam welded steel copper dissimilar joints

Cracking as one of the most common weld defects for joining dissimilar metals can lead to challenges as lack of mechanical properties, lack of joint tightness, lowered electrical conductivity or can be a point of attack for corrosion. Joints between stainless steel and copper also suffer from weld metal cracking which is caused by the effect of liquid copper on the microstructure of solidifying steel matrices. The crack formation is dependent on the dilution of copper in the weld metal, the overall metal intermixing and thermal stresses while cooling down. To investigate the crack susceptibility of laser beam welds with that material combination, lap joints with stainless steel on the top side were welded with a wide range of parameter settings to create different weld metal compositions. The joints were evaluated regarding metal intermixing, cracking, micro hardness and shear tensile strength by metallographic cross sections, x-ray spectroscopy line scans, x-ray spectroscopy element mapping and shear tensile tests to create sufficient datasets for analyses. The results show a correlation between the mixing ratio of copper and the formation of hot cracks with a critical amount of approximately 10 w co .% copper in the fusion zone. Based on that, a hypothesis in order to reduce cracks by decreasing the amount of copper in Fe-rich weld metals or to create copper dominated weld metals was put forward. The crack formation has no influence on the tensile shear strength, which is dependent on the connection width reached between the sheets with a maximum shear strength of 9.6 kN at full penetration of both sheets and shows ductile fraction behavior. Consequently, the crack formation in this welding configuration at copper contents above 10 w co .% has to be weighed against the better mechanical properties at higher connection width and mixing ratios for joining stainless steel and copper. Hardness measurements of the weld metal show results mostly independent of the overall mixing ratio with median values of 170 HV0.1.

Interface characteristics and reaction mechanism of steel/Al welds produced by magnetic field assisted laser welding-brazing

In this paper, we describe experimental laser welding-brazing aluminum alloy to galvanized steel using an external magnetic field. The morphology, microstructure and phase transition at interface was carefully investigated using scanning electron microscope, energy diffraction spectrum and X-Ray Diffractometer. The reaction mechanism of steel/Al welds was also discussed. The results showed that the banded structures with zigzag pattern morphology were produced near the steel matrix. The thickness difference at interface was closely associated with characteristics of laser heat source. The introduction of Zn element in filler metals induces the presence of η-Al5Fe2Zn0.4 phase and δ-FeZn10 phase at the steel interface. These non-brittle phases have good ductility, which can effectively reduce the susceptibility of hot cracking of weld metal and improve the behavior of interface bonding. Meanwhile, fine columnar crystals and eutectic structures formed near the Al matrix as the result of dissolution of Al matrix and regulation of the ampere force. In addition, it has been also found that the metallurgical reaction at interface can be mainly divided into three stages: the solute transfer process, the initiation and the growth of non-brittle phases. The driven effect of magnetic field on molten pool can effectively control the size and distribution of non-brittle phases such as Zn-Al eutectic phases, greatly improving the interfacial performance.

Characterization of hot cracking in multi-pass weld metal of high manganese austenitic steel

ABSTRACT In multi-pass welding of high manganese austenitic steel, weld metal is solidified in austenite single phase and hot cracking may occur depending on residual stress. In order to identify the cracking morphology, a fracture surface of the cracking of weld metal in multi-pass welding test was observed. The fracture surface indicated a dendritic morphology and a bunching pattern; therefore, it is considered that the crack in the multi-pass weld metal is caused by residual liquid film or remelting liquid film. Varestraint test was carried out in order to clarify the characterization of the crack, and then the fracture surface of cracks obtained by the test was observed. Transverse-type and longitudinal Varestraint test were used for getting typical fracture surfaces of solidification cracking in weld metal, and liquation cracking in reheat weld metal and heat affected zone of base metal, respectively. Comparing the fracture surfaces of cracks of Varestraint test and crack in practice, the fracture surface of the solidification cracking was most similar to the crack in multi-pass weld metal in this study. Thus, it is considered from comparing the fracture surfaces that solidification cracking might mainly occur in the multi-pass welding of the high manganese steel.

Rolls crack resistance increase by reducing welding stresses and heat input

The rolling mills working and backup rolls operate under high specific pressures, abrasion and corrosion wear, thermal cycling conditions and they are produced of high carbon steel, prone to hot and cold cracks formation. Therefore, crack resistance and wear resistance increase is an important scientific-technical problem. It has been established that the deposited metal crack resistance is largely determined by welding stresses, which are formed as a result of heat input and thermal deformation cycle, imbalance, at which the energy is zero, and energy increase. According to the superposition law in multilayer electric arc welding, welding stresses are summed up during surfacing of each metal layer, which leads to welding stresses increase and deposited metal scaling. The welding stresses and heat input influence on the deposited metal crack resistance has been established. With increasing the deposited metal thickness, the deformations and welding stresses increase, which leads to cracks formation and weld metal scalings. It has been established by calculation and experiment that the optimum the deposited metal thickness per the rolls radius is 25 mm. With increasing the weld metal thickness up to 40 mm, welding stresses sharply increase, under the action of which cold cracks form and the deposited metal scaling. The welding stresses main role in crack formation has been confirmed. Minimum energy result in maximum quality, weld metal crack resistance and wear resistance. The high-speed surfacing at low heat input process, which provides welding stresses reduction, fine-grained microstructure, the absence of deposited metal scalings, and the rolls crack and wear resistance increase, has been developed

Ultrasonic vibration assisted tungsten inert gas welding of dissimilar metals 316L and L415

Ultrasonic vibration assisted tungsten inert gas welding was applied to joining stainless steel 316L and low alloy high strength steel L415. The effect of ultrasonic vibration on the microstructure and mechanical properties of a dissimilar metal welded joint of 316L and L415 was systematically investigated. The microstructures of both heat affected zones of L415 and weld metal were substantially refined, and the clusters of δ ferrite in traditional tungsten inert gas (TIG) weld were changed to a dispersive distribution via the ultrasonic vibration. The ultrasonic vibration promoted the uniform distribution of elements and decreased the micro-segregation tendency in the weld. With the application of ultrasonic vibration, the average tensile strength and elongation of the joint was improved from 613 to 650 MPa and from 16.15% to 31.54%, respectively. The content of Σ3 grain boundaries around the fusion line zone is higher and the distribution is more uniform in the ultrasonic vibration assisted welded joint compared with the traditional one, indicating an excellent weld metal crack resistance.

Effect of surface treatments on microstructure and stress corrosion cracking behavior of 308L weld metal in a primary pressurized water reactor environment

Effect of surface treatments on microstructure and stress corrosion cracking (SCC) of 308L weld metal in primary pressurized water reactor environment was evaluated by microstructure characterization and bent beam tests. The results showed that no SCC was observed on colloidal silica slurry polished surface while the change in composition and etched phase boundary promote SCC initiation after electropolishing. Further, milling and grinding produce a nanocrystalline layer and an underlying deformed layer on the surface. The nano-sized δ ferrite phase has a detrimental effect on SCC due to the synergistic effect of high concentration of dislocations and its nano size.

Characterization of Hot Cracking in Multi-Pass Weld Metal of High Manganese Austenitic Steel

Characterization of Hot Cracking in Multi-Pass Weld Metal of High Manganese Austenitic Steel

Grain refining in weld metal using short-pulsed laser ablation during CW laser welding of 2024-T3 aluminum alloy

The 2024 aluminum alloy is used extensively in the aircraft and aerospace industries because of its excellent mechanical properties. However, the weldability of 2024 aluminum alloy is generally low because it contains a high number of solutes, such as copper (Cu), magnesium (Mg), and manganese (Mn), causing solidification cracking. If high speed welding of 2024 aluminum alloy without the use of filler is achieved, the applicability of 2024 aluminum alloys will expand. Grain refining is one of the methods used to prevent solidification cracking in weld metal, although it has never been achieved for high-speed laser welding of 2024 aluminum alloy without filler. Here, we propose a short-pulsed, laser-induced, grain-refining method during continuous wave laser welding without filler. Bead-on-plate welding was performed on a 2024-T3 aluminum alloy at a welding speed of 1 m min−1 with a single mode fiber laser at a wavelength of 1070 nm and power of 1 kW. Areas in and around the molten pool were irradiated with nanosecond laser pulses at a wavelength of 1064 nm, pulse width of 10 ns, and pulse energy of 430 mJ. The grain-refinement effect was confirmed when laser pulses were irradiated on the molten pool. The grain-refinement region was formed in a semicircular shape along the solid–liquid interface. Results of the vertical section indicate that the grain-refinement region reached a depth of 1 mm along the solid–liquid interface. The Vickers hardness test results demonstrated that the hardness increased as a result of grain refinement and that the progress of solidification cracking was suppressed in the grain refinement region.

Hot crack susceptibility in multi-pass welds of reduced activation ferritic/martensitic steel F82H

The research and development of nuclear fusion reactors are going on conducting to acquire a next-generation energy source. It is supposed to be that the reduced activation ferritic/martensitic (RAFM) steel F82H is adopted as a structural material of the blanket module, which is the device set on the inner wall of fusion reactors. As welding for thicker plates of F82H, multi-pass welding will be adopted to the joints. In the case of multi-pass welding, hot cracking is one of serious defects in welds and is concerned in welds reheated by following weld passes. Therefore, the objectives of this study are to evaluate hot crack susceptibility in multi-pass welds of F82H and to clarify the cause of hot cracking in multi-pass welds of F82H. The hot crack susceptibility in multi-pass welds is evaluated by the longitudinal Varestraint test with double-bead and triple-bead types. From the observation of fractured surface occurred in welds of F82H after the Varestraitnt test, the crack is identified as ductility-dip crack. The cause of hot crack in multi-pass welds of F82H is clarified by Vickers hardness test, SEM microstructure observations and X-ray diffraction pattern analyses. Based on these tests, when multi-pass welding is conducted for the F82H steels with high Ta contents, it should be considered to control welding conditions for prevention of hot cracking in weld metal as well as high strength martensitic steels. These results suggest that the cause of the crack is intragranular hardening by the precipitation of TaN during welding thermal cycles.

Welding processes for Inconel 718- A brief review

Inconel 718 is being extensively used for high-temperature applications, rocket engines, gas turbines, etc. due to its ability to maintain high strength at temperatures range 450-700°C complimented by excellent oxidation and corrosion resistance and its outstanding weldability in either the age hardened or annealed condition. Though alloy 718 is reputed to possess good weldability in the context of their resistance to post weld heat treatment cracking, heat affected zone (HAZ) and weld metal cracking problems persist. This paper presents a brief review on welding processes for Inconel 718 and the weld defects, such as strain cracking during post weld heat treatment, solidification cracking, and liquation cracking. The effect of alloy chemistry, primary and secondary processing on the HAZ cracking susceptibility, influence of post/pre weld heat treatments on precipitation, segregation reactions, and effect of grain size etc. discussed and concluded with future scope for research.

Fracture mechanic and charpy impact properties of a crack in weld metal, HAZ and base metal of welded armor steel

Welding of armored steel is complicated by the high percentage of carbon in the base metal, the presence of faults in the form of cracks and pores that occur in the weld metal and heat affected zone (HAZ) during the welding process. For heavy structural engineering such as military armored vehicles that are frequently under the influence of impact loads, it is important to know the fracture toughness in all zones of the welded joint. The crack formed in base metal or HAZ, due to dynamic or impact loads, can easily continue to propagate to the fusion line, after which its accelerated growth may occur. The fracture mechanics testing was applied to SEN (B) test specimens, which investigated cracks initiation and certain fracture mechanics parameters. Due to the significant interest in quantifying the resistance of material to propagation of cracks, the fracture mechanic was measured in the zone of base metal, weld metal and HAZ, at temperature 20 °C. The fracture toughness in the base metal is 86.1 MPa*m1/2, while in HAZ and weld metal zones is 286 MPa*m1/2 and 355 MPa*m1/2, respectively.

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.

Disk Laser Weld Brazing of AW5083 Aluminum Alloy with Titanium Grade 2

Disk laser weld brazing of dissimilar metals was carried out. Aluminum alloy 5083 and commercially pure titanium Grade 2 with the thickness of 2.0 mm were used as experimental materials. Butt weld brazed joints were produced under different welding parameters. The 5087 aluminum alloy filler wire with a diameter of 1.2 mm was used for joining dissimilar metals. The elimination of weld metal cracking was attained by offsetting the laser beam. When the offset was 0 mm, the intermixing of both metals was too high, thus producing higher amount of intermetallic compounds (IMCs). Higher amount of IMCs resulted in poorer mechanical properties of produced joints. Grain refinement in the fusion zone occurred especially due to the high cooling rates during laser beam joining. Reactions at the interface varied in the dependence of its location. Continuous thin IMC layer was observed directly at the titanium–weld metal interface. Microhardness of an IMC island in the weld metal reached up to 452.2 HV0.1. The XRD analysis confirmed the presence of tetragonal Al3Ti intermetallic compound. The highest tensile strength was recorded in the case when the laser beam offset of 300 μm from the joint centerline toward aluminum alloy was utilized.

Cr-Mo鋼の溶接金属の再熱割れ感受性に及ぼすCおよびBの影響

Reheat cracking during post weld heat treatment (PWHT) generally occurs in the coarse grain HAZ (heat affected zone) of Cr-Mo steel and 780MPa class high strength steel. Although reheat cracking in the weld metal of Cr-Mo steel has also become well-known recently, the effect of alloy elements in the weld metal on reheat cracking had not been investigated in detail. In particular, the small amounts of alloy elements such as carbon and boron in the weld metal are affected partly by dilution components from the base metal. The purpose of this study was to clarify the effect of the carbon and boron contents on reheat cracking susceptibility in the weld metal of Cr-Mo steel. Reheat cracking tests were carried out by the C-ring and constant stress methods. Reheat cracking susceptibility and the hardness of weld metal containing up to 0.08mass% carbon clearly increased with increasing boron contents over 3ppm. However, reheat cracking of weld metal containing approximately 7ppm boron was suppressed by increasing the carbon content in spite of an increase in hardness. The constant stress reheat cracking tests showed experimentally that the high temperature strength of the grain boundary in weld metal containing boron decreased with increasing temperature during PWHT. Secondary Ion Mass Spectrometry (SIMS) and precipitate analysis revealed that the existence form of boron on the grain boundary changed from dissolved to precipitated during PWHT, and thermo-dynamic calculation showed an increase of M23C6 carbide with increasing carbon contents. Based on these results, it was estimated that the reheat cracking susceptibility of weld metal increased by intergranular embrittlement due to precipitation of boron nitride and decreased by grain boundary strengthening due to the increase of M23C6 carbide.

バレストレイン試験による690合金レーザ多層盛溶接金属の延性低下割れ感受性評価

Ductility-dip cracking susceptibility in the laser multipass weld metal of alloy 690 was quantitatively evaluated using different filler metals varying the contents of P and S. In order to synthesize a ductility-dip crack in the laser multipass weld metal, the cross-bead longitudinal-Varestraint test with laser welding was applied under the various welding speed. The ductility-dip temperature range (DTR) was increased with an increase in P and S contents in the weld metal, and S was more effective to enhancing the DTR compared with P. Furthermore, the DTR was decreased with an increase in the welding speed. A numerical simulation of grain boundary segregation of P and S revealed that the segregated concentrations of P and S at grain boundaries were increased with an increase in the P and S contents in the weld metal, and that those were slightly decreased with an increase in the welding speed due to the rapid heating and cooling rates. It follows that the changes in ductility-dip cracking susceptibility with the filler metal composition and welding speed were consistent with the grain boundary segregation behaviours of P and S during laser multipass welding process. According to the regression analysis of the DTR, ductility-dip cracking in the laser multipass weld metal would be inhibited by reducing the segregated concentration at grain boundary (P+2.42S) to less than approx. 8at%.

Research on the Damage Identification of Weld Metal Cracking of Metal Structure Based on PVDF

A new detection method for measuring weld crack of crane’s metal structure is developed.It works by combining polyvinylidene fluoride (PVDF) with curvature operational shapes (COS) algorithm. First, the theory of damage identification using the imaginary part of frequency response function was analyzed, and the extraction approach of COS was illuminated in detail. Then, the fitting method which is called gapped-smoothing method (GSM) was chosen to obtain the COS of healthy structure.Next, experiments were carried out on a steel plate with weld cracks based on PVDF. The experiment result expresses that the positions of cracks could be located precisely and the index is very sensitive to the different length of cracks. Therefore it can provide reliable information for positioning and quantitative analysis of the weld cracks.

Cold hole expansion effect on the fatigue crack growth in welds of a 6061-T6 aluminum alloy

Compact test specimens were extracted from a 6061-T6 aluminum alloy welded plate with a thickness of 9mm to analyze the cold hole expansion effect on fatigue crack growth tests conducted in mode I cyclic loading. At R=0.1, a sharp crack in base metal, weld metal and heat affected zone was propagated from 17 to 24mm. The fatigue crack growth at 24mm (α=a/W=0.3) was delayed by drilling a hole at the crack tip and applying a cold hole expansion of 4.1%. The residual stress fields due to cold hole expansion were determined with the finite element method. The fatigue crack growth testing was continued up to a crack length of 35mm (α∼0.43) at the same R, and crack opening displacements of the post-expansion crack were also determined with the finite element method. The results were expressed in terms of crack length versus number of cycles, as well as, fatigue crack growth rate as a function of applied and effective stress intensity factor range. The cold hole expansion contributed to delay the fatigue crack growth in base metal, and to a lesser extent in the weld metal and heat affected zone. A crack closure effect was determined by means of load versus crack opening displacement curves of the post-expansion crack, which was, completely or partially closed, in welded zones with compressive residual stress fields. The fracture surfaces of each welded zone were analyzed to elucidate the crack nucleation zone and its relation with the residual stress field. In all cases the crack was initiated at the surface of the specimen where the residual stresses were positive.