Weld Cracking Research Articles

Эскпериментальное исследование дифракции упругих волн на модели трещины

Small opening notches are used to simulate cracks in butt welds. The study of the influence of the notch edges orientation on their detectability when using pulse-echo and diffraction methods of ultrasonic testing. It is shown that the processes occurring during the elastic waves scattering on cracks must be modeled by a three-dimensional problem. However, theoretical analytical and numerical studies in this area most often concern two-dimensional problems of elastic waves diffraction, when the target studied edge is located on the acoustic axis of the ultrasound transmitter and / or receiver and is oriented perpendicular to the incident beam. The article presents experimental results illustrating the influence of the target point (edge) orientation in three-dimensional problems on the received signals both when using diffraction schemes of the TOFD type, and in the classical ultrasonic testing by the pulse-echo method according to the "tandem" scheme and with the turn of the transducers according to the "duet ".

Development and testing of fixture to automate the welding process for hydro end cover plates

A simple mechanical fixture is developed to overcome the difficulties encountered in welding of hydro end cover plates with pipes using shielded metal arc welding (SMAW) process. This paper relates to semi automation of hydro end cover plate with pipe welding in submerged arc welding (SAW) machine for which the fixture is designed to avoid manual welding to eliminate cracks. Hydro end cover consists of a pipe of SA335 P12 grade material and a plate of carbon steel of higher thickness and it is welded manually. Presently, the pipes of hydro end covers are heated by Liquefied Petroleum Gas (LPG) burner to obtain necessary pre-heat and the inter pass temperature. Due to higher thickness and faster cooling rate crack occurs at weldment. Manual welding of the Hydro end cover plate results in more LPG consumption, more electrode wastage, cracks, laborious and unsafe way of crack removal, and poor surface finish. Hence, the need was felt to develop an apparatus to complete the welding of hydro end covers pipes with plate in automated mode in SAW machine. Welding of hydro end covers pipes with a plate in SAW machine using the developed fixture eliminated welding cracks. In addition, cycle time is reduced by 76%, and saving of 480 kg of LPG per job is obtained.

The hot cracking susceptibility subjected the laser beam oscillation welding on 6XXX aluminum alloy with a partial penetration joint

A laser beam oscillation method using Galvano mirrors, which allows wide weld beads and controls thermal stress distribution, was suggested to suppress the formation of solidification cracks in laser welds. In order to understand the solidification cracking behavior in relation to the bead shape, laser beam oscillation welding was performed under various oscillation widths and frequency conditions. To evaluate the effect of the oscillation parameter on solidification cracking susceptibility, a regression analysis based on the shape of the bead was performed. Stress distribution generated during the laser beam oscillation welding process was also analyzed using finite element modeling simulation. From the results, it was demonstrated that a high shrinkage stress field at the bottom of the partial penetrated bead suppresses the solidification cracking.

Підвищення тріщиностійкості при аргонодуговому високошвидкісному наплавленні на низькій погонній енергії

The rolling mills are operated under high specific pressures, therefore the rolls are produced from high carbon steel 90HF, prone to hot and cold cracking. Therefore, crack resistance and wear resistance increase is an important scientific and technical problem. An effective way to increase crack resistance is arc and energy concentration, which increase the surfacing process. Arc concentration due to electrode diameter decrease provides increase in magnetic field induction, electromagnetic pressure of compression, pinch effect, the weld pool liquid metal crystallization speed, crack resistance and wear resistance. It also provides droplets and microstructure grinding, welding stresses reduction. It has been established that with the carbon content increase, the heat input decreases, thus ensuring heat input decrease, welding stresses reduction, liquid metal crystallization rate increase, microstructure grinding, the interatomic compression pressure and deposited metal crack resistance increase. The argon-arc high-speed surfacing at low heat input of roll necks with chromium-nickel wire, which provides arc and energy concentration, heat input and welding stresses reduction, crystallization rate increase, microstructure grinding, interatomic distance reduction, the pinch effect and interatomic pressures of compression enhancement, rolls crack resistance, wear resistance and durability increase, has been developed

Geometrical degradation of electrode and liquid metal embrittlement cracking in resistance spot welding

Abstract Electrode degradation during the resistance spot welding (RSW) of coated steels has been a major challenge in automobile manufacturing as it affects the weld quality in terms of nugget size, defects, and mechanical properties. In this work, we investigate the effect of electrode degradation on such a defect, Zn-assisted liquid metal embrittlement (LME) cracking, in RSW by producing 400 consecutive welds of galvannealed TRIP steel. Infrared thermography, carbon imprinting, dynamic resistance, optical imaging, SEM, and EDS were used to characterize various phenomena during consecutive welding. LME crack severity was found to be unaffected in the first 80 consecutive welds. However, the severity declined sharply between 80–200 welds, and further, it remained low in 200–400 welds. The electrode experienced geometrical degradation (increase in the radius of curvature and face diameter) and metallurgical degradation (Cu-Zn-Fe alloy layer formation) during consecutive welding. The geometrical degradation, specifically the radius of curvature, was confirmed as the main factor affecting LME cracking. On the other hand, metallurgical degradation did not affect the LME cracking in the first 200 welds as its influence was overcome by the geometrical degradation. However, a small impact of metallurgical degradation was detected in 200–400 welds in the form of local rise and fall in the temperature and LME crack length.

Amelioration of weld-crack resistance of the M951 superalloy by engineering grain boundaries

Fusion weld is a portable and economical joining and repairing method of metals. However, weld cracks often occur during the fusion weld of Ni-base superalloys, which hinder the applications of fusion weld on this kind of materials. In this work, the effects of microstructures of grain boundaries (GBs) of the prototype M951 superalloy on its weldability were investigated. The precipitated phases, the elemental segregations on GBs, and the morphologies of GBs can be largely altered by regulating the cooling rates of pre-weld heat treatments. With decreasing the cooling rate, chain-like M23X6 phase precipitates along the GBs, accompanying segregations of B, and GBs becomes more serrated in morphology. During fusion weld, the engineered GBs in the M951 superalloy with a low cooling rate favor the formation of the continuous liquid films on GBs, which together with the serrated GB morphology significantly prevents the formation of weld cracks. Our findings imply that the weld-crack resistance of the superalloys can be ameliorated by engineering GBs.

Double-Probe Ultrasonic Detection Method for Cracks in Steel Structure

To investigate the feasibility analysis of ultrasonic detection methods applied in the fatigue crack characteristics of steel structures, the double-probe ultrasonic detection method was applied to the prefabricated crack specimens fabricated from of flat steel plate. The test features including length, width, depth, angle, and crack location were considered. Based on the calculation of geometric relationship and experimental results, a method for judging the crack tip position was developed. The formulae for determining the depth and angle of crack were not only established but also analyzed the detection accuracy of the double-probe penetration method. The feasibility of this method in weld crack detection was verified by a combination of the finite-element simulation and actual experiment. The results showed that the ratio of crack tip wave height to crack free wave height ωK is related to the K value (K value is one of the parameters of the angle probe, which is defined as the tangent value of angle β between the incident wave and an interface normal line), but the influence of crack depth and width can be ignored. Due to higher detection accuracy for crack depth and angle, a double-probe penetrating method could improve the detection accuracy for crack angle by nearly 5% more than the single probe pulse reflection method. Therefore, application of the double-probe penetrating method had a significant impact on accurate crack detection of rib-to-deck weld in the practical issue.

Segregation Effect on Solidification Cracking in Spot Welding of the 6XXX Aluminum

Solidification cracking is a critical phenomenon, especially in the welding of AA6XXX, due these alloys present a wider freezing temperature range. The amount of liquid at the end of the solidification is a dominant factor in promoting or reducing the number of cracks. This paper proposes to assess the effect of the heat input in controlling the cracking during the spot welding in AA6061-T6. Four deposit conditions, made with GTAW, were assessed, in which the cracking degree was quantified and compared with the resulting microstructure. This work confirms and explains why the heat input governs the constitutional cooling, which simultaneously controls the microsegregation amount. With low heat input, the segregation is interdendritic, and the eutectic liquid gathers within the grains, which reduces the cracking susceptibility. A high heat input promotes the higher accumulation of eutectic liquid at the grain boundaries, facilitating cracks’ formation and growth. A high concentration of eutectic liquid promotes the healing effect, reducing the formation of cracks.

Model-assisted ultrasonic calibration using intentionally embedded defects for in-process weld inspection

Automated in-process Non-Destructive Testing (NDT) systems are rapidly gaining traction within the manufacturing industry as they reduce manufacturing time and costs. When considering calibration and verification of such systems, creating defects of known geometry and nature during the deposition of a weld can: (I) help examine the capability of the automated system to detect and characterise defects, (II) be used to form a database of signals associated with different defect types to train intelligent defect classification algorithms, and (III) act as a basis for in-process gain calibration during weld inspection at high temperatures, where the ultrasound beam can be skewed as a result of velocity gradients. In view of this, this paper investigates two unique methodologies for introducing: (a) lack of fusion weld defects by embedding tungsten in the weld and (b) creating artificial weld cracks by quenching to imitate the real cracking scenarios. According to the results of Phased Array Ultrasound Testing (PAUT) inspections, the methodologies used for embedding the artificial defects were successful. The validity of inspections was also verified by extracting micrographs from the defective sections of the welds, and model-based simulations were carried out to gain a better understanding of the wave propagation path and interaction with the generated defects.

Solidification cracking sensibility of narrow gap laser welding on ITER-grade austenitic stainless steel

This study aimed to investigate the solidification cracking in narrow gap laser welding (NGLW) of ITER grade austenitic stainless steel 316LN. The results show that NGLW of ITER grade 316LN presents high solidification cracking sensitivity. The cracking always occurred in the centerline of build-up weld with a certain depth, not in root and cosmetic layers. The crack mostly propagates on the surface of the weld and it could be be healed by the following layer welding. The healing efficiency depends on the overlapping zone between the two layers. Other various laser welding processes such as autogenous laser welding (ALW), double-sided NGLW, and narrow gap pulsed laser welding (NGPLW) were studied. These welding processes present better cracking resistance than that of NGLW because of the stress distribution, microstructural characteristic and constraint condition of welded joints.

Friction Stir Welding: A Solution to Avoid Weld Cracking in Borated Stainless Steel

We have successfully demonstrated first direct experimental evidence of defect-free friction stir weld joints of 304B4 stainless steel using different process parameters. Precipitate size and its distribution, material flow and influence on mechanical performance are highlighted. EPMA study corroborated the formation of chromium- and iron-rich boride precipitates in the joints. Joint performance is significantly enhanced by material flow driven by heat input and distribution of fine boride particles.

Methods and technologies of electroslag welding with controlled thermal cycle

Introduction. Improving the quality and operational reliability of welded structures of power equipment is an urgent task of welding production. Its solution is possible on the basis of the development or selection of advanced methods and technologies of electroslag welding (ESW), which eliminate the causes of the formation of tempering cracks (TC) in thick-plate welds. This paper considers a comparative assessment and recommendations on the selection of such advanced ESW methods. The work objectives are to solve the problem of forming a fine-grained, uniform, crack-resistant metal structure of a welded joint with high mechanical characteristics and to reduce the negative impact of the ESW thermal cycle on the base metal. The solution to this problem is possible on the basis of a reasonable choice of methods and technologies for ESW with regulated (controlled) thermal cycle. Materials and Methods. A comparative analysis of advanced methods and technologies of ESW with a controlled thermal cycle is carried out; a comparison of their pros and cons is provided; practical recommendations on the selection of advanced methods for controlling the thermal cycle parameters are offered. Results. It is shown that moderate heat input at high-speed ESW in a narrow gap provides a single pass to form a welded joint with a finer-grained structure and high mechanical properties compared to the in-house technologies of ESW and automatic submerged-arc welding. Recommendations for practical use of the method in welding production are given. Discussion and Conclusions. The results obtained are recommended to be used in the development of ESW technology for thick-sheet welded structures of nuclear and thermal power equipment that enables to abandon postwelding heat treatment (normalization and high tempering).

Research and Improvement of Welding Repair Technology for Large Steel Castings of Marine Diesel Engine Based on CAD Software

CAD (Computer Aided Drafting) is the Massachusetts Institute of Technology in the United States to propose interactive graphics research program. Marine cast steel parts generally have features such as large cross-section dimensions, complex shapes, and hard to repair once damaged. In this context, this article takes the basic introduction to CAD software as the starting point, focuses on the common cracks and causes of welding cracks in the welding of large steel castings, and takes the repair of diesel engine cylinders as an example to analyze steel castings. Common welding repair methods. This paper analyzes the cracks and causes of weld cracks commonly found in the welding of large steel castings, and take the repair of diesel cylinders as an example, analyzed the common welding repair methods for steel castings. The welding repair through the cylinder shows that under the strict control of the welding process, the heterogeneous cold welding repair process is practically applicable to the on-site repair. And cracks may occur in the nickel-based welds after the diesel engine actually operates. The welding repair process should be strictly controlled and appropriate measures should be taken to eliminate the welding residual stress.

Influence of Ultrasound on Pore and Crack Formation in Laser Beam Welding of Nickel-Base Alloy Round Bars

Welding by laser beam is a method for creating deep and narrow welds with low influence on the surrounding material. Nevertheless, the microstructure and mechanical properties change, and highly alloyed materials are prone to segregation. A new promising approach for minimizing segregation and its effects like hot cracks is introducing ultrasonic excitation into the specimen. The following investigations are about the effects of different ultrasonic amplitudes (2/4/6 µm) and different positions of the weld pool in the resonant vibration distribution (antinode, centered, and node position) for bead on plate welds on 2.4856 nickel alloy round bars (30 mm diameter) with a laser beam power of 6 kW. The weld is evaluated by visual inspection and metallographic cross sections. The experiments reveal specific mechanisms of interaction between melt and different positions regarding to the vibration shape, which influence weld shape, microstructure, segregation, cracks and pores. Welding with ultrasonic excitation in antinode position improves the welding results.

Investigation of Magnetic Memory Signal of Propagation of Buried Crack under Applied Load

ABSTRACT The timely detection of crack defects considerably helps prevent accidents caused by metal component failure. Further, magnetic memory detection technology has the advantage of detecting damage earlier than traditional nondestructive testing technology; however, the relationship between magnetic memory fields and welding cracks needs to be studied. Specimens with buried welding cracks were fabricated to study the magnetic memory field parameters of the propagation process of welding cracks. Variations in the magnetic memory signals of the crack at different loading stages were characterized. The magnetic memory detection method can effectively detect the buried welding crack defects. The magnetic field intensity gradient (dH/dx) demonstrated a regular change with the increase in the applied tensile load (P), which can be considered in two stages: In the first stage (P < 120 kN), dH/dx gradually decreased with P, and in the second stage (P > 120 kN), it rapidly increased before fracture.

Liquid zinc penetration induced intergranular brittle cracking in resistance spot welding of galvannealed advanced high strength steel

This study aims to explore the mode of Zn transportation and the failure mechanism of cracking associated with liquid metal embrittlement (LME) using fractography as the key technique. A three-point bend test was performed on a TRIP steel resistance spot weld to open the LME crack in the form of a free fracture surface for the fractographic investigation. The presence of liquid Zn on the fracture surface was revealed by the Fe-Zn phase transformation and the spike-like morphology of the residual Zn, confirming that the mode of Zn transportation in LME cracks was liquid penetration through the austenite grain boundary. In addition, the fractography of the bend test samples and electron backscattered diffraction of the cracks revealed the failure mode of the LME crack as a complete intergranular brittle fracture without the generation of any microplasticity. Thus, the underlying failure mechanism of cracking in Zn-LME can be explained by the Stoloff-Johnson-Westwood-Kamdar brittle fracture model induced by the decohesion of interatomic bonds. Overall, a dramatic reduction in the interatomic bond strength by lowering the surface energy of the grain boundary with liquid Zn penetration causes the decohesion-induced intergranular brittle cracking.

Hydrogen-assisted cracking in GMA welding of high-strength structural steels using the modified spray arc process

High-strength structural steels are used in machine, steel, and crane construction with yield strength up to 960 MPa. However, welding of these steels requires profound knowledge of three factors in terms of avoidance of hydrogen-assisted cracking (HAC): the interaction of microstructure, local stress/strain, and local hydrogen concentration. In addition to the three main factors, the used arc process is also important for the performance of the welded joint. In the past, the conventional transitional arc process (Conv. A) was mainly used for welding of high-strength steel grades. In the past decade, the so-called modified spray arc process (Mod. SA) has been increasingly used for welding production. This modified process enables reduced seam opening angles with increased deposition rates compared with the Conv. A. Economic benefits of using this arc type are a reduction of necessary weld beads and required filler material. In the present study, the susceptibility to HAC in the heat-affected zone (HAZ) of the high-strength structural steel S960QL was investigated with the externally loaded implant test. For that purpose, both Conv. A and Mod. SA were used with same heat input at different deposition rates. Both conducted test series showed same embrittlement index “EI” of 0.21 at diffusible hydrogen concentrations of 1.3 to 1.6 ml/100 g of arc weld metal. The fracture occurred in the HAZ or in the weld metal (WM). However, the test series with Mod. SA showed a significant extension of the time to failure of several hours compared with tests carried out with Conv. A.

Fatigue analysis of a bucket wheel by using Linear Elastic Fracture Mechanics

An analysis by using the concepts of the Linear Elastic Fracture Mechanics (LEFM) was conducted in order to study the crack propagation in the welded joint of a bucket wheel that failed at service after approximately one year of operation. Some aspects related to the welded joint were considered in the analysis, such as the occurrence of residual stresses in the structure, the magnification factor of the stress intensity factor (SIF) due to the weld geometry and crack closure phenomenon. Stress intensity factors were numerically obtained for the evaluated cracks, considering tensile and shear loads. Walker equation was used for determining the propagation rate. A fatigue life consistent with the estimation of the number of cycles until the failure of the bucket wheel was obtained when considering the propagation of a preexisting crack in the structure in a field of residual tensile stresses across the thickness of the plate and along the weld bead. It was evaluated that fatigue life based on S-N curves, for a weld detail similar to the weld joint under study, was higher than the estimated number of cycles until the bucket wheel failure, indicating that some defect may have remained after manufacture of the wheel and compromised its useful life.

Towards an explanation of liquid metal embrittlement cracking in resistance spot welding of dissimilar steels

Automotive advanced high-strength steels and ultra-high-strength steels, such as Q&P980 steel with a Zn coating, are prone to liquid metal embrittlement (LME) surface cracking during resistance spot welding, while traditional low carbon steels (LCSs) do not appear to undergo LME. In this work, galvanized Q&P980 steel sheets were welded with LCS sheets. LME cracks were found on both the Q&P980 steel and LCS sides. However, the severity of LME cracking on the Q&P980 side was much higher than that on the LCS side, indicating that Q&P980 steel has a higher LME susceptibility than LCS, which was also proven by a hot tensile test. The higher LME susceptibility of Q&P980 was attributed to its lower reactivity with liquid Zn, higher achievable stress and increased number of LME-susceptible grain boundaries. Micro-analysis revealed that Zn most likely entered the steel matrix via diffusion and not via liquid penetration, and stress-assisted diffusion is the likely mechanism for LME.

Spectral analysis for crack detection during TIG welding using acoustic emission techniques

In this study, the tungsten inert gas (TIG) welding process was applied to high-carbon steel plates in order to simulate hot cracking in welds. A customised acoustic emission (AE) system was used to capture the AE waveforms generated during welding and cooling of the sample plates. The AE signals were analysed using fast Fourier transform (FFT) and short-time Fourier transform (STFT) algorithms. Comparison of the features arising from different sources observed in the frequency spectra of the acquired AE signals was carried out. The results demonstrate the possibility of applying the AE technique for monitoring and detecting signals generated from cracking activities using frequency domain analysis.