Weld Solidification Cracking Research Articles

•Microstructure Evolution and Solidification Cracking in Austenitic Stainless Steel Welds

•Microstructure Evolution and Solidification Cracking in Austenitic Stainless Steel Welds

Weld Solidification Cracking Behaviour of AA2195 Al–Cu–Li Alloy

In this study, weld solidification cracking behaviour of AA2195 Al–Cu–Li alloy was studied and compared with conventional AA2219 and AA2014 aluminium alloys. Cracking susceptibility was evaluated using varestraint test and Gleeble® hot ductility test and the slope of liquidus temperature as function of liquid fraction was also evaluated. Solidification cracking susceptibility of AA2195, AA2219 and AA2014 alloys was ranked based on the above methods. Consistent trend in cracking susceptibility was observed in all the methods where AA2195 and AA2219 alloys showed highest and lowest cracking susceptibility, respectively.

Study of Solidification Cracking Susceptibility during Laser Welding in an Advanced High Strength Automotive Steel

Susceptibility to weld solidification cracking in transformation-induced plasticity steel sheets was studied using a modified standard hot cracking test used in the automotive industry. To vary the amount of self-restraint, bead-on-plate laser welding was carried out on a single-sided clamped specimen at increasing distances from the free edge. Solidification cracking was observed when welding was carried out close to the free edge. With increasing amount of restraint, the crack length showed a decreasing trend, and at a certain distance, no cracking was observed. With the aid of a finite element-based model, dynamic thermal and mechanical conditions that prevail along the transverse direction of the mushy zone are used to explain the cracking susceptibility obtained experimentally. The results indicate that the transverse strain close to the fusion boundary can be used as a criterion to predict the cracking behavior. The outcome of the study shows that optimum processing parameters can be used to weld steels closer to the free edge without solidification cracking.

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.

Numerical Investigations on Residual Stress in Laser Penetration Welding Process of Ultrafine‐Grained Steel

Weld solidification crack prevention in the laser penetration welding process is essential for the strength of the welded component. The formation of solidification cracks can ultimately be attributed to welding residual stresses, and preventive measures should be taken during welding. In this study, the effects of residual stresses on the laser penetration welding quality of ultrafine‐grained steels were investigated. A heat source model was established through the analysis of the metallography of the cross section of the heat‐affected zone (HAZ) of ultrafine‐grained AN420s‐grade steel, and the chemical composition of the weld bead was obtained using an FLS980‐stm Edinburgh fluorescence spectrometer. Furthermore, the constitutive coupling relation between the temperature and material flow stress was established based on the Gibbs function, and the welding residual stress was obtained by setting trace points in a finite element analysis (FEA) model based on experimental data of the weld bead cross section under different welding conditions. The results show that weld solidification cracks will form when the residual stresses exceed the material flow stresses in the weld bead, and the residual stresses can be decreased through a reasonable increase of the welding speed. The results indicate that the proposed criterion has high accuracy and can be used to predict the formation of weld solidification cracks in the laser penetration welding process.

High Accurate Evaluation of Weld Solidification Cracking Susceptibility by In-situ Observation Technique

High Accurate Evaluation of Weld Solidification Cracking Susceptibility by In-situ Observation Technique

Effect of post-weld heat treatment on microstructure and mechanical properties of friction stir welded SSM7075 aluminium alloy

7XXX series aluminium alloys generally present low weldability by fusion welding methods because of the sensitivity to weld solidification cracking, vaporization of strengthening alloys and other defects in the fusion zone. Friction stir welding (FSW) can be deployed successfully with aluminium alloys. We presented the effect of post-weld heat treatment (PWHT) on the microstructure and mechanical properties of SSM7075 joints. Semi solid plates were butt-welded by FSW at a rotation speed of 1110 r/min, welding speeds of 70 and 110 mm/min. Solution treatment, artificial aging, and T6 (solution treatment and artificial aging combined) were applied to the welded joints, each with three samples. It was found that the T6 joints at the speed of 70 mm/min yielded the highest tensile strength of 459.23 MPa. This condition best enhanced the mechanical properties of FSW SSM7075 aluminium alloy joints.

Effect of Chemical Composition on Susceptibility to Weld Solidification Cracking in Austenitic Weld Metal

The influence of the chemical composition, especially the niobium content, chromium equivalent Creq, and nickel equivalent Nieq, on the weld solidification cracking susceptibility in the austenite single-phase region in the Schaeffler diagram was investigated. Specimens were fabricated using the hot-wire laser welding process with widely different compositions of Creq, Nieq, and niobium in the region. The distributions of the susceptibility, such as the crack length and brittle temperature range (BTR), in the Schaeffler diagram revealed a region with high susceptibility to solidification cracking. Addition of niobium enhanced the susceptibility and changed the distribution of the susceptibility in the diagram. The BTR distribution was in good agreement with the distribution of the temperature range of solidification (ΔT) calculated by solidification simulation based on Scheil model. ΔT increased with increasing content of alloying elements such as niobium. The distribution of ΔT was dependent on the type of alloying element owing to the change of the partitioning behavior. Thus, the solidification cracking susceptibility in the austenite single-phase region depends on whether the alloy contains elements. The distribution of the susceptibility in the region is controlled by the change in ΔT and the segregation behavior of niobium with the chemical composition.

Effect of energy transfer modes on solidification cracking in pulsed laser welding

In this study, solidification cracking in pulsed laser welding of fully austenitic, AISI Type 316 stainless steel has been analysed at different energy transfer modes. The pulse parameters have been selected appropriately to obtain conduction, transition and keyhole mode welds. Conduction and transition mode welds exhibit higher susceptibility to cracking than keyhole mode welds. It is observed that both heat input and energy transfer mode affect the cooling rate and hence influence solidification cracking. Microstructures of the fusion zone have been analysed, and the cooling rate experienced by the weld is estimated from the mean cell size in the weld. It is found that the critical cooling rate below which cracking does not occur is ∼104 K s− 1.

Using pulse shaping to control temporal strain development and solidification cracking in pulsed laser welding of 6082 aluminum alloys

High-speed observation of visible and infrared radiation was performed to measure the molten pool geometry, velocity of the solid–liquid interface and temperature profile during laser spot welding of aluminum. Hot cracking occurred at a late stage of solidification for the investigated laser pulse shapes. Hot cracking could be minimized by using a pulse shape with two distinct power levels and a final cooling slope to shut down the laser power. The drop of the laser power from the first to the second power level led to a high cooling rate and high interface velocity at the beginning of solidification. This drop in temperature and molten pool diameter released strains originating from thermal contraction and solidification shrinkage at the beginning of solidification, where spot welding is expected to have a higher ductility. After this initial high solidification rate, low interface velocities were observed during solidification within the second power level. The final solidification rate increased again as a function of the cooling time of the last laser pulse section. This type of solidification process was also found in metallographic microstructures with greater dendritic structures during solidification within the second power level. The strain release at the beginning of solidification minimized residual strains for the remaining solidification, so that crack-free and full penetration bead-on-plate seam welding with overlapping spot welds was possible.

Influence of Cr on Weld Solidification Cracking in Fe-15Mn-0.5C-3.5Al-xCr Alloys

The solidification cracking sensitivity of Fe-15Mn-0.5C-3.5Al-xCr (x= 5, 12 mass%) alloys was evaluated using a longitudinal Varestraint test and compared with that of austenitic Fe-18Mn-0.6C alloy. Weld microstructures of Low Cr (5 mass%) and High Cr (12 mass%) alloys revealed duplex structures with a mixture of austenite and δ ferrite. The amounts of residual δ ferrite and (Cr, Fe, Mn)23C6 carbide remarkably increased with increasing Cr content. A small amount of Cr addition (5 mass%) provided negligible influence on the solidification cracking susceptibility. However, the welds of high Cr alloys demonstrated excellent resistance to solidification cracking due to healing by the eutectic liquid. The addition of Cr enhanced the formation of a low melting point (γ + (Cr, Fe,Mn)7C3) eutectic during solidification by increasing the eutectic formation temperature and simultaneously decreasing the eutectic C content.

Prediction of solidification cracking in laser welds of type 310 stainless steels

The occurrence of solidification cracks in laser welds of type 310 stainless steels was predicted by numerical analyses of the solidification brittle range (ductility curve for cracking) and thermal strain in the weld metal. The solidification brittle range in laser welding was estimated from that in arc welding based on the numerical analyses of supercooling (for calculating dendrite tip temperature) and segregation (for calculating completely solidified temperature) during rapid solidification. The calculated solidification brittle range was reduced with an increase in the welding speed because of the enhanced supercooling and the inhibited solidification segregation. The thermal strain analysis by FEM suggested that solidification cracks would occur in SUS310S welds at laser travelling velocity of 60 mm/s applying the initial strain of 1.5%, while no solidification cracks in SUS310EHP welds at any laser travelling velocities applying the higher initial strain of 2.2%. The cantilever type cracking test in laser welding revealed that the predicted results of occurrence of solidification cracks were consistent with experimental ones.

Prediction of solidification cracking in pulsed laser welding of 2024 aluminum alloy

Laser welding of aluminum alloys can be associated with solidification cracking. The severity of cracking in these alloys depends on various factors, such as the initial temperature of the base metal and the temporal amplitude of the laser pulse. The purpose of this investigation is to understand this correlation, and thus to put forward a criterion for solidification cracking in laser welding of 2024 aluminum alloy. The criterion for cracking is devised based on a modification of the existing criteria, to account for non-steady conditions, and interpreted with respect to the loci of the relevant isotherms and the length of the vulnerable zone in the melt pool, during the solidification stage. Based on this criterion and the respective experimental observations, it is demonstrated that welding with suitable ramping down of the laser pulse can lead to the elimination of solidification cracking in the examined alloy.

Modeling of transport phenomena and solidification cracking in laser spot bead-on-plate welding of AA6063-T6 alloy. Part I—the mathematical model

In this study, a transient unified model including simulation of the temperature, velocity, solute (Mg2Si) concentration and stress fields, free surface, and laser-induced plasma, has been developed to predict the transport phenomena and solidification cracking susceptibility during laser spot bead-on-plate welding of aluminum alloy. The model consists of the modeling of heat, momentum and mass transports in the metal and plasma zones, thermomechanical modeling, and evaluation of solidification cracking. The full set of mathematical equations and numerical methods are presented. The main challenges and the corresponding solutions for the modeling are discussed. In this model, the lever-rule based on the phase diagram was used to deal with the macroscale segregation at the solid–liquid interface, while the solute transfer due to the diffusion and convection were calculated by the conservation equations for transport phenomena. The solute redistribution in the weldment is coupled with the changes of liquidus and solidus temperatures of the material. The total strain consists of the elastic, viscoplastic, and thermal parts that are coupled with the calculated temperature, velocity, and solute in the weldment. The criterion for the weld solidification cracking was established based on the strain theory, in which the cracking initiates only when the strain exceeds the threshold strain in the brittle temperature range (btr).

Solidification cracking in laser GMA hybrid welding of thick-walled parts

Laser GMA hybrid welds, producing partial penetration, were conducted on stiff tubes made of S460NH. Experiments, using a design-of-experiments plan were conducted to examine the influence of the welding parameters on the occurrence of solidification cracks. Results say that cracks diminish, when high levels of arc power are applied, while their number increases with rising laser beam power. The weld velocity had no measurable impact.

Solidification cracking susceptibility of modified 9Cr1Mo steel weld metal during hot-wire laser welding with a narrow gap groove

Hot-wire laser welding with a narrow gap groove was applied to ASTM A213 grade T91 steel in the application of ultra super critical boilers. A filler wire according to AWS A 5.28: ER90S-G was used. The effect of the depth-to-width ratio (D/W) of a weld shape on the susceptibility to solidification cracking was investigated. With a groove width of 3 mm, solidification cracking did not occur with a D/W ratio of less than 0.6 and more than 1.2. The hot-wire laser welding method with a narrow gap groove seemed to be efficient for practical use, when the higher D/W condition was used without solidification cracking. The high temperature strain, which occurred during solidification, was computationally calculated in order to make clear the effect of D/W ratios on the susceptibility of solidification cracking in theory. From in situ observation using a high-speed camera of the hot-wire laser welding phenomena, a three-dimensional Finite Element Method (FEM) was simulated to estimate an equivalent plastic strain in the weld metal during welding. An approach to the moving heat source consistent with such phenomenon was proposed and validated based on experimental measurements. The simulation results presented that a moving heat source by hot-wire laser welding was able to produce a particular weld shape at a higher D/W ratio with a lower strain rate, which corresponded with the relationship between D/W ratios and solidification cracking in experiments. Therefore, such a hybrid process is a very interesting alternative process to reduce the solidification cracking in narrow gap welding, especially in modified 9Cr1Mo steel.

Hot cracking in pulsed laser processing of a nickel based superalloy built up by electrospark deposition

A cast precipitation hardened nickel based superalloy was built up by electrospark deposition and then subjected to pulsed laser welding. The resistance of electrospark deposition layer to liquation and solidification cracking in pulsed laser welding was significantly higher than that of the cast alloy. It is shown that the extreme cooling rates involved in the solidification of electrospark deposition droplets result in the prevention of formation of grain boundaries terminal solidification constituents, which are the sources of liquation cracking in the cast alloy.

Investigation on Mechanical Properties and Microstructure of SSM 356-T6 Aluminium Alloy by Diffusion Bonding

SSM 356-T6 aluminium alloys generally present low weldability by fusion methods because of the sensitivity to weld solidification cracking, porosities, change microstructure in weld zone and other defects in the fusion zone. Diffusion bonding can be deployed successfully with aluminium alloys. This paper presents the technique to conserve the globular weld structure of SSM 356-T6 aluminium alloy. The effect of joining parameters on the microstructure and mechanical properties of diffusion bonding butt joints of semi-solid metal 356-T6 aluminium alloy were investigated by conditions as follows: contact pressure at 0.4, 0.9, 1.8, 2.4 and 2.7 MPa, for 3 hours holding time and temperature at 495°C under argon atmosphere at 4 liters per minute. The results showed that condition used contact pressure 2.4 MPa, with 3 hours holding time and temperature at 495°C, under argon atmosphere provided. The highest joint strength reaching to 182.2 MPa, which had joint efficiency of 61.34 percents compared with base material. In addition, microstructure in welded zone after welding is still in globular structure, but the grain size was increased when the higher bonding temperature was used. The results of this investigation have shown that an average hardness is around 121.2 HV.

Modelling of hot cracking in welding with a cellular automaton combined with an intergranular fluid flow model

Hot cracking phenomena in welds are still a major issue to choose suitable welding conditions. Solidification cracking in welds depends on microstructure morphology, thermal and mechanical loadings. It is still difficult to discriminate the influence of the different phenomena because they are all connected. To investigate solidification cracking, numerical modelling that integrates most of these phenomena is developed in this paper. Thermal and mechanical fields are computed with a finite element model at the process scale. The thermal field is combined with a cellular automaton (CA) to predict microstructure at a mesoscale. Based, on this prediction, the intergranular network is extracted. Finally, the pressure in the intergranular fluid network is computed during solidification. The fluid flow model along grain boundaries predicts an eventual nucleation of pore/void in the remaining liquid by investigating the maximum pressure drop in the solidifying microstructure. The numerical model is able to describe some hot cracking phenomena observed during experimental tests.

Initiation and growth mechanisms for weld solidification cracking

Solidification cracking is a weld defect common to certain susceptible alloys rendering many of them unweldable. It forms and grows continuously behind a moving weld pool within the two phase mushy zone and involves a complex interaction between thermal, metallurgical and mechanical factors. Despite decades long efforts to investigate weld solidification cracking, there remains a significant lack of understanding regarding its underlying mechanisms. Criteria developed to evaluate alloy weldability will be examined in terms of proposed solidification cracking models. Crack initiation is discussed in terms of different criteria: critical stress to fracture the interdendritic liquid, critical strain to exceed the mushy zone ductility and critical hydrogen content to nucleate and grow a pore. Crack growth has been characterised in terms of a critical stress to fracture the liquid film surrounding a grain and critical strain rate interdependent with liquid feeding of the mushy zone opening. Experimental data to form a weld solidification crack are compiled, revealing the considerable amount of information available in the literature on this topic.