Low Alloy Steel Weld Research Articles

Analysis of toughness of welding alloys for high strength low alloy shipbuilding steels

In previous work by the present authors a model was developed for the estimation of the tensile properties (strength and ductility) of ferrous alloys intended for the welding of high strength low alloy steels used in the construction of ships. The method used to model the properties as a function of a large number of variables was based on a neural network within a Bayesian framework. This method is particularly useful when attempting to understand complex non-linear phenomena where the distribution of data within the input space is not obvious. In the present work, a similar approach is used to model the toughness (characterised by Charpy and dynamic tear tests) of the same alloys. The level of noise in the experimental data is perceived to be high, but it has nevertheless been possible to recognise reasonable trends and uncertainties when making predictions. For example, the toughness shows a non-linear deterioration as the oxygen concentration is increased; this behaviour is expected but can now be expressed quantitatively.

Kinetics of manganese in MAG/MIG welding with a 18/8/6 wire

The paper deals with a study of MAG/MIG welding of low-alloy ferritic steel and highalloy austenitic steel with a 18/8/6 wire. Manganese burn-off from the wire in welding a single-V butt weld was studied. It was found that manganese burns off in the arc during melting of a droplet at the wire end, and from the weld pool during weld formation. The range of manganese burn-off depends mainly on the type of shielding gas used and the arc length, i.e., from the arc voltage. The manganese burn-off increases with an increase of the content of active gases, i.e., CO 2 and O 2 , in the neutral gas, i.e., argon. It also increases with an increase in arc voltage. The longer the welding arc, the longer exposition of the filler material to the welding arc and the wider the penetration, which allows manganese vapours to evaporate from the weld pool. The most important finding is that manganese burn-off from the 18/8/6 wire during welding of austenitic stainless steel with low-alloy ferritic steel is considerably strong, i.e., from 20% to 30%; nevertheless the wire concerned is perfectly suitable for welding of different types of steel.

Microstructure of martensite–austenite constituents in heat affected zones of high strength low alloy steel welds in relation to toughness properties

Microstructure and fracture properties relationships have been investigated in the heat affected zones (HAZs) of a high strength low alloy steel used for offshore applications. Metallographic examinations of simulated HAZ microstructures were conducted to investigate the detailed microstructure of the martensite–austenite (M–A) constituents. Using scanning and transmission electron microscopy, various microstructures were found for the M–A constituents. In mixed particles, retained austenite was located at the periphery of the islands. Chemical and/or mechanical effects could possibly account for the stabilisation of this austenite phase. In situ cooling experiments in the transmission electron microscope showed that stacking faults play an important role in the thermal stability of austenite. Impact properties of simulated HAZ microstructures are strongly affected by both the bainitic microstructure and M–A constituents. In particular, freshly transformed high carbon martensite was shown to be much more deleterious than retained austenite.

Modeling of inclusion growth and dissolution in the weld pool

The composition, size distribution, and number density of oxide inclusions in weld metal are critical factors in determining weldment properties. A computational model has been developed to understand these factors, considering fluid flow and the temperature field in the weld pool during submerged are (SA) welding of low-alloy steels. The equations of conservation of mass, momentum, and energy are solved in three dimensions to calculate the velocity and temperature fields in the weld pool. The loci and corresponding thermal cycles of thousands of oxide inclusions are numerically calculated in the weld pool. The inclusions undergo considerable recirculatory motion and experience strong temperature gyrations. The temperature-time history and the computed time-temperature-transformation (TTT) behavior of inclusions were then used to understand the growth and dissolution of oxide inclusions in the weld pool. The statistically meaningful characteristics of inclusion behavior in the weld pool, such as the residence time, number of temperature peaks, etc., were calculated for several thousand inclusions. The calculated trends agree with experimental observations and indicate that the inclusion formation can be described by combining thermodynamics and kinetics with the fundamentals of transport phenomena.

Influence of heat input and travel speed on microstructure and mechanical properties of double tandem submerged arc high strength low alloy steel weldments

An evaluation is presented of the microstructural characteristics and mechanical properties of welds in 20 mm thickness high strength low alloy steel HSLA 80, of Australian manufacture. In total, nine butt joints were prepared using the double tandem (four wire) submerged arc welding process in which both heat input and travel speed were varied. The inclusion size distribution was determined for selected welds and showed that heat input had a major effect. Colour etching techniques were used to reveal the solidification structure, which in turn correlated with welding parameters. As the heat input increased, the cooling rate decreased resulting in a larger cellular dendritic cell spacing, decreased acicular ferrite content, and coarser acicular ferrite laths. The effect of travel speed on delta ferrite cell spacing and prior austenite grain size was found to be co-dependent on the heat input and the thermal profile resulting from multiple electrode welding. These results show that increased deposition rates can be achieved by increasing the travel speed and current density without sacrificing joint quality.

Influence of heat input and travel speed on microstructure and mechanical properties of double tandem submerged arc high strength low alloy steel weldments

An evaluation is presented of the microstructural characteristics and mechanical properties of welds in 20 mm thickness high strength low alloy steel HSLA 80, of Australian manufacture. In total, nine butt joints were prepared using the double tandem (four wire) submerged arc welding process in which both heat input and travel speed were varied. The inclusion size distribution was determined for selected welds and showed that heat input had a major effect. Colour etching techniques were used to reveal the solidification structure, which in turn correlated with welding parameters. As the heat input increased, the cooling rate decreased resulting in a larger cellular dendritic cell spacing, decreased acicular ferrite content, and coarser acicular ferrite laths. The effect of travel speed on delta ferrite cell spacing and prior austenite grain size was found to be co-dependent on the heat input and the thermal profile resulting from multiple electrode welding. These results show that increased deposition rates can be achieved by increasing the travel speed and current density without sacrificing joint quality.

Experimental investigation of gas tungsten arc welding and comparison with theoretical predictions

An experimental investigation in gas tungsten arc welding with the hydrogen addition to argon was made. The hydrogen addition to argon makes the arc constrict and the energy concentrate in the arc, which produces increase in arc power. Experimental welding was carried out on three base metals, i.e., low-alloy steel, high-alloy stainless steel, and an aluminum alloy, using no filler material and in argon with the addition of 0.5-20% hydrogen. In welding of stainless steel with the addition of 20% hydrogen to argon, the quantity of the base metal melted increases by three to five times, with the other parameters remaining the same, in welding of low-alloy steel by three times, and in welding of aluminum by six to nine times. The experimentally obtained results were compared with the theoretical ones. With both steels, the experimental and theoretical results agreed well, but with aluminum, they differed very much.

Use of the implant test and acoustic emission technique to investigate hydrogen‐assisted cracking in the fusion zone of welded HSLA‐80 steel

Summary Hydrogen‐assisted cracking in the fusion zone (FZ) was studied, using flux‐cored wire (AWS E 70T5 and AWS E 120 T5‐K4) and a CO2 + 5% H2 gas mixture to induce high values of diffusible hydrogen in high strength, low alloy steel (HSLA‐80) welds. An acoustic emission measurement system (AEMS) based on a root mean square (RMS) voltmeter was coupled to the implant test apparatus (NF 89–100) to determine energy, amplitude and number of signals. Using optical microscopy and scanning electron microscopy (SEM), it was observed that, in all tests, cracks were initiated in the partially molten zone and propagated in the coarse‐grained region of the heat affected zone (HAZ) when E 70 T5 wire was used and quasi‐cleavage (QC) fracture mode was predominant. When E 120 T5 K.4 wire was used, the cracks were propagated vertically across the FZ and the mixed fracture mode was predominant. A significant relationship between acoustic emission (AE) parameters and fracture modes was found in the cracking mechanism.

Microstructural and mechanical aspects of tempered ICCGHAZ of SQV-2A low alloy steel weld

Microstructural and mechanical aspects of tempered ICCGHAZ of SQV-2A low alloy steel weld

Fracture modes and acoustic emission characteristics of hydrogen-assisted cracking in high-strength low-alloy steel weldment

The aim of the present paper is to study the relationship between the fracture modes in hydrogen-assisted cracking (HAC) in microalloied steel and the emission of acoustic signals during the fracturing process. For this reason, a flux-cored arc weld (FCAW) was used in a high-strength low-alloy steel. The consumable used were the commercially available AWS E120T5-K4 and had a diameter of 1.6 mm. Two different shielding gases were used (CO2 and CO2+5% H2) to obtain complete phenomenon characterization. The implant test was applied with three levels of restriction stresses. An acoustic emission measurement system (AEMS) was coupled to the implant test apparatus. The output signal from the acoustic emission sensor was passed through an electronic amplifier and processed by a root mean square (RMS) voltage converter. Fracture surfaces were examined by scanning electron microscopy (SEM) and image analysis. Fracture modes were related with the intensity, the energy and the number of the peaks of the acoustic emission signal. The shielding gas CO2+5% H2 proved to be very useful in the experiments. Basically, three different fracture modes were identified in terms of fracture appearance: microvoid coalescence (MVC), intergranular (IG) and quasi-cleavage (QC). The results show that each mode of fracture presents a characteristic acoustic signal.

Model for inclusion formation in low alloy steel welds

Oxide inclusion formation in low alloy steel welds is described with a model as a function of weld metal composition and process parameters. The model was developed by coupling thermodynamic and kinetic considerations. Thermodynamic calculations considered the effect of the alloying elements and kinetic equations allowed, describing oxide formation during weld cooling. The model showed that weld cooling rate influences the inclusion characteristics and therefore must be taken into consideration. This inclusion model is capable of predicting the composition, size, number density, and oxidation sequence of inclusions and was verified with published data. The inclusion model was coupled with numerical heat transfer and fluid flow models to extend the model to a wide range of welding process conditions.

Uso del ensayo de implante y la técnica de emisión acústica para estudiar el agrietamiento asistido por hidrógeno en la zona fundida en la soldadura de un acero HSLA-80

Weld metal hydrogen assisted cracking was studied using two flux cored wire (AWS E 70T-5 and AWS E 120 T5-K4) and a mixture gas of CO 2 + 5% H 2 to induce high values of diffusible hydrogen in high strength low alloy steel (HSLA-80) weldments. An Acoustical Emission Measurement System (AEMS) RMS voltmeter was coupled to the implant test (NF 89-100) apparatus to determine energy, amplitude and event numbers of signal. All cracks were initiated in the partially melted zone and propagated into the coarse-grained region of the heat affected zone when E 70 T5 consumable was used, and the quasi-cleavage fracture mode was predominant. When E 120 T5 K4 consumable was used the cracks propagated vertically across the fusion zone, and a mixed fracture mode was the most important. A significant relationship between acoustic emission parameters and fracture modes was found.

Effects of Crack Starter Bead Preparation in Drop-Weight Test on Nil-Ductility Transition Temperature

The procedure for making crack starter weld deposit on drop-weight test (DWT) specimens was altered from two passes to one pass in about 1990. The effects of some parameters of crack starter weld process on drop-weight test results were studied. Results of this study indicated that length of overlap of the second pass and height of crack starter beads were most effective on nil-ductility temperature (TNDT). When overlap length and bead height of two-pass deposit were small enough, TNDT obtained by two-pass deposit became lower than one-pass TNDT, the discrepancy being by as much as 25°C. TNDT values for 24 Japanese steels were determined using two different DWT methods, one-pass deposit and two-pass deposit having small overlap length and bead height. The difference of TNDT depending on DWT method could be seen only for high-toughness low-alloy steel base metals. For other materials (i.e., low-to-medium-toughness low-alloy steel base metals, weld metals, and high-toughness carbon steels), TNDTS by two-pass and one-pass deposits were essentially the same. For lower-toughness steels, TNDT was frequently lower than the temperature of vTcv − 33°C), and thus, the reference nil-ductility temperature RTNDT was determined from Charpy impact test results. These results can be taken as a way of interpreting the past toughness evaluations made for operating plants using the two-pass TNDT.

Fracture behaviour of specimens with surface notch tip in the heat affected zone (HAZ) of strength mis-matched welded joints

The generally accepted conditions for the strength overmatched welded joints of high strength steel are not clearly defined. In this paper, the fracture mechanics analysis of specimens, with surface notch tips completely embedded in the heat affected zones was conducted. The results showed that the strength of mismatching of a welded joint caused a redirection of the crack propagation towards the low strength region of the welded joint. This redirection of the crack propagation affected the values of the critical CTOD. In the cases of the overmatched welded joints containing a soft root layer it is possible to achieve a comparable fracture behaviour related to the homogeneous overmatched welded joint if the impact toughness of the soft root layer is higher than the impact toughness of the overmatched weld metal. Such a type of welded joint is therefore preferable for the welding of high strength low alloy steels, because it enables the manufacturing of a welded joint without preheating.

Effect of welding process on the ballistic performance of high-strength low-alloy steel weldments

The resistance against projectile penetration of the various zones in the weldments of a high-strength low-alloy steel has been studied. A comparison has been made between weldments obtained through three welding processes, namely: shielded metal arc welding (SMAW); gas tungsten arc welding (GTAW); and flux cored arc welding (FCAW). In all of the weldments, the projectile passed through all of the weld zones. However, the ballistic limit has been found to be highest in the case of the SMAW weld and least in respect of FCAW welds. The heat-affected zone (HAZ) of SMAW was resistant to penetration and exhibited the highest ballistic limit, whilst the HAZ of FCAW exhibited an intermediate performance. The ballistic performance of the weldments has been explained on the basis of the weld-zone microstructure, the hardness gradients across the weldments and the thermal efficiencies of the three welding processes.

Creep crack growth in low alloy steel weldments

Developments in the determination and analytical representation of creep crack growth property data during the past 30 years are reviewed. The testing and data analysis of weldments involve additional complexities, and these are appraised with respect to low alloy steel weldments. Creep crack initiation and growth properties are dependent on creep deformation and rupture ductility characteristics. Consideration is given to the relationship between these properties using data determined for a ½Cr½ Mo¼V/2½CrMo pipe joint.

Thermodynamic estimation of inclusion characteristics in low alloy steel weld metals

Inclusion characteristics are extremely important factors which affect the weld metal microstructure. Estimation of the inclusion characteristics in low alloy steel weld metals was attempted using thermodynamic calculation. Reasonable quantitative agreement is found between the calculated results and experimental observations in the literature, indicating that the present approach is useful for controlling inclusions in weld metals and optimising weld chemistry. It is also suggested that thermodynamic phase stability exerts a significant influence on the inclusions in low alloy steel weld metals.

Absorption and transport of hydrogen during gas metal arc welding of low alloy steel

Although hydrogen induced cracking remains a major problem in the welding of steels, the present methods of managing hydrogen in the weldment are mostly empirical in nature. In recent years, numerical modelling of heat transfer and fluid flow has provided detailed insight into the physical processes in welding. However, very little effort has been made in the past to use these transport phenomena based calculations to understand the dissolution of hydrogen in the weld metal and its subsequent transport in the liquid and solid regions. The aim of the present work was to address this important need. Heat transfer, fluid flow, and hydrogen transport calculations in transient, three-dimensional form are used to predict the spatial distribution of hydrogen concentration in the weld metal during gas metal arc welding of mild steels for different welding conditions. The enhanced hydrogen solubility in the weld metal above that predicted by Sieverts law was determined from a model for the partitioning of hydrogen between the weldment and its plasma environment. The model considers the presence of a superequilibrium concentration of atomic hydrogen which is significantly higher than that produced by thermal dissociation. The results indicate that for a meaningful prediction of the hydrogen concentration in the weld metal, hydrogen absorption at the weld pool surface, transport of hydrogen within the weld pool, and the diffusion of hydrogen away from the solidified weld metal should be considered simultaneously. The agreement between the experimental and predicted results indicates significant promise for predicting weld metal hydrogen concentration in fusion welds from fundamentals of transport phenomena.

Absorption and transport of hydrogen during gas metal arc welding of low alloy steel

Although hydrogen induced cracking remains a major problem in the welding of steels, the present methods of managing hydrogen in the weldment are mostly empirical in nature. In recent years, numerical modelling of heat transfer and fluid flow has provided detailed insight into the physical processes in welding. However, very little effort has been made in the past to use these transport phenomena based calculations to understand the dissolution of hydrogen in the weld metal and its subsequent transport in the liquid and solid regions. The aim of the present work was to address this important need. Heat transfer, fluid flow, and hydrogen transport calculations in transient, three-dimensional form are used to predict the spatial distribution of hydrogen concentration in the weld metal during gas metal arc welding of mild steels for different welding conditions. The enhanced hydrogen solubility in the weld metal above that predicted by Sieverts law was determined from a model for the partitioning of hydrogen between the weldment and its plasma environment. The model considers the presence of a superequilibrium concentration of atomic hydrogen which is significantly higher than that produced by thermal dissociation. The results indicate that for a meaningful prediction of the hydrogen concentration in the weld metal, hydrogen absorption at the weld pool surface, transport of hydrogen within the weld pool, and the diffusion of hydrogen away from the solidified weld metal should be considered simultaneously. The agreement between the experimental and predicted results indicates significant promise for predicting weld metal hydrogen concentration in fusion welds from fundamentals of transport phenomena.

Thermodynamic study of inclusion formation in low alloy steel weld metals

The formation and stability of inclusions in low alloy steel welds were investigated using equilibrium calculations. Based on the results, the origin of inclusions effective in acicular ferrite production is discussed. Particular emphasis is placed on the effect of the Al/O ratio and titanium addition on inclusion formation since these two factors are experimentally critical to acicular ferrite production. Mullite (2SiO2.3Al2O3) is found to be formed in addition to Ti3O5 in the steel melt at 1800 K when the melt has a wt-%Al/wt-%O ratio of ∼0·6 optimum for acicular ferrite production. However, the mullite is unstable in the austenite and galaxite (MnO.Al2O3), having the spinel structure, becomes stable at the lower temperatures. Therefore, it is proposed that galaxite is responsible for the nucleation of acicular ferrite. The formation of the galaxite should be in the solid state after weld solidification, being associated with pre-existing mullite. Titanium additions are found to be beneficial to acicular ferrite production by decreasing the formation of ineffective glassy oxide.