Low Alloy Steel Weld Research Articles

Fatigue life prediction of strength mis-matched high strength low alloy steel welds

Welding of high strength low alloy steels (HSLA) involve usage of low, even and high strength filler materials (electrodes) than the parent material depending on the application of the welded structures and the availability of the filler materials. The base material used in this investigation is HSLA-80 steel of weldable grade. Shielded metal arc welding (SMAW) process has been used to fabricate the single bevel butt joints. Centre cracked tension (CCT) specimen has been used to evaluate the fatigue crack growth behaviour of the welded joints. Fatigue crack growth experiments have been conducted using servo hydraulic controlled fatigue testing machine at constant amplitude loading ( R = 0). A method has been proposed to predict the fatigue life of HSLA steel welds using fracture mechanics approach by incorporating influences of mis-match ratio (MMR), post weld heat treatment (PWHT) and notch location.

Influences of post weld heat treatment on fatigue life prediction of strength mis-matched HSLA steel welds

Welding of High Strength Low Alloy Steels (HSLA) involve usage of low, even and high strength filler materials (electrodes) than the parent material depending on the application of the welded structures and the availability of the filler materials. In the present investigation, the influences of post weld heat treatment (PWHT) on fatigue life prediction of under matched (UM), even matched (EM) and over matched (OM) weld metals have been studied. The base material used in this investigation is HSLA-80 steel of weldable grade. Shielded Metal Arc Welding (SMAW) process has been used to fabricate the single ‘V’ butt joints. Centre Cracked Tension (CCT) specimen has been used to evaluate the fatigue crack growth behaviour of the welded joints. Fatigue crack growth experiments have been conducted using servo hydraulic controlled fatigue testing machine at constant amplitude loading ( R=0). A method has been proposed to predict the fatigue life of HSLA steel welds using fracture mechanics approach by incorporating influences of mis-match ratio (MMR) and post weld heat treatment (PWHT).

Effect of Notch Location on Fatigue Crack Growth Behavior of Strength-Mismatched High-Strength Low-Alloy Steel Weldments

Welding of high-strength low-alloy (HSLA) steels involves the use of low-strength, equal-strength, and high-strength filler materials (electrodes) compared with the parent material, depending on the application of the welded structures and the availability of filler material. In the present investigation, the fatigue crack growth behavior of weld metal (WM) and the heat-affected zone (HAZ) of undermatched (UM), equally matched (EM), and overmatched (OM) joints has been studied. The base material used in this investigation is HSLA-80 steel of weldable grade. Shielded metal arc welding (SMAW) has been used to fabricate the butt joints. A center-cracked tension (CCT) specimen has been used to evaluate the fatigue crack growth behavior of welded joints, utilizing a servo-hydraulic-controlled fatigue-testing machine at constant amplitude loading (R=0). The effect of notch location on the fatigue crack growth behavior of strength mismatched HSLA steel weldments also has been analyzed.

Influences of post-weld heat treatment on fatigue crack growth behaviour of strength mismatched HSLA steel welds

Welding of high strength low alloy steels (HSLA) involves usage of low, even and high strength filler materials (electrodes) compared with the parent material depending on the application of the welded structures and the availability of the filler material. In the present investigation, the influences of post-weld heat treatment (PWHT) on fatigue crack growth behaviour of under matched (UM), equal matched (EM) and over matched (OM) weld metals has been studied. The base material used in this investigation is HSLA-80 steel of weldable grade. The Shielded Metal Arc Welding (SMAW) process has been used to fabricate the single 'V' butt joints. Centre Cracked Tension (CCT) specimens have been used to evaluate the fatigue crack growth behaviour of the welded joints. Fatigue crack growth experiments have been conducted using servo hydraulic controlled fatigue testing machine at constant amplitude loading (R = 0). From this investigation, it has been found that the fatigue performance of over matched joints is superior compared to under matched and equal matched joints. Moreover, PWHT reduced the magnitude of the tensile residual stress field in the weld region and subsequently enhanced the fatigue performance of the joints irrespective of weld metal strength mismatch.

The effect of nickel, manganese and copper on the irradiation sensitivity of low alloy steel welds

It was observed by LM Davies that ‘Eastern’ and ‘Western’ reactor pressure vessel steels have similar spans of irradiation sensitivity. In this paper the similarities and differences between these steels are explored by comparison between published data on VVER steels, and data and models developed on Western type welds with similar nickel contents to the VVER-440 and VVER-1000 steels. This comparison requires that allowance be made for irradiation temperature, dose rate and manganese effects. This can only be done approximately; even so, the results show encouraging similarities in behaviour between the Eastern and Western categories of steel.

Normalizing heat treatment effect on low alloy steel weld metals

In equipment manufacturing, there are occasions that the base metal (BM) need to be hot or cold worked prior to welding. After welding, the components have to be submitted to a normalizing heat treatment in order to recover its original mechanical properties. In this work four different low alloy steel weld metals (WM) both in the as welded condition and after normalizing heat treatment have been studied. Optical and scanning electron microscopy were used to observe the WM microstructure. Tensile and Charpy V toughness testing and microhardness measurements were used to evaluate the WM mechanical properties. Results show that normalizing breaks the original columnar structure in the as welded condition to an equiaxial structure similar to the one of the BM. Due to low carbon content of the WM it was observed a high decrease on the tensile properties specially the yield strength after normalizing. In respect of toughness, the normalizing heat treatment was observed to increase the Charpy V energy, except for one WM where a great content of martensite-austenite-bainite constituent was formed. Opposite to others post weld heat treatments, normalizing modifies significantly the microstructure and the resulting mechanical properties of the WM. Although normalizing is always beneficial to the BM, care must be taken in order to select welding consumables.

Micro-Macro Combined Simulation of the Damage Progress in Low-Alloy Steel Welds Subject to Type IV Creep Failure

A simulation method for microscopic creep damage at grain boundaries in the fine-grain heat-affected zone of low-alloy steel welds involving high energy piping was proposed on the basis of the combination of elastic-creep FEM analysis and random fracture resistance modeling of the materials. First, the initiation and growth-driving forces of small defects were concretely determined based on microscopic observation of the damage progress at the grain boundaries of the material, taking into account dependence on stress and temperature. Then, a simulation procedure combining the stress distribution from elastic-creep FEM and the random fracture resistance model was proposed, and this procedure was applied to the simulation of the microscopic damage progress in a welded joint model test and in actual power piping. The results in terms of the simulated number density of small defects throughout the wall thickness were in good agreement with the observed results.

Prediction of cooling rate and microstructure in laser spot welds

Theoretical and experimental investigations have been carried out to examine the influence of laser power and on time on the weld thermal cycle and weld metal microstructure and hardness during laser spot welding of low alloy steel. A transient heat transfer model that takes into account the temperature dependence of material properties and latent heat of phase transformation is employed to simulate thermal cycles and cooling rates experienced by the material under various combinations of power and on times. Two models for predicting the microstructure and hardness of the weld pool metal from the cooling rates are used to evaluate the results.

Cold cracking studies on low alloy steel weldments: effect of filler metal composition

The resistance to hydrogen cracking of Cr - Mo, Ni - Cr - Mo and Si - Mn steels which are employed in armoured vehicle construction was evaluated under implant test conditions. Austenitic stainless steel filler (AWS E312), which is reported to be resistant to hydrogen assisted cracking, was used to study the cracking tendency of all the three steels. Four other fillers, namely a nickel based filler (ENiCrFe-3), a low carbon, low alloy steel, a mild steel (AWS E6013) and a matching filler for Cr - Mo, were employed to evaluate their relative cracking tendency. Cr - Mo and Ni - Cr - Mo steels exhibited high cracking tendency while Si - Mn steel was resistant to cracking with the E312 filler. Cr - Mo steel was resistant to cracking with the nickel based filler, the low carbon, low alloy steel and the matching filler. The observed cracking tendency of the steels is linked to a susceptible interface/fusion boundary microstructure.

Assessment of some factors influencing the fatigue life of strength mis-matched HSLA steel weldments

Abstract Welding of high strength low alloy steels (HSLA) involve usage of low, even and high strength filler materials (electrodes) than the parent material depending on the application of the welded structures and the availability of the filler material. In this investigation an attempt has been made to assess the influences of mis-match ratio (MMR), post-weld heat treatment (PWHT) and notch location on fatigue life of HSLA steel welds. Shielded metal arc welding (SMAW) process has been used to fabricate the butt joints. Centre cracked tension (CCT) specimen has been used to evaluate the fatigue life of welded joints. Fatigue experiments have been conducted using servo hydraulic controlled fatigue testing machine at constant amplitude loading ( R =0). Design of experiments (full factorial design) concept has been used to optimise the number of experimental conditions. A procedure has been developed to assess and optimise the above chosen factors to attain a maximum fatigue life value by incorporating (i) response table and response graph, (ii) normal probability plot and (iii) analysis of variance (ANOVA) techniques.

Influences of MMR, PWHT and notch location on fatigue life of HSLA steel welds

Welding of High Strength Low Alloy Steels (HSLA) involves usage of lower, more even and higher strength filler materials (electrodes) than the parent material depending on the application of the welded structures and the availability of the filler material. In this investigation an attempt has been made to study the influences of mis-match ratio (MMR), Post Weld Heat Treatment (PWHT) and notch location on fatigue life of HSLA steel welds. A Shielded Metal Arc Welding (SMAW) process has been used to fabricate the butt joints. A Centre Cracked Tension (CCT) specimen has been used to evaluate the fatigue life of welded joints. Fatigue experiments have been conducted using a servo hydraulic controlled fatigue testing machine at constant amplitude loading ( R=0). The Design of Experiments (full factorial design) concept has been used to optimise the number of experimental conditions. Analysis of Variance (ANOVA) method has been used to identify the significance of main and interaction effects. A mathematical model has been developed to predict the fatigue life of HSLA steel welds using Regression analysis.

Effect of mis-match ratio (MMR) on fatigue crack growth behaviour of HSLA steel welds

Welding of High Strength Low Alloy Steels (HSLA) involves usage of low, even and high strength filler materials (electrodes) than the parent material depending on the application of the welded structures and the availability of the filler material. In the present investigation, the fatigue crack growth behaviour of under matched (UM), equal matched (EM) and over matched (OM) weld metals has been studied. The base material used in this investigation is HSLA-80 steel of weldable grade. Shielded Metal Arc Welding (SMAW) process has been used to fabricate the single “V” butt joints. Centre cracked tension (CCT) specimen has been used to evaluate the fatigue crack growth behaviour of the welded joints. Fatigue crack growth experiments have been conducted using servo hydraulic controlled fatigue testing machine at constant amplitude loading ( R=0). Effect of mis-match ratio (MMR) on fatigue crack growth behaviour of HSLA steel welds has been analysed in detail.

Temperature, macrostructure and hardness in high strength low alloy steel welds

A series of welds have been fabricated in high strength low alloy steel (HSLA100) plate by gas metal arc welding at heat inputs of 1.0, 1.6 and 2.2 kJ mm-1. Slices from the welds were then polished and the macrostructure was observed. Hardness maps were then determined over the entire weld zone, including the heat affected zone and the base plate. Correlations were then made between the hardness maps and the macrostructure. A bead on plate weld was made using the same heat inputs and was used to determine the temperature regimes in the weld as well as thermal profiles of the weld region. Relationships showing good correlations were observed between the various microstructures, the macrostructure, the calculated thermal profiles, and the hardness values.

Analysis of the unstable fracture behaviour of a high strength low alloy steel weldment

Local brittle zones (LBZ) cause the unstable fracture behaviour of weld metals. This threatens the safe service of welded structures and makes structural assessment procedures difficult. Therefore, the unstable fracture behaviour of an overmatched high strength low alloyed steel weldment was experimentally investigated. It showed that any interaction between two adjacent weld metal matrix and soft weld metal inclusions produces LBZ, causing local unstable fracture behaviour. The formation of a low hardness region is attributed to the multipass welding reheating process between Ac 1 and the self-tempering temperature. The presence of partly solid metallic inclusions with a high content of alloying elements and pro-eutectoid ferrite microstructure were found to be additional causes for the local unstable fracture behaviour of the weld metal. Local strength mis-match induced the yielding and strain hardening in the soft weld metal inclusions, contributing significantly to unstable fracture behaviour. Thus, a significantly different scatter of experimental results can be obtained. In the cases of specimens with through-the-thickness crack, not only is the scatter significantly lower, but the toughness itself.

Performance of Welded High-Strength Low-Alloy Steels in Sour Environments

Sulfide stress cracking (SSC) susceptibility of gas metal arc welded API 5L X70 and X80 line pipe steel was tested using standard and modified NACE TM0177 (Method A) testing. Two applied stresses and three concentrations of dissolved hydrogen sulfide (H2S) were used. The effect of peak weld hardness was examined by using three weld conditions. Sev- eral welds meeting the HRC 22 requirement failed by SSC. Welds containing hardness exceeding 248 HV were resistant to SSC at low H2S concentrations. The centerline segregation region (CSR) observed in the X70 pipe steel played an impor- tant role in the SSC and hydrogen-induced cracking (HIC) susceptibility of the welds. The X80 material was more sus- ceptible at lower hardness values due to localized softening during welding, and subsequent plastic deformation upon loading. An extrapolation to in-service weldments indicated that the NACE MR0175 requirements may be conservative for high-strength low-alloy steel welds not in direct contact with the sour environment.

528 低合金鋼溶接熱影響部の微視クリープ損傷進展の評価

528 低合金鋼溶接熱影響部の微視クリープ損傷進展の評価

OS12W0391 Advanced creep damage analysis of low-alloy steel welds considering the microscopic damage progress

OS12W0391 Advanced creep damage analysis of low-alloy steel welds considering the microscopic damage progress

In situ observations of non–equilibrium austenite formation during weld solidification of an Fe–C–Al–Mn low–alloy steel

The microstructure and properties of a welded alloy are influenced by the combined effects of solidification and subsequent solid–state transformations that occur during weld cooling. These phase transformations are further influenced by the cooling rate that the weld experiences and thus by the type of welding process that is used. In this research, microstructure development of a low–alloy steel weld was investigated under the high cooling rates produced by stationary arc welds. These welding conditions are different from the slow weld–cooling conditions, where δ–ferrite forms as the primary solidification phase. The cooling rates of the stationary welds used in this study were of the order of 10 3 K s –1 , which were high enough to induce the formation of the non–equilibrium austenite phase during solidification. This non–equilibrium mode of solidification was directly observed using an in situ time–resolved X–ray diffraction technique using synchrotron radiation, and the resulting microstructures were examined using optical microscopy.

Inclusion Formation and Microstructure Evolution in Low Alloy Steel Welds.

The paper presents an overview of research performed at Oak Ridge National Laboratory on inclusion-formation, weld-solidification, and solid-state transformations in low-alloy steel welds. The competition between oxide and nitride formation in Fe-C-Al-Mn self-shielded flux-cored arc steel welds was predicted using computational thermodynamics. Nonequilibrium austenite phase selection was monitored in a Fe-C-Al-Mn weld using an in situ time-resolved X-ray diffraction technique. The competition between acicular ferrite and bainite formation from austenite was evaluated in Fe-C-Mn steel welds containing small amounts of titanium.

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.