Composition Of Weld Metal Research Articles

The Influence of Alloy Composition on Microstructure and Performance of Mixed-Smelting Alloy and Weld Metal.

In the present work, the Q345B low-alloy steel with different contents and ER309L stainless steel were melted together to obtain new alloys. The aim was to design the composition of weld metal (Q345B low-alloy steel as the base material and ER309L welding wire as the filler material) and improve the corrosion resistance of the weld metal. During the welding process, the composition of the weld metal was controlled to match the new alloys by changing the welding heat input. A relationship curve between fusion ration and welding heat input was obtained. The research focused on analyzing the effect of mixed-smelting ratio between Q345B and ER309L and welding heat input on the microscopic structure and corrosion performance of the prepared samples. The results show that the melted alloys containing 20% to 30% Q345B consist of a ferrite (δ) phase and austenite (A) phase, the samples containing 45% to 50% Q345B consist of a martensite (M) phase and austenite (A) phase, and the sample containing 40% Q345B consists of a martensite (M) phase, ferrite (δ) phase, and austenite (A) phase. As the mixed-smelting ratio of Q345B/ER309L increased, the corrosion resistance of samples decreased gradually. For the weld metal, the fusion ration between Q345B base material and ER309L welding wire increases with the welding heat input. When the heat input changed from 0.645 kJ/mm to 2.860 kJ/mm, the composition of the weld metal was consistent with the melted alloys containing 20-45% Q345B. The microstructure and corrosion resistance of the weld metal could be designed by the melting means, which has important guiding significance for engineering applications.

Timed Thermodynamic Process Model Applied to Submerged Arc Welding Modified by Aluminium-Assisted Metal Powder Alloying

An EERZ (effective equilibrium reaction zone) model was applied to the modified SAW (submerged arc welding) process to simulate the SAW process metallurgy in the gas-slag-metal reaction system. The SAW process was modified by adding Al as a de-oxidizer with alloying metal powders of Cr, Cu, and Ti. The static gas-slag-metal equilibrium model can accurately calculate the weld metal oxygen content (ppm O) for conventional SAW but not for the modified SAW process. The static equilibrium model overpredicts the reaction of Al. EERZ model runs were made for 2000–2500°C because this is the reported temperature range in the SAW arc cavity. The weld metal composition was adequately calculated, especially the weld metal ppm O, at the following effective equilibrium temperatures: 2400°C for Al-Cr additions, 2200°C for Al-Cr-Cu additions, and 2000°C for Al-Cr-Cu-Ti additions. Model results show that Ti metal powder can serve a de-oxidizer role in the presence of Al, resulting in Ti loss to the slag. Ti is also lost to the gas phase as TiF3(g) and TiF2(g) compared to little loss of Cr to the gas phase as Cr(g) and CrO to the slag phase.

Assessment of fatigue crack growth resistance of newly developed LTT alloy composition for the repair of high strength steel structures

Tensile residual stress (TRS) is a well-known factor that deteriorate the integrity of welded joints. Fatigue failure is accelerated by the existence of TRS introduced during the welding process. There have been efforts in the last two decades to develop filler alloys that can reduce TRS by introducing compressive residual stress (CRS) to oppose the TRS in high strength steel welded joints. These works are based on the theory of austenite (γ) to martensite (α’) transformation and the filler is often called a low transformation-temperature (LTT) alloy. Many studies have reported that the fatigue strength (FS) of weld joint made with LTT alloy is many times better than that of the conventional fillers. It is reported to be particularly useful in the repair of high strength steel structures. However, studies on the fatigue crack growth (FCG) behaviour of these LTT alloys is scarce. In this work, we developed Fe-CrNiMo based LTT weld metal composition, assessed its FCG behaviour and compared the results with that of a conventional welding wire (ER70S-6). It is found that ER70S-6 weld metal obtained under relatively fast cooling is extremely tough, but the associated heat affected zone (HAZ) has poor resistance to FCG which obscured the benefit of the tough weld metal. High heat input or condition that results to slow cooling of the ER70S-6 weldment deteriorates its resistance to FCG. Unfortunately, despite its low martensite start temperature of 231±7 and the anticipated beneficial effect of induced CRS, the LTT alloy studied had the lowest FCG resistance. The LTT alloy appears to have an intrinsic microstructural feature or a ‘fault line’ that reduced its resistance to FCG. While the LTT alloy weld metal has poor resistance to FCG, the associated HAZ resisted FCG more than the HAZ associated with ER70S-6 weld metal. It is observed that aligning the ER70S-6 weld metal perpendicular to the crack front produced the highest resistance to fatigue crack initiation and propagation. In the case of ER70S-6, it is believed that the weld metal induced a CRS at the notch tip which resulted to the high fatigue resistance. In the case of the LTT alloy, perpendicular alignment of the weld metal produced slight improvement.

Comments on the Numerical Models for Correlating Weld Metal Composition to Microstructure and Properties

There has been a steady rise in the use of computational tools to model or describe weld microstructure and properties from data sets containing a wide range of inputs and outputs measured by experiments. The tools range in sophistication from simple two-factor correlations in spreadsheets to artificial neural networks.

Effect of shielding gas on MIG welding performance with austenitic wire

Two different shielding gases, Ar + CO2 and Ar + He + N2, were used for MIG welding of a 20 mm 10CrNi3MoV steel plate. The effects of shielding gases on the chemical composition, microstructure, purity, and low-temperature impact toughness of weld metal were studied in detail. N-containing shielding gas can increase the nitrogen content in the weld metal, change the solidification mode of deposited metal, reduce ferrite content in the weld metal, and significantly improve the low-temperature impact toughness of deposited metal. The purity of weld in the ternary inert gas atmosphere is high, which is beneficial to the improvement of low-temperature toughness. The ferrite content of the ternary joint is higher than that of the binary joint, and the strength of the ternary joint is much higher than that of the binary joint.

Metallurgical and mechanical properties of hydrogen charged carbide-free bainitic weld metals

Hydrogen embrittlement is a major concern during the welding of high-strength steels. The susceptibility of the welds to hydrogen embrittlement increases with increase in weld strength. The ever-increasing demand to increase the strength of steels necessitates the development of novel welding procedures and fillers to produce welds of high strength and with resistance to hydrogen embrittlement. In this current work, the susceptibility of carbide-free bainitic weld metals to hydrogen embrittlement is studied with varying volume fractions of constituent phases. Using three different weld metal compositions, six different weld metal microstructures of carbide-free bainite were generated. The hydrogen saturation behaviour of the various weld metals was studied by cathodic electrolytic charging and subsequent diffusible hydrogen measurements by the hot extraction method. Tensile tests were conducted on various weld metals with and without hydrogen charging to evaluate their susceptibility to hydrogen embrittlement. The results show that the carbide-free bainite weld metals are highly resistant to hydrogen embrittlement despite their very high strength.

Upgrading the prediction model for Mn content in submerged arc welded metal via CALPHAD technology: Case study into typical acidic and basic fluxes

Fluxes (the granular materials containing oxides and CaF2) serve vital functions with respect to atmospheric shielding, arc stabilization, and weld metal composition control during the submerged arc welding process. Mn content must be carefully controlled since it dictates the toughness of the weldment. The slag-metal equilibrium model has been applied for decades to predict the Mn content in submerged arc welded metal, although there are several limitations regarding its application. With the aim of compensating for the limitations of the slag-metal equilibrium model, this study has been undertaken to upgrade the slag-metal equilibrium model to the gas-slag-metal equilibrium model via CALPHAD technology. Then, the Mn content in the weld metal is predicted by using both slag-metal and gas-slag-metal equilibrium models for typical acidic and basic fluxes. The capabilities of the models to predict Mn content is evaluated from the perspective of thermodynamics. It is concluded that the gas-slag-metal equilibrium model, which is independent of the basicity index model, possesses higher prediction accuracy than the slag-metal equilibrium model. Furthermore, the transfer direction of Mn, as well as Mn content are predictable even when no MnO is contained in the initial flux. Based on the measured and thermodynamic data, the mechanisms pertinent to Mn transfer in the welding process have been interpreted, and the limitations of the gas-slag-metal equilibrium model have been summarized.

Probing Element Transfer Behavior during the Submerged Arc Welding Process for CaF2-SiO2-Na2O-Cr2O3 Agglomerated Fluxes: A Thermodynamic Approach

Submerged arc welding joins metal by the heating of the electrode, base metal, and flux in the arc plasma, while the weld pool is protected under the granular flux and molten slag. Due to complex chemical reactions occurring between the arc plasma, weld pool, and molten slag (flux), flux essentially affects the weld metal composition, which, in turn, dictates the mechanical properties of the weldment. Therefore, fine-tuning the weld metal composition is essential to ensure a sound weld, and efforts worldwide have been focused on the control mechanism of flux on the weld metal composition. Recently, agglomerated fluxes have been widely applied due to low energy consumption during manufacture. The Cr2O3-bearing agglomerated flux is one of the most commonly used flux types in fields of heavy industrial applications. However, few works concern the element transfer behavior when Cr2O3-bearing agglomerated fluxes are used. Within this framework, typical agglomerated CaF2-SiO2-Na2O-Cr2O3 fluxes with varying Cr2O3 content from 10 to 50 wt.% are designed and applied to Q345A steel. The influence of Cr2O3 content upon the transfer behaviors of essential elements, including O, Cr, and Mn, is quantified and interpreted from the point of thermodynamics. By incorporating a gas-slag-metal equilibrium consideration, the assumptions made in previous studies are justified. Additionally, evidence regarding the loss of Cr and Mn to the arc plasma is provided, and a possible thermodynamic approach to predict element transfer levels is proposed. It is revealed that the gas-slag-metal equilibrium consideration is able to qualitatively analyze the transfer behaviors involved in the submerged arc welding system, even under high temperatures. Based on the quantitative data, the practical implications as well as limitations of the gas-slag-metal equilibrium model are proposed.

Element Transfer Behavior for CaF2-Na2O-SiO2 Agglomerated Flux Subject in Submerged Arc Welding Process

From a thermodynamic perspective, the present study has been performed to investigate the effect of SiO2 level in agglomerated fluxes on the element transfer behavior of essential elements, by applying CaF2-Na2O-SiO2 agglomerated fluxes with varying SiO2 contents. Element transfer behavior is quantified by the Δ value. The impact of SiO2 and heat input upon element transfer behavior is interpreted. Additionally, a possible thermodynamic approach to predict high basicity flux O potential and weld metal composition is proposed and evaluated. It is revealed that the consideration of the gas-slag-metal equilibrium is able to place constraints on the transfer behaviors (of O, Si, and Mn) and formation of gases. In submerged arc welding metallurgy, the empirically determined basicity index models proposed by Tuliani have been applied for more than 50 years to predict flux O potential and weld metal oxygen content. However, it is well known by welding practitioners that the flux basicity index model can only predict the changing trend of flux O potential when the flux basicity index is lower than 2.0. The present study has proposed a new thermodynamic method to identify the flux O potential for fluxes with a basicity index higher than 2.0. Additionally, the experimental evidence for the Mitra kinetic model has been provided.

Understanding the role of Ti addition on the corrosion and passive film characteristics of Nb stabilized AISI 347 weld

AbstractA multipass multilayer weld pad was fabricated on AISI 347 base metal with filler combinations of AISI 321 and AISI 347, to understand the role of Ti addition on metallurgical, corrosion, and passive film characteristics of the AISI 347 weld. Weld layers with Nb content of 0.53 wt.%, 0.47 wt.%, 0.23 wt.% and Ti of 0 wt.%, 0.21 wt.%, 0.33 wt.%, respectively, were extracted from fabricated weld pad. Selected weld metal compositions were subjected to thermal aging at 750°C for 24 h to investigate the influence of varying precipitation induced in these welds. Ti addition in AISI 347 weld showed lower enrichment of C and Cr at dendritic regions resulting in reduced Cr depletion, lower sensitization, enhanced pitting potential, and repassivation ability compared to conventional Nb stabilized AISI 347 weld. Passive film characteristics studied by electrochemical impedance spectroscopy and X‐ray photoelectron spectroscopy depicted formation of more protective, and dense passive film with higher Cr, Ni, and O concentrations for Ti added AISI 347 weld relative to conventional ones. Therefore, Ti addition via the use of Ti stabilized filler in the Nb stabilized AISI 347 weld proved to be efficient in enhancing its corrosion performance by forming a more protective passive oxide film.

Mathematical modeling to predict the weld dilution in FCA welding of stainless steel 301 plates

Flux-cored arc welding (FCAW) is a type of arc welding that employs a constantly supplied consumable tubular electrode that is loaded with a suitable flux. FCAW is gaining popularity as a method of producing high-quality welds for metals such as structural steel, and nickel-based alloys, which are extensively used in industry. Dilution is defined as the change in weld metal composition induced by mixing of the base metal or previously placed weld metal. The current paper analyses the influence of (FCAW) process factors such as welding voltage, wire feed rate, and welding speed on the weld dilution of 301 austenitic stainless steel plates. An attempt is made to build a mathematical relationship between the input parameters and the response parameters, which in this instance is dilution. The statistical technique of design of experiments is used to conduct the studies in a systematic manner. A central composite face-centered approach was used to create the mathematical model. ANOVA was used to evaluate the model's adequacy, and the results were examined using graphical representations.

Application of Copper as Stabiliser in Aluminium Assisted Transfer of Titanium in Submerged Arc Welding of Carbon Steel

The element transfer of Ti from molten flux to the weld metal is limited to less than 310 ppm Ti in the submerged arc welding of carbon steel. This limitation is due to the high oxygen partial pressure prevailing at the molten flux-weld pool interface. Our previous study illustrated that the use of Al powder in combination with Ti powder improves the transfer of Ti to the weld metal to 4% Ti, whilst maintaining 509 ppm O in the weld metal. The weld metal ppm O should be controlled at 200 to 500 ppm O to maintain weld metal toughness. In this study, the addition of Cu powder with Ti and Al powder is applied to illustrate the stabiliser effect of Cu in the weld pool. The role of Cu as weld pool stabiliser is due to its decrease of the temperature required to melt Ti into the weld pool, so increasing the quantity of metal powder melted into the weld pool. The weld metal composition improved to 5.1% Ti, 3.6% Cu, and 371 ppm O. Thus, the role of Al in controlling the partial oxygen pressure at the molten flux-weld pool interface is maintained in the presence of Cu powder.

Fine-Tuning Weld Metal Compositions via Flux Optimization in Submerged Arc Welding: An Overview

Fine-Tuning Weld Metal Compositions via Flux Optimization in Submerged Arc Welding: An Overview

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.

Recycling of steel slag as a flux for submerged arc welding and its effects on chemistry and performance of welds

The slag generated by the steel plant has been utilized to produce submerged arc welding flux. The flux produced by recycling steel slag has been applied in the submerged arc welding process. The effects of recycled slag on the chemical composition, microhardness, and microstructure of weld metal have been evaluated. For chemical composition, weld pads were prepared and beads on plates for bead geometry were deposited. It has been found that the chemistry of welds deposited using recycled steel slag is acceptable in accordance with ASME specifications. It is further observed that the addition of 10% CaCO3, 20% SiO2, and 6% MnO to the steel slag during recycling provided 0.10% carbon, 0.11% Si, and 0.8% Mn, respectively, in the weld metal. The microstructure of welds produced using recycled steel slag contains acicular ferrite which is desirable for improved tensile and impact strength. The microhardness of weld metal prepared using recycled steel slag is 220.9 VHN, which is more than that of weld metal deposited with fresh flux. Smooth surface appearance and desirable bead profile having deeper penetration were obtained. It is interesting to note that the cost of recycled steel slag is economical by 62% in comparison with equivalent virgin flux available in the market. The developed technology after fine-tuning will be transferred to the industry for practical applications.

The effect of flux chemistry on element transfer in Submerged Arc Welding: application of thermochemical modelling

Post-weld slag and weld metal analyses were used to interpret the effects of different commercial flux compositions on element transfer between molten flux (slag) and weld metal in Submerged Arc Welding (SAW). Selected fluoride based flux compositions cover a wide range of basicity index (BI) values of 0.5–3.0. Thermochemical modelling in FactSage software is used to simulate the welding process in terms of gas-slag-metal equilibria. The importance of the gas phase in SAW element transfer is illustrated. The model provides improved accuracy in predicted weld metal oxygen values (ppm O) compared to the generally used empirical relationship of weld metal ppm O vs. flux BI. Model predicted oxygen values are within 150 ppm of the analysed values, compared to the empirical relationship values which are within 240 ppm from the analysed values. The model provides resolution in ppm O values at BI > 1.8. This information is lacking in the empirical relationship with constant ppm O of 250 ppm at BI > 1.8. The measured ppm O values follow the Fe–FeO equilibrium trend with a positive offset. The relative level of oxygen to deoxidation elements (Ti, Al, Mn, Si) in the weld metal is an important factor in oxide inclusion engineering. This model will aid in the specification of flux formulations to attain specific weld metal compositions for maximum acicular ferrite formation. In this way the weld metal mechanical properties can be improved. This model will reduce the number of welding tests required to develop new flux formulations.

Assessment of the chemical composition of LTT fillers on residual stresses, microstructure, and mechanical properties of 410 AISI welded joints

The present paper aims to characterize the welding residual stresses, microstructure, and mechanical properties of some AISI 410 plates welded with low-transformation temperature (LTT) fillers containing different Ni wt.%. The LTT fillers with 11 wt.% Cr and Ni content varying between 3 and 11 wt.% were produced using an arc melting furnace. Effect of Ni wt.% on Ms of LTT fillers was studied using a dilatometer. Five-millimeter-thick AISI 410 plates were welded by GTAW using LTT fillers mentioned above and ER410 conventional filler as a reference. Welding residual stresses were measured by using the hole drilling strain gage method (HDSG). Analyzing the effect of welding dilution on the chemical composition of weld metal was carried out using energy-dispersive X-ray spectroscopy (EDS) followed by a dilatometric test for the evaluation of weld metals Ms after welding. Microstructural examinations show that conventional filler leads to ferritic–martensitic weld metal while in the cases welded with LTT fillers, delta ferrite (δ-ferrite) is decreased when Ni increases. Also, by increasing Ni more than 9 wt.%, the retained austenite is detected in the weld metal. Furthermore, weld metal hardness rises with increasing Ni. Performing tensile and impact tests on welded joints endorse the successful use of LTT fillers for welding the AISI 410 plates.

Effect of weld metal composition on impact toughness properties of shielded metal arc welded ultra-high hard armor steel joints

Abstract Nowadays, ultra-high hard armor (UHA) steels are employed in armor tracked vehicle (ATV) construction because of their high hardness, high strength to weight ratio, and excellent toughness. UHA steels are usually welded using austenitic stainless steel (ASS) welding consumables, to avoid hydrogen-induced cracking (HIC). The use of ASS consumables to weld the above steel was the only available remedy because of higher solubility of hydrogen in the austenitic phase. In this investigation, an attempt was made to investigate the effect of ASS consumables (with different Cr eq /Ni eq ratio) on solidification mode, impact toughness and microstructural characteristics of shielded metal arc (SMA) welded UHA steel joints. The welded joints were characterised based on impact toughness properties, hardness, and microstructural features. As the ferrite number increases with an increase in Cr eq /Ni eq ratio result in different solidification mode (A, FA, F). It is also found that ferrite number of weld metal has appreciable influence on impact toughness and has inversely proportional relationship with impact toughness of the welded joints.

Effect of Disk Laser Beam Offset on the Microstructure and Mechanical Properties of Copper—AISI 304 Stainless Steel Dissimilar Metals Joints

Deoxidized oxygen free copper C12200, 1 mm in thickness, was welded to 1-mm thick AISI 304 stainless steel with disk laser. The butt-welded joints were produced with different welding parameters. Full factorial design of experiment (DoE) approach consisting of three factors and two levels was utilized. Laser powers used for welding were 1.3 and 1.9 kW and welding speeds of 20 and 30 mm/s. Two beam offsets were tested, namely, 100 μm toward copper side and 200 μm toward AISI 304 steel. It was found that beam offset possesses the largest influence on the welded joints’ tensile strength. Tensile strengths attained values more than 3.7 times higher in comparison to the AISI 304 steel beam offset. When lower laser power was used, the higher tensile strength was attained for copper sheet offset. Higher microhardness was observed when laser beam was offset to AISI 304 steel side. The average microhardness of the weld metal was higher than that of the weaker base material, copper sheet. Energy dispersive X-ray spectroscopy (EDS) analysis confirmed the heterogeneity in elemental composition across the welded joint interface, being lower when laser beam was offset to AISI 304 steel side. On the other hand, the copper content dropped to the average composition of weld metal at the distance of about 140 μm from copper-weld metal interface.

The Effects of TIG Welding Rod Compositions on Phase Distributions and Corrosion Properties of Dissimilar 304L and 420 Stainless Steel Welds

304L austenitic and 420 martensitic stainless steels are demanded in wide range of industries. 304L alloy exhibits good resistance to oxidizing medias up to 760°C and they also maintain superior impact properties at cryogenic temperatures while 420 alloy provides the strength values close to tool steels in with satisfactory corrosion properties in ambient atmospheres. In this work; 420 plate is TIG (Tungsten Inert Gas) welded with 304L plate with both thicknesses of 3 mm. Welding operation is applied by two passes under pure argon gas also with shielding the weld root. 3 types of TIG welding rods; ER312, ER316L and ER2209 are used in TIG welding for ensuring 3 different weld metal compositions. The effects of TIG welding rod type on weld metal phase ratios with microstructural and corrosion properties are investigated. Microstructural inspections and corrosion (weight loss) tests are applied to all joints after welding operations. The sample joined by ER312 TIG rod transformed the weld metal into dendritic microstructure and the sample joined by ER2209 TIG rod resulted in globular type of weld metal microstructure. The specimen that welded by ER316L type TIG welding rod resulted in the best corrosion test values among all welded samples.