Steel Welding Process Research Articles

Corrosion behaviors according to the welding process of superduplex stainless steel welded tubes: Gas tungsten arc welding vs. laser beam welding

The corrosion behaviors of superduplex stainless steel welded tubes in an acidic brine environment were examined by comparing the welds formed by the two welding processes of tungsten inert gas (TIG) welding and laser beam (LB) welding. In contrast to TIG-welds with a larger bead size, higher oxide inclusion, and lower N content, the poor corrosion resistance of as-welded LB-weld sample recovered after post-weld heat treatment (PWHT) by restoring the phase balance and dissolving the deleterious inhomogeneities around the fusion line. The key metallurgical factor controlling the corrosion behavior of LB-welded steel tubes, and underlying corrosion mechanism were also provided.

Element diffusion and microstructure evolution at interface of stainless steel/Ti alloy joint by laser welding with AgCuTi filler metal

Joining of 304 stainless steel and TC4 titanium alloy was of great interest for applications in the marine, and aerospace fields. However, the direct welding process of steel and titanium will generate a large number of brittle Ti–Fe intermetallic compounds results in crack in joint. In this study, in order to avoid the formation of Ti–Fe intermetallic compounds, the connection between stainless steel and titanium alloy is successfully realized by adding AgCuTi filler metal. A section of unmelted stainless steel was retained by laser offset welding, and the filler was diffusion bonding with the base metals on both sides by heat conduction, ensuring that the filler was not melted. Since Fe and Cu elements have high solid solubility in liquid state, so the stainless steel and filler interface formed a good connection. There was no Ti–Fe intermetallic compounds found in the joint, and Ti2Cu and AgTi2 intermetallic compounds with better ductility was formed at the filler-TC4 interface. In order to further explore the element diffusion distribution at the interface of the joint. The temperature distribution model in the fusion zone was established, and obtained the temperature field of the joint. The diffusion coefficients of Fe, Cu and Ti elements were calculated by Arrehenius formula. It was verified that the diffusion of Ti elements in the filler resulted in the aggregation of Ti elements at the filler-TC4 interface. The microstructure mechanism for formation of the brazed weld was proposed.

Investigation on residual stress of EQ56 high strength steel butt weld

In the welding process of high-strength steel (HSS), the intense temperature change in joints induces the formation of welding residual stress (WRS), which increases the fatigue crack growth rate. Developing an effective finite element (FE) model for accurately predicting the WRS distribution is critical to improve the quality of welded structures. Experimental tests and numerical simulations were carried out to investigate the WRS distribution of EQ56 HSS. The thermal expansion curves at various heating and cooling rates were measured through thermal simulation experiments for achieving the continuous cooling transformation (CCT) diagram of EQ56 HSS. Based on the CCT diagram, the thermo-metallurgical-mechanical (TMM) FE model was developed to consider the influence of solid-state phase transformation (SSPT) on distribution and magnitude of WRS for welded EQ56 HSS joints, as well as material hardening law. Comparison of predicted WRS distribution and experimental data shows that plastic hardening laws of materials significantly affect the precision of WRS distribution, and combined hardening law gives most reliable prediction. The FE model considering SSPT behavior provides more accurate estimation of WRS distribution than those without considering SSPT behavior.

Analisis Kekuatan Tarik Sambungan Plat Stainless Steel 316L pada Proses Spot Welding

This study aims to determine the effect of variations in welding current and distance on the strength of the weld on 316L stainless steel material through a tensile test. The type of research method and data collection will begin through the welding process of eighteen pairs of stainless steel plates using spot welding. Welding will be carried out with variations in the current and distance of the welding points. After carrying out the stainless steel welding process, a tensile test will then be carried out to determine the effect of current variations and the distance of the welding points on the strength of the welded joints in stainless steel. Based on the results of the test data obtained, it shows that a voltage of 1.75 V produces an electric power of 6317.88 Watts and a voltage of 2.20 V produces an electric power of 9249.93 Watts with a constant welding time of 2 seconds. The highest tensile strength is specimen D with a spacing of 10 mm and a voltage of 2.20 V, which is 14,765 N, while the lowest tensile strength is specimen C with a spacing of 30 mm and a voltage of 1.75 V, which is 10,224 N. At a current voltage of 1.75 Volts, the welding distance is 20 mm produced is 3490.17 Mpa and a current voltage of 2.20 Volts 20 mm welding distance produced is 3682.33 Mpa the results obtained the greater the current used, the greater the resulting tensile strength. The value of the elastic modulus is inversely proportional to the current strength and welding distance. This can be shown in the results of the tensile strength test data obtained, namely specimens with a current of 1.75 volts with a welding distance of 10 mm have a greater modulus value than specimens with a current of 2.20 volts with a welding distance of 10 mm.

The Microstructure Prediction during the Welding Process of Fe–C–Si Steel Using Physical and Numerical Simulation: A Comparative Study

Overall, medium‐carbon, multiphase steels subjected to welding processes can be described as difficult and require dedicated process conditions. In these investigations, an attempt is made to characterize the welding process of commercial 55Si7 steel with a high carbon equivalent (CE = 0.73). An experimental tungsten inert gas (TIG) welding process is performed by the use of preheating. Then, to understand and explain the processes during welding, a numerical (finite element method [FEM]) and physical (dilatometry) simulation is carried out. Measurement points located in the heat‐affected zone (HAZ) are selected based on the obtained data of thermal cycles. Significant differences in the results obtained with the three approaches are assessed and indicated. The cause of the discrepancies in the test results is also identified. The essence of the implementation of material data, which precisely defines the kinetics of phase transformation, is confirmed. A detailed analysis of the contribution of the phases is performed, together with their morphological assessment, as well as the hardness distributions are conscientiously compared. Moreover, it seems that the segregation of the chemical composition of austenite and the initial microstructure plays a crucial role in terms of the quality of the prediction.

Effect of the current waveform on the droplet transfer in CMT welding high-nitrogen steel

During the welding process of high-nitrogen steel, droplet bursts often occurs, which is caused by the escape of nitrogen. To analyze the influence of the current waveform on the cold metal transfer (CMT) welding process of high-nitrogen steel, a high-speed camera and current and voltage sensors were used to establish a simultaneous acquisition system for droplet transfer visualization and electrical parameter waveform monitoring. In this way, the characteristics of the droplet transfer behavior of the high-nitrogen steel CMT welding process were analyzed. The results showed that the solubility of nitrogen in the droplet decreased as the energy input rose, causing nitrogen to escape in the form of bubbles. When the pressure difference inside and outside of the droplet was greater than the surface tension, droplet cracking occurred. In the CMT welding process of high-nitrogen steel, the peak stage of the current waveform had a relatively high influence on droplet transfer. The condition of stable droplet transfer was that the peak phase current was 100–150 A, the time was 4.55–6 ms, and the maximum energy input in the peak stage was 15.5 J per CMT cycle. The current in the waiting phase, which was under 100 A, did not affect the droplet transfer behavior but did affect the shape of the molten pool. The increase in the peak wire feed speed reduced the CMT cycle time, but had little effect on droplet transfer.

Finite element modelling and experimental validation of microstructural changes and hardness variation during gas metal arc welding of AISI 441 ferritic stainless steel

Grain growth and hardness variation occurring in high-temperature heat affected zone (HAZ) during the welding processes are two thermal dependant aspects of great interest for both academic and industrial research activities. This paper presents an innovative finite element (FE) model capable to describe the grain growth and the hardness decrease that occur during the gas metal arc welding (GMAW) of commercial AISI 441 steel. The commercial FE software SFTC DEFORM-3D™ was used to simulate the GMAW process, and a user subroutine was developed including a physical based model and the Hall–Petch (H-P) equation to predict grain size variation and hardness change. The model was validated by comparison with the experimental results showing its reliability in predicting important welding characteristics temperature dependant. The study provides an accurate numerical model (i.e. user subroutine, heat source fitting, geometry) able to successfully predict the thermal phenomena (i.e. coarsening of the grains and hardening decrease) that occur in the HAZ during welding process of ferritic stainless steel.

Holding Time pada Sifat Fisik Pengelasan SMAW Baja ASTM-A36 melalui Uji Penetran

In the industrialized world, low-carbon steel was often used as a construction material. One of the problems obtained in the low carbon steel welding process was its nature susceptible to shakes. The minimize the formation of residual voltage in the connection area (Heat Affected Zone) can be done by the Post Weld Heat Treatment (PWHT) process The purpose of this study was to find out the effect caused by variations in heat treatment on heating steel ASTM A36 (Holding Time) to penetrant tests and determine the suitable temperature given to ASTM A36 steel after the welding process. The PWHT process was carried out with several variations of Holding Time, namely 1 hour, 2 hours, and 3 hours at 400 °C. Based on penetrant testing showed that the best value in Holding Time was 3 hours with no appearance of porosity defects

Effect of electron beam welding parameters on temperature and stress field of AISI P20 tool steel in vacuum roll-cladding process

Vacuum roll-cladding (VRC) is an effective method to produce high-quality ultra-heavy AISI P20 plate steel. In the process of VRC, reasonable welding process of electron beam welding (EBW) can significantly avoid welding cracks and reduce the cost. In this paper, the electron beam welding process of AISI P20 tool steel was simulated by using a combined heat source model based on finite element method, and the temperature field and stress field under different welding parameters were studied respectively. The results showed that welding parameters have a greater effect on weld penetration than that of weld width, making the aspect ratio increases with the increase of welding current, and decrease with the increase of welding speed. The weld morphologies were consistent with those of the modeling, and the measured thermal heat curves were in good agreement with those of simulated, which verified the feasibility and effectiveness of temperature fields. The results of stress fields under different welding parameters indicated that welding speed of 300mm/min and welding current of 60mA result in lower residual stress at welded joint, which means lower risk of cracking after EBW. The results of this study have been successfully applied to industrial production.

Prediction of HAZ Microstructure and Hardness for Q960E Joints Welded by Triple-Wire GMAW Based on Thermal and Numerical Simulation.

Since heat affected zone (HAZ) is the weak area of welded joints, this article proposes a method to predict the HAZ microstructure and hardness for the triple-wire gas metal arc welding (GMAW) process of Q960E high strength steel. This method combines welding thermal simulation and numerical simulation. The microstructures and hardness of Q960E steel under different cooling rates were obtained by thermal simulation and presented in a simulated HAZ continuous cooling transformation (SH-CCT) diagram. The cooling rate in HAZ were obtained by numerical simulation with ANSYS software for the triple-wire welding of Q960E thick plates. By comparing the cooling rate with the SH-CCT diagram, the microstructure and hardness of the HAZ coarse-grained region were accurately predicted for multiple heat input conditions. Further, an ideal heat input was chosen by checking the prediction results. This prediction method not only helps us to optimize the welding parameters, but also leads to an overall understanding of the process-microstructure-performance for a complex welding process.

A Study on Determining Weld Joint Hardening and a Quality Evaluation Algorithm for 9% Nickel Weld Joints Using the Dilution Ratio of the Base Material in Fiber Laser Welding

The demand for LNG-powered ships and related equipment is rapidly increasing among major domestic and foreign carriers due to the strengthened IMO regulations on the sulfur content of ship fuel oil. LNG operation in a cryogenic environment requires a storage tank and fuel supply system that uses steel with excellent brittleness and fatigue strength. A ship using LNG is very sensitive to explosion and fire. For this reason, 9% Ni is often used, because ships require high quality products with special materials and structural technologies that ensure operability at cryogenic temperatures. However, research to derive uniform welding quality is urgent because the deterioration of weld quality in the 9% Ni steel welding process is caused by high process difficulty and differences in welding quality depending on a welder’s skill set. This study proposes a method to guarantee a uniform quality of 9% Ni steel in a fiber laser welding process by categorizing weld joint hardness according to the dilution ratio of a base material and establishing a standard for quantitative evaluation.

A Study on the Weldment Hardening Discrimination Procedure and Improvement of Flux Cored Arc Welding Process of ASTM A553-1 (9% Nickel Steel) Material Using Bead Geometry Distribution

As a result of strengthened sulfur content standards for ship fuel oil in IMO regulations, major domestic and foreign carriers have a high and growing demand for liquefied natural gas (LNG) powered ships and related equipment. For LNG operation in a cryogenic environment, a storage tank and fuel supply system that uses steel with excellent brittleness and fatigue strength is required. Ships that use LNG have a high vulnerability to explosion and fire. For this reason, 9% Ni is typically used, since a ship requires high quality products with special materials and structural technologies that guarantee operability at cryogenic temperatures. However, there is an urgent need for research to derive a uniform welding quality, since high process difficulty and differences in welding quality related to a welder’s skills can cause a deterioration of the weld quality in the 9% Ni steel welding process. For 9% Ni steel, the higher the dilution ratio of the base metal, the lower the strength. In order to secure the required strength, excessive dilution of the base metal should be avoided, and the relationship between dilution ratio and strength should be investigated. According to previous research, if it exceeds 25% it may be lower than the API standard of 363 MPa for hardening welds. Therefore, in this study, the flux cored arc welding process is performed by establishing criteria that can be evaluated based on the SVM method in order to determine the structure of the weld to be cured according to the dilution rate of the base metal. We would like to propose a multipurpose optimization algorithm to ensure uniform quality of 9% Ni steel.

Effect of Mg Addition on the Microstructure and Properties of a Heat-Affected Zone in Submerged Arc Welding of an Al-Killed Low Carbon Steel.

To reveal the effect of Mg treatment on the microstructure evolution behavior in the actual steel welding process, the microstructure and properties of Al-deoxidized high-strength ship plate steel with Mg addition were analyzed after double-side submerged arc welding. It was found that the Al–Mg–O + MnS inclusion formed under 26 ppm Mg treatment could promote acicular ferrite (AF) nucleation in the coarse-grained heat-affected zone (CGHAZ) and inhibit the formation of widmanstätten ferrite and coarse grain boundary ferrite. In the fine-grained heat-affected zone (FGHAZ) and intercritical heat-affected zone (ICHAZ), polygonal ferrite and pearlite were dominant. Al–Mg–O+MnS cannot play a role in inducing AF, but the grain size of ferrite was refined by Mg addition. The impact toughness in HAZ of the Mg-added steel was higher than that of Mg-free steel. With the heat-input rising from 29.55 to 44.11 kJ/cm, it remained relatively stable in Mg-treated steel. From the fusion line to the base metal, the micro-hardness of the fusion zone, CGHAZ, ICHAZ and FGHAZ decreased to some extent after Mg addition, which means the cold cracking tendency in the welding weak zone could be reduced. Finally, the mechanisms of Mg-containing inclusion-induced AF were also systematically discussed.

Research for the Optimal Flux-Cored Arc Welding Process of 9% Nickel Steel Using Multi Object Optimization with Solidification Crack Susceptibility.

The environment of the global shipbuilding market is changing rapidly. Recently, the International Maritime Organization (IMO) has tightened regulations on sulfur oxide content standards for marine fuels and tightened sulfur oxide emission standards for the entire coastal region of China to consider the environment globally and use LNG as a fuel. There is a tendency for the number of vessels to operate to increase significantly. To use cryogenic LNG fuel, various pieces of equipment, such as storage tanks or valves, are required, and equipment using steel, which has excellent impact toughness in cryogenic environments, is required. Four steel types are specified in the IGG Code, and 9% Ni steel is mostly used for LNG fuel equipment. However, to secure safety at cryogenic temperatures, a systematic study investigating the causes of quality deterioration occurring in the 9% Ni steel welding process is required and a discrimination function capable of quality evaluation is urgent. Therefore, this study proposes a plan where the uniform quality of 9% Nickel steel is secured by reviewing the tendency of the solidification crack susceptibility among the quality problems of cryogenic steel to establish the criteria for quality deterioration and to develop a system capable of quality discrimination and defect avoidance.

Microstructural analysis and mechanical behavior of the HAZ in an API 5L X70 steel welded by GMAW process

This study aimed to investigate the heat-affected zone (HAZ) behavior in an API 5L X70 steel welded by the gas metal arc welding process (GMAW). In the steel welding processes, this region is very critical due to microstructural and allotropic transformations that affect the mechanical properties. Three samples were welded using a robotic arm with different welding speeds, thus obtaining three different heat inputs, which were 2.0 kJ/mm, 2.5 kJ/mm, and 3.0 kJ/mm. For all heat inputs, the microstructures of the HAZ showed the Widmanstatten ferrite, Acicular ferrite, bainite, and martensite and retained austenite, which influenced the mechanical properties of this region. The electron backscattering diffraction analysis showed that the presence of low-angle grain boundaries (2–15°) increases the fracture toughness. The kernel average misorientation map and the results of the Charpy impact test showed that the heat input of 3.0 kJ/mm lead to characteristics of the HAZ that are remarkably similar to the base metal (BM).

15/15 Ti Stainless Steel Welding Process Optimization for GEN IV Nuclear Application in the GEMMA Project Frame

This paper deals with activities carried out in the frame of GEMMA project on welded samples of 15/15 Ti stainless steel. The focus of GEMMA project has been on the investigation of material properties and associated welded joints for GEN IV nuclear plants. The RCC-MRx code uses the standard Base Metal Grade nomenclature (EN/ISO), but provides also additional specifications. Titanium stabilized “15-15Ti” stainless steel has been the primary choice for fuel cladding of current fast spectrum research reactor projects. The choice of cladding material is based on past experiences and the availability of material databases from similar steel grades proven in past sodium-cooled fast reactors programs [1-4]. On the basis of ENEA past experience, a strict specification has been written to realize a new heat treatment of this special stainless steel (SS). One of the main problems faced with this material is the high tendency to crack after the welding process. Several preliminary welding tests permitted to select TIG and laser welding processes for the 15/15 Ti SS. This fact because the main applications involve small thicknesses without filler material. The welding of the 15/15 Ti was performed using a fully automated TIG work station at ENEA CR-Casaccia. The base materials to evaluate the welding parameters were 15/15 Ti plates 100 X 170 X 3 mm welded under different shielding gas atmospheres and process parameters arrangements that permitted to obtain good quality joints avoiding catastrophic hot-cracking. The welded samples underwent a mechanical and metallographic characterization and the main results are here presented.

Effect of powder feeding mode on the stability and nitrogen distribution of high nitrogen steel welding process

Abstract The effect of powder feeding mode on the stability and nitrogen distribution of the high nitrogen steel (HNS) welding process was evaluated. The N loss of the joint was serious while the tensile strength was reduced to about 63.4 % in the absence of any effective measure. Four different configurations of powder feeding were designed to study the feasibility of powder feeding in the laser CMT hybrid welding process. And the powder feeding process was analyzed by arc shape and current-voltage curves which were collected by the Acuteye V4.0 welding observation system at 4000 frames/s. The most stable configuration was to fill the powder behind the arc. But non-uniformity was observed in the microstructure and properties in these configurations. The difference of ferrite content and tensile strength between the arc zone and laser zone reached 4.9 % and 150 MPa, respectively. A multi-stream powder feeding assisted laser-CMT welding method was proposed to improve the powder distribution and arc stability. The powder distribution was similar to the theoretical range and narrowed the ferrite content gap between the arc and laser zone to 1.3 %, and also the arc became stable even when a proportion of N2 was used. The tensile strength of the HNS welded nitride by CrN powder could reach 1198 MPa, which was 24.5 % higher than that of the non-nitride joint. However, the combination of N2 and powder nitriding needs to be explored in the future work.

Thermodynamic analysis on tin precipitation behavior in Ti-bearing peritectic steel after magnesium treatment

TiN, which is ubiquitous in Ti-bearing steel, has a critical influence on both the mechanical properties and the welding process of steel, and therefore researche on the precipitation behavior of TiN in molten steel bath is of great significance. In this paper, Ti-bearing peritectic steel was taken as the study object and FactSage was adopted to explore how the precipitation behavior of typical inclusions in steel was affected by the steel composition. Furthermore, microsegregation models were used to analyze the precipitation process of TiN at solidification front, and the calculation results were finally verified by scanning electron microscope (SEM). Research showed that a multitude of dispersed particles of high melting oxide MgAl2O4 or MgO always existed in molten steel after magnesium treatment. In consideration of the segregation and enrichment of solute elements at the solidification front, the Ohnaka microsegregation model was employed to compute the precipitation during solidification. In the event of the solid fraction reaching 0.95 or more, the concentration product of [Ti][N] at the solidification front exceeded the equilibrium concentration product, then TiN began to precipitate. MgO or MgAl2O4 cores were generally found in TiN particles of peritectic steel after the magnesium treatment, which was consistent with the thermodynamic calculation results. Moreover, the average size of TiN particles was reduced by approximately 49%. This demonstrated that Mg-rich high melting inclusions were formed after the magnesium treatment, by which the heterogeneous nucleation of TiN was promoted it; therefore, favorable nucleation sites were provided for further refining the high-temperature ferrite phase.

Computer prediction of α/γ phase fraction in multi-pass weld of duplex stainless steel and microstructural improvement welding process

A computer simulation of the α/γ phase transformation in a multi-pass weld of duplex stainless steel (DSS) was made to predict the distribution of the γ phase fraction in the heat-affected zone (HAZ). The kinetic equations including rate constants of the dissolution behavior as well as the precipitation behavior of the γ phase were determined by an isothermal heat treatment test. Based on the kinetic equations determined, the distribution of the γ phase fraction in a multi-pass weld of lean DSS was calculated by applying the incremental method combined with a heat conduction analysis of the welding process. The γ phase fraction was reduced in the higher temperature HAZ; however, that in the reheated HAZ was increased and recovered to the base metal level. Microstructural analysis revealed that the calculated results of the γ phase fraction in the multi-pass weld were consistent with experimental ones. Based on the computer prediction, the microstructural improvement welding (“reheat bead welding”) process, an analogous concept to the temper bead welding technique, is newly proposed for recovering the γ phase fraction in the weld just as in the as-welded situation.

Hybrid welding of steel 4330V

The article describes the hybrid welding process (Laser-MAG) of 4330V steel. This steel is a high-strength, micro-alloy material with tempered martensite structure. The microstructure of tempered martensite is obtained through the heat treatment process and through the vanadium micro-additive. Due to the high carbon content (approx. 0.3%), this material causes problems during welding and requires heat treatment before and after welding. The material’s high strength and plastic properties make this material desirable on the market. Hybrid welding is a process of joining materials, where a laser beam is used to achieve deep penetration into the material, and the use of a MAG welding source results in an additional electric arc that supports the melting process of the base metal and the additional material completes the weld. Using a robotic station for hybrid welding, a 11mm thick butt joint was made of 4330V steel without heat treatment processes before and after welding. The joint was welded from two sides. After welding, a number of tests were performed to determine the properties after welding. Visual and penetration testing, macro and microscopic tests, Vickers hardness test, tensile strength test and bending test on both sides were performed. The tests showed a properly made joint with numerous splashes, but unfortunately transverse cracks in the weld were detected which resulted from the stretching of one weld by the other. Macro and microscopic examinations revealed the correct execution of the joint on a full penetration cross-section, the martensitic structure in the heat affected zone and in the weld was visualized. Destructive testing revealed, among others, an increase in hardness in HAZ (Heat affected zone) to a level of about 500HV, high tensile strength at the level of the base metal. The cracks formed on the face mean that the welding process needs to be refined to eliminate such defects.