Effect Of Welding Thermal Cycle Research Articles

Microstructure and properties of Ti–6Al–4V alloy welded joint by keyhole gas tungsten arc welding

In this paper, 12 mm Ti6Al4V titanium was successfully welded in a single pass using the keyhole gas tungsten arc welding technology, without special edge preparation or the addition of a filler material. The microstructure and properties of the welded joint are studied. The microstructure of the joint was classified and characterized in detail according to the difference of the effect of welding thermal cycle, and the difference of the top, middle and bottom microstructure of the joint was compared and analyzed. The microhardness of transverse joint fluctuates in the range of 50HV0.2. The difference of longitudinal microhardness is about 100HV0.2. The lowest is 280 HV0.2, and the highest is 378 HV0.2. The tensile strength of the joint reaches 925 MPa. The fracture position of the joint is located in the base metal. The Charpy impact energy of the weld center reaches 50J, which is 56% higher than that of the base metal 32J, and the weld metal shows good toughness.

HF pulse effect on microstructure and properties of AC TIG butt-welded joint of 6061Al alloy

Abstract Butt joint welding of 6 mm thickness of 6061 aluminum alloy was used to characterize the high frequency (HF) pulse modulated square wave AC TIG (HFPM AC TIG) welding with filler wire addition. The heat input required for achieving fully penetrated weld is remarkably reduced by the modulation HF pulse. The weld penetration is increased and weld width is decreased at the same equivalent current. The width of partially melted zone, dissolution zone and overaged zone are all decreased. The formation of columnar grain around the fusion line is suppressed and the formation of the equiaxed grain is promoted. The number density and average size of micro-pores in weld metal are greatly reduced. The softening effect of welding thermal cycle is significantly relieved. The strength and elongation of the welded joint are increased by 8.5 % and 19.8 % respectively, and the strength and elongation of the weld metal are increased by 6.1 % and 46.1 % respectively.

Estimation of Residual Stresses by Nanoindentation in an Experimental High Strength Microalloyed Steel Subjected to Rapid Thermal Cycles

The effect of welding thermal cycles on the microstructure and residual stresses was studied in the welding zone of an experimental high strength microalloyed steel with an acicular ferrite and quasi-polygonal ferrite microstructure. Autogenous gas tungsten arc welding was performed on a plate of microalloyed steel to produce a weld bead neglecting the weld joint design and the selection of filler material. To obtain a high welding quality, the welding speed and distance between the electrode and plate was controlled with a small vehicle. To determine the residual stresses, nanoindentation tests were performed in each one of the welding zones and subzones of the heat-affected zone (HAZ). These results showed that all of the nanoindentations presented pile-up and sink-in, and thus, a modification was proposed to calculate the actual contact area and determine the residual stresses. Tensile residual stresses were presented in the coarse-grained HAZ (grain boundary ferrite, acicular ferrite, and bainite); fine-grained HAZ (polygonal ferrite); subcritical HAZ (acicular ferrite and quasi-polygonal ferrite); and base material (acicular ferrite and quasi-polygonal ferrite). The fusion zone (acicular ferrite and bainite) and intercritical HAZ (quasi-polygonal ferrite) had compressive residual stresses.

Effect of weld thermal cycle on metallurgical and corrosion behavior of friction stir weld joint of AA2014 aluminium alloy

Friction stir welding of AA2014 aluminium alloy was performed at seven different speed combinations. Weld thermal cycles were measured at all the speed parameters and corresponding peak temperatures were observed at higher tool rotation speed and lower welding speed. Hardness and tensile tests were performed to study the mechanical properties of the weld joints. Corrosion behavior was studied using immersion, Tafel and electrochemical impedance spectroscopy tests. Optical microscopy, FESEM, XRD and transmission electron microscopy were used to investigate the metallurgical behavior of the weld joints. Microhardness and corrosion resistance were found higher at low rotation speed and high traverse speed. Corrosion behavior has been discussed in light of microstructure.

Numerical and experimental investigation of thermal field and residual stress in laser-MIG hybrid welded NV E690 steel plates

A numerical simulation with sequential coupled thermal-mechanical finite element model has been performed for analyzing the temperature field, residual stresses and distortions in NV E690 weldment fabricated by hybrid laser-arc welding (HLAW). For the detailed validation of applicability of the proposed model, simulated and experimentally measured weld pool shape, residual stresses and distortions were compared. The comparison results showed that decent agreement was realized between the predicted weld pool dimension and measured weld bead geometry, suggesting the utility of the combined heat source model for predicting the transient temperature distribution during HLAW. Besides, the simulation results denoted that higher tensile stress distributed in the fusion zone and the surrounding heat affected zone. There was a qualitative agreement in terms of the numerical and experimental results of longitudinal stress and transverse stress. Additionally, the relative error of angular distortion between the experimental and numerical results was 28.18% and the absolute error value was 0.217°. In addition, increasing the heat input increased the peak temperature, residual stresses, and distortions in the weldment. Comparison of the numerical and experimental results suggested that the developed model can be effectively used to estimate welding residual stresses and distortions in hybrid welded steel plates. What is more, the effect of welding thermal cycles on microstructure evolution of the weld bead was also evaluated.

Effect of welding thermal cycle on microstructural evolution of Al–Zn–Mg–Cu alloy

Al–Zn–Mg–Cu alloys are used extensively in high-speed train applications; however, the occurrence of softening in the heat-affected zone after welding limits their development. In this work, the effect of the welding thermal cycle on the softening and aging behaviors of a 7xxx aluminum alloy was investigated by examining the state of the strengthening precipitates. The microstructure and solvus temperature range of the precipitates of 7N01P-T4 were characterized using TEM and DSC analysis, respectively. It was found that the softening behavior of the aluminum alloys was closely related to the volume fraction and size of the hardening precipitates, which were greatly affected by the peak temperature of the welding thermal cycle. In addition, η′ and η precipitates were observed to be primarily responsible for the increase in the mechanical and electrical properties during the room-temperature natural aging. A phenomenological connection was thus uncovered between the characteristic parameters of the thermal cycle and the precipitation behavior, providing insight for the design of the welding process for 7N01 alloys.

Effect of welding thermal cycle on structural and phase weld metal transformations for heat-resistant Cr–Mo–V steels

Results are presented for dilatometric and metallographic investigations and determination of microhardness for weld metal made of the materials for the automatic welding of VVER reactor vessels and oil hydrocracking reactor vessels. It is found that small differences in the content of alloying elements, such as nickel, chromium, molybdenum, and vanadium, cause differences in the structure of the weld metal before heat treatment.

Comparison of procedures for evaluation of effect of welding thermal cycle on impact toughness of HAZ metal of welded joints from low-alloy steels

Comparison of procedures for evaluation of effect of welding thermal cycle on impact toughness of HAZ metal of welded joints from low-alloy steels

Сопоставление методик оценки влияния термического цикла сварки на ударную вязкость металла ЗТВ сварных соединений низколегированных сталей

Сопоставление методик оценки влияния термического цикла сварки на ударную вязкость металла ЗТВ сварных соединений низколегированных сталей

Effect of Weld Thermal Cycles on Microstructures and Mechanical Properties in Simulated Heat Affected Zone of a HY 85 Steel

Physical weld simulation for single and two-pass weld of a HY 85 steel has been done using thermo mechanical simulator at constant heat input of 22 kJ/cm. Attempt has been made to investigate the causes behind the deterioration of mechanical properties in the coarse grain heat affected zone (CGHAZ) in single pass and subsequent improvement in the mechanical properties of CGHAZ region in the two-pass weld. HY 85 steel finds wide applications in the making of ship hull. Impact toughness at −50 °C for CGHAZ in the single pass weld has been found to be 49 J. However, impact toughness improves to 122 J in the super critical reheated CGHAZ region for two-pass weld. This improvement in the impact toughness has been observed due to reaustenitization of fine prior austenite grains of average size of 44 µm from 99 µm, refinement of bainitic ferrite lath, and M–A constituents during second pass weld.

Inclusions and Microstructure of Ce-Added Weld Metal Coarse Grain Heat-Affected Zone in Twin-Wire Submerged-Arc Welding

In high heat-input multi-pass twin-wire submerged-arc welding, weld metal of previous pass will be affected by the heat input of subsequent one and form coarse-grained heat-affected zone (CGHAZ). This study focused on the effects of welding thermal cycle on the inclusions and microstructure of Ce-alloyed weld metal CGHAZ. According to the study of inclusions and microstructure of weld metal CGHAZ, it was found that the composition and type of the inclusions did not change under the effect of welding thermal cycle. Although the inclusions were coarsened slightly, the promoting ability to acicular ferrite (AF) was not deprived after thermal cycling. There are three types of AF in weld metal CGHAZ, which include oxy-sulfides of Ce inclusions-promoted AF, home-position-precipitated AF, and sympathetic AF. Results showed more than 80% of microstructure was AF, which greatly benefited the mechanical properties of weld metal CGHAZ, even though granular bainite and M-A constituents were generated.

Artificial Neural Networks to Estimate the Thermal Properties of an Experimental Micro-Alloyed Steel and Their Application to the Welding Thermal Analysis

The effect of welding thermal cycles on the micro-structure and micro-hardness of the heat-affected zone (HAZ) of an experimental micro-alloyed steel was studied. Due to the experimental difficulties involved in acquiring the thermal cycles, these were determined by applying the solutions of Rosenthal’s equations for thick and thin plates. However, to perform this thermal analysis, it requires knowledge of the thermal properties of the micro-alloyed steel; therefore, the implementation of two artificial neural networks (ANNs) was proposed as tools to estimate the thermal conductivity and the heat capacity as a function of the chemical composition and temperature. The ANNs were trained with information obtained from the literature review and then tested with steels that were not used for the training step, but with thermal known properties. A good approximation between the actual and the estimated properties was observed. It was determined that the microstructural characteristics of the welding zone are a function of the thermal cycles, although there is no great difference in micro-hardness. Martensite was not observed in the welding zone; therefore, the welds of this steel, under these welding conditions, could not be susceptible to hydrogen induced cracking (HIC).

Effect of welding thermal cycles on the structure and properties of simulated heat-affected zone areas in X10CrMoVNb9-1 (T91) steel at a state after 100,000 h of operation

The article presents results of structural tests (light, scanning electron and scanning transmission electron microscopy) of X10CrMoVNb9-1 (T91) creep-resisting steel after approximately 100,000h of operation. It was ascertained that the parent metal of T91 steel is characterized by the microstructure of tempered martensite with M23C6 carbide precipitates and few dispersive precipitates of MX-type niobium and vanadium carbonitrides. The most inconvenient change in T91 steel precipitate morphology due to long-term operation is the appearance of the Laves Fe2Mo phase which along with M23C6 carbide particles forms elongated blocks and conglomerates on grain boundaries. The article also presents results of tests related to the effect of simulated welding thermal cycles on selected properties of X10CrMoVNb9-1 (T91) grade steel at a state after approximately 100,000h of operation. The tests involved the determination of the chemical composition of the steel tested as well as impact tests, hardness measurements and microscopic metallographic examination (based on light microscopy) of simulated heat-affected zone (HAZ) areas for a cooling time (t8/5) restricted within a range between 3s and 120s, with and without heat treatment. The tests revealed that, among other results, hardness values of simulated HAZ areas in X10CrMoVNb9-1 (T91) steel do not guarantee cold crack safety of the steel at the state without additional heat treatment. It was also observed that simulated welding thermal cycles of cooling times t8/5=3, 12, 60 and 120s do not significantly affect the toughness and hardness of simulated HAZ areas of the steel tested.

Effect of welding thermal cycle on structure-phase transformations and properties of haz metal of alloyed 30Kh2N2MF type medium-carbon steel

Effect of welding thermal cycle on structure-phase transformations and properties of haz metal of alloyed 30Kh2N2MF type medium-carbon steel

Dissimilar spot welding of dual phase steel/ferritic stainless steel: phase transformations

Phase transformations in dissimilar resistance spot welds of dual phase steel and ferritic stainless steel are analysed. In contrast to a full martensitic microstructure predicted by the Schaeffler and Balmforth diagrams, a ferrite–martensite microstructure was observed in the fusion zone. The formation of ferrite phase in the fusion zone can be attributed to the rapid cooling rate of resistance spot welding, which suppresses the post-solidification ferrite–austenite transformation. The grain growth and martensite formation were main metallurgical features of the heat affected zone of ferritic stainless steel side. Microstructure gradient of heat affected zone in dual phase steel side was dictated by martensitic transformation. The effect of weld thermal cycle on the mechanical performance of the joint is discussed.

Prediction of CGHAZ Microstructure and Property of JG590 Steel with Weld Simulation Technology

A three-dimensional analytical calculation model of GMAW heat transfer was established, and the weld temperature field of JG590 with different welding parameters was analyzed by numerical simulation. The phase transformation in CGHAZ of JG590 steel was studied by physical simulation. SH-CCT diagrams, the effects of weld thermal cycle on microstructure, impact toughness and hardness were obtained. The results show that the critical cooling time of bainite, ferrite and pearlite appeared are respectively 8s, 110s and 150s. The critical cooling time that martensite takes to finish transferring is 35s. When t8/5 is below 10s, CGHAZ has a better toughness and when t8/5 is beyond 15s, there is a wide range decrease on the toughness. In this paper prediction of CGHAZ microstructure and property of JG590 steel was realized based on the analytical calculation model of GMAW heat transfer and physical simulated results mentioned above

Synchrotron diffraction analysis of retained austenite in welded transformation induced plasticity (TRIP) steels

A quantitative analysis of the retained austenite (RA) fractions in gas tungsten arc welded silicon and aluminium containing transformation induced plasticity steels was carried out by synchrotron X-ray diffraction measurements. The variation in RA transverse to the weld line was measured to study the effect of weld thermal cycles on the stabilisation of austenite in the heat affected zone (HAZ) and the fusion zone (FZ). The results showed that the FZ of silicon based steels contained a higher amount of RA (∼7%) than aluminium based steels, which contained only ∼4%. During the solidification of the weld pool, aluminium was found to partition to solidifying δ-ferrite and to stabilise the soft δ-ferrite grains at the fusion boundaries. Owing to this partitioning, the HAZ was enriched in carbon and the RA content was found to increase with distance from the fusion boundaries. In contrast, this partitioning behaviour was not present in silicon based transformation induced plasticity steels and a lesser amount of RA was found in the coarse grained HAZ than in the FZ.

Corrosion behavior of CLAM steel weldment in flowing liquid Pb-17Li at 480 °C

CLAM (China Low Activation Martensitic) steel is considered as one of the candidate structural materials in liquid LiPb blanket concepts. Welding is one of the essential technologies for its practical application, CLAM steel weldment shows a great difference with base metal due to the effect of welding thermal cycle. In order to investigate the corrosion behavior and mechanism of CLAM weldments in liquid Pb-17Li, the experiments were performed by exposing the TIG weldment samples in flowing LiPb at 480 °C. The weight loss test of exposed specimens show that in 500 h, 1000 h dynamic conditions, corrosion resistance of CLAM steel weldment is poor, SEM analysis shows that the thicker martensite lath in weld area lead to higher corrosion amount, EDS results show that the influence of corrosion on surface elements is small, and surface corrosion is even, EDX analysis shows that the penetration of Pb-17Li does not exist in the joint. With the increasing of exposure time, the corrosion rate decreases. Metallographic analysis shows that the presence of Cr has great influence on the corrosion resistance of the steel matrix. The area short of Cr in thick martensite lath of CLAM steel weldment is easily corroded. After a series of theoretical and experimental analysis, a basic presumably corrosion behavior model is established, which makes contributions to the in-depth understanding of the corrosion mechanism of CLAM weldments.

Effect of Welding Thermal Cycle on the Microstructure and Mechanical Properties in Multi-Pass Submerged-Arc Welding

To research effect of welding thermal cycle on the microstructure and mechanical properties of welded joint, two pieces of 60mm thick plates were welded together using automatic submerged-arc welding (SAW) method with suitable welding parameters. After 17 passes welding, the microstructures and phases of the welded joint was carefully observed and analyzed by using a Carl Zeiss optical microscope in different zones of welded joint, and the surface micro-hardness of the welded joint was measured systematically by using microscopic-hardness tester Lycra. Afterwards, the mechanical properties of the weld metals were measured through stretching. Through a series of measurements and observations, the welding experiment results indicate that effect of welding thermal cycle on the microstructure and mechanical properties of welding joint is great, the grains of the bottom of the weld metal are certainty smaller and more uniform, and the bottom of the weld metal have more excellent mechanical properties.

Effect of simulated welding thermal cycle on microstructure and mechanical properties of X90 pipeline steel

Abstract The effect of welding thermal cycle simulation on the microstructure and mechanical properties of X90 pipeline steel was investigated by means of microstructure analysis, tensile- and Charpy impact-tests. At the heat input of 15 kJ/cm, the microstructure of coarse-grained heat affected zone is mainly composed of lath bainite and granular bainite, resulting in excellent strength and toughness. At 25 kJ/cm with two thermal cycles, however, strength and impact toughness decrease due to the formation of more polygonal ferrite with coarser grains.