Papers by Keyword: HAZ

Abstract: Non-metallic inclusions in weld metals often have a role inducing the formation of acicular ferrite, which is known to improve the toughness and other properties of the weld metal. The ability of the inclusions to promote the acicular ferrite formation depends on various factors such as chemical composition, morphology and size of the inclusions. In multipass welding, additional thermal cycles affect the inclusions in the pre-existing weld passes, potentially causing compositional and morphological changes in the inclusions. These changes may influence the inclusions’ ability to promote the formation of acicular ferrite. In the current study, the thermal cycles of multipass welding were produced on a single pass weld by physical simulation. Coarse-grained heat-affected zones (CGHAZ-W) in weld metal were simulated using three different cooling times from 800 °C to 500 °C (t_8/5). Inclusions in the heat-affected zones of the weld were analyzed using field emission scanning electron microscope equipped with energy dispersive spectroscope (FESEM-EDS), after which they were classified according to their chemical composition. The results showed that the inclusion content in the weld metal was affected by the thermal cycles. In the CGHAZ-W simulation the number of Mn-bearing inclusions increased compared to the unaffected single-pass weld metal. Increasing cooling time was observed to increase the area fraction of MnS in CGHAZ-W. The increase of these inclusions was expected to affect the microstructure by increasing the acicular ferrite fraction.

Abstract: The application of high-strength steels is increasing rapidly nowadays, and steels with more than 1000 MPa yield strength are usually used in welded structures. The welding of these materials has many difficulties, so very important the precise technology planning, and disciplined work during welding. The weldability of these materials is commonly investigated field in case of joining. The application of ultra-high strength steels expands rapidly, and in the last years, it started to use them as a base material for hardfacing. Besides the wearing, there is a claim about higher strength of base materials in case of relatively extremely loaded machines. Because this ultra-high strength steel appears as a base material for hardfacing and it brings new challenges for welding technologists. In case of joining, the welding technology is complicated, usually need preheating before welding, is important to calculate and to use the right t_8/5 cooling time, and basically necessary to decrease the heat input as much as possible. The bad effect of welding heat input can be compensated by the filler material too in some cases. In contrast in case of hardfacing the base material itself usually has a big thickness, and no joint preparation, additionally important to reach deep fusion on the surface. It basically determines the heat input which has a different heat cycle as in case of joining. Therefore, the heat affected zone (HAZ) differs from the HAZ in case of joining application. In this investigation, four different hardfacing were made with four different technological parameters by robotic gas metal arc welding on S1100QL steel. During the welding parameter determination, we try to find a series of heat inputs from the lowest to the practically usable highest heat input. For the experiments, two filler materials used, one for the buffer zone, and for the hardfacing itself. Microstructural evaluation and hardness tests were made on the specimens which can show the differences between the heat affected zones.

Abstract: This research is focused on the effect of welding parameter conditions, using Gas Metal Arc Welding, on the macrostructure, mechanical properties, and quality of dissimilar steel weld joints. In this study, the selected joints were low carbon steel (AISI 1015) and austenitic stainless steel (304L SS). The welding current used had three different variations, such as 100, 110, and 120 A. The solid wire electrode used was ER70S6, with a diameter of 1.2 mm. Identification of the macrostructure in the heat-affected zone (HAZ), micro-Vickers hardness, and tensile tests carried out for each GMAW joint specimen. The results were then discussed. The macrostructure of dissimilar steel welded joints at a welding current of 100 A produced a good quality of welded joints and penetration compared to those using welding currents of 110 and 120 A, which had excessive penetration and caused distortion and deformation. The microhardness of the weld metal area was far higher than in other areas. At the current 100 A, the micro-Vickers hardness value of stainless steel 304L SS closing the heat-affected zone (HAZ) had increased from 209 to 226 HV. Likewise, For the welding current of 110 A, the micro-Vickers hardness value rose from 249 to 259 HV, and for the welding current of 120 A, the hardness increased from 225 to 227 HV. In the weld metal area, micro-Vickers hardness for each welding current was 318, 364, and 366 HV, while in the low carbon steel area, the hardness value decreased significantly to 180, 190, and 196 HV. At the current of 100 A, the lowest tensile strength was 359.28 MPa, and yield strength was 303.82 MPa. The tensile strength and yield strength for the current of 110 A were 367.24 MPa and 309.83 MPa, respectively. Meanwhile, at the current of 120A, the tensile strength was at the highest that is 374.86 MPa, and the yield strength value was 315.67 MPa. This study found that the dissimilar steel welded joints experienced an increase in the hardness value of the weld metal, and the tensile test results show that the welded steel joints fractured in the low carbon steel area.

Abstract: The present work investigated the effects of Al, Si, and N content on the impact toughness of the coarse-grained heat-affected zone (CGHAZ) of Ti-containing low-carbon steel. Simulated CGHAZ of differing Al, Si, and N contents were prepared, and Charpy impact toughness was determined. The results were interpreted in terms of microstructure, especially martensite-austenite (M-A) constituent. All elements accelerated ferrite transformation in CGHAZ but at the same time increased the amount of M-A constituent, thereby deteriorating CGHAZ toughness. It is believed that Al, Si, and free N that is uncombined with Ti retard the decomposition of austenite into pearlite and increase the carbon content in the last transforming austenite, thus increasing the amount of M-A constituent. Regardless of the amount of ferrite in CGHAZ, its toughness decreased linearly with an increase of M-A constituent in this experiment, indicating that HAZ toughness is predominantly affected by the presence of M-A constituent. When a comparison of the effectiveness is made between Al and Si, it showed that a decrease in Si content is more effective in reducing M-A constituents.

Abstract: The influence of post weld heat treatments (PWHT) at 400°C, 600°C, 900°C on microstructures in heat affected zone (HAZ) of dissimilar welds between carbon steel and austenitic stainless steel was studied. As-welded condition, the fully Martensitic layer along the fusion line, Widmanstatten Ferrite, Bainite, Pearlite phases in the HAZ of carbon side and the fully austenitic zone in the weld metal can be observed. After PWHT, the microstructures of these zones were dramatically modified as a result of carbon diffusion from the carbon steel toward the weld metal. Decarburization of the base metal led to the formation of a zone with large Ferrite grains. Bainite or fine Pearlite were formed by carbon diffused to both the interfacial Martensite and the purely Austenite zone. The lowest hardness value in the decarburization zone was 92HV on average after PWHT at 900°C and the peak hardness value that was documented in the carburize zone with 366HV at 600°C. Carbides precipitation (M₂₃C₆, M₇C₃) were found in both the HAZ of carbon steel and austenitic stainless steel.

Abstract: In glass industry, laser cladding is an innovative surfacing technique allowing to deposit a layer of nickel to protect glass mold against corrosion, abrasion and thermal fatigue. This method (powder fusion by projection), well known in additive manufacturing represents a real technological leap for the glass industry. But during laser cladding of Ni-based powder on gray cast iron, cracks can be observed for some process conditions. These cracks are often due to the Heat Affected Zone that creates structural stresses linked to the development of a martensitic structure in the ferritic matrix of the lamellar graphite cast iron. The aim of this work is to observe the impact of laser cladding (without substrate pre-heating usually employed to limit cracking) on the coating behavior but also on the flake-graphite cast iron substrates. The microstructure and the mechanical properties were studied (SEM and microanalysis, microhardness) around the interface cladding/substrate. Also, the impact of the processing parameters (power P (1500-2300 W), scanning speed v (2.5-10 mm/s) and powder feeding rate PFR (24.5-32.5 g/min) was studied by using the ANOVA (ANalysis Of VAriance) technique. It has been observed that laser cladding on graphite cast iron is possible without cracks by limiting the linear energy induced by the process. Also, an optimization of the processing parameters (P, v, PFR) in order to obtain the industrial expected geometry of the coating has been proposed.

Abstract: To predict austenite grain growth behavior in the heat-affected zone (HAZ) in low alloy steels, a new calculation model is proposed herein. This model mainly considers the solute-drag effect and pinning effect, which restrain the austenite grain growth. To calculate the solute-drag effect, the grain boundary concentration of each element is obtained by Hillert’s Law. Calculations are performed by simulating the HAZ with a temperature gradient using the phase field method for two dimensions. This calculation demonstrates the possibility of quantitatively predicting the pinning force for welding heat inputs.

Abstract: The welding thermal simulation of 2507 Super Duplex Stainless Steel (SDSS) was investigated using Gleeble-3800 thermo-mechanical simulator. The morphology evolution of austenite and ferrite under different t_8/5 and t_12/8 were observed and compared. The impact tests and pitting corrosion tests under different t_8/5 and t_12/8 were conducted. The results showed that the austenite content increased and the austenitic morphology changed from allotriomorphic structure to strip or coarse-blocky structures with the increase of t_8/5 and t_12/8. The effect of t_12/8 on the microstructure of welding Heat Affect Zone (HAZ) was more distinct than that of t_8/5. The impact toughness of HAZ with the increase of t_12/8 was improved due to higher austenite content, while that with the increase of t_8/5 was slightly decreased due to the formation of intermediate phase, such as σ phase. The corrosion tests showed that the pitting resistance of HAZ was improved with the increase of t_8/5 and t_12/8, while the effect of t_12/8 was especially evident.

Abstract: Different microstructures in the weld zone of a metal structure including a fusion zone and a heat affected zone, are formed as compared to the base material. Consequently, the mechanical properties in the weld zone are different from those in the base material to a certain degree owing to different microstructures and residual welding stresses. When a welded structure is loaded, the mechanical behavior of the welded structure might be different from the case of a structure with homogeneous mechanical properties. It is known that obtaining the mechanical properties in the weld is generally difficult owing to the narrow regions of the weld and interfaces. As an alternative way to obtain the weld mechanical properties, the weld mechanical properties of Alloy800HT, SUS316L, and Alloy617, were recently measured using an instrumented indentation technique, and the representative weld mechanical properties of these materials were estimated with a 95% lower confidence level for later structural analyses of the welded structures.

Abstract: To improve the weld quality of AA 5083 plate using AA 5356 filler rod, an automatic TIG welding system is developed, by which welding speed can be controlled and a uniform speed is obtained. Welding of aluminium 5083 plate is carried out for different welding currents and welding speeds. In this work, the effect of welding speed and current on, the tensile strength of the weld, hardness at the three different zones viz. weld metal, HAZ and base metal are investigated. The temperature is measured at the HAZ and base metal. The hardness and temperature on the weld zone and the base metal are greatly influenced by the welding speed and current. It is found that the weld strength is influenced by different values of weld current and speed, but sometimes with high current, welding speed has no specific effect on the tensile strength of the weld. The effect of material deposition rate on the weld strength in uniform welding is studied. The weld thickness to width ratio is an important aspect in the analysis of weld strength. The values obtained for current and speed are taken for optimizing the strength and hardness, using Taguchi method and utility concept.