Papers by Keyword: Heat Input

Abstract: As a result of R&D efforts about the advanced materials, an ultra-high strength steel (UHHS) and a carbon fiber reinforced thermos-plastic (CFRTP) have been developed. In this study, various advanced multi-material dissimilar lap joints using UHHS, CFRTP and an aluminum alloy of A5083P-O were fabricated by the resistance spot welding (RSW), refill friction stir spot welding (RFSSW), friction stir spot welding (FSSW) and laser irradiation assistance plastic welding (LIAPW). Where, the total heat input for each joining method was varied in order to examine the influence of welding condition on joint performances, which were the tensile shear strength, shear fatigue property and corrosion shear fatigue property. The tensile shear strength of UHHS and A5083P-O joined by RFSSW is almost two times of that produced by RSW, and this difference seems to be mainly caused by the difference of joint area. The difference of joint area also affects the tensile shear strength of UHHS & CFRTP or A5083P-O &CFRTP lap joints made by FSSW and LIAPW, and the joint strength of LIAPW is larger than that of FSSW. As for the shear fatigue tests, it is found that the fatigue strength seems to decrease almost monotonically with increasing the applied load regardless of the types of dissimilar materials. Moreover, through the corrosion shear fatigue tests for A5083P-O and CFRTP joined by FSSW or LIAPW, it is found that the corrosion fatigue property seems to be controlled by the crack propagation behavior.

Abstract: Currently, the most promising high-tech and productive process is friction stir welding. An important element of this technology is the determination of the material temperature in the stir zone, which can be determined by calculation based on the amount of heat input introduced into the welding zone. To determine this value, experimental of the dependence of heat input on the tool rotation speed and welding speed were carried out. For this, a scheme of experiments has been selected in which the material to be welded (aluminum alloy AMg5) is modeled as an experimental tube with a diameter of 20 mm, and the tool (made of tool steel R6M5) is modeled as a working plate. On the designed and manufactured stand, studies of the dependence of the heat-liberation value for the speeds of rotation of the experimental tube 42-105 rad/s were carried out. In this case, due to the pressing force of the experimental tube and the working plate, a constant temperature of the place of friction was maintained. The obtained experimental data were used to calculate the heat-liberation value and heat power on each concentric ring 2 mm wide at the end of the working tool with a diameter of 20 mm, as well as the total heat power for different speeds of rotation and welding.When carrying out experiments on the bench, heat losses were determined by thermal conductivity along the rod on which the experimental tube is fixed, as well as from the working plate made of tool steel through the gasket onto the working table and by convection from the surface of the rotating experimental tube into the environment. The calculation results showed that each of these losses does not exceed 3-10%. These losses are taken into account in the heat supply calculations.

Abstract: The success of Dissimilar Metal Welding (DMW) occurred in optimal Heat-input (HI) parameters. The quality of welding joints was affected by dilution, hardness value, and intermetallic microstructure. DMW quality research was carried out on stainless steel SA SS312-TP304 and SA 53GrB carbon steel using the GTAW (Gas Tungsten Arc Welding) process with Heat-input of 1866.6 to 2362.2 J/mm. Visual observation on weld joints was not found weld defects. The optimal dilution area in the Schaeffler Diagram was obtained 35.35% austenitic area and without ferrite content. The lowest hardness value on carbon steel was 145 HV. The highest hardness value of 197 HV occurred in filler-metal dilution on carbon steel, so the difference in the value of hardness was high. The hardness value on stainless steel was 184 HV and in filler-metal stainless steel dilution was 172– 90 HV, so the difference in hardness value was low. Microstructure filler-metal dilution on stainless steel was austenite-dendritic, filler-metal dilution on carbon steel was fine-grained dendritic, and on allweld metal coarse-grained dendritic metal. HAZ stainless steel austenite microstructure and ferrite-pearlite carbon steel with an indication of a ferrite net. Observation of dilution, hardness value, and microstructure in DMW did not have a significant effect. This welded joint could be used as a reference in the DMW fabrication process for stainless steel and carbon steel pipe connections.

Abstract: The study was conducted to evaluate the impact toughness of flux-cored arc welded of SM570-TMC steel joint under different heat inputs, 0.9 kJ/mm (low heat input) and 1.6 kJ/mm (high heat input). Welding wire containing 0.4%Ni was selected on this experiment. Multi-pass welds were performed on SM570-TMC steel plate of 16 mm in thickness with a single V-groove butt joint on flat position (1G). The evaluation consists of observations on microstructure using an optical microscope and SEM-EDS, and mechanical properties including tensile, microhardness Vickers and Charpy V-notch (CVN) impact test at temperatures of 25, 0 and-20 °C. Results showed that the impact toughness of the base metal (BM) was higher than the weld metal (WM) at all test temperatures. Hardness and impact toughness of WM at low heat input was observed higher than when applied a high heat input. The welded samples at low and high heat inputs had high of tensile strength, and the fracture seemly occurs on the BM. Microstructure observation showed that at a high heat input, larger grains and microsegregation were observed. It might affect on decreasing their impact property.

Abstract: Nickel-base superalloys are used as a land-base turbine engine due to its excellent properties at elevated temperatures. Nickel base superalloy, grade IN-738. Laser welding is commonly chosen for the refurbishment of the turbine blade. This paper aims to focus on understanding welding speed parameters in laser welding method. With constant power at 400 watts, welding speeds were varied from 1, 3, 5, and 8 mm/s. All of these alloys have no cracks found in fusion zone, HAZ, and bulk area. Increasing welding speed results in less heat energy input, reduces the penetration depth and weld pool area. The 1mm/s, which were subjected to the highest heat energy input, results in very small size of the γ’ precipitates in the fusion zone due to re-precipitation of the γ’ precipitates during the solidification process. The fusion zone also exhibits the highest hardness. The size of the γ’ precipitates in HAZ area are much larger, compared to the fusion zone The bulk areas have no effect from the heat and showed much larger size of the γ’ precipitates, which was caused by microstructural degradation during service, leads to the lowest hardness value among the three zones.

Abstract: This work investigated microstructure and impact toughness of multi-pass flux-cored arc welded SM570-TMC steel. A comparison was made between weldments fabricated with average heat input of 0.9 kJ/mm and 1.4 kJ/mm, respectively. SM570 steel plate with 16 mm nominal thickness and 1.2 mm diameter of E81-Ni1 flux-cored wire were selected in this experiment. Multi-pass flux-cored arc welding (FCAW) was performed using carbon dioxide shielding gas. Then the weldments were observed using optical microscopy, scanning electron microscope (SEM) and electron probe micro analyzer (EPMA). The steel joint strength was measured via tensile test, and Charpy impact test was performed at three different test temperatures. The microstructure observation exhibited the base metal mainly consist of ferrite and pearlite features, while the weld metal contained the acicular ferrites, polygonal ferrites and M-A constituent at both different heat inputs. The impact toughness of base metal is superior than weld metals. The weld metals fabricated at average heat input of 0.9 kJ/mm have a higher low temperature impact toughness than using heat input of 1.4 kJ/mm. The acicular ferrites amount that significant reduced at the higher heat input may degrade the toughness at low temperature.

Abstract: Laser beam welding is one of the most favorable welding technique and its importance in industry is demanding due to higher welding speeds and lower dimensions and distortions in the welds. Moreover, its high strength to weld geometries and minimal heat affected zones makes favorable for various industrial applications. In the present study, laser welding of titanium alloy was investigated to observe the effects of parameters on the bead geometry and metallurgical properties. The laser power and welding speeds were varied to identify their impact on the formation of weld geometry. The width and depth of the fusion zone is varied with welding conditions. The finer grains identified in weld zone and the width of heat affected zone was significantly changes with laser welding power. The mechanical properties of the weld joint are controlled by obtaining optimum weld bead geometry and width of the head affected zone in the welds.

Abstract: Several case studies have shown that welding of stainless steel to galvanized steel leads to evolution of zinc which can penetrate through the steel and result in cracking, the present study focuses on determination of the effect of zinc on the mechanical behaviour of such weld joints. Welding was carried out using two shielding gas combinations. The other variations in parameters were heat input and presence or absence of zinc coating at the weld location. Tensile tests showed that the ductility of weld specimen improved when the coating was stripped off the samples prior to welding. Impact strength of weld specimens also followed similar trend. The impact strength was found to be improved when welding was done using Ar+2%He+2%O₂ as shielding gas. The compressive strength was found to be similar. To explain the mechanical behaviour of the welded specimen, microstructural characterization of the weld region was carried out.

Abstract: There are various base metals that might be subjected to friction stir welding (FSW). They have different yield strength, ultimate tensile strength and other mechanical characteristics that influence the complex phenomena of the FSW process. The nature, mechanical characteristic and other properties of the base metals introduce also certain requirements for the FSW equipment, because FSW is a mechanical process.Experimental data of the FSW of the following materials are presented and compared:- similar overlapped sheets of aluminium alloy EN AW 5754, having the thickness 1.0 mm; - dissimilar overlapped sheets of 3 - 6 mm thickness of the base metal couples: aluminium alloy EN AW 1200 / copper Cu 99 ET, aluminium alloy EN AW 5754 / copper Cu 99, aluminium alloy EN AW 6082 / copper Cu 99 ET;- sheets of nickel alloy, inconel 718, thickness 8 - 10 mm, by friction stir processing. The characteristics of the FSW tool are described and the main technology parameters are mentioned: overlap, rotational speed of the FSW tool, rotational direction, travel speed, thrust force, as well as electric current of the motor for the rotating motion of the tool.Other important factors are also taken into account: sizes and positioning of the sheets (up or down), rolling direction of the sheets, room temperature, temperature of the sheets, material and temperature of the support plate.The linear energy of the FSW process is the main parameter. This is an indirect parameter, because it must be calculated, based on the previous mentioned parameters. According to the definition, the linear energy depends directly on the mechanical power developed during the stirring process, respectively it depends indirectly on the travel speed.On the other hand, the heat input is directly proportional to the linear energy and the thermal efficiency of the transfer of the heat produced by the friction of the shoulder and pin, to the nugget zone, where the weld metal is produced. These quantities are also analysed.For these materials the power developed by the motor for the rotational movement is determined, as well as the mechanical torque applied to the FSW tool. All these data are important for the design of the FSW equipment, in order to realize its main technical characteristics, depending on the base metals.Conclusions on the results are exposed, with important consequences for the industrial applications of the FSW process.

Abstract: The weldability of high strength steel of grade 10G2FBY with a yield strength of 500 MPa is conducted in this paper according to the criterion of cold cracks formation in the seam root of plates with a thickness of 18 and 36 mm. The study was carried out in accordance with GOST 26388-84 on samples of type IX at ambient temperatures from –20 to +20 °С at heat input energy from 5.8 to 14.3 kJ/cm. After welding, the plates were cooled in the air for 24 hours. The main criterion for assessing weldability is the presence or absence of cold cracks after welding. The welding was made with a soft wire 4Y42 with a yield strength of 420 MPa. Cold cracks in high strength steel 10G2FBU for thicknesses of 18 and 36 mm are not detected in heat input over 10.3 kJ/cm by welding at the temperature of +20 °С, at the same time when welding at an ambient temperature of -20 °С cracks are not detected when running over energy of 14.7 kJ/cm. Critical cooling rate in which no cracks appeared was 55 °С/s at the temperature of welding +20 °С, and it was 44 °С/s at a temperature of welding –20 °С for both thicknesses. The criterion HV_max<300 HV is a necessary but insufficient condition for the prevention of cold cracking in steels of the type 10G2FBU. In the conditions of the experiment, cold cracks in the weld seam are absent at a hardness of no more than 250-260 HV, which is probably due to the presence of diffusive hydrogen, which is not regulated in the regulations for the supply of this steel grade