جستجوی مقالات مرتبط با کلیدواژه « welding current » در نشریات گروه « مواد و متالورژی »

The welding of Hastelloy B-2 Ni-Mo base superalloy was carried out with the aim of investigating the effect of current intensity and frequency on the microstructural evolutions of the welded areas. For this purpose, the PC-GTAW process and the ERNiCrMo-2 filler metal was used. While other parameters were kept constant in this process, the frequency was changed at 10, 30 and 50 Hz, and pulse current was changed in the form of 80:20 and 60:40. The effect of current intensity and frequency on the microstructure of the weld metal was investigated by optical microscopy, scanning electron microscopy and EDS accessory was employed for analyzing the precipitates formed. The results showed that a decrease in the maximum current intensity led to a reduction in the heat input applied to the workpiece, resulting in a severe decrease in the size of the dendrites in the weld metal along with a reduction in the grain size of the HAZ and eventually, a significant decrease in the amount of molybdenum carbides in interdendritic regions of the weld metal will be resulted. By increasing the frequency led to increasing the width and the depth of weld. With increasing the frequency, the overlapping of the pulses increases and the heat is applied the molten pool at a shorter time interval and thus, the weld dimensions increase. The microstructural studies showed that increasing the frequency led to an increase in dendrites of the weld metal along with an increase in the extent of the HAZ.

The effect of electron beam welding current changes on the microstructure and mechanical properties of the Nb-based alloy has been investigated. The electron beam welding was applied with 4 different currents of 20, 24, 30 and 35 mA on 3mm thick plates. The aspects including different welding regions, geometry and depth of welding penetration, as well as the effect of heat input on the weldability are investigated. The mechanical properties including tensile and microhardness values of the weld was also measured. The results show that in a sample with a 30 mA welding current, the optimum conditions for the depth of penetration, weldability and the geometry of the weld are obtained. The welds showed a cellular structure, and intercellular dendrites in the central region of the weld have been caused due to microsegregations created between the cells. In HAZ, severe recrystallization and grain growth has occurred. Because of the high thermal conductivity of niobium, the HAZ size is relatively large. Based on the 3D Rosenthal’s equation, the recrystallization temperature of alloy was calculated as 713 °C. It is observed that as G × R increases, the grain size in the central line of the weld decreases. The hardness profile shows that the hardness of the weld zone and the HAZ is significantly less than that of the base metal due to elimination of work hardening effect. The tensile strength of the weld for a sample with a current of 30 mA was 281MPa, which is 53% of the tensile strength of the base metal and the weld was broken from the HAZ.

In the present study, the effects of the length, thickness, welding current, welding sequence, holding time in the fixture and similarity of the base metals on welding residual distortion of dissimilar joint between carbon steel CK4 and stainless steel AISI409 were firstly investigated on the basis of a verified finite element model. Then, considering the welding current, fixing time and sequence of welding operation, the magnitude of welding residual distortion was minimized. The results showed that in the studied dissimilar joint, the minimum distortion occurred when the welding current was about 95A; fixing time was 120 sec and symmetric layout was used.