Mehdi Asle Taghipour, Reza Dehmolaei, Seyed Reza Alavi Zaree, Mohammad Reza Tavakoli Shoushtari,
Volume 7, Issue 1 (8-2021)
Abstract
The microstructure and mechanical properties of HSLA-100 steel weld joints was investigated. Welding with three heat input of 0.820, 1.176 and 1.392 kJ / mm was performed using E12018 electrode. Microstructural studies were performed using scanning electron and optical microscopes. The mechanical properties of welded joints were evaluated by impact and microhardness tests. Microstructural studies showed that with increasing the heat input, the amount of acicular ferrite in the weld metal decreased and the amount of polyhedral and quasi-polygonal ferrite increased. It was found that with increasing the heat input, the amount of layered bainite in the heat affected zone increased and the amount of granular bainite decreased. Due to the decrease in the amount of acicular ferrite in the weld metal microstructure with increasing inlet temperature, the amount of hardness and impact energy decreased. The results showed that the increase in heat input due to the reduction of the acicular ferrite of the weld metal and the dissolution of precipitates in the coarse grain heat affected zone has caused a decrease in hardness in these zones. It was found that with increasing the heat input due to decreasing the acicular ferrite, the impact energy of the weld metal decreased by 29% (from 45 joules at an heat input of 0.82 to 32 joules at an heat input of 1.392 kJ / mm). It was found that at all heat inputs, the impact energy of the base metal is greater than the impact energy of the weld metal.
Mehdi Mizabi Ask, Majid Belbasi,
Volume 9, Issue 2 (8-2024)
Abstract
In this study, the effect of heat input on the microstructure and mechanical properties of the joint of two dissimmilar steels D6AC and VCN 200 steel was investigated. For this purpose, the samples were welded with the current intensity of 130, 145 and 160 Ampers by GTAW process and using ER120 SG welding wire with a diameter of 2.4 mm. The metallographic results showed that the microstructure of the weld metal consisted of lath martensite and acicular ferrite phases, which increased the volume fraction of ferrite from 5 to 32% with the increase of heat input, and the morphology of the ferrite changed from acicular to polygonal ferrite due to the decrease in the cooling rate. The HAZ area microstructure consist of bainite, lath martenrite and ferrite. The highest strength value was obtained in the welded sample with low heat input. With the increase of heat input, the tensile strength has decreased from 1064 to 875 MPa. Also, with the increase of heat input, the impact energy has increased in the welding zone due to the increase of stable phases, and in the HAZ zone due to the growth of the primary austenite grains and the reduction of the grain boundary locking effect. The results of the fracture analysis showed that the fracture occurred in the weld zone with low heat input, brittle fracture, and in the HAZ area, combination of ductil and brittle fracture occurred. However, with the increase in heat input, dutil fracture occurred in the welding zone and brittle fracture occurred in the HAZ zone due to grain growth.
