Metallurgical and mechanical properties of laser welded high strength low alloy steel

Abstract

The study aimed at investigating the microstructure and mechanical properties of Neodymium-Doped Yttrium Aluminum Garnet (Nd:YAG) laser welded high strength low alloy (HSLA) SA516 grade 70 boiler steel. The weld joint for a 4 mm thick plate was successfully produced using minimum laser power of 2 kW by employing a single pass without any weld preheat treatment. The micrographs revealed the presence of martensite phase in the weld fusion zone which could be due to faster cooling rate of the laser weldment. A good correlation was found between the microstructural features of the weld joints and their mechanical properties. The highest hardness was found to be in the fusion zone of cap region due to formation of martensite and also enrichment of carbon. The hardness results also showed a narrow soft zone at the heat affected zone (HAZ) adjacent to the weld interface, which has no effect on the weld tensile strength. The yield strength and ultimate tensile strength of the welded joints were 338 MPa and 549 MPa, respectively, which were higher than the candidate metal. These tensile results suggested that the laser welding process had improved the weld strength even without any weld preheat treatment and also the fractography of the tensile fractured samples showed the ductile mode of failure.

Analysis of Selected Properties of Welded Joints of the HSLA Steels

“…Experimentally obtained results correspond to the relevant literature sources, such as Pamnani et al [28], Nathan et al [29], Haribalaji, Boopathi and Balamurugan [30], Oyyuaravelu [31], and Values of the cooling time t 8/5 were obtained within range 28.5 to 32 s. Different theoretical formulas predict that values could range from 24 s (Ito-Bessyo formula) to 65 s (formula of limited thickness) [25], so the experimentally obtained values are in compliance with theoretically predicted ones.…”

The Optimization of Process Parameters and Microstructural Characterization of Fiber Laser Welded Dissimilar HSLA and MART Steel Joints

“…In addition, various morphologies (i.e., columnar and equiaxed) in FZ could be a reason for the various hardness. However, some researchers have focused to determine an empirical formula for FZ hardness using CE values; in the present study, the measured hardness of FZ is higher than the calculated values using the mentioned formulas [31,36]. The calculated hardness values using the formulas given in the literature are 434 HV and 365 HV.…”

“…where f(C) is the accommodation factor and is calculated as; In the welding process, final microstructures are affected by peak temperature and the cooling rate of the relevant zones, and carbon equivalent (CE) value resulted from the chemistry of the steels [29][30][31][32]. Although there are numerous formulae for calculating CE, Yurioka's formula was used in this study because of its suitability for C-Mn steels [33].…”

Investigation of the Effects of Submerged Arc Welding Process Parameters on the Mechanical Properties of Pressure Vessel Steel ASTM A283 Grade A

“…It was also found that suitable SAW factors improved both tensile strength and hardness properties, which affect the pearlite density in the ferrite phase shown in Figure 6. Oyyaravelu et al [19] reported that the highest hardness and tensile strength clearly prompted the formation of martensite and pearlite phases in the weld metal and heat-affected zone. Related observations have been made by Lah et al [20], where the highest mechanical properties of pressure vessel steel weld were a result of pearlite density and fine pearlite phase.…”