Showing 4 results for Ashiri
R. Ashiri, M. Shamanian, H. R. Salimijazi, Y. Park, M. R. Salmani,
Volume 6, Issue 2 (Journal OF Welding Science and Technology 2020)
Abstract
Nowadays, the use of advanced high strength steels (AHSSs) in body-in-white is one of the hot applied strategies which is followed by the most of the automakers. The study of weldability and weld challenges facing these steels in resistance spot welding process as the most widely used process in the assembly lines of the automotive industry is essential to use the outstanding mechanical responses of AHSSs. This study can result in improvement of mechanical performance of the resistance spot welds of AHSSs. Our results indicate that AHSSs experiences different welding challenges which this work aims to study them by discussing their causes, mechanisms involved and potential ways to address them.
Engineer Amri Hossein Jafarzade, Engineer Mohammad Saeed Shahriari, Ph.d Ruhollah Ashiri,
Volume 9, Issue 2 (Journal OF Welding Science and Technology 2025)
Abstract
Repair welding of nickel-based superalloy Inconel 939, which was under working conditions of 100,000 hours, was performed by gas tungsten arc welding using Inconel 617 filler metal. The main objective of this study is to investigate and analyze the challenges during welding such as irregular distribution of primary MC carbides and crack formation in the heat-affected zone, and also to investigate the effect of post-welding heat treatment cycle on the microstructure and hardness of different weld zones. During welding, a crack of 91 micrometers length was observed in the heat affected zone, which due to the presence of a liquation film and accumulation of carbides around the crack, the crack was categorized as a liquation crack. Then, due to post-welding heat treatment, improvement of microstructural characteristics and hardness of the weld zone, partial melted zone, and heat-affected zone was observed, which resulted in homogenization of the hardness profile of the weld. In other words, in post-weld heat treatment, the improvement and uniformity of carbides allow for a better response to hardness properties in different welded areas. It was observed that post-welding heat treatment caused the crack formed during welding to grow and spread to reach a length of 386 micrometers, which was classified as a strain-aging crack due to its formation and growth during post-welding heat treatment.
Hamidreza Pooreskandari, Masoud Goodarzi, Rouholah Ashiri,
Volume 9, Issue 2 (Journal OF Welding Science and Technology 2025)
Abstract
Nickel-based superalloys are among the most critical materials used in high-temperature components of gas turbines, where their replacement costs and potential turbine damage necessitate effective protection and repair strategies. Optimizing repair methods to enhance efficiency and reduce costs has therefore been a continuous focus. The aim of this study is to improve the repair process of Inconel 738LC superalloy by reducing the susceptibility to liquation cracking. Activated tungsten inert gas (A-TIG) welding was performed on Inconel 738LC using a welding current of 60 A. Titanium dioxide (TiO₂) powder was employed as an activating flux, and weldments with four flux concentrations were examined. The microstructure w:::::as char:::::acterized using optical microscopy and scanning electron microscopy. The results revealed that flux concentration had a significant influence on penetration depth, with a concentration of 1 g/mL producing the maximum effect. At this concentration, weld penetration increased by 68% and weld pool volume by 63%, while the heat-affected zone width decreased by 12%. Arc imaging and quantitative/qualitative analysis demonstrated a constricted and focused plasma arc column in the presence of TiO₂ flux. Microstructural examinations further revealed suppression of columnar dendrite growth. It was found that TiO₂ flux enhances weld penetration and pool volume by constricting the arc and activating a reversed Marangoni flow, while simultaneously reducing HAZ width. However, the increased weld pool volume also intensified contraction stresses, leading to liquation cracking in the weld with the largest pool volume.
A. Bahmani, R. Ashiri,
Volume 11, Issue 1 (Journal OF Welding Science and Technology 2025)
Abstract
This research looks at how microstructure and mechanical properties change in resistance spot welds of QP980 advanced high-strength steel. It specifically focuses on the effects of zinc coating and how it influences weld nugget formation, mechanical properties, and fracture behavior. The study involved microscopic examinations, mechanical tests, and finite element simulations to determine the thermal history of different weld zones. A key finding was that rapid cooling during the welding process led to the formation of, metastable phases, such as martensite, in both the weld nugget and the heat-affected zone. A finite element model of the welding process was used to simulate heat distribution and analyze the microstructure in various weld regions. This model showed that reaching the peak temperature during four-pulse resistance spot welding is delayed. This delay, along with proper hold times, helps prevent the formation of voids. The simulated thermal history and the rapid heating/cooling conditions effectively predicted the evolution and transformation of the microstructure in different weld areas. It was found that the presence of a zinc coating, and the resulting reduction in electrical contact resistance, delayed the formation of the weld nugget at lower welding currents. However, at higher currents, the primary source of heat generation shifted from contact resistance to bulk resistance within the steel sheet. This led to larger weld nuggets in coated samples compared to uncoated ones. While uncoated samples showed higher weld nugget hardness (512 Vickers) and greater tensile-shear strength (with a maximum load-bearing capacity of 28.1 kN in uncoated samples versus 24 kN in coated samples), coated samples were able to achieve the critical weld nugget size for a change in fracture mode at lower welding currents (9 kA compared to 9.5 kA).
