Weldability and Impact Energy Properties of High-Hardness Armor Steel
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Weldability and Impact Energy Properties of High-Hardness Armor Steel Aleksandar Cabrilo, Katarina Geric, Milos Jovanovic, and Lazic Vukic (Submitted September 20, 2017; in revised form January 18, 2018) In this study, the weldability of high-hardness armor steel by the gas metal arc welding method has been investigated. The study was aimed at determining the weakness points of manual welding compared to automated welding through microhardness testing, the cooling rate, tensile characteristics and nondestructive analysis. Detailed studies were performed for automated welding on the impact energy and microhardness in the fusion line, as the most sensitive zone of the armor steel weld joint. It was demonstrated that the selection of the preheating and interpass temperature is important in terms of the cooling rate and quantity of diffusible and retained hydrogen in the weld joint. The tensile strength was higher than 800 MPa. The width of the heat-affected zone did not exceed 15.9 mm, measured from the weld centerline, while the impact energy results were 74 and 39 J at 20 and – 40 °C, respectively. Keywords
gas metal arc welding, hardness, high-hardness armor steel, instrumented Charpy impact toughness, porosity
1. Introduction High-hardness armor steel requires careful control of the welding procedure to avoid loss of heat-affected zone hardness and to prevent hydrogen-assisted cold cracking. Material hardness is strongly dependent on the welding temperature history. The key to controlling the amount of softening in the heat-affected zone is to maintain a high peak temperature gradient close to the weld bead (Ref 1). The microstructure of the heat-affected zone is a function of the cooling rate imposed by the welding process and the chemical composition of the base plate (Ref 2). The microstructure of the heat-affected zone impacts the hardness level and the ballistic performance of the weld joints. The control of the heat input should allow the width of the heat-affected zone to remain within 15.9 mm, measured from the weld centerline, which is compliant with the standard MIL-STAN-1185 (Ref 3). Industrial robots are widely used in many applications due to their ability to perform operations quickly, repeatedly and accurately. Process flexibility and welding possibility in various positions are the main reasons for using robots (Ref 4). For high-hardness steels, welder training requires time and skill and incurs additional costs. Therefore, the price of manual work by a trained welder is very high. Even the most experienced welders make mistakes during the welding process, which are usually unacceptable for armor steels. In the case of products for ballistic protection, heat input is crucial. Therefore, the
Aleksandar Cabrilo and Katarina Geric, Faculty of Technical Sciences, University of Novi Sad, Trg D. Obradovic´a 6, Novi Sad 21000, Serbia; Milos Jovanovic, Welding Institute, Ptujska 19, 1000 Ljubljana, Slovenia; and Lazic Vukic, Faculty of Engineering, University of Kragu
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