WELD METAL TENSILE STRENGTH DETERMINED BY TESTING FLAT MICRO TENSILE AND ROUND TENSILE SPECIMENS Nenad Gubeljak 1) , Marko Rakin 2) , Jožef Predan 1) , Bojan Medjo 2) , Aleksandar Sedmak 3) 1) Faculty of Mechanical Engineering, University of Maribor Smetanova 17, Maribor, Slovenia 2) Faculty of Technology and Metallurgy, University of Belgrade Karnegijeva 4, Belgrade, Serbia 3) Faculty of Mechanical Engineering, University of Belgrade Kraljice Marije 16, Belgrade, Serbia Corresponding author: marko@tmf.bg.ac.rs 1. Introduction Welded joints are highly inhomogeneous parts of welded structures. Microstructures and mechanical properties in different regions of a joint can vary significantly. For some purposes, i.e. for determining the fracture behaviour, it is very important to know the local values of the yield strength, ultimate tensile strength and other quantities. However, it is rather difficult to determine the tensile properties of heat affected zone, or some specific welds (i.e. laser welds) due to their small dimensions, but it is important for a complete understanding of the joint behaviour. In the absence of the exact properties of HAZ, a flaw assessment procedure using the base metal properties could lead to an unsafe result. Micro-hardness measured over the joint width can show the differences in strength, but it is not sufficient for determining accurate values of mechanical properties, especially the hardening exponent [1]. Therefore, micro tensile specimens are often used for determining the tensile properties through the zones of the welded joint [2]. In this work, properties of the joints are determined by testing flat micro tensile (MTS) specimens, Fig. 1, and also round tensile (RT) specimens, Fig. 2. 2. Experimental Results and Discussion Testing is conducted on high-strength low- alloyed (HSLA) steel welded joints. The base metal (BM) is HSLA steel NIOMOL 490; details about the joints fabrication are given in [3]. Overmatched (OM) and undermatched (UM) joints are analysed. Chemical composition of the base metal and both filler materials is also given in [3]. Micro tensile specimen (dimensions and position in the joint) are shown in Fig. 1; round tensile specimen is shown in Fig. 2. Fig. 1. Micro tensile specimen Fig. 2. Round tensile specimen The results (yield strength and ultimate tensile strength) obtained by testing the MTS specimens across OM and UM welded joints are given in Figs. 3 and 4, respectively.