Effect of the welding mode and filler content on the structure of microalloyed Nb/Ti steel weldments
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EFFECT OF THE WELDING MODE AND FILLER CONTENT ON THE STRUCTURE OF MICROALLOYED Nb/Ti STEEL WELDMENTS N. Baji,1 V. Šijaki-Žeravi,2 M. Rakin,3 and K. Kovaevi 4 We describe the changes in the proportions of some microconstituents in the structure of the weld metal and the heat-affected zone and analyze the mechanical and technological properties of the welded joints of high-strength microalloyed Nb/Ti steel made by the E-process and MAG-process of welding with modification of the composition of the filler and welding parameters. The influence of different structures of the filler material and welding parameters on the microstructures of the HAZ and weld metal is studied with an aim to explain the changes in the mechanical and technological properties of the welded joints of microalloyed Nb/Ti steel. Keywords: microalloyed steels, weld metal, heat-affected zone, thermomechanical processing, microstructure.
Depending on the quality, the microalloyed steels for X-grade wires can be alloyed with Nb, V, Ti, or with a combination of these three metals. The main property of microalloyed steels is their fine-grain ferritic structure with grain sizes of up to No. 13 according to the ASTM standard. It is well known that mechanical and technological properties of welded joints are directly related to both the chemical composition of the filler and the structures of the weld metal (WM) and the heat-affected zone (HAZ). The microstructures of welded joints of fine-grain microalloyed steels consist of three basic ferrite modifications: acicular ferrite, primary ferrite and Widmanstätten ferrite appearing as a result of different mechanisms of transformation and characterized by different effects exerted upon the strength and ductility of welded joints. In addition, the small size of the grains of acicular ferrite and the presence of high-carbon boundaries also ensure the maximum resistance to crack initiation [1, 2]. By applying different technologies of welding and the methods of postweld heat treatment, it is possible to obtain the entire spectrum of different structures in the HAZ and WM and establish a series of properties of the same fine-grain microalloyed steel and the changes in the mechanical and technological properties of welded joints. Therefore, the aim of the present work is to determine the optimal combination of the composition of the filler and welding parameters aimed at getting the highest possible values of tensile strength and toughness of the welded joints of microalloyed Nb/Ti steel prepared by using the E- and MAG-processes of welding. Materials and Welding Processes The experimental welding of prepared specimens (plates) made of microalloyed Nb/Ti steels was carried 1 2 3 4
IHIS Research and Development Center, Belgrade, Serbia. Faculty of Mechanical Engineering, Belgrade, Serbia. Faculty of Technology and Metallurgy, Belgrade, Serbia; e-mail: [email protected] (corresponding author). Institute of Ferrous Metallurgy, Nikši, Montenegro.
Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 46,
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