Structure and mechanical properties of thick-walled joints of Ti-6-4 titanium alloy made by electroslag welding

Abstract

The results of studies of the quality of the electroslag welds (ESW) of 100 mm thick Ti-6AI-4V plates are presented. ESW was performed using a consumable nozzle made of Ti-6Al-4V alloy with two welding wires made of SPT2 alloy. The study of the properties of the welded joints included X-ray inspection, chemical and gas analysis, optical metallography, phase composition analysis, mechanical tensile and impact tests and fractographic analysis. As a result of the research, the following was established. X-ray inspection and optical metallography of the welded joint showed the absence of surface and internal defects in the weld metal and heat-affected zone (HAZ). The gas composition of the weld metal meets the requirements of the standard for the Ti-6Al-4V alloy. The tensile strength of the weld metal is on average 90% of the strength of the base metal and the impact toughness (KCU) of the weld metal is 1.6 times higher than that of the base metal. The weld and HAZ metal is characterized by mixed-type transcrystalline fracture with areas of both ductile and brittle fractures. The mechanical properties of the welded joint are primarily related to the grain size and microstructure of weld metal and HAZ, which are formed under conditions of a low cooling rate and high heat input used for the ESW process.