Experimental study of crack resistance during welding of high-strength steel with increased cold resistance

The team of the Nosov Magnitogorsk State Technical University has developed a new steel characterized by increased strength (Yield Strength ≥ 950 MPa, Tensile Strength ≥ 1200 MPa) and cold resistance (KCV-70 ≥ 30 J/cm2), which makes its application promising in heavy engineering, including for the manufacture of welded structures of heavily loaded equipment. The main requirement for steel designed to work at low temperatures is a guaranteed fracture toughness at operating temperatures. In this regard, the choice of key welding parameters for high-strength steels for critical structures operated at subzero temperatures is one of the main problems, since the risk of cold cracks increases. The paper evaluates the resistance of the steel under study to the formation of cold cracks by the TEKKEN test method. The influence of linear energy in the range from 7.3 to 15.6 kJ/cm2 on the length of the sections of the zone of thermal influence with a coarse-grained structure (overheating zone) and with a fine-grained structure (normalization zone) has been studied. It has been shown that welding with low linear energy without preheating forms cold cracks. It has been found that preheating to 100 °C during welding with a linear energy of 7.3 kJ/cm2 prevents the formation of cold cracks since it leads to a decrease in the cooling rate of the metal, a decrease in the temperature difference in the welding zone and in peripheral areas, a decrease in macrostresses and a decrease in the amount of Widmanstetten ferrite. For the studied high-strength steel of increased cold resistance, the parameters of the arc welding mode are recommended to ensure the technological strength of the welded joint.The study was carried out by the Federal State Budgetary Educational Institution of Higher Education “MSTU named after G. I. Nosov” at the expense of the grant of the Russian Science Foundation No. 23-19-20018 dated 04/20/2023, as well as funds of the Ministry of Education and Science of the Chelyabinsk Region (Agreement No. 164 dated 06/28/2024), https://rscf.ru/project/23-19-20018/.