PECULIARITIES OF STRUCTURAL TRANSFORMATION IN THE HEAT EFFECTED ZONE OF WELDED JOINTS OF SPECIAL HIGH-STRENGTH STEELS

Annotation. Purpose. The construction of thermokinetic diagrams of austenite decomposition and the establishment of the influence of the rate of cooling of specimens-imitators of HAZ metal on the structure and properties of high-strength steels Quardian 500 and Armstal 500, depending on the carbon content. Methodology. As a material for this study, high-strength structural steels Quardian 500 and Armstal 500 with a carbon content of 0.26 and 0.29%, respectively, have been selected. The effect of the kinetics of the decay of austenite on the structure, phase composition, hardness of these steels after simulation of the TWC on the Gleeble installation of 3800 imitation samples cooled in the temperature range 600 ... 500 ° C with a given velocity W6 / 5 = 1, 3, 5, 7, 10, 20, 30 ° C / c. On the basis of the obtained data, the built-in thermokinetic diagrams of austenite decomposition are established and the influence of the cooling rate of samples of the HAZ metal imitators on the structure and strength properties of high-strength steels is established. Findings. The conducted complex of studies showed that for high-strength Quardian 500 steel with a carbon content of 0.26%, cooling in the W6/5 range from 20 ° С / с to 30 oС/с leads to the formation in the over-heating zone of a predominantly martensitic structure and an increase in hardness from 4850 to 4980MPa. At that time, as for steel Armstal 500 with a heavier carbon content - 0.29%, cooling in the W6/5 range from 7 ° С / с to 30 oС/с leads to the formation in the over-heating zone of a predominantly martensitic structure and an increase in hardness from 5160 to 5390 MPa, which provides an increase in static strength. Originality. For Quardian 500 and Armstal 500 steels, the regularities of the influence of carbon content on the structure formation in the HАZ metal steel have been established and the propensity to brittle failure has been estimated. Practical value. Investigation of the kinetics of the decay of the austenite, the structure and properties of the HAZ metal of welded joints of these steels made it possible to establish the most optimal welding regimes that provide the most favorable structure and phase composition for obtaining the required high complex of mechanical properties of welded joints of high-strength structural steels.