Structural Transformations of the Metal of Heat-Affected Zone of Welded Joints of High-Strength Armor Steels

We construct the thermokinetic diagrams of austenite decomposition and analyze the influence of the rate of cooling of specimens simulating the metal of the heat-affected zone (HAZ) on the structure and durability of Quardian-500 and Armstal-500 high-strength steels. The regularities of the influence of carbon on the structure formation in the HAZ metal are determined for these steels and the susceptibility to brittle fracture is estimated. It is shown that, in Quardian-500 steel with a carbon content of 0.26%, a predominantly martensitic structure with a hardness of 4850–4890 MPa is formed in the zone of overheating for cooling rates of 20–30°C/sec, whereas in Armstal-500 steel with a carbon content of 0.29%, the transformation of overcooled austenite in the HAZ of simulating specimens occurs at cooling rates of 7–30°C/sec and is accompanied by the formation of martensitic structure with a hardness of 5160–5390 MPa, which improves the static strength of the products.