Improvement of weldability and evaluation criteria for high-strength pipe steel heat-affected zone reliability

Criteria are formulated for evaluating weldability on the basis of methods simulating welding thermal cycles and analysis of austenite polymorphic transformation kinetics in the thermally affected zone. Results are provided for evaluating the joint heat-affected zone (HAZ) cold resistance under the influence of thermal action during welding of thick-walled pipes for considerable heat input and the tendency for cold cracks during welding with small heat input. The effect of alloying elements, i.e., nickel and chromium, and also vanadium and molybdenum in steels microalloyed with niobium on ductile-brittle failure parameters during impact testing is demonstrated. Microalloying niobium-containing steels with vanadium and molybdenum leads to HAZ metal embrittlement. Optimum cooling rates after welding are determined with which HAZ metal cold resistance at down to –30°C is provided are determined.