Solution annealing of thick walled large-diameter super duplex stainless steel pipes by induction heat treatment

摘要

Longitudinally submerged arc welded large diameter SDSS pipes require solution annealing to dissolve inter-metallic phases and to generate the desired austenite/ferrite ratio within the area of weld and HAZ. According to ASTM A 928 solution annealing shall be performed after welding within the temperature range of 1025 °C to 1125 °C followed by quenching using water or air. It is also a well known fact that lower solution annealing temperatures cannot ensure a proper dissolving of inter-metallic phases. In contrast, rapid cooling from higher temperatures can lead to nitride precipitations. Within the framework of an order, 26 SDSS (UNS S32750) 18" pipes with a wall thickness of 36.2 mm and lengths of 9,000 mm were produced. For this order the solution annealing was conducted by means of a continuous induction heat treatment facility. This process is characterized by a more rapid heating and a shorter holding time compared to conventional furnace heating and by the fact that the pipes are quenched only from the outside surface.