Significance of cracks in the heat-affected-zone of steels for elevated temperature application

Abstract

Damage and failure of welded joints are classified according to the crack position. Type IV cracking occurs in welded joints in creep-resistant steels, due to enhanced rate of creep void formation in the presence of coarse grained carbide particles in fine-grained and intercritically annealed regions of the heat-affected zone. Creep damage accumulation causes premature failure. So, the evaluation of residual service life of equipment operating at elevated temperatures in power plants and in process industry requires analysis of material behavior in sub critical and in creep regime. The occurrence of type IV cracks is observed in 9-12% chromium steels. The problem can be solved by reaustenitisation and tempering heat treatment, but this is a rare practical option, and components have to be designed taking into account reduced creep strength and life. .

Oštećenje i lom zavarenih spojeva klasifikuju se prema položaju prslina. Prsline IV grupe javljaju se u zavarenim spojevima čelika otpornih na puzanje, zbog povećane brzine formiranja šupljina u prisustvu čestica krupnozrnih karbida u finozrnim i interkritičnim žarenim područjima zone uticaja toplote. Akumulacija oštećenja puzanjem izaziva prevremeni otkaz komponente. Zbog toga je za ocenu preostalog veka opreme za rad na povišenoj temperaturi u termoelektranama i u procesnoj industriji potrebna analiza ponašanja materijala u dokritičnom režimu i u režimu puzanja. Pojava prslina IV grupe je uočena kod čelika sa 9-12% hroma. Problem se može eliminisati termičkom obradom - ponovnom austenitizacijom i otpuštanjem, ali je to retko izvodljivo i zato se komponente moraju projektovati tako da se uzme u obzir smanjenje čvrstoće puzanja i veka. .