No abstract

In the collaborative programme between MPA, Stuttgart, and the Institute for Materials Science and Welding Technology at the Technical University, Graz, within the framework of COST 505 “Materials for Steam Turbines”, the creep‐rupture behaviour of the dissimilar weldment 1%CrMoV/12%CrMoV was investigated. Independent of the effects given by the welding process, weld metal and post weld heat treatment, the fine‐grained zone in the HAZ of the lower alloyed steel grade was life‐determining after long‐time creep loading. The decarburized coarse grained HAZ near the fusion line is critical at higher stress levels, e.g. breakdowns.

Langzeitbeanspruchte, gebrochene Zeitstandproben, die in Querrichtung aus SchweiBverbindungen entnommen waren, wurden metallografisch untersucht. Es handelte sich dabei vorwiegend um artgleiche bzw. nicht artgleiche SchweiBverbindungen von CrMo-und CrMoV-legierten stahlen, Schwerpunkt der metallografischen Auswertung war die Ermittlung der Bruchlage und des Schi:idigungsmechanismus. 1m Langzeitbereich, der in der Regel mit einem deutlichen Ruckgang der Verforrnunqsfahiqkeit verbunden ist, konnte in fast allen Fallen der auBere, d. h. felnkorniqe Bereich der WarmeeinfluBzone als art maxi maier Krlechschadiqunq bzw. als Versagensstelle ermittelt werden. Bei hohen Beanspruchungen kann sich die Bruchlage in andere Bereiche der WEZ bzw. in den Grundwerkstoff oder das SchweiBgut verlagern. 1m Vergleich zur Zeitstandfestigkeit des Grundwerkstoffs ergeben sich bei SchweiBverbindungen werkstoff-, temperatur-und belastungsspezifische Reduzierungen der Zeitstandfestigkeit.Failure behaviour of long-term loaded creep specimens cut from weldments of creep-resistant power-plant steels. Specimens transversely cut from weldments and tested up to failure in long-term creep tests were subjected to metallographic examinations. The weldments were mainly similar and dissimilar joints between CrMo-and CrMoV-steels. The investigations were focussed on the determination of fracture location and damage mechanisms. In the long-term range, where usually a reduction of strain to failure occurs, maximum creep damage as well as fracture location were observed in the fine-grained HAZ in most cases. At high stresses, a migration of the fracture location into other parts of the HAZ, or even into the base metal or weld metal can take place. Dependent on material, temperature and stress a reduction of the welds' creep strength in comparison to the base metal occurs.

Finite element modelling of the creep deformation of T91 steel weldments, welded using the manual metal arc (MMA) and submerged arc (SA) welding processes, was carried out to predict creep curves for both of the weldments under different stresses and compared with the experimental data. The stress and strain redistribution across the length of the transverse‐weld specimens has also been predicted. Data of creep tests at 600°C at stresses between 90‐130 MPa for the base metal, the MMA and SA weld metals, and the simulated heat‐affected zone were used to determine Garofalo's equation for creep strain. Finite element meshes for both of the weldments were constructed after calculating the HAZ locations using Rosenthal's heat flow equation.