LONG-TERM CREEP BEHAVIOUR OF E911 HEAT RESISTANT 9 CR STEEL WELDMENTS FABRICATED WITH FILLER METALS OF DIFFERENT CREEP STRENGTH

摘要

In this work an XllCrMoWVNb9-l-l (E911) pipe with an outside diameter of 355 mm and a wall thickness of 43 mm was welded with three different filler metals by GTAW and SMAW process. The used filler metals differed in creep strength level, compared to E911 grade pipe base material creep strength. The long term objective of this work was to study the influence of weld metal creep strength on the overall creep behavior of the welded joints. Uni-axial creep tests at 600°C (873 K) and stresses ranging from 70 to 130 MPa were performed using cross-weld samples of all three welds. Fractured samples were investigated by optical microscopy, electron microscopy and hardness testing. The results showed that the use of under-matching weld metal of P91 -type led to premature fracture in the weld metal at higher stress levels. At lower stresses the fracture location was shifted into the fine-grained heat affected zone (HAZ) and samples failed by characteristic Type IV failure mode. The use of matching (E911 type) and overmatching (P92 type) filler material increased the time to rupture only at high stress levels. The fracture mode for all samples at lower stress levels was identified as characteristic Type IV failure.