Fracture Behavior Of Welded Joints Research Articles

Licht- und elektronenmikroskopische Untersuchungen zur Beschreibung des Zeitstandverhaltens von Schweißverbindungen moderner Kraftwerkswerkstoffe/ The Use of Light and Electron-Microscopic Investigations to Characterise the Creep Behaviour of Welded Joints in Modern Power Station Materials

The microstructural characterisation of welded joints subject to creep and the formation of the heat affected zone (HAZ) in Tungsten alloyed high temperature 9-12% Chromium steels is extremely important in modern power station construction. In these investigations, creep specimens were made available taken from fabrication welds in steel castings and welded joints in thick walled large diameter pipes. The results of the hardness measurements carried out, together with the qualitative and quantitative results of metallographical investigations are presented. Special attention is paid to softening in the HAZ and the effect which this has on the creep resistance and fracture behaviour of welded joints. A similar softening effect to that occurring in the pipe material P91, is also observed in the Tungsten modified variants. TEM investigations with the aid of energy filtering (EFTEM) were used to clarify the mechanisms taking place. The results obtained from tests on actual welds confirm the information gained from the basic trials carried out.

Fracture behaviour of welded joints fabricated in HSLA steels of different strength level

Effects of strength differences (mismatch) between weld metal and two base metals, as well as local variations of strength within weld HAZ zones, on the fracture toughness properties of welded joints were discussed. Due to high global weld joint mismatch, fracture deviation from CGHAZ into weld or base metal occurred. This event occurred in both weld joints provided on steels of equal and different strength level. Therefore, the result was not a correct measurement of HAZ fracture toughness. The significance of the local crack tip opening displacement measurement technique was also discussed by comparing the CTOD results of δ5 and British Standard δBS. Some differences in the two methods were discussed, in particular, for CGHAZ toughness weld joints provided on steels of equal and different strength level.