Investigations in fracture mechanics failure concepts with thermomechanically rolled steels

Thermomechanically rolled steels and a conventional structural steel were examined by instrumented Charpy tests, fracture mechanics tests and tensile tests with cracked tensile specimens, up to a maximum load of 4 MN. Part of the experiments particularly examined the behaviour of the heat affected zone, HAZ, of submerged arc welded joints. Locally very brittle areas in the HAZ were found to have a strong effect in fracture mechanics tests, but not so in the tensile tests. The load limits of the tensile specimens were estimated by the K1 concept, CTOD concepts, the EPRI method, and the R6 method. The numerical calculations and approximation yielded within the limits of applications good agreement with the experimental results, sometimes even very good agreement. Problems remain with the calculation of critical lengths of defects according to the R-curve procedure of the EPRI Handbook. There were no systematic differences observed in the applicability of the various failure analysis concepts, or their accuracy, with regard to the conventional structural steel St 52-3 or the TM steels of different strength and ductility (StE 460 and StE 480) used for the experiments. (orig./DG)