Sysweld crack
![Sysweld crack Sysweld crack](https://www.e-sciencecentral.org/upload/jwj/thumb/jwj-35-4-41f20.gif)
The crack length dependency of the threshold value was evaluated by means of microstructure-dependent fatigue crack resistance curves (R-curves). But the crack propagation rates of the microstructures of the heat-affected zone are above the base metal. The investigations proofed that, in case of thermomechanical rolled pipeline steels, the microstructural dependent threshold values within the heat-affected zone can even be higher than the base metal.
![Sysweld crack Sysweld crack](http://paradamonster.fun/phcdj/BrYJX2KnF-A1YkfgLg37fAHaE-.jpg)
The weld process changes the microstructure and the residual stress conditions within the heat-affected zone strongly. The extensive experimental investigations show that the long crack threshold depends essentially on the local different microstructures. In addition to tensile tests and hardness measurements, both these microstructural zones and the base metal were characterized by cyclic crack propagation curves and fatigue tests. At first, the microstructures of the heat-affected zone (coarse-grained, fine-grained and intercritical zone) of a representative double submerged arc welded longitudinal seam were reproduced with a GLEEBLE(R) thermal simulator. In this work, a finite element based method for fracture mechanical fatigue assessment of welded high strength steel joints with consideration of local microstructures, residual stresses and a weld post treatment is presented. Therefore, the lightweight design potential of such high strength steels cannot be used properly. Several codes, reports and guidelines are nowadays applicable for dimensioning, but due to the difficult estimation of the process influences they are quite conservative. The dimensioning of welded pipeline components made of thermomechanically rolled highstrength fine-grained structural steels is a great challenge for application engineers.