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Martensitic 9 %-Cr steels like P91 and P92 can show an increased susceptibility to delayed hydrogen assisted cracking. The focus of this study was the microstructure and heat treatment effect on the mechanical properties of P92 base material and P91 multi-layer weld metal in both as-welded and post weld heat treated (PWHT) condition.
Tensile tests with hydrogen free reference samples and electrochemically hydrogen charged samples were carried out, the mechanical properties were assessed and supported by dedicated fractographic analysis. In addition, hydrogen and microstructure dependent fracture criteria were calculated. All investigated microstructures showed a hydrogen influenced degradation of the mechanical properties compared to the hydrogen free reference samples. In that connection, the as welded martensitic P91 weld metal had the highest degree of degradation in presence of hydrogen. The P91 PWHT weld metal and the P92 base material had comparable properties. From that point of view, a significantly increased risk for hydrogen assisted cold cracking during welding fabrication of P91 weld joints must be considered before any heat treatment is conducted.
Wasserstoff erfüllt die zentrale Rolle für die Umwandlung der bisherigen fossil-basierten Energieerzeugung und -nutzung auf eine dekarbonisierte, nachhaltige Form. Dazu muss der Wasserstoff erzeugt, gespeichert, transportiert werden, bevor er wieder der Nutzung zugeführt wird. Hierzu sind entlang der gesamtem Prozesskette Wasserstofftechnologien notwendig, die einen sicheren Betrieb erfordern. Hierbei kommt dem schweißtechnischen Anlagen- und Behälterbau wesentliche Bedeutung zu, insbesondere (aber nicht ausschließlich) für Speicherung und Transport des Wasserstoffes. Der vorliegende Beitrag gibt einen kurzen Überblick, wo und wie die konventionelle Schweißtechnik hierzu wichtige Beiträge leistet. Die additive Fertigung, also das „Drucken“ von Bauteilen wird dabei zunehmend wichtiger, entlang der gesamtem Prozesskette der Wasserstofftechnologien. Gleichwohl darf nicht unterschätzt werden, dass auch wesentlicher Bedarf an der Erweiterung und teilweiser Neufassung von bestehenden Regel- und Normenwerken besteht.
Adaption of Heat Control Concepts for Welding Stress Optimization in High-strength Steel Components
(2016)
High-strength structural steels from 690 MPa are increasingly applied at present. Major reasons are lightweight design trends and potential cost reductions. The structural design of welds and their manufacturing become more challenging with increasing material strength. By reasons of a higher yield ratio of these steels, the development of high residual stresses has to be avoided, since they are detrimental to the components safety and performance. Local restraint stresses and welding loads due to external shrinkage restraints occur. Frequently, this leads to critical tensile residual stresses in the weld and HAZ. In this study, influences of welding process parameters and restraint conditions on the residual stress state in welded components of high-strength steels were investigated. Multilayer GMAW tests under free shrinkage and experiments under well-defined restraints in special in-house developed testing facilities were accomplished. The tests permitted analyses of the resulting local residual stresses measured by means of X-ray diffraction and global reaction stress build-up while welding and cooling. Significant effects were found for heat control, seam configuration and restraint condition. Besides high restraints, elevated preheating and interpass temperatures lead to increased welding stresses. An adaption of welding parameters considering heat control, weld run sequence and seam configuration proved to be beneficial.