Influence of the submerged arc welding in the mechanical behaviour of the P355NL1 steel - part II: analysis of the low/high cycle fatigue behaviours

A normalized fine grain carbon low alloy steel, P355NL1 (EN10028-3), intended for service in welded pressure vessels, where notch toughness is of high importance, has been investigated. Applications with this steel usually require the intensive use of welds. One of the most common welding processes that are used in the manufacturing of pressure vessels is the submerged arc welding. This welding process is often automated in order to perform the main seam welds of the body of the vessels. The influence of the automated submerged arc welding, in the mechanical performance, is investigated. In this paper (Part II) the low and high cycle fatigue and crack propagation behaviours are compared between the base and welded materials. Several series of small and smooth specimens as well as cracked specimens made of base, welded and heat affected materials, respectively, were fatigue tested. Strain, stress and energy based relations for fatigue life assessment, until crack initiation, are evaluated based on experimental results and compared between the base and welded materials. Finally, the fatigue crack propagation behaviours are compared between the base, welded and heat affected materials.