Fatigue Crack Growth Behaviour in Welded Joints of Armour Steel

Welded joints are widely recognized as the most critical point in structures made of armour steels due to pronounced thermal effects, microstructural heterogeneity, and the degradation of mechanical and fatigue properties. This study investigates the mechanical properties and fatigue crack growth resistance of a welded joint produced on SA 500 armour steel, with the aim of preserving the properties of the base material as much as possible. To achieve this, a welding procedure incorporating a high-strength filler wire and optimized welding parameters was applied. Hardness and tensile testing was conducted to evaluate the extent of property degradation caused by welding. The results demonstrate that the applied welding process effectively limited the reduction in hardness and tensile strength, achieving values reasonably close to those of the base material. In addition, fatigue crack growth behaviour was investigated in accordance with ASTM E647, using both the Paris law and the McEvily law. The obtained fatigue crack growth curves and threshold stress intensity factor (ΔKth) values indicate the nearly identical fatigue behaviour of the base material and the heat-affected zone, confirming the successful preservation of base material fatigue behaviour in the thermally affected zone. Moreover, the weld metal exhibited superior resistance to fatigue crack initiation and growth. Overall, the results confirm that the proposed welding approach provides favourable mechanical and fatigue performance for welded joints in armour steel applications.