Mechanical properties and fracture behaviour of PROTAC 500 armour steel

Knowledge of mechanical properties, fracture toughness, and fatigue crack growth is a crucial prerequisite for the reliable and safe application of armour steel in protective structures. This study presents an experimental characterisation of PROTAC 500 armour steel, produced by heat treatment by low-temperature tempering at 220 °C. Mechanical testing included hardness measurement, tensile testing, and impact toughness evaluation. The measured hardness is 533 HV, while tensile testing reveals a tensile strength of 1677 MPa. The Charpy impact toughness reaches 42 J/cm², indicating a favourable combination of high strength and resistance to fracture. Fracture toughness is determined in accordance with the ASTM E1820 standard using the unloading compliance method with value of 105 MPa·m1/2. The fatigue crack growth behaviour is analysed using the Paris and McEvily law, with a determined threshold for crack propagation DKth = 7.87 MPa·m1/2. Obtained results provide a reliable assessment of the material behaviour under both static and cyclic loading conditions. Through comprehensive evaluation of mechanical and fracture parameters, a complete characterisation of the armour steel is achieved.