Toughness Behaviour in Armour Steel Welds

The process of welding armor steel is a complex process not only due to high percentage of carbon in the base metal, but also because of possible welding faults, appearing in the weld metal zone in the form of cracks and pores. Austenitic filler material is traditionally used for welding armor steels, thus avoiding the negative effect of hydrogen content due to slow diffusion towards the sensitive fusion line. For heavy structural engineering such as armored military vehicles, which are frequently under the effect of impact and dynamic load, it is important to know the dynamic properties of the most sensitive area of welded joints, the weld metal zone. Instrumented impact testing was made on Charpy V specimens. The impact energy results were 56 J and 29 J for crack initiation and propagation, respectively. Due to a significant interest in quantification of material resistance to crack initiation and propagation, the fatigue crack growth rate was measured in the welded metal zone, while the resistance to crack growth in the weld metal was tested by the amount of austenite transformed into martensite. Accordingly, the threshold stress concentration factor was 10 MPa m1/2. XRD spectral analysis revealed direct transformation of γ - austenite into α’ - martensite

Fracture toughness of base and weld metal of aluminum alloy EN AW 7049A T652 FSW joint

The paper analyses the impact of the tool geometry on the friction stir welding (FSW) method on fracture toughness values of the base metal (BM) and weld metal (WM) of a butt welded joints of a high strength aluminium alloy. Values of fracture toughness were obtained using single-edge notched bend (SENB) specimens with fatigue pre-crack sampled from the BM and TMAZ (thermo-mechanically affected zone). Single specimen method was used according to ASTM E 1820 and parameters of elastic-plastic fracture mechanics were determined (CTOD crack tip opening displacement and the J integral). Although the welding tools had different values of cone angle (α = 2.5° - 10°) and the variable length of the pin (h = 5.1 mm - 5.4 mm) at a constant ratio of the number of tool revolutions and the speed of welding, the largest value of fracture toughness has the retreating side of the weld, then the advancing side of the WM, while the BM has the lowest value. This is the effect of recrystallization process in the retreating side of the WM due to combined rotating-straight forward motion of the tool during which the softened material is repeatedly transformed from one side to the other side around the centre of the tool