Lamellar, lamellar-brittle, and lamellar-ductile failure of welded joints

1. The low parameters of the static, dynamic, and cyclic fracture toughness of rolled metal in the z-direction are one of the reasons for formation of lamellar cracks in welded structures characterized by the presence of macro- and microsteps and ledges. It is shown that lamellar fracture takes place in various loading conditions both in the pure form and in the form of mixed lamellar-ductile, lamellar-brittle, or lamellar-fatigue cracks. 2. The occurrence of two types of lamellar cracking was confirmed: high-temperature lamellar cracking in materials contaminated with nonmetallic inclusions, and low-temperature lamellar cracking in the so-called clean steels with a very small number of nonmetallic inclusions. In high-temperature lamellar tearing, the reduction of the fracture toughness of the metal in tests in the z-direction takes place both at high and at low temperatures and, consequently, the formation of lamellar, lamellar-ductile and lamellar-brittle cracks may take place in welding, assembling, and service of structures. In low-temperature lamellar cracking, the fracture toughness decreases mainly at low temperature. This must be taken into account in using steels produced by controlled rolling for welded structures where the metal of members and welded joints is subjected directly to tensile loading in the z-direction. 3. To prevent lamellar, lamellar-ductile, and lamellar-brittle cracks, additional requirements ensuring satisfactory ductility and fracture toughness in the z-direction should be imposed on the materials used for welded structures; this relates mainly to the members and welded joints in which the metal works in the z-direction.