Isı girdisi ve ısıl döngülerin gaz altı kaynak yöntemi ile kaynaklanmış API 5L x70m çeliğinin kırılma tokluğuna etkisi.

High strength low alloy steels are widely used in line pipe applications since they have reasonably high strength and toughness due to their micro-alloying elements and production via thermomechanically controlled process. During welding of these steels, microstructures of the fusion zone and the heat affected zone consisting globular and acicular ferrite alter due to induced heat and thermal cycles. Consequently, changes in the microstructure affects the mechanical properties such as fracture toughness. Gas metal arc welding used in line pipe applications has several advantages such as high quality welds in short time, simplicity, no extra flux is needed, and no slag. The primary aim of this work to understand the effects of heat input and number of thermal cycles in gas metal arc welding on the fracture toughness of API 5L X70M steel. Effects of heat input and thermal cycles originating from weld passes on formation of local brittle zones and effect of local brittle zones on general fracture mechanism were investigated. Particular emphasis has been placed on the coarse grained heat affected zone.Thesis (M.S.) -- Graduate School of Natural and Applied Sciences. Metallurgical and Materials Engineering