Cryogenic fracture toughness of 9%Ni steel flux cored arc welds

The fracture toughness was investigated by using Crack Tip Opening Displacement (CTOD) test at room temperature (23 °C) and low temperature (−193 °C). With the increase of welding heat input, the austenitic fraction of the weld increased but the number of precipitated phases decreased. At room temperature, the fatigue cracks propagated transgranularly when precipitation was scarce. When precipitation was extensive on grain boundaries, crack propagation was intergranular. At −193 °C, most cracks propagated in intergranular mode. A small amount of precipitated phases also caused fatigue cracks to grow along grain boundaries. Some large precipitates on the propagation path of fatigue cracks were broken. Precipitates reduced the resistance of crack propagation at austenite grain boundaries. The influence of precipitates on grain boundaries increased at low temperature. The number and size of precipitates should be controlled strictly in the FCAW process of 9%Ni steel.