Abstract
Relationship between the microstructure and the fracture behavior of welds which were tested by Charpy impact on SUS329J1 (Fe-25Cr-5Ni-0.1N) stainless steel has been studied.
Volume fraction of γ phase decreases at HAZ which has been heated over 1400K. At the region over 1600K, the morphology of γ also change to Widmanstatten and the Kurdjumov-Sachs relation exists between γ and α phase, so the phase boundary has good coherency.
There is certain relationship between crack propagation and microstructure. When the Charpy test performed at room temperature, tearing or voids occur in α region, because the ductility and strength of γ phase are higher than ones of α. γ phase is deformed at the circumference of dimple and γ maintains the ductility of duplex steel.
Consequently, the fracture toughness increases with increasing the γ volume fraction.
At low temperature, cleavage fracture occurs in a phase, same time γ phase plays the part of a little obstacles to crack propagation. In Widmanstätten like γ, Charpy impact value slightly increases with increasing the volume fraction of γ phase. In band like γ, a separation of α-γ phase boundary occurs and the crack propagates zigzag manner, so the impact value increases more substantially than widmanstätten like γ in the case of crack propagation normal to the γ phase.
