Study on cracking characteristics on aging of super duplex stainless steel weld metal

Abstract

In the present study, we carried out a flux cored arc welding using a super duplex stainless steel as a filler metal and analysed the cause of cracking that occurred at the aging treatment for 30 min at 850°C. The stress concentration effect by the notch of the welding bead affected the hot cracking susceptibility, and the impact value of weldment was remarkably decreased due to the precipitation of secondary phases. In addition, the precipitation of σ of the adjacent area to the crack was measured to be higher by ∼12 wt- than the non-adjacent area to the crack. As a result of analysis of fracture plane, it was embrittled by segregation of impurities or inclusions, which acted as a starting point of the crack, and the crack grew according to the widely distributed σ phase.

Corrosion and cracking characteristics upon aging of hyper duplex stainless steel weld

“…It was observed that the σ -phase and χ -phase were broadly distributed, mainly around the ferrite and austenite grain boundaries or the secondary austenite of the ferrite base. This is in agreement with existing theories that ferrite is transformed into the σ -phase and secondary austenite [13,28,29]. The eutectic reaction increases the precipitation of secondary phases and the EBSD analysis revealed that as the aging time increases, the σ -phase and χ -phase, which contain high Cr or Mo contents, are observed not only at the ferrite/austenite grain boundary but also at the grain boundary of ferrite.…”

“…This increase in the hardness value appears to be caused by hardening due to simple secondary-phase precipitation, which is different from secondary hardening occurring in high-alloy steels, such as DSSs, due to carbides [18-20]. Electrolytic etching was performed using a 10% KOH solution for precipitation phase observation, and reddish-brown precipitates, such as the σ-phase and χ-phase, were observed through the OM (Figure 4) [13,16]. Such precipitates showed a tendency to increase gradually as the heat treatment time increased.…”

“…This eutectic reaction reduces δ-ferrite and increases the precipitation of σ -phase. Accordingly, DSS welds become more susceptible to cracks and thus cracking occurs [13].…”

SCC behaviours of austenitic stainless steel Z3CN20-09M in high temperature water

“…During FEA a double linear isotropic hardening model was used. Density, elasticity modulus and nuxy used in FEA were 7?57 g cm 23 , 193 GPa and 0?3 respectively.…”

“…Former studies also showed that the effect of boundaries and second phases (including ferrite) to crack propagation. [21][22][23] Z3CN20-09M stainless steel, which contains a certain amount of ferrite (more than that in 304SS, less than that in duplex stainless steels), is usually fabricated as primary coolant pipe in nuclear power plants. Some researches have been carried out on Z3CN20-09M stainless steel, [24][25][26][27] however few of them refers SCC behaviours.…”