A simplified prediction way of the ferrite-austenite phase ratio in the heat affected zone of duplex stainless steel has been proposed on the basis of the metallurgical principal of phase transformation. In the heat affected zone (HAZ), especially in the vicinity of the fusion boundary in duplex stainless steel, the excess amount of ferrite phase can be formed resulting in the deterioration of the performance in weldment. The amount of ferrite phase in the HAZ is influenced by the cooling rate in the welding thermal cycle.
The proposed formula to predict the ferrite-austenite phase ratio is as a function of cooling rate and that consists of the constants determined by the type of duplex stainless steel with various chemical compositions. The validity was confirmed by the good fit between the results calculated with the proposed formula and the experimental data referred in the papers.

View full abstract

Stress corrosion cracking (SCC) of carbon steel is likely to occur in CO₂ loaded aqueous amine solutions. However, the effect of material factors on the SCC has been unclear. In this study, we investigated the effect of intergranular cementite on SCC in a 20% monoethanolamine (MEA) solution with CO₂. Slow strain rate tensile testing (SSRT) was conducted in the amine solution, and the crack depth and velocity of a carbon steel with intergranular cementite were higher than those of another steel without intergranular cementite. According to this investigation, intergranular cementite is considered to increase SCC susceptibility. In addition to this metallurgical aspect in carbon steel, two mechanisms of SCC in the amine solution were discussed.

View full abstract