Changes in corrosion and fracture properties of cast stainless steels through heat treatments

In this study, after austenitization heat treatment was applied at 1025oC of duplex and super duplex stainless steels produced by casting method, tempering heat treatment was applied at 400oC, 500°C, 600°C and 700oC, and cooling process was carried out in air and oil. The microstructure, toughness and hardness properties of the obtained samples were examined in detail. Light optical microscope and scanning electron microscope (SEM) was used for microstructure investigations. The ferrite-austenite phase balance of the samples was determined with the Feritscope. In addition, the corrosion test was applied to the samples according to ASTM A923-03 Method A. As a result of the applied heat treatments, intense sigma phase formation was detected in ferrite areas of 1.4462 duplex stainless steel and thus the toughness values decreased. In 1.4410 material, chromium nitrite (Cr2N) formation occurred at the ferrite austenite interface. In the corrosion experiments, no microstructural corrosion formation was observed in 1.4410 material. However, intense corrosion formations of the 1.4462 material were identified microstructurally in the ferrite areas because of taking place sigma phases.