Microstructural characteristics and corrosion behavior of a super duplex stainless steel casting

The machining of super duplex stainless steel castings is usually complicated by the difficulty involved in maintaining the dimensional tolerances required for given applications. Internal stresses originating from the solidification process and from subsequent heat treatments reach levels that exceed the material's yield strength, promoting plastic strain. Stress relief heat treatments at 520 °C for 2 h are an interesting option to solve this problem, but because these materials present a thermodynamically metastable condition, a few precautions should be taken.The main objective of this work was to demonstrate that, after solution annealing at 1130 °C and water quenching, stress relief at 520 °C for 2 h did not alter the duplex microstructure or impair the pitting corrosion resistance of ASTM A890/A890M Grade 6A steel. This finding was confirmed by microstructural characterization techniques, including light optical and scanning electron microscopy, and X-ray diffraction. Corrosion potential measurements in synthetic sea water containing 20,000 ppm of chloride ions were also conducted at three temperatures: 5 °C, 25 °C and 60 °C.