Chromium nitrides effects on low temperature impact toughness and durability of duplex stainless steels forgings.

The chromium nitrides effects on duplex stainless steels low temperature impact toughness and durability were investigated. A duplex rolled ring was cut as different blocks, and different Cr₂N amounts were obtained by trial heat treatments, with the solution annealing furnace temperature set at low and high levels, 1040 and 1140 °C respectively, and the transfer time ranging between 5 and 120 s in order to prevent the σ phase formation. Micrographic examinations, low temperature Charpy impact tests and durability assessments were carried out on specimens sampled from the blocks cores. The material strength was evaluated by hardness tests. The results showed how an increase in transfer time allows the N diffusion in the austenite phase, reducing the nitrides quantity in the ferrite phase. A synergistic effect between the transfer time and the solution annealing temperature on the amount of intermetallic particles was observed. Clear effects of the Cr₂N presence on both material low temperature impact toughness and pitting corrosion resistance were found.