Cooling of Duplex Stainless-Steel Bars With Different Water and Air Impinging Jet Flow Rates

Super duplex stainless steel (SDSS), known for its high corrosion resistance and mechanical properties, is widely used in applications in aggressive environments, such as marine and petrochemical industries. However, intermetallic precipitates may form during cooling from high temperatures, detrimentally affecting the steel's properties, especially its impact toughness. Since cooling after solution annealing is a key step in production to obtain a precipitation-free component, it is important to understand to what extent the cooling process can be optimized and adjusted in terms of cooling rates and their effect on the quality of steel. The aim of this study is to study the effect of cooling rate on the quality of SDSS. For this purpose, the Impinging Jet Quenching Technique (IJQT) was employed to perform continuous and controlled cooling of 80 mm diameter SDSS 2507 solid bars with water and air jets of different flow rates to cover a wide range of cooling rates. The bars were analyzed through microstructure analysis using a scanning electron microscope, hardness tests, impact toughness tests, and fracture surface observations using a stereo light microscope. The results showed a consistent decrease in impact toughness throughout the tests with decreasing cooling capacity, which facilitated the σ-phase precipitation.