Enhancing Fatigue and Fracture Properties of Super Duplex Stainless Steel by Friction-Stir Processing

The use of austenitic-ferritic or duplex stainless steels (DSSs) is increasing in several industries because such steels possess various properties that result in better performances compared to traditional austenitic and ferritic steel grades. DSSs and particularly super DSSs are considered excellent materials for desalination plants, seawater systems, pressure vessels, heat exchangers, water heaters, rotors, impellers, shafts, offshore platforms, and high-capacity pumps installed in desalination, power plants and petrochemical plants. Loadings are often cyclical in nature due to various operational needs. The accumulation of fatigue damage at defects produces cracks that can propagate and lead to catastrophic failures. Fatigue failures are known to represent 80 to 90% of the total failures in industry. Therefore, understanding the fatigue behavior of emerging materials such as super duplex stainless steels (SDSS) is an essential element in the design of structures and machine components. The fatigue behavior of materials is known to be affected by a number of parameters, among these is the surface condition and the residual stress state. A number of techniques such as shot peening and laser shock peening are employed for refining grains on the surface and strengthening materials by creating compressive residual stresses. Friction stir processing (FSP) is a new technique that we believe will enhance SDSSs fatigue and fracture properties. The proposed research intends to optimize friction stir processing of SDSS (UNS S32750) and then investigate and characterize the fatigue damage and crack growth of processed material. The effects of FSP on fracture toughness, crack initiation and fatigue crack propagation characteristics of SDSS will be studied. The proposed experimental program will provide profound insight into the friction stir processing of SDSS and determine FSP effects on its fatigue behavior, which will lead to a more accurate estimation of fatigue life or better design decisions. The project duration is 30 months (24 working months) at the cost of SAR 268,100.00.