To improve the properties of metal parts, the metal surface is usually treated with temperature methods - the material is heated and cooled. Stainless steel AISI 316L is a common alloy that is used for the production of chemical and aerospace equipment, biomaterials, handrails in the pool, jewelry. A possible alternative to temperature treatment is shot peening. A strong air flow strike the metal with small particles. This makes the surface harder and creates residual compression stresses, as well as reduces the grain size. Scientist from RUDN University together with colleagues from Italy and Turkey found out that shot peening increases the endurance of AISI 316L steel.
"AISI 316L stainless steel is widely used in the aerospace, food and chemical industries, as well as in the production of biomaterials due to its high corrosion resistance and exceptional biocompatibility. Shot blasting is one of the cold working processes that makes it stronger. This process takes place without heating - small pellets hit the surface of the material at a certain speed. Each shot mechanically deforms the material, creating grains. We decided to conduct a comprehensive study of AISI 316 L in order to learn more about this process under various conditions," said Kazem Reza Kashyzadeh, Associate Professor of the Department of Transport of RUDN University.
Scientists experimentally investigated 42 types of shot peening with different intensity and different coverage area. They have determined the microstructure of steel after processing, grain size, surface topography, hardness, wettability and other parameters. The researchers also found optimal peening parameters and studied the residual stress - the ability not to collapse under the action of cyclic loads - of stainless steel treated in this way.
The optimal parameters turned out to be an intensity of about 25 (it is measured using the so-called Almen test by bending the test plate, which is subjected to the same treatment as the material under study) and 1500% coverage area (that is, the device passes through each area of the material 15 times). It turned out that this makes it possible to increase the fatigue strength of the material by 81.25%.
"To determine the optimal values of the intensity and coverage area, we examined the samples obtained under these conditions. The results showed that shot peening significantly increases fatigue strength. We concluded that it is possible to achieve results close to experimental observations," said Kazem Reza Kashyzadeh, Associate Professor of the Department of Transport of RUDN University.