Abstract
The fatigue performance of 00Cr17Ni12Mo2 (AISI 316) and 00Cr17Ni14Mo2 (AISI 316L) stainless steels represents an important part of their application potential. The fatigue performances of AISI 316 and AISI 316L steels have been studied extensively in the literature. The influence of mechanical properties, chemical composition and microstructural factors on the fatigue properties of these two materials is discussed in this paper. Research shows that strain aging, cold working, and fatigue notch effect on the fatigue strength of these steels. Microstructural features such as grain size and grain boundary segregation also have a large effect on fatigue performance.
Introduction
Stainless steel is a widely used alloy in a variety of industries including the food, medical, chemical and aerospace industries. AISI 316 and AISI 316L steels are two well-known grades of stainless steel. These two materials have similar chemical composition, but differ in their nominal content of carbon, nitrogen, and manganese. In addition, their chemical combination provides an improved resistance to pitting and other forms of chemical corrosion. AISI 316 and AISI 316L steels are often used in the production of components such as pumps, valves, and chemical reactors that are exposed to aggressive chemical environments and need to be able to withstand high temperatures. The fatigue performance of these materials is vital for their use in these applications.
Characterization of AISI 316 and AISI 316L Steels
The two materials of interest, AISI 316 and AISI 316L, have different chemistries. AISI 316 stainless steel is a martensitic stainless steel that contains a nominal composition of 16–18 % Cr, 12–14 % Ni, 2–3 % Mo, 2–3 % Mn, 0.5–2 % Si, and is carbon-free. AISI 316L stainless steel is a ferritic stainless steel that contains a nominal composition of 16–18 % Cr, 12–14 % Ni, 2–3 % Mo, 0–1 % Mn, 0.5–2 % Si, and up to 0.030 % C. These differences can lead to different mechanical properties, such as strength and hardness, for the two materials.
Mechanical Properties of AISI 316 and AISI 316L Steels
The mechanical properties of AISI 316 and AISI 316L steels were studied using standard tensile and hardness tests. The results showed that AISI 316 stainless steel had a higher tensile strength and higher yield strength than AISI 316L stainless steel at temperatures from 20 to 500 ºC. The hardness of AISI 316 was also higher than that of AISI 316L at temperatures from 20 to 500 ºC.
Fatigue Performance of AISI 316 and AISI 316L Steels
The fatigue performance of AISI 316 and AISI 316L steels has been extensively studied in the literature and is an important consideration when these materials are used in application. The fatigue performance of the two materials is affected by both mechanical properties and chemical composition. In addition, strain aging, cold working, fatigue notch effect and microstructural features such as grain size and grain boundary segregation may play a role in the fatigue performance of these steels.
Strain Aging
Strain aging is a phenomenon in which the yield strength of a material increases as a result of exposure to an applied strain. It has been shown that the fatigue performance of AISI 316 and AISI 316L steels is improved by strain aging. The magnitude of the improvement depends on the amount of time in which the material is exposed to the strain and the magnitude of the strain.
Cold Working
It is well-known that cold working of austenitic stainless steels can result in significant improvements in their mechanical properties. It has also been observed that cold working can lead to an improvement in the fatigue performance of AISI 316 and AISI 316L steels. Cold working can increase both the fatigue strength and fatigue life of these materials.
Fatigue Notch Effect
Fatigue tests have been conducted with samples of both AISI 316 and AISI 316L steels having a variety of different notch shapes and notch depths. It has been observed that the fatigue performance of these steels can vary depending on the notch geometry. In general, deeper and more complex notch shapes can lead to lower fatigue strengths and shorter fatigue lives.
Grain Size and Grain Boundary Segregation
The fatigue performance of AISI 316 and AISI 316L steels is also affected by grain size and grain boundary segregation. It has been observed that finer grain sizes lead to higher fatigue strengths and longer fatigue lives in these materials. In addition, the presence of grain boundary segregation can lead to a decrease in fatigue strength and fatigue life.
Conclusion
The fatigue performance of AISI 316 and AISI 316L steels is affected by a number of different factors, including mechanical properties, chemical composition, strain aging, cold working, fatigue notch effect, and grain size and grain boundary segregation. These materials have been studied extensively in the literature and have been found to have excellent fatigue performance.
