Effect of slip characteristics on fatigue properties of high-manganese steels in air & corrosive environment

Abstract

This research investigates the high-cycle fatigue properties of high-manganese twinning-induced plasticity (TWIP) steels, in the contexts of stacking fault energy (SFE) and carbides, both in the ambient and in corrosive seawater environments. High-manganese TWIP steels exhibit exceptional mechanical properties, but the explicit role of carbides and their fatigue behavior especially in corrosive environments remains unclear. Understanding the fatigue behavior of TWIP steels is crucial for optimizing their utilization in various industries. Thus, this study aims to provide a comprehensive understanding on the corrosion behavior and fatigue properties of high-manganese TWIP steels in seawater condition. The first part of the research specifically examines the high-cycle fatigue properties of high-manganese TWIP steels, with a focus on stacking fault energy (SFE). Four kinds of TWIP steels with different SFE values, achieved through the control of alloy composition, were studied. The results indicated that the high-cycle fatigue properties of high-manganese TWIP steels were not solely dependent on conventional tensile properties such as yield strength (YS) and ultimate tensile strength (UTS). Microstructural features, especially the interaction between twins and grain boundaries, were found to play a significant role in determining the fatigue behavior of these materials. The addition of aluminum to the steels enhanced their fatigue properties, primarily due to the increased SFE, promoting cross-slip and relieving stress concentration on grain boundaries, thereby retarding crack initiation. The second part of the research investigated the influence of carbides on the fatigue properties of high-manganese TWIP steels. Three kinds (NbV, NbV-HT, and NbVAl) specimens with distinct carbide distributions and compositions were examined. The presence of small-sized carbides (less than 10 nm) in NbV specimens obstructed the propagation or initiation of deformation twins, suggesting that carbides enhance the fatigue resistance of the material by impeding twin formation. In contrast, NbV-HT specimens with larger carbides, despite its improved tensile properties, exhibited poorer fatigue performance, emphasizing the critical role of carbide size in determining fatigue properties. The NbVAl specimen, with its high SFE, demonstrated that a high SFE could enhance fatigue resistance. The findings suggest that optimal fatigue performance may be achieved with high-manganese steel (HMS) containing fine carbides and high SFE. In conclusion, the study highlights the critical role of carbides, particularly their size and distribution, in determining the fatigue properties of high-manganese steels. The third part of the research investigates the fatigue properties of high-manganese TWIP steels in corrosive environments, specifically those close to seawater conditions. The research aims to deepen the understanding of material-environment interactions and optimize the utilization of these steels in corrosion-prone applications. Four distinct types of high-manganese steels with controlled aluminum and chrome content were manufactured and subjected to fatigue testing in a simulated seawater environment. Chromium containing alloys significantly enhanced corrosion resistance, leading to improved fatigue life. Fracture surface analysis revealed that fracture initiation occurred at the surface, exhibiting cleavage fracture with visible traces of protrusion or twin/slip. Additional microcracks were observed compared to those of air tests. Corrosion characteristics were examined, revealing that aluminum (Al) and chromium (Cr) interacted with oxygen (O) to form a passivation film that inhibited corrosion. The steel variants containing Cr exhibited the highest Ecorr values, indicating superior corrosion resistance. X-ray photoelectron spectroscopy (XPS) analysis identified a notable absence of elements contributing to the formation of a protective passive film. After the corrosion process, the quantity of aluminum oxide (Al2O3) noticeably increased, and this thin layer might play a role of enhancing to fatigue properties of HMS. Cr added HMS make 20nm thickness of stable oxide layer, which significantly improve corrosion resistance. Overall, this research contributes to our understanding of the fatigue behavior of high-manganese TWIP steels and their performance in corrosive marine environments. The findings provide valuable insights for the design and utilization of TWIP steels in the industrial applications, particularly in seawater parts. Further research can continue to explore the complex relationship between SFE, carbides, corrosion resistance, and fatigue properties to optimize the performance and durability of TWIP steels in various applications.