Fatigue Behavior of Metastable Austenitic Stainless Steels in LCF, HCF and VHCF Regimes at Ambient and Elevated Temperatures

Smaga Smaga,Daniel Daniel,Sorich Sorich,Boemke Boemke,Skorupski Skorupski,Beck Beck

doi:10.3390/met9060704

Smaga Smaga, Daniel Daniel + Show 4 more

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https://doi.org/10.3390/met9060704

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Journal: Metals	Publication Date: Jun 21, 2019
Citations: 24	License type: CC BY 4.0

Affiliation: University of Kaiserslautern

Abstract

Corrosion resistance has been the main scope of the development in high-alloyed low carbon austenitic stainless steels. However, the chemical composition influences not only the passivity but also significantly affects their metastability and, consequently, the transformation as well as the cyclic deformation behavior. In technical applications, the austenitic stainless steels undergo fatigue in low cycle fatigue (LCF), high cycle fatigue (HCF), and very high cycle fatigue (VHCF) regime at room and elevated temperatures. In this context, the paper focuses on fatigue and transformation behavior at ambient temperature and 300 °C of two batches of metastable austenitic stainless steel AISI 347 in the whole fatigue regime from LCF to VHCF. Fatigue tests were performed on two types of testing machines: (i) servohydraulic and (ii) ultrasonic with frequencies: at (i) 0.01 Hz (LCF), 5 and 20 Hz (HCF) and 980 Hz (VHCF); and at (ii) with 20 kHz (VHCF). The results show the significant influence of chemical composition and temperature of deformation induced ´-martensite formation and cyclic deformation behavior. Furthermore, a “true” fatigue limit of investigated metastable austenitic stainless steel AISI 347 was identified including the VHCF regime at ambient temperature and elevated temperatures.

Highlights

In the early stages of the development of stainless steels, the passivity of the material and, its “stainlessness” was the main scope of development [1,2]
Since the chromium contents of typical austenitic stainless steels exceed 16 wt%, their equilibrium microstructure at room temperature would be fully ferritic, if no other austenite stabilizing alloying elements were added to the material
The present paper focuses on microstructural changes in metastable austenitic stainless steels, their cyclic deformation and transformation behavior at ambient and elevated temperatures in the whole fatigue regime from low cycle fatigue (LCF) to very high cycle fatigue (VHCF)

Summary

Introduction

In the early stages of the development of stainless steels, the passivity of the material and, its “stainlessness” was the main scope of development [1,2]. Chemical passivity of steels in many environmental conditions is achieved by alloying at least about 11 wt% chromium to the base material. Due to an excellent combination of mechanical and technological properties, as well as corrosion resistance, austenitic stainless steels are the most prevalent group of stainless steels—widely used for components in nuclear power and chemical plants as well as a great variety of industrial, architectural and biological applications [3,4,5,6]. Since the chromium contents of typical austenitic stainless steels exceed 16 wt%, their equilibrium microstructure at room temperature would be fully ferritic, if no other austenite stabilizing alloying elements were added to the material. Elements most often used to obtain an austenitic microstructure are nickel, manganese, carbon and nitrogen. Because carbon has a very high affinity with chromium, chromium carbides are prone to develop at Metals 2019, 9, 704; doi:10.3390/met9060704 www.mdpi.com/journal/metals

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