1- Introduction

2- Experimental method

3- Results and discussion

4- Conclusions

References

Abstract

The deuterium permeation behavior of palladium-coated 316L stainless steel and 430 stainless steel was studied by the gas permeability testing device in this study. The results show that the deuterium permeability of the palladium-coated 316L stainless steel tested at 350 °C∼650 °C was very close to the Forcey’s results. This way, the conformity to some other reported results has been verified for the gas permeability testing device. The deuterium permeability for the oxidized 430 stainless steel was compared with that for the palladium-coated 430 stainless steel at temperature range of 350 °C–600 °C. The deuterium permeability for the oxidized 430 stainless steel was reduced by one order of magnitude compared with that for the palladium-coated 430 stainless steel. However, the activation energy of deuterium permeation as gas form for the oxidized 430 stainless steel was almost the same as that for unoxidized 430 stainless steel.

Introduction

Zirconium hydride is used as the reactor moderator in the thermionic space nuclear power and it easily decomposes hydrogen in the operating environment. The released hydrogen penetrates into the core through the relevant structural components, affecting the physical parameters of the reactor [1]. Compared with 316L austenitic stainless steel, 430 ferritic stainless steel has the advantages of good thermal conductivity, low thermal expansion coefficient and low sensitivity to stress corrosion cracking. It is selected as one of the alternative reactor core materials for structural components of the thermionic space nuclear power. Therefore, investigating the hydrogen permeation behavior of 430 ferritic stainless steel has important engineering application value for the development of thermionic space nuclear power. A lot of research has been carried out on the preparation and properties evaluation of hydrogen isotope permeation barrier coatings for the fusion reactor. However, 316L stainless steel or low-activity ferritic/martensitic steel was used as the substrate material in most of these studies [2–15]. There are few reports on the hydrogen isotope permeation behavior of 430 ferritic stainless steel. In the present study, the deuterium permeability of palladium-plated 316L stainless steel was first tested and compared with the reported values to verify the conformity to other reported results for the gas permeability testing device. Then the deuterium permeation behavior of the palladium-plated 430 stainless steel as well as that with natural oxide film was investigated.

The area of biomaterials is a continuous research area. Among others, stainless steels are also used in medical applications such as fracture plates, wires, sutures and implants etc. Surgical grade 316 L stainless steel is specifically used for medical application. It primarily contains nickel, chromium and molybdenum wherein the purpose of nickel is to retain the FCC structure of stainless steel almost at any temperature unlike conventional steel which has ferrite (BCC structure) in ambient temperature. Also, nickel imparts a polished and glossy finish to surgical grade stainless steel which is an important factor to keep it hygienic. But, the harmful effect of nickel on human body has been investigated and reported for quite some time now. The adverse effect of nickel (Ni) ions that release from stainless steel upon crevice and pitting corrosion has led to the evolution of Ni-free stainless steel with high nitrogen content. This paper briefly reviews the effect of nickel release in human body and let go the presence of nickel in stainless steel by uplifting nitrogen content in it. Furthermore, the groundbreaking findings on Nifree stainless steel in last 10 years are presented and the possibilities of further developments have been hypothesized.

Introduction

Metals are predominantly used as implants in biomedical industries. The foremost criterion for choosing any implant material is its biocompatibility. The reason for choosing metallic implant is its superior mechanical strength and corrosion resistance. The most commonly used biomedical alloys are grade 5 Ti6Al4V, CoCrMo and stainless steel (AISI 316L) [1,2]. The fabrication of stainless steel is comparatively easier than Ti-alloys and CoCr alloys. Although stainless steel is used as implants at places but its application is confined to bone healing, screws and fixations. Stainless steel is present in three microstructures which are austenite, martensite and ferrite. There is one other kind which is the duplex stainless steel; it basically contains both austenite and ferrite structure [3]. These structures are attributed to proper adjustments in its chemistry which later reflects in its properties. For instance, austenitic steel doesn’t possess ferromagnetism properties like its counterpart martensitic and ferrite steel. One of the preferential attribute of implants is the non-existence of ferromagnetic property which is why austenitic stainless steels are preferred over martensitic and ferrite steels for implant material. The other advantages of austenitic steels are their FCC structure, low yield strength to tensile strength ratio, better formability and corrosion resistance among others. 316 L Stainless steel is basically Fe-based alloys containing carbon (C of maximum 0.03%), chromium (Cr of atleast 16%) and nickel (Ni of atleast 10%). Homogenous corrosion resistance is the most important characteristics of stainless steel. Corrosion resistance is not an intrinsic property but the behavior of material surface in interaction with environment.

1- Introduction

2- Experimental investigation

3- Finite element modeling

4- Analytical study

5- Conclusions

References

Abstract

The use of concrete-filled stainless steel tubular (CFSST) members is relatively innovative and new. CFSST columns can be used for bridge piers, multi-story buildings and other supporting structures. However, a common mode of failure with these type of tubular composite columns is inelastic outward local buckling occurring at the column ends. Therefore, this paper presents the results of experimental, numerical and analytical investigations into the behavior of circular CFSST columns strengthened by carbon fiber reinforced polymer (CFRP) wrap and subjected to axial compression loading. The experimental investigation comprised three series of tests. The main variables tested were the diameter to thickness ratio of the stainless steel tube and the thickness of the CFRP wrap. 3D finite element models (FEMs) were developed for CFRP-wrapped CFSST columns using the ABAQUS software and were validated with experimental results. An extensive parametric study was carried out by using the validated FEMs. It was shown from the experimental and FEMs results that CFRP jacketing was highly effective in improving the axial load carrying capacity and axial shortening capacity of the CFSST columns. Finally, an analytical model based on the FE parametric study results was proposed to predict the axial load carrying capacity of the CFRP-wrapped CFSST columns.

Introduction

Recently, stainless steel material has been used as a construction material, while it was previously only used for special purposes or for decoration due to its advantages over carbon steel which include its aesthetic appearance, high resistance to corrosion, ease of maintenance and high fire resistance. Taking into account the long-term cost, stainless steel material can be selected as a competitive material [1]. In addition, one of the reasons for considering stainless steel as a competitive structural material is its favorable mechanical properties and its high ductility. Stainless steel material exhibits a nonlinear stress- strain relationship with no defined yield point, unlike carbon steel material [2]. Many investigations have been conducted into the structural behavior of unfilled (hollow) stainless steel sections. Important early reported studies exploring the structural performance of hollow stainless steel sections were performed by Rasmussen and Hancock [3]. Subsequently, a series of studies has been performed to understand more about these tubular sections [4–7]. These studies have contributed greatly to the expansion of information on the structural performance of stainless steel elements and, at the same time, have highlighted some shortcomings in the existing design standards such as American stainless steel design specifications SEI/ASCE-8 and EN 1993-1-4. For the sake of simplification, these existing design standards disregarded some mechanical characteristics observed in stainless steel, such as strong strain hardening and the rounded stress-strain relationship. This simplification method, adopted in the existing standard codes, includes using an elastic perfectly plastic bilinear material model that leads to a significant degree of conservatism. A new, efficient and more rational method has been developed to consider the particular stress-strain characteristics of stainless steel [8–10]. Instead of considering that the maximum design stress limit is the 2% proof stress, as in the existing standards, a new method called the continuous strength method (CSM) [11–16] has been developed as a deformation-based design method to exploit the noticeable strain hardening in the determination of stainless steel cross-section resistances. However, the initial high cost of stainless steel material has limited the extensive use of stainless steel material in structural construction. Hence, concrete-filled stainless steel tube (CFSST) columns have been developed to balance the high initial stainless steel material cost, as well as to enhance the structural behavior.

1- Introduction

2- Materials and Methods

3- Results and Discussion

4- Summary of Passive Behaviour

5- Conclusions

References

Abstract

The corrosion behaviour of type 316L stainless steel in aqueous 30–50 wt%. NaOH at temperatures up to 90 °C has been elucidated. Exposure to room temperature environment showed parabolic weight loss behaviour, with corrosion rates of up to 0.4 mm/year. Higher NaOH concentrations and exposure temperatures resulted in a reduced stability of the electrochemical passivity domain, associated with higher corrosion rates. Exposure to de-aerated 50 wt%. NaOH presented corrosion rates of up to 0.5 mm/year at open circuit potential, with maximum corrosion rates under polarisation of up to ≈ 18 mm/year. The formation of a dark iron-oxy-hydroxide and nickel-oxide was observed, with exposure to temperatures in excess of 50 °C. The behaviour of type 316L stainless steel in hot caustic environment is compared to types 204, 304, 2205 stainless steel, and nickel alloy 200.

Introduction

The corrosion of stainless steel in hot caustic environment has been the subject of a number of investigations, typically with a focus on Kraft pulping liquors [1–11]. The material performance in these environments is governed by the stability of the passive surface flm, which develops as a function of alloy microstructure, chemical composition, and associated environmental interactions. Austenitic stainless steels generally show high corrosion rates when exposed to concentrated, deaerated alkaline aqueous environment at temperatures above 60 °C, with typical corrosion rates of 0.05–2 mm/year. Very dilute caustic solutions show reduced corrosion susceptibility, for example, with exposure to mildly caustic environment up to pH 12, resulting in corrosion rates of 0.01 mm/year [12–14]. The latter investigation also concluded that temperature is key for understanding material behaviour in these environments, directly afecting corrosion rates of stainless steel in NaOH containing environment [6, 7]. In NaOH environment at room temperature, rates as low as a few μm/year have been reported [6, 15–22]. Based on the Pourbaix diagrams of Iron, Chromium and Nickel, the possibility of forming a passive flm with exposure to caustic pH supports the argument of using stainless steel in these media. A summary of the corrosion behaviour of stainless steels with exposure to diferent caustic environments is provided in [12]. The aim of this paper is to provide a comprehensive overview of the corrosion performance of type 316L in hot caustic aqueous environments. The project was centered on identifying alloy composition and environment-related parameters, including temperature, de-aeration, and NaOH concentration, to better understand the passivation behavior of stainless steels microstructure.

This paper is concerned with the behaviour of composite beams made from stainless steel. Steel-concrete composite members are widely used in the design and construction of modern structures such as bridges and high rise buildings. Depending on the degree of composite action, a significant increase in strength and stiffness performance is gained compared to a bare steel or concrete section. This results in savings not only in construction depth but also in terms of material consumption, which means also lower environmental impact and reduced energy consumption [1]. Composite beams which are subjected to positive bending (i.e. sagging) offer a particularly efficient use of the constituent materials. In this case, the steel section is subjected to tensile stresses whilst the concrete slab acts primarily in compression, thus utilising the favourable characteristics of each material. It is generally desirable for plastic design that composite beams have a ductile cross-section, in which strain hardening develops in the lower flange before the collapse moment is reached [2]. However, for calculating the load-bearing capacity of composite beams, design codes such as Eurocode 4 [3] generally neglect strain hardening effects and employ a rigid-plastic analysis of the cross-section, thus providing conservative predictions of the capacity in many cases, particularly when ductile materials such as stainless steel are employed. Stainless steel has been employed in construction since the 1920s, when the main usage was in building facades. Nowadays, stainless steel has become popular in a wide range of construction and load-bearing applications due to its excellent mechanical properties such as higher strength and ductility, better retention of strength and stiffness at high temperature [4] and excellent corrosion resistance properties, compared with carbon steel. Stainless steel does not require coatings to be applied, thus leading to life-cycle cost savings relative to carbon steel especially for offshore steel structures [5], as well as reducing maintenance and rehabilitation costs. In recent years, stainless steel has been the subject of intensive research in order to provide useful, efficient and reliable design guidance for engineers. The vast majority of research into stainless steel has been focussed on bare steel elements. Researchers have investigated the flexural behaviour of stainless steel columns subjected to compressive loading or combined compression and bending moment (e.g. [6–9]) and beams (e.g. [10–13]) as well as beams and columns under fire conditions (e.g. [14]). The use of stainless steel in composite structures has hitherto received little attention from the engineering community and research studies have generally been limited to investigating the behaviour of concrete-filled stainless steel columns under different loading conditions using experimental and numerical analysis. Lam et al. [15] conducted experiments on the behaviour of axially loaded concrete-filled stainless steel elliptical sections made from normal and high strength concrete. Uy et al. [16] carried out experiments on concrete-filled stainless steel circular, square and rectangular sections of short and slender columns subjected to combined axial compression and bending moment. The behaviour of concrete-filled stainless steel circular and square tubular sections subjected to axial compression under fire conditions has also been studied through a series of experiments [17]. Moreover, nonlinear finite-element analysis was used to investigate the performance of concrete-filled stainless steel tubular columns of square, L-, T-, and + shape sections under axial compression or combined compression and bending moment [18, 19]. To date, there has been no research available in the public domain on traditional composite beams (i.e. a bare steel section connected to a concrete slab through shear connectors) using stainless steel. The following section describes the context in which these members are highly relevant in the current era.

The elastic and plastic properties of hydrogen charged duplex stainless steel (DSS) at high strain rate and high pressure are important for the understanding of their durability at applications combining hydrogen and mechanical load. Measurements of elastic plastic properties at high strain rate in stainless steel alloys can be achieved by dynamic loading [1]. In this paper we compare between the effect of high strain rate (105 s-1) and low strain rate (10 7 s-1) in order to add another milestone to the hydrogen embrittlement failure model [2]. We study on low strain rates via tensile machine and on high strain rate via plate impact experiments by dynamic loading. In this work, dynamic loading is reported for duplex stainless steel (DSS) which combines austenitic and ferritic (BCC, Į) phases. The effect of hydrogen in DSS under quasi-static loading has been investigated elsewhere [3], [4], yet its effect under dynamic loading was not studied and was previously covered by us in 2014 [5], [6]. Comparison between strain rates at different levels provide insights to the details of hydrogen behaviour at different deformation levels, in order to relate dynamic to static data. Hydrogen behaviour at different deformation levels was studied by thermal desorption spectrometry (TDS). The potential failure mechanism and hydrogen diffusion related to it will be discussed in details.

2. Experimental procedure

2.1. Material properties

In this work we used the lean duplex stainless steel (LDS), LDX 2101. The microstructure of LDS consists of equiaxed grains with an average grain size of about 20 ȝm as was describes by us in previous studies [7]–[9]. Its chemical composition is Fe—0.026C—4.9Mn—21.53Cr—1.53Ni—0.2Mo—0.22N—0.63Si—0.001S—0.025P wt%. The hydrogen charging condition was gas-phase hydrogen charging at 300 o C and 60 MPa pressure for 3 hr. This charging procedure created a homogenous hydrogen content of 54 wt ppm along the samples’ bulk. The microstructure of the gas-phase hydrogen charged LDS, published in different works by us [7]–[9], revealed the appearance of needle shaped sigma (ı) phase with the Fe(CrMo) composition. This phase plays an important role in the hydrogen embrittlement model.