Ferritic stainless steels in structural applications

Ferritic stainless steels are low cost, price-stable, corrosion-resistant materials. Although widely used in the automotive and domestic appliance sectors, structural applications are scarce owing to a dearth of performance data and design guidance. The characteristics of ferritics make them appropriate for structures requiring strong and moderately durable structural elements with attractive metallic surface finishes. The present paper provides an overview of the structural behaviour of ferritic stainless steels, including a summary of the findings of a recent European project (SAFSS) on ferritics. Laboratory experiments have been completed including material tests as well as structural member tests, both at ambient and elevated temperatures. The experimental data is supplemented by numerical analysis in order to study a wide range of parameters. The findings of this work have enabled design guidance to be proposed, as discussed herein

Buckling response of ferritic stainless steel columns at elevated temperatures

This paper presents a numerical study on the buckling behaviour of ferritic stainless steel columns in fire. Finite element models were developed and validated against existing test results to predict the elevated temperature non-linear response of ferritic stainless steel columns. A total of nine austenitic and three ferritic stainless steel column tests were replicated using the finite element analysis package ABAQUS. Parametric studies were performed to investigate the effects of variation of load level and global slenderness on the elevated temperature buckling response of ferritic stainless steel columns, and to extend the range of structural performance data. Both the experimental and numerical parametric study resultswere compared with the current design rules in EN 1993-1-2 (2005) and recent proposed modifications thereof by Ng and Gardner (2007), Uppfeldt et al. (2008) and Lopes et al. (2010).The European Community's Research Fund for Coal and Steel (RFCS) under grant agreement no. RFSR-CT-2010-00026, Structural Applications of Ferritic Stainless Steels

Reliability assessment of design rules for stainless steel structures

This paper presents a re-evaluation of the current partial resistance factors recommended in EN 1993-1-4 for the design of stainless steel elements. Material data from key stainless steel producers were collected and carefully analysed, and representative values of the over-strength and the coefficient of variation (COV) of the material yield strength and ultimate tensile strength, necessary for performing reliability analysis, were established. The EN 1990 Annex D First Order Reliability Method (FORM) was applied to a substantial pool of experimental results. At the cross-section level, stub column and in-plane bending test results were used to assess the γM0 partial resistance factor. At the member level, flexural buckling and lateral-torsional buckling test results were used to evaluate the γM1 partial resistance factor. It is revealed that the current recommended partial resistance factors in EN 1993-1-4 (γM0 = γM1 = 1.1) cannot generally be reduced, and in some cases, modified design resistance equations are required, if the current safety factors are to be maintained

Tribological behavior of 316L stainless steel reinforced with CuCoBe + diamond composites by laser sintering and hot pressing: a comparative statistical study

The aim of this work was to perform a statistical analysis in order to assess how the tribological properties of a laser textured 316L stainless steel reinforced with CuCoBe - diamond composites are affected by diamond particles size, type of technology (laser sintering and hot pressing) and time of tribological test. The analysis started with the description of all response variables. Then, by using IBM® SPSS software, the Friedman’s test was used to compare how the coefficient of friction varied among samples in five-time points. From this test, results showed that there was no statistically significant difference in the coefficient of friction mean values over the selected time points. Then, the two-samples Kolmogorov-Smirnov (K-S) test was used to test the effect of the diamond particles size and the type of technology on the mean of the coefficient of friction over time. The results showed that, for both sintering techniques, the size of the diamond particles significantly affected the values of the coefficient of friction, whereas no statistical differences were found between the tested sintering techniques. Also, the two-way ANOVA test was used to evaluate how these factors influence the specific wear rate, which conducted to the same conclusions drawn for the previous test. The main conclusion was that the coefficient of friction and the specific wear rate were statistically affected by the diamond particles size, but not by the sintering techniques used in this work.This work was supported by FCT national funds, under the national support to R&D units grant, through the reference projects UIDB/04436/2020 and UIDP/04436/2020. Additionally, this work was supported by FCT with the reference projects UIDB/00319/2020 and PTDC/CTM-COM/30416/2017

Fire testing and design of stainless steel structures

Despite significant progress in recent years in the development of room temperature design guidance for stainless steel structures, fire resistant design has received relatively little attention. This paper reports on studies carried out to investigate the performance of unprotected stainless steel beams and columns in fire. Material tests were carried out on five grades of stainless steel to determine strength and stiffness retention factors at elevated temperatures; both strength and stiffness retention were shown to be superior to that of carbon steel beyond 600 ∘C. The temperature development characteristics of a range of stainless steel sections were investigated, and compared to those of carbon steel sections. Full scale fire tests were conducted on six stainless steel columns, and four stainless steel beams. Finite element modelling of the tests was carried out, and parametric studies were performed to supplement the test data. All tests were carried out as part of the European project ‘Development of the use of stainless steel in construction’. Design recommendations for stainless steel columns and stainless steel beams supporting a concrete slab, based on the ECCS model code for fire engineering, were validated against the test and finite element results. These recommendations have been incorporated into the Euro Inox/SCI Design Manual for Structural Stainless Steel, and implemented in Eurocode 3: Part 1.2, with minor adjustments for consistency with carbon steel

Structural design of high-strength austenitic stainless steel

Efficient use of material is an important factor in achieving economical and sustainable structures. Typically, annealed austenitic stainless steel has a material strength of around 220 N/mm2, somewhat lower than that of common structural carbon steel grades. This lower strength, coupled with the higher material cost, puts stainless steel at a significant disadvantage when considering material selection, despite its other desirable properties. However, the strength of stainless steel may, at relatively low expense, be considerably enhanced through modification of the chemical composition and through the process of cold working due to the strain hardening nature of the material. This strength enhancement has not generally been utilised in practice due to a lack of knowledge on the structural behaviour of this high-strength material. Given the high material cost of stainless steel, the need to optimise the efficiency of design methods and to develop the performance, availability and diversity of the current product range is clear. To this end, this paper describes tests, numerical modelling and the development of design guidance for high-strength stainless-steel members in a range of structural configurations. Material tensile tests, member tests in compression and member tests in bending have been described. The results of the tests have been successfully replicated numerically, and subsequent sensitivity studies and parametric studies have been performed. Test and numerical results have been compared against two design methods developed for standard-strength material (Eurocode 3 Part 1.4 and the deformation capacity based design method). The comparisons have revealed that both design methods provide a similar level of reliability to that offered for standard-strength material, and thus, extension of both design methods to the high-strength grades has been recommended