PSI - Issue 43

Stanislav Seitl et al. / Procedia Structural Integrity 43 (2023) 113–118 Author name / Structural Integrity Procedia 00 (2022) 000 – 000

114

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material assumptions similar to carbon steel. Significant advances in the use of stainless steel in construction are described, for example, in Gardner (2005), Baddoo (2008), Gedge (2008) and Gardner (2019). The purpose of this work is to compare the microstructure and related basic mechanical properties of AISI 304 steel supplied in the form of different flat bars by two suppliers. Note that, mechanical properties are important for practical applications (input data) in civil engineering structural probabilistic analysis, see e.g. Kala et al. (2017, 2019), Krejsa et al. (2018), Seitl et al. (2018), (2022). 2. Material AISI 304 The AISI 304 steel in the shape of flat bars with cross section dimension 10×55 mm and 20×60 mm from two producers hereafter referred to as A (Asia – India company) and E (Europe – Italy company) was investigated. The chemical composition of the investigated steel grades fulfills the EN 10025-2:2004 standard. The composition according to the material lists of the investigated materials is given in Tab. 1. The composition of E steel is identical for both types of flat bar (PL20-E and PL10-E), however, there is a difference (in the frame of the EN standard) in the case of PL20-A and PL10-A bars. Heat treatment for all studied bars was annealing at 1050 °C followed by water quenching. Mechanical properties guaranteed by producers are presented in Tab. 2.

Table 1. Chemical compositions of AISI 304 for given flat bars according to material lists

Material Grade PL20-E PL10-E PL20-A PL10-A

C (%)

Si (%) 0.31 0.31 0.45 0.35

Mn (%) 1.69 1.69 1.05 1.22

P (%)

S (%)

Cr (%)

Ni (%) 8.05 8.05 8.05 8.03

Mo (%) 0.49 0.49 0.35 0.62

Ti (%)

Cu (%) 0.47 0.47 0.49 0.69

Co (%)

N (%)

Al (%)

0.019 0.019 0.021 0.018

0.035 0.035 0.037 0.036

0.024 0.024 0.020 0.027

18.31 18.31 18.05 18.22

0.003 0.003 0.003 0.001

0.196 0.090 0.006 0.196 0.090 0.006

0.130 0.071 - 0.150 0.082 -

Table 2. Declared mechanical properties of AISI 304 by producers at 25 °C.

R p, 0.2 [MPa]

R p 1.0 [MPa]

Elongation [%]

R m [MPa]

Material Grade

PL20-E PL10-E PL20-A PL10-A

601 601 627 654

285 285 295 321

302 302 357 361

51 51 47 47

3. Testing methods and experimental results 3.1. Microstructure analysis

Light microscopy was used for observation of microstructure. Specimens were extracted from delivered bars in longitudinal direction. Specimen surface was mechanically and finally electrolytically polished. The microstructure has been highlighted using Beraha II etchant. Examples of microstructure are shown in Fig. 1. The grain size is in a broad range 10 - 14 0 μm . A small amount of δ -ferrite (up to 5 %) is present. The E material contains a lot of deformation twins (due to straightening of semiproduct), Fig. 1a) and b), in comparison to material A, Fig. 1c), d). 3.1. Vickers Hardness determination The samples for indentation tests were grinded and polished by conventional metallographic methods. The Vickers hardness was determined on a microhardness tester DuraScan 70 G5 with pyramid shaped diamond indenter with an