PSI - Issue 33

S. Schoenborn et al. / Procedia Structural Integrity 33 (2021) 757–764 S. Schoenborn, T. Melz, J. Baumgartner, C. Bleicher / Structural Integrity Procedia 00 (2019) 000–000

759

3

2. Materials and experimental 2.1. Material Data

For the investigations a ferritic chromium steel 1.4521 (X2CrMoTi18-2 / AISI 444) was used. The chemical composition and the mechanical properties are compiled in Table 1 and Table 2. The material is characterized by excellent corrosion resistance, especially against local corrosion as a result of chloride ions in aqueous electrolytes, which is why it finds application in pipelines. The body-centered cubic (bcc) lattice structure has a comparatively high diffusion rate for hydrogen, although the solubility is low [8].

Table 1. Chemical composition of the used material 1.4521 (X2CrMoTi18-2 / AlSI 444) in wt-%.

C

Si

Mn

P

S

Cr

Mo

Ni

Ti

0.018

0.423

0.644

0.024

<0.01

18.18

1.92

0.012

0.363

Table 2. Mechanical Properties of the used material 1.4521 (X2CrMoTi18-2).

Proof stress R p0.2 [MPa]

Tensile strength R m [MPa]

Fracture elongation A 5 [%]

Contraction at break Z [%]

Uniform elongation A g [%]

Material

1.4521

373

523

14.8

36.2

80

2.2. Specimens The test material was procured for the strain and force-controlled fatigue tests in the form of round bar material as a semi-finished product. Subsequently, the final specimen geometries were produced by machining. The surface conditions of the specimens were achieved by machining processes typical for components (fine turning). All specimens examined have a finely turned surface with a roughness R z ≤ 2.5 µm, so that an influence of the surface condition on the fatigue strength can be excluded. Unnotched and Hourglass (K t ≈ 1.0) as well as notched specimens with different notch sharpness (K t ≈ 2.0 and 2.7) were examined in order to take into account the influence of a notch effect and thus an increased local stress, Fig. 1. A C

B

D

Fig. 1. Dimension of the tested specimens; (A) unnotched round specimen K t ≈ 1.0 long, (B) Hourglass specimen K t ≈ 1.0 short, (C) mildly notched specimen K t ≈ 2.0, (D) sharply notched specimen K t ≈ 2.7.