PSI - Issue 23

Aleš Materna et al. / Procedia Structural Integrity 23 (2019) 425–430 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

428

4

Fig. 2. Axisymmetric FEM model of cold-pressing and subsequent indentation of 08Ch18N10T steel

3. Results and discussion

3.1. Microstructure of 08Ch18N10T 08Ch18N10T steel consists mainly of austenitic grains of average size 120 µm containing many twins. δ -ferrite was also observed. With increasing deformation (compare longitudinal sections of variously deformed states in Fig. 3) the slip bands in grains progressively occur.

Fig. 3. Micro-structure of undeformed (left) and cold-deformed 08Ch18N10T austenitic steel with thickness reduction 10 % (middle) and 20 % (right)

3.2. Effect of annealing on hardness of 08Ch18N10T The hardness change due to the annealing at 700 °C is summarized in Table 3 and plotted in Fig. 4. The hardness of cold-formed 08Ch18N10T steel increases with the value of thickness reduction. This is still valid after annealing, but the differences in hardness are smaller. No monotonous dependence of the hardness on annealing time was observed. Generally, the undeformed steel exhibits hardness growth due to annealing whereas cold-deformed steel slightly decreases in hardness.

Table 3. Hardness of hardened 08Ch18N10T steel before and after annealing at 700 °C for various annealing times .

Hardness HV5 Annealing time @700 °C [h]

Thickness reduction [%]

0

1

2

4

6

175.6 ± 4.9 225.3 ± 18.3 264.8 ± 14.1

184.2 ± 2.8 214.3 ± 6.5 245.3 ± 5.8

191.4 ± 3.6 204.2 ± 6.1 257.9 ± 7.1

190.2 ± 3.8 219.0 ± 10.1 258.0 ± 7.2

200.3 ± 2.7 210.6 ± 8.0 245.6 ± 11.3

0

10 20