PSI - Issue 69

Pekka Kantanen et al. / Procedia Structural Integrity 69 (2025) 53–60

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Fig. 3. (a) Engineering stress-strain curves and (b) strain hardening rates of the IA materials treated at 650 °C and 700 °C. Lower IAT temperature resulted in higher yield and tensile strength but reduced uniform and total elongations. The IAT 650 °C material also exhibited higher strain-hardening capabilities (n 4-6 values in Table 1) while maintaining similar yield-to-tensile strength ratios compared to the IAT 700 °C material. 3.2. Punched and tensile tested material characterization Microhardness profile measurement results for prepared base material, punched edge, and tensile tests specimen samples are presented in Fig. 4. In Fig. 5 the microhardness measurement indentations are visible in the Nital-etched edges and tensile specimen sample cross-sections. The base material hardness profiles showed no change in the material hardness towards the W-EDM edge for both materials. The punched edges exhibited significant difference in the strain-hardening near the hole edges between the two samples. Additionally, deformation towards the sheared edge and void formation along material flow lines were observed, with the IAT 700 °C material demonstrating higher maximum hardness and deeper shear-affected zone than the IAT 650 °C material. In tensile test specimens, hardness profiles implied more uniform material flow compared to punched edges. Necking was observed to be more pronounced in the IAT 700 °C tensile specimen sample compared to the IAT 650 °C sample (Fig. 5), consistent with the higher post-uniform elongation. Notably, in both 650 and 700 °C tensile test samples, hardness did not revert to base material levels even 8 mm distance from the fracture surface located in the uniform elongation area, as shown in Fig. 6. The hardness difference observed between base material sample and tensile specimen grip area measurements of IAT 650 °C material may be a result of local microstructural differences.

Fig. 4. Microhardness profiles measured from the base material, punched edge, and tensile test specimen samples of (a) 650 °C and (b) 700 °C IAT material. Standard deviations of the measurements are given.