PSI - Issue 60

Behrooz Tafazzolimoghaddam et al. / Procedia Structural Integrity 60 (2024) 575–581 Author name / StructuralIntegrity Procedia 00 (2019) 000–000

580

6

3.3. Hardness A hardness map of the weld cross section is presented in Figure 5. The overlay deposition clearly shows enhanced hardness expected from 75Ni13.5Cr2.7B-3.5 Si. The hardness changes suddenly from the weld to the substrate region. This indicates that the weld did not cause significant changes in the microstructure of the substrate except at interface. The hardness map also shows that no significant plastic deformation occurred during the EDM cut which means less possibility of cutting induced artifacts.

Figure 5 Hardness (HV 0.5) of the hardfaced specimen at the EDM cut cross section. The hardness map also indicates no significant plasticity during the contour cut

A line profile of the hardness through the thickness of the plate is shown in Figure 6. The hardness is mostly above 300 HV 0.5 at the overlay and sharply drops to values below 200 HV 0.5 in the substrate. The sudden drop in the hardness could indicate a narrow region of dilution and Heat Affected Zone (HAZ). Hardness value in the substrate is typical for annealed AISI 316L SS.

0 100 200 300 400

HV0.5

-0.2

0

0.2

0.4

0.6

0.8

1

Normalized through thickness distance

Figure 6 Hardness line profile at x = 20 mm vertical path as shown in Figure 5

4. Conclusions The residual stress in PTA clad of AISI 316 SS with N75Ni13.5Cr2.7B-3.5 Si was measured using the contour method. The results showed the magnitude and the distribution of the residual stresses in as-welded specimen. The maximum tensile stress region is at the centre of the substrate, leaning towards the weld end possibly due to the geometry of the deposition and slower cooldown process. The contour method is a reliable technique for determining residual stress when multiple materials are being assessed, such as in welds and cladding applications. The cut surface can be characterized metallurgically and the boundaries carefully mapped into the model materials property assignment. With nondestructive analysis, such as neutron diffraction, this is not possible and errors caused by unknown proximity to the boundary cannot be avoided easily. The micrographs showed that the overlapping region for the deposit is about 10µm as expected for dissimilar deposit. A hardness map of the weld cross section was created to find the hardness distribution at the clad and the substrate. This map also showed that the EDM cut has not caused noticeable plasticity which verifies the cutting method and that the contour measurement results are clear of artefact caused by cutting induced plasticity. The speed of welding and other parameters of weld defines the distribution and the magnitude of the residual stress by affecting the weld solidification, phase transformation and the bonding between the clad and the substrate. Further study is underway to characterize these effects by testing more samples with various weld parameters as well as numerical simulation of PTA.