Issue 78

A. A. Frantsuzov et alii, Fracture and Structural Integrity, 78 (2026) 474-488; DOI: 10.3221/IGF-ESIS.78.27

standard plates can be explained by the limited resolution of the plate method, since the difference between two adjacent standard plates is approximately 2 μ m in this grain-size range.

Average grain diameter (rounded), μ m

Standard deviation (rounded), μ m

Approach

Median, μ m

EBSD reconstruction, ×500

6.8 (7)

3.3 (3)

6

EBSD reconstruction, ×1000

5.7 (6)

2.9 (3)

5

EBSD reconstruction, ×3000

4.9 (5)

2.2 (2)

5

Lineal intercept, operator 1, ×500

8.3 (8)

3.8 (4)

7

Lineal intercept, operator 2, ×500

6.1 (6)

3.5 (4)

6

Manual diagonal measurements, ×500

7.2 (7)

2.7 (3)

7

ASTM E112, ×100

11.2 (11)

—

—

Table 3: Average grain size evaluated using different methods.

Finally, the PAG reconstruction performed using MTEX was compared with an optical micrograph of the same area after chemical etching (Figure 14). Although the correspondence is not perfect, the reconstructed PAG structure shows reasonable agreement with the etched microstructure, indicating that the EBSD-based reconstruction approach is viable for this steel. Moreover, because optical identification of some PAG boundaries is limited by weak etching contrast and chemical banding, EBSD-based reconstruction may provide a more reliable estimate of the PAG structure than chemical etching alone. However, this assumption can only be fully validated by direct in situ observation of austenite followed by the analysis of the martensitic transformation after in situ quenching, as demonstrated in [19].

Figure 14: Same spot of a sample, observed using chemical etching and EBSD PAG reconstruction method overlay.

D ISCUSSION

comparative overview of PAGS evaluation methods in high-grade pipeline steels should begin with the fact that all methods assess either visible or reconstructed prior austenite grain morphology. Therefore, the obtained grain size depends not only on the actual PAG structure, but also on how completely the boundaries are revealed or reconstructed, and also on the measurement procedure used, such as direct grain measurements, lineal intercepts, or standard plates grain-size comparison. Chemical etching remains the most direct method for visualizing prior austenite grain boundaries. However, in high-grade pipe steels, the quality of PAG revelation is often inconsistent. This is caused by the relatively fine grain size, local variations A

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