Internal defect database of mechanically deformed ferritic steel via X-ray computed tomography

Steel is widely utilized as a structural material due to its favorable mechanical properties, cost-effectiveness, and reliability, and it is expected to remain critical in engineering applications. The properties and durability of steel are significantly influenced by internal defects formed during mechanical deformation. Quantitative analysis of the formation and evolution of these defects is essential for developing materials that are both sustainable and tailored to specific applications. However, acquiring statistically meaningful datasets of internal defects is complex, time-consuming, and costly, resulting in a scarcity of comprehensive studies. In this study, we present two comprehensive datasets obtained from mechanically deformed ferritic steel samples using X-ray computed tomography (X-CT): (1) tensile deformation and (2) fatigue deformation. The database includes detailed quantitative descriptions of 938 defect features from 135 tensile-tested samples and 2,305 defect features from 152 fatigue-tested samples. Each dataset comprises high-resolution X-CT images and quantified internal defect metrics, facilitating detailed statistical analysis.

Methods
Tensile testing

The tests were conducted at room temperature with a strain rate of 10-3 s-1, and local strains of the specimens were measured using a digital image correlation (DIC) instrument. X-CT scanning was performed using a ZEISS Xradia 520 Versa with the following conditions: 160 kV output voltage, 10 W power, and 3 μm step size. Internal topology data of deformed specimens were obtained by scanning areas of 3×3×33 mm3 located 3 mm away from the fracture surface of fractured specimens. The acquired data was divided into 3-5 regions.

Fatigue testing

The tests were conducted with an r-ratio of 0.1 and a maximum stress amplitude range of 630-680 MPa. X-CT scanning was performed on a 3×x3×x3 mm3 area at the center of the gauge of the specimen after interrupting the test at a specific cycle. The same conditions were used as in the tensile case, except for the measurement area. After that, an additional fatigue test was conducted, and X-CT scanning was performed again. This process was repeated until the specimen was destroyed.

TDA analysis

Persistent homology (PH) processing was used to provide information about defect density, defect size, and homogeneity of defects.