The analysis of shape and morphology of individual particles is essential for the grouping into inclusions. For inclusion formation a particle is considered to have a round or elongated shape. The definition of where round is getting elongated depends on the standard. The particle shape in combination with the distance to next neighboring inclusion(s) is decisive for the grouping of single particles to aligned inclusions. Note: The shape definition and the grouping rules differ from standard to standard. Therefore, a direct comparison of standard results on the base of individual inclusions is usually complex.

As a Supervisor, you can copy and edit pre-configured standard templates, see Standard Template Editor.

For detailed information on inclusion inspection with the NMI Analysis module, see NMI Global Results View and NMI Field Based Inspection View

Each standard has its own grouping rules but the underlying principles are comparable and therefore described based on the definitions of EN 10247.

One single inclusion (particle)

Width (W) and Length (L) of an inclusion (particle). Source: DIN EN 10247 Micrographic examination of the non-metallic inclusion content of steels using standard pictures.
Width (W) and Length (L) of an inclusion (particle). Source: DIN EN 10247 Micrographic examination of the non-metallic inclusion content of steels using standard pictures.

Calculation of the nearest neighbor to group inclusions

The nearest neighbor is defined by the distance between the inclusions perpendicular to the main deformation direction (t) and the distance between the inclusions in the main deformation direction (e). If the distance criteria are fulfilled, one stringer is formed and rated as one inclusion. If the distance criteria are not fulfilled, two isolated inclusions are rated.

Formation of Stringers

Distance Criteria (t) and (e) between two particle. Source: DIN EN 10247 Micrographic examination of the non-metallic inclusion content of steels using standard pictures.
Distance Criteria (t) and (e) between two particle. Source: DIN EN 10247 Micrographic examination of the non-metallic inclusion content of steels using standard pictures.

Two particles - one stringer
-> Rated as one inclusion

Two particles - no stringer
-> Rated as two inclusions

If e ≤ 40 µm and t ≤ 10 µm:
L = L1 + e + L2
w = w1 + t + w2

If e > 40 µm or t > 10 µm:
L1 = L1 w1 = w1
L2 = L2 w2 = w2

If the distance criteria are fullfilled, the two inclusions are combined to one inclusion stringer with two particles. The calculation of the total length and width for the inclusion stringer is shown according to the standard EN 10247 in the Figure above. Note: The calulation might differ depending on the standard and the standard specific inclusion type.

Agglomeration of stringers to group inclusions

1 2 3
Source: DIN EN 10247 Micrographic examination of the non-metallic inclusion content of steels using standard pictures.

1

Eight particles
Two stringer
One inclusion

2

Eight particles
Two stringer
One inclusion

3

16 particles
Four stringer
One inclusion

Based on the inclusion size calculation all inclusions are classified per type and size for each individual standard. The resulting standard specific ratings are used in the different methods for further calculation and result presentation. The ratings and calculated characteristic values determine the cleanliness of steel.