Steel Man: September 2024

Standard for determination of non-metallic inclusions in steel

1. Scope

Microscopic evaluation method for nonmetallic inclusions in rolled or forged steels with compression ratio greater than or equal to 3 by standard spectrogram.

2 Sampling

The morphology of inclusions depends to a large extent on the degree of compression deformation of the steel, so it is only possible to compare the measured results on the sections prepared by sample billet after similar degree of deformation.

The polished surface area of the specimen for measuring inclusion content shall be approximately 200mm²(20mm X10mm) and shall be parallel to the longitudinal axis of the steel, located halfway from the outer surface of the steel to the center.

If the product standard does not specify, the sampling method is as follows:

Steel rods or billets with a diameter or side length greater than 40mm: the inspection surface is the partial radial section from the outer surface of the steel to the center.

3. principle

The observed test site was compared with the standard spectrum, and each type of inclusion was rated.

These rated images are equivalent to a square field of view with an area of 0.50mm² on a longitudinally polished plane 100 times lower.

According to the morphology and distribution of inclusions, the standard rating chart is divided into five categories: A, B, C, D and DS.

These five categories of inclusions represent the most commonly observed types and forms of inclusions:

Class A (sulfides) : A single gray inclusion with high ductility and a wide range form ratio (length/width), generally with rounded ends.

Class B (alumina) : most undeformed, angular, small shape ratio (generally <3), black or bluish particles, arranged in a line along the rolling direction (at least 3 particles).

Class C (silicates) : A single black or dark gray inclusion with high ductility and a wide range form ratio (generally ≥3), with an acute Angle at the end.

Class D (spherical oxides) : non-deformed, angular or round, small shape ratio (generally <3), black or bluish, irregularly distributed particles.

Class DS (single particle spherical class) : round or nearly round, diameter ≥13μm of single particle inclusion.

Each type of inclusion is divided into two series of fine and coarse according to the different width of non-metallic inclusion particles.

4. Determination of inclusion content

The sample was magnified 100 times under the microscope, and the inclusion grade was evaluated in the field of view of a square with a side length of 71mm and an actual area of 0.5mm².

Method A is used for production inspection

The entire finish should be inspected. For each type of inclusion, the number of levels of the standard picture corresponding to the worst field of view on the examined surface is recorded by fine and coarse series.

For individual inclusions whose length exceeds the side length of the field of view (0.71mm), or whose width or diameter is greater than the maximum of the coarse system (see Table 2), they should be assessed as super-size inclusions and recorded separately. However, these inclusions should still be included in the rating of the field of view.

For strip inclusions that are not in a straight line, if the longitudinal distance between the two inclusions is less than or equal to 40μm and the transverse distance along the rolling direction is less than or equal to 10μm, it shall be regarded as an inclusion.

If the widths of inclusions within an inclusion are different, the maximum width of the inclusion shall be regarded as the width of the inclusion.

If the inclusion length is too long or the width is too large, it should be recorded separately and included in the field of view for rating (the length of the extra long is 0.71mm).

5. Inclusion grade calculation (measurement rating picture grade of inclusions above 3)

Class A sulfide (length L expressed by μm) : Lg(i)=[0.560 5lg(L)]-1.179

Class B alumina: Lg(i)=[0.462 6lg(L)]-0.871

Class C silicate: Lg(i)=[0.480 7lg(L)]-0.904

Class D spherical oxides, where n is the amount in each field of view: Lg(i)=[0.5lg(n)]-0.301

DS class single particle spherical oxide, d is diameter: i=[3.311g(d)]-3.22