Non-metallic inclusions in square steel tubes

Square steel tubes, available in either Type A513 or A500 Grade B depending on size and wall thickness, are a versatile welded structural grade material. These tubes are ideal for various structural applications, general fabrication, and repair work. They are widely used in industrial maintenance, farm equipment, transportation, truck beds, trailers, frames, and more. The box-like configuration of square tubes offers greater strength and rigidity compared to angles or channels. Additionally, with the right equipment and expertise, these steel shapes are easy to weld, cut, form, and machine.

Characteristics of Non-Metallic Inclusions in Square Tubes

Non-metallic inclusions, though present in small quantities within square pipes, significantly affect the pipe's performance, making their detection a crucial part of the production process. Understanding the sources, composition, forms, hazards, distribution, and microscopic characteristics of these inclusions is key to controlling or reducing their presence in square and rectangular tubes and thus enhancing product quality.

To identify the types of non-metallic inclusions in square tubes, the following characteristics can be observed:

Aluminum Oxide:

These inclusions are typically undeformed, angular, and appear as small black or bluish particles arranged in a row along the rolling direction, with at least three particles present.

Spherical Oxides:

These are undeformed, angular or rounded inclusions, small in size, black or bluish, and irregularly distributed.

Single-Particle Spherical Inclusions:

These are round or nearly round single-particle inclusions with a diameter of 13 μm or greater.

Sulfides:

These are single gray inclusions known for their high ductility and wide range of aspect ratios. In square and rectangular tubes, the ends are generally rounded.

Silicates:

These inclusions also exhibit high ductility, have wide aspect ratios, and appear as black or dark gray inclusions, often with sharp ends.

Traditional inclusion types can be assessed by comparing their morphology with the five categories mentioned above and noting their chemical characteristics. Additionally, phases such as borides, carbides, carbonitrides, or nitrides in square and rectangular tubes can be evaluated based on their morphology and chemical characteristics, following a similar comparison method.