Stainless steel medium and heavy plates refer to steel plates with a thickness of 4–25.0 mm; plates with a thickness of 25.0–100.0 mm are called heavy plates, and those exceeding 100.0 mm are called extra-heavy plates. They are widely used in manufacturing various containers, furnace shells, furnace plates, bridges, as well as automotive dead steel plates, low-alloy steel plates, bridge steel plates, shipbuilding steel plates, boiler steel plates, pressure vessel steel plates, patterned plates, automotive frame plates, certain tractor parts, and welded components.

During use, attention must be paid to defects in stainless steel medium and heavy plates. Small longitudinal cracks, peak‑shaped cracks, edge line cracks, inclusions, and scabs on the plate surface affect surface quality, lead to product reclassification, and degrade product quality.

The typical morphologies of several defects are described below:

Small longitudinal cracks – These appear on the plate surface with a length of less than 200 mm, a width of less than 3 mm, and a depth of less than 0.3 mm.

Peak‑shaped cracks – These cracks all occur on the lower surface of the plate, at a distance of 5–60 mm from the edge. Their macroscopic direction is perpendicular to the rolling direction, and they appear as “mountain‑peak” shapes.

Edge line cracks – These cracks mainly occur at a distance of 20–80 mm from the plate edge, taking the form of multiple parallel longitudinal cracks of varying sizes. The rule is that the thicker and wider the plate, the more severe this type of defect.

Inclusions and scabs – Inclusions and scabs exhibit a regular distribution. They are especially evident after edge flame scarfing (for crack inspection) or flame cleaning of scratches on the slab, as well as other conditioning operations.

Possible cause analysis:

Small longitudinal cracks are caused by fine impurities entering the mold.

Peak‑shaped cracks are mainly due to subcutaneous transverse corner cracks on the outer arc of the slab.

Edge line cracks are caused by the side‑turning of the slab edges toward the surface during rolling.

Inclusions and scabs result from inadequate cleaning of surface oxidation slag during conditioning.

To reduce the occurrence of the above defects, the following measures should be actively taken:

Regularly inspect the mold, especially the water quality, to check whether small impurities have entered and caused changes in water quality.

Strictly control equipment operation beyond its service life, ensure timely maintenance of the segment sections, and avoid deep scratches on the slab caused by local roller stoppage in the segments.

Implement zone‑controlled water distribution in the bending section, dynamically control the corner temperature of slabs with different widths and end sections, and prevent the corner temperature from entering the brittle zone during slab bending.

Use slabs with a wide cross‑section to produce large‑width plates as much as possible, reduce the broadening amount during plate rolling, thereby alleviating the uneven edge deformation during rolling of wide plates and mitigating the width‑wise extent of edge line cracks.