GB/T 14977-2025General requirement for surface condition of hot-rolled steel sheet and plate (English PDF)

5.1 General requirements for steel plate surfaces

Regardless of whether the steel plate is delivered with or without mill scale removed, the manufacturer shall take necessary measures to ensure that the surface quality of the steel plate meets the requirements. The manufacturer may only consider visually observable surface discontinuities. Mill scale produced during rolling and heat treatment may conceal surface discontinuities.

If the purchaser requires that all visually observable surface discontinuities be identified, evaluated, repaired (if necessary) before delivery, the order shall specify products with mill scale removed.

If the purchaser discovers defects in the material during subsequent mill scale removal or processing, meanwhile the defects are caused by the manufacturer, THEN, the manufacturer is allowed to repair and resubmit the material according to the requirements of the product standard.

5.2 Measurement of surface discontinuity depth and affected area

5.2.1 Depth measurement

To distinguish between surface discontinuities and defects, the depth of representative surface discontinuities shall be measured on the product surface if necessary. The depth is measured after removing the representative surface discontinuity by grinding.

5.2.2 Measurement of affected area

If necessary, the affected area of surface discontinuities shall be measured according to the following requirements.

a) Isolated surface discontinuities. Draw a continuous line 20 mm from the periphery of the surface discontinuity, or draw a rectangle 20 mm from its edge, to determine the affected area, as shown in Figure 1.

b) Clustered surface discontinuities. Draw a continuous line 20 mm from the periphery of this group of surface discontinuities, or draw a rectangle whose vertical and horizontal sides are 20 mm from the connecting line of this group of surface discontinuities. If this group of surface discontinuities is less than 20 mm from the edge of the steel plate, the edge of the steel plate shall be used as the reference, as shown in Figure 2.

c) Strip-shaped surface discontinuities. Draw a rectangle whose vertical and horizontal sides are 20 mm from the connecting line of this group of surface discontinuities. If this group of surface discontinuities is less than 20 mm from the edge of the steel plate, the edge of the steel plate shall be used as the reference, as shown in Figure 3.

d) Multiple surface discontinuities (including clustered surface discontinuities and strip-shaped surface discontinuities) with an edge distance of less than 40 mm can be considered as a single clustered surface discontinuity.

Units are in millimeters

Appendix C (Informative)

Description of common surface discontinuities

C.1 Rolled-in scale and pitting

Appears on the rolled surface in various shapes, thicknesses, frequencies.

Rolled-in scale is usually caused by insufficient removal of scale before, during, or after hot rolling.

C.2 Indentations and roll marks

Marks that appear periodically due to damage to the rolls or pinch rolls.

Indentations (depressions) or roll marks (protrusions) may be distributed at fixed intervals or irregularly along the entire length and width of the rolled product.

Indentations may be caused by the rolls or protrusions on the rolls.

C.3 Scratches and grooves

Mechanical abrasions of varying widths, depths, lengths on the surface, mostly parallel or perpendicular to the rolling direction.

They may have slight curling and rarely contain scale. This damage is caused by friction during relative movement between the rolled product and the equipment.

C.4 Spills and slivers

Irregular and flaky small surface discontinuities.

Spills extend along the rolling direction, whose extent depends on the amount of deformation. In some areas, they are still connected to the base metal, appearing as small scab-like particles.

C.5 Blisters

Blisters are located below the surface, varying in shape and size, appear during hot rolling.

C.6 Hot tears

Material discontinuities of varying direction, length, width, depth in the surface area, occurring in a preferred direction, (or) distributed within a limited area.

Hot tears occur during the processing of ingots, blooms, continuously cast slabs, are

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