GB/T 28300-2025Surface quality classes for hot-rolled bars and wire rod (English PDF)

4.1 Ordering

If not explicitly specified in the product standard, the following shall be specified when ordering.

a) Surface quality class (see Table 1), which is class A if not specified;

b) Portion (z) (default value see Table 1, other requirements negotiable);

c) Inspection and testing methods, determined by the supplier if not specified.

Note. See Appendix D for guidelines on surface quality class application.

4.2 Marking

Surface quality requirements shall be marked according to Table 1.

Example 1.

The supplier and buyer agree on a surface quality class of B and a portion (z) of 1% (default value), surface quality GB/T 28300-B.

Example 2.

The supplier and buyer agree that the surface quality class is C and the portion (z) for the delivery lot is 0.5%, surface quality GB/T 28300-C-z0.5.

6.1 General

6.1.1 Based on the steel surface quality requirements, the manufacturer shall, according to its own responsibility and judgment, take appropriate measures to supervise its production.

Note. The manufacturer typically checks the surface quality requirements of the coiled ends after rolling.

6.1.2 The purchaser has the right to choose an appropriate method to inspect the surface quality of the delivered materials.

6.2 Inspection and testing methods

6.2.1 General requirements

6.2.1.1 The measurement methods used to detect surface discontinuities and the depth

or height of surface discontinuities shall be sufficiently accurate; the measurement results shall be reproducible.

6.2.1.2 Non-destructive testing methods (see 6.2.2 and 6.2.3.1) and process testing

methods (see 6.2.2) may be used.

Note. Considering that continuous inspection equipment for wire rods is not easy to meet the accuracy requirements for measuring the depth or height of defects, it is usually only possible to inspect the ends of the coil. Therefore, it cannot be proven that there is no depth or height greater than the specified value throughout the entire coil.

6.2.2 Testing methods for surface discontinuities

The following methods or other suitable methods are applicable to the testing of surface discontinuities.

a) Non-destructive testing methods.

- Visual inspection;

- Magnetic flux methods, e.g., magnetic particle testing or magnetic probe testing;

- Inductive method (eddy current);

- Dye penetration test.

b) Process testing methods.

- Hot upsetting test (according to YB/T 5293);

- Cold upsetting test (according to YB/T 5293);

- Torsion test (according to GB/T 239.1, GB/T 239.2).

6.2.3 Measurement methods for surface discontinuity depth or height

6.2.3.1 Non-destructive testing methods.

- Magnetic flux measurement method, using a rotating or fixed probe;

- Inductive method;

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