GB/T 1979-2025Evaluation of macrostructural defects in structural steels - Acid etching method and ultrasonic testing method (English PDF)

1 Scope

GB/T 1979 is the Chinese standard for judging the macrostructural defects of structural steel: the porosity, segregation, cracks and inclusions that a billet carries out of the caster or the ingot mould and that no amount of downstream processing removes. It covers two routes. The acid etching method cuts a cross-section, etches it and rates what appears against a series of standard rating diagrams, separated into a mould-casting series, a continuous-casting series and typical defects. The ultrasonic method examines the material without cutting it, and applies where the section is uniform. The 2025 edition replaces both GB/T 1979-2001 and GB/T 7736-2008, bringing the two into one document. It applies to carbon structural steel, alloy structural steel and spring steel in forged and rolled billet form, and other steels may use it as a reference. In practice this is the text a steel supply contract points to when it sets an acceptance level for internal quality.

This document describes the evaluation of macrostructural defects in structural steels using acid etching and ultrasonic testing methods. It includes the principle, defect classification, characteristics, causes, and evaluation principles, the classification of rating diagrams and applicable scopes of the acid etching method, as well as the principle, instruments and equipment, reference blocks, testing conditions and procedures, and result evaluation of the ultrasonic testing method. This document applies to the evaluation of macrostructural defects in carbon structural steel, alloy structural steel, and spring steel (forged and rolled billets). The evaluation of macrostructural defects in other steels may take this document as a reference.

2 Normative References

The contents of the following documents constitute indispensable clauses of this document through the normative references in the text. In terms of references with a specified date, only versions with a specified date are applicable to this document. In terms of references without a specified date, the latest version (including all the modifications) is applicable to this document.

GB/T 226 Test Method for Macrostructure and Defect of Steel by Etching

GB/T 9445 Non-destructive Testing - Qualification and Certification of Personnels

GB/T 23905 Non-destructive Testing - Blocks for Ultrasonic Testing

GB/T 27664.2 Non-destructive Testing - Characterization and Verification of Ultrasonic Test Equipment - Part

3 Terms and Definitions

The following terms and definitions are applicable to this document.

Appendix B

(normative) Ultrasonic Testing Method B.1 Instruments and Equipment B.1.1 Ultrasonic testing instrument The performance indicators of the ultrasonic testing instrument shall meet the requirements of JJG 746. B.1.2 Probe The probe shall have a frequency of 2 MHz ~ 10 MHz, be capable of penetrating the steels under test and meeting the requirements of detection resolution. The probe chip diameter (side length) should preferably not exceed 28 mm. A probe with a relatively low frequency can be used when inspecting continuous casting billets. Probe parameters shall be tested in accordance with the method in GB/T 27664.2 and meet the requirements. B.1.3 Coupling agent A coupling agent with good coupling effect and harmless to the human body and steel surface should be selected. B.2 Personnel Personnel engaged in testing shall participate in training in accordance with GB/T 9445 or corresponding documents and obtain an ultrasonic testing qualification certificate. Those who issue test reports shall obtain a Level 2 or higher ultrasonic testing qualification certificate. B.3 Reference Blocks B.3.1 The acoustic performance of the reference blocks shall be the same as or similar to that of the steels under test. There shall be no echoes on the reference blocks that may affect the use. B.3.2 When using a dual-crystal probe, at least two artificial defects of the same size should be machined on the reference blocks; when using a straight probe for testing, at least one artificial defect located in the far-field region should be machined on the reference blocks to determine the static detection sensitivity. B.3.3 The location of the artificial defects on the reference blocks shall be able to cover the scanning range of the acoustic wave on the steel cross-section. B.3.4 For steels with a testing size greater than three times the near-field region of the probe, the static detection sensitivity can be determined using the workpiece bottom wave calculation method, and the diameter of the flat-bottom hole can be selected as phi