GB/T 1979-2025 Evaluation of macrostructural defects in structural steels—Acid etching method and ultrasonic testing method English, Anglais, Englisch, Inglés, えいご
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ICS 77.040.99 CCS H 24
NATIONAL STANDARD OF THE PEOPLE'S REPUBLIC OF CHINA
GB/T 1979-2025
Replace GB/T 1979-2001, GB/T 7736-2008
Evaluation of macrostructural defects in structural steels—Acid etching method and ultrasonic testing method
Issued data 2025-08-29 Implemented data 2026-03-01
Issued by State Administration for Market Regulation
Standardization Administration of China
Contents
Foreword
1 Scope
2 Normative References
3 Terms and Definitions
3.1 Applicable to Ingot-Cast Materials
3.2 Applicable to Continuous-Cast Materials
3.3 Applicable to Both Ingot-Cast and Continuous-Cast Materials
4 Evaluation Methods
4.1 General Principles
4.2 Acid Etching Method
4.3 Ultrasonic Testing Method
5 Inspection Reports
5.1 Acid Etching Method
5.2 Ultrasonic Testing Method
Appendix A (Normative) Macrostructural Defect Rating Charts
Appendix B (Normative) Ultrasonic Testing Method
Evaluation of Macrostructural Defects in Structural Steel - Acid Etching and Ultrasonic Testing Methods
1 Scope
This document describes the evaluation of macrostructural defects in structural steel using acid etching and ultrasonic testing methods, including the principles of acid etching, defect classification, characteristics, causes, evaluation criteria, rating chart classification and scope of application, as well as the principles, equipment, reference blocks, testing conditions and procedures, and results evaluation of ultrasonic testing.
This document applies to the evaluation of macrostructural defects in carbon structural steel, alloy structural steel, and spring steel (forged/rolled billets). Other steel types may refer to this document for macrostructural defect evaluation.
2 Normative References
The following documents' contents are indispensable clauses through normative references in this document. For dated references, only the edition corresponding to the date applies; for undated references, the latest edition (including all amendments) applies.
GB/T 226 Acid Etching Test Method for Macrostructures and Defects in Steel
GB/T 9445 Qualification and Certification of Personnel for Non-destructive Testing
GB/T 23905 Reference Blocks for Ultrasonic Testing
GB/T 27664.2 Non-destructive Testing - Characteristics and Verification of Ultrasonic Testing Equipment - Part 2: Probes
JJG 746 Ultrasonic Flaw Detector
3 Terms and Definitions
The following terms and definitions apply to this document.
3.1 Applicable to Ingot-Cast Materials
3.1.1
General Looseness
Microvoids and accumulated low-melting-point components, gases, and non-metallic inclusions formed during solidification between the main and secondary axes of dendritic crystals in ingots.
3.1.2
Ingot Segregation
Caused by compositional segregation and impurity accumulation at the boundary between columnar crystal zone and central equiaxed crystal zone during ingot solidification.
3.1.3
Riser Segregation
Caused by carburizing effect of insulating materials containing carbon near the riser.
3.2 Applicable to Continuous-Cast Materials
3.2.1
Frame Segregation
Caused by solute element enrichment at solidification front, uneven solidification rates, and steel flow during solidification.
3.2.2
White Band
Formed during continuous casting due to improper electromagnetic stirring, where solute-rich steel flows out of the solidification front with reduced temperature gradient.
3.3 Applicable to Both Ingot-Cast and Continuous-Cast Materials
3.3.1
Center Porosity
Caused by volumetric shrinkage during solidification and gas evolution/impurity accumulation in the final solidification zone.
3.3.2
Spotty Segregation
Spot-like compositional segregation caused by slow cooling during crystallization.
Note 1: When spots are dispersed across the section, it's general spotty segregation; when at edges, it's edge spotty segregation.
Note 2: Spotty segregation worsens with high gas/inclusion content, indicating poor crystallization conditions.
3.3.3
Center Segregation
Caused by compositional segregation due to selective crystallization or slower cooling at the center.
3.3.4
Subsurface Blowholes
Caused by poor mold cleaning, inadequate deoxidation, high gas content, or wet raw materials.
3.3.5
Residual Shrinkage Cavity
Formed by concentrated volumetric shrinkage during solidification, sometimes with secondary cavities.
3.3.6
Skull Patch
Caused by oxide film incorporation during pouring that fails to float out before solidification.
3.3.7
Axial Intergranular Cracks
Formed at fragile grain boundaries in the final solidification zone due to gas/inclusion enrichment and tensile stress.
Note: Uneven microstructure may create "spider web" etching patterns, which don't warrant rejection. Retesting after heat treatment is recommended.
3.3.8
White Point
Hydrogen-induced cracks formed during cooling after hot working.
3.3.9
Air Entrapment
Caused by high gas content in steel.
3.3.10
Visible Non-metallic Inclusions/Slag Inclusions
Resulting from refractory material contamination during smelting.
3.3.11
Foreign Metal Inclusions
Caused by incomplete alloy melting or foreign metal contamination.
4 Evaluation Methods
4.1 General Principles
4.1.1 This document specifies two evaluation methods: acid etching (primary) and ultrasonic testing (supplementary for uniform cross-sections). Ultrasonic detection disputes shall be resolved by acid etching results.
4.1.2 Acceptable defect levels shall be specified in product standards/technical agreements.
4.2 Acid Etching Method
4.2.1 Sample Preparation
Cross-section preparation and display shall comply with GB/T 226. Etching time varies by steel composition, dimensions, and heat treatment status. Over-etching must be avoided.
4.2.2 Standard Rating Charts
4.2.2.1 Rating charts are categorized by smelting process, defect type, and size (see Table 1).
4.2.2.2 For bars <40mm, defects are rated at reduced scale except general/center porosity and ingot segregation.
4.2.2.3 For bars >250mm, defects are rated at enlarged scale based on reference charts.
4.2.3.4 When comparing and evaluating the defect level of steel materials (billets) of other sizes, the severity of the defects shall be reduced or enlarged according to the defect rating charts.
4.2.3.5 The acid etching method is the arbitration method for evaluating low defects.
4.3 Ultrasonic Testing Method
4.3.1 When using ultrasonic testing to evaluate macrostructural defects, the performance indicators of instruments and equipment, personnel qualifications, reference blocks, operational steps, and testing methods shall comply with the provisions of Appendix B.
4.3.2 After ultrasonic testing, if no defect reflection waves are detected under the static sensitivity of Table B.1 or Table B.2, the batch shall be judged as qualified for ultrasonic low inspection, and the result shall be reported as "low qualified". Otherwise, samples shall be taken at the positions where reflection waves are present for acid etching testing, and the acid etching test results shall prevail.
5 Inspection Reports
5.1 Acid Etching Method
The inspection report shall include the following items:
a) This document number;
b) Grade, smelting furnace number, specification, and sample number;
c) Inspection results;
d) Etchant, etching method, etching temperature, and etching duration;
e) Inspection report number, date, inspector, and reviewer.
5.2 Ultrasonic Testing Method
The inspection report shall include at least the following items:
a) This document number;
b) Grade, smelting furnace number, specification, and product standard;
c) Flaw detector model, probe model, testing method, and testing sensitivity;
d) Inspection results;
e) Operator and qualification level;
f) Inspection report number, date, and reviewer.
