YB/T 4003-1997: Standard Diagrams for Macrostructure Defects in Continuous Casting Steel Slab

YB/T 4003-1997 — Standard Diagrams for Macrostructure and Defect in Continuous Casting Slab

Standard Number: YB/T 4003-1997
Issued: August 4, 1997
Effective: December 1, 1997
Issuing Authority: Ministry of Metallurgical Industry, People’s Republic of China
Original Title: 连铸钢板坯低倍组织缺陷评级图

1. Scope

This standard specifies the test specimens used for macrostructure defect evaluation of continuously cast steel slabs by acid etching and sulfur print methods, as well as the morphological characteristics, causes, and rating principles of defects.

This standard applies to the evaluation of macrostructure defects in the cross-section of slabs produced by continuous casting processes, including carbon steel, silicon steel, low alloy steel, etc. Slab dimensions: thickness 150mm–300mm × width 1,000mm–2,000mm. Alloy steel continuous casting slabs may also be referenced.

The acceptable levels and non-permissible defects for each type shall be specified in the relevant technical conditions or mutual agreements.

2. Referenced Standards

• GB 226-91 — Acid Etch Test Method for Macrostructure and Defects of Steel
• GB 4236-84 — Sulfur Print Test Method for Steel

3. Test Specimens

Specimens shall be cut according to relevant technical conditions. If no technical conditions are specified: For single-heat continuous casting, specimens are taken from the slab corresponding to the middle stage of casting; for multi-heat continuous casting, specimens are taken from the middle slab of the second heat in each cycle. Specimens are cut from the full cross-section or half cross-section (greater than half the slab width).

Acid etching and sulfur print display methods shall be performed according to GB 226 and GB 4236 respectively.

4. Classification and Evaluation of Macrostructure Defects

4.1.1 Center Segregation

Morphology: On the acid-etched specimen surface, dark spots or bands with deeper corrosion appear in the central region. On sulfur print, spots or concentrated bands of varying color intensity in the central area. Segregation bands are classified into three types: continuous, intermittent, and dispersed distribution.

Cause: During solidification of molten steel, low-melting-point elements such as sulfur and phosphorus are pushed to the center of the slab due to segregation during crystallization.

Evaluation: Acid etch method per A1 rating chart (Appendix A), sulfur print method per B1 rating chart (Appendix B). Rated by segregation type, band thickness, or spot size. Class A: continuously distributed bands; Class B: intermittently distributed bands; Class C: bands formed by discontinuously aggregated spots.

4.1.2 Porosity (Shrinkage Porosity)

Morphology: Light-colored round or irregular spots and voids on the acid-etched specimen or sulfur print.

Cause: Caused by non-dense structure due to rapid columnar crystal growth from high casting temperature, as well as slab bulging or liquid state factors.

Evaluation: Per A2 rating chart (Appendix A), rated by the number, size, and density of spots and voids, or the width of open cracks.

4.1.3 Intermediate Cracks and Subsurface Cracks

Morphology: Linear or curved defects visible on the acid-etched specimen or sulfur print within the columnar crystal region.

Cause: Intergranular cracking formed due to high content of S, P, and other elements in the steel, as well as slab bulging.

Evaluation: Acid etch per A3 chart (Appendix A), sulfur print per B2 chart (Appendix B). Rated by crack length, thickness, and quantity.

4.1.4 Corner Cracks

Morphology: Short cracks or sulfur segregation lines appearing at corners on the acid-etched specimen or sulfur print.

Cause: Formed by stress on the corner structure due to concave or convex depressions on the slab’s narrow or wide edges.

Evaluation: Acid etch per A4 chart (Appendix A), sulfur print per B3 chart (Appendix B). Rated by the size of cracks or sulfur segregation lines.

4.1.5 Triangular Zone Cracks

Morphology: Radial cracks or sulfur segregation lines appearing in the triangular zone at both ends on the acid-etched specimen or sulfur print.

Cause: Poor secondary cooling causes concave or convex depressions on narrow or wide edges, resulting in columnar crystal cracking in the triangular zone under stress.

Evaluation: Acid etch per A5 chart (Appendix A), sulfur print per B4 chart (Appendix B). Rated by crack or sulfur segregation line length.

4.1.6 Aluminum Oxide (Al₂O₃) Inclusions

Morphology: Deep-corroded small dark spots aggregated into defects or light yellow spots aggregated into cloud-like defects on the acid-etched specimen or sulfur print, commonly appearing in a band area at 1/4 thickness on the inner arc side of the slab.

Cause: Formed in aluminum-containing steel during casting due to secondary oxidation of molten steel.

Evaluation: Acid etch per A6 chart (Appendix A), sulfur print per B5 chart (Appendix B). Rated by inclusion size, quantity, and distribution.

4.1.7 Pinhole Bubbles

Morphology: Pinhole-shaped dark spots on the acid-etched specimen or sulfur print.

Cause: Formed by gases absorbed in molten steel.

Evaluation: Per B6 chart (Appendix B). Rated by dark spot size and distribution.

4.1.8 Honeycomb Bubbles

Morphology: Strip-shaped and elliptical gas pores oriented perpendicular to the slab surface on the acid-etched specimen or sulfur print.

Cause: Caused by poor deoxidation of molten steel or moisture in the tundish system.

Evaluation: Acid etch per A7 chart (Appendix A), sulfur print per B7 chart (Appendix B). Rated by bubble size and distribution.

4.1.9 Silicate Inclusions

Silicate inclusion inspection provisions as specified in the standard.

4.2 Rating Levels

All defect ratings are classified into levels from 0.5 to 3.0, with the starting rating level at 0.5.

4.3 Evaluation Method

Each defect is limited to what is visible to the naked eye, and evaluated by comparison with the rating charts according to severity.

4.4 Standard Dimensions

The standard slab size for reference images is 210mm × 1,300mm. When evaluating defects on slabs of other sizes, the rating charts should be scaled proportionally.

4.5 Rating Charts

This standard includes acid etch macroscopic rating charts (Appendix A) and sulfur print rating charts (Appendix B) for continuous casting steel slab defects. The applicable rating chart shall be specified in the relevant technical conditions or mutual agreements.

5. Inspection Report

The inspection report shall include the following contents:

• a) Entrusting unit
• b) Steel grade, heat number, slab specifications
• c) Inspection method
• d) Defect type, evaluation level, and any necessary explanations
• e) Inspector and inspection date

Appendix A — Acid Etch Rating Charts for Continuous Casting Steel Slab Defects

• A1 — Center Segregation Rating Chart
• A2 — Porosity Rating Chart
• A3 — Intermediate Crack Rating Chart
• A4 — Corner Crack Rating Chart
• A5 — Triangular Zone Crack Rating Chart
• A6 — Al₂O₃ Inclusion Rating Chart
• A7 — Honeycomb Bubble Rating Chart

Appendix B — Sulfur Print Rating Charts for Continuous Casting Steel Slab Defects

• B1 — Center Segregation Rating Chart
• B2 — Intermediate Crack Rating Chart
• B3 — Corner Crack Rating Chart
• B4 — Triangular Zone Crack Rating Chart
• B5 — Al₂O₃ Inclusion Rating Chart
• B6 — Pinhole Bubble Rating Chart
• B7 — Honeycomb Bubble Rating Chart

Original Document (PDF)

The original Chinese standard document can be downloaded here:

📄 Download YB/T 4003-1997 PDF (Original)