YB/T 153-1999: Macrostructure Defect Rating Diagrams for Continuous Casting Billets – English Translation
YB/T 153-1999: Standard Diagrams for Macrostructure Defects in Continuous Casting Billets of Quality Carbon Structural Steel and Alloy Structural Steel
Standard Number: YB/T 153-1999
Publishing Authority: National Metallurgical Industry Bureau of the People’s Republic of China
Publication Date: August 19, 1999
Implementation Date: January 1, 2000
1. Scope
This standard specifies the morphological characteristics, causes, and evaluation principles for macrostructure defects in continuous casting square (and rectangular) billets and round billets of quality carbon structural steel and alloy structural steel.
This standard applies to the evaluation of macrostructure defects on cross-sectional acid-etched specimens of continuous casting billets of quality carbon structural steel, alloy structural steel, spring steel, etc. The billet size range covers: square or shaped billets of 100–300 mm, and round billets of 90–350 mm. Other sizes of continuous casting billets may be used for reference. According to agreements between supplier and purchaser, it may also be applied to stainless steel and bearing steel continuous casting billets.
2. Reference Standards
GB/T 226-1991 — Acid Etching Test Method for Macrostructure and Defects of Steel
3. Classification and Evaluation
3.1 Specimen Display Method
The specimen display method shall be performed in accordance with GB/T 226.
3.2 Morphological Characteristics, Causes, and Evaluation Principles
3.2.1 Center Porosity
Morphological Characteristics: Voids and dark spots concentrated in the central region on the acid-etched specimen.
Cause: Volume contraction during solidification of molten steel without sufficient replenishment, and gas segregation and impurity accumulation during final solidification.
Evaluation Principle: Evaluated based on the quantity, size, and concentration degree of dark spots and voids in the central region.
3.2.2 Center Segregation
Morphological Characteristics: Darker etched spots appearing in the central region, sometimes with grayish-white bands and porosity surrounding the spots.
Cause: During solidification, selective crystallization and slower cooling in the central region cause composition enrichment in the core.
Evaluation Principle: Evaluated based on the size, depth, and area of the segregated spots.
3.2.3 Shrinkage Cavity (Pipe)
Morphological Characteristics: Irregular voids appearing in the central region of the acid-etched specimen.
Cause: Developed columnar crystals and local columnar crystal bridging, causing concentrated shrinkage in the last-to-solidify central region without adequate liquid steel replenishment.
Evaluation Principle: Evaluated based on the size of the cavities.
3.2.4 Internal Cracks
3.2.4.1 Corner Cracks
Morphological Characteristics: Located at the corners, at a certain depth from the surface and perpendicular to it. When severe, cracks extend inward along the diagonal.
Cause: Improper internal/external cooling intensity and uneven cooling in the mold.
Evaluation Principle: Evaluated based on crack width, length, quantity, and distance from the surface.
3.2.4.2 Subsurface Cracks
Morphological Characteristics: Cracks at the boundary between fine equiaxed crystals and columnar crystals, extending inward along the columnar crystals.
Cause: Mold deformation, excessive local friction, misalignment, uneven cooling, bulging, and excessive straightening stress.
Evaluation Principle: Evaluated based on crack width, length, quantity, and distance from the surface.
3.2.4.3 Intermediate Cracks
Morphological Characteristics: Cracks in the columnar crystal region, extending along columnar crystals.
Cause: Uneven cooling, temperature recovery after leaving the secondary cooling zone, generating thermal stress. Excessive mechanical stress. Developed columnar crystals also promote crack formation.
Evaluation Principle: Evaluated based on crack width, length, and quantity.
3.2.4.4 Center Cracks
Morphological Characteristics: Cracks appearing in the central region of the acid-etched specimen.
Cause: Stress from solidification shrinkage during final solidification, billet bulging, improper secondary cooling regime, excessive straightening stress, high superheat, and high gas content.
Evaluation Principle: Evaluated based on crack width, length, and quantity.
3.2.5 Subsurface Bubbles (Blowholes)
Morphological Characteristics: Elongated cracks or elliptical gas pores distributed dispersely or regularly beneath the surface, growing along the columnar crystal direction.
Cause: Poor deoxidation, secondary oxidation, high gas content, non-dry raw materials or casting systems, inadequate mold lubrication.
Evaluation Principle: Evaluated based on quantity, size, and distribution density.
3.2.6 Non-Metallic Inclusions
Morphological Characteristics: Non-metallic particles of various shapes and colors on the acid-etched specimen, or pits left after corrosion and spalling.
Cause: Deoxidation products during smelting and slag entering the mold without floating out.
Evaluation Principle: Evaluated based on quantity, size, and concentration degree of inclusions.
3.2.7 White Bright Band
Morphological Characteristics: A white bright band with strong corrosion resistance and dense structure.
Cause: Improper electromagnetic stirring, high flow velocity of molten steel, reduced temperature gradient at the solidification front.
Evaluation: Record the distance from the edge and the width of the band.
3.2.8 Slag Inclusion
Morphological Characteristics: Block-shaped or granular materials of various shapes and colors.
Cause: Vortex formation during pouring at low tundish level draws slag into the mold, or excessive wave fluctuation entraps slag into molten steel.
Evaluation: Record the size, quantity, and position of slag inclusions.
3.2.9 Foreign Metal Inclusion
Morphological Characteristics: Dense areas with clear or unclear boundaries on the acid-etched specimen.
Cause: Added alloy materials or foreign metals dropped during casting that did not fully melt.
Evaluation: Record the size and position of foreign metal inclusions.
3.2.10 Scab (Lapped Skin)
Morphological Characteristics: Skin-like folds appearing on the surface or subsurface.
Cause: Improper mold conditions and excessive fluctuation of the molten steel surface.
Evaluation: Record the depth, length, and position.
3.3 Rating Charts
Defects requiring rating are each divided into four grades. Non-rated defects are shown with one typical image. The actual size of the rating chart edge (or diameter) is 100 mm. All rating charts are shown in Appendix A.
3.4 Evaluation Method
Each defect type is evaluated separately by comparison with the rating charts according to severity. When severity falls between two adjacent grades, a half-grade may be assigned. Rating charts may be proportionally scaled for other billet sizes.
3.5 Acceptable Grade
Whether each defect is permissible and the acceptable grade shall be specified in the relevant product standards.
4. Test Report
The test report shall include:
- a) Entrusting organization
- b) Inspection grade/steel grade
- c) Heat number of the inspected specimen
- d) Specimen number
- e) Continuous casting billet specifications
- f) Inspection results: defect type, evaluation grade, and any situations to be noted
- g) Inspector, reviewer, and inspection date
Appendix A — Rating Diagrams
The standard includes the following rating diagrams:
- Figure A1 — Center Porosity (Grades 1–4)
- Figure A2 — Center Segregation (Grades 1–4)
- Figure A3 — Shrinkage Cavity (Grades 1–4)
- Figure A4 — Corner Cracks (Grades 1–4)
- Figure A5 — Subsurface Cracks (Grades 1–4)
- Figure A6 — Intermediate Cracks (Grades 1–4)
- Figure A7 — Center Cracks (Grades 1–4)
- Figure A8 — Subsurface Bubbles (Grades 1–4)
- Figure A9 — Non-Metallic Inclusions (Grades 1–4)
- Figure A10 — White Bright Band
- Figure A11 — Slag Inclusion
- Figure A12 — Foreign Metal Inclusion
- Figure A13 — Scab
- Figure A14 — Lapped Skin
Download Original Standard PDF
The original Chinese version of this standard is available for download below:
Download YB/T 153-1999 — Macrostructure Defect Rating Diagrams (Original PDF)
Disclaimer: This English translation is provided for reference purposes only. In case of any discrepancy, the original Chinese standard YB/T 153-1999 shall prevail.
WhatsApp: +86-18658777855
Email: 1007788887@qq.com
