YB/T 153-2015 Standard diagrams for macrostructure and defects in high quality structural steel continuous casting blank
1 Scope
This standard specifies the morphological characteristics, causes, rating principles, evaluation methods, and test report for macrostructure and defects in high quality structural steel continuous casting blanks.
This standard is applicable to the evaluation of acid-etched macrostructure and defects on transverse sections of continuous casting blanks of high quality carbon structural steel, alloy structural steel, spring steel and other grades. Upon agreement between the supplier and the purchaser, it may also apply to the evaluation of continuous casting blanks of other steel grades.
This standard is applicable to continuous casting blanks with the following dimensional ranges: Continuous casting square billets or rectangular billets with side lengths from 100mm to 550mm, and continuous casting round billets with diameters from 90mm to 1,000mm (hereinafter collectively referred to as "continuous casting blanks"). It may serve as a reference for continuous casting blanks of other dimensions.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 226 Test method for macrostructure and defect of steel by etching
YB/T 4149-2006 Continuously cast round billet for seamless steel tube rolling
3 Classification and evaluation
3.1 Specimen revealing method
The cutting and revealing of specimens shall comply with GB/T 226.
3.2 Morphological characteristics, causes and evaluation principles for various defects (or structures)
3.2.1 Center porosity
Morphological characteristics: Voids and dark spots concentrated at the center of the acid-etched specimen.
Causes: Insufficient molten steel feeding to compensate volume shrinkage during solidification of molten steel, and gas precipitation and inclusion accumulation during the final solidification stage.
Evaluation principle: The evaluation is based on the number, size, and density of dark spots and voids at the center of the specimen.
3.2.2 Center segregation
Morphological characteristics: Dark heavily etched patches at the center of the acid-etched specimen, sometimes surrounded by off-white bands and porosity.
Causes: Selective crystallization during molten steel solidification, combined with slow cooling at the center of the continuous casting blank, resulting in composition segregation at the core.
Note: Bulging of the continuous casting blank aggravates the degree of segregation.
Evaluation principle: The evaluation is based on the size and darkness of the dark patches.
3.2.3 Shrinkage cavity
Morphological characteristics: Irregular cavities at the center of the acid-etched specimen.
Causes: Well-developed columnar crystals and local columnar crystal "bridging" during solidification of molten steel; concentrated shrinkage in the last-solidified central part without supplementary molten steel feeding.
Evaluation principle: The evaluation is based on the size of the cavities.
3.2.4 Internal cracks
3.2.4.1 Corner cracks
Morphological characteristics: Cracks generated at the corners of the acid-etched specimen, at a certain depth from the surface, and perpendicular to the surface or parallel to the diagonal. In severe cases, the cracks extend inward.
Causes: Improper and uneven cooling intensity of the molten steel inside and outside the mould, causing the stress on the corners of the continuous casting blank to exceed the strength of the steel.
Evaluation principle: The evaluation is based on the distance from the surface, width, length and number of cracks.
3.2.4.2 Subsurface cracks
Morphological characteristics: Cracks generated at the junction of the fine equiaxed crystals and columnar crystals at the edge of the acid-etched specimen and extending inward along the columnar crystals.
Causes: Mould deformation, excessive local friction, misalignment, uneven cooling of the mould and secondary cooling zone, bulging of the continuous casting blank, and excessive straightening stress.
Evaluation principle: The evaluation is based on the distance from the surface, width, length and number of cracks.
Contents
Foreword II
1 Scope
2 Normative references
3 Classification and evaluation
4 Test report
Annex A (Normative) Standard diagrams for macrostructure and defects in continuous casting square billets or rectangular billets with side lengths not less than 100mm and not greater than 300mm
Annex B (Normative) Standard diagrams for macrostructure and defects in continuous casting square billets and rectangular billets with side lengths greater than 300mm and not greater than 550mm
Annex C (Normative) Standard diagrams for macrostructure and defects in continuous casting round billets diameters not less than 90mm and not greater than 350mm
Annex D (Normative) Standard diagrams for macrostructure and defects in continuous casting round billets with diameters greater than 350mm and not greater than 1,000mm
YB/T 153-2015 Standard diagrams for macrostructure and defects in high quality structural steel continuous casting blank
1 Scope
This standard specifies the morphological characteristics, causes, rating principles, evaluation methods, and test report for macrostructure and defects in high quality structural steel continuous casting blanks.
This standard is applicable to the evaluation of acid-etched macrostructure and defects on transverse sections of continuous casting blanks of high quality carbon structural steel, alloy structural steel, spring steel and other grades. Upon agreement between the supplier and the purchaser, it may also apply to the evaluation of continuous casting blanks of other steel grades.
This standard is applicable to continuous casting blanks with the following dimensional ranges: Continuous casting square billets or rectangular billets with side lengths from 100mm to 550mm, and continuous casting round billets with diameters from 90mm to 1,000mm (hereinafter collectively referred to as "continuous casting blanks"). It may serve as a reference for continuous casting blanks of other dimensions.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 226 Test method for macrostructure and defect of steel by etching
YB/T 4149-2006 Continuously cast round billet for seamless steel tube rolling
3 Classification and evaluation
3.1 Specimen revealing method
The cutting and revealing of specimens shall comply with GB/T 226.
3.2 Morphological characteristics, causes and evaluation principles for various defects (or structures)
3.2.1 Center porosity
Morphological characteristics: Voids and dark spots concentrated at the center of the acid-etched specimen.
Causes: Insufficient molten steel feeding to compensate volume shrinkage during solidification of molten steel, and gas precipitation and inclusion accumulation during the final solidification stage.
Evaluation principle: The evaluation is based on the number, size, and density of dark spots and voids at the center of the specimen.
3.2.2 Center segregation
Morphological characteristics: Dark heavily etched patches at the center of the acid-etched specimen, sometimes surrounded by off-white bands and porosity.
Causes: Selective crystallization during molten steel solidification, combined with slow cooling at the center of the continuous casting blank, resulting in composition segregation at the core.
Note: Bulging of the continuous casting blank aggravates the degree of segregation.
Evaluation principle: The evaluation is based on the size and darkness of the dark patches.
3.2.3 Shrinkage cavity
Morphological characteristics: Irregular cavities at the center of the acid-etched specimen.
Causes: Well-developed columnar crystals and local columnar crystal "bridging" during solidification of molten steel; concentrated shrinkage in the last-solidified central part without supplementary molten steel feeding.
Evaluation principle: The evaluation is based on the size of the cavities.
3.2.4 Internal cracks
3.2.4.1 Corner cracks
Morphological characteristics: Cracks generated at the corners of the acid-etched specimen, at a certain depth from the surface, and perpendicular to the surface or parallel to the diagonal. In severe cases, the cracks extend inward.
Causes: Improper and uneven cooling intensity of the molten steel inside and outside the mould, causing the stress on the corners of the continuous casting blank to exceed the strength of the steel.
Evaluation principle: The evaluation is based on the distance from the surface, width, length and number of cracks.
3.2.4.2 Subsurface cracks
Morphological characteristics: Cracks generated at the junction of the fine equiaxed crystals and columnar crystals at the edge of the acid-etched specimen and extending inward along the columnar crystals.
Causes: Mould deformation, excessive local friction, misalignment, uneven cooling of the mould and secondary cooling zone, bulging of the continuous casting blank, and excessive straightening stress.
Evaluation principle: The evaluation is based on the distance from the surface, width, length and number of cracks.
Contents of YB/T 153-2015
Contents
Foreword II
1 Scope
2 Normative references
3 Classification and evaluation
4 Test report
Annex A (Normative) Standard diagrams for macrostructure and defects in continuous casting square billets or rectangular billets with side lengths not less than 100mm and not greater than 300mm
Annex B (Normative) Standard diagrams for macrostructure and defects in continuous casting square billets and rectangular billets with side lengths greater than 300mm and not greater than 550mm
Annex C (Normative) Standard diagrams for macrostructure and defects in continuous casting round billets diameters not less than 90mm and not greater than 350mm
Annex D (Normative) Standard diagrams for macrostructure and defects in continuous casting round billets with diameters greater than 350mm and not greater than 1,000mm
