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GB/T 1979-2001 English PDF (GBT1979-2001)

GB/T 1979-2001 English PDF (GBT1979-2001)

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GB/T 1979-2001: Standard diagrams for macrostructure and defect of structural steels

This Standard specifies and describes the classification, characteristics, causing reasons and assessment principles, classification and the scope of application of the standard diagram, assessment methods and test report of acid-pickling macrostructure-defect of structural steel.
GB/T 1979-2001
GB
NATIONAL STANDARD OF THE
PEOPLE REPUBLIC OF CHINA
ICS 77.040.01
H 24
Replacing GB/T 1979-1980
Standard diagrams for macrostructure
and defect of structural steels
ISSUED ON. DECEMBER 17, 2001
IMPLEMENTED ON. MAY 1, 2002
Issued by. General Administration of Quality Supervision, Inspection and Quarantine
Table of Contents
Foreword ... 3
1 Scope .. 5
2 Normative references ... 5
3 Cutting and display method of the test-sample .. 5
4 Classification, characteristics, causing reasons and assessment principles of the defects ... 5
5 Classification and applicable scope of the standard diagram ... 10
6 Assessment method ... 10
7 Test report ... 12
Appendix A ... 13
References ... 65
Foreword
This revision of this Standard modifies the following provisions (diagrams). - Modify the previous spot-segregation character into the spotted segregation; - Partially modify and supplement the assessment principle of the previous ingot-shape segregation and subsurface blowholes.
- Partially modify and supplement the characteristics and assessment principle of the previous peeling.
- Partially modify the causing reason of the previous white spot.
- Modify and supplement the characteristics and assessment principle of the previous axial inter-crystalline cracks.
- The previous standard diagram I. appropriately modify the general-porosity grade-4 diagram;
- The previous standard diagram II. appropriately modify the ingot-shape segregation grade-4 diagram;
- The previous standard diagram III. cancel the rating of the peeling; retain the previous diagram as the representative diagram.
The main amended and additional contents of this revision are as follows. - The provisions of "2 - Normative references", "3 - Cutting and display method of test- sample" AND "7 - Test report";
- The defect name, characteristics, causing reasons, assessment principles and diagrams of white-band AND center segregation;
- The defect name, characteristics, causing reasons and assessment principles of cap segregation;
- 4 ingot-shape-segregation grading diagrams which are less than 40mm;
- There are totally 12 diagrams of general-porosity, central-porosity and ingot-shape- segregation grading diagrams with 4 diagrams for each one, greater than 250mm. Appendix A of this Standard is normative.
This Standard replaces GB/T 1979-1980 ?€?Diagram of a low magnification texture blemish grading of structural steel?€? from the date of implementation.
Standard diagrams for macrostructure
and defect of structural steels
1 Scope
This Standard specifies and describes the classification, characteristics, causing reasons and assessment principles, classification and the scope of application of the standard diagram, assessment methods and test report of acid-pickling
macrostructure-defect of structural steel.
This Standard is applicable to assess the allowable and unallowable defects in the acid-pickling macrostructure of the cross-section of carbon structural steel, alloy structural steel and spring steel products (forging billet, rolling billet). According to the agreement between the supply-demand parties, it can also be used to assess the defects in other steel?€?s macrostructure.
2 Normative references
The provisions in following documents become the provisions of this Standard through reference in this Standard. For the dated references, the subsequent amendments (excluding corrections) or revisions do not apply to this Standard, however, parties who reach an agreement based on this Standard are encouraged to study if the latest versions of these documents are applicable. For undated reference documents, the latest versions apply to this Standard.
GB/T 226 Test method for macrostructure and defect of steel by etching
3 Cutting and display method of the test-sample
The test-sample shall be cut and displayed according to the provisions of GB/T 226. Through the agreement between the supply-demand parties, other display methods of test-sample can also be used.
4 Classification, characteristics, causing reasons and
assessment principles of the defects
4.1 General porosity
Characteristic. on the acid-pickling test-piece, it appears that the tissue is not compact; it appears as the dark spots and the gaps, which are dispersed on the whole cross- section. Most of the dark spots appear as the roundness or oval. Through the observation under the magnifying glass, most of the gaps appear as the irregular holes or round pinhole. These dark spots and gaps generally appear between the principal axis and each secondary axis of the thick dendritic crystal. The porosity zone is dark; the axis is bright. If the difference of the corrosion degree between the dark zone and bright zone is not large, then it shall not generate pits.
Causing reason. When the liquid steel is solidifying, the core of each crystal shall grow up in the form of dendritic crystal. Between the principal axis and each secondary axis of the dendritic crystal, there exists micro-gap which is generated when the liquid steel solidifies; and precipitate some low-melting-point constituent elements, gas and non- metallic inclusions. After the acid corrosion, these micro-gaps and precipitated materials appear with tissue porosity.
Assessment principles. it depends on the quantity, size and distribution state of the dark spots and gaps, which are dispersed throughout the cross-section, and it should be determined through the consideration of the thickness degree of the dendritic crystals.
4.2 Central porosity
Characteristic. The central part of the acid-pickling test-piece appears centrally- distributed gaps and the dark spots. The main difference between it and the general porosity is that the gaps and dark spots only exist at the central portion of the test- sample, rather than disperse throughout the cross-section.
Causing reason. it is caused by the tissue porosity which is due to the volume shrinkage during solidification of liquid steel; and at the central part of steel ingot, the gas is separated out and collected due to the final solidification; and the aggregation extent of the inclusions is serious.
Assessment principles. it shall be determined by the quantity, size and density of dark spots and gaps.
4.3 Ingot segregation
Characteristic. The frame strap which appears deeper corrosion on the acid-pickling test-piece, and it is consisted of dark spots and gaps, similar to the shape of the original ingot cross section, generally square.
Causing reason. during the crystallization process of the steel ingot, due to the influence of crystallization rules, it is caused by the component segregation and the impurity aggregation at the junction of the columnar crystal zone and central-isometric crystal zone.
Assessment principles. it is determined according to the area size and quantity of the central dark spots.
4.7 Cap-mouth segregation
Characteristics. on the central part of the acid-pickling test-piece, it appears the dark and easily-corroded metal zone.
Causing reasons. it is caused by the carbon-increase that the carbonaceous heat- insulating padding near the cap-mouth effects to the metal.
Assessment principles. it is determined according to the size of the dark area (it is determined according to the standard diagram V ?€?Central segregation diagram?€? in Appendix A).
4.8 Subsurface blowholes
Characteristic. On the acid-pickling test-piece, it appears as the elongated slit which is distributed in dispersed or clustered form, or oval air hole. Most of the elongated slits are perpendicular to the surface of the steel products (billet).
Causing reasons. it is caused by that the cleaning of inner wall of steel-ingot mold is poor, and the protective slag is not dried, etc.
Assessment principles. measure the maximum distance from the blowholes to the surface of steel products (billet).
4.9 Residual shrinkage cavity
Characteristics. on the central region of the acid-pickling test-piece (most cases), it appears irregular slits or holes; it is often accompanied with severe porosity, inclusions (slag inclusions) and component segregation on or near it.
Causing reasons. it is from the shrinkage cavity which is generated by the concentrated shrinkage of the volume during the solidification of the liquid steel, AND during hot working, partial residuals can be generated due to the incomplete resection; the secondary shrinkage cavity may also occur sometimes.
Assessment principles. it is determined according to the size of the slits or holes. 4.10 Peeling
Characteristics. on the acid-pickling test-piece, some of them appear shiny-white curved strip or irregular dark-black line, and there are air holes and inclusions on or around i...

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