YB/T 4002-2013 English PDF (YB/T4002-2013)

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YB/T 4002-2013: Standard diagrams for macrostructure and defects in continuous casting billets
YB/T 4002-2013
YB
FERROUS METALLURGICAL INDUSTRY STANDARD
OF THE PEOPLE’S REPUBLIC OF CHINA
ICS 77.040.99
H 24
YB/T 4002-2013
Replacing YB/T 4002-1991
Standard diagrams for macrostructure and defects in
continuous casting billets
ISSUED ON: APRIL 25, 2013
IMPLEMENTED ON: SEPTEMBER 01, 2013
Issued by: Ministry of Industry and Information Technology of the People’s
Republic of China
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative references ... 4
3 Sample interception and display methods ... 4
4 Classification and assessment of macrostructure and defects in continuous casting
billets ... 4
5 Standard diagrams ... 8
6 Assessment methods ... 8
7 Inspection report ... 8
Annex A (normative) Standard diagrams for macrostructure and defects in continuous
casting billets1) ... 10
Annex B (informative) Schematic diagrams for macrostructure and defects in
continuous casting billets1) ... 11
Standard diagrams for macrostructure and defects in
continuous casting billets
1 Scope
This Standard specifies the morphological characteristics, causes and assessment
principles for macrostructure and defects in continuous casting billets.
This Standard applies to the assessment of acid-etched macrostructure and defects in
the cross-section of billets such as carbon steel and low alloy steel produced by
continuous casting processes. The cross-sectional dimensions of square billets range
from 90 mm ~ 400 mm in side length, and rectangular billets can also be used this as a
reference.
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
3 Sample interception and display methods
The sample interception and display methods shall be implemented in accordance with
the provisions of GB/T 226. Other sample display methods may also be used upon
agreement between the supplier and the purchaser.
4 Classification and assessment of macrostructure and defects
in continuous casting billets
4.1 Center porosity
Morphological characteristics: Voids and dark spots concentrated in the center of the
acid-etched test piece.
Cause: The structure porosity caused by the volume shrinkage of the billet during
solidification and the serious gas precipitation and inclusion accumulation in the center
of the billet due to final solidification.
Assessment principle: According to Annex A, assess basing on the number, size and
density of dark spots and voids.
4.2 Center segregation
Morphological characteristics: Dark spots with deep corrosion appear in the center of
the acid-etched test piece.
Cause: During the solidification process of molten steel, due to the influence of the
crystallization rule and the slow cooling of the center of the billet, the components in
the center are segregated.
Assessment principle: According to Annex A, assess basing on the size of dark spots
with deep corrosion in the center.
4.3 Shrinkage
Morphological characteristics: Irregular voids in the center of the acid-etched test piece.
Cause: The volume of molten steel shrinks concentratedly during solidification and the
corresponding molten steel is not replenished in time.
Assessment principle: According to Annex A, assess basing on the size of voids.
4.4 Internal crack
4.4.1 Corner crack
Morphological characteristics: At the corners of the acid-etched test piece, it has a
certain depth from the surface and is perpendicular to the surface, and it will expand
diagonally inward when the crack is serious.
Cause: It is formed by the denting and severe off-square of the sides of the corners of
the billet, which causes local stress.
Assessment principle: According to Annex A, assess basing on the number, size and
distance from the surface of cracks.
4.4.2 Subsurface crack
Morphological characteristics: At the edge of the acid-etched test piece, it is generated
at the interface between fine equiaxed crystals and columnar crystals and expands
inwards along the columnar crystals.
Cause: It is caused by the deformation when straightening the bulging billet using a
guide roller.
Assessment principle: According to Annex A, assess basing on the number, size and
distance from the surface of cracks.
Assessment principle: According to Annex A, assess basing on the number and size of
inclusions.
4.7 White light band
Morphological characteristics: Bright white bands with strong corrosion resistance and
dense structure on the acid-etched test piece.
Cause: Improper electromagnetic stirring, fast movement of molten steel, reduced
temperature gradient at the solidification front, and liquid steel enriched in solutes at
the solidification front flows out to form a bright white band.
Assessment principle: According to Annex A, record the distance from the edge and the
width of the band.
4.8 Slag inclusion
Morphological characteristics: Lumps or particles of different shapes and colors on the
acid-etched test piece.
Cause: Low liquid level pouring in the tundish creates a vortex that sucks the slag into
the crystallizer and the slag fails to float and separate, or the liquid level in the
crystallizer fluctuates too much and the slag is drawn into the molten steel and fails to
float before solidification, forming a center slag inclusion. Slag inclusions within 10
mm from the surface of the continuous casting billet are called subsurface slag
inclusions.
Assessment principle: According to Annex A, record the size, number and location of
slag inclusions.
4.9 Dissimilar metal inclusion
Morphological characteristics: Metal blocks with a color different from the matrix
structure and no certain shape on the acid-etched test piece. Some have obvious
boundaries with the matrix structure, and some have unclear boundaries.
Cause: The alloy material added or the dissimilar metal dropped in during the pouring
process is not completely melted.
Assessment principle: According to Annex A, record the size and location of dissimilar
metal inclusions.
4.10 Overturning oxidation film
Morphological characteristics: In the acid-etched test piece, some show bright white
curved bands with pores and inclusions on or around them; some show irregular dark
lines; some are strips composed of dense voids and inclusions.
Cause: Due to the excessive fluctuation of the liquid level in the crystallizer during the
pouring process, or the shallow insertion of the nozzle, improper inclination angle, etc.,
the oxidation film on the liquid surface is rolled into the liquid steel and the molten steel
fails to surface before solidification.
Assessment principle: According to Annex A, record the length and position of
overturning oxidation film.
4.11 Snow flake
Morphological characteristics: Generally, zigzag-shaped fine hair lines on the parts of
the acid-etched test piece except the edge area, distributed in radial, concentric circles
or irregular shapes.
Cause: The hydrogen content in steel is high.
Assessment principle: According to Annex A, record the length and location of cracks.
5 Standard diagrams
5.1 The standard diagrams of various types of defects are divided into 5 levels, and the
diagram of level 0 (Annex A) is a shared picture.
5.2 The actual size of the side length of the diagrams in Annex A is 100 mm. When
comparing and assessing the structural defect levels of steel billets of other sizes, it can
scale down or enlarge the standard diagrams according to each structural defect.
6 Assessment methods
6.1 Various types of defects are limited to those that are visible to the naked eye, and
will be compared and assessed separately based on their severity according to the
standard diagrams. When the severity is between two adjacent levels, it can be rated as
half a level.
6.2 Whether the various types of defects in the standard diagrams of this Standard are
allowed to exist and the qualification level shall be specified in the corresponding
technical conditions or the agreement between the parties.
7 Inspection report
The inspection report shall include the following contents:
a) Entrusting organization;
b) Steel designation for inspection;