Micrographic examination of the non-metallic inclusion content of steels using standard pictures

This draft European Standard defines a method of microscopic non-metallic endogenous inclusion assessment using picture charts.
The method does not apply to particles of a length or diameter less than 3,0 µm or a width smaller than 2,0 µm. If defined by a product standard or agreement between the involved parties for certain special products, inclusions with a width below 2,0 µm can be evaluated by length alone.Inclusions with dimensions exceeding the upper limits in Table 2 are evaluated as belonging to the maximum class and noted separately with their true dimensions (see 7.5.6).
It is assumed, if particles are elongated or if there are stringers of particles, that they are parallel to each other. Other arrangements are not covered by this draft standard. This draft European Standard applies to samples with a microscopic precipitation approaching random distribution.
From the data of measurements obtained by this method, evaluation according to other standards can be established.
This draft European Standard does not apply to free cutting steels.
NOTE   The basic principle of this draft European Standard allows the determination of non-metallic inclusion content by image analysis techniques.

Metallographische Prüfung des Gehaltes nichtmetallischer Einschlüsse in Stählen mit Bildreihen

Dieser Europäische Normentwurf legt ein Verfahren zur mikroskopischen Kennzeichnung von nichtmetallischen endogenen Einschlüssen unter Verwendung von Richtreihenbildern fest.
Das Verfahren gilt nicht für Teilchen mit einer Länge oder einem Durchmesser kleiner als 3,0 µm oder einer Breite kleiner als 2,0 µm. Sofern in einer Produktnorm oder durch Vereinbarung zwischen den Beteiligten für spezielle Produkte festgelegt, können Einschlüsse mit einer Breite kleiner als 2,0 µm ausschließlich nach ihrer Länge bewertet werden. Einschlüsse, deren Maße die in Tabelle 2 angegebenen oberen Grenzen überschreiten, werden als zugehörig zur größten Klasse gewertet und gesondert mit ihren tatsächlichen Maßen aufgezeichnet (siehe 7.5.6).
Es wird vorausgesetzt, falls Teilchen gestreckt sind oder falls zeilenförmige Anordnungen von Teilchen auftreten diese parallel zueinander liegen. Andere Anordnungen werden durch diesen Normentwurf nicht berück¬sichtigt. Dieser Europäische Normentwurf gilt für Proben mit mikroskopischen Agglomerationen unter der Annahme einer makroskopisch regellosen Verteilung.
Aus den mit den hier beschriebenen Verfahren erzielten Messwerten kann eine Auswertung nach anderen Normen abgeleitet werden.
Dieser Europäische Normentwurf gilt nicht für Automatenstähle.
ANMERKUNG   Das Grundprinzip dieses Europäischen Normentwurfes ermöglicht die Bestimmung des Gehaltes an nichtmetallischen Einschlüssen mittels Bildanalysetechnik.

Détermination micrographique de la teneur en inclusions non-métalliques des aciers à l'aide d'images- types

Ce projet de Norme européenne définit une méthode de cotation des inclusions microscopiques endogènes non-métalliques à l'aide d'images types.
La méthode ne s'applique pas aux particules de longueur ou diamètre inférieure à 3,0 µm ou de largeur inférieure à 2,0 µm. Lorsque cela est défini dans la norme de produit ou par accord entre les parties intéressées, les inclusions de largeur inférieure à 2,0 µm peuvent être évaluées uniquement selon leur longueur. Les inclusions allongées de longueur supérieure aux limites indiquées au Tableau 2 sont comptées comme faisant partie de la classe maximum et notées séparément avec leurs dimensions réelles (voir 7.5.6)
Il est admis que si les particules sont allongées ou si elles sont en amas, elles sont parallèles entre elles. D'autres dispositions ne sont pas couvertes par ce projet de Norme. Ce projet de Norme européenne s'applique aux échantillons présentant une ségrégation microscopique présentant une distribution au hasard.
À partir des données des mesures obtenues par la présente méthode, une évaluation selon d'autres normes peut être établie.
Ce projet de Norme européenne n'est pas adapté aux aciers de décolletage.
NOTE   Le principe de base de ce projet de Norme européenne permet la détermination de la teneur inclusionnaire par les techniques d'analyse d'image.

Mikrografsko ugotavljanje deleža nekovinskih vključkov v jeklih z uporabo standardnih slik

Ta osnutek evropskega standarda opredeljuje metodo mikroskopskega ugotavljanja deleža nekovinskih vključkov v jeklih z uporabo slik.
Metoda se ne uporablja za delce dolžine ali premera manj kot 3,0 μm ali širine, manjše od 2,0 μm. Če tako določa standard za izdelek ali sporazum med vpletenimi strankami za določene posebne izdelke, je mogoče ugotoviti delež vključkov s širino pod 2,0 μm samo po dolžini. Ugotavljanje deleža vključkov z merami, ki presegajo zgornje meje v tabeli 2, se izvaja ob predpostavki, da pripadajo najvišjemu razredu in se posebej zabeležijo s svojimi dejanskimi dimenzijami (glej 7.5.6).
Če so delci podolgovati ali če obstajajo ostanki delcev, se predpostavlja, da so med seboj vzporedni. Druge ureditve niso zajete v osnutku tega standarda. Ta osnutek evropskega standarda se uporablja za vzorce z mikroskopskimi usedlinami, ki se približujejo naključni porazdelitvi.
Iz podatkov meritev, pridobljenih s to metodo, je mogoče izvesti vrednotenje v skladu z drugimi standardi.
Ta osnutek evropskega standarda se ne uporablja za avtomatna jekla.
OPOMBA: Osnovno načelo tega osnutka evropskega standarda omogoča določanje vsebnosti nekovinskih vključkov s pomočjo tehnik za analizo slike.

General Information

Status
Published
Public Enquiry End Date
02-Mar-2016
Publication Date
22-Oct-2017
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
28-Jul-2017
Due Date
02-Oct-2017
Completion Date
23-Oct-2017

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SLOVENSKI STANDARD
SIST EN 10247:2017
01-december-2017
0LNURJUDIVNRXJRWDYOMDQMHGHOHåDQHNRYLQVNLKYNOMXþNRYYMHNOLK]XSRUDER
VWDQGDUGQLKVOLN

Micrographic examination of the non-metallic inclusion content of steels using standard

pictures

Metallographische Prüfung des Gehaltes nichtmetallischer Einschlüsse in Stählen mit

Bildreihen

Détermination micrographique de la teneur en inclusions non-métalliques des aciers à

l'aide d'images- types
Ta slovenski standard je istoveten z: EN 10247:2017
ICS:
77.040.99 Druge metode za Other methods of testing of
preskušanje kovin metals
77.080.20 Jekla Steels
SIST EN 10247:2017 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 10247:2017
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SIST EN 10247:2017
EN 10247
EUROPEAN STANDARD
NORME EUROPÉENNE
July 2017
EUROPÄISCHE NORM
ICS 77.040.99 Supersedes EN 10247:2007
English Version
Micrographic examination of the non-metallic inclusion
content of steels using standard pictures

Détermination micrographique de la teneur en Metallographische Prüfung des Gehaltes

inclusions non-métalliques des aciers à l'aide d'images- nichtmetallischer Einschlüsse in Stählen mit Bildreihen

types
This European Standard was approved by CEN on 18 January 2017.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this

European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references

concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN

member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by

translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management

Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,

Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels

© 2017 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 10247:2017 E

worldwide for CEN national Members.
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SIST EN 10247:2017
EN 10247:2017 (E)
Contents Page

European foreword ....................................................................................................................................................... 5

Introduction .................................................................................................................................................................... 6

1 Scope .................................................................................................................................................................... 7

2 Normative references .................................................................................................................................... 7

3 Terms and definitions ................................................................................................................................... 7

4 Symbols and abbreviations ...................................................................................................................... 10

5 Principles ........................................................................................................................................................ 12

6 Brief practical guide .................................................................................................................................... 13

6.1 Basic rules for evaluation .......................................................................................................................... 13

6.2 Evaluation according to the default rating methods ....................................................................... 14

7 Sampling .......................................................................................................................................................... 14

7.1 General ............................................................................................................................................................. 14

7.2 Degree of reduction ..................................................................................................................................... 15

7.3 Size and location of test area ................................................................................................................... 15

7.4 Number of specimens ................................................................................................................................. 15

7.5 Preparation of specimens ......................................................................................................................... 16

8 Test method ................................................................................................................................................... 16

8.1 Magnification ................................................................................................................................................. 16

8.2 Microscope settings for image analysis and manual analysis ..................................................... 16

8.3 Field of view ................................................................................................................................................... 17

8.4 Definition of the pictures of the chart ................................................................................................... 17

8.4.1 Size and Shape ............................................................................................................................................... 17

8.4.2 Parameters ..................................................................................................................................................... 17

8.4.3 Arrangement of the pictures .................................................................................................................... 17

8.5 Procedure........................................................................................................................................................ 18

8.5.1 General ............................................................................................................................................................. 18

8.5.2 Several inclusions of mixed sizes in one field .................................................................................... 18

8.5.3 Scanning .......................................................................................................................................................... 18

8.5.4 Assessment and evaluation ...................................................................................................................... 19

8.5.5 Evaluation of different types of inclusions ......................................................................................... 19

8.5.6 Recording of results .................................................................................................................................... 19

9 Types of assessment .................................................................................................................................... 19

9.1 Worst inclusion method: method P ....................................................................................................... 19

9.1.1 Principle .......................................................................................................................................................... 19

9.1.2 Evaluation of P (worst length) .............................................................................................................. 20

9.1.3 Evaluation of P (worst diameter)......................................................................................................... 20

9.1.4 Evaluation of P (worst area) .................................................................................................................. 20

9.2 Worst field method: method M................................................................................................................ 20

9.2.1 Principle .......................................................................................................................................................... 20

9.2.2 Evaluation of M (rating according to number) ............................................................................... 20

9.2.3 Evaluation of M (rating according to length) ................................................................................... 20

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9.2.4 Evaluation of M (rating according to diameter) .............................................................................. 20

9.2.5 Evaluation of M (rating according to area) ....................................................................................... 21

9.3 Average field method: method K ............................................................................................................. 21

9.3.1 Principle ........................................................................................................................................................... 21

9.3.2 Scanning of a specimen for average field assessment ..................................................................... 21

9.3.3 Evaluation........................................................................................................................................................ 21

9.3.4 Evaluation of K , K for elongated and K , K for globular inclusions..................................... 21

n L n d

9.3.5 Evaluation of K and K .............................................................................................................................. 22

n a

10 Test report ...................................................................................................................................................... 22

Annex A (normative) Type of inclusions ........................................................................................................... 34

Annex B (normative) Parameters and assessments to be used if not otherwise specified ............ 37

Annex C (informative) Examples for inclusions of different types .......................................................... 38

Annex D (informative) Shape factor ................................................................................................................... 42

Annex E (informative) Examples for magnification ...................................................................................... 43

Annex F (informative) Details of the eyepiece graticules ........................................................................... 45

Annex G (normative) Manufacturing specifications of the eyepiece graticule.................................... 46

G.1 General ............................................................................................................................................................. 46

G.2 Narrow field microscopes.......................................................................................................................... 46

G.3 Broad field microscopes ............................................................................................................................. 48

Annex H (normative) Calculation basis for the pictures of the chart ..................................................... 50

Annex I (normative) Rules for classification ................................................................................................... 52

I.1 Definition of classes ..................................................................................................................................... 52

I.2 Classification of length ................................................................................................................................ 52

I.3 Classification of width ................................................................................................................................. 52

I.4 Classification of diameter .......................................................................................................................... 52

Annex J (informative) Comparison of inclusion types in different standards ..................................... 53

Annex K (informative) Worst inclusion assessment ..................................................................................... 54

Annex L (informative) Worst field assessment ............................................................................................... 58

L.1 General ............................................................................................................................................................. 58

L.2 Evaluation of M ............................................................................................................................................ 58

L.3 Evaluation of M , M and M .................................................................................................................... 58

n L d

L.4 Evaluation of M and M ............................................................................................................................ 58

n a

Annex M (informative) Average field assessment ......................................................................................... 62

M.1 General ............................................................................................................................................................. 62

M.2 Evaluation of K , K and K ......................................................................................................................... 62

n L d

M.3 Evaluation of K and K ............................................................................................................................... 62

n a

M.4 Restricted assessment ................................................................................................................................ 62

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EN 10247:2017 (E)

Annex N (normative) Calculation basis for the assessment ....................................................................... 74

N.1 Worst inclusion assessment ..................................................................................................................... 74

N.2 Worst field assessment .............................................................................................................................. 74

N.3 Average field .................................................................................................................................................. 75

Annex O (informative) Edge Errors correction .............................................................................................. 77

O.1 General ............................................................................................................................................................. 77

O.2 Measurement ................................................................................................................................................. 77

O.3 Large inclusions ............................................................................................................................................ 77

Annex P (normative) Calculation of average values of parameters for one class .............................. 79

Annex Q (normative) Average values of parameters ................................................................................... 80

Bibliography ................................................................................................................................................................. 81

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EN 10247:2017 (E)
European foreword

This document (EN 10247:2017) has been prepared by Technical Committee ECISS/TC 101 “Test

methods for steel (other than chemical analysis)”, the secretariat of which is held by AFNOR.

This European Standard shall be given the status of a national standard, either by publication of an

identical text or by endorsement, at the latest by January 2018, and conflicting national standards shall

be withdrawn at the latest by January 2018.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN shall not be held responsible for identifying any or all such patent rights.

This document supersedes EN 10247:2007.

The many changes in the current revision result from only a few basic adjustments. The length to width

limit ratio for globular inclusions has been changed from 1,3 to 3 (Annex I), and the mathematical

principles underlying the chart have been more clearly defined (Annex H). These two changes have led

to many numerical changes in Table 2 and Figure 11, where moreover some classes have been deleted

and others added. The rules of assessment have changed, most notably to allow stringer formation from

two particles upward (Subclause 3.1.2, Annex B), to exclude stringer formation between a stringer and

a single particle (Subclause 3.1.2), and to consistently define the classification of inclusions by shape,

arrangement, and colour (Clause 3, Annexes A and B). Finally, the assessment and recording sheets

have been redesigned to simplify manual use (Annexes K, L, and M).

According to the CEN-CENELEC Internal Regulations, the national standards organisations of the

following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,

Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,

France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,

Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and the United Kingdom.
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SIST EN 10247:2017
EN 10247:2017 (E)
Introduction

This document establishes procedures for the assessment of inclusions in steels, based on their

morphology using standard pictures.

These procedures include principles that yield results coherent with consolidated individual inclusion

measurements and expressed in physical units.

The chart of standard pictures is derived from mathematical principles. In distinction to other inclusion

rating standards, in this standard the order of the classification begins with the length (row index q).

The results may be directly computed from field assessments. The same precision level is achieved by

using the same method in manual evaluation and computer controlled measurements.
2 2 2 2

The results are in physical units: length in μm/mm , number/mm , areas in μm /mm .

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EN 10247:2017 (E)
1 Scope

This European Standard defines a method of microscopic non-metallic endogenous inclusion

assessment using picture charts.

The method does not apply to particles of a length or diameter less than 3,0 µm or a width smaller than

2,0 µm. If defined by a product standard or agreement between the involved parties for certain special

products, inclusions with a width below 2,0 µm can be evaluated by length alone. Inclusions with

dimensions exceeding the upper limits in Table 2 are evaluated as belonging to the maximum class and

noted separately with their true dimensions (see 8.5.6).

It is assumed, if particles are elongated or if there are stringers of particles, that they are parallel to each

other. Other arrangements are not covered by this draft standard. This draft European Standard applies

to samples with a microscopic precipitation approaching random distribution.

From the data of measurements obtained by this method, evaluation according to other standards can

be established.
This draft European Standard does not apply to free cutting steels.

NOTE The basic principle of this draft European Standard allows the determination of non-metallic inclusion

content by image analysis techniques.
2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and are

indispensable for its application. For dated references, only the edition cited applies. For undated

references, the latest edition of the referenced document (including any amendments) applies.

EN ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories

(ISO/IEC 17025)

ISO 9042, Steels — Manual point counting method for statistically estimating the volume fraction of a

constituent with a point grid
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1 General:
3.1.1
particle
single precipitate, in general non-metallic
3.1.2
stringer

arrangement of at least 2 particles, normally aligned, that meet the proximity conditions e ≤ 40 µm and

t ≤ 10 µm

Note 1 to entry: For formation of stringers particles with L < 3 µm or w < 2 µm are not taken into account

(see Figure 5).

Note 2 to entry: See Figure 3 for proximity conditions, Figure 7 and Annex B and Annex C for examples

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EN 10247:2017 (E)
3.1.3
inclusion

general designation of a ratable feature composed of at least one particle, defined by the size and

proximity of its constituents

Note 1 to entry: The inclusion can describe a single particle; a single stringer; or an agglomeration of stringers.

Note 2 to entry: Stringers that meet the proximity conditions e ≤ 40 µm and t ≤ 10 µm form an agglomeration of

stringers (see Figure 4). Formation of inclusions by combining stringers and single particles is not permitted.

Note 3 to entry: If elongated and globular particles are combined (see Figure 6), in general the result is treated

as one inclusion.
Note 4 to entry: For further examples see Figure 7.
3.1.4
test area
area on the polished surface of the specimen to be evaluated
3.2 Proximity:
3.2.1
distances between particles

distance e between the particles in the direction of main deformation and distance t in the direction

perpendicular to it
Note 1 to entry: See Figure 3 for illustration.
3.2.2
distance between stringers
similar to that for the distance between particles
Note 1 to entry: See Figure 4 for illustration.
3.2.3
scattered
random arrangement of particles
Note 1 to entry: For example see Annex C. This is defined in one field of view.
3.3 Parameters:
3.3.1
length

dimension of an inclusion in the main deformation direction, usually larger than the width

3.3.2
diameter

maximum dimension of inclusion classified according to column 6 (globular inclusion)

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EN 10247:2017 (E)
3.3.3
width
dimension of inclusion perpendicular to the direction of principal deformation

Note 1 to entry: In particular for inclusions consisting of more than one particle, a subscript of “total” can be

used to distinguish its width from the individual widths of the particles.

Note 2 to entry: For inclusions consisting of a single particle, the width is the maximum dimension

perpendicular to the main deformation direction (see Figure 1).

For inclusions consisting of a single stringer, the width is the width of the confining rectangle (see Figure 2).

For inclusions consisting of an agglomeration of stringers, three cases apply:

— Case a) two stringers for which 0 ≤ e ≤ 40 µm, t ≤ 10 µm: the width of this inclusion is the width of the widest

stringer (w = w ; w > w ; see Figure 4 a)).
total 1 1 2

— Case b) two stringers for which e < 0 µm, t ≤ 10 µm: the width of this inclusion is the sum of the stringers’

widths and the distance t (wtotal = w1 + w2 + t; see Figure 4 b)).

— Case c) an agglomeration of more than two stringers: the width of this inclusion is the widest width obtained

by applying the rules in case a) and b) (see Figure 4 c))
3.3.4
area
area of the equivalent ellipse, calculated as
a= × Lw× , (1)
total
or, in the case of globular particles,
ad× (2)
Note 1 to entry: For details see 3.3.2 and Figures 1, 2, and 4.
3.3.5
shape factor
exponent f in the formula:
π f
× L
 L 
= (3)
 
a 1µm
 
Note 1 to entry: For details see Annex D.
3.4 Classes:
3.4.1
elongated particles
particles with a ratio L/w ≥ 3
Note 1 to entry: See Figure 1 for illustration.
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EN 10247:2017 (E)
3.4.2
globular particles
particles with a ratio L/w < 3
Note 1 to entry: See Figure 1 for illustration.
3.4.3
type

distinction of inclusions according to their shape, arrangement, and colour, and, if desired, by their

apparent chemical composition
Note 1 to entry: See Annex A for illustration.
3.5 Others:
3.5.1
lot

unit of material processed at one time and subject to similar processing variables

3.5.2
restricted values

values of the average field assessment restricted to inclusions of a specified size range, or restricted to

inclusions of specified types
Note 1 to entry: See Annex M.4 and Tables M.6 and M.7 for further detail.
4 Symbols and abbreviations

For the purposes of this document, the following symbols and abbreviations apply.

Symbol Unit Designation
A area of field of view on the specimen
B polished surface
D diameter of product
G magnification
H µm length of measuring frame on the specimen
-, µm,
K average field assessment
2 2
µm /mm
L µm length of inclusions
-, µm,
M worst field assessment
2 2
µm /mm
MD main deformation direction (e.g. rolling direction)
number of fields
number of specimens
P worst inclusion assessment
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Q factor for K-assessment
R restricted values
a area of inclusions
average (mean) value of n, L, w, a ....
av or
b mm width of the plate
b black
c coloured (pink or yellow) (typically nitrides)
d µm diameter of inclusions
distance between the particles in the main deformation
e µm
direction
f shape factor
g grey (typically sulphides)
i inclusion index
j field index
k column number
m type of inclusion index
max index of maximum value of n, L, w, d, a (in j or s)
n number of assessed particles, inclusions
number of assessed inclusions per specimen
p particle index
q row number
s specimen index
distance between the particles perpendicular to the
t µm
main deformation direction
u µm scale unit in microscope eyepiece
v mm width of polished surface
w µm width of inclusions
x variable
α scattered, elongated inclusion type
α scattered, elongated, black inclusion type
αc scattered, elongated, coloured inclusion type
αg scattered, elongated, grey inclusion type
β aligned, globular inclusion type
βb aligned, globular, black inclusion type,
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EN 10247:2017 (E)
β aligned, globular, coloured inclusion type
βg aligned, globular, grey inclusion type
γ aligned, elongated inclusion type
γb aligned, elongated, black inclusion type
γc aligned, elongated, coloured inclusion type
γg aligned, elongated, grey inclusion type
δ scattered, globular inclusion type
δb scattered, globular, black inclusion type
δc scattered, globular, coloured inclusion type
δ scattered, globular grey inclusion type
Combined symbols shall be written with indices.
EXAMPLE K average field assessment for length;
n number of inclusions in a field;
average number of inclusions per field.
5 Principles

This standard consists of a comparison between inclusions observed in a field of view and chart

pictures. The chart classifies inclusions into four different types according to their shape (8.4 /

Annex H). The minimum requirements for applying this method are a square measuring frame of

0,71 mm x 0,71 mm overlaid on the viewfield at a magnification of 100:1 (see Figure 9), along with the

chart – or alternatively a measuring scale and Table 2 of this draft standard.

An inclusion according to this standard can consist of a single particle, a stringer of particles, or an

agglomeration of stringers. All inclusions are treated as ellipses (see Figure 1), with special rules for

agglomerations of stringers (3.1.3 / Figure 4). Inclusions are classified according to shape, arrangement,

and size (Annex A). A classification by colour is also permiss
...

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