IS 13691: Determination of total or effective thicknesses of thin surfaces hardened layers

11 Pages·1993·1.2 MB·English

by  Bureau of Indian Standards

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IS 13691 (1993): Determination of total or effective
thicknesses of thin surfaces hardened layers [MTD 22:
Metallography and Heat Treatment]
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Satyanarayan Gangaram Pitroda
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i‘
SI 13691 : 3991
0SI 0794 : 1979

Indian Standard
LEETS - NOITANIMRETED FO LATOT OR
EVITCEFFE THICKNESS FO THIN
SURFACE-HARDENED SREYAL
UDC 41’966 : 71’026 : 5’587’126

@ SIB 3991
BUREAU OF INDIAN STANDARDS
KANAM ,NAVAHB 9 RUDAYAB HAHS RAFAZ GRAM
NEW IHLED 200011
March 1993 Price Group 2
Metallography and Heat Treatment Sectional Committee, MTD 22
NATIONAL FOREWORD
This Indian Standard which is identical with IS0 4970 : 1979 ‘Steel - Determination of total or
effective thickness of thin surface-hardened layers’, issued by the International Organization for
Standardization ( IS0 ), was adopted by the Bureau of Indian Standards on the recommendation
of the Metallcgraphy and Heat Treatment Sectional Committee ( MTD 22 ) and approval of the
Metallurgical Engineering Division Council.
In the adopted standard certain conventions are not identical with those used in Indian
Standard. Attention is especially drawn to the following:
a) Wherever the words ‘International Standard’ appear referring to this standard, they
should be read as ‘Indian Standard’.
b) Comma ( , ) has been used as a decimal marker, while in Indian Standards, the current
practice is to use point ( . ) as the decimal marker.
The Technical Committee has reviewed the provisions of IS0 2639 ‘Steel - Determination and
verification of the effective depth of carburized and hardened cases’, and IS0 3754, ‘Steel -
Determination of effective depth of hardening after flame or induction hardening’, to which
reference is made in the text, and has decided that they are acceptable for use in conjunction
with this standard.
IS 13691 : 1993
IS0 4970 : 1979
Indian Standard
LEETS - NOITANIMRETED FO LATOT OR
EVITCEFFE THICKNESS FO THIN
SURFACE-HARDENED SREYAL
1 Scope and field of application 2.1.1 Selection and preparation of sample
:
This International Standard specifies a method of measuring The sample may be one of the following types
the total or effective thickness of thin surface-hardened layers,
with thicknesses of less than or equal to 0.3 mm, obtained! for
example, by mechanical’ (shot blasting, shot peening, etc.), a) a section perpendicular to the longitudinal axis of the
thermal.(flame or induction hardening, etc.) or thermochemical product, or, if the product has no longitudinal axis, a sec-
(carbonitriding, carburizing and hardening, etc.) treatment. tion perpendicular to the surfac’e at a location to be agreed
between the parties concerned;
It is not applicable to thin surface layers which are not
continuous with the basis metal.
b) a longitudinal section obtained by machining a 1 mm
NOTE - Surface-hardened layers with thicknesses of more than
deep flat (this method applies only to round bars - see
0,3*Fm are covered by IS0 2639, Steel - Determination and verifica-
tion of the effective ‘depth of carburized and hardened cases; and figure 1); other depths of flat may be specified;
IS0 3754, Steel - Determination of effective depth of hardening after
flame or induction hardening.
c) an oblique section; the thinner the layer, the more acute
the angle a between the plane of the section and the sur-
2 Methods of measurement
face must be (see figure 2). As it is a difficult operation to
: determine the angle a, it is preferable, wherever possible, to
The two methods usually selected are
use an oblique section with a groove having a depth close to
- the presumed thickness of the thin layer (see figure 3). It is
the micrographic method;
then possible to calculate the thickness of the thin layer
without having to measure the angle a (see 2.1.2).
- the microhardness measurement method.
Small samples (with a section of less than 4 cm2) shall be
The choice of the method and its accurac y depend on the
examined all round their perimeter. Where samples are large,
nature of the thin layer and on its presumed t hickness. Since several samples shall be selected to ensure that they are fully
the method used also affects the result obtained, the choice
representative. Sections taken from the corners of polygonal
has to be made by prior agreement between the parties
products, being special points, shall not be included.
concerned.
The number and relative position of the various samplings shall
2.1 Micrographic method be specified by agreement between the parties concerned.
This method consists in examining the structural variations, Using the customary methods, micrographic polishing shall be
from the periphery inwards to the centre, brought about by the carried out so as to avoid rounding off the sharp edges of the
treatment. section, thus varying the angle of the oblique section. To en-
sure that this does not occur, the sample shall be mounted or
The total thickness of the thin surface layer is defined as the shall be held in a clamp. The surface of the product may, if
distance from the surface ekamined to the limit beyond which necessary, be piotected by depositing a metal coating on it
no visible structural variation is detected, as compared with the electrolytically.
structure of the unaffected metal.
Etching using 2 to 4 % nital (i.e. a 2 to 4 % solution of nitric
The effective thickness is defined as the distance from the acid in alcohol) or another appropriate reagent, will show up
surface examined to the limit of a reference structure.11 the structure of the steel.
--
1) When, for example, the reference structure is martensitic, the effective thickness is termed martensitic

1
r
IS 13691:1993
1s04970:1979
2.1.2 Measurement 2.2 Microhardness measurement method
The total or effective thickness of the thin layer shall be This method consists in determining the changes in Vickers
measured either using a micrometer eyepiece, or directly on the microhardnessl )under a 2,94 N (300 gf) load, measured from
ground glass screen of a projection microscope. In most cases the circumference inwards to the centre of the product.
the recommended minimum magnification is200 x .
Where the thickness of the hardened surface layer is not com-
By a preliminary examination at low magnification it will be patible with the size of the impression, other loads maybe used
possible to ensure that there is no significant variation in the by prior agreement between the parties concerned.
thickness of the surface layer along the perimeter examined.
The total thickness of the thin surface layer is defined by the
Several measurements (at least five) shall be taken on the part distance from the surface to the limit beyond which the tiard-
where the surface layer shows a uniform thickness, qnd these ness of the unaffected metal is reached.
shall be taken at regularly spaced points. The thickness of the
surface layer istaken as the average of these measurements. The effective thickness isdefined by the distance from the sur-
face to the limit beyond which the required hardness (reference
NOTES hardness) is reached.
1 In the case of the machined flat (seefigure 1), the thickness of the i
layer, e, isgiven by the formula
2.2.1 Selectionand preparationof sample
e. R–~R2+b2–2b~2 Rf–.f2
where The sample may be one of the following types :
b isthe distance measured on the flat;
a) a section perpendicular to the longitudinal axis of the
J isthe depth ofthe flat; product, or, if the product has no longitudinal axis, a sec-
tion perpendicular to the surface at a location to be agreed
R isthe radius of the sample.
between the parties concerned (this section is identical to
If the flat is 1mm deep, this formula issimplified as follows : that used in the micrographic examination);
e=R– ~R2+b2_2b~~
b) a longitudinal section identical to that used in the
2 In the case of asimple oblique section (see figure 2), the thickness micrographic examination;
of the layer, e, isgiven bythe formula
e=l sina c) a test piece with steps : these steps are pFecision-
ground from the surface of the product to the part where
where
the structure is that of the basis metal, and are 0,05 or
/ isthe distance measured; 0,10 mm thick (see figure 4); the stepped test piece isto be
used when a limiting value for the thickness of the surface
a isthe angle of the oblique section layer isspecified;
3 In the case of a grooved oblique se c tion (sea figure 3), the
thickness of the layer, e, is given by the formula d) a simple or grooved oblique section identical to that

i used in the micrographic examination.
e = e’—
/’
The sample is prepared in exactly the same way as for the
where micrographic method, although the sample does not undergo
etching, in order to simplify the measurement of the size of the
/ isthe distance measured;
impression, During the machining of the steps, precautions
/’ isthe length of the groove m the oblique section; shall be taken to avoid causing any structural changes as a
e’ isthe depth of the groove. result ofgrinding.

1) The Knoop microhardness method may be used.
2
IS13691:1993
I/
ISO4970:1979
\
2.2.2 Measurement ting a graph of variations in hardness against the distance to
the surface.
The hardness impressions shall be situated along one or several
parallel lines normal to the surface and inside a 1,5 mm wide NOTE - In the case of the machined flat or the oblique section, the
interval, W (see figure 5). The first impression shall be situated thickness of the layer is calculated using the formulae in 2.1.2.
at a distance from the surface equal to approximately twice the
length of its diagonal.
3 Test report
:
The distance between two adjacent impressions, S, shall not be The test report shall contain the following information
less than 2,5 times the length of the diagonal. The difference
between the distances from each impression to the surface a) the grade and the treatment of the material;
(d2 - d, for example) shall not exceed 0,l mm, and the
accumulated distance shall be measured to an accuracy of b) the numb&r and locations of samples taken from the
+ 25 pm. The diagonals of the impressions shalt be measured piece;
to an accuracy of * 0,75 pm.
c) the method of measuring adopted, and the procedure;
The impressions shall be made under a 29 N (300 gf) load d) the type of thickness measured (total or effective);
and measured with the aid of an optical device providing a
magnification of about 400 x . e) the results of measurements enabling the thickness of
the surface layer to be defined;
These determinations shall be carried out on the surface in two f) any abnormalities observed during measurement;
specific areas to be agreed between the parties concerned. For
each one of these areas, the results shall provide data for plot- g) any incidents occurring during measurement.
b

-
Figure 1 Longitudinal section obtained by machining a fiat

Figure 2 - Simple oblique section
3
IS13691:1993
iso4970:1979
Figure 3 - Grooved oblique section
Figure 4 - Stepped test piece

Figure 5 - Siting of the microhardness impressions

_
4
Reprography Unit, BIS, New Delhi, In
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