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UDC 669.14 : 620.172 : 536.4
IS0
I N TERN AT I ON A L O R GA N IZ AT1 O N FOR STA N DARD IZATlO N
IS0 RECOMMENDATION
R 783
MECHANICAL TESTING OF STEEL AT ELEVATED TEMPERATURES
DETERMINATION OF LOWER YIELD STRESS AND PROOF STRESS
AND PROVING TEST
1st EDITION
July 1968
COPYRIGHT RESERVED
The copyright of IS0 Recommendations and IS0 Standards
belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of ISO.
For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
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BRIEF HISTORY
The IS0 Recommendation R 783, Mechanical testing of steel ar elevated temperatures - Deter-
mination of loweryield stressand proof stress and proving test, was'drawn up by Technical Committee
ISO/TC 17, Steel, the Secretariat of which is held by the British Standards Institution (BSI).
Workon this question by the Technical Committee began in 1961 and led, in 1965, to the adop-
tion of a Draft IS0 Recommendation.
In December 1966, this Draft IS0 Recommendation (No. 930) was circulated to all the IS0
Member Bodies for enquiry. It was approved, subject to a few modifications of an editorial nature, by
the following Member Bodies :
Australia Hungary South Africa,
Austria India Rep. of
Brazil Israel Spain
Canada Netherlands Sweden
Chile New Zealand Switzerland
Norway
Czechoslovakia Thailand
Denmark Poland Turkey
Finland Portugal U.A.R.
France Romania United Kingdom
Five Member Bodies opposed the approval of the Draft :
Belgium
Germany
Italy
Japan
U.S.A.
The Draft IS0 Recommendation was then submitted by correspondence to the IS0 Council,
which, decided, in July 1968, to accept it as an IS0 RECOMMENDATION.
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ISO/R 783-1968 (E)
IS0 Recommendation R 783 July 1968
MECHANICAL TESTING OF STEEL AT ELEVATED TEMPERATURES
DETERMINATION OF LOWER YIELD STRESS AND PROOF STRESS
AND PROVING TEST
1. SCOPE
This IS0 Recommendation describes the determination of lower yield stress and proof stress of steel
in which the test temperature does not exceed 1000 OC.*
2. PRINCIPLE OF TEST
The test consists of heating uniformly a test piece to a prescribed temperature and then subjecting it
to tensile stress at that temperature with a view to
determining the lower yield stress (Re) or proof stress (I?,.,),
(a)
proving that the proof stress is above a specified minimum value.
(b)
3. DEFINITIONS
3.1 Gauge length. At any moment during the test, the prescribed part of the cylindrical or prismatic
portion of the test piece on which elongation is measured. In particular,
Original gauge length (L,). Gauge length measured at ambient temperature before the test piece
is strained.
3.2
Extensometer gauge length (Le). The length of the parallel portion of the test piece used for the
measurement of extension by means of an extensometer. This length may differ from Lo.
3.3
Stress (actually “nominal stress”). At any moment during the test, load divided by the original
cross-sectional area of the test piece at ambient temperature.
3.4 Yield stresses. In a steel which exhibits a yield phenomenon a point is reached during the test at
which plastic deformation, soon after it has been initiated, continues to occur at nearly constant
stress .
For the purpose of this IS0 Recommendation the following definitions apply :
3.5 Yield stress (Re)
3.5.1 Upper yield stress (Re,). The value of stress measured at the commencement of plastic defor-
mation at yield (see clause 12.3 and Fig. 2(b), 2(c), 2(d) and 2(e)).
or
The value of stress measured at the first peak obtained during yielding even when that peak
is equal to or less than any subsequent peaks observed during plastic deformation at yield.
This limit of 1 O00 OC is fixed as a function of the condition of test, particularly for the tolerances on temperature
in section 7. In particular, it does not imply that the conception of the proof stress from room temperature up to
1000 OC is equally significant for all steels.
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ISO/R 783-1968 (1
3.5.2 Lower yield stress (ReL). The lowest value of stress measured during plastic deformation at
yield, ignoring any initial transient effects which might occur (see clause 12.3 and Fig. 2(b),
2(c), 2(d) and 2(e)).
Proof stress (non-proportional elongation) (Rp). Stress at which a non-proportional elongation,
3.6
equal to a specified percentage of the original gauge length, occurs. When a proof stress (R,) is
specified. the non-proportional elongation should be specified (e.g. 0.2 and the symbol used
for the stress should be supplemented by an index giving the prescribed percentage of the origi-
nal gauge length (e.g. RpO,Z ).
4. SYMBOLS AND DESIGNATIONS
Number Designation
1
Diameter of parallel length of test section of test piece of
circular cross-section
2 External diameter of tube
3 Thickness of a flat bar or thickness of tube
4 Width of a flat bar or of specimen cut from tube
5
Original gauge length measured at ambient temperature before
application of load
6 Parallel length of test piece
7 Total length of test piece
8 Extensometer gauge length
9
Gripped ends of test piece
10 Original cross-sectional area of gauge length
11 Proof stress (non-proportional elongation)
(0.2 'L proof stress)
12 Upper yield stress
13 Lower yield stress
*
Any symbol used should be followed by the temperature at which the test is made.
NOTE. ~ See Figure 1.
5. TEST PIECE
The cross-section of the test piece may be circular, square, rectangular, or, in special cases, of
5.1
some other shape.
5.2 There should be transition curves (fillets) between the gripped ends and the parallel length; the
gripped ends may be of any shape to suit the holders of the testing machine.
The tolerances on the preparation of the test pieces should be in accordance with those given in
5.3
the Table, Page 8.
5.4 As a general rule, the diameter of the parallel length of machined cylindrical test pieces should
be not less than 4.0 mm (0.16 in).
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ISO/R 783-1968 (E)
FIG. l(a) - Test piece of circular cross-section
i-
I r--/- Il I
FIG. l(b) - Test piece of rectangular cross-section
r--
I
L--
O
@
FIG. FIG. l(c) l(c) - - Strip Strip test test piece piece cut cut from from tube tube
FIG. l(d) - Tubular test piece
NOTE. - The numerical symbols in Figures l(a), l(b), l(c) and l(d) are explained in section 4.
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ISO/R 783-1968 (E)
TABLE ~ Tolerances on dimensions of test pieces
Tolerance on form
Machining tolerance*
Designation Nominal dimensions
on nominal dimensions
IS0
Values
(IS0 j, 12)
Symbols
Diameter of machin, over 3 mm
* 0.06 mm 0.03 mm
ed circular-section to 6 mm
test piece
over 6 mm
(metric units)
I 0.075 nim 0.04 mm
to 10mm
over 10 mm
? 0.09 mm 0.04 rnm
to 18mm
over 1 8 mni
* 0.105 mni 0.05 mm
to 30mm
IT 9
Diameter of machin. over O. 1 19 in
it 0.002 5 in
0.001 in**
ed circular-section to 0.237in
test piece
over 0.237 in
(inch units)
10.003 in 0.001 in**
to 0.394in
over 0.394 in
it 0.003 5 in 0.002 in**
to 0.709in
over 0.709 in
* 0.004 in 0.002 in**
to 1.182in
Dimensions of
crosssection of
Same tolerances as for diameter of
rectangular-section
circular-section test pieces
test piece, machined
on the four faces
Dimensions of over 6 nim
0.22 mm
cross-section of to 10mm
rectangular-section
over 10 mm
test piece,
0.27 mni
to 18mm
unmachined on two
opposite faces
over 18 mm
0.33 mm
(metric units)
to 30mm
over 30 mm
0.39 mm
to 50mm
IT 13
Dimensions of over 0.237 in
0.009 in
cross-section of to 0.394in
rectangular-section
over 0.394 in
test piece,
0.010 in
to 0.709in
unmachined on two
opposite faces
over 0.709 in
0.012 in
(inch units)
to 1.182in
over 1.182in
0.016 in
to 1.969in
*
The machining tolerance applies when it is desired to use the nominal cross-section without measurement or
calculation.
** Rounded off to 0.001 in.
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ISO/R 783-1968 (
6. MEASUREMENT OF EXTENSION
The extension should be measured by means of an extensometer. The extensometer should be such
that any measurement of extension does not differ from the true value of that extension by more than
0.01 'L of the extensometer gauge length, and should be of a type that will take account of the exten-
sions on both sides of the test piece. The parallel length should be not less than 25 mm (I in) and
should preferably be not less than 50 mm (2 in). The extensometer gauge length should be not less
than 10 mm and at the centre of the parallel length. Departures from the specified length should not
exceed 2 O/". The extensometer may be attached to the parallel portion or to the enlarged ends of the
test piece;in the latter case, the extension is calculated on the assumption that the observed extension
has occurred wholly within the parallel length. When determining lower yield stress, it may not be
necessary to measure extension in certain circumstances (see clause 10.4) and an extensometer can be
dispensed with.
NOTE. - The additional deformation which occurs between the points of attachment of the extensometer and the
ends of the parallel length will lower the proof stress value. This effect is usually so small that it can be ignored.
7. HEATING APPARATUS
7.1 The heating apparatus for the test piece should be such that the test piece can be heated to a
temperature which, at any time throughout the duration of the test and at any point within the
gauge length. does not deviate from the specified temperature by more than f 5 "C for tempera-
tures up to and including 800 "C or * 6 "C for temperatures over 800 "C up to and including
1000 Oc.
7.2 The temperature-measuring equipment should be frequently calibrated.
8. MEASUREMENT OF TEMPERATURE
8.1 Temperature-measuring equipment with a sensitivity of 1 "C should be provided to indica. the
temperature of the test piece.
8.2 In general, not less than three thermocouples,* one at each end and one in the middle of the
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