Table Of ContentTensile-2>npact Resistance of Carbon-Molybdenum Welds
At Elevated Temperatures
THESIS
Submitted in p artial fulfilment
of the requirements for the
degree of
MASTER OF MECHANICAL ENCINEERING
at the
POLYTECHNIC INSTITDTE OF BROOKLYN
Marcel A* Cordovi
June 1942
Approved:
Thesis A&fiser
H ead of Peparrment
ProQuest Number: 27591418
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The author wishes to express his appreciation to
Professor Otto H. Henry, thesis adviser, for his
valuable advice and friendly criticissag*
Thanks are due to ISr* H.S.Blumberg of the M. W.
Kellogg Company for supplying the necessary mate
ria l to produce the specimens.
Special thanks are due to Mrs. Renee M. Cordovi
for her help in the course of the work.
C O N T E N T S
Introduction. ........................ 1
Tensile-Impact Testing. 3
A. General Diecussion. .................... 3
B. At Polytechnic Institute............... 6
Apparatus and Method. .............................................. 7
A. Calibration of Machine. . . . . . . . . . . . . . . . . . . 10
B. Calibration of S c a le ................... 13
C. Temperature C o n tro l............................. 17
D. Temperature Measurement................ 23
E. Calibration of Thermocouple................... 27
M aterials Tested ............................................................... 30
A. Molybdenum in Steel ..................... 32
B. Welding Iblybdenum Steels .............. 33
Hon-Destructive Tests............... 34
A. Macroscopic Examination...................................... 34
B• Rockwell Survey. .......... 34
C . Microscopic Examination. ............. 37
Results and Conclusions. ...................................... 43
A. Tabulation of R esults. ........... 44
B. Results P lo tte d ......................................... 45
Suggestions ........................ 53
B ibliography.... .................................................. 54
I N T R O D U C T I O N
The service requirements of power-plant piping in 1915 were seldom
higher than 200 Ihs., 500 degrees Fahrenheit; by 1930, a period of 15
years, these requirements were raised to 1300 lb s., 750 degrees Fahren
h eit; today modern power-plants are being designed for operating tempe
ratures of 950 degrees Fahrenheit , 1800 lbs. working pressure and
possibly higher. This fact makes the specifications, fabrication and
rigid testing of power-plant m aterials and joints a necessity.
The basic consideration in performing tests on a material for a
given service, is that the material should simulate the actual service
as closely as possible. Thus, in designing an apparatus to be used at ab
normal temperatures, it is essential that the designer have precise know
ledge of the physical properties of the metals to be used and also of
the characteristics of the different joints specified at the temperatures
to which they are to be subjected in service.
During the past few years, welding and welding design have made a
gigantic step forward. Today welding is not considered as just another
way of joining m etallic parts but rather the way of doing the job quick
ly , precisely and efficiently. It is, therefore, very important that all
phases and possibilities of welding be thoroughly surveyed and fully
understood. In addition, it is equally important that the different phy
sical properties and characteristics of welds under different performance
conditions should also lie studied. A good deal has already been done in
testing welds in tension, compression, shear, bending and torque. Since
welds, like any other structural elements, often must withstand suddenly
2.
applied loads, it is not unnatural that inpact tests are frequently
used. Furthermore, in order to test all zones of a single welded Joint
in impact, which is very desirable in numerous instances, it seemed
advisable to start using tensile inpact tests for welds.
Up to the present time, the tensile inpact test has been applied to
welds only at relatively low velocities and at room or subnormal tempe
ratures. % ile considerable attention has been and s till is being given
to the effect of elevated temperatures upon the general properties of
metals, little work, if any, has been done in the field of tensile-
impact testing of welds at higher than room temperatures.
Much of the equipment in industry is subjected to high temperatures.
Therefore, the effect of elevated temperatures on equipment is of para
mount importance. A pre-knowledge of the exact way in which a weld is
going to behave w ill furnish the possibility for adequate compensation
and precaution in order to ameliorate these conditions in the original
design. This w ill undoubtedly and invariably result in enormous saving
in time, money and labor- the three synchronized factors that move the
wheels of industry. The present Emergency has, more than ever before,
served to prove to confirmed skeptics the gigantic possibilities and
important role that welding is playing today and w ill play in the future.
The author, in undertaking to make an investigation on the effect
of elevated temperatures on the tensile-impact resistance of some welds,
has fully realized the significance of his task and hopes that this inves
tigation w ill be a worthwhile and timely contribution to an art whose
importance in the field of industry increases hourly.
Brooklyn, New York
June 1, 1942
«%:
T E N S I L E - I M P A C T T E S T I N G
3.
A* general Discussion
The tensile-impact test is a simple test to determine completeness
of processing and affords the design engineer information both as to the
safety of the material and its ability to withstand impact loading.
Inpact testing as normally performed with notch bars is objection
able because of large errors inherent in the method of testing and
especially those due to errors in machining the notch. Notch tensile
specimens are more satisfactory being less sensitive to errors of oacMn -
ing or to accidental variations in the structure of the m aterial.
In tensile-impact testing the energy values are sensitive to non -
homogeneities of the test specimen and especially of those located near
the surface. By examination of the fracture it can be determined whether
abnormal values are due to unusual defects such as errors in machining,
internal cracks, non-metallic particles, slag or other defects of local
nature or insufficient heat-treatm ent. Abnormal values of a discontinuous
nature not representative of the material may be recognized and discarded.
Results of tests are not highly sensitive to errors or irregularities in
machining. By careful examination of the fracture, rather reliable opinions
as to irregularities and incompleteness of processing can be formed.*
* g.F.Jenks, "Application of Tension-Impact Tests", Transactions of
The American Society of Mechanical Engineers,)%y 1937
4.
Many facts in the tensile-impact test remain to be elucidated.
A formula of limited application relating size bf specimen to ten
sile-im pact value has been evolved by garcia*. Using a Charpy pendu
lum, Duwez** found that plots of tensile-impact energy and elongation
to fracture vs. length of parallel section (specimen o.59 inch diameter
0.39 to 4.3 inches parallel section, mde of copper, aluminum or steels
with tensile strength equal from 57,000 to 120,000 lbs. per square inch)
were straight lines. Extrapolated to zero length of parallel section
the lines resulted in the determination of a "specific ” elongation and
"specific" energy which were independent of length and characteristic
of each m aterial. The effect of velocity was not studied.
The kinetic energy or velocity of the blow, however, is an important
factor in tensile - impact testing. In studying tension-impact specimens,
Jenks*** found that m terials required a constant energy to rupture
independent of the velocity of loading provided certain critical velocities
were not exceeded. This critical or "transition" velocity appears to be
a fundamental property of a m aterial. Tensile-impact tests permit the
separation of this fundamental property from the record of impact strengths
and the determination of the optimum values.
* garcia, V.L., "International Association for Testing lb.terials Congress"
London, group A, 32-33 (1937)
** Duwez,P., "Arcos", 15 (83) 1772-1779, January 1938.
*** Jenks,g.F. "Trans. A.S.M.E.", 59, 313-318 (1937)
