Damping Properties of Selected Steels and Cast Irons: Bureau of Mines Report of Investigations/1987
Damping Properties of Selected Steels and Cast Irons: Bureau of Mines Report of Investigations/1987
Damping Properties of Selected Steels and Cast Irons: Bureau of Mines Report of Investigations/1987
906s 1
BUREAU OF MINES
Robert C. Horton, Director
Library of Congress Cataloging in Publication Data:
Visnapuu, A. (Aarne)
Damping properties of selected steels and cast irons.
Bibliography: p. 14-15.
ILLUSTRATIONS
TABLES
h hour lb pound
ABSTRACT
'Research physicist.
2 p hysical science technician.
3Metallurgist.
Rolla R esearch Center, Bureau of H.ines, Rolla, MO.
2
INTRODUCTION
stLess concent r ations around the em- p ro pe r ties relati ve to gray cast i r on ,
brittling graphite flakes (~); however, such as increased ductility and tensile
us~ful toughness is practically nil. and yield strength.
This has limited the use of gray cast Steels tend to exhibit low SDC's in
irons to applications where toughness is comparison with those of the cast irons,
not a major factor. Ductile irons have which is attributable to the absence
nodular graphite dispersed in continuous of free graphite. Damping in steels
matrices similar to those of steel, which increases somewhat with the carbon con-
imparts toughness and ductility and per- tent, and spheroidization tends to fur-
mits plastic deformation, but markedly ther enhance damping capacity.
reduces damping -capacity relative to that
of gray cast irons. Ductile irons are PURPOSE OF THIS INVESTIGATION
actually a family of materials; they
differ as a result of factors such as This investigation was conducted as
composition, section size, cooling rate, part of the Bureau's research effort to
and- -he-at tr-e-a-t-men-t, and can be proce-ss-ecl C-0nserve resources and increase produc-
into a wide range of properties (~-lQ). tivity through improved performance and
Compared with steels, ductile irons have develop safer materials. Baseline SDC's
generally inferior ductility, weldabil- were determined for representative indus-
ity, and impact and fatigue resistance, trial and structural carbon steels and
but superior castability, machinability, cast irons and were correlated to the
wear and corrosion resistance, and damp- respective carbide and graphite micro-
ing capacity. Compacted graphite cast structures. Selected materials were sub-
irons have structures that are intermedi- jected to carburizing, spheroiclizing, and
ate in terms of form, to the flakes of annealing heat treatments to delineate
gray cast iron and the nodules of ductile their influence on damping and other
iron. Graphite in compacted graphite properties. The data reported is in-
cast i ron h as r ounded tips, relative tended to supplement the meager damping
to the flakes in gray cast iron, but capacity information available on these
is continuous in the sense that flakes materials and to serve as a benchmark
are continuous in the matrix (actually against which ongoing developmental work
they are relatively long-range colonies can be compared. The ultimate goal is to
on a microscopic scale). This graph- use this information to produce new iron--
i te morp,hology, which may be associated base high-damping materials or to alter
with some graphite tending toward flakes the structure of existing materials to
or nodules, imparts certain desirable improve damping.
EXPERIMENTAL PROCEDURE
The carbon and alloy steels investi- 1144, 4140, and 4340 steels were carbu-
gated in this study were of the following rized for 3 h at 925 0 C using sodium
AISI grades: 1020, 1035, 1045, 1095, carbonate, barium carbonate, and char-
1117, 1144, 4140, and 4340. The steels coal. The 1045, 1144, 4140, and 4340
were selecl:ea as being representaEive steels were then given a spheroidizing
of commercially available steels. Speci- heat treatment by holding at 750 0 C for 6
mens for measuring damping capacity and h, cooling at , 30 0 C/h to 650 0 C, and
oiher physical properties were prepared holding at 650 0 C for 36 h. The 1095
from commercial hot-rolled rod stock that steel was spheroidized by holding at 715 0
varied in diameter from 3/4 to 2-1/4 in. C for 6 h, followed by a 36-h hold at
In addition to SDC evaluation in the 680 0 C.
as-received condition, measurements were Cast irons were prepared il1 60- and
made after selective heat treatment to 120-lb heats by induction melting in
alter the carbide morphology. Damping magnesium oxide crucibles. The temper-
capacity specimens of the 1045, 1095, ature was monitored with Pt, Pt-10 Rh
4
FIGURE 1.-Mlcrostructures of carbon and alloy steels (X 500). AISI designations: A, 1045; B, 1144; C, 1095; D, 1117.
6
FIGURE 1.- Mlcrostructures of carbon and alloy steels (X 500)-Continued. AISI designations: E, 4140; F, 4340; G, 1035; H, 1020.
7
FIGURE 3.-Mlcrostructures of spheroidized heat·treated carbon and alloy steels (X 500). AISI designations: A, 1045; S, 1144; C,
1095; D, 1095 (fully spheroldlzed).
I
Ii
9
FIGURE 3.-Microstructuresol spheroldlzed heat·treated carbon and alloy steels (X 500)-Continued. AISI designations: E,
4140; F, 4340:
damping before heat treatment. For com- and the distribution of ferrite in the
parison, the SDC of a fully spheroidized matrix~ For steels characterized by a
1095 steel is included in table 2, and defined intergranular boundary between
a photomicrograph of this steel is pre- the pearlite colonies and ferrite matrix
sented in figure 3. or grains, damping increases as inter-
The results of the SDC measurements on granular boundary surfaces become
selected caLbon and alloy steels indicate rougher, thus producing higher stress
that damping is primarily dependent on concentrations. When the steels are heat
the shape of the intergranular boundaries treated, the pearlite colonies tend to
10
lose their identity as the lamellar car- higher damping at the 20,OOO-psi stress
bides begin to spheroidize and the fer- level than the fully spheroidized steel.
rite agglomerates into a more continuous Manipulating these parameters in steels
form. It is surmised that as the grain can enhance, or also reduce, the inherent
boundaries disappear during spheroidiza- damping associated with them.
tion, they lose their influence on damp-
ing, and the stress concentrations asso- CAST IRONS
ciated with the phase boundaries become
~redominant. For a gi ven carbon content, The damping capacities of selected duc-
more phase-boundary surface area is pres- tile, compacted graphJ.te, and gray cast
ent for partially spheroidized carbides iron specimens were measure ~ Table - :3
than for fully spheroidized carbides. presents the SOC measurements for eight
Partially spheroidized particles are more cast irons, and table 4 presents their
sharply faceted and would tend to exhibit compositions and mechanical properties.
higher damping. As spheroidization in- Figure 4 shows their etched microstruc-
creases, the total cementite surface area tures. In the photomicrographs {-f-i-g.- 4),
becomes smaller and smoother ; whereas ferrite appears light; pearlite, dark
t~e ferrite becomes more continuous. The gray; graphite, gray-to-black; and pri-
decrease in surface area and i-ncreased mary carbide particles, light. The eight
smoothness would tend to decrease damp- cast irons were selected to demonstrate
ing; whereas, increased ferrite would change in SDC with graphite morphology
tend to increase damping. This was ob- and are representative of all the cast
served in the AISI 1095 steels, where irons tested. SDC-versus-stress curves
the partially spheroidized steel had are presented in figure 5 for two
FIGURE 4.-Microstructures of cast irons (X 100). Specimens A through D as listed In tables 3 and 4. See text for description of
microstructures.
12
FIGURE 4.-Microstructures of cast Irons (X 100)-Continued. Specimens E through H as listed in tables 3 and 4. See text for
description of microstructures.
13
in the bulk matrix, as are the flakes of inverse relationship between SDC and
gray cast iron; but, compared with the elongation and tensile and yield
sharp edges of flakes, the rounded edges strength. SDC increases as percent elon-
are less effective for stress concentra- gation and tensile and yield strength de-
tion and resultant vibration energy dis- crease. This is not unexpected, because
sipation. For a given matrix, these the trend follows the sequence of graph-
rounded edges account, to a large extent ite mo r phology from nodular to compacted
for the SDC of compacted graphite cast to flake or their various combinations.
iron falling between those of ductile and Thus, in the absence of SDC data for cast
gray c-a-st- i r on. irons, elongation and tensile and yield
Comparison of the cast iron damping ca- strength information can - be U-8-€!·d--t-G-~a-r:
pacities in table 3 with the mechan- rive at an estimate of their damping
ical properties in table 4 indicates an capabilities.
CONCLUSIONS
The steels and cast irons investigated boundaries and the presence of ferrite
here represent only a small fraction of in the matrix. Damping improves with
the carbide and graphite morphologies rougher intergranular contact, increased
possible for these materials. The intent ferrite, or their various combinations.
of the study was to provide baseline Heat treatments that accentuate these
damping capacity data for some common conditions · in the matrix increase damp-
structural and engineering materials, and ing. Compared to carbon and alloy
to determine relationships between damp- steels, cast irons even with the lowest
ing capacity and material microstructure. SDC's exhibit better damping in most
The results indicate that damping in cases. The SDC of some alloy steels can
both the steels and cast irons examined be increased to the level of cast iron
is strongly dependent on th~ leve~ of____S_D_C~'s~b
~y~. h
~e~a_
t~t~
r~e_
a~t_i_n~g~.__________
stress associated with the intergranular
REFERENCES
10. Cowen, P. S. Part 2: Heat Treat- 12. Schwaneke, A. E., and R. W. Nash.
ment of Ductile Iron Castings. Foundry, An Improved Torsion Pendulum for Mea-
v. 99, No. 10, 1971, pp. 78-81. suring Internal Damping. Rev. Sci. In-
11. American Society for Testing and strum., v. 40, 1969, pp. 1450-1453.
Materials. Standard Method and Defini- 13. Nash, R. W., and A. E. Schwaneke.
tions for Mechanical Testing of Steel A Digital Instrumentation Package for
Products. ANSljASTM A370-77 in 1981 an Improved Torsion Pendulum. BuMines
Annual Book of ASTM Standards: Part 2, RI 8774, 1983, 9 pp.
Ferrous Castings; Ferroalloys. Philadel-
phia, PA, 1981, pp. 187,..242.