In most organic solvents (carbon tetrachloride, amyl acetate, ethyl acetate, diisopropyl ether, turpentine, and the like), ATM-IT and ATM-I are resistant both at normal and also at elevated temperatures, but are not resistant in methyl ethyl ketone. Thereupon, the same relationships are observed: while after 42 days of testing, the ATM-I material was completely degraded, specimens of ATM-IT maintained their form and lost strength only to the extent of 26.95%. It may be assumed that this difference in the behavior of these materials is to be found in the technology of their manufacture. ATM-IT graphite sheeting is obtained as a result of heat treatment of ATM-I to 190~ In the process of this heat treatment, products having a high concentration of cross-links are formed in the polymeric binder. This confers a large stiffness on the material and is the reason for the development of intermolecular forces, which increases its heat resistance [i]. It is known [2] that phenol--formaldehyde oligomers and polymers are subject to oxidation at relatively low temperatures (70-80~ for oligomers of the resole type and 150~ for oligomers of the novolac type), with formation of carbonyl and aldehyde groups. The latter, however, at temperatures over 180-200~ are prone to further transformations which lead to the formation of additional cross-links in the molecules, as a result of which the phenol-formaldehyde polymers are rather stable products in oxidative media up to 250~ A similar conclusion may also be drawn relative to the increase in chemical resistance of graphite sheeting ATM-IT as compared with ATM-I. From the results of the tests performed of the chemical resistance of graphite sheetings in various corrosive media, these materials may be recommended for wider use instead of the hard-to-get and expensive stainless steels and nonferrous metals. LITERATURE CITED l.

2.

V. V. Korshak, Heat-Resistant Polymers [in Russian], Nauka, Moscow (1969). V. V. Korshak, V. A. Sergeev, L. V. Kozlov, and L. I. Komarova, "Thermal and thermooxidative degradation of phenol--formaldehyde oligomers of the novolac type," Plast. Massy, No. 2, 33-35 (1966).

TECHNICAL REQUIREMENTS FOR A MATERIAL FOR ELASTIC ELEMENTS OF COMPRESSORS V. A. Pchelintsev, I. A. Tananko, N. V. Emel'yanova

UDC 621.51-33.002.3:621.642.2-143--62-192

Increasing the reliability of compressors is related to the problem of increasing the service life of its basic parts, including the plates of its straight-through valves and diaphragms, the solution of which depends not only upon the quality of the design developments but also upon the properties of the material used under service conditions. To produce the plates of straight-through valves and membranes, 09KhI5N8Yu steel is used primarily. It is a high-strength precipitation-hardening stainless steel of the transition class. Very frequently [1-3] the level of mechanical properties of the sheet is related only to the phase composition obtained directly after working or heat treatment, completely disregarding the structural condition of the material before cold plastic deformation and the role of the structure formed in deformation of the material at increased (up to 200~ temperatures, i.e., under service conditions. In the All-Union Scientific-Research and Design Technology Institute for Compressor Machinery we have investigated the influence of the "deformation prehistory" of strip material on the change in its mechanical properties in deformation under increased temperature conditions for the purpose of more soundly based requirements for the supply of strip maTranslated from Khimicheskoe i Neftyanoe Mashinostroenie, No. 6, pp. 19-21, June, 1980.

348

0009-2355/80/0506-0348507.50

9 1981 Plenum Publishing Corporation

TABLE I Physicomechanicalp r o p e r t i e s ea ,d t3

0 0

.....

0

.,~"~

~E ~oE

.E~

E t:xOa ~ ed q.~ ~3,,o

SM

o,6s

~M-3

0,45 0,39 0,76

S -I S -2 -

o,o 0,63 o,~o

0,38

s 3

31

4g

34

.44 50

554 1892 4804 6745 1245 2937 5728 7549 8969

149 306 383 409 171 317 376 412 435

92 115 160 llO 132 144 140

22 56 77 95 34 45 94 121 127

14 8,5

3o,S 50 B5 ~2 31,5 37 51

g

terial for the production of elastic compressor elements. Investigations made earlier [4, 5] showed that for 09KhI5N8Yu steel strip a significant spread in mechanical properties in the as-received condition and a differing degree of the change in them in the 20-300~ temperature range are characteristic. One of the features of transition class steels is a varying content of martensitic phase after melting, which is characterized by the value of magnetizabiiity of the cast sample [6], which confers on them properties close to the proper ~ ties of austenitic or martensitic steels. An analysis of more than 40 heats in steel plants supplying billets for the production of sheet made it possible to establish that the value of the magnetizability of samples of these heats varies from 1.5 to 14 mV. Therefore, even before rolling, the sheets from different heats have varying phase composition. Subsequent cold plastic deformation increases the difference in physicomechanical properties of the strip of different heats, even under identical rolling conditions since the degree of work hardening depends upon the quantity of martensite. The change in properties of 09KhI5N8Yu steel was investigated* both in rolling of 200 x 200 x t mmsamples (t is thickness) with different numbers of passes and degrees of deformation and in continuous rolling of lots of strip differing in phase composition as determined from the value of magnetic saturation induction before the final cold plastic deformation cyc• After each pass samples were taken from the strip for analysis of the physicomechanical properties and the structural condition of the metal. The phase composition was determined metallographical!y on a "Neofot-2" instrument after electropolishing and etching i0 x 60 x t mm samples in an electrolyte of 45 ml H3PO4, 25 ml H2SO4, 4 ml CrO~, and 26 ml H20 and also by x-ray diffraction on a URS-501M unit fromthe change in intensity of the diffraction lines from the (iii) and (ii0) planes of the crystalline lattices for the yand ~phases respectively~ The photographs were taken in chromium emission, and the intensities of the interference lines were determined at points at intervals of 5 min on the background and 2 min in the zone of the maximum. The value of magnetic saturation induction was determined on a "Ferrotester" instrument. The mechanical properties were determined in testing samples on an IMASh-5S unit modernized to determine strain curves in the 20-300~ range. The fatigue tests were made on an "Amsler" machine with asymmetric loading and a base of 5"10 ~ cycles. The microhardness was determined as the average of five measurements on a PMT-3 instrument with a 50 g load. An analysis of the change in physicomechanical properties of samples with different values of magnetic saturation induction in the original condition showed (Table I) that the lot with a magnetic saturation induction of 1245 G work hardens more. At the same time, samples of finished strip from the lot with a lower magnetic saturation induction in the original condition (554 G) have a higher fatigue limit. In accordance with the results of the investigations of [7, 8] it may be assumed that in cyclic deformation of the samples of lot SM-3 distortion of the crystalline lattice of the residual austenite and a secondary martensitic transformation occurs to a greater degree than in cyclic deformation of samples of lot S-4, which promotes relaxation of stresses in overstressed areas and retarded failure of the material as a result of this process. *Engineers V. G. Marchenko and E. A. Savchenko participated in the investigations.

349

~~176 ~-~Z-T---1~,~ ~ ~ 1 7 6

~.

I !I

\.~\._i +~ l~J." \J.

~,~

I

o 20~ ~E

~to

L

,10 ~ 4OL1 =.

a

[/

;,.

go a

b

~E ~EE IO0

"r----

80

IO E~ 6

0

tOO ~00 T," C

J

~=

c

1o

!f

15 ~.

--"

~. . ~ o

o

~-T--F--I~,~o

I

I

12

b

to

k ...... ~ lOO ~OOT," d

I1o

~.

r~ O

Fig. i

tO0

2OO T,~ d

o

o

loo

zoor,~

Fig. 2

Fig. i. The temperature relationship of mechanical properties for samples of 09KhlSNSYu steel of lot SM (Table i): a) SM; b) SM-I; c) SM-2; d) SM-3; ) ~o.2 = f(T); .... ) o t = f(T); ) = f (T). Fig. 2. The temperature relationship of mechanical properties for samples of 09KhlSNSYu steel of lot S (Table i): a) S; b) S-l; c) S-2; d) S-3; e) S - 4 ; - - ) oo.= = f(r); .... ) s t = f(T); ....... ) = f (T). The truth of such an assumption is confirmed by the results of tensile tests after cyclic loading at stresses corresponding to the fatigue limit. The yield strength of samples of lot SM-3 increases by %8% in comparison with the yield strength of the same samples in the before-test condition. For samples of lot S-4 this does not occur. From Figs. 1 and 2 and Table I it may be seen that a sharp drop in ductility at lower temperatures corresponds to a higher martensite content in cold-rolled 09KhI5N8Yu steel. With a reduction in ductility of high-strength steels there is an increase in their sensitivity to a different type of stress raiser [9]. This is especially dangerous for the thin sheet material of the membranes and valve plates where surface micrononuniformities, microcracks occurring in cutting of the plates, and products of precipitation of compressed gas in the restraint zone of the membranes and in the zone of the valve openings with the radial grooves on the profiled surface of the limiting disk of the membrane block may serve as stress raisers. Therefore, the different phase composition of the blanks determines the different level of mechanical properties and of the resistance to failure under cyclic loads. The presence of 40-50% residual austenite in the structure of the material after cold plastic deformation promotes an increase in the level of fatigue strength in cyclic loading. We should also note the influence of the phase composition of the strip material on absorption of the energy of oscillations. A record of the movement of samples in fatigue tests made with the use of strain gauges on a unit imitating the forces of loading of valve plates [4] shows that for one lot of samples the oscillations are not extinguished before the next load cycle, while for another lot of samples the oscillations are completely extinguished before the next load cycle (Fig. 3). If we take into consideration that the sample dimensions and test conditions are identical, then such a phenomenon may be caused by the different properties of the material in relation to the dissipation of the energy of mechanical oscillations, which is related to the quantity and mobility of dislocations and point defects of the crystalline lattice [ii]. Apparently, the differing quantity in the volume of the material of residual austenite, for the structure of which a higher dislocation mobility is characteristic than for a martensite structure, determines the intensity of extinguishing oscillations in deformations caused by the test machine.

350

120

a 0

~ 40

O

b Fig, 3

0

I0 20 30 4ae,%

Fig. 4

Fig. 3. Oscillograms of movement of samples of 09KhI5N8Yu steel with various contents Y of residual austenite in the structure: a) y = 25-30%; b) Y = 40-50%. Fig. 4. The relationship of the physicomechanical properties of 09KhI5N8Yu steel to the degree of deformation ~: - - ) 0o~ = f(~); .... ) O t = f(~); ---.-.-) B = f(E).

The damping capacity may be the reason for the tendency of a material toward failure under conditions of the long action of working stresses since the application of oscillations is equivalent to the action of additional loads. A low capacity to absorb energy may have an especially strong influence in the zone of impact of the unrestrained edge of the plate with the limiter or the seat particularly since in recent years in reciprocating compressors there has been a tendency to increase the average speed of the piston, which leads to an increase in dynamic loads on the plate and a decrease in the period between load cycles, An analysis of the change in properties of 09KhI5N8Yu steel in rolling 200 x 200 • t mm pieces of a single heat shows that the properties most sensitive to a change in the strut ture of the material are yield strength and magnetic saturation induction (Fig~ 4), The tensile strength, which with a sheet thickness of less than 0.6 mm is the determining property in current specifications, characterizes to a lesser degree the change in structure in rolling. The y i e l d s t r e n g t h and the magnetic saturation induction increase most rapidly with a deformation of more than 30%. At the same time, the ratio of yield strength to tensile strength approaches unity. The results of x-ray diffraction analysis show that in the initial stage of deformation there is an increase in martensite phase and refinement of the austenite blocks~ With an increase in the degree of deformation together with the martensite transformation there is strong distortion of the crystalline lattices of both phases, as a result of which there is a strong increase in the yield strength of the material. If we take into consideration that a material with a ratio of nominal yield strength to tensile strength of 0.75 may be considered reliable, then the degree of deformation of the strip must be more than 40%~ The intensity of deformation (the degree of deformation in a single pass) and the number of passes have a substantial influence not only on the yield strength and magnetic saturation induction but also on the uniformity of distribution of the phase composition across the thickness of the strip. By metallographic and x-ray diffraction methods a greater quantity of martensite was found on samples after fractional rolling (a small degree of deformation per pass) in comparison with samples with a small number of passes (larger degree of deformation per pass) with an equal total deformation. Apparently, an increase in the intensity of deformation, leading to an increase in temperature in the zone of deformation [I0], causes stabilization of the austenite against the martensite transformation. Earlier, it was established [4] that the presence of a more plastic phase in the surface layer promotes an increase in the resistance of t h e m a t e r i a l to failure under cyclic loads~

351

Therefore, to obtain strip of 09KhI5N8Yu high-strength steel with a small spread in values of mechanical properties and satisfying the service conditions at increased temperatures the specifications for supply of the strip must specify the fol!owing requirements: the strip must be made of billets with a controlled value of magnetization of the cast sample of 4 mV; the total degree of deformation must be 35 • 3%; and the yield strength after rolling must be not less than 70 kgf/mm 2. LITERATURE CITED i.

2. 3.

4.

5.

6. 7.

8.

9. i0. Ii.

352

N. I. Moskvin, A. L. Belinkii, and M. M. Kristal', "The influence of cold plastic deformation and heat treatment on the structure and properties of KhI5N9Yu steel," Metalloved. Term. Obrab. Met., No. I0, 12-15 (1964). S. M. Altukhov and V. A. Rumyantsev, Membrane Compressors [in Russian], Mashinostroenie, Moscow (1967). T. V. Pryanichnikova, Z. A. Vashchenko, and A. P. Kokko, "The influence of microstructure and heat treatment on the yield strength of KhI5N9Yu steel," Metal!oved. Term. Obrab. Met., No. 6, 23-26 (1978). V. A. Pchelintsev, V. G. Marchenko, and L. A. Sosnovskii, "The influence of the structural condition of sheet of KhlSN9Yu steel on the strength and fatigue properties," Vest. Mashinostr., No. 6, 78-79 (1976). V. A. Pchelintsev, V. G. Marchenko, and E. A. Savchenko, "The stability of the mechanical properties of materials for the elastic elements of compressor machinery," in: Scientific Proceedings of the All-Union Scientific-Research Institute for Compressor Machinery on "The Design, Investigation, Technology, and Organization of Production of Compressor Machinery" [in Russian] (1978), pp. 83-87. Ya. M. Potak, High-Strength Steels [in Russian], Metallurgiya, Moscow (1972). V. L. Aleksandrov, I. I. Bogachev, and R. I. Mints, "The question of the resistance of austenitic steels under cyclic loading," Fiz. Met. Metalloved., 22, No. 5, 737-743 (1966). V. G. Gorbach, Yu. A. Avetisyan, and P. M. Kozlov, "The transformation of austenite into martensite in cyclic deformation," Fiz. Met. Metalloved., 40, No. 6, 1216-1222 (1975). N. G. Orekhov, L. M. Pevzner, A. S. Tarantova, and S. G. Kishkin, "The deformation aging of high-strength steels," Metalloved. Term. Obrab. Met., No. i0, 46-52 (1969). F. F. Khimushin, "The cold deformation of stainless steel," Kachest. Stal', No. 4, 36-47 (1934) . Vo M. Kondratov, "Internal friction in martensitic aging Fe--Cr--Ni steels," Probl. Prochn., No. 5, 18-23 (1971).