U.S. patent application number 13/399181 was filed with the patent office on 2012-06-14 for piston ring material for internal combustion engine.
This patent application is currently assigned to HITACHI METALS, LTD.. Invention is credited to Kunichika Kubota, Katsuhiko OHISHI, Toshihiro Uehara.
Application Number | 20120145289 13/399181 |
Document ID | / |
Family ID | 38625065 |
Filed Date | 2012-06-14 |
United States Patent
Application |
20120145289 |
Kind Code |
A1 |
OHISHI; Katsuhiko ; et
al. |
June 14, 2012 |
Piston Ring Material For Internal Combustion Engine
Abstract
A piston ring material that when formed into a piston ring
product, maintains excellent properties, and that at the production
of piston ring rod, realizes excellent processability and shape
stability. There is provided a piston ring material for internal
combustion engine comprising, by mass, 0.5 to less than 0.7% C,
1.0% or less Si, 1.0% or less Mn, 12.0 to 16.0% Cr, 3.0% or less Mo
and/or W (Mo+1/2W), 0.02 to 0.14% N and the balance Fe and
unavoidable impurities, wherein the relationship of contained C, N
and Cr satisfies the formulae: 25.ltoreq.43.22C (%)+42.45N
(%)-0.02Cr (%).ltoreq.40, and 0.15.ltoreq.0.92C (%)+0.67N
(%)-0.03Cr (%).ltoreq.0.30.
Inventors: |
OHISHI; Katsuhiko; (Yonago,
JP) ; Uehara; Toshihiro; (Yonago, JP) ;
Kubota; Kunichika; (Higashiizumo, JP) |
Assignee: |
HITACHI METALS, LTD.
Tokyo
JP
|
Family ID: |
38625065 |
Appl. No.: |
13/399181 |
Filed: |
February 17, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12161092 |
Jul 16, 2008 |
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PCT/JP2007/058482 |
Apr 19, 2007 |
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13399181 |
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Current U.S.
Class: |
148/589 |
Current CPC
Class: |
C22C 38/02 20130101;
C22C 38/001 20130101; C22C 38/04 20130101; C21D 6/00 20130101; F16J
9/26 20130101; C21D 1/76 20130101; C22C 38/22 20130101 |
Class at
Publication: |
148/589 |
International
Class: |
C21D 9/40 20060101
C21D009/40; C21D 6/00 20060101 C21D006/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 20, 2006 |
JP |
2006-116254 |
Claims
1. A method of producing a rod for a piston ring for an internal
combustion engine comprising subjecting a piston ring material to
cold drawing and/or cold rolling to give a desired sectional shape
of the piston ring, heating the piston ring material having the
desired sectional shape to 1000 to 1100.degree. C., and subjecting
the heated material to quenching and subsequent tempering so as to
form the rod for the piston ring, the rod having an adjusted
hardness, and the piston ring material consisting of, by mass, 0.5%
or more and less than 0.7% of C, 1.2% or less of Si, 1.0% or less
of Mn, 12.0-16.0% of Cr, Mo and/or W in an amount that satisfies
the formula (Mo+1/2W).ltoreq.3.0%, 0.04-0.13% of N, 0.1% or less of
P, and 0.1% or less of S, with the balance Fe and unavoidable
impurities, wherein the relationship of the contained C, N and Cr
in the piston ring material satisfies the formulas of
29.ltoreq.43.22C (%)+42.45N (%)-0.02Cr (%).ltoreq.40 and
0.15.ltoreq.0.92C (%)+0.67N (%)-0.03Cr (%).ltoreq.0.30.
2. The method according to claim 1, wherein C is contained in an
amount of 0.60-0.68% by mass in the piston ring material.
3. The method according to claim 1, wherein Cr is contained in an
amount of 14.0-16.0% by mass in the piston ring material.
4. The method according to claim 1, wherein the relationship of the
contained C, Cr and N by mass % satisfies the formulas of
29.ltoreq.43.22C (%)+42.45N (%) -0.02Cr (%).ltoreq.35 in the piston
ring material.
5. The method according to claim 1, wherein the relationship of the
contained C, Cr and N by mass % in the piston ring material
satisfies the formulas of 0.18.ltoreq.0.92C (%)+0.67N (%)-0.03Cr
(%).ltoreq.0.30.
6. The method according to claim 1, wherein Mo and/or W are
containing in an amount that satisfies the formula (Mo+1/2W) is
>1.5% to 3.0% by mass in the piston ring material.
7. The method according to claim 1, wherein Mo and/or W are
contained in an amount that satisfies the formula (Mo+1/2W) is
1.6-2.5% by mass in the piston ring material.
8. The method according to claim 1, wherein Mo is selected from Mo
and/or W in the piston ring material.
9. The method according to claim 1, wherein Si is contained in an
amount of 0.1-1.0% by mass in the piston ring material.
10. The method according to claim 6, wherein Mo is selected from Mo
and/or W in the piston ring material.
11. The method according to claim 7, wherein Mo is selected from Mo
and/or W in the piston ring material.
12. A method for producing a rod for a piston ring for an internal
combustion engine comprising subjecting a piston ring material to
cold drawing and/or cold rolling to give a desired sectional shape
of a piston ring, heating the piston ring material having the
desired sectional shape to 1000 to 1000.degree. C. and subjecting
the heated material to quenching and subsequent tempering so as to
form the rod for the piston ring, the rod having an adjusted
hardness, and the piston ring material consisting of, by mass,
0.60-0.68% of C, 0.1-1.0% of Si, 1.0% or less of Mn, 14.0-16.0% of
Cr, 1.6-2.5% of Mo, and 0.04-0.13% of N, 0.1% or less of P, and
0.1% or less of S, with the balance Fe and unavoidable impurities,
wherein the relationship of the contained C, Cr and N in the piston
ring material satisfies the formulas of 29.ltoreq.43.22C (%)+42.45N
(%)-0.02Cr (%).ltoreq.35 and 0.18.ltoreq.0.92C (%)+0.67N (%)-0.03Cr
(%).ltoreq.0.30.
13. A method for producing a rod for a piston ring for an internal
combustion engine comprising subjecting a piston ring material to
cold drawing and/or cold rolling to give a desired sectional shape
of a piston ring, heating the piston ring material having the
desired sectional shape to 1000 to 1100.degree. C. and subjecting
the heated material to quenching and subsequent tempering so as to
form the rod for the piston ring, the rod having an adjusted
hardness, and the piston ring material consisting of, by mass, 0.5%
or more and less than 0.7% of C, 1.2% or less of Si, 1.0% or less
of Mn, 12.0-16.0% of Cr, Mo and/or W in an amount that satisfies
the formula (Mo+1/2W).ltoreq.3.0%, 0.04-0.13% of N, 0.1% or less of
P, and 0.1% or less of S, with the balance Fe and unavoidable
impurities, wherein the relationship of the contained C, N and Cr
in the piston ring material satisfies the formula of
29.ltoreq.43.22C (%)+42.45N (%)-0.02Cr (%).ltoreq.40 and
0.15.ltoreq.0.92C (%)+0.67N (%)-0.03Cr (%).ltoreq.0.30, and wherein
the material has a reduction of area of 45% or more according to a
tensile test.
14. The method according to claim 1, wherein Mo and/or W are
contained in an amount that satisfies the formula (Mo+1/2W) is 2.5%
or less by mass in the piston ring material.
15. The method according to claim 14, wherein Mo and/or W are
contained in an amount that satisfies the formula (Mo+1/2W) is 1.7%
or less by mass in the piston ring material.
16. The method according to claim 12, wherein Mo is contained in an
amount of 1.7% or less by mass in the piston ring material.
17. The method according to claim 1, wherein the hardness of the
rod for the piston ring is adjusted to 35 HRC or more by
tempering.
18. The method according to claim 12, wherein the hardness of the
rod for the piston ring is adjusted to 35 HRC or more by
tempering.
19. The method according to claim 13, wherein the hardness of the
rod for the piston ring is adjusted to 35 HRC or more by
tempering.
20. The method according to claim 13, wherein Mo and/or W are
contained in an amount that satisfies the formula (Mo+1/2W) is 2.5%
or less by mass in the piston ring material.
Description
[0001] This application is a divisional of application Ser. No.
12/161,092 filed on Jul. 16, 2008, which is a National Stage of
International Application No. PCT/JP2007/058482 filed Apr. 19,
2007, claiming priority based on Japanese Patent Application No.
2006-116254, filed Apr. 20, 2006, the contents of all of which are
incorporated herein by reference in their entirety.
TECHNICAL FIELD
[0002] The present invention relates to a piston ring used for
internal combustion engine or a piston ring used with its sliding
surface being subjected to nitriding treatment, and particularly to
a material having excellent characteristics as a piston ring in
addition to cold drawing or rolling workability at the production
of piston ring.
BACKGROUND ART
[0003] As for piston rings for internal combustion engines,
particularly, motorcar engines, use of conventional piston rings
made of cast iron is gradually switched to use of so-called steel
piston rings obtained by working rod materials such as steel flat
rods into rings. This is due to the necessity to make thinner the
rings or improve mechanical strength of the rings for meeting the
demands such as weight-saving, decrease of fuel cost, speeding up
and increase of output of internal combustion engines. Another
large factor is the effect of conspicuous shortening of steps for
production of rings.
[0004] The switching to steel piston rings has already been carried
out in top rings and oil rings which are used under high load, and
Si--Cr steels or martensitic stainless steels of 11-17% Cr have
been used as materials of the piston rings. Furthermore, there are
used many of piston rings made of the above materials which are
subjected to chromium plating or nitriding treatment. Generally,
piston ring materials are required to have scuffing resistance and
wear resistance, and these characteristics tend to improve with
increase of the amount of carbides resulting from increase of
amounts of Cr and C added, and with coarsening of carbides.
However, carbides in such form cause deterioration of fatigue
characteristics of piston ring materials and further cause breakage
of piston rings when the piston ring materials are worked into
rods, and the rods are subjected to bending to form rings.
[0005] Under the circumstances, there is disclosed an invention in
which a piston ring material having both fatigue characteristics
and scuffing resistance after nitriding treatment is provided by
adding in combination nitrogen N and carbon C to a martensitic
stainless steel (Patent Document 1). Furthermore, based on the
technology of adding N to a martensitic stainless steel and fining
Cr carbide, it is disclosed to provide a nitrided piston ring made
of martensite steel which is excellent in wear resistance, scuffing
resistance, cracking resistance and fatigue characteristics, by
fining the nitride in the nitrided layer to allow the nitride to be
present in a large amount and besides forming a microstructure
where lamellar grain boundary compounds in the nitrided layer are
in fine state (Patent Document 2).
[0006] Patent Document 1: JP-A-2001-271144
[0007] Patent Document 2: JP-A-2002-030394
DISCLOSURE OF INVENTION
Problem to be Solved by the Invention
[0008] As one example of general production steps for piston ring,
an ingot adjusted to a desired composition is produced, and the
ingot is subjected to hot rolling, annealing, cold drawing, and
cold rolling to give a desired sectional shape of piston ring, then
quenching and tempering, and coiling into a shape of ring.
Thereafter, the ring is subjected to a strain-removing heat
treatment for removing residual stress accumulated in the material,
a rough working, a pre-nitriding acid treatment, a gas nitriding, a
working for removal of side nitrided layer, and a finishing
working. The resulting piston ring comprising the N-added steel is
excellent in mechanical strength, particularly, wear resistance,
scuffing resistance and fatigue characteristics, but are inferior
in cold workability such as drawing or rolling in rod working to
require many annealing steps in the working steps, resulting in a
problem of increase in cost. Another problem is that the shape
becomes unstable after the strain-removing heat treatment conducted
for removal of residual stress in the material. Thus, further
improvement is required.
[0009] The object of the present invention is to provide a piston
ring material which maintains excellent mechanical properties when
formed into a piston ring product, is improved in cold drawing and
rolling workability at production of piston ring rod, can reduce
production cost of piston ring, and has shape stability after the
strain-removing heat treatment.
Means for Solving the Problem
[0010] The inventors have conducted intensive research on the
influence of components on cold workability in production of piston
ring. They have further conducted intensive research on the
influence of components on shape stability in the strain-removing
heat treatment. As a result, it has been found that extremely
excellent cold workability and shape stability even after the
strain-removing heat treatment can be obtained without damaging the
mechanical characteristics as a piston ring by severely controlling
amounts of C, Cr and N which are main constituent elements of the
piston ring material and which form carbide and nitride, and
furthermore by severely controlling mutual relation of the amounts
of the elements. Thus, the present invention has been
accomplished.
[0011] That is, the present invention relates to a piston ring
material for internal combustion engine which contains, by mass,
0.5% or more and less than 0.7% of C, 1.0% or less of Si, 1.0% or
less of Mn, 12.0-16.0% of Cr, 3.0% or less of Mo and/or W
(Mo+1/2W), and 0.02-0.14% of N, with the balance Fe and unavoidable
impurities, wherein the relationship of the contained C, N and Cr
satisfies the formulas of 25.ltoreq.43.22C (%)+42.45N (%)-0.02Cr
(%).ltoreq.40 and 0.15.ltoreq.0.92C (%)+0.67N (%)-0.03Cr
(%).ltoreq.0.30.
[0012] Preferably, the piston ring material satisfies one or more
ranges, by mass, of 0.60-0.68% of C, 0.1-1.0% of Si, 14.0-16.0% of
Cr, more than 1.5% and 3.0% or less (more preferably 1.6-2.5%) of
Mo and/or W (Mo+1/2W), and 0.04-0.13% of N, or furthermore the
relationship of the contained C, N and Cr satisfies the formulas of
29.ltoreq.43.22C (%)+42.45N (%)-0.02Cr (%).ltoreq.35 and/or
0.18.ltoreq.0.92C (%)+0.67N (%)-0.03Cr (%).ltoreq.0.30. Of course,
a piston ring material which satisfies all of these requirements is
desirable. Furthermore, it is desirable to select Mo from Mo and/or
W.
ADVANTAGES OF THE INVENTION
[0013] The piston ring material according to the present invention
maintains excellent characteristics when formed into a piston ring
product, and has excellent cold workability and shape stability at
production of piston ring rod. Therefore, the present invention
contributes largely to improvement of performance of piston ring,
and simplification of production steps, namely, reduction of
cost.
BEST MODE FOR CARRYING OUT THE INVENTION
[0014] The feature of the present invention is as follows. Based on
the finding that particularly N which forms nitride gives a great
influence on characteristics for C and Cr which form carbides and
are main constituent elements of the piston ring material, a piston
ring material excellent in cold workability at the production of
piston ring and shape stability after heat treatment is provided by
severely controlling the correlation of the above elements. The
present invention will be explained in detail below.
[0015] C is an important element in the present invention, and not
only C enhances scuffing resistance and wear resistance by forming
carbides, but also a part of C forms solid solution in the base to
improve strength and fatigue characteristics. For attaining these
purposes, C must be added in an amount of at least 0.5%. However,
if the content exceeds 0.7%, workability into rods or rings
deteriorates. Especially, in the case of piston ring, since it is
important to cheaply produce the piston ring by increasing
productivity, the content is specified to be less than 0.7%.
Preferred range is 0.60-0.68%.
[0016] Si is added usually as a deoxidizer, but it influences
behavior of temper softening of steel, and influence of Si is
important particularly for low alloy steels. Si is necessary for
inhibiting temper softening and enhancing heat resistance. However,
if Si is added in a too large amount, cold workability is
deteriorated, and hence the upper limit of Si is specified to be
1.2%, and it is preferably 1.0%. On the other hand, the lower limit
is preferably 0.1%.
[0017] Like Si, Mn is also an element necessary as a deoxidizer,
and if it is added in a too large amount, hot workability is
deteriorated. Therefore, the upper limit of Mn is specified to be
1.0%.
[0018] As for Cr, a part of Cr bonds to C to form a carbide to
enhance wear resistance, and a part of Cr forms a solid solution in
the base to enhance corrosion resistance. Furthermore, since Cr
increases temper softening resistance, it is necessary for
improving heat settling resistance of piston ring or ensuring
hardenability to obtain sufficient hardness after heat treatment.
When nitriding treatment is carried out, Cr has the effects to
further improve scuffing resistance and wear resistance of the
piston ring because of forming fine nitride in the nitrided layer.
In order to obtain these effects, Cr must be added in an amount of
at least 12.0%, but addition of it in a too large amount causes
decrease of thermal conductivity to promote increase of contact
surface temperature caused by sliding, thereby to damage seizing
resistance and besides increase carbide or particle size to cause
conspicuous deterioration of workability. Thus, the upper limit is
specified to be 16.0%. Preferred range is 14.0-16.0%.
[0019] Not only Mn and W per se bond to C to form hard carbides,
but also a part of Mn and W form solid solution in the Cr carbide,
and hence the Cr carbide per se is toughened, resulting in
improvement of wear resistance. Furthermore, they contribute as
secondary hardening elements in tempering, and hence are effective
for improving heat settling resistance of piston ring. Moreover, a
steel piston ring material is generally heated to 900-1100.degree.
C. for imparting wear resistance, scuffing resistance and fatigue
characteristics of piston ring, and then hardened under rapid
cooling, and thereafter tempered at a relatively high temperature
to adjust the hardness to 35-45 HRC, and Mo and W have the effect
to stabilize the hardened structure, which makes it possible to
convert the secondary carbide precipitated at 900-1100.degree. C.
to M.sub.23C.sub.6 having fine particle size, whereby precipitation
of M.sub.7C.sub.3 can be inhibited. That is, by fixing the
secondary carbide formed at a temperature of 900-1100.degree. C.,
it becomes possible to obtain structure which is stable even when
the hardening temperature somewhat changes.
[0020] For alloy steels comprising C and Cr in the amounts based on
those of the present invention, the above heating temperature of
about 1000.degree. C. is suitable for obtaining hardenability,
namely, mechanical characteristics. That is, if the heating
temperature is too low, sufficient hardness cannot be obtained,
and, on the other hand, if it is too high, austenite particles
become coarser to cause decrease of toughness. Therefore,
considering balancing of these characteristics, the above hardening
temperature range should be employed. Addition of Mo and W is
necessary for obtaining the above effects, and particularly
adjustment of the lower limit of their amounts is important. As for
the lower limit of the amounts of Mo and/or W which are controlled
by the formula (Mo+1/2W), the amounts are preferably more than
1.5%, preferably 1.6% or more. However, addition of them in too
large amounts not only results in increase of hard carbide and
extreme increases of abrasion wear of cylinder, but also causes
deterioration of workability. Therefore, the upper limit of the
amounts of Mo and/or W which are controlled by the formula
(Mo+1/2W) is specified to be 3.0% in the present invention. It is
preferably 2.5%. Mo can give the similar effect in an amount which
is half the amount of W and furthermore has the effect to improve
softening resistance, and can inhibit heat settling at tempering or
strain-removing heat treatment. Therefore, from the point of
advantageousness in cost and heat treatment characteristics, it is
desirable to add Mo alone without addition of W.
[0021] N is an element which is relatively stable even at high
temperatures and prevents eutectic Cr carbide (M.sub.7C.sub.3)
difficult to control its form by hot working temperature or heat
treatment temperature from crystallization into primary crystal
austenite grain boundary. Thus, it becomes possible to inhibit
conspicuous deterioration of scuffing resistance or deterioration
of workability which is caused by the presence of coarse Cr
carbide. Moreover, since N has the effect to make finer the
carbide, not only fatigue characteristics, but also mechanical
characteristics are improved, and tensile strength is improved
without causing deterioration of workability. For obtaining this
effect, at least 0.02% of N is necessary, but if it is added in a
too large amount, gas pores are formed in steel ingot and
furthermore ingot making in the air becomes difficult, resulting in
increase of cost. Therefore, the amount of N is 0.14% or less.
Preferred range is 0.04-0.13%.
[0022] In the piston ring material of the present invention, the
remainder element other than the above elements is Fe, but
naturally unavoidable impurities are present. Moreover, when impact
stress is applied in using as a piston ring, Ni may be added in an
amount of 2.0% or less for the purpose of improving toughness, and
Cu may be added in an amount of 4% or less for the purpose of
strengthening the matrix to improve heat settling resistance.
[0023] Moreover, in order to meet the further demand for wear
resistance, there may be added at least one of V and Nb in an
amount of 3.0% or less in total. Not only V and Nb form carbide by
bonding to C, but also a part of them form solid solution in the Cr
carbide to strengthen the carbide. Furthermore, Al may be added in
an amount of 1.5% or less for improving the hardness of nitrided
layer formed on the surface of steel by nitriding treatment
conducted for the purpose of imparting wear resistance to a piston
ring made of steel. In addition, Co may be added in an amount of
1.0% or less for improving corrosion resistance, and B may be added
in an amount of 100 ppm or less for improving hardness of the
matrix.
[0024] P and S which are impurity elements are preferably added in
the amounts as small as possible, but in order to extremely reduce
the amounts, selected expensive starting materials must be used,
and, besides, high cost is required for refining by dissolution.
However, in the present invention, they may be contained in the
ranges of P.ltoreq.0.1% and S.ltoreq.0.1% which cause no
particularly serious problems in characteristics and
production.
[0025] In addition, the present invention provides a piston ring
material which has not only mechanical characteristics as a piston
ring product, but also cold workability at production of piston
ring rod and furthermore shape stability after heat treatment. The
greatest feature of the present invention resides in properly
controlling the amounts of C, Cr and N contained for obtaining
these characteristics. The reasons will be explained in detail
below.
[0026] The cold workability of piston ring material at the
production of rod depends largely upon amount or size of carbide in
the steel, and is governed mainly by the contents of Cr and C. N is
effective for fining the carbide, and furthermore, N per se forms
fine nitride to prevent agglomeration and coarsening of nitride.
Therefore, by controlling the amounts of the three elements within
proper ranges, the workability can be improved with maintaining
mechanical characteristics as piston ring product. As a result of
conducting a research on the optimum relation among the amounts of
C, Cr and N which can exhibit these effects to the maximum, it has
been found that it can be evaluated by the relation using factors
obtained by multiple regression analysis when workability is taken
as objective variable and C, Cr and N are taken as explanatory
variables, and thus it is necessary to severely control the
relation.
[0027] That is, it is to control the contents of C, N and Cr in the
steel to satisfy the formula: 25.ltoreq.43.22C (%)+42.45N
(%)-0.02Cr (%).ltoreq.40. If this value is less than 25,
workability is satisfactory, but mechanical characteristics, wear
resistance and scuffing resistance as piston ring deteriorate, and
if it is more than 40, workability deteriorates, and hence drawing
and rolling at the production of rod material become difficult to
require a plurality of annealing steps, resulting in increase of
cost. Preferred range of the value according to the above formula
is 29-35.
[0028] In the production of piston ring, after coiling into a shape
of ring, a strain-removing heat treatment for removing residual
stress accumulated in the material is carried out, and there is the
problem of the shape becoming unstable after the treatment. It has
been confirmed by the inventors that the mechanism of the changing
of shape is affected by mainly the amount and size of the carbide
in the steel as in the case of workability. As a result, the
inventors have clarified that by mutual controlling, within proper
ranges, of the amounts of Cr and C which form mainly carbide, and N
which makes fine the carbide, stable shape can be obtained even
after the strain-removing heat treatment with maintaining the
mechanical characteristics as piston ring.
[0029] That is, it is to adjust the contents of C, Cr and N in the
steel to satisfy the mutual relation of 0.15.ltoreq.0.92C (%)+0.67N
(%)-0.03Cr (%).ltoreq.0.30 in the relation using proper factors
obtained by multiple regression analysis when mechanical
characteristic is taken as objective variable and C, Cr and N are
taken as explanatory variables as in the above case. If this value
is less than 0.15, shape stability cannot be obtained, and if it is
more than 0.30, mechanical characteristics as piston ring
deteriorate. Preferred range of the value according to the above
formula is 0.18-0.30.
[0030] By properly adjusting C, Cr and N to satisfy the above two
formulas, there can be provided a piston ring material having both
characteristics of workability and shape stability without causing
deterioration of product characteristics. As a result, it becomes
possible to provide piston ring materials stable in
characteristics.
[0031] For the piston ring material of the present invention having
features in composition, it is desirable to apply to the ingot
making step a process capable of carrying out micro-adjustment of
components. For example, the dissolution step is preferably carried
out with an induction furnace or vacuum furnace which causes less
incorporation of impurities from the outside. Furthermore, in the
casting step, there may be used re-dissolution method or continuous
casting method which is advantageous for avoiding segregation or
presence of non-metallic inclusions in addition to usual ingot
making method.
Example 1
[0032] 10 kg of ingots were prepared by high frequency vacuum
induction dissolution. These ingots were subjected to hot working
to make rod materials of 15 mm square. Subsequently, they were
subjected to annealing, and thereafter to a given hardening
treatment (1000-1060.degree. C.) and a given tempering treatment
(600-640.degree. C.) to make Samples Nos. 1-7 adjusted to about 40
HRC in hardness. Values .alpha. and .beta. (see footnotes of Table
1) calculated from chemical composition of each sample and contents
of C, Cr and N are shown in Table 1.
TABLE-US-00001 TABLE 1 Sample Composition (mass %)*.sup.1 No. C Si
Mn P S Cr Mo W N Fe .alpha.*.sup.2 .beta.*.sup.3 The present 1 0.65
0.40 0.31 0.004 0.002 13.0 0.29 <0.01 0.05 Bal. 29.956 0.242
invention 2 0.64 0.38 0.31 0.003 0.002 15.1 1.47 <0.01 0.09 Bal.
31.179 0.196 3 0.67 0.40 0.32 0.006 0.002 15.3 1.51 <0.01 0.11
Bal. 33.321 0.231 Comparative 4 0.84 0.39 0.32 0.007 0.002 14.8
1.53 <0.01 0.05 Bal. 38.131 0.362 Example 5 0.87 0.38 0.31 0.006
0.002 15.0 1.52 <0.01 0.11 Bal. 41.971 0.424 6 0.74 0.39 0.33
0.007 0.002 14.9 0.75 <0.01 0.12 Bal. 36.779 0.314 7 0.60 0.41
0.31 0.005 0.002 14.9 1.32 <0.01 0.06 Bal. 28.181 0.145
*.sup.1Al < 0.05%, Contents of other elements are less than
0.01% *.sup.2.alpha. = 43.22C (%) + 42.45N (%) - 0.02Cr (%)
*.sup.3.beta. = 0.92C (%) + 0.67N (%) - 0.03Cr (%)
[0033] For evaluation of rod workability as piston ring material,
reduction of area (%) in tensile test was measured. JIS 14A
contraction type test pieces (whole length: 110 mm, length of
parallel part: 45 mm, diameter of parallel part: 7 mm, distance
between gages: 35 mm) were obtained from the material after
annealing, and subjected to tensile test at room temperature to
collect the values of reduction of area (%) of each sample. In the
use as piston ring, when this value is 45% or more, there are no
problems in cold drawing and rolling, and this value is employed as
indication for excellent workability.
[0034] Next, for evaluation of shape stability of piston ring, the
following V-shape bending test was conducted. A test piece of 3 mm
square.times.80 mm in length as shown in FIG. 1 was obtained from
the material adjusted to 40 HRC in hardness, and markings were put
on a side surface of the test piece at an interval of 50 mm. On the
assumption that the test piece is worked into a ring, the test
piece was indented at a fixed speed so that indentation reached 10
mm as shown in FIG. 2. The distance L.sub.0 between the markings
(average value of upper distance L.sub.0A and lower distance
L.sub.0B) was measured. Then, a heat treatment simulating the
strain-removing heat treatment for removing the given residual
stress was carried out at 600.degree. C. for 1 hour in Ar
atmosphere, and thereafter the distance L.sub.1 between the
markings was again measured. Ratio of change was obtained from the
thus obtained L.sub.0, L.sub.1 in accordance with the following
formula.
{(L.sub.1-L.sub.0)/L.sub.0}.times.100 (%)
[0035] The inventors have confirmed that when this ratio of change
at 600.degree. C. is in the range of 0.15-0.3%, there is no problem
in shape stability in the use as piston ring. Therefore, 0.15-0.3%
is employed as target value as an indication for shape
stability.
[0036] Results of evaluation of the workability (reduction of area)
and shape stability (ratio of change) are shown in FIG. 3. From the
results, it can be seen that the piston ring materials of the
present invention which were severely adjusted in the amounts of C,
N and Cr were superior to the comparative materials in cold
workability and shape stability before and after heat
treatment.
Example 2
[0037] 10 kg of ingots were prepared by high frequency vacuum
induction dissolution. These ingots were subjected to hot working
to make rod materials of 15 mm square. Subsequently, they were
subjected to annealing, and thereafter to a given hardening
treatment (1000-1060.degree. C.) and a given tempering treatment
(600-640.degree. C.) to make Samples Nos. 8-13 adjusted to about 40
HRC in hardness. Values .alpha. and .beta. (see footnotes of Table
2) calculated from chemical composition and contents of C, Cr and N
of each sample are shown in Table 2.
TABLE-US-00002 TABLE 2 Sample Composition (mass %)*.sup.1 No. C Si
Mn P S Cr Mo W N Fe .alpha.*.sup.2 .beta.*.sup.3 The present 8 0.64
0.40 0.29 0.005 0.002 15.3 1.6 <0.01 0.09 Bal. 31.175 0.190
invention 9 0.67 0.41 0.31 0.005 0.002 14.7 1.7 <0.01 0.10 Bal.
32.908 0.242 10 0.67 0.40 0.31 0.006 0.002 14.8 1.6 <0.01 0.11
Bal. 33.331 0.246 11 0.67 0.41 0.30 0.006 0.002 15.1 1.6 <0.01
0.12 Bal. 33.749 0.244 12 0.66 0.40 0.31 0.005 0.002 15.1 1.6
<0.01 0.13 Bal. 33.742 0.241 13 0.66 0.40 0.31 0.005 0.002 15.1
1.6 <0.01 0.14 Bal. 34.166 0.248 *.sup.1Al < 0.05%, Contents
of other elements are less than 0.01% *.sup.2.alpha. = 43.22C (%) +
42.45N (%) - 0.02Cr (%) *.sup.3.beta. = 0.92C (%) + 0.67N (%) -
0.03Cr (%)
[0038] For evaluation of workability and shape stability of piston
ring, the same tensile test and V-shape bending test as above were
conducted. The results are shown in FIG. 4. From the results, it
can be seen that the piston ring materials of the present invention
which were severely adjusted in the amounts of C, N and Cr and
contained Mo in a proper amount had stably both the characteristics
of cold workability and shape stability before and after heat
treatment.
Example 3
[0039] 2600 kg of ingots were prepared by an atmospheric
dissolution furnace. These ingots were subjected to hot working to
make a rod material of 15 mm in diameter, which was referred to as
Sample No. 14. Values .alpha. and .beta. (see footnotes of Table 3)
calculated from chemical composition and contents of C, Cr are
shown in Table 3.
TABLE-US-00003 TABLE 3 Sample Composition (mass %)*.sup.1 No. C Si
Mn P S Cr Mo W N Fe .alpha.*.sup.2 .beta.*.sup.3 The present 14
0.64 0.38 0.29 0.024 0.002 14.8 1.6 <0.01 0.11 Bal. 32.034 0.219
invention *.sup.1Al < 0.05%, Contents of other elements are less
than 0.01% *.sup.2.alpha. = 43.22C (%) + 42.45N (%) - 0.02Cr (%)
*.sup.3.beta. = 0.92C (%) + 0.67N (%) - 0.03Cr (%)
[0040] Successively, it was subjected to annealing, and thereafter
to a given hardening treatment (1040.degree. C.) and a given
tempering treatment (600-640.degree. C.) to make a rod material
adjusted to about 40 HRC in hardness, and carbide distribution at
longitudinal section was measured. A light microscope was used for
the measurement to obtain the size of carbides (in terms of
diameter of equivalent circle) in 6 visual fields of structure
which were viewed at random at 200.times. magnification (FIGS. 5)
and 1000.times. magnification (FIG. 6). The viewing areas were
8.times.10.sup.-2 mm.sup.2 (200.times. magnification) and
3.2.times.10.sup.-2 mm.sup.2 (1000.times. magnification). The
results of measurement are shown in FIG. 7 and FIG. 8. It can be
seen from the results that most of the carbides formed in the
material had a size of 1 .mu.m or less and were finely distributed.
In the piston ring material of the present invention, cold
workability at the production of rod material and shape stability
at the strain-removing heat treatment after coiling were both
improved by the fining of carbides.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] FIG. 1 This is a schematic view of shape of test piece used
for V-shape bending test in Examples 1 and 2.
[0042] FIG. 2 This is a schematic view showing method of V-shape
bending test in Examples 1 and 2.
[0043] FIG. 3 This shows the relation between cold workability
(reduction of area) and shape stability (ratio of change) of piston
ring materials of the present invention and the comparative example
in Example 1.
[0044] FIG. 4 This shows the relation between cold workability
(reduction of area) and shape stability (ratio of change) of piston
ring materials of the present invention in Example 2.
[0045] FIG. 5 This is a structural photograph (200.times.) of the
piston ring material of the present invention in Example 3.
[0046] FIG. 6 This is a structural photograph (1000.times.) of the
piston ring material of the present invention in Example 3.
[0047] FIG. 7 This shows carbide size distribution (viewed at
200.times. magnification) of the piston ring material of the
present invention in Example 3.
[0048] FIG. 8 This shows carbide size distribution (viewed at
1000.times. magnification) of the piston ring material of the
present invention in Example 3.
DESCRIPTION OF REFERENCE NUMERALS
[0049] 1. Test piece (3 mm square.times.80 mmL), 2. Markings, 3.
Punch
* * * * *