J. M.

Larson
Chief Engineer of Materials. Engine Waives—Design and
L. F. Jenkins Material Evolution
Chief Engineer of Valves.
This paper reviews the design and material evolution of poppet valves used in
S. L. Narasimhan reciprocating internal combustion engines in the United States. Driving forces which
led to the current state-of-the-art technology, such as needs for improved durability
Materials R. & D. Supervisor.
and cost effectiveness, are described. This paper also endeavors to predict how valve
materials, design, and construction will change over the next two decades in
J. E. Belmore response to continual engine performance improvement demands in a worldwide
Division Manager—Engineering Services.
competitive environment. As a basis for understanding the past evolution and future
trends in valve design, the key operating parameters that affect valve function are
Eaton ECD—Engineering Center, detailed.
Marshall, Ml

Exhaust Valve Operating Environment

The selection of base materials and heat treatments used for corrosive constituents [4]. The potential severity of corrosive
exhaust valves depends upon the operating environment in attack is a function of the chemical composition of the valve
each specific engine application. Key factors of this environ- alloy, its metallurgical characteristics such as grain size and
ment are the operating temperature, the imposed stress levels, microconstituent phases, and the valve operating
and the corrosive nature of the products of combustion to environment.
which the value is exposed [1-3]. There are several problems related to corrosive attack of
valve materials. An obvious concern is the prevention of
Operating Temperature. The operating temperature of the proper sealing of the valve seat-cylinder seat interface. An ad-
exhaust valve is a function of the specific output of the engine, ditional problem is overall material loss in highly stressed
the relative efficiency of the combustion process, and the ef- areas of the valve which could lead to breakage. A less
fectiveness of the engine cooling system. The temperature pro- recognized concern is the effect of the corrosive medium on
file is particularly dependent upon the temperature of the ex- the basic fatigue life of valve materials. This phenomenon can
haust gases. The higher exhaust gas temperatures typical of play a significant role in not only alloy selection but also in the
spark ignition (gasoline) engines result in significantly higher choice of heat treatments to be applied to the materials.
heat input into the port side of the exhaust valve, producing
Figure 4 illustrates the effect of a leaded fuel environment
higher valve temperatures in this area than are seen in com-
on the fatigue strength of Nimonic 80A, a nickel base
pression ignition engines, as shown in Fig. 1.
superalloy, at an operating temperature of 815°C (1500°F).
Imposed Stress Levels. Every combustion event imposes (Refer to Table 1 for all alloy compositions discussed in this
high pressures on the combustion chamber side of the valve paper.) A fine-grain microstructure achieved without solution
head, generating cyclic tensile stresses on the port side of the treatment optimizes the fatigue resistance of Nimonic 80A in
valve head, as shown in Fig. 2. The magnitude of these stresses an air environment. In the presence of a leaded fuel environ-
is a function of the peak combustion pressure of the engine ment the situation is reversed. A coarse-grained, solution-
and is considerably higher for compression ignition than spark treated structure offers the best fatigue strength, thus resisting
ignition engines. corrosion fatigue more effectively [5].
The valve seating event imposes cyclic tensile stresses at the
junction of the stem and fillet on the port side of the head. Intake Valve Operating Environment
Valve seating initiates at a single contact point due to the in-
Selection of the materials and their associated heat
herent thermal distortion of the cylinder seat at high output
treatments for intake valves must take into account the same
conditions, as shown in Fig. 3. Bending stresses created by this
environmental operating factors as the exhaust valve.
initial single-point contact of the valve and cylinder seat in-
crease the magnitude of these valve seating stresses. Operating Temperature. The operating temperature of
the intake valve is generally a function of the intake charge
Corrosive Environment. The exhaust valve head is ex-
temperature and the effectiveness of the engine cooling
posed to products of combustion which often contain highly
system. Primarily due to the cooling effect of the incoming
Contributed by the Internal Combustion Engine Division and presented at the
charge, the operating temperature is significantly lower than
Internal Combustion Engine Division Technical Conference, Oakbrook, Il- that of the exhaust valve.
linois, October 5-7, 1986. Manuscript received at ASME Headquarters July 9,
1986. Imposed Stress Levels. The intake valve is subjected to the

Journal of Engineering for Gas Turbines and Power OCTOBER 1987, Vol. 109 / 355
Copyright © 1987 by ASME
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 500
(73}

Spark I g n i t i o Compression Ignition

400
(58)

(44)

L _J
A Fine grain - a i r
800 750 700 650 600 600 650 700 750 800
200 A Fine grain - leaded environment
(1472) (1292) (1112) (1112} (1292) (1472) (29)
G Coarse gra n - air
Temperature deg C (deg F) Temperature deg C (deg F) H Coarse gra n - leaded environment

Fig. 1 Comparison of typical exhaust valve temperature profiles for

spark and compression ignition engines; temperatures are along axis of (15)
a valve head section
Cycles to Failure

Fig. 4 Effect of corrosive environment on the fatigue life of Nimonic

80Aat815 c C(1500°F)

Exhaust Valve Construction

400 The use of iron and nickel base austenitic alloys for exhaust
(58). valves is primarily dictated by the elevated temperature fatigue
strength requirements in the head portion of the valve [5, 7],
Depending on other performance and cost objectives, the final
construction of the valve can be one of several designs.
One-Piece Design. A one-piece valve represents the most
ZOO
(29)
cost-effective design when an iron base austenitic alloy is used.
This design is widely employed in passenger car applications
(Fig. 5a).
Wafer or Tip Welded Design. There are several valve gear
configurations in use where one-piece austenitic valves may
experience an unacceptable level of tip wear or scuffing. To
minimize or eliminate this concern, a hardenable martensitic
steel may be welded to the tip of the valve and heat treated to
maximum hardness. This design has seen extensive usage in
passenger car engines and limited application in heavy-duty
engines (Fig. 5b).
Two-Piece Design. In a two-piece design, the austenitic
alloy head is welded to a hardenable martensitic stem. In con-
Fig. 2 Tensile stresses on the surface of the port side of the valve head trast to the use of a tip weld, this design enables one to extend
from combustion loading
the selective full hardening of the tip end through the keeper
groove area to maximize low-temperature fatigue strength.
The balance of the martensitic stem, used in the hardened and
tempered condition, enhances valve stem scuffing resistance.
This design has increasingly penetrated the passenger car
market and is predominant in the heavy-duty sector (Fig. 5c).
bending stress imposed at this
side movement of
stem restricted
location as a result of combustion
loading forcing valve to close
Seat Welded Design. Iron base austenitic alloys used in
by valve guide heavy-duty applications often lack adequate wear and/or cor-
rosion resistance to withstand the operating environment at
the seat face. In these cases, hard facing alloys with superior
wear and/or corrosion resistance may be applied to the seating
i n i t i a l single point contact
of valve with seat face by gas or shielded arc techniques [8] (Fig. 5d).

Fig. 3 Bending stress imposed at the junction of the head and fillet
Internally Cooled Design. An internally cooled valve con-
surfaces tains a cavity partially filled with a coolant, typically sodium
or sodium potassium. The coolant transports heat from the
valve head to the valve stem for dissipation through the valve
guide to the cylinder head cooling medium. This significantly
same imposed stresses from the combustion event and valve reduces the valve head temperature, which minimizes or
seating as the exhaust valve. eliminates detrimental corrosive attack by the products of
Corrosive Environment. While the combustion chamber combustion (Fig. 5e).
side of the intake valve head is exposed to the same products
of combustion as the exhaust valve, its relatively low operating Intake Valve Construction
temperature generally precludes concern for detrimental cor- The use of carbon steel, low alloy steel, or corrosion-
rosive attack [6]. resistant martensitic stainless steel is primarily dictated by

356 / Vol. 109, OCTOBER 1987 Transactions of the ASME

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 Table 1 Compositions of valve materials
Nominal Compositions of Martensitic Valve Materials
Material Composition (weight percent)
designation Mn Si Cr Ni Mo Fe Other
SAE 1541 0.40 1.50 0.23 - - - Bal.
SAE 1547 0.47 1.50 0.23 - - - Bal.
SAE 3140 0.40 0.80 0.28 0.65 1.25 - Bal.
SAE 4140 0.40 0.88 0.28 0.95 - 0.20 Bal.
SAE 8645 0.45 0.88 0.25 0.50 0.55 0.20 Bal.
Silchrome 1 0.45 0.80 max 3.25 8.50 0.50 max - Bal.
SilXB 0.80 0.80 max 2.12 20.00 1.35 - Bal.
422 SS 0.22 0.75 0.50 max 11.75 0.75 1.08 Bal. W 1.08
V 0.25
TI (610) 0.75 0.30 0.30 4.00 - 0.70 Bal. W 18.00
V 1.00

Nominal Compositions of A ustenitic Valve Steel Materials

Material Composition (weight percent)
designation Mn Si Cr Ni Fe Other
21-2N 0.55 8.25 0.25 max 20.38 2.12 0.30 Bal.
21-4N 0.53 9.00 0.25 max 21.00 3.88 0.46 Bal.
21-12 0.20 1.50 1.00 21.25 11.50 - Bal.
23-8N 0.33 2.50 0.75 23.00 8.00 0.32 Bal.
Silchrome 10 0.38 1.05 3.00 19.00 8.00 _ Bal.
Gaman H 0.52 12.25 2.65 21.25 _ 0.45 Bal.
XCR 0.45 0.50 0.50 23.50 4.80 - Bal. Mo 2.80
TXCR 0.40 4.30 0.80 24.00 3.80 _ Bal. Mo 1.40
TPA 0.45 0.50 0.60 14.00 14.00 - Bal. W 2.40
Mo 0.35

Nominal Compositions of Superalloy Valve Materials

Material Composition (weight percent)
designation Mn Si Cr Ni Fe Other
N-155 0.12 1.50 1.00 max 21.25 19.50 Bal. Co 19.75
'40 3.50
W 2.50
Nb 1.00
TPM 0.04 2.25 0.08 16.0 Bal. 6.50 Ti 3.05
Inconel 751 0.06 0.50 max 0.50 max 15.50 Bal. 7.00 Ti 2.30
AI 1.22
Nb + Ta 0.95
Nimonic
80A 0.10 max 1.00 max 1.00 max 19.50 Bal. 3.0 max Ti 2.25
Al 1.40
Pyromet 31 0.04 0.20 max 0.20 max 22.60 56.50 Bal. Ti 2.25
Al 1.25
Mo 2.00
Nb 0.85

Nominal Composition of Typical Valve Seat Facing Materials

Material Composition (weight percent)
designation Mn Si Cr Ni Co W Mo Fe
Stellite 6 1.20 0.50 1.20 28.00 3.00 Bal. 4.50 0.50 3.00
Stellite F 1.75 0.30 1.00 25.00 22.00 Bal. 12.00 _ 3.00
Stellite 1 2.50 0.50 1.30 30.00 1.50 Bal. 13.00 0.50 3.00
Eatonite 2.40 0.50 1.00 29.00 Bal. 10.00 15.00 _ 8.00
Eatonite 3 2.00 0.50 1.20 29.00 Bal. _ _ 5.50 8.00
Eatonite 6 1.75 0.75 1.30 28.00 16.50 - * 4.50 Bal.
VMS 585 2.25 _ 1.00 24.00 11.00 - - 5.50 Bal.

*May substitute W for Mo according to formula Mo = W/2.

moderate to low temperature strength requirements. Since US Spark Ignited Engine Valve Design and Materials
these families of alloys can be selectively hardened to address
Evolution
the durability concerns of the tip and keeper groove, the final
construction of the valve is usually the one-piece design shown
in Fig. 5(a). In applications such as high peak pressure com- Exhaust Valves. The evolution of the material content for
pression ignition engines and dry fuel (e.g., natural gas) spark exhaust valves used in spark ignition engines is chronologically
ignition engines where seat face wear resistance is inadequate, illustrated in Fig. 6. For each material type the date of in-
a seat welded design, shown in Fig. 5(d), is used. troduction and the span of usage is depicted. The associated

Journal of Engineering for Gas Turbines and Power OCTOBER 1987, Vol. 109/357

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 progression of events related to valve configuration and developments, imposed ever-increasing demands on exhaust
manufacturing processes is shown in Table 2. valve needs. By 1919, there were 23 different aircraft exhaust
The first US gasoline fueled automobile was produced by valve alloys [12, 13]. Cutlery type stainless steels, similar to the
the Duryea brothers in 1892 [9]. This vehicle was powered by a SAE 440 series, found their way into valves. These martensitic
spark ignited engine containing wrought iron or carbon steel materials, later termed Silchrome 1 and Silchrome XB, were
valves made by a blacksmith. A two-piece valve with a cast the most prominent exhaust valve materials used through the
iron head screwed or riveted onto a steel stem was soon 1920s [14]. These materials were extremely hard, corrosion
developed to improve corrosion and seat face wear resistance resistant, and strong up to about 590°C (1100°F), but
[10]. This design was used in the Wright brothers' first suc- tempered rather quickly at higher operating temperatures.
cessful flight. In 1906, Thompson formed a company, now Austenitic stainless steels, produced by Krupp, were used in
part of TRW, and introduced the mass produced alloy steel several German aircraft engines. However, these materials
head, resistance welded to a carbon steel stem [11]. were only used on a very limited basis in the United States.
The Great War, and its associated rapid aircraft engine During the Great War, refractory elements such as
tungsten, molybdenum, and vanadium were added to these
materials to improve their hot strength and seat wear
resistance [15]. By the mid-1930s, austenitic stainless steels,
Table 2 Poppet engine valve design chronology such as 21-12 and Silchrome 10, were widely used in
automotive engines. These materials had reasonable strength,
Valve Design Decade of Introduction creep, and fatigue resistance up to 820°C (1500°F), although
Riveted or threaded martensitic stem 1890 they exhibited considerably lower strength at low to moderate
Hardened tip end of stem 1900 temperatures than earlier Silchrome martensitic alloys.
Resistance welded martensitic stem 1900 The Rich Company, now part of Eaton Corporation, began
Seat faced with Ni-20 percent Cr 1920
Combustion faced with Ni-20 percent Cr 1920 manufacturing tool steel valves during World War I [16]. As a
Internally cooled 1920 tool maker, Rich recognized that 18W-4Cr-lV tool steels had
Seat faced with Co based alloys 1930 excellent hot strength. Unfortunately, these materials had ex-
Tip faced with Co base alloys 1930 tremely poor corrosion resistance and poor weldability. The
Chromium-plated stem 1930
Oxalate stem coating 1930 corrosion problem was further exacerbated by the demands of
Nitrided stem 1940 high-performance aircraft engines developed during this
Seat faced with nickel base alloys 1940 period. Ethyl Corporation's 1919 introduction of tetraethyl
Aluminized head 1940 lead to gasoline further increased corrosion susceptibility [12].
Wafer welded tip 1950
Friction welded martensitic stem 1960 These corrosion problems were circumvented by several
Nickel-plated head 1970 novel approaches. Bright Ray (Ni-20%Cr) coatings were ap-
Seat faced with Fe base alloys 1980 plied to the seat and combustion face of the valve for corro-
sion resistance. By 1940 Bright Ray had been supplanted by
Stellite (cobalt based) seat facing, providing both wear and
corrosion resistance. Facings were eventually utilized on most
KEEPER GROOVE - NTERNAL CAVITY
heavy-duty exhaust valves.
In the mid-1920s, Heron, of Ethyl Corporation, invented
the sodium-cooled valve [13]. This not only decreased
SEAT FACE WEED temperatures and, thus, corrosion, but also decreased the
COMBUSTION FACE N
likelihood of preignition, commonly called "knock." Without
the internally cooled valves, advances in aircraft engine per-
a) One-piece 6) WaCer or c) Two-piece d) Seat welded e) [eternally
tip welded cooled formance and application would have been considerably cur-
Fig. 5 Cross-sectional view of typical exhaust valve constructions tailed in the 1920s and 1930s, and the history of World War II

U.S. SPARK IGNITED ENGINE POPPET EXHAUST VALVE MATERIAL & DESIGN EVOLUTION

Carbon S t t t l ( U a r l . m i l l c )

Coil Iron

Alloy S I . . I ( M o r l . n . l t l c )

^'-yr,:1^,
c
°•!cNol,-tct^<--cus,,••l

^-•ffx'cir
(NlSSpfpfi'mlVnlc ! 0 * )

Cr
(2M.-4N1;C27-2N,j'"
C-N.-£j-e-N,,...

1880 1900 1920 1940 1960 1980 2000

YEARS
Fig. 6 Family listed in austenitic unless specified martensitic; all are
wrought alloys except where stated as cast; alloy listed is typical exam-
ple of family

358/Vol. 109, OCTOBER 1987 Transactions of the ASME

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 might have been totally different. A typical internally cooled is being expended to improve the quality and heat treat
valve design is illustrated in Fig. 5(e). response of these materials, but it will be difficult to find a less
Wear on the tip of the austenitic valve stem was avoided by expensive material with properties that are comparable to
welding the stem.with Stellite alloys. This approach has been these medium carbon steels.
replaced by resistance welding a martensitic alloy to the valve
tip, commonly referred to as the wafer welded design.
In the early 1930s, Ford introduced the Cast 14-14 austenitic Future Evolution of Spark Ignited Engine Valve Design
exhaust valve material. Most US engines were using wrought
austenitic alloys at this time. However, Ford used stainless The spark ignited engine is expected to remain the dominant
steel radiator shells and wanted to utilize their own internally power plant for passenger car applications in the United
created stamping scrap better to make the cast austenitic States. By contrast, in commercial truck and aircraft applica-
valves. tions, diesel and turbine engines are replacing the gasoline
In the late 1930s, the XCR and TXCR austenitic exhaust engines. As such, the vast majority of new valve-related engine
valves were commercialized in passenger car engines. These design activity will be concentrated in the passenger car sec-
alloys were similar to Silchrome 10 and 21-12 and hardened by tion. The most significant driving forces for the future evolu-
sigma phase formation. The precipitation of sigma phase in- tion of the passenger car spark ignited engine will be improved
creased the volume fraction of hard phases, improving wear fuel economy and reduced initial engine costs.
resistance. However, these alloys were difficult to weld and
had a brittleness which tended to increase during service, caus- Exhaust Valves. Any fuel economy gains made as a result
ing a degradation of ductility and corrosion resistance [17]. of improvements in the basic combustion process are expected
Aircraft applications continued to be more demanding and to be manifested in reduced exhaust gas temperature, and thus
World War II greatly expedited the use of a new group of lower valve operating temperatures. Also, the exclusive use of
materials known as superalloys [18]. The first superalloy used lead-free fuels virtually eliminates any detrimental corrosive
was called N-155. N-155 was followed by Inconel M (TPM) environment. It is conceivable that the combination of these
and Nimonic 80A. Although most of these alloys were two factors may permit substitution of a lower cost austenitic
developed for gas turbines, they have served well in heavy- or martensitic alloy for the austenitic valve steel (21-2N)
duty exhaust valve applications and Nimonic 80A is still the presently in use.
material of choice for reciprocating aircraft engines. Reduced valve gear friction has also sucessfully
Prior to World War II, nitrogen had been added to demonstrated fuel economy gains [20]. This has resulted in
Silchrome 10 and 21-12 as an austenite stabilizer. Later, Jen- widespread usage of roller cam followers. For those valve gear
nings [19] at Armco discovered that if over 0.2 percent configurations where roller cam followers are not practical or
nitrogen was added to austenitic steels with sufficient carbon, cost effective, reduced valve weight can accomplish the same
a precipitation hardenable grade would result. His work objective. Reduced valve weight permits the use of lighter
culminated in the development of 21-4N alloy that virtually re- valve spring loads, which results in a significant reduction in
placed all other passenger car engine exhaust valve alloys in friction between the flat cam follower and the cam shaft. This
the 1950s. This material was especially attractive economically reduced weight can be achieved through substantial reduction
because of its lower nickel content. Its strength properties of the cross-sectional thickness of the valve head and stem.
were substantially improved over prior alloys by the combina- Alternative means include a hollow stem steel configuration or
tion of carbon and nitrogen, resulting in carbonitride use of low-density materials such as titanium [3]. Considerable
precipitation. The low silicon content made it much less material and process development effort will be required to
susceptible to lead oxide corrosion than the other available make these latter alternatives cost effective.
austenitic alloys. Fuel economy gains may also be achieved through favorable
A relatively slight modification of 21-4N (decreasing the adjustment of parameters such as compression ratio and spark
nickel content by 2 percent) lead to the more cost-effective advance. Unfortunately, preignition occurs during certain
21-2N austenitic valve steel in the early 1960s. This alloy transient modes of engine operation which preclude these ad-
dominates the passenger car exhaust valve material market to- justments. Industry discussion has centered on the hot exhaust
day and is expected to do so in the foreseeable future. Friction valve as a cause of the preignition. If this could be
welding replaced resistance welding in the 1960s as a cost sav- demonstrated, internal cooling would provide yet another
ing measure and a quality improvement. The low-cost, reliable means to reduce fuel consumption. Again, a large develop-
exhaust valve design currently used for passenger cars incor- ment effort in material and processing would be required to
porates 21-2N head material friction welded to a carbon steel produce a cost-effective product. However, there would be an
stem. additional benefit; internal cooling would permit use of
The most recently commercialized valve alloy in spark ig- simpler alloys with a significant reduction in strategic alloy
nited engines is referred to as 23-8N. This alloy was developed content, e.g., chromium, manganese, nickel.
by Tanzan, also of Armco, for heavy-duty diesel applications There is also a large industry effort to reduce oil consump-
[7]. It has also found limited application in sodium cooled tion in evolving passenger car engines. One approach to this is
valves used in heavy-duty gasoline engines, e.g., delivery truck to reduce significantly the amount of oil reaching the valve
engines. stem/valve guide interface. In the present environment,
chromium plating applied to the valve stem has been an effec-
Intake Valves. Until World War I, the intake valve for tive means of adhesive wear prevention. With reduced lubrica-
spark ignited engines was the same in design and materials as tion, however, there is the potential need for the development
the exhaust valve. Cutlery steels found intake valve applica- of improved antiscuff coatings.
tion during that period, and their predecessors, Silchrome 1
and Silchrome XB, are still used in heavy-duty and aircraft
applications. Intake Valves. Alloy changes from the presently used SAE
The environmental demands are much less for the intake 1541 and 1547 are not anticipated due to improvements made
valve than for the exhaust valve. As a result, the main factor to the basic combustion system. The identified benefits for
affecting its evolution has been cost reduction. Current spark weight reduction in exhaust valves apply to the intake valves,
ignited passenger car engines use low alloy steels such as SAE as do concerns for reduction in lubrication to the valve
1541 or 1547 for intake valve applications. Considerable effort stem/valve guide interface.

Journal of Engineering for Gas Turbines and Power OCTOBER 1987, Vol. 109/359

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 U.S. COMPRESSION IGNITED ENGINE POPPET EXHAUST VALVE MATERIAL & DESIGN EVOLUTION

Cr-Nl-c'St.«l (21-12)

C-NI-^W,,...

Cr
(2i-«*C2T-IN"'

(N155Nlrnkc'»lnB.°V51S,TmS"°c,»0A)

Cr-%U?-C-NSt..,

1900 1920 1940 1960 1980 2000

YEARS
Fig. 7 Family listed is austenitic unless specified martensitic; all are
wrought alloys except where stated as cast; alloy listed is typical exam-
ple of family

US Compression Ignited Engine Valve Design and The 1970s also saw the development of nickel and iron base
Material Evolution seat facing alloys such as Eatonite 3, 5, and 6 [23]. In 1978,
political instabilities in Zaire resulted in a "cobalt crisis"
Exhaust Valves. R. Diesel conceived the first compression which necessitated and greatly expedited the substitution of
ignited engine in 1892, but World War I propelled the develop- these alloys for the cobalt based Stellite alloys. Very little
ment of the first high-speed Diesel engines in Germany and the Stellite is expected to be used in Diesel engines by the late
United Kingdom [9]. By the late 1930s the high-speed normal- 1980s. It should also be noted that the use of these materials
ly aspirated Diesel engine was firmly established in the truck, was in part made possible by the development of the plasma
bus, and heavy-duty construction equipment industries. The transferred arc seat facing technology [8]. Plasma transferred
first valve materials used were identical to those for spark ig- arc welding is replacing the oxy-acetylene process used since
nited engines, but the more severe environmental conditions the introduction of the first Stellite faced valve.
forced a considerably different course of evolution as shown
in Fig. 7. Intake Valves. Diesel intake valve material has actually
changed very little since the introduction of Silchrome 1,
The first US Diesel exhaust valves were of the cutlery steel
Cr-Si-C martensitic steel. The exceptions are those Diesel
type, i.e., Silchrome 1. However, their poor high-temperature
engine manufacturers who wish to use the same material in
strength necessitated the use of 21-12 and Silchrome 10
their intake valves as in the exhaust valves. Both a 12 percent
materials. The much higher peak combustion pressures
super Cr steel (similar to 422 SS) and 21-2N have found
associated with Diesel engine operation created high contact
limited use in those instances where Sil 1 has failed to meet the
stresses and considerable adhesive wear at the valve seat inter-
service requirements.
face. The wear problem was addressed by hard facing the
valve seats with Stellite type cobalt base alloys.
As was the case for the Great War, World War II greatly ex- Future Evolution of US Compression Ignited Valves
pedited the development of the Diesel engine. Molybdenum and Materials
and tungsten were added to alloys similar to 21-12 in order to The heavy-duty exhaust valve offers the greatest opportuni-
improve strength and seat wear resistance. An alloy known as ty for future development. As multistage turbocharging and
TPA proved to be the leader using this approach. adiabatic approaches increase peak pressures and
Superalloys soon found their way into Diesel engines. N-155 temperatures, current designs and materials will not meet the
was the first superalloy and TPM (Inconel M) came soon strength, wear resistance, and corrosion resistance re-
thereafter. These alloys were followed by Inconel 751, quirements. More wear resistant, metallic, and ceramic
Nimonic 80A and Nimonic 90 in the late 1950s and early 1960s coatings will find application, particularly in Diesel engines
[21]. converted to natural gas and those powered with residual
Although developed for spark-ignited engines, 21-4N and fuels. To meet the consequent high seating loads and adhesive
its later variant 21-2N found applications in the 1950s and wear resistance requirements, ceramic monolithic or com-
1960s vintage Diesel engines as well as in recent passenger car posite components offer many advantages over their metallic
Diesel engines. A high nitrogen version of these alloys, Gaman counterparts [24]. These materials, as well as aluminides, offer
H, had even better seat face wear resistance, and also found much higher temperature capability (2000° to 2200°F versus
application in two-cycle Diesel engines [22]. In the 1960s, one 1700°F) making them extremely attractive for adiabatic Diesel
engine manufacturer used cast Stellite heads in order to use engines.
high-sulfur fuels. These changes also supplemented the
development of turbocharged Diesels to improve efficiency.
Summary
Although virtually no new passenger car valve materials
were introduced in the 1970s or 1980s, substantial changes oc- Exhaust valves have evolved in response to changing ap-
curred in the Diesel exhaust valve alloy applications. Armco plication needs: higher temperatures, more severe corrodents,
developed an alloy called 23-8N [7] which was based on 21-4N higher imposed stresses. The carbon steel and cutlery grades
but was more carefully balanced to improve long term stability used in early engines have been superseded by specially
and seat facing weldability. Because of these improvements, it alloyed, precipitation hardened austenitic materials. One-
has virtually replaced Silchrome 10 and 21-12N. piece valves have been replaced by two-piece, internally cooled
In the late 1970s, Pyromet 31 alloy was also introduced. designs with welded seat hardfacings.
Because of its improved sulfidation resistance, higher Intake valves have also evolved with less significant changes
strength, and better seat face wear resistance, it proved to be a in materials, although cost has played a more important role
better substitute for several superalloys. than for exhaust valves. Today's intake valve materials offer

3 6 0 / V o l . 109, OCTOBER 1987 T r a n s a c t i o n s of the A S M E

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 many alternatives for different engine applications with better 6 Zinner, K., "Investigations Concerning Wear of Inlet Valve Seats in
Diesel Engines," ASME Paper No. 63-OGP-l, 1963.
durability and at very low cost. 7 Jenkins, L. F., and Larson, J. M., "The Development of a New
Yet, today's valves are not the ultimate in valve technology. Austenitic Exhaust Valve Material," SAE Publication 780245, 1978.
Tomorrow's intake and exhaust valves will be lighter weight, 8 Milligan, J., and Narasimhan, S., "A Powder Fed Plasma Transferred
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provided input to this paper. Particular credit should be ex- 14 Handforth, J. R., "Metallurgical Problems Arising From Internal Com-
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Schaefer, P. Crisenbery, and R. Martin for their effort in 16 "Exhaust Valve Steels," Automobile Engineering, Mar. 1962, pp. 93-97.
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stitute of Metallurgical Engineers, Vol. 179, No. 5, 1964-1965, pp. 145-180.
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