U.S. patent application number 13/425018 was filed with the patent office on 2013-09-26 for heat treatment process for engine ring gear.
This patent application is currently assigned to BRUNSWICK CORPORATION. The applicant listed for this patent is Terrance Cleary. Invention is credited to Terrance Cleary.
Application Number | 20130248058 13/425018 |
Document ID | / |
Family ID | 49210655 |
Filed Date | 2013-09-26 |
United States Patent
Application |
20130248058 |
Kind Code |
A1 |
Cleary; Terrance |
September 26, 2013 |
Heat Treatment Process for Engine Ring Gear
Abstract
The present disclosure relates to methods of hardening toothed
gear parts for engines. The method results in a uniformly hardened
gear with minimized distortion.
Inventors: |
Cleary; Terrance; (Fond du
Lac, WI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Cleary; Terrance |
Fond du Lac |
WI |
US |
|
|
Assignee: |
BRUNSWICK CORPORATION
Lake Forest
IL
|
Family ID: |
49210655 |
Appl. No.: |
13/425018 |
Filed: |
March 20, 2012 |
Current U.S.
Class: |
148/586 |
Current CPC
Class: |
C21D 9/40 20130101; C21D
9/32 20130101 |
Class at
Publication: |
148/586 |
International
Class: |
C21D 9/32 20060101
C21D009/32 |
Claims
1. A method of hardening a toothed gear comprising steel, the steel
comprising an iron alloy comprising about 0.2-0.8 % carbon, the
method comprising (a) heating the gear to a temperature greater
than the austenitizing temperature of the steel. (b) quenching the
gear to a temperature between the Martensite temperature for the
steel and a temperature about 20.degree. F. higher than the
Martensite start temperature for the steel, namely the quenching
temperature, and holding the gear at the quenching temperature
until the gear is quenched to the quenching temperature uniformly
throughout; and (c) further quenching the gear in ambient air
conditions.
2. The method of claim 1, wherein in step (a) the gear is heated to
a temperature greater than about 1400.degree. F.
3. The method of claim 1, wherein in step:(a) the gear is heated lo
a temperature greater than about 1500.degree. F.
4. The method of claim 1, wherein in step (a) the gear is heated to
a temperature greater than about 1600.degree. F.
5. The method of claim 1, wherein in step (a) the gear is heated to
a temperature between about 1400-1800.degree. F.
6. The method of claim 1, wherein step (a) is performed for at
least about 3 minutes.
7. The method of claim 1, wherein step (a) is performed for at
least about 1 hour.
8. The method of claim 1, wherein step (a) is performed by placing
the gear into a molten salt bath.
9. The method of claim 1, wherein step (a) is performed until the
gear is completely transformed to austenite.
10. The method of claim 1, wherein in step (b). the gear is
quenched to a temperature between about 250-1000.degree. F.
11. The method of claim 1, wherein in step (b) the gear is quenched
to a temperature between about 350-650.degree. F.
12. The method of claim 1, wherein in step (b) the gear is quenched
to a temperature between about 395-630.degree. F.
13. The method of claim 1, wherein step (b) is performed for at
least about 1 minute.
14. The method of claim 1, wherein step (b) is performed for at
least about 3 minutes.
15. The method of claim 1, wherein step (b) is performed for about
3-6 minutes.
16. The method of claim 1, wherein step (b) is performed by placing
the gear into a molten salt bath or a molten lead bath.
17. The method of claim 1, wherein the gear is quenched at a rate
of at least about -100.degree. F./second.
18. The method of claim 1, further comprising step (d) subsequently
heating the quenched gear to a temperature above the Martensite
start temperature for the steel of which the gear is comprised and
subsequently quenching the further heated gear.
Description
FIELD
[0001] The present disclosure relates to heat treatment processes
for steel parts. In particular, the disclosure relates to heat
treatment processes for steel, engine ring gears.
BACKGROUND
[0002] Traditionally, steel ring gears for engines have been
manufactured by one of two processes. The first process is
conventionally referred to as "quench and temper." In this process,
the gear is heated above the austenitizing temperature for the
steel of which the gear is made and then the gear is rapidly
quenched (i.e., cooled) to room temperature. The cooled part
subsequently is tempered (i.e., heated) to add toughness. The
strength and hardness of the gear is generally uniform throughout
the part. While this process is inexpensive, it may result in
distortion from volumetric changes due to the microstructural
transformation that occurs in the process, mainly from rapid
quenching. As such, the part typically must be further machined
after hardening adding expense to the manufacturing method.
[0003] The second process is referred to as "induction hardening"
and is widely used for toothed gear rings. In induction hardening,
only about the outer 10% of the gear is quenched and tempered
(i.e., the portion of the gear comprising the teeth). For a typical
gear ring, having an outer radius that is about 15-25 mm larger
than an inner radius, this induction heating would involve
quenching and tempering only about the outer 1.5 mm of the gear.
This process, unlike conventional quench and temper, results in
minimal distortion at the teeth portion. However, only the outer
1.5 mm of the ring gear is in a high strength condition and the
rest of the ring gear is low strength.
SUMMARY
[0004] The present disclosure relates to methods of hardening
toothed gear parts for engines. The method results in a uniformly
hardened gear with minimized distortion. Gears suitable for the
method typically comprises steel. In some embodiments, the carbon
content of the steel is between about 0.2-0.8% carbon.
[0005] The first step of the method typically includes heating the
gear to a temperature above the austenitizing temperature for the
steel of which the gear is comprised. For most types of steel, this
first step typically includes heating the gear to a temperature of
greater than about 1400.degree. F. (typically greater than about
1500.degree. F.). The austenitizing temperature for steel is
determined partially by the carbon content of the steel and is
inversely proportional to the carbon content of the steel. For
example, the austenitizing temperature for 0.02% carbon steel is
approximately 1600.degree. F. while the austenitizing temperature
for 0.08% carbon steel is approximately 1500.degree. F. In the
disclosed methods, a suitable temperature range to which the gear
is heated may include a range of about 1400-1800.degree. F. The
gear typically is heated to a temperature above the austenitizing
temperature for the steel of which the gear is comprised for at
least about 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 minutes (e.g., 2-10
minutes), depending on the thickness or height of the gear.
[0006] The gear may be heated by processing that include, but are
not limited to, placing the gear in a molten salt bath. Multiple
gears may be processed simultaneously in a molten salt bath.
Preferably, the gear or gears are placed in the salt bath such that
a maximum surface area of the gear or gears are in contact with
molten salt.
[0007] Subsequently to heating the gear to a temperature above the
austenitizing temperature for the steel of which the gear is
comprised, the gear is quenched to a quenching temperature which
may be between the Martensite start temperature (Ms temperature)
for the steel of which the gear is comprised and a temperature
about 20.degree. F. above the Ms temperature or 15, 10, or
5.degree. F. above the Ms temperature). For many types of steel,
the Ms temperature typically is between about 250-1000.degree. F.
(more typically between about 350-650.degree. F., even More
typically between about 350-630.degree. F.).
[0008] In the disclosed methods, the gear is cooled rapidly from
the austenitizing temperature to the quenching temperature (which
is a temperature nearly above the Ms temperature) in order to
minimize transformation of the austenite structure to a ferritic
structure. For example, the gear may be quenched at a rate that is
more quickly than about -100, -200, -300, -400, or -500.degree.
F./second. For a medium carbon unalloyed steel, a suitable rate may
be at least about -200.degree. F./second.
[0009] The gear typically is held at the quenching temperature
until the entire gear is completely quenched throughout to the
quenching temperature (e.g., generally in a homogenous temperature
condition for all elements of the gear). For example, the gear may
be held at the quenching temperature for at least about 1, 2, 3, 4,
5, or 6 minutes (e.g., 3-6 minutes). Factors that may determine the
minimum holding time at the quenching temperature may include the
thickness or height of the gear. The gear may be quenched by
processes that include, but are not limited to, placing the gear in
a molten salt bath or a molten lead bath.
[0010] Subsequently to quenching the gear to the quenching
temperature, the gear is further quenched to a temperature below
the Martensite finish temperature (Mf temperature) for the steel of
which the gear is comprised. Mf temperatures typically are less
than about 750, 500, 250, or 100.degree. F. The gear may be
quenched in this step by processes that include, but are not
limited to, placing the gear in ambient air conditions (e.g., at a
temperature of about 70.degree. F. or less). Optionally, the gear
treated as such subsequently may be tempered by further heating the
gear.
BRIEF DESCRIPTION OF THE FIGURES
[0011] FIG. 1 illustrates a convention quenching and tempering
process.
[0012] FIG. 2 is a representation of a toothed gear hardened by
induction heating.
[0013] FIG. 3 illustrates one embodiment of the hardening process
disclosed herein.
[0014] FIG. 4 illustrates the relationship between Martensite start
temperature (Ms temperature), Martensite finish temperature (Mf
temperature), and carbon content of steel.
[0015] FIG. 5 illustrates configuration differences for a gear
hardened by induction heating and an embodiment of a gear hardened
by a hardening process, as disclosed herein.
DETAILED DESCRIPTION OF THE FIGURES
[0016] Disclosed herein is a method for manufacturing a toothed
gear part for an engine. The method may be described using several
definitions as discussed below.
[0017] Unless otherwise specified or indicated by context, the
terms "a", "an", and "the" mean "one or more." In addition,
singular nouns such as "gear" should be interpreted to mean "one or
more gears," unless otherwise specified or indicated by
context.
[0018] As used herein, "about", "approximately," "substantially,"
and "significantly" will be understood by persons of ordinary skill
in the art and will vary to some extent on the context in which
they are used. If there are uses of the term which are not clear to
persons of ordinary skill in the art given the context in which it
is used, "about" and "approximately" will mean plus or minus
.ltoreq.10% of the particular term and "substantially" and
"significantly" will mean plus or minus >10% of the particular
term.
[0019] The presently disclosed methods include. heating steps and
cooling steps. As known in the art, the cooling steps may otherwise
be referred to as "quenching."
[0020] Ring gears are generally attached to the flywheel of an
internal combustion engine and they interface via teeth with an
electric starter motor to start the engine. In order to improve
strength and durability of the gear, the gear is commonly subjected
to a heat treatment process.
[0021] Conventional quenching and tempering involves heating the
entire gear above the austentizing temperature for the steel of
which the gear is made and quenching the entire gear (i.e., rapidly
cooling the gear) to room temperature. (See FIG. 1). The entire
cooled part subsequently is tempered (i.e., subsequently heated) to
add toughness. This process may result in distortion from
volumetric changes due to the microstructural transformation that
occurs as the gear is subjected to a large temperature range during
the process, mainly during rapid quenching. As such, the entire
part typically requires machining after hardening.
[0022] A more common process in industry for hardening ring gears
is to selectively heat via induction the outer portion of the ring
comprising the teeth to improve mechanical properties of the teeth
of the gear while minimizing distortion of the gear only at the
heated portion. FIG. 1 shows a gear having been selectively heated
and hardened at the outer portion comprising the teeth, where the
teeth are hardened to Rockwell C 40-60, while the remainder of the
gear has a hardness no higher than Rockwell C 30.
[0023] The presently disclosed methods may otherwise be referred to
"martempering" as disclosed in FIG. 3. In the presently disclosed
methods, the entire toothed gear is heated to a temperature above
the austenitizing temperature for the steel of which the gear is
comprised. Typically, this temperature is greater than about 1400,
1500, or 1600.degree. F.
[0024] Subsequently, the heated gear is quenched (or cooled) to a
temperature that is about the Martensite start temperature (Ms
temperature) for the steel of which the gear is comprised or
slightly above the Ms temperature (e.g., 20, 15, 10, or 5.degree.
F. above the Ms temperature) but to a low enough temperature to
mitigate an austenite to ferrite+cementite reaction. This
temperature or temperature range is referred to herein as the
"quenching temperature." For many types of steel, the Ms
temperature typically is between about 250-1000.degree. F. (more
typically between about 350-650.degree. F., even more typically
between about 350-630.degree. F.). Suitable quenching temperatures
may be within a range delineated by the Ms temperature and a
temperature 20, 15, 10, or 5.degree. F., above the Ms
temperature.
[0025] Gears manufactured by the disclosed methods typically
comprise steel, and in particular steel that is comprised mainly of
iron with a carbon content of about 0.2 0.8% carbon. Medium carbon
steel having a carbon content of about 0.3-0.6% is particularly
suitable. However, suitable steel for the disclosed methods may
include, but is not limited to, steel designated by the Society of
Automotive Engineers (SAE) under the following designation numbers:
1050, 1065, 1066, 1084, 1086, 1090, 4095, 1350, 4063, 4150, 4365,
5140, 5160, 8750, and 50100.
[0026] The Ms temperature is indirectly proportional to carbon
content of the steel. (See FIG. 4). Specific Ms temperatures of SAE
designated steel are as follows: 1050 steel--610.degree. F.
(320.degree. C.); 1065 steel--525.degree. F. (275.degree. C.); 1066
steel--500.degree. F. (260.degree. C.); 1084 steel--395.degree. F.
(200.degree. C.); 1086 steel--420.degree. F. (215.degree. C.); 1095
steel--410.degree. F. (210.degree. C.); 1350 steel--450.degree. F.
(235.degree. C.), 4063 steel--475.degree. F. (245.degree. C.); 4150
steel--545.degree. F. (285.degree. C.); 4365 steel--410.degree. F.
(210.degree. C.); 5140 steel--630.degree. F. (330.degree. C.); 5160
steel--490.degree. F. (255.degree. C.); and 8750 steel--545.degree.
F. (285.degree. C.). In some embodiments, Ms temperatures may be
calculated according to a formula Ms (.degree. F.)=1002-793 (%
C)-87(% Mn)-64(% Ni)-54(% Cr)-45(% Mo)+{50(% Co)-45(% Si)} or Ms
(.degree. C.)=539-423 (% C)-30.4(% Mn)-17.7(% Ni)-12.1(% Cr)-75(%
Mo)+{10(% Co)-7.5(% Si)}.
[0027] Subsequently to quenching the heated gear to the quenching
temperature, the gear is further quenched below the Martensite
finish temperature (Mf temperature). For many types of steel, the
Mf temperature is less than about 700.degree. F. or less than about
500, 250, 100, or 50.degree. F. (or less than about 400, 300, 100,
50, or 25.degree. C.). The Mf temperature, like the Ms temperature
is indirectly proportional to carbon content of the steel. (See
FIG. 4). The gear may be quenched in this step by processes that
include, but are not limited to, placing the gear in ambient air
conditions (e.g., at room temperature or at a temperature of about
70.degree. F. or less).
[0028] The disclosed methods typically produce a toothed gear
having a uniform hardness with limited distortion. Typically, the
gear has a uniform hardness in the range of about Rockwell C 40 to
Rockwell C 60.
[0029] The presently disclosed methods may be utilized to
manufacture gears having a uniform hardness while using a reduced
amount of raw material (i.e., steel) to produce the gear. For a
gear hardened by induction heating, the gear must have a root
diameter (RD=diameter measured from the base of a tooth) and inner
diameter OD) of suitable dimensions to provide strength for the
gear. (See FIG. 5). Because a gear hardened by induction heating is
not hardened throughout, the gear must have a smaller inner
diameter in order to provide a suitable width for the gear
((RD-ID)/2=width) to compensate for the lack of uniform hardness.
For a gear hardened by the process disclosed herein, the inner
diameter may be larger because the gear has: a uniform hardness
throughout. As such, a gear hardened by the process disclosed
herein may have a width (i.e., (RD-ID)/2) that is less than the
width for a gear hardened by induction heating. In some
embodiments, the inner diameter of a gear hardened by the methods
disclosed herein may be 5, 10, or 15% larger than the inner
diameter of a gear hardened by induction heating. In some
embodiments, the width ((RD-ID)/2) of a gear hardened by the
methods disclosed herein may be 10, 20, 30, 40, or 50% less than
the width of a gear hardened by induction heating. In some
embodiments, gear hardened by the process disclosed herein may have
a mass that is 5, 10, 15, 20, 25, 30, or 35% less than the mass for
a gear hardened by induction heating.
[0030] In the present description, certain terms have, been used
for, brevity, clearness and understanding. No unnecessary
limitations are to be implied therefrom beyond the requirement of
the prior art because such terms are used for descriptive purposes
only and are intended to be broadly construed. The different
systems and methods described herein may be used alone or in
combination with other systems and methods. Various equivalents,
alternatives and modifications are possible within the scope of the
appended claims. Each limitation in the appended claims is intended
to invoke interpretation under 35 U.S.C. .sctn.112, sixth paragraph
only if the terms "means for" or "step for" are explicitly recited
in the respective limitation.
[0031] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art, to make and use the invention. The patentable
scope of the invention is defined by the claims, and may include
other examples that occur to those skilled in the art. Such other
examples are intended to be within the scope of the claims if they
have structural elements that do not differ from the literal
language of the claims, or if they include equivalent structural
elements with insubstantial differences from the literal languages
of the claims.
* * * * *