USOO70.

40080B2

(12) United States Patent (10) Patent No.: US 7,040,080 B2

Okawa et al. (45) Date of Patent: May 9, 2006

(54) TRACK LINK PRODUCTION METHOD AND (56) References Cited

TRACKLINK PRODUCED BY THE SAME
U.S. PATENT DOCUMENTS
(75) Inventors: Kazuhide Okawa, Yawata (JP); 4.419,152 A * 12/1983 Grilli et al. ................. 148,654
Hiroshi Sunada, Hirakata (JP) 5,500,058 A * 3/1996 Hirakawa et al. . ... 148,649
5,759,309 A * 6/1998 Watts et al. ...... ... 148,654
(73) Assignee: Komatsu Ltd., Tokyo (JP) 6,742,853 B1* 6/2004 Takeno et al. .............. 305,185
FOREIGN PATENT DOCUMENTS
(*) Notice: Subject to any disclaimer, the term of this
patent is extended or adjusted under 35 JP 57-051.583 3, 1982
U.S.C. 154(b) by 344 days. JP 60-075514 4f1985
JP 5-9488 2, 1993
(21) Appl. No.: 10/391,499 * cited by examiner
(22) Filed: Mar. 18, 2003 Primary Examiner David B. Jones
(74) Attorney, Agent, or Firm Frishauf, Holtz, Goodman &
(65) Prior Publication Data Chick, P.C.
US 2003/023OO69 A1 Dec. 18, 2003
(57) ABSTRACT
(30) Foreign Application Priority Data There are proposed a track link production method capable
Jun. 14, 2002 (JP) ............................. 2002-174848 of providing markedly improved wear life with good cost
performance and a track link produced by this method. To
(51) Int. Cl. this end, the track link production method includes a heat
FI6C 7700 (2006.01) treatment process (Steps 4, 5) of applying quenching and
B26D 55/20 (2006.01) low temperature tempering treatment to a whole link mate
B2IL 5/00 (2006.01) rial after hot forging (Step 2), and is designed Such that
C2ID I/06 (2006.01) desired machining is applied to the link material (Step 3)
before the heat treatment process (Steps 4, 5) and such that
(52) U.S. Cl. ............................. 59/35.1:59/8:305/201; after the heat treatment process (Steps 4, 5), tempering (Step
305/185; 148/654; 148/649 6) and finish machining (Step 7) are sequentially applied to
Some of the parts which have undergone the machining
(58) Field of Classification Search ...................... 59/4, process, the some parts including at least parts where high
59/8, 35.1: 305/185, 201: 148/654, 649 dimensional accuracy is required.
See application file for complete search history. 4 Claims, 6 Drawing Sheets
A PROCESS CHART OF ATRACKLINK PRODUCONMETHOD
ACCORDENG TO ONE EMBODIMENT OF THE INVENTION

PROCESS rROCESS
CRER

MATERIAL (RounD oR souARE BAR)

HOTORGING
2 OO (O)
MACHINING: PARS 11,12,13, 4,15,16,17
INFIG.2 (ROUGH PROCESSING)

ENIRE quENCHING (WATER, OL soLUBLE

AGENT OR SIMLARQUENCHING MEDIUM)

NREEMERING
(Low TEMPERATURE TEMPERING)

PARTATEMPERING: MEISHBORHOOO HATCH

of ARTS 3, 4, 5 INFIG.2 AREA:
TEMERING

MACHINING: PARTS 112,13,14, 15,16,17

INFIG.2 (FINISH MACHINING)

IF THE AMoUNT OF STRAININSTEPS5, 6 Is NoTA PRACTICAL PROBEM,

Nish ACHINENG N Sip MAY city.
U.S. Patent May 9, 2006 Sheet 1 of 6 US 7,040,080 B2

F.G. 1
U.S. Patent May 9, 2006 Sheet 2 of 6 US 7,040,080 B2

FIG 2
U.S. Patent May 9, 2006 Sheet 3 of 6 US 7,040,080 B2

FIG 3
A PROCESS CHART OF A TRACKLINK PRODUCTION METHOD
ACCORDING TO ONE EMBODIMENT OF THE INVENTION

is
PROCESS
ORDER
PROCESS

MATERIAL (ROUND OR SQUARE BAR)

HOT FORGING O OO (O)

MACHINING: PARS 11,12,13,14, 15, 16, 17
IN FIG.2 (ROUGH PROCESSING)

ENTIRE QUENCHING (WATER, OIL, SOLUBLE

AGENT OR SIMLARQUENCHING MEDIUM)

ENTRE TEMPERING
(LOW TEMPERATURE TEMPERING)

PARTIAL TEMPERING NEGHBORHOOD HATCHED

6 OF PARTS 13,14, 15 NFIG.2 AREA
EMPERING

MACHINING: PARTS 11,12,13,14,15, 16, 17

7 NFIG.2 (FINISH MACHINING)

IF THE AMOUNT OF STRAIN INSTEPS 5, 6 IS NOT APRACTICAL PROBLEM,

FINISH MACHINING INSTEP 7 MAYBE OMITTED
U.S. Patent May 9, 2006 Sheet 4 of 6 US 7,040,080 B2

FIG. 4
A GRAPH SHOWING ACOMPARISON
BETWEEN THE HARDNESS DISTRIBUTION
OF A FINISHED PRODUCT OT AND
THAT OF A PRODUCT OT

48M 50 FINISHED PRODUCT CRT

45 --------------N-------------Yr-------------------
GREEN BODY HARDNESS
PRODUCT CRT y

30

e-se
RANGE OF
SOFTENED AREA
(SOFT ZONE)

10 20 30 40
DISTANCE FROM
(WHEELTREAD) SURFACE -->

- FINISHED PRODUCT QT: TRACKLINK OF THE PRESENT EMBODIMENT

- PRODUCT GT: TRACKLINK OF THE PRIOR ART
U.S. Patent May 9, 2006 Sheet 5 of 6 US 7,040,080 B2

FIG. 5
A PROCESS CHART OF A TRACKLINK PRODUCTION METHOD
ACCORDING TO THE PRIOR ART

PROCESS

MATERIAL (ROUND OR SQUARE BAR)

HOT FORGING
l

ENTIRE QUENCHING (WATER, OIL, SOLUBLE

AGENT OR SIMILAR QUENCHING MEDIUM)

ENTRE TEMPERING
(HIGH TEMPERATURE TEMPERING)

MACHINING: PARTS 11,12,13,14, 15, 16, 17

IN FIG.2 (ROUGH PROCESSING)

WHEEL TREAD PART INDUCTION

QUENCHING (WATER OR SOLUBLE
AGENT) AREA MARKED
l With WAVY
LINE:
OUENCHING
TEMPERING
WHEELTREAD PARTEMPERING
(LOW TEMPERATURE TEMPERING)

MACHINING: PARTS 11,12,13,14, 15, 16, 17

IN FIG.2 (FINISH MACHINING)

IF THE AMOUNT OF STRAIN INSTEPS 6,7 IS NOT APRACTICAL PROBLEM,

FINISH MACHINING IN STEP 8 MAYBE OMITTED.
U.S. Patent May 9, 2006 Sheet 6 of 6 US 7,040,080 B2

FIG. 6
A GRAPH SHOWING ATEMPERATURE DISTRIBUTION
WHERE HIGH-FREOUENCY HEATING IS APPLIED
TO ATRACKLINK

a TEMPERATUREMEASUREMENT
POSITION: WHEELTREA CENTER
TEMPERATURE MEASUREMEN
DIRECTION: DIRECTION INDICATED
BYARROW A
WHEELTREAD A

OOO (O)
v www vessed duo
AUSTENTE TEMPERATURE
prowest were 08th A Pales a stone tow app sas up as as

ENTRE EMPERING TEMPERATURE

DISTANCE FROM -Ge.

WHEELTREAD
 US 7,040,080 B2
1. 2
TRACK LINK PRODUCTION METHOD AND deeper hardened layer, heating time becomes longer with the
TRACK LINK PRODUCED BY THE SAME result that the temperature of the wheel tread part becomes
too high, leading to an increase in crystal grain size and
TECHNICAL FIELD consequently a decrease in the toughness of the wheel tread
part.
The present invention relates to a method of producing a Further, if induction heating is again applied to the link
track link which is a component of an endless track crawler material which has once undergone entire quenching and
belt for use in construction equipment such as hydraulic tempering treatment in Steps 3 and 4, the link material will
excavators and bulldozers and a track link produced by the have the temperature distribution shown in FIG. 6 and the
SaC. 10 part a which is insufficiently heated will be brought into a
condition similar to the case where high temperature tem
BACKGROUND ART pering is done. As a result, a layer (i.e., the so-called soft
Zone) having hardness lower than the hardness already
For example, a crawler belt for the undercarriage of a attained by thermal refining is formed as indicated by IQT
bulldozer is constituted by track shoes, track links, coupling 15 (Induction Quenching Tempering) product line in the
pins, track bushings and seals. Each track shoe is fastened to hardness distribution comparative graph of FIG. 4, so that
laterally paired track links with bolts and nuts (see FIG. 1). the strength of the link material becomes insufficient and, in
Each track link has (a) a wheel tread which comes in rolling consequence, peeling of the hardened layer occurs.
contact with a track roller, (b) a shoe mounting Surface to The invention is directed to overcoming the above prob
which a track shoe is attached, (c) a pin hole for receiving lems and a primary object of the invention is therefore to
a coupling pin inserted therein, (d) a bushing hole for provide a track link production method capable of providing
receiving a track bushing inserted therein, (e) a seal counter markedly improved wear life with good cost performance
bore to which a seal is fit, (f) shoe bolt holes for receiving and a track link produced by this method.
track shoe clamping bolts inserted therein, and (g) shoe nuts
bearing Surface on which track shoe clamping nuts sit. 25 DISCLOSURE OF THE INVENTION
The above track link is conventionally produced by a
production method comprised of Such steps as shown in In a first aspect of the invention, the above object can be
FIG. 5. Specifically, a round (square) bar made of high accomplished by a track link production method including:
strength steel such as SMn based steel, SCM based steel or a heat treatment process of applying quenching and low
SNCM based steel is first prepared (Step 1). Then, this 30 temperature tempering treatment to a whole link material
material is formed by hot forging into a link material which after hot forging,
is substantially similar, in form, to a finished product (Step wherein desired machining is applied to the link material
2). Thereafter, the link material is entirely quenched by a before the heat treatment process,
quenching medium Such as water or oil (Step 3). Subse wherein after the heat treatment process, tempering and
quently, this quenched link material is tempered at a high 35 finish machining are sequentially applied to some of the
temperature of about 400° C. to 650° C. (Step 4), thereby parts which have undergone the machining process, said
obtaining a high-strength, tempered, martensitic (Sorbite) Some parts including at least parts where high dimensional
metal structure. In this way, the hardness of the link material accuracy is required and parts where delayed failure may be
is made to be HRC25 to HRC 40 to ensure fatigue strength. caused by high stress due to press-fitting of a pin or bushing.
Then, the link material is machined at the parts to be formed 40 According to the first aspect, by the heat treatment process
into a wheel tread, shoe mounting Surface, pinhole, bushing in which quenching and low temperature tempering treat
hole, Seal counterbore, shoe bolt holes and shoe nut bearing ment is applied to a whole link material after hot forging, the
Surfaces, so that they have their respective specified sizes whole green body of the link material is hardened, resulting
(Step 5). Of these machined parts, the wheel tread part is in formation of a deep hardened Zone on the wheel tread
Susceptible to wear caused by earth and sand because high 45 surface of the link. Accordingly, the wear life of the track
surface pressure would be imposed on the wheel tread part link can be significantly improved. In addition, since the
with earth and sand trapped between the wheel tread part and desired machining is applied to the link material before the
the track roller. To withstand the wear caused by earth and heat treatment process, that is, the link material in an easily
sand, the wheel tread part undergoes induction quenching processable condition with comparatively low hardness,
and tempering (Steps 6, 7) to form a hardened layer having 50 accuracy defects due to difficult processing and poor cost
a thickness of about 5 to 15 mm and a hardness of about performance can be prevented. Further, since after the heat
HRC45 to HRC55. Then, finish machining is applied to the treatment process, tempering (partial tempering) is applied
machined parts, thereby finishing a track link (Step 8). to some of the parts of the link material which have
A track link usually loses its function and ends its service undergone the machining process, the some parts including
life when the wear of the wheel tread proceeds so that the 55 at least parts where high dimensional accuracy is required
flange of the track roller interferes with the track link or and parts where delayed failure may be caused by high stress
when the wheel tread becomes so thin that it is not strong due to press-fitting of a pin or bushing, strain inevitably
enough to bear the weight of the vehicle any longer. It is caused by the heat treatment can be removed and the link
therefore necessary to improve the wear life of the wheel material is softened and brought into an easily processable
tread as much as possible. To this end, it is effective to 60 condition. As a result, finish machining after the partial
increase the depth of the hardened layer of the wheel tread. tempering can be easily and reliably performed and dimen
However, the Surface hardening method Such as ordinary sional accuracy can be ensured at low cost while preventing
induction quenching and tempering process has the disad delayed failure.
vantage that the hardened layer to be formed with the In a second aspect of the invention, there is provided a
method is relatively shallow (about 15 mm), no matter how 65 track link produced by the track-link production method
good the hardenability of the used material. If the heated according to the first aspect, the track link having a hardness
Surface region is deepened with the intention of obtaining a of at least HRC40 in an area extending from a wheel tread
 US 7,040,080 B2
3 4
that comes into contact with a track roller to a center core the seal counter bore 15 being concentric with each other.
and a grain size of at least GhS in the center core. The track link 10 is further provided with shoe bolt holes 16
According to the second aspect, since wear resistance can and shoe nut bearing surfaces 17. Inserted into each shoe
be ensured for a long time owing to the high-strength, bolt hole 16 is a bolt for attaching the track shoe 3. Seated
hardened Zone formed in the area extending from the wheel on each shoe nut bearing Surface 17 is a nut for attaching the
tread to the center core, the wear life of the track link can be track shoe 3. Note that the spaces designated by reference
markedly improved. numeral 18 are windows for accommodating mounting nuts.
In a third aspect of the invention, there is provided a track In the present embodiment, the track link 10 is manufac
link having a hardness of HRC40 or less in the circumfer tured in the production method comprised of the steps
ences of a pin hole and a bushing hole. 10 shown in FIG. 3. More specifically, a round or square bar
According to the third aspect, since the hardness of the made of high strength steel such as SMn based steel, SCM
areas around the pinhole and bushing hole is HRC40 or less, based steel or SNCM based steel is first prepared (Step 1).
delayed failure due to high stress caused by press-fitting of Then, this raw material is formed by hot-forging into a link
a pin or bushing can be prevented, finish machining can be material which has a form substantially similar to a finished
easily and reliably carried out, and dimensional accuracy can 15 product (Step 2). Subsequently to the hot-forging, the link
be assured at low cost. material is subjected to natural cooling so as to be brought
into an easily processable condition with comparatively low
BRIEF DESCRIPTION OF THE DRAWINGS hardness, and Such a link material then undergoes the
desired machining process including processing for forma
FIG. 1 is an exploded perspective view of a crawler belt tion of the wheel tread 11, the shoe mounting surface 12, the
according to an embodiment of the invention. bushing hole 13, the pin hole 14, the seal counter bore 15,
FIG. 2 is an outside view of a track link. the shoe bolts 16, the shoe nut bearing surfaces 17 and others
FIG. 3 is a process chart of a track link production method (Step 3). In the stage of Step 3, the parts (e.g., the bushing
according to one embodiment of the invention. hole 13, the pin hole 14 and the seal counterbore 15) which
FIG. 4 is a graph showing a comparison between the 25 require high dimensional accuracy are Subjected to only
hardness distribution of a finished product QT and that of a rough processing. On the other hand, the parts (e.g., the
product IQT. wheel tread 11, the shoe mounting surface 12, the shoe bolt
FIG. 5 is a process chart of a track link production method holes 16 and the shoe nut bearing surfaces 17) which require
according to the prior art. tolerance of normal level or other parts whose dimensional
FIG. 6 is a graph showing a temperature distribution in a 30 accuracies are not important may be subjected to not only
case where high-frequency heating is applied to a track link. rough processing but also Substantial finish machining
according to the parts. Among the parts to be subjected to the
BEST MODE FOR CARRYING OUT THE machining in Step 3, the parts which have already attained,
INVENTION in the forging of Step 2, dimensional tolerance of the same
35 level that can be obtained by the rough processing may skip
Reference is now made to the accompanying drawings to the rough processing of Step 3. By applying the desired
describe a track link production method and a track link machining process to the link material before undergoing the
produced by the same according to a preferred embodiment heat treatment process (described later), that is, the link
of the invention. The present embodiment is associated with material in an easily processable condition having compara
one application of the invention to a bulldozer which is a 40 tively low hardness, accuracy defects and poor cost perfor
kind of track type (caterpillar tread type) vehicles incorpo mance due to difficult processing can be prevented.
rated in construction equipment. The following heat treatment is then applied to the whole
FIG. 1 shows an exploded perspective view of a crawler link material which has undergone the machining of Step 3.
belt according to the present embodiment of the invention. Specifically, the link material is rapidly cooled from a
FIG. 2 is an outside view of a track link. 45
The bulldozer according to the present embodiment has a temperature of 750° C. or more (more preferably, about 850°
vehicle body (not shown) and crawler belts 1 which are C.), using water, oil, a soluble agent or a quenching medium
respectively disposed at both sides of the vehicle body, for having similar effectiveness, whereby quenching of the
forward and backward traveling and turning of the vehicle whole material is carried out (Step 4). Thereafter, low
body. Each crawler belt 1 includes a track chain 2 wound 50 temperature tempering is applied to the link material so as
around an idler (not shown) and a sprocket (not shown), and not to destroy the martensitic structure which has been
track shoes 3 clamped to the track chain 2 by bolts (not formed in the quenching process of Step 4, and in the low
shown) and nuts (not shown). Rotation of each sprocket temperature tempering, the whole link material is tempered
allows each crawler belt 1 to rotate between the idler and the at a temperature of 150° C. to 300° C. (Step 5). By virtue of
sprocket. In this way, the vehicle body travels or turns. 55
the heat treatments of Steps 4 and 5, the green body of the
The track chain 2 has laterally paired track links 10 which link material is entirely hardened, at which time the hardness
are circularly connected through coupling pins 4 and track of the region of the link material from the wheel tread 11 to
bushings 5. As shown in FIG. 2, each track link 10 has a at least the center core (depth about 30 mm) is HRC
wheel tread 11 which comes in rolling contact with a track
roller (not shown) while supporting the weight of the vehicle 60 (Rockwell Hardness) 40 or more, or more preferably,
body positioned on the upper surface of the track link 10. HRC45 to HRC55.
Opposite to the wheel tread 11 is a shoe mounting surface 12 The parts which need to be free from strain inevitably
to which the track shoe 3 is attached. At one end of the track caused by the foregoing heat treatment, and above all, the
link 10, a bushing hole 13 is defined into which a track circumferences of the parts (e.g., the bushing hole 13, the pin
bushing 5 is inserted. At the other end, there are provided a 65 hole 14 and the seal counter bore 15) which require high
pin hole 14 into which the coupling pin 4 is inserted and a dimensional accuracy and are susceptible to delayed failure
seal counter bore 15 to which a seal is fit, the pinhole 14 and due to high stress caused by press-fitting are partially
 US 7,040,080 B2
5 6
tempered at a high temperature of about 400° C. to 650° C.
(hereinafter referred to as “partial tempering') by induction TABLE 2
tempering or frame baking, so that strain is removed and the
TEM CONDITIONS
material is softened to a hardness (HRC 40 or less) which
provides comparatively high processibility and less risks of 5
RAW MATERIAL SNCM431 SCM44OMod SCM435
delayed failure, while assuring necessary strength (Step 6).
The desired parts including the parts which require high FORGING HEATING 1200° C.-12SO C. e- e
dimensional accuracy are subjected to finish processing, TEMPERATURE
whereby they are set to their respective specified dimen TREATMENT AIR COOLING e- e

sional values (Step 7). The parts which require normal 10 AFTERFORGING
PARTS TO BE PARTS 11, 12, 16, e- e
tolerance, the parts whose dimensional accuracies are not PROCESSED 17, IN FIG. 2
important and the parts (other than the press-fit parts of the AFTERFORGING (NOTE 1)
pins and bushings) in which high stress is not caused by ENTIRE 850° C. e- e
press-fitting may skip the finish machining of Step 7, pro QUENCHING
vided that the levels of strain at the stages of Steps 5 and 6 15 TEMPERATURE
in these parts are not a practical problem. By applying QUENCHING OIL e- e
tempering treatment (partial tempering treatment) to at least MEDIUM
the parts which require high dimensional accuracy and the ENTIRE 2OO C. e- e

parts which are susceptible to delayed failure due to high TEMPERING

TEMPERATURE
stress caused by press-fitting of a pin or bushing, among the PARTS SUBJECTED NEIGHBORHOOD e- e
parts of the link material which have undergone the prior TO PARTIAL OF PARTS 13, 14,
machining process Subsequently to the heat treatments of TEMPERING 1S IN FIG. 2
Steps 4 and 5, delayed failure can be prevented; strain PARTS SUBJECTED PARTS 13, 14, 15 e- e
inevitably caused by the heat treatment can be removed; and TO PROCESSING IN FIG. 2
the material can be softened and brought into easily pro 25 AFTERPARTIAL (NOTE 2)
cessable condition to carry out easy, reliable finish process TEMPERING
ing after the partial tempering, so that good cost perfor (PARTS SUBJECTED
TO FINISH
mance and high dimensional accuracy can be ensured.
The track link 10 is produced through Steps 1 to 7 MACHINING)
described earlier. FIG. 4 shows a comparison in terms of 30
Note 1:
hardness distribution between a finished product QT (QT: Since it was found that each of the parts (i.e., the bushing hole, the pin
Quenching and Tempering for hardening the entire section), hole and the seal counter bore) designated by reference numerals 13, 14,
that is, a track link produced by the production method of the 15 in FIG. 2 had a dimensional tolerance of the same level as obtained by
present embodiment and a product IQT (IQ: Induction the rough processing in hot forging, the rough processing in Step 3 of the
Quenching, T: Tempering), that is, a track link produced by present embodiment was omitted for the bushing hole 13, the pin hole 14
35 and the seal counter bore 15.
the conventional method. According to the present embodi Note 2:
ment, the entire link material is Subjected to quenching and Since it was found that the amount of strain in each of the parts (i.e., the
low temperature tempering in the heat treatments of Steps 4 wheel tread, shoe mounting Surface, shoe bolt holes and shoe nut bearing
and 5, whereby the link material is wholly hardened. As a surfaces) designated by reference numerals 11, 12, 16, 17 in FIG. 2 after
the entire tempering step (i.e., Step 5 of the present embodiment) was not
result, a soft Zone which is the problem of the prior art is not 40 a practical problem, the finish machining (i.e., Step 7 of the present
created; a deep hardened Zone is formed so as to extend from embodiment) was omitted for the wheel tread 11, the shoe mounting Sur
the wheel tread 11 to the center core as indicated by finished face 12, the shoe bolt holes 16 and the shoe nut bearing surfaces 17.
product line QT in FIG. 4; and a grain size of Gh 5 or more
can be assured up to its center core because the link material TABLE 3
of the present embodiment is not partially exposed to high 45
temperature unlike induction quenching. Accordingly, the ITEM RESULTS

wear life of the track link 10 can be markedly improved QUALITY OF MATERIAL SNCM431 SCM44OMod SCM435
while ensuring high strength. SURFACE HARDNESS HRC30 HRC34 HRC31
Next, a track link production method and track links AFTERFORGING AND AIR
produced by the same will be concretely described accord COOLING
SURFACE HARDNESS HRCS4.5 HRCS6.2 HRCS4
ing to an example of the invention. AFTER ENTIRE QUENCHING
In this example, the materials shown in Table 1 were used AND TEMPERING
and track links were produced by the production method of HARDNESS OF CENTER HRC43.5 HRC45.7 HRC42.5
the invention under the manufacturing conditions shown in 55 CORE AFTERENTIRE
QUENCHING AND
Table 2. As a result, track links having quality shown in TEMPERING
Table 3 were gained.

TABLE 1.
C Si Mn P S N Cr Mo N B

SNCM431 O.31 O.22 O.71 O.O21 O.O2O 1.65 0.71 O.16

SCM 440 Mod O40 O23 O.41 O.O1O O.OO8 - 1.01 OSO
SCM435 O.35 0.21 O.6S O.O2S O.O21 1.0S 0.16
 US 7,040,080 B2
8
2. A track link produced by the method of claim 1,
TABLE 3-continued wherein the track link comprises a center core and a wheel
ITEM RESULTS
tread that is adapted to contact a track roller, and
wherein the track link has a hardness of at least HRC40
5
QUALITY OF MATERIAL SNCM431 SCM44OMod SCM435 in an area extending from the wheel tread to the center
SURFACE HARDNESS OF HRC30 HRC31-38 HRC28 core, and a grain size of at least GhS in the center core.
PARTIALLY TEMPERED
PARTS
37 33 3. The track link according to claim 2, wherein the track
GRAIN SIZE OF CENTER Gh 6 OR e- GS OR link further comprises a pinhole and a bushing hole, and the
CORE AFTERENTIRE MORE MORE 10 track link has a hardness of not more than HRC40 around
QUENCHING AND
TEMPERING
circumferences of the pin hole and the bushing hole.
4. A method for producing a track link, wherein the track
link comprises: a wheel tread, a shoe mounting Surface to
It is understood from Table 3 that, the track links produced which a track shoe is attachable, a bushing hole, a pin hole,
from the above materials with the production method of the 15
a seal counter bore concentric with the pin hole, shoe bolt
invention are all hard from the link wheel tread to the core, holes, and shoe nut bearing Surfaces, said method compris
having Rockwell hardness high enough to withstand wear ing:
and are strong, having grain sizes of Gh 5 (JIS GO551: See hot forging a link material to have a form Substantially
Austenite Grain Size Nos.) or more, so that markedly
improved wear life can be achieved. similar to a final form of the track link;
The invention claimed is: machining the link material to process at least the wheel
1. A method for producing a track link, said method tread, the shoe mounting Surface, the shoe bolt holes
comprising: and the shoe nut bearing Surfaces:
hot forging a link material; then applying a heat treatment process to an entirety of the
machining the link material;
25 link material, said heat treatment process comprising
then applying a heat treatment process to an entirety of the quenching and low temperature tempering the entirety
link material, said heat treatment process comprising of the link material;
quenching and low temperature tempering the entirety then tempering parts of the link material Surrounding the
of the link material; 30
bushing hole, the pin hole and the seal counter bore;
and
then tempering parts of the link material which at least
one of: (i) require high dimensional accuracy, and (ii) finish machining at least the bushing hole, the pin hole
are Susceptible to delayed failure caused by high stress and the seal counter bore.
due to press-fitting; and
finish machining said parts of the link material.