Note: Descriptions are shown in the official language in which they were submitted.
3~
This invention relates to a surface treatment pro- -
cess which is applied to a workpiece such as a valve cam for
an engine, for instance, for giving high abrasion or wear-
resistant properties to a slide surface thereof.
As for a process of this kind, there has been
hiterto known one in which a workpiece made of a metalli.c
material such as cast iron or the like is formed a-t its sur-
face with a remelting treatment layer by a process in which
there is generated on the surface a molten portion by a
plasma arc~and the remelted portion is then solidified by
cooling. According to this process, the remelting treatment
layer is only a hardened layer of chilled structure obtained
by increasing the cooling speed at the time of solidifica-
tion of the molten portion by cooling, for instance, and
therefore is defective in that, in the case of the applica-
tion of this process to a valve cam, for instance, it is not
always easy to give it sufficiently large wear-resistant
properties.
As for a workpiece having at its slide surface
wear-resi.stant and bite-resistant properties, there has been
hitherto known one that is manufactured by a powder metall-
urgy process, in which a material metallic powder, as a
mother material, and a sulfide powder are mixed together,
and the resultant mixture is molded under pressure and sin-
tered or one that is manufactured by a casting process in
which a molten metal is added with a sulfide powder, and
the resultant mixture is agitated and cast. These processes,
however, are disadvantageous in terms of cost, because the
sulfide, which is comparatively expensive is also mixed in
unnecessary portion of the product. Additionally, the sulfide
is kept at a high temperature for a comparatively long time,
during the sintering step in the powder metallurgy process
-- 1 --
31~
ancl during the time for:m the charging step to the sol.idi.-
fyin~ step in the c~sting pro~ess, so that the particles
thereof are decomposed and the remaining amount thereof
becomes very small, and thus it is difficult to obtai.n a
product having suffi.cien-tly large wear-resistant and bite-
resistant properties.
The invent-ion provides a surEace treatment process
by wh.ich -the foregoing defects are rernoved and there is
obtained a surface treatmen-t layer which has i.mproved such
properties.
According to the present invention there is pro-
vided a surface treatment process for a workpi.ece made of a
metallic material comprising: (a) moving a plasma torch
along the surface of the~workpiece a-t a uniform speed,
whereby a portion of said surface is melted by the plasma
arc genera-ted by the plasma torch and -the molten surface is
agitated turbulently by the plasma gas jet from the plasma
-torch, the flow rate of said plasma gas being a-t leasc 0.5
~ rl~e~ e ~
l/rninute; (b)Aconveying into an upstream portion of the
plasma arc a stream of powdered addi-tive agent carried in an
inert gas, whereby the powdered additive agent is first
hea-ted by the plasma arc and then is forcibly introduced by
the action of the plasma gas jet into the molten surface of
the workpiece wherein it is dispersed and mixed uniformly to
give a uniform melted mixture of metallic material and
additi.ve agent, said additive agent consisting of a material
which is different from the metallic material of the work-
piece; and (c) allowing the uniform melted mixture of
metallic material and addi.tive agent to solidify as a result
of the cooling action of the surrounding cold mass of metal-
lic ma-terial, whereby a surface with improved mechanical
properties is obtained.
The present invention also provides a workpiece
,~ ~~ 2 -
31~
/
made of a metallLc mate.~ial, characteri~ed i.n that its
surface contains a metal, me-tal alloy or non-me-tal, which is
no-t p.resent in the bulk of the workpiece.
In this case, -the addi-tive agent is powder of at
least one kind selected from metals such as Ni, Cr, Mo or
the like, alloys the~eof, carbides such as WC, SiC, Mo2C,
Cr3C2, B4C or the like, borides such as BN, TiB or the like,
sulfides such as MoS2, WS2, FeS or the like and oxides such
23~ sio2 or the like~?~fC~ c~,f~
~ 2a -
This invention process will be explained more in
details with reference to the accompanying drawings, in
which:-
F~ig. 1 is an explanatory diagram showing one ex-
ample of an apparatus for carrying out the process of the
invention;
Figs. 2-6 are explanatory diagrams showing res-
pective steps of the process;
Fig. 7 is a diagram showing the relationship bet-
ween the ratio % by volume of Cr sulfide and the abrasion
loss; and
- 15
Fig. 8 is a diagram showing the relationship bet~
ween the ratio % by volume of an iron sulfide and the abrasion
loss.
Referring to the drawings, numeral 1 denotes a
workpiece such as a valve cam or the like made of a metallic
material such as cast iron, aluminium alloy or the like,
and numeral 2 denotes a plasma torch facing the same. As
shown clearly in Fig. 1, the torch 2 is provided at its
center with an electrode 3, and around the electrode 3 with
a nozzle 5 through an operation gas passage 4, and also around
the nozzle S with a shield cap 7 through a shield gas pass-
age 6, and the nozzle 5 is provided at its forward end por-
tion thereof a plasma gas passage 8 which is in communica
tion with the operation gas passage 4, and the nozzle 5 is
also provided at the interior space thereof with a cooling
water passage 9. Thus, a plasma gas jet is blown against
the workpiece 1 through the plasma gas passage 8, and at the
same time a plasma arc 10 is generated therethrough between
the workpiece 1 and the electrode 3 to be applied ~o the
workpiece 1, and thereby a molten portion 11 is ~ormed on
- 3
':
3~
the surface of the workpiece 1. Thus, if -the torch 2 is
caused to scan along the workpiece 1, the mol-ten portion 11
is formed continuously and extended along on the scanning
line and the extended molten portion is gradually solidified
by cooling from the starting end thereof, so that there is
produced a remelting treatment layer. This process is not
especially different from a conventional one.
Powder of a material different in kind from -the
metallic material of the workpiece 1 is prepared as an addi-
tive agent 12 for the process, and is
introduced, alon~ with the plasma arc 10, into the molten portion
11 so as to be ~orcibly mixed in the molten portion. As for a
means therefor, as shown clearly in ~ig. 1, for instance~ a mixing
tube 13 made of ceramics, for instance, is so provided on the torch
2 as to project at its forward end toward the foregoing plasma arc
10, and the foregoing additive agent 12 is conveved by an argon gas,
for instance, -through the interior of the mixing tube 13 so as to be
supplied into the arc 1OJ ~hus, the additive agent 12 is introduced,
along with the arc 10, into the remelted portion 11 for being mixed
therein.
More in detail~ the flowing speed of the plasma jet at the
plasma torch 2 is 20 m/sec., the flowing speed of the shield gas
at the outer periphery thereof is 0.33 m/sec., and the conveying
speed of the powder is 7 m/sec., for instance, which is above 1.5 -
3 times the flowing speed of the shield gas. ~hus, the powder
may so overwhelm the shield gas flow as to be introduced into the
plasma jet.
Respective op0ration modes of thi~ invention process are as
shown in Figs. 2 - 6. Namely, in the first place, there is generated
the plasma arc 10, as shown in ~igs~ 2 and 3, between the plasma torch
2 and the workpiece 1 and thereby there is created on the surface of
the workpiece 1 a molten portion 11, as shown in ~ig. 3. On the other
hand, the additive agent 12 is conveyed by the argon gas, for instance,
through the interior of the mixing tube 13, and thereby~ as shown in
~ig. 4, the additive agent 12 is introduced into the plasma arc 10
on an upstream side thereof and is accelerated in speed by the arc
10, and is introduced, along with the arc 10, into the remelted
~J~ ~ 3~
portion 11 ~or being violently mixed therein.
At this time, the plasma -torch 2 is scar~ed in one side direc-
tion thereof and thereby, as shown in ~ig~ 5, the molten portion 11
is continuously elongated in the sca~ning direction, and is solidi~ied
the
from/starting end portion thereof in ~equence by being rapidly cooled
by a large cold mass inherent to the remainder portion of the work-
piece 1. ~hus, there is produced the remelting treatment layer lla.
During this operation, every part of the elongated molten portion 11
is agitated violently and be flown turbulently by the arc and accord-
ingly powders of the additive agent 12 contained therein are dispersed
substantially uniformly in the molten portion by the foregoing agita-
tion action, and the resultant remelting tea-tment layer lla is obtained
with such a state that the additive agent 12 is substantia:Lly uniform-
ly dispersed in the solidified layer as shown in ~ig. 6, for instance,
so that the remelting treatment layer has an improved property corres-
ponding to the additive agent 12, for instance, a wear-resisting
property.
~ he gas flowing rate of the plasma jet at the plasma arc 10 is
smaller than that in the case of a usual plasma melting and is, for
instance, 0.3 - 3.0 ~/min., and at this time the conveying speed of
the additive agent 12 is 0~5 m/sec., for instance, and the electric
current and the voltage of the arc 10 are 30 - 200 A and 20 - 30 V,
for instance, and tbe powder of the additive agent 12 is usually
below 200 micron in size and is preferably below 100 micron~
Wben powders of the additive agent 12 are mixed in the mol-ten
portion 11, the same are dispersed in its original powder form, or
at least some of thereof are molten by heat to make an alloy or a
--6--
, .~
~ 3
compound in the remelted portion 11.
Embodyin~ Exam~le 1
~ he apparatus shown in ~ig. 1 is used, and the workpiece 1
made of a FC30 Ohkoshi type abrasion test piece is treated as
follows:-
Under the condition that the plasma electric current is 50 A9the plasma gas flowing rate is 0.8 ~/min., and the plasma torch
scanning speed is 0.5 m/min., the resultant molten portion is formed
on the whole surface thereof~ and Cr powders used as the additive
agent 12 are mixed therein. The Cr powders are in the range of 5
100 micron in particle diameter, and the supply rate thereof is 0.2
g/min.
~ hus, the molten layer is formed have tbe depth of 1.8 mm from
the surface, and is solidified to become a chilled structure by a
rapid cooling and thus there is produced a remelting treatment layer
containing the Cr powders dispersed nearly uniformly in the whole
region thereof in a contact ratio of about 1.2% by volume.
The resultant product is represented by A, and a product having
a simple remelting treatment layer is represented by B~ An abrasion
test is carried out in respect of each thereof to obtain the ~ollow-
irg results.
Cr v/O ~pecific abrasion a~ount
_ _ _ _ __
A 2 8 6 x 1o~8 mm /kg
B _ _ _ _ _
A rotor used in t~e test is one prepared by such a process that
a raw material of SCM 420 is sub~ected to a carburizin~ treatment and
--7--
$i~
then is applied with a hard chrome plating of 80 micron in thick-
ness, The abrasion speed is 1.36 m/sec., the final load is 3.1 kg~
and the abrasion distance is 200 m.
Embod~ing Example 2
~ he apparatus shown in ~ig. 1 is used1 and the workpiece 1
made of a S50C Ohkoshi type abrasion test piece is treated as
follows:-
~ he whole surface of the test piece is treated under thecondition that the plasma electric current is 100 A, the plasma
gas flowing rate is 0.8 ~/min.~ and the plasma torch scanning speed
îs 0.5 m/min., and resultant molten portion is added with Mo2C powders
as the additive agent 12. ~he powders are in the range o:E 2 - 30 micron
in size, and the conveying rate thereof is 0.6 g/min. ~he resultantm~lten
layer is formed to have the depth of 1.2 mm from the surface, and is
solidified into one having a martensite structure. Thus, there is
produced a remelting treatment layer containing the powders of Mo
dispersed substantially unifromly in the whole region thereof in a
content ratio of about 3.6% by volume.
The resultant product is represented by C, and a product having
a simple remelt treatment layer is represented by D. An abrasion
test is carried out in respect of each thereof to obtain the following
results.
Mo V/o I Specific abrasion amount
_ . _
C5~2 ¦ 7~8 x 10 7 mm2/kg
. ,
D O ¦ 8.5 x 10 6mm2/kg
. _. ~ _~
~ 3
Embodying Example 3
The apparatus shown in Fig. 1 is used, and the workpiece 1
made o~ a Ni-10~u alloy Ohkoshi type abrasion test piece is
treated as follows -
The whole surface thereof is scanned by the plasma torchunder the condition that t~e plasma electric current is 100 A,
the plasma gas flowing rate is 0.8 ~/minv and the plasma torch
scanning speed is 0.5 m/min., and TiB powders as the additive
agent 12 are mixed in the molten portion. ~be supply rate there-
of is 0.4 g/min. ~he resultant molten layer is formed to have
the depth of 1.0 mm9 and is solidified to become a remelting
treatment layer containing the TiB powders dispersed substantially
uniformly in the whole region thereof in a contant ratio of about
2.6 % by volume.
The resultant product is represented by E, and a product composed
only of the remelt treatment layer is represented by ~, An abrasion
test is carried out to obtain the following results.
, , , ~
_ Ti~ / Speclflc abrasion amount
E 2.6 4,0 x 10 6 mm2/kg
_ , . " --
~ __
Embod ing Example 4
The apparatus shown in ~ig~ 1 is used, and the workpiece 1
made of a ~C30 Ohkoshi type abrasion test piece is treated as
follows:-
~ he whole surface thereof is treated under the conditionthat the plasma electric current is 50 A, the plasma gas flowing
rate ls 0.8 Q/min. and the plasma torch scanning speed is 0.5 m/min.,
-9-
.3~3
and ~eS powders as the additive agent 12 are mixed in the resultant
molten layer. The powders are 5 - ~0 micron in size, and are 0.3
g/min., in conveying rate. The molten layer is formed to have the
depth of 1.6 mm, and is solidified hy cooling into a remelting
treatment layer of chilled structure. The added FeS particles and
the resultant (FeMn)S particles generated by a reaction between
part of the FeS powders and a comp-onént Mn of the mother material
in the contained in such a state that those particles are dispersed
nearly uniformly in the whole region thereof in a content ratio of
about 20% b~ volume.
~he resultant product is represented by G, and a product hav- ;
ing a simple remelt treatment layer is represented by H. An abra-
sion test is carried out in respect of each thereof to obtain the
following results.
~eMn)~ ~o Specific abrasion amount
G 2.0 6.9 x 10 8 mm /kg
_. _ __
H O 2.2 x 10 7 mm2/kg
l ~ _ _ . ~ . _~
Embodyin~ ~Xa~le 5
~ he apparatus shown in ~ig. 1 is used, and the workpiece 1
made of an Al alloy AC2~ Ohkoshi type abrasion test piece is treat-
~d as follows:-
~ he whole surface thereof is treated under the condition thatthe plasma electric current is 100 A, the plasma gas flowing rate
is 0~8 ~/min., and the plasma torch scanning speed is 0.8 m/min,,
and the resu~tant molten layer is mixed with A1203 powders as the
- 10--
.. . . .. ... .... . . .
~ 3~
additive agent 12. The powders are 0.5 - 10 micron in size, and
0.6 g/minO in conveying rate. The remelting treatment layer
solidified by cooling thereof is fo~med to have the depth of 0.8
mm, and contains the A1203 powders, substantially uniformly
dispersed state in the whole region of the solidified layer in a
content ratio of about 6.0% by volume~
The resultant product is represented by I, and a product hav-
ing a simple remelt treatment layer is represented by J An abrasion test
is carried out in respct of them to obtain the following results.
IA120~o ¦ Specific abrasion amount
I ¦ 6.0 8.3 x 10 6 mm /kg
J 6.2 x 10 5 mm2/kg
As will be clear from each of the ~oregoing embodying examples,
the workpiece 1 in each example is extremely improved in its abrasion
resisting property by the additive agent mixed therein.
~mbod in~, ~xam~le 6
_ _ _ _
~ he apparatus shown in ~ig. 1 is used, and the workpiece 1 for
a stator made of a FC30 Ohkoshi type abrasion test piece is treated
as described below. ~amely, a slide surface thereof is treated
under the condition that the plasma arc electric current is 80 A,
the plasma gas flow rate is 0.8 ~ /min.j and the plasma torch scanning
speed is 0.3 m/min., and the molten portion 11 thereof is added with
Cr2S powders of 2 - 10 micron in si3e by being conveyed at a ra-tio
3 thus
of 1.2 g/min. by an Ar gas. ~he resultant molten layer/formed has
the deptb of 1.2 mm from the surface thereof, and after solidifica-
tion thereof there is formed a remelting treatment layer containing
.
--11--
~l$~3~3
such a dispersed particles of a mixture of a Cr series sulfide
comprising (CrFe)2$3, ~CrFeMn)2S3, ~CrFe)3S4, (CrFeMn)3S~ gene-
rated by the reaction of the added Cr2S3 with Fe of the mother
material Fe and an alloying element Mn thereof. This Cr sulfide
mixture is 7.5% in volume ratio, and those particle sizes thereof
are about 1-8 micron. In this process, the molten portion 11 is
rapidly solidified, by the cold mass of the remaining portion of
the motor metallic material into a chilled structure of ledebur-
ite deposi-tion, in which (CrFe)2S3, (CrFe)3S4, (CrFeMn)2S3 and
(CrFeMn)3S4 are dispersed therein.
The resultant product is subjected to a grinding treat-
ment at its slide surface to obtain a test piece K. For compari-
son purpose, there is made a product having a simple remelting
treatment layer of chilled structure not added with the Cr2S3
powders.
This product is subjected to a grinding treatment at
its slide surface to obtain a test piece L. In almost the same
manner as in the embodying Example 1, an abrasion test is carried
out in respect of each thereof to obtain the following results.
~ . ~
Disperse~ material con~aining ratio Speciflc aDra-
_ % ~ ~ v~ ume _ io~ ~ ;
Kv ~r sulfide ~ 7.~ _ ~
l _ 2 2x~10_ mm /~kg
Embodyinq Example 7
The apparatus shown in Fig. 1 is used, and the work-
piece 1 made of a carbon steel of ~e and C (0.50%). Namely, a
slide surface thereof is molten under the condition that the
plasma arc current is 80 A, the plasma arc AR gas flowing rate
- 12 -
,, .
,
`~
is 1 ~/min., and the plasma torch zigzag scanning speed ls 0.3 m/minO,
and the molten portion 11 thereof is supplied with a mixture of 50
weight % of Cr3C2 powders of 2 - 10 micron and 50 weight % of MoS2
powders of 5 - 60 micron at a supply rate of 0.1 g/min. by the Ar
gas. As a result of solidification thereof there is formed such a
remelting treatment layer that, particles of chrome sulfides compris-
ing Cr2S3 and Cr3S4 produced by the reaction between the components
of the mixture powders are uniformly distributed in t~e molten layer
11 having the depth of 1.4 mm from the surface thereof. ~be chrome
sulfides are about o~5o/o by volume in containing ratio and about 1 - 9
micron in particle siYIe. ~he resultant product is subjected to a
grinding treatment at its slide surface to be used as a test piece M.
~or comparison purpose, a product having a simple remelting treatment
layer is prepared to be used as a test piece N. In almost the same
manner as in the embodying example 1, an abrasion test is carried out
in respect of eac~ thereof to obtain the following resul~s.
~est piece Dispersed Containing Speclflc abrasion amount
material by ~olume
. _ _ _ ___
M Cr sulfide 0.5 % 3.6 x 10 6 mm2/kg
. _ _ _ _ _ _ _ _
N _____ --- 8.5 x 10 6 mm2/kg
.
8mbod in ~ - ~
~ be apparatus shown in ~ig. 1 is used, and the workpiece 1
which is a cam lift portion of a cam shaft made of ~C30 for being
built in an engine for a motorcar is subjected to such a remelting
treatment as described below. Namely, the surface thereof is treated
3~
under the condition that the plasma arc electric current is 60 A,
the plasma arc Ar gas flow rate is 0.5 Q/min., and the torch sca~ning
speed is 1 m/min~, and ~ powàers oI 2 ~ 10 micron in size as
the additive agent 12 are supplied to the molten layer 11 a-t a
supply rate of 0.6 g/min. ~hus, after solidification thereof, there
is formed a remelting treatment layer, that is, a chilled hardened
layer of 1.8 mm in thickness containing therein various kinds of
Cr sulfides such as (CrFe~2S3, (Cr~eMn)2S3, (Cr~e)3S~ and (Cr~eMn)3S4
which are uniformly dispersed therein. The Cr sulfides are 2.2% by
v31ume in containing ratio and are 1 - 8 micron in particle size,
and the hardened layer thereof is HRC 58 in hardness.
~ he resultant cam shaft is subjected, at its cam surface, to a
grinding treatment to obtain a test piece O used for a service test,
that is, an operational ~uitability test. On the other hand, a cam
shaft of the same material as above is subjected to a remelting
treatment which is under the same condition as above, but is not
added with any additive agent, to obtain a cam shaft test member P.
~he hardened layer thereof is 1.9 mm in thickness and is HRC 51 in
hardness.
Service test condi_ion
~ ngine speed 1,000 r.p.m. Oil temperature 65C
~ est time 200 hours
As a result of the tests, the abrasion loss amount of the cam
top of the test member O is 10 micron in depth, while the abrasion
loss amount of the cam top of the test member P is 120 micron in
depth.
-14-
~f~ 3~3
~ he apparatus shown in Fig~ 1 is used, and the workpiece 1
which is a valve rocker arm made of ~CM420 for being built in an
engine for a motorcar is applied at its slipper surface with such
a remelting treatment as described below. Namely, the slipper
surface portion thereof is treated under the condition that the
plasma arc current is 45 h, the plasma arc Ar gas flowing rate is
o.5 R~min., the troch scanning speed is 0.8 m/min., and the supply
rate of Cr2S3~powders of 2 - 10 micron in size is O.L~ g/min., where-
by a molten portion is formed on the slipper surface and is added
with the powders. As a result of dolidifying the molten portion,
there is obtained such a remelting treatment layer, tha-t is~ a
cbilled hardened layer containing evenly dispersed particles of Cr
sulfides comprising a mixture of (CrFe~2S3, (Cr~eMn)2S~, (Cr~e)3S~
and (CrFeMn)~S4 generated by reaction of the additive Cr2S3 with
the main component ~e and a partisl component Mn of the mother
material. ~he hardened layer lS 1 . O mm in thickness and the Cr
sulfides thereof contained therein are 3.4% by volume . The product
is subjected to a carburizing treatment and is then subjected to a
grinding treatment to obtain a test piece Q. On the other hand,
the slipper surface of a valve rocker arm of the same materiaI as
above is not subjected to a -simple remelting treatment but is
subjected to only a carburizing treatment to obtain a test piece R.
A service test is carried out in respect of each of these two test
pieces under the condition as listed below. As a result thereof,
it has been found that the abrasion loss amount in depth of the
s}ipper surface of the test piece Q is 3 micron, and that of the
slipper surface of the test piece is 50 micron.
-15-
3~3
Test Condition:
Engine speed 1,000 r.p.m. Oil temper2ture 65C
Test operation time 2~0 hours
EmbodYin~ Exam~le 10
~ he apparatus shown in Fig. 1 is used, and the workpiece 1
which is a stator made of a ~CD55 Ohkoshi type abrasion test
piece is subjected to such a remelting treatment as described below.
Namely~ a slide surface thereof is treated under the condition that
the plasma arc electric current is 80 A, the plasma arc Ar gas flow
rate is ~ /min. and the troch scanning speed is 0.3 m/min. The
molten layer thus formed is supplied with the additive agent of ~eS
powders of 5 - 40 micron in size at a supply rate of 1.5 gjmin.
conveyed by an Ar gas. ~he molten layer is 1.2 mm in thickness.
During this operation, some of the FeS powders added reacts with
the main component ~e and an Mn component of the mother material and
o generate (~eMn)S, and as a result o~ solidification thereof, there
hardened
is produced a remelting treatment layer, that is, a/layer containing
uniformly distributed particles of iron sulfides comprising a
mi*ture of FeS and (~eMn)S. The distributed particles are 1 - 9 in
particle size, and is 15% by volume in containing ratio. The
resultant product is subjected to a grinding treatment at its slide
surface to obtain a test piece S. ~or comparison purpose, the work-
piece 1 of the same material as above is subjected to a simple
remelting treatment under the same condition as above, without
addition of any additi~e agent~to obtain a test piece ~. An
abrasion test is carried out i~ the same ma~ner as in the embodying
example 1, in respect of each of the two test pieces S, ~, to obtain
-16-
the following results.
~est ~isperseà I Con~aining I Spe~ci~ic a~~rasion amount
plece sulfide ~ ratlio /o by ~ _ _ _ _
S FeS and ¦ 15% 14 . 5 x 10 8 mm2/kg
(~eMn)S l l
2.2 x 10-7 m~2/~g
Embodying Example 11
~ he apparatus shown ain ~ig. 1 is used, and the workpiece 1
which is a stator made of/S50C abrasion test piece is subjected to
the remelting treatment as described below. Namel~, a slide surface
thereof is treated under the condition that the plasma arc electric
current is 80 A, the plasma arc Ar gas flowing rate is 1 ~ /min., and
the troch zigzag scanning speed is 0.3 m/min. ~he resultant molten
layer of the depth of 1.4 mm is supplied with MoS powders of 10 -
40 micron in size at such a supply rate of 0.15 g/min. conveyed by
an Ar gas. Consequently, there is obtained a hardened layer contain-
ing uniformly dispersed particles of ~eS and (~eMn)S generated by
reaction of the additive MoS with the components ~e and Mn o~ the
mother material. ~he resultant particles are about 1 - 7 micron
in size, and are about 0.8% by volume in content ratio.
~ he resultant product is applied at its slide surface with a
grinding treatment to obtain a test piece U. ~or comparison purpose,
the workpiece 1 of the same material as above is subjected to a simple
remelting treatment u~der the same condition as above~ but without
addition of any additive agent, to obtain a test piece V.
~ he same abrasion test as above is carried out in respect of
these test pieces to obtain the following results.
_17-
~3~
_ _ ~ -- I ~r ~ - ~ 1
est Dispersed Contalnlng S?eclllc abraslon amoun~
iece sulfide ratio
% by Vo
__ I ~
UFeS and o 8 o/O ! 4.2 x lo-6 mm2/kg
(FeMn)S
_ _ _; -
V _ _ ~ 8.5 x 10-6 mm2/Xg
_
Embod~ln~ Example 12
~ he apparatus shown in ~igo 1 is used, and the workpiece 1
which is a cam lift portion of a cam shaft of FC30 for being built
in an engine for a motorcar is subjected to the remelti~g treat-
ment as described below. Namely, the surface of the cam lift por-
tion is moltened under the condition that the plasma arc electric
current is 60 A, the plasma arc Ar gas flowing rate is 0.5~ /min.,
and the torch scanning speed is 1 m/min. ~he additive agent of WS2
powders of 2 - 10 micron in size is supplied to the molten portion
at a supply rate of 0.6 g/min. conveyed by gas. ~he resultant
molten layer is 1.8 mm in depth and is solidified. Consequently,
there is formed a hardened layer containing uniformly dispersed
particles of Fe~ and (~eMn)~ generated by reaction of the additive
WS2 with composition elements ~e, Mn of the mother material. The
dispersed particles are about 1 - 10 micron in size, and are 2.8 %
'Dy volume in content ratio. ~he hardened layer is HRC5~ in hard-
ness. ~his cam shaft is subjected to a grinding treatment to obtain
a test piece W. A cam shaft of the same material as above is
subjected to a simple remelting treatment to obtain a test piece X.
The hardened layer thereof is HRC51 in hardness. A serving test is
made in respect of each of these test pieces, under t~e condition
-18-
that the engine speed is 1,000 r.p.m., the oil tempera~ure is 65C,
and the rest operation ! imP ~ s 2~0 hours. As a resulv tnereof, the
abrasion loss amount Or the vest piece U is 30 micron in depth, and
that of the test piece V is 12G micron in dep-th.
~mbod~in~ Exam~le 13
~ .
~ he apparatus shown in Fig. 1 is used, and the workpiece 1 which
is a valve rocker arm made of SCM420 for being built in an engine for
a motorcar is subjected, at its slipper surface, to the remelting
treatment as described below. Namely, the slipper surface is applied
with the remelting treatment under the condition that the plasma arc
current is 45 A, the plasma arc Ar gas flowing rate is 0.5 R/min., and
the plasma torch scanning speed is 0~8 m/min. ~he additive agent of
powders FeS is conveyed by an Ar gas and is supplied to the resultant
remelted portion at a supplying rate of 0~4 g/min. After solidifica-
tion thereof there is produced a hardened layer containing dispersed
particle (Fe~n)S, generated by reaction of some of the added ~eS
powders with a component Mn of the mother material, and the added
~eS particles. ~he particles FeS, and (FeMn)S are about 1 - 8
micron in size~ and are about 3.2% by volume in content ratioO ~he
workpiece 1 thus treated is then subjected to a caburizing treat-
ment for being further improved in hardness of the slipper surface
thereof~ ~he hardened layer is about 1.2 mm in thickness, and has
such a wear-resisting structure layer that the foregoin~ sulfides
are mixed in the caburized hardened layer. ~he product is applied
at -ts surface with a grinding treatment to obtain a test piece W.
~or comparison,the workpiece 1 of the same material as above is
applied with a simple remelting treatment, and is then formed into
-19-
3~1
that having a wear-resisting structure layer by the same carburizing
treatment as above to obtain a test piece X~ In respect of each of
'hese test pieces W, X, a service test is carried out under the condi-
tion that the engine speed is 1~000 r.p.m., the oil temperature is
65C, and the test operation time is 200 hours~ As a result thereof,it
has been found that the test piece W is 10 micron in depth in abrasion
loss amount and the test piece X is 50 micron in depth in abrasion
loss amount.
As will be clear from the foregoing embodying examples 1 - 13,
if any of various kinds of additives such as of Cr, Mo? TiB, A1203,
~eS and other sulfides or the like is mi~ed in the molten layer of the
workpiece to be treated, the resultant remelting treatment layer is
improved in its wear-resisting property as compared with that not
added therewith. Especially~ a Cr series sulfide, in comparison
with other sulfides, is advantageous in that the same is so high in
stability at a high temperature that it is not decomposed, even at
a temperature of above l,000C to result in producing a very stable
slide surface and, in addition, serves as a lubricant.
~ he additive powder to be used is usually below 200 micron in
particle diameter and is preferably below 100 micron. ~nen the
powder particles are added in the molten layer formed on the surface
of the workpiece to be treated, the same is changed into liquid
are applied
particles ard at the same time~ in this liquid state, with the
current of the plasma arc, so that the molten layer is agitated ~`
violently and at the same time the liquid particles contained
therein are finely divided by such a turbulent flow of molten metal
and the finely divided particles are solidified by cooling action of
-20- - -
~ 3~3
the cold mass of the mother metallic material. Accordingly, there
is obtained such a surface trea-tment layer that the finely divided
solid particles thereof a~e dispersed in the solidified metallic
layer. lt is preferable that the dispersed particles contained in
the solidified layer are in the range of about; 1 - 20 micron in
diameter, and an internal stress concentration ratio is decreased
thereby, so that the product is excellent in pitching-resisting
property~ bite-resisting property, and other properties, and in
addition the lubrication effect of the sulfide can be easily given
uniformly on the slide surface thereof. Additionallyj if a fric-
tion movement t~ereof is repeated during operation of the product,
the particles content therein are expanded, and thereby a coating
of the sulfide of from several ten to several handred A in thick-
ness is liable to be formed on the surface thereof.
According to this invention, the remelting treatment time is
usually only about 1 second or below, so that it is advantageous
in that there is not caused a substantial loss of the additive
amount caused by a thermal decomposition thereof.
Fig. 7 shows a result of examination of relations between a
content ratio of a Cr sulfide and an abrasion loss amount of a
product, in respect of a cam shaft made of ~C30 for a motorcar
engineO As will be clear therefrom, an effect for improving
an abrasion or wear reslsting property is exerted from above
nearly 0.2% by volume and is remarkable by addition of a small
amount thereof. However, if the addition amount thereof is
above about 12% by volume, the product tends to be lowered in its
thoughness, and more addition thereof becomes expensive. Therefore,
-21-
3 ~
from the viewpoint of economy, it is preferable to limlt the
addition amount thereo~ to about 12% at the maximum.
Fig. 8 shows a result of examination of relations between
a content ratio of an iron sulfide (F~ + (~eMn)S) and an abrasion
loss amount of a product, in respect of a cam shaft of ~C30 for a
motorcar engine. In this case, the ef~ect of the sulfide is
exerted when the addition thereof is above 0.5%. However, even if
the addition amo~nt thereof is increased, to more than about 20%,
more improvement is not made, so that it is preferable from an
ecconomincal viewpoint that the addition thereof is limited to
about 20% at the maximum.
Thus, according to this invention, during the time when a
workpiece is being moltened at its surface by a plasma arc, powders
of any kind of material other than the material of the workpiece are
introduced, along with the arc, into the resultant molten portion for
being mixed therein, so that the powders can be dispersedly contained
in the molten portion layer, and after solidification thereof there
can be obtained a remelting treatment layer which has been improved
in wear-resisting property.
Therefore, when this invention process is applied to a slide
surface of a valve cam for an engine, for instance, there can be
produced one having an excellent wear-resisting property, and the
operation thereof is comparatively simple, and in addtion, the
additive powders are not subjected to the heat for a long time.
so that there hardly occurs a thermal decomposition loss of
efficient distributed particles.
-22-
