U.S. patent application number 13/378415 was filed with the patent office on 2012-04-12 for engine component comprising corrosion-protection layer and method for manufacture of engine components.
Invention is credited to Magnus Bergstrom.
Application Number | 20120085310 13/378415 |
Document ID | / |
Family ID | 43356615 |
Filed Date | 2012-04-12 |
United States Patent
Application |
20120085310 |
Kind Code |
A1 |
Bergstrom; Magnus |
April 12, 2012 |
ENGINE COMPONENT COMPRISING CORROSION-PROTECTION LAYER AND METHOD
FOR MANUFACTURE OF ENGINE COMPONENTS
Abstract
An engine valve comprising a chromiferous steel and a protective
surface layer (5) which consists of iron chrome oxide. A method for
manufacture of an engine valve with a protective layer includes an
engine component of a chromiferous steel which is heated (200) at a
predetermined temperature for a predetermined time so that a layer
(5) of iron chrome oxide is formed on the engine component's
surface, and the engine component is then cooled (300) to room
temperature.
Inventors: |
Bergstrom; Magnus;
(Saltsjobaden, SE) |
Family ID: |
43356615 |
Appl. No.: |
13/378415 |
Filed: |
June 14, 2010 |
PCT Filed: |
June 14, 2010 |
PCT NO: |
PCT/SE2010/050661 |
371 Date: |
December 15, 2011 |
Current U.S.
Class: |
123/188.11 ;
148/287; 148/320; 148/325; 148/333 |
Current CPC
Class: |
F01L 3/04 20130101; F01L
2301/00 20200501; C23C 8/14 20130101; F01L 3/08 20130101; C23C 8/10
20130101 |
Class at
Publication: |
123/188.11 ;
148/287; 148/320; 148/325; 148/333 |
International
Class: |
F01L 3/04 20060101
F01L003/04; C22C 38/18 20060101 C22C038/18; C23C 8/10 20060101
C23C008/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 16, 2009 |
SE |
0950464-8 |
Claims
1. An engine component comprised of a chromiferous steel and a
corrosion-protection surface layer over the steel, the surface
layer consists of iron chrome oxide, wherein the engine component
is manufactured according to a method which comprises the steps of:
providing an engine component comprised of a chromiferous steel;
heating (200) the engine component in air at a temperature of 150
to 500.degree. C. for a predetermined time so that the surface
layer of iron chrome oxide is formed from the chromiferous steel on
the surface of the engine component; and thereafter cooling the
engine component to room temperature.
2. The engine component according to claim 1, in which the engine
component comprises a steel with a chrome content of at least 8 wt
% and up to 88 wt % of iron.
3. The engine component according to claim 1, in which the engine
component comprises a steel with a chrome content of 20-22 wt % and
an iron content of 58-65 wt %.
4. The engine component according to claim 1, in which the engine
component is heated at a temperature of between 250 and 350.degree.
C. for 1-3 hours.
5. The engine component according to claim 1, in which the surface
layer consists of FeCr2O4 and is of spinel type.
6. The engine component according to claim 1, in which the surface
layer has a thickness of 5-20 .mu.m.
7. The engine component according to claim 1, in which the surface
layer has a hardness of about 1500 HV0.1.
8. An engine component according to claim 1, wherein the engine
component (1) is an engine valve or a valve guide or a valve
seat.
9. A method for manufacture of an engine component having a
corrosion-protection layer, comprising the steps of: providing an
engine component comprised of a chromiferous steel; heating the
engine component in air at a temperature of 150 to 500.degree. C.
for a time so that the corrosion-protection layer of iron chrome
oxide is formed from the chromiferous steel on the surface of the
engine component; then cooling (300) the engine component to room
temperature;
10. The method according to claim 9, in which the engine component
is heated in air with raised oxygen content.
11. The method according to claim 9, in which the engine component
comprises a steel with a chrome content of at least 8 wt % and up
to 88 wt % of iron.
12. The method according to claim 9, in which the engine component
is heated at a temperature of between 250 and 350.degree. C. for
1-3 hours.
13. The method according to claim 9, in which the engine component
comprises a steel with a chrome content of 20-22 wt % and an iron
content of 58-65 wt %.
14. An engine component comprised of a chromiferous steel and a
corrosion-protection surface layer over the steel, the surface
layer comprises iron chrome oxide, wherein the engine component is
manufactured according to a method which comprises the steps of:
providing an engine component comprised of a chromiferous steel;
heating (200) the engine component in air at a temperature of 150
to 500.degree. C. for a time so that the surface layer of iron
chrome oxide is formed from the chromiferous steel on the surface
of the engine component; and thereafter cooling the engine
component to room temperature.
Description
TECHNICAL FIELD
[0001] The invention relates to an engine component comprising a
corrosion-protection layer and to a method for manufacture of
engine components which comprise a corrosion-protection layer.
BACKGROUND
[0002] Components of combustion engines are often subject to
corrosion due to the conditions which prevail in the engine. A
typical engine component is engine valves arranged in combustion
engines to control the flow of air to the engine's cylinders and to
control the flow of exhaust gases from the cylinders. During
operation of the engine, the valves are subject to great stresses
due to the high pressures and temperatures which prevail in the
engine's cylinders. Particularly in diesel engines which use
emission-reducing exhaust gas recirculation (EGR) for the engine's
combustion, a raised content of nitric acid and sulphuric acid in
the inlet air to the cylinders also occurs. In this context, the
composition of inlet gases and exhaust gases often results in
corrosion on valve discs and valve stems. The corrosion lowers the
strength of the valve and increases the risk of failure, with
serious consequences for the engine, particularly if the valve
breaks in the valve disc. In engine valves, intercrystalline
corrosion may occur in the valve disc, often leading to valve
failure.
[0003] The valves are also subject to wear due to the repetitive
movement which the valve performs in the engine. In particular, the
valve stem is subject to wear caused by friction between valve stem
and valve guide.
[0004] Examples of other components subject to corrosion in the
engine are valve guides and valve seats.
[0005] Coating of engine valves with protective layers is a known
practice. Specification U.S. Pat. No. 5,271,823 refers to an engine
valve which comprises a wear-resistant layer consisting of chrome
oxide and chrome carbide. The layer is applied to the engine valve
by electroplating of the valve in a liquid solution which contains
chrome ions, followed by heat treatment.
[0006] Specification U.S. Pat. No. 4,495,907 refers to a method for
coating of components in a combustion engine with wear-resistant
and thermally insulating layers. According to the method, the
component is first coated by flame-spraying with a layer of
thermally insulating material. The layer formed is thereafter
impregnated with a solution which contains a chrome compound. After
completion of impregnation, the layer is heat-treated, thereby
converting the chrome compound with which the layer is impregnated
to chrome oxide.
[0007] The protection of engine valves with layers of metallic
chrome is also known. These valves are usually coated by
electroplating.
[0008] A problem with the layers described above is that they do
not provide sufficiently good protection against corrosion of the
substrate component. This is due largely to the fact that the
layers applied do not adhere well to the surface of the part and do
not exhibit sufficient tightness. The methods described are also
labour-intensive and involve complicated thermal coating processes
and handling of liquid chemicals. The layers formed by the above
methods are also often thick, resulting in the components having to
be ground to final dimensions in a subsequent grinding
operation.
[0009] An object of the invention is therefore to propose an engine
component which has high resistance to corrosion. A further object
of the invention is to propose an effective method for manufacture
of corrosion-resistant engine components.
SUMMARY OF THE INVENTION
[0010] The above objects are achieved by an engine component which
comprises a chromiferous steel and a corrosion-protection surface
layer characterised in that the surface layer consists of iron
chrome oxide.
[0011] The iron chrome oxide layer has high tightness and exhibits
good adhesion to the engine component's surface. The engine
component is thereby effectively protected against corrosion in a
very acid environment. The tribological characteristics of the iron
oxide layer also make it possible for it to be used as a wearing
layer and to protect the stem of the valve against wear.
[0012] The engine component is with advantage manufactured by a
method comprising the steps of: [0013] providing an engine
component which comprises a chromiferous steel; [0014] heating the
engine component at a predetermined temperature for a predetermined
time so that a layer of iron chrome oxide is formed on the surface
of the engine component; [0015] cooling the engine component to
room temperature;
[0016] The iron chrome oxide layer is thus formed directly on the
steel surface of the engine component by oxidation of chrome and
iron on the surface of the engine component. The iron chrome oxide
layer therefore acquires good adhesion to the steel surface of the
engine component. The iron chrome oxide layer formed also has very
good tightness which, in combination with the good adhesion,
renders the layer very resistant to corrosion in an acid
environment. The iron chrome oxide layer formed as above
consequently protects the substrate component effectively against
corrosion. The tribological characteristics of the iron chrome
oxide layer also make it possible for it to be used as a wearing
layer and to protect the component against wear.
[0017] The engine component comprises with advantage a steel with a
chrome content of at least 8 wt % and up to 88 wt % of iron. A
chrome content of at least 8 wt % and iron are necessary for a
layer of iron chrome oxide to be formed. The engine component
preferably comprises steel with a chrome content of 20-22 wt % and
an iron content of 58-65 wt %. The high chrome content promotes the
formation of chrome iron oxides whereby a tight oxide layer is
quickly formed upon heating of the steel.
[0018] With advantage, the engine component is heated at a
temperature of between 150.degree. C. and 500.degree. C. As the
formation of the iron chrome oxide layer is a diffusion-controlled
process, the temperature needs to be at least 150.degree. C. for
the layer to grow. At lower temperatures, the growth of the layer
ceases, rendering the layer too thin to provide good corrosion
resistance. As the growth of the thickness of the oxide layer takes
place very quickly at high temperatures, the temperature should not
exceed 500.degree. C., because in that case the layer thickness
would become difficult to control. At temperatures over 500.degree.
C. there is also greater risk of changes in the structure of the
steel and greater risk of deformation of the engine component's
dimensions.
[0019] The period of time for which the engine component is heated
depends on the temperature and the intended thickness of the layer.
With advantage, the heating time adopted is within the range of 1-5
hours.
[0020] The engine component is preferably heated at a temperature
of between 250 and 350.degree. C. for 1-3 hours. This results in a
thin and tight iron chrome oxide layer which exhibits very good
adhesion to the engine component's steel surface.
[0021] The layer consists with advantage of FeCr.sub.2O.sub.4 and
is of spinel type. Such an oxide is particularly suitable for
corrosion protection in that it forms a tight layer largely free
from pores.
[0022] The layer has with advantage a thickness of 5-20 .mu.m. The
layer needs to be at least 5 .mu.m thick to achieve good corrosion
protection. High layer thicknesses increase the risk of the layer
flaking. A layer thickness of up to 20 .mu.m, preferably 10 .mu.m,
provides very good corrosion protection in combination with good
wear resistance of the layer.
[0023] The layer has with advantage a hardness of about 1500 HV0.1.
This results in good wear resistance of the oxide layer.
[0024] The engine component is preferably an engine valve or a
valve guide or a valve seat. In modern highly stressed diesel
engines with relatively large amounts of exhaust gas recirculation
(EGR) these components are subject to corrosion in the acid
environment. These components are particularly suited to protection
by iron chrome oxide layers, being components usually made of
chromiferous steel.
[0025] The invention relates also to a method for manufacture of an
engine component comprising a corrosion-protection layer,
characterised by the steps of: [0026] providing an engine component
which comprises a chromiferous steel; [0027] heating the engine
component at a predetermined temperature for a predetermined time
so that a layer of iron chrome oxide is formed on the surface of
the engine component; [0028] cooling the engine component to room
temperature.
[0029] The protective layer is formed by oxidation of the engine
component's surface without supply of substances other than oxygen
from the atmosphere in the furnace. The result is a simple and
effective method for manufacturing an engine component with a
corrosion-protection layer. As the method makes it possible to form
a thin and very tight layer, subsequent treatment such as grinding
of the valve is avoided.
[0030] According to an alternative, the engine component is heated
in air. This results in a simple and cost-effective manufacturing
method in that only air is supplied. A further advantage is that
the method is suitable for simple types of furnace which are open
to the atmosphere.
[0031] According to an alternative, the engine component is heated
in air with raised oxygen content. The raised oxygen content causes
the oxide layer to form more quickly, making it possible to
minimise the heat treatment time.
[0032] In the method according to the invention, the engine
component comprises with advantage a steel with a chrome content of
at least 8 wt % and up to 88 wt % of iron, preferably a steel with
a chrome content of 20-22 wt % and an iron content of 58-65 wt
%.
[0033] The engine component is with advantage heated at a
temperature of between 150 and 500.degree. C. The engine component
is preferably heated at a temperature of between 250 and
350.degree. C. for 1-3 hours.
DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1: A side view of an engine component according to the
invention.
[0035] FIG. 2: A cross-section of an engine component according to
the invention.
[0036] FIG. 3: A flowchart illustrating the method according to the
invention for manufacture of an engine component.
[0037] FIG. 4: An enlargement of a sample from an engine valve
which was heat-treated at 350.degree. C. in air for 3 hours.
DESCRIPTION OF EMBODIMENTS
[0038] FIG. 1 illustrates an engine component according to a first
embodiment of the invention. It depicts an engine valve, but the
engine component may also take the form of other components, e.g. a
valve seat or a valve guide.
[0039] The engine valve 1 is intended to control the flow of air
and exhaust gases in the cylinder of a combustion engine. With
advantage, the engine valve is dimensioned for diesel engines to
power heavy vehicles. These types of engines may use relatively
large amounts of exhaust gas recirculation (EGR), particularly if
this exhaust cleaning method is mainly intended to keep the
engine's emissions below permissible limit values. Nevertheless,
the engine valve may also be dimensioned for other types of
engines, e.g. petrol engines for passenger cars or motor
cycles.
[0040] The engine valve 1 comprises a valve disc 2 intended to
cooperate with a valve seat in the engine. The valve disc 2 has in
the diagram a planar upper surface 3 which, in the engine, faces
towards the combustion chamber. The engine valve also comprises a
valve stem 4 intended to move in a valve guide in the engine.
[0041] FIG. 2 depicts a cross-section through the engine valve in
FIG. 1. The engine valve's body 6 is made of a chromiferous steel.
The engine valve's surface or parts of its surface take the form of
a layer 5 of iron chrome oxide. The iron chrome oxide layer is a
spinel oxide with the chemical formula FeCr.sub.2O.sub.4 and may be
5-20 .mu.m thick. The layer is preferably 5-10 .mu.m thick. The
iron chrome oxide layer has a hardness of about 1500 Vickers
(HV0.1) and is tight, i.e. without pores.
[0042] The method according to the invention for manufacturing an
engine component which comprises a corrosion-protection and
wear-resistant surface layer is described below. The main steps of
the method may be followed in the flowchart in FIG. 3.
[0043] As a first step 100, an engine component made of a
chromiferous steel is produced.
[0044] The engine component, e.g. an engine valve, is with
advantage manufactured by forging and by cutting machining. The
material in the engine component consists of a steel with at least
8 wt % of chrome and the remainder iron. It is important that the
steel contains iron and at least 8 wt % of chrome if iron chrome
oxide is to be formed during the subsequent heating. For example,
the engine valve consists of a steel which contains 8-10 wt % of
chrome and up to 88 wt % of iron, e.g. 86-88 wt % of iron. The
remainder takes the form of other alloy substances, e.g. C, Si, Mn
and Ni. The engine valve preferably comprises 20-22 wt % of chrome
and 58-65 wt % of iron. The remainder takes the form of other alloy
substances, e.g. C, Si, Mn, Ni, N, W, Nb and Ta. Examples of
suitable steel grades are DIN 1.4718 and DIN 1.4822.
[0045] In a second step 200, the engine component is heated at a
predetermined temperature for a predetermined time so that a layer
of iron chrome oxide is formed on the engine component's
surface.
[0046] To this end, the engine component is placed in a furnace and
heated to the predetermined temperature. When the material heats
up, the oxygen in the furnace atmosphere reacts with chrome and
iron on the engine component's steel surface to form a tight layer
of iron chrome oxide. As the oxide forms directly on the engine
component's surface, the layer has very good adhesion to the
surface.
[0047] The thickness of the layer increases thereafter as oxygen
atoms from the furnace atmosphere diffuse, through the iron chrome
oxide layer formed, to the underlying steel surface and oxidise the
latter. The layer formed thus grows inwards from the surface of the
engine component towards the centre of the engine component. The
rate at which the oxygen atoms diffuse through the oxide layer
formed depends on the temperature. High temperature results in a
high diffusion rate, increasing the thickness of the layer quickly.
At lower temperatures, the diffusion rate is lower and the layer
therefore grows more slowly. The final thickness of the layer
therefore depends on the temperature at which the layer is heated
and how long the layer is heated.
[0048] The temperature adopted is with advantage in the range 150
to 500.degree. C. A temperature over 150.degree. C. is necessary
for the oxide layer to form. Over 500.degree. C., the rate of
growth of the oxide layer becomes too high, as the diffusion rate
increases exponentially with temperature. The thickness of the
layer therefore becomes difficult to control, increasing the risk
of the layer becoming too thick. There is also greater risk of
changes in the structure of the material and greater risk of
deformation at temperatures over 500.degree. C.
[0049] The period of time adopted for heating the engine component
is based on the intended thickness of the layer and the temperature
at which the engine component is heated. With advantage, the time
adopted is within the range 1-5 hours. The engine component is
preferably heated at a temperature within the range 250.degree.
C.-350.degree. C. for 1 to 3 hours. This results in an iron chrome
oxide layer with a thickness of 5-10 .mu.m which is also tight and
has good adhesion to the substrate. According to an particularly
preferred embodiment, the engine component is heated at 350.degree.
C. for 3 hours, resulting in a 10 .mu.m thick iron chrome oxide
layer.
[0050] The furnace is heated electrically or by burners and may for
example be a batch furnace for batch production or a pusher furnace
for continuous production. The atmosphere in the furnace consists
typically of air. According to an alternative, the atmosphere in
the furnace may consist of air with raised oxygen content. Adding
oxygen gas to the furnace atmosphere increases the growth rate of
the iron chrome oxide layer in that more oxygen atoms are available
for the oxidation process.
[0051] In a further step 300, the engine valves are cooled to room
temperature. According to an alternative, the cooling is effected
by the engine valves being taken out of the furnace and being
placed in still air until they have cooled to room temperature.
According to a further alternative, the engine valves are cooled by
a fan.
DESCRIPTION OF EXAMPLE
[0052] A concrete example illustrating the invention in more detail
is described below.
[0053] Four engine valves are made of a steel of grade DIN 1.4822.
The valves are numbered MV1, MV2, MV3, MV4. Samples are sawn from
the disc of each valve MV1, MV2, MV3, MV4. The samples sawn from
valves MV3 and MV4 are heat-treated in air for 3 hours at
350.degree. C. in an electrically heated batch furnace. After the
heat treatment, the weight of the samples is determined. The
samples sawn from valves MV1 and MV2 are left in untreated state as
reference material. The weight of these samples is also
determined
[0054] A heat-treated sample from engine valve MV3 is examined by
microscope. FIG. 4 is an enlarged image of the sample. It shows
part of the engine valve (on the right in the diagram) on which an
iron chrome oxide layer has formed (the narrow white region to the
left in the diagram). The thickness of the layer formed is measured
as 10 .mu.m and, as may be seen in FIG. 4, the layer is tight, i.
e. without pores. The hardness of the layer is measured in a
Vickers hardness tester as 1500 HV0.1.
[0055] Thereafter the corrosion resistance of the heat-treated
samples from engine valves MV3 and MV4 and the corrosion resistance
of the untreated samples from the reference engine valves MV1 and
MV2 are investigated.
[0056] The investigation procedure is as follows:
[0057] A solution of 720 ml of fully deionised water, 20 ml of
sulphuric acid with density 1.84 g/cm3 and 25 g of iron (III)
sulphate is prepared.
[0058] The solution is brought to the boil at about 100.degree. C.
in four separate glass flasks provided with water-cooled
cooler.
[0059] A sample from each engine valve MV1, MV2, MV3 and MV4 is
thereafter placed in the respective flask. The samples are heated
in the solution for 60 minutes at boiling point, with return of
vaporised water to the solution via the water-cooled cooler so that
the concentration of the solution remains constant.
[0060] The samples are then taken out of the flasks and the weight
of the samples is determined again. The weight loss of the
respective samples is determined from the difference between their
weight before and after treatment in the solution. The weight loss
is the percentage weight lost by sample as a result of corrosion in
the acid solution. The weight loss provides a measure of the
corrosion resistance in that large weight loss means low corrosion
resistance and small weight loss means high corrosion resistance.
Table 1 shows the weight loss of the samples after the corrosion
experiment.
TABLE-US-00001 TABLE 1 Results of corrosion experiment Weight
Weight before after corrosion corrosion Weight test test loss
Sample (gram) (gram) (percent) MV1 14.8020 6.4856 56 MV2 17.1188
8.6180 50 (untreated) MV3 15.1527 15.1499 0.02 MV4 14.0249 14.0240
0.01 (treated, 350.degree. C., 3 hours, air)
[0061] Table 1 shows a weight loss of only 0.01 to 0.02 percent by
the samples from the heat-treated engine valves MV3 and MV4. In
contrast, the samples from the untreated engine valves MV1 and MV2
have lost about fifty percent of their weight as a result of
corrosion in the acid solution. The results of the corrosion
experiment therefore show that the iron chrome oxide layer formed
at low temperature protects engine valves MV3 and MV4 against
corrosion in an acid environment.
[0062] The invention described above may be given various
alternative embodiments within the scope of the claims set out
below.
* * * * *