SE533842C2 - Engine component including corrosion protection layer and method for manufacturing engine component - Google Patents

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.

Description

25 30 533 842 It is known to coat motor valves with protective layers. Document US5271823 discloses a motor valve which comprises an abrasion resistant layer consisting of chromium oxide and chromium carbide. The layer is applied to the motor valve by electroplating the valve in a liquid solution containing chromium ions and subsequent heat treatment.

Document US4495907 discloses a method for coating components of an internal combustion engine with abrasion resistant and thermally insulating layers.

According to the method, the component is first coated by injection molding with a layer of thermally insulating material. The formed layer is then impregnated with a solution containing a chromium compound. After the impregnation is completed, the layer is heat-treated, whereby the chromium compound with which the layer has been impregnated is converted to chromium oxide.

It is also known to protect motor valves with layers of metallic chrome.

These valves are usually coated by electroplating.

A problem with the layers described above is that they do not provide sufficient protection against corrosion of the underlying component. This is largely due to the fact that the applied layers show weak adhesion to the surface of the part and that the layers do not show a sufficiently high density. The methods described are also labor intensive and include complicated thermal coating processes as well as the handling of liquid chemicals.

Furthermore, the layers formed by the above methods often become thick, whereby the final dimension of the components must be ground for a subsequent grinding operation.

An object of the invention is therefore to provide an engine component which has a high resistance to corrosion. A further object of the invention is to provide an efficient method for manufacturing corrosion-resistant engine components. SUMMARY OF THE INVENTION The above object is achieved by an engine component comprising a chromium-containing steel and a corrosion-protective surface layer characterized in that the surface layer consists of iron-chromium oxide, according to claim 1.

The iron chromium oxide layer has a high density and shows good adhesion to the surface of the engine component. This effectively protects the engine component against corrosion in very acidic environments. The tribological properties of the iron oxide layer further mean that it can be used as a wear layer and protect the valve shaft against wear.

The engine component is suitably manufactured by a method comprising the steps of: - providing an engine component comprising a chromium-containing steel; - heating the engine component at a predetermined temperature and for a predetermined time so that a layer of iron chromium oxide forms on the surface of the engine component; - cooling the engine component to room temperature; The iron chromium oxide layer is then formed directly on the steel surface of the engine component by oxidation of chromium and therefore the steel surface of the engine component. The formed iron chromium oxide layer further has iron on the surface of the engine component.

The iron chromium oxide layer has very good adhesion at very high density, which in combination with the good adhesion makes the layer The iron chromium oxide layer formed as above consequently effectively protects it very resistant to corrosion in acidic environments. underlying component against corrosion. The tribological properties of the iron chromium oxide layer further mean that it can be used as a wear layer and protect the component against wear. The engine component suitably comprises a steel with a chromium content of at least 8% by weight and up to 88% by weight of iron. A chromium content of at least 8% by weight and iron is necessary for the formation of iron chromium oxide layers.

Preferably, the engine component comprises a steel with a chromium content of 20 - 22% by weight and an iron content of 58 - 65% by weight. The higher chromium content favors the formation of chromium iron oxides, whereby a dense oxide layer is quickly formed when the steel is heated.

Suitably the engine component is heated at a temperature between 150 ° C to 500 ° C. Since the formation of the iron chromium oxide layer is a diffusion-controlled process, the temperature should be at least 150 ° C for the layer to grow. At lower temperatures, the growth of the layer stops, whereby the layer becomes too thin to give good corrosion resistance. Since the growth of the oxide layer thickness is very fast at high temperatures, the temperature should not exceed 500 ° C because the layer thickness then becomes difficult to control. At temperatures exceeding 500 ° C, the risk of changes in the structure of the steel and the risk of deformation of the dimensions of the motor component also increases.

The time during which the motor component heats up depends on the temperature and the thickness of the layer. Preferably, the heating time is selected in the interval 1 - 5 hours.

Preferably, the engine component is heated at a temperature between 250 to 350 ° C for 1-3 hours. Thereby a thin and dense iron chromium oxide layer is produced which exhibits a lot against good adhesion of the steel surface of the engine component.

The layer suitably consists of FeCr2O4 and is of the spinel type. Such an oxide is particularly suitable for corrosion protection because it forms a dense and substantially pore-free layer. 533 842 The layer suitably has a thickness of 5 - 20 μm. The layer should be at least 5 μm thick in order to obtain a good corrosion protection. At high layer thicknesses, the risk of the layer flaking increases. Up to a layer thickness of 20 μm, preferably 10 μm, very good corrosion protection is obtained in combination with good wear resistance of the layer.

The layer suitably has a hardness of about 1500 HVO.1. good abrasion resistance of the oxide layer is achieved.

Thereby Preferably, the engine component is a motor valve or a valve guide or a valve seat. In modern high-load diesel engines with a share (EGR), these components are exposed to corrosion in the acidic environment. These components are especially relatively large exhaust gas recirculation suitable for protection with iron chromium oxide layers since the components are usually made of chromium-containing steels.

The invention also relates to a method for manufacturing an engine component comprising a corrosion-protective layer! of the steps: - providing an engine component comprising a chromium-containing steel: - heating the engine component at a predetermined temperature and for a predetermined time so that a layer of iron chromium oxide is formed on the surface of the engine component; - cool the engine component to room temperature.

The protective layer is formed by oxidation of the surface of the engine component without the addition of substances other than oxygen from the atmosphere in the furnace. Thereby a simple and efficient method is obtained for manufacturing an engine component with a corrosion-protective layer. Since the method enables the formation of thin and very dense layers, subsequent treatment such as grinding of the valve can be avoided. 10 15 20 25 30 533 842 According to an alternative, the engine component is heated in air. This achieves a simple and cost-effective manufacturing method because only air is supplied. An additional advantage is that the method is suitable for simple oven types that are open to the atmosphere.

According to an alternative, the engine component is heated in air with elevated oxygen content. The elevated oxygen content causes the oxide layer to form faster. Thereby, the time for the heat treatment can be minimized.

In the method according to the invention, the engine component suitably comprises a steel with a chromium content of at least 8% by weight and up to 88% by weight of iron, preferably a steel with a chromium content of 20 - 22% by weight and an iron content of 58-65% by weight.

Suitably the engine component is heated at a temperature between 150 to 500 ° C. Preferably, the engine component is heated at a temperature between 250 to 350 ° C for 1-3 hours.

DESCRIPTION OF THE FIGURES Figure 1: A side view of an engine component according to the invention.

Figure 2: A cross section of an engine component according to the invention.

Figure 3: A flow chart describing the method according to the invention for manufacturing an engine component.

Figure 4: A magnification of a sample from a motor valve heat-treated at 350 ° C in air for 3 hours.

DESCRIPTION OF EMBODIMENTS Figure 15 discloses an engine component according to a first embodiment of the invention. Figure 1 shows a motor valve, but the motor component can also consist of other components, such as a valve seat or a valve control.

The engine valve 1 is intended to control the flow of air and exhaust gases in the cylinder of an internal combustion engine. Suitably, the engine valve is dimensioned for diesel engines for driving heavy vehicles. For these types of engines, the use of exhaust gas recirculation (EGR) can be relatively extensive, especially if this exhaust gas cleaning method is the main one to keep the engine emissions below the permissible limit values. Nevertheless, the engine valve can also be dimensioned for other types of engines, such as petrol engines for cars or motorcycles.

The motor valve 1 comprises a valve plate 2 which is intended to cooperate with a valve seat in the motor. The valve plate 2 has in the figure a flat upper surface 3 which, in the engine, is directed towards the combustion chamber. Furthermore, the motor valve comprises a valve shaft 4 intended to move in a valve control in the motor.

Figure 2 shows a cross section through the motor valve in figure 1. The body 6 of the motor valve consists of a chromium-containing steel. The surface of the motor valve or parts of its surface consists of a layer 5 of iron chromium oxide. The iron chromium oxide layer is a spinel oxide with the chemical formula FeCr 2 O 4 and can be 5 - 20 μm thick.

Preferably the layer is 5 - 10 μm thick. The iron chromium oxide layer has a hardness of about 1500 Vickers (HVO.1) and is dense, ie without pores.

In the following, the method according to the invention for manufacturing an engine component which comprises a corrosion-protecting and durable surface layer is described. The main steps in the method can be followed in the fate diagram in Figure 3. In a first step, 100, an engine component consisting of a chromium-containing steel is produced. 10 15 20 25 30 533 842 The motor component, eg a motor valve, is suitably manufactured by forging and cutting machining. The material in the engine component consists of a steel with at least 8% by weight of chromium and the remaining proportion of iron. It is important that the steel contains at least 8% by weight of chromium co-iron in order for iron chromium oxide to be formed during the subsequent heating. For example, the motor valve consists of a steel that contains 8-10% by weight of chromium and up to 88% by weight of iron, eg 86-88% by weight of iron. The remaining proportion consists of other alloying elements such as C, Si, Mn and Ni. and 58 - 65% by weight of iron. The remaining proportion consists of other alloying elements such as C, Si, Mn, Ni, N, W, Nb and Ta. Examples of suitable steels are the steel grades DIN 14718 and DIN 1.4822.

Preferably, the motor valve contains 20 - 22% by weight of chromium in a second stage, 200 the motor component is heated at a predetermined temperature for a predetermined time so that a layer of iron chromium oxide is formed on the surface of the motor component.

The motor component is then placed in an oven and heated to the predetermined temperature. When the material is heated, the oxygen in the furnace atmosphere reacts with chromium and iron on the steel surface of the engine component, forming a dense layer of iron chromium oxide. Since the oxide layer is formed directly on the surface of the motor component, the layer has very good adhesion to the surface.

The thickness of the layer then increases as oxygen atoms from the furnace atmosphere diffuse through the formed iron chromium oxide layer to the underlying steel surface and oxidize it. The layer formed thereby grows from the surface of the motor component inwards towards the center of the motor 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, with the layer rapidly increasing in thickness. At lower temperatures, the diffusion rate is lower and the layer therefore grows more slowly. The final thickness of the layer is therefore dependent on the temperature at which the layer is heated and how long the layer is heated. The temperature is suitably selected in the range 150 to 500 ° C. A temperature above 150 ° C is necessary for the oxide layer to form. Above 500 ° C, the growth rate of the oxide layer becomes too high because the diffusion rate increases exponentially with temperature. The thickness of the layer therefore becomes difficult to control and the risk of the layer becoming too thick increases. Furthermore, the risk of changes in the structure of the material exceeds 500 ° C increases. and the risk of deformation at temperatures The time at which the motor component is heated is selected on the basis of the thickness at which the layer is to have and the temperature at which the motor component is heated. Preferably, the time is selected in the interval 1 - 5 hours. Preferably, the engine component is protected at a temperature in the range of 250 ° C - 350 ° C for 1 to 3 hours. This provides an iron chromium oxide layer with a thickness of 5 - 10 μm, the layer is also dense and has good adhesion to the substrate. According to a particularly preferred embodiment, the motor component is heated at 350 ° C for 3 hours, whereby a 10 μm thick iron chromium oxide layer is provided.

The furnace is heated electrically or with a burner and can be, for example, a batch furnace for batch production or a cutting furnace for continuous production. The atmosphere in the oven typically consists of air. According to an alternative, the atmosphere in the furnace may consist of air with elevated oxygen content. By adding oxygen to the furnace atmosphere, the growth rate of the iron chromium oxide layer increases because your oxygen atoms are available for the oxidation process.

In a further step, 300 the motor valves are cooled to room temperature. According to an alternative, the cooling takes place by removing the motor valves from the oven and placing them in stagnant air until they have cooled to room temperature. According to an additional alternative, the motor valves are cooled by a fan.

DESCRIPTION OF EXAMPLES The following is a concrete example which describes the invention in more detail. 10 15 20 25 30 533 842 10 Four motor valves were made of a steel of the type DIN 1.4822. The valves were numbered MV1, MV2, MV3, MV4. Samples were sawn out of the plate of each valve MV1, MV2, MV3, MV4. The samples sawn out of valves MV3 and MV4 were heat treated in air for 3 hours at 350 ° C in an electrically heated batch furnace. After the heat treatment, the mass of the samples was determined. The samples sawn out of valves MV1 and MV2 were left untreated as reference material. The mass of these samples was also determined.

A heat-treated sample from the motor valve MV3 was examined under a microscope.

Figure 4 is an enlarged view of the sample. Figure 4 shows a part of the motor valve (on the right in the picture) on which an iron chromium oxide layer has formed (the narrow white area on the left in the picture). The thickness of the formed layer was measured to 10 μm and as can be seen from Figure 4, the layer is dense, i.e. without pores. The hardness of the layer was measured in a Vickers hardness tester to 1500 HVO.1.

Then, the corrosion resistance of the heat-treated samples from the motor valves MV3 and MV4 and the corrosion resistance of the untreated samples from the reference motor valves MV1 and MV2 were examined.

The test was carried out as follows: A solution was prepared from 720 ml of completely deionized water, 20 ml of sulfuric acid with a density of 1,84 g / cm3 and 25 g of ferrous sulphate.

The solution was brought to a boil at about 100 ° C in four separate glass flasks equipped with water-cooled coolers.

A sample from each motor valve MV1, MV2, MV3 and MV4 was then placed in a glass flask. The samples were heated in the solution for 60 minutes. During boiling, evaporated water was returned to the solution via the water-cooled condenser so that the concentration of the solution was kept constant.

The samples were then taken out of the glass flasks and the mass of the samples was determined again. From the difference between the mass of each sample before and after treatment in the solution, the mass loss of the samples was determined. The mass loss is the mass, in percent, that each sample lost due to corrosion in the acidic solution. The mass loss is a measure of the corrosion resistance, with large mass loss means low corrosion resistance and small mass loss high corrosion resistance. Table 1 shows the mass loss of the samples after the corrosion tests, Sample Mass before Mass after Mass loss corrosion test corrosion test (percent) (grams) (grams) MV1 14.8020 6.4856 56 MV2 17.1188 8.6180 50 (untreated) MV3 15.152? 15.1499 0.02 MV4 14.0249 14.0240 0.01 (treated, 350 ° C, 3 hours, air) Table 1: Results from corrosion tests Table 1 shows that the samples from the heat-treated motor valves MV3 and MV4 show only one mass loss of 0.01 to 0.02 percent.

The samples from the untreated motor valves MV1 and MV2, on the other hand, lost about fifty percent of their weight due to corrosion in the acid so that the iron chromium oxide layer formed at low temperature protects the motor valves solution. The results from the corrosion tests show MV3 and MV4 against corrosion in acidic environments. The invention described in the above can be given various alternative embodiments within the scope of the following claims.

Claims (12)

10 15 20 25 30 533 842 lay PATENT REQUIREMENTS Engine component (1) comprising a chromium-containing steel and a corrosion-protective surface layer (5), characterized in that the surface layer (5) consists of iron chromium oxide, the engine component being manufactured according to a method comprising the steps of: - providing (100) an engine component (1) comprising a chromium-containing steel; heating (200) the engine component (1) in air at a temperature of 150 to 500 ° C and for a predetermined time so that a layer (5) of iron chromium oxide forms on the surface of the engine component; cooling (300) the engine component (1) to room temperature. The engine component of claim 1, wherein the engine component comprises a steel having a chromium content of at least 8% by weight and up to 88% by weight of iron. The engine component according to claim 1, wherein the engine component comprises a steel having a chromium content of 20 - 22% by weight and an iron content of 58 - 65% by weight. The engine component according to any one of claims 1 to 3, wherein the engine component is heated at a temperature between 250 to 350 ° C for 1 to 3 hours. The engine component according to any one of the preceding claims, wherein the layer (5) consists of FeCr 2 O 4 and is of the spinel type. The motor component according to any one of the preceding claims, wherein the layer (5) has a thickness of 5 - 20 μm. The motor component according to any one of the preceding claims, wherein the layer (5) has a hardness of about 1500 HVO.1. 10 15 20 533 842 1H Engine component according to one of the preceding claims, characterized in that the engine component (1) is a motor valve or a valve control or a valve seat. A method of manufacturing an engine component comprising an anti-corrosion layer characterized by the steps of: - providing (100) an engine component comprising a chromium-containing steel; heating (200) the engine component in air at a temperature of 150 to 500 ° C and for a predetermined time so that a layer (5) of iron chromium oxide forms on the surface of the engine component; cooling (300) the engine component to room temperature; The method of claim 9, wherein the engine component is heated in air with elevated oxygen content. The method according to any one of claims 9 or 10, wherein the engine component comprises a steel with a chromium content of at least 8% by weight and up to 88% by weight of iron, preferably a steel with a chromium content of 20-22% by weight and an iron content of 58-65%. weight%. The method according to any one of claims 9 to 11, wherein the engine component is heated at a temperature between 250 to 350 ° C for 1 to 3 hours.