EP2980234A1

EP2980234A1 - Valve seat

Info

Publication number: EP2980234A1
Application number: EP15179135.7A
Authority: EP
Inventors: Min Gu Kang; Ju Sung Kim; Keun Chul Song; Sang Beom Kim
Original assignee: Doosan Infracore Co Ltd
Current assignee: HD Hyundai Infracore Co Ltd
Priority date: 2014-07-30
Filing date: 2015-07-30
Publication date: 2016-02-03
Anticipated expiration: 2035-07-30
Also published as: CN105316600B; CN105316600A; KR20160015449A; KR102199856B1; EP2980234B1

Description

[Technical Field]

The present disclosure relates to a valve seat used for gas and diesel engines.

[Background Art]

In general, a valve seat, which is one of the component parts of an engine, is closely adhered to a valve face, to provide an airtight combustion chamber. Since the valve seat is exposed to combustion gases at high temperature, and continuously contacted with the valve face, physical properties such as heat resistance and wear resistance are required.
In order to secure the physical properties as described above, a technology of manufacturing a valve seat by containing lead (Pb) in materials for manufacturing the valve seat has been proposed in the related art. Since the valve seat containing lead (Pb) is excellent in wear resistance and inexpensive, but includes lead (Pb) which causes environmental problems, the use range thereof is limited, and there is a problem in that the valve seat is melted in a high-temperature environment.
Further, a technology of manufacturing a valve seat by using a material including hard particles, such as Fe-Mo or Fe-Cr, has been proposed, but since the valve seat has extremely high wear resistance, there is a problem of damaging the valve which is a counterpart material.

[Disclosure]

[Technical Problem]

In order to solve the aforementioned problems, an object of the present disclosure is to provide a valve seat having excellent physical properties such as heat resistance and wear resistance.

[Technical Solution]

In order to achieve the aforementioned object, the present disclosure provides a valve seat including 0.8 to 1.7 wt% of carbon (C), 0.5 to 1.5 wt% of silicon (Si), 0.5 to 1.5 wt% of manganese (Mn), 0.01 to 1.0 wt% of sulfur (S), 2.0 to 6.0 wt% of chromium (Cr), 7.0 to 16.0 wt% of molybdenum (Mo), 2.0 to 8.0 wt% of nickel (Ni), 0.01 to 3.0 wt% of tungsten (W), 0.01 to 1.0 wt% of vanadium (V), 14.0 to 25.0 wt% of cobalt (Co), and the balance of iron and impurities.
The valve seat of the present disclosure may include a bainite structure, a structure including a silicide to which cobalt (Co) and molybdenum (Mo) are combined, a martensite structure including chromium composite carbide, and an austenite structure in the structure of the valve seat.
In this case, it is preferred that the bainite structure is present in an amount of 2 to 12 vol% based on a total 100 vol% of the valve seat.
Further, it is preferred that a ratio of the area, which the bainite structure occupies at the cut surface formed by cutting the valve seat, is 2 to 12% of the area of the cut surface.
Meanwhile, the valve seat of the present disclosure may be a valve seat in which copper (Cu) or a copper alloy is infiltrated into pores in the structure.
In addition, the valve seat of the present disclosure may be a valve seat to which an iron-based sintered material is further combined.

[Advantageous Effects]

The valve seat of the present disclosure includes predetermined ranges of carbon, silicon, manganese, sulfur, chromium, molybdenum, nickel, tungsten, vanadium, and cobalt, and thus has excellent physical properties such as heat resistance and wear resistance. Furthermore, the valve seat of the present disclosure does not include lead (Pb), and thus, may also reduce the occurrence of environmental problems.

[Description of Drawings]

FIG. 1 is a perspective view illustrating a valve seat according to an exemplary embodiment of the present disclosure.
FIG. 2 is a reference view for describing Experimental Example 1 of the present disclosure.
FIG. 3 is an image in which the cut surface of the valve seat according to Example 1 of the present disclosure is analyzed.
FIG. 4 is a reference view for describing Experimental Example 4 of the present disclosure.

[Mode for Invention]

Hereinafter, the present disclosure will be described.

1. Valve seat

The valve seat of the present disclosure includes predetermined ranges of carbon, silicon, manganese, sulfur, chromium, molybdenum, nickel, tungsten, vanadium, and cobalt, and thus has excellent physical properties such as heat resistance and wear resistance, and this will be described in detail as follows.
The valve seat of the present disclosure includes 0.8 to 1.7 wt% of carbon (C) based on the total weight. When the content of carbon is less than 0.8 wt%, the formation of the carbide structure in the structure of the valve seat deteriorates, and when the content of carbon exceeds 1.7 wt%, the ferrite structure remains in the structure of the valve seat, so that wear resistance of the valve seat may deteriorate. Therefore, it is preferred that carbon is included in the aforementioned range.
The valve seat of the present disclosure includes 0.5 to 1.5 wt% of silicon (Si) based on the total weight. When the content of silicon is less than 0.5 wt%, production of a silicide produced by combining molybdenum (Mo) and cobalt (Co) deteriorates, so that wear resistance of the valve seat may deteriorate, and when the content of silicon exceeds 1.5 wt%, compressibility and sinterability may deteriorate when the valve seat is manufactured. Therefore, it is preferred that silicon is included in the aforementioned range.
The valve seat of the present disclosure includes 0.5 to 1.5 wt% of manganese (Mn) based on the total weight. When the content of manganese is less than 0.5 wt%, processability of the valve seat may deteriorate, and when the content of manganese exceeds 1.5 wt%, compressibility and sinterability may deteriorate when the valve seat is manufactured. Therefore, it is preferred that manganese is included in the aforementioned range.
The valve seat of the present disclosure includes 0.01 to 1.0 wt% of sulfur (S) based on the total weight. When the content of sulfur is less than 0.01 wt%, production of a material combined to manganese deteriorates, and when the content of sulfur exceeds 1.0 wt%, the carbide structure is excessively formed in the structure of the valve seat, so that processability may deteriorate when the valve seat is manufactured. Therefore, it is preferred that sulfur is included in the aforementioned range.
The valve seat of the present disclosure includes 2.0 to 6.0 wt% of chromium (Cr) based on the total weight. When the content of chromium is less than 2.0 wt%, formation of the carbide structure in the structure of the valve seat deteriorates, so that wear resistance of the valve seat may deteriorate, and when the content of chromium exceeds 6.0 wt%, compressibility and sinterability deteriorate when the valve seat is manufactured, and wear resistance becomes excessively high, so that a degree that the valve, which is a counterpart material, is damaged may be increased. Therefore, it is preferred that chromium is included in the aforementioned range.
The valve seat of the present disclosure includes 7.0 to 16.0 wt% of molybdenum (Mo) based on the total weight. When the content of molybdenum is less than 7.0 wt%, production of the silicide to which cobalt and molybdenum are combined deteriorates, so that wear resistance of the valve seat may deteriorate, and when the content of molybdenum exceeds 16.0 wt%, compressibility may deteriorate when the valve seat is manufactured. Therefore, it is preferred that molybdenum is included in the aforementioned range.
The valve seat of the present disclosure includes 2.0 to 8.0 wt% of nickel (Ni) based on the total weight. When the content of nickel is less than 2.0 wt%, formation of the austenite structure in the structure of the valve seat deteriorates, so that wear resistance and heat resistance of the valve seat may deteriorate, and when the content of nickel exceeds 8.0 wt%, toughness of the valve seat becomes excessively high, and formation of the bainite structure deteriorates, so that wear resistance of the valve seat may deteriorate. Therefore, it is preferred that nickel is included in the aforementioned range.
The valve seat of the present disclosure includes 0.01 to 3.0 wt% of tungsten (W) based on the total weight. When the content of tungsten is less than 0.01 wt%, formation of the carbide structure in the structure of the valve seat deteriorates, so that wear resistance of the valve seat may deteriorate, and when the content of tungsten exceeds 3.0 wt%, wear resistance of the valve seat becomes excessively high, so that a degree that the valve, which is a counterpart material, is damaged may be increased. Therefore, it is preferred that tungsten is included in the aforementioned range.
The valve seat of the present disclosure includes 0.01 to 1.0 wt% of vanadium (V) based on the total weight. When the content of vanadium is less than 0.01 wt%, formation of the carbide structure in the structure of the valve seat deteriorates, so that wear resistance of the valve seat may deteriorate, and when the content of vanadium exceeds 1.0 wt%, compressibility and sinterability may deteriorate when the valve seat is manufactured. Therefore, it is preferred that vanadium is included in the aforementioned range.
The valve seat of the present disclosure includes 14.0 to 25.0 wt% of cobalt (Co) based on the total weight. When the content of cobalt is less than 14.0 wt%, production of the silicide to which cobalt and molybdenum are combined deteriorates, so that wear resistance and heat resistance of the valve seat may deteriorate, and when the content of cobalt exceeds 25.0 wt%, compressibility and sinterability may deteriorate when the valve seat is manufactured. Therefore, it is preferred that cobalt is included in the aforementioned range.
The valve seat of the present disclosure includes the balance of iron (Fe) and impurities (for example, phosphorus (P), sulfur (S), and the like) in addition to the aforementioned components.
For the valve seat of the present disclosure, it is preferred that a bainite structure, a structure including a silicide to which cobalt (Co) and molybdenum (Mo) are combined, a martensite structure including chromium composite carbide, and an austenite structure co-exist in the structure of the valve seat. This is because it is possible to provide a valve seat in which wear resistance and heat resistance are excellent, and a degree that that the valve, which is a counterpart material, is damaged is minimized when the aforementioned structures co-exist.
That is, the martensite structure including chromium composite carbide improves wear resistance of the valve seat, but when the structure is present alone, wear resistance of the valve seat becomes excessively high, so that a degree that the valve, which is a counterpart material, is damaged is increased. However, since the bainite structure, which increases wear resistance of the valve seat while less damaging the valve that is a counterpart material, and the austenite structure, which secures toughness of the valve seat, co-exist along with the martensite structure in the valve seat of the present disclosure, it is possible to minimize a degree that the valve, which is a counterpart material, is damaged while wear resistance is excellent.
Further, as a structure including a silicide to which cobalt (Co) and molybdenum (Mo) are combined exists in the structure of the valve seat of the present disclosure, combining properties between the structures are improved, so that the valve seat of the present disclosure also has excellent heat resistance.
Herein, in consideration of wear resistance of the valve seat and a degree that the valve, which is a counterpart material, is damaged, it is preferred that the bainite structure present in the structure of the valve seat of the present disclosure is present in an amount of 2 to 12 vol% based on the total 100 vol% of the valve seat. Specifically, the volume of the bainite structure may be calculated by the following method, and in this case, the ratio of the calculated volume to the total volume of the valve seat is 2 to 12 vol%.
That is, at each point of A₁, A₂, and A₃ in the valve seat, the valve seat is cut in a direction vertical to the ground surface, and then the area of the bainite structure found at each cut surface is measured. Herein, the area of the bainite structure may be measured through an image analysis of the cut surface. Thereafter, the volume (V) of the bainite structure may be calculated by the following equation. $V = (area that the bainite structure occupies at the cut surface of A_{1} point + area that the bainite structure occupies at the cut surface of A_{2} point + area that the bainite structure occupies at the surface of A_{3} point) \times \frac{π}{3}$
When a degree that the bainite structure occupies in the structure of the valve seat is converted into vol% as described above, the degree is preferably 2 to 12 vol%, and when a degree that the bainite structure occupies at the cut surface produced by cutting the valve seat is converted into area%, the degree is preferably 2 to 12% of the area of the cut surface.
Meanwhile, the valve seat of the present disclosure may further include copper (Cu) or a copper alloy (for example, Cu-Zn, Cu-Co, Cu-Fe-Mn, Cu-Fe-Mn-Zn, and the like) infiltrated into pores in the structure in order to increase combining properties of the structure. Herein, the content of copper (Cu) or a copper alloy present in the structure of the valve seat is not particularly limited, but in consideration of processability of the valve seat, the content is preferably 1.0 to 25.0 wt% based on the total weight of the valve seat regardless of the chemical composition of the valve seat of the present disclosure.
Furthermore, an iron-based sintered material may be further combined to the valve seat of the present disclosure in order to reduce the costs. That is, the valve seat of the present disclosure may have a dual-layer structure in which a part, which is closely adhered to a valve face (a part which is contacted with the valve), is composed of the component and composition described above and a part, which is not closely adhered to the valve face (a part which is not contacted with the valve), is composed of an iron-based sintered material. In this case, the component and composition of the iron-based sintered material are not particularly limited, but 0.1 to 1.5 wt% of carbon (C) and 0.1 to 25 wt% of copper (Cu) are included based on the total weight of the iron-based sintered material, and the balance may be composed of iron (Fe) and impurities.

2. Engine

The present disclosure provides an engine including the valve seat described above. The kind of engine of the present disclosure is not particularly limited, but the engine may be a gas or diesel engine.

[Examples 1 to 9] Manufacture of Valve Seat

A valve seat having the shape as in FIG. 1 was molded by selecting the powder of each component through a powder metallurgical method, and then mixing and pressing the powder. Thereafter, the valve seat having the composition in the following Table 1 was each manufactured by sinteringvalve seat in a sintering furnace, and subjected the valve seat to post-processing (heat treatment). In this case, when the molded valve seat was sintered, a process of infiltrating copper (Cu) was added to Examples 6 to 9. Meanwhile, the composition of each valve seat manufactured was confirmed by an inductively-coupled plasma-mass spectrometer.

[Table 1]

Classification	Chemical Component (wt%)
Classification	C	Si	Mn	S	Cr	Mo	Ni	Cu	Pb	W	V	Co	Fe / Impurities
Example 1	1.2	1.0	1.0	0.5	3.6	11	4.4	-	-	1.4	0.4	21	Bal.
Example 2	1.2	1.0	1.0	0.6	4.3	12	4.5	-	-	1.4	0.4	19	Bal.
Example 3	1.0	0.9	1.0	0.5	3.1	10	5.0	-	-	0.6	0.2	21	Bal.
Example 4	1.3	1.4	1.0	0.5	2.8	15	5.0	-	-	0.9	0.3	18	Bal.
Example 5	1.1	0.8	1.1	0.5	5.6	9	3.7	-	-	2.0	0.6	25	Bal.
Example 6	1.2	1.0	1.0	0.5	3.6	11	4.4	5	-	1.4	0.4	21	Bal.
Example 7	1.2	1.0	1.0	0.5	3.6	11	4.4	15	-	1.4	0.4	21	Bal.
Example 8	1.2	1.0	1.0	0.5	3.6	11	4.4	25	-	1.4	0.4	21	Bal.
Example 9	1.2	1.0	1.0	0.5	3.6	11	4.4	30	-	1.4	0.4	21	Bal.

[Comparative Examples 1 to 11] Manufacture of Valve Seat

The valve seat having the composition in the following Table 2 was each manufactured by applying the method which is the same as in Example 1. In this case, a process of sintering the molded valve seat, and then impregnating lead (Pb) was added to Comparative Examples 5 and 9, and a process of infiltrating copper (Cu) when the molded valve seat was sintered was added to Comparative Examples 6, 8, 10, and 11. Meanwhile, the composition of each valve seat manufactured was confirmed by an inductively-coupled plasma-mass spectrometer.

[Table 2]

Classification	Chemical Component (wt%)
Classification	C	Si	Mn	S	Cr	Mo	Ni	Cu	Pb	W	V	Co	Fe / Impurities
Comparative Example 1	1.2	0.3	1.0	0.5	1.7	4	5.3	-	-	1.4	0.4	6	Bal.
Comparative Example 2	1.4	1.4	1.1	0.6	6.5	16.5	3.4	-	-	2.6	0.8	25.5	Bal.
Comparative Example 3	1.2	0.2	1.0	0.5	1.3	2.5	6.0	-	-	1.4	0.4	3	Bal.
Comparative Example 4	1.4	0.4	1.1	0.6	6.7	18	4.0	-	-	2.7	0.9	29	Bal.
Comparative Example 5	1.0	-	-	-	3.0	5	-	-	20	6.0	3.0	-	Bal.
Comparative Example 6	1.0	-	-	-	3.0	5	-	20	-	6.0	3.0	-	Bal.
Comparative Example 7	0.6	1.0	1.0	0.5	5.5	13	0.5	0.3	-	3.5	1.0	20	Bal.
Comparative Example 8	1.0	1.1	1.1	0.5	5.0	15	0.6	15	-	2.5	1.5	25	Bal.
Comparative Example 9	0.8	1.5	-	-	1.0	8	1.0	3	10	-	-	10	Bal.
Comparative Example 10	1.0	1.0	1.2	0.6	1.5	12	0.2	12	-	-	-	15	Bal.
Comparative Example 11	0.5	0.8	2.0	1.4	2.0	13	-	12	-	-	-	16	Bal.

[Experimental Example 1] Analysis of Cut Surface of Valve Seat

The valve seat manufactured in Example 1 was vertically cut (see FIG. 2), the cut surface was polished and etched, and then observed by an optical microscope (200 times magnification was applied), and the results are shown in FIG. 3.
Referring to FIG. 3, it can be confirmed that a bainite structure, a structure including a silicide to which cobalt (Co) and molybdenum (Mo) are combined, a martensite structure including chromium composite carbide, and an austenite structure co-exist in the structure of the valve seat.

[Experimental Example 2] Evaluation of Ratio of Bainite Structure

The valve seat was cut in a direction vertical to the ground surface at A₁, A₂, and A₃ points (see FIG. 1) of each valve seat manufactured in Examples 1 to 5 and Comparative Examples 1 to 4, the cut surface was polished and etched, and then observed by an optical microscope to measure the area of the bainite structure found at each cut surface.

Thereafter, the volume (V) that the bainite structure occupies at the valve seat was calculated by the following equation, and the results are shown in the following Table 3.

V = (area that the bainite structure occupies at the cut surface of A_{1} point + area that the bainite structure occupies at the cut surface of A_{2} point + area that the bainite structure occupies at the surface of A_{3} point) \times \frac{π}{3}

[Table 3]

Classification	Ratio of Area that Bainite Structure Occupies at Cut Surface			Ratio of Volume that Bainite Structure Occupies at Valve Seat
Classification	A₁%	A₂%	A₃%	V%
Example 1	6.6	7.9	9.2	7.9
Example 2	7.1	9.5	8.1	8.2
Example 3	7.7	6.2	7.7	7.2
Example 4	11.0	12.2	9.9	11.0
Example 5	7.2	6.3	6.2	6.6
Comparative Example 1	1.5	1.6	2.1	1.7
Comparative Example 2	13.5	12.2	13.8	13.2
Comparative Example 3	1.1	0.6	1.1	0.9
Comparative Example 4	14.2	14.7	15.1	14.7

Referring to Table 3, it can be confirmed that in the valve seat of the present disclosure (Examples 1 to 5), the bainite structure is present in an amount of 2 to 12 vol% based on the total 100 vol% of the valve seat.

[Experimental Example 3] Evaluation of Wear Resistance and Heat Resistance

Wear resistance was evaluated by applying the valve seats manufactured in Examples 1 to 5 and Comparative Examples 1 to 11 to a rig tester which simulated an engine valve train system, and the results are shown in the following Table 4. In this case, the test conditions and evaluation methods of the rig tester were as follows.
- Cam rotation speed: 1,100 rpm
- Temperature of valve seat: 150°C / 300°C
- Test time: 20 hours
- Evaluation method: the shape of a contact surface at which the valve and the valve seat were contacted was measured by a shape measuring machine, and then the maximum wear depth was analyzed at the measured shape.

[Table 4]

Classification	Wear amount						Rate of change in wear amount (%)
	150°C			300°C
	Valve seat	Valve	Total	Valve seat	Valve	Total
Example 1	0.9	0.6	1.5	1.0	0.7	1.7	13.3
Example 2	1.4	0.5	1.9	1.7	0.5	2.2	15.8
Example 3	1.8	0.5	2.3	2.1	0.6	2.7	17.4
Example 4	1.5	0.4	1.9	1.6	0.5	2.1	10.5
Example 5	1.3	0.7	2.0	1.4	0.8	2.2	10.0
Example 6	1.0	0.6	1.6	1.1	0.7	1.8	12.5
Example 7	1.2	0.7	1.9	1.3	0.9	2.2	15.8
Example 8	1.4	0.9	2.3	1.6	1.1	2.7	17.4
Example 9	1.7	1.2	2.9	2.0	1.5	3.5	19.9
Comparative Example 1	2.2	0.7	2.9	2.8	0.8	3.6	24.1
Comparative Example 2	2.0	1.0	3.0	2.3	1.3	3.6	20.0
Comparative Example 3	2.2	0.7	2.9	3.0	0.8	3.8	31.0
Comparative Example 4	2.1	0.9	3.0	3.0	0.7	3.7	23.3
Comparative Example 5	2.0	0.7	2.7	2.7	1.2	3.9	44.4
Comparative Example 6	1.8	1.0	2.8	2.6	1.1	3.7	32.1
Comparative Example 7	4.0	1.1	5.1	4.8	1.7	6.5	27.5
Comparative Example 8	2.1	0.9	3.0	2.7	1.1	3.8	26.7
Comparative Example 9	2.2	1.1	3.3	3.7	1.3	5.0	51.5
Comparative Example 10	3.0	1.0	4.0	4.3	1.2	5.5	37.5
Comparative Example 11	3.1	0.8	3.9	4.0	1.2	5.2	33.3

Referring to Table 4, it can be confirmed that the valve seats (Examples 1 to 9) of the present disclosure have excellent wear resistance. Further, it can be confirmed that the rate of change in wear amount is low even though the temperature was increased from 150°C to 300°C, which supports that the valve seat of the present disclosure has excellent heat resistance.

[Experimental Example 4] Evaluation of Post-Processability

The post-processability was evaluated by the following method when the valve seats in Examples 1 and 6 to 9 were manufactured, and the results are shown in FIG. 4.

Evaluation method: the molded valve seat was sintered, the depth of cut according to the post-processing was measured, and then the relative amount was calculated by defining the depth of cut in Example 6 as 1.

Referring to FIG. 4, it can be confirmed that as the content of copper (Cu) infiltrated in Example 9 is higher than those in Examples 1 and 6 to 8, the cutting amount is increased when the post-processing is performed. This supports that it is preferred that the content of copper (Cu) infiltrated does not exceed 25 wt% in consideration of post-processability.

Claims

A valve seat comprising 0.8 to 1.7 wt% of carbon (C), 0.5 to 1.5 wt% of silicon (Si), 0.5 to 1.5 wt% of manganese (Mn), 0.01 to 1.0 wt% of sulfur (S), 2.0 to 6.0 wt% of chromium (Cr), 7.0 to 16.0 wt% of molybdenum (Mo), 2.0 to 8.0 wt% of nickel (Ni), 0.01 to 3.0 wt% of tungsten (W), 0.01 to 1.0 wt% of vanadium (V), 14.0 to 25.0 wt% of cobalt (Co), and a balance of iron and impurities.
The valve seat of claim 1, wherein the valve seat comprises a bainite structure, a structure comprising a silicide to which cobalt (Co) and molybdenum (Mo) are combined, a martensite structure comprising chromium composite carbide, and an austenite structure in the structure of the valve seat.
The valve seat of claim 1, wherein a bainite structure is present in an amount of 2 to 12 vol% based on a total 100 vol% of the valve seat.
The valve seat of claim 1, wherein a ratio of an area that a bainite structure occupies at the cut surface formed by cutting the valve seat is 2 to 12% based on the area of the cut surface.
The valve seat of claim 1, wherein copper (Cu) or a copper alloy is infiltrated into pores in the structure.
The valve seat of claim 1, wherein an iron-based sintered material is further combined to the valve seat.
An engine comprising the valve seat of any one of claims 1 to 6.