JP2008291807A - Engine valve - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an engine valve wherein durability of a valve main-body constituting the engine valve is improved, and the mass production is facilitated. <P>SOLUTION: A valve head 14 (valve main-body) of the engine valve 10 is composed of a Ni-based alloy containing C of 0.02-0.1% (percentage by mass), Cr of 18-21%, Co of 12-15%, Mo of 3.5-5%, Al of 1.2-1.6%, Ti of 2.75-3.25%, and B of 0.003-0.01%. The surface hardness of the Ni-based alloy is 30-40 in Rockwell hardness C-scale (HRC), and the grain-size number in the metallographic structure is at least 5.0. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an engine valve for opening and closing an intake port or an exhaust port of an internal combustion engine such as an automobile engine.

  When a four-stroke engine of an automobile is operated, an intake process in which a mixed gas of fuel and air is introduced into a combustion chamber via an intake port, a compression process in which the mixed gas is compressed in the combustion chamber, A combustion process in which the mixed gas is combusted and expanded, and an exhaust process in which the mixed gas that has been combusted is discharged from an exhaust port are repeated. Each of the intake port and the exhaust port is provided with an intake valve and an exhaust valve that can be opened and closed. The intake valve is set to open only in the intake process, and the exhaust valve is set to open only in the exhaust process. Yes.

  Conventionally, an intake valve and an exhaust valve (hereinafter referred to as an engine valve when both are collectively referred to) are made of a steel material having excellent heat resistance as a raw material and an umbrella having a diameter larger than that of the shaft part. It is produced by providing the part integrally. The umbrella part in this contact | abuts to the valve seat provided in the inlet port or the exhaust port.

  By the way, from the viewpoint of global environmental protection and resource protection in recent years, automobiles are required to reduce nitrogen oxide, sulfur oxide, and hydrocarbons contained in exhaust gas and to improve fuel efficiency. In response to this demand, attempts are currently being made to increase the temperature in the combustion process of the engine, increase the engine speed, and reduce the amount of engine oil used.

  In order to obtain an engine that can be stably operated even under the severe conditions described above, each member constituting the engine needs to be excellent in durability. Therefore, regarding the engine valve, it has been proposed to provide a build-up portion made of a Co-base alloy or a Ni-base alloy that has high hardness and good corrosion resistance at a portion that comes into contact with the valve seat in the umbrella portion. In order to further improve durability, it is becoming mainstream to form the entire umbrella portion with a Ni-based alloy (for example, see Patent Documents 1 and 2).

JP-A-7-109539 Japanese Patent Laid-Open No. 11-229059

  However, the Ni-base alloys described in Patent Documents 1 and 2 have a problem that it is not easy to perform the forming process. That is, in order to produce an umbrella part, press work which presses a work is needed, but this press work cannot be performed, and eventually an umbrella part cannot be provided.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an engine valve having an umbrella portion that is easy to mold and has excellent durability.

In order to achieve the above object, the present invention provides an engine valve having a shaft member made of a steel material and a valve body that is joined to the shaft member and has a larger diameter than the shaft member.
The valve body is at least C: 0.02-0.1%, Cr: 18-21%, Co: 12-15%, Mo: 3.5-5%, Al: 1.2-% by mass% It consists of a Ni-based alloy containing 1.6%, Ti: 2.75-3.25%, B: 0.003-0.01%,
The surface hardness is 30 to 40 in terms of C-scale Rockwell hardness (hereinafter also referred to as HRC), and the grain size number of the crystal grains in the metal structure is 5.0 or more.

  First, a Ni-based alloy containing the above components in the above composition ratio exhibits extremely excellent wear resistance and high temperature strength. For this reason, the valve body made of the Ni-based alloy may be worn or fatigued even if the air intake and exhaust ports that have become hot when the internal combustion engine is operated are repeatedly separated and seated. Suppressed over a long period of time.

  That is, by selecting the Ni-based alloy as a raw material for the valve body, an engine valve that exhibits excellent durability over a long period of time can be configured.

  In addition, Ni-base alloys having a surface HRC of 30 to 40 and a grain size number of 5.0 or more in the metal structure are easily deformed during upsetting and press forming, and cracks and the like are remarkable. Not likely to occur. For this reason, since the valve body can be efficiently molded, the production efficiency of the engine valve is improved, and the yield of the valve body and thus the engine valve is improved. In other words, the engine valve can be mass-produced with a high yield, and thus the manufacturing cost can be reduced.

  In addition to the above-described components, the Ni-based alloy is Si: 0.15% or less, Mn: 0.1% or less, P: 0.015% or less, S: 0.015% or less, Fe: 2 % Or less may be further contained.

  According to the present invention, since the engine valve is provided using a Ni-based alloy having a predetermined component / composition ratio as a raw material, production efficiency and yield are improved. That is, it is easy to industrially mass-produce engine valves, and this combined with a good yield reduces the manufacturing cost.

  Furthermore, since the valve body made of the Ni-based alloy is remarkably excellent in wear resistance and strength at high temperatures, it is possible to provide a long-life engine valve.

  Hereinafter, preferred embodiments of an engine valve according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic overall side view of an engine valve 10 according to the present embodiment. In this case, the engine valve 10 includes a stem portion 12 as a shaft portion that extends linearly, and an umbrella portion (valve body) that is provided at one end portion of the stem portion 12 and has a larger diameter than the stem portion 12. 14). The umbrella part 14 is seated and separated from an intake port or an exhaust port of a cylinder head constituting an automobile engine (internal combustion engine) (not shown). The engine valve 10 is preferably installed at an exhaust port through which exhaust gas having a high temperature passes.

  Here, a curved portion 16 having a relatively large radius of curvature is provided between the stem portion 12 and the umbrella portion 14. In other words, the umbrella part 14 continues to the stem part 12 via the bending part 16.

  The umbrella portion 14 is connected to the curved portion 16 and has a first tapered portion 18 that has a tapered diameter, and is connected to the first tapered portion 18 and is inclined at an angle different from the first tapered portion 18. A second taper portion 20 having an enlarged diameter, and a disk-like portion 22 having a substantially equal diameter connected to the second taper portion 20, wherein the second taper portion 20 is an intake / exhaust gas of the internal combustion engine. It functions as a seating part seated on the port. Further, the corners of the disk-shaped part 22 are curved by chamfering.

  And in this case, the umbrella part 14 is C: 0.02 to 0.1%, Cr: 18 to 21%, Co: 12 to 15%, Mo: 3.5 to 5%, Al: 1.2 to 1.6%, Ti: 2.75 to 3.25%, B: 0.003 to 0.01%, Si: 0.15% or less, Mn: 0.1% or less, P: 0.015% or less S: 0.015% or less, and Fe: 2% or less. In addition, a number is the mass% and is the same also below.

  C forms a carbide together with Ti, Cr, and Mo. Along with this, coarsening of crystal grains is suppressed and creep rupture strength is improved. If it is less than 0.02%, this effect is poor. On the other hand, if it exceeds 0.1%, the ductility of the crystal grain boundary is lowered while the grindability is lowered.

  Cr is a component that improves the oxidation resistance of the umbrella portion 14. Therefore, in order to ensure sufficient oxidation resistance, the Cr ratio is set to 18% or more. However, when Cr is excessively present, an embrittled phase is generated. In order to avoid this, the Cr ratio is set to 21% or less.

  Co is dissolved in an austenite base to improve workability, while it functions to increase high temperature strength. If it is less than 12%, it is difficult to obtain this effect. Moreover, since Co is expensive, if it exceeds 15%, it is disadvantageous in terms of cost.

  Mo is a component that improves high-temperature strength and corrosion resistance. If it is less than 3.5%, this effect is poor. On the other hand, if it exceeds 5%, the tissue tends to become unstable.

  Al precipitates the γ 'phase together with Ti, thereby making the umbrella portion 14 a precipitation strengthened alloy. That is, the high temperature strength is further improved. In order to ensure this effect, the Al ratio is set to 1.2% or more. In addition, when Al exists excessively, hot workability will fall. Therefore, Al is suppressed to 1.6% at the maximum.

  Ti is a component that suppresses the coarsening of crystal grains by forming carbide with C, and precipitates a γ ′ phase together with Al to improve high-temperature strength, and the ratio is 2.75% or more. Set to It is because it will become difficult to acquire said effect if it is less than 2.75%. However, if it exceeds 3.25%, the corrosion resistance tends to decrease.

  B serves to improve the strength and ductility of the umbrella portion 14 by being present at the grain boundaries. If it is less than 0.003%, this effect is poor. On the other hand, if it exceeds 0.01%, workability is lowered.

  Si is a component that contributes as a deoxidizing element. However, when it exists excessively, it causes a decrease in high temperature strength. In order to avoid this, the proportion of Si is set to 0.15% or less.

  Mn, like Si, contributes to deoxidation. If Mn is also present excessively, the high temperature strength tends to be lowered, so the ratio is set to 0.1% or less.

  P and S may be contained as impurities as long as they are 0.015% or less.

  Fe is an element useful for forming an austenite base that softens in a high temperature range and improving hot workability. For this reason, it is added at a ratio of 2% or less.

  In the umbrella portion 14 of the engine valve 10 according to the present embodiment including the above components, the austenite base is stabilized by Ni as the main component, and exhibits excellent high-temperature strength.

  And the surface hardness of this umbrella part 14 shows 30-40 by HRC. Moreover, the particle size number of the crystal grain in a metal structure is 5.0 or more.

  The engine valve 10 can be manufactured as follows.

  First, after cutting a rod-shaped member made of a Ni-based alloy having the above-described component / composition ratio and having an HRC of 30 to 40 and a crystal grain size number in a metal structure of 5.0 or more to a predetermined length, One end of the rod-shaped member is heated to perform upsetting, and the one end is formed into a substantially spherical shape. By this upsetting, the shaft portion remains at the other end.

  Here, the Ni-based alloy is hardly cracked even when the molding temperature is increased and the molding speed is increased. For this reason, upsetting can be advanced efficiently. Also, so-called rough skin is unlikely to occur.

  Next, press molding is performed on the one end portion having a substantially spherical shape to obtain a preform having a shape close to the umbrella portion 14 shown in FIG. Even in the process of forming the preform, cracks and the like hardly occur. On the other hand, for example, even when Ni-based alloys having the same composition and composition ratio are subjected to upsetting and press molding using a rod-shaped member having a grain size number of 4, the majority of the cases are either Cracks occur during the molding process.

  As can be understood from this, by selecting the Ni-based alloy as a raw material, the umbrella portion 14 can be manufactured with a high yield. That is, since industrial mass production is easy, manufacturing cost can be reduced. In addition, the reliability of quality is improved.

  Next, the end surface of the shaft portion of the preform and the end surface of the rod-shaped body having a predetermined length are joined by friction welding. This rod-shaped body becomes the stem portion 12. In addition, what is necessary is just to use the thing made from SUH11M as a rod-shaped body, for example.

  Thereafter, predetermined heat treatment such as quenching and tempering, straightening, annealing, and the like are performed, and further various polishing processes are performed, whereby the engine valve 10 as a final product is obtained.

  Since the umbrella portion 14 of the engine valve 10 includes the above-described components, it has excellent wear resistance and high-temperature strength. Therefore, the umbrella portion 14 is seated on the intake or exhaust port of the cylinder head that has become hot during engine operation. Even if the separation is repeated, wear and fatigue are suppressed over a long period of time. That is, it is excellent in high temperature durability (heat resistance) and has a long life.

  As described above, the use of the Ni-based alloy not only facilitates mass production, but also provides an engine valve 10 that exhibits excellent characteristics.

  In the above-described embodiment, a Ni-based alloy containing Si, Mn, P, S, and Fe is selected, but these are not essential components. That is, you may make it provide the umbrella part 14 from the Ni base alloy which does not contain these.

  The material of the stem portion 12 is not particularly limited to SUH11M, and may be other steel materials, various Ni-based alloys including the Ni-based alloy, and other alloys. Good.

1 is a schematic overall side view of an engine valve according to an embodiment.

Explanation of symbols

10 ... Engine valve 12 ... Stem part 14 ... Umbrella part (valve body)

Claims (2)

In an engine valve having a shaft member made of steel, and a valve body that is joined to the shaft member and has a larger diameter than the shaft member,
The valve body is at least C: 0.02-0.1%, Cr: 18-21%, Co: 12-15%, Mo: 3.5-5%, Al: 1.2-% by mass% It consists of a Ni-based alloy containing 1.6%, Ti: 2.75-3.25%, B: 0.003-0.01%,
The engine valve is characterized in that its surface hardness is 30 to 40 in terms of C-scale Rockwell hardness, and the grain size number of the crystal grains in the metal structure is 5.0 or more.   2. The engine valve according to claim 1, wherein the Ni base alloy constituting the valve main body is Si: 0.15% or less, Mn: 0.1% or less, P: 0.015% or less, and S: 0 in mass%. An engine valve characterized by further containing 0.15% or less and Fe: 2% or less.

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