JPH03226546A - Engine intake valve clad by welding - Google Patents

Abstract

PURPOSE:To manufacture an engine intake valve excellent in toughness and wear resistance by cladding the face surface of an intake valve in an internal combustion engine with high carbon Cr-Mo series alloy iron having a specified compsn. by welding. CONSTITUTION:At the time of manufacturing an engine intake valve clad by welding in an internal combustion engine, a clad by welding part constituted of, by weight, 1.1 to 1.9% C, 25 to 33% Cr, 3 to 8% Mo, <1.5% Si and the balance Fe and having <=5mum dendrite secondary arm spacing value (DAS value) is formed on the face surface of valve stock by cladding by a laser welding method or the like. The clad by welding part excellent in toughness and wear resistance can be formed on the face surface of the intake valve.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to an engine valve for internal combustion engines, more specifically, an overlay engine valve for intake in which a built-up portion is provided on the valve face to improve the performance of the face. Regarding.

1. In the conventional technology, Co-based alloys, N1-based alloys, etc. are mainly used as overlay materials for engine valves for both C1 intake and exhaust engine valves. However, these Co-based alloys, Ni
Since both base alloys are expensive, the use of inexpensive Fe-based alloys as overlay materials has been considered in recent years.

One of the reasons behind this is the development of high-density energy sources for overlay heat sources. In other words, whether the welding was done by fusion welding using an oxygen-acetylene gas flame or by the conventional general method, or whether this method used materials that could be overlaid or materials with good overlay properties such as Co-based alloys and some Ni-based alloys. It was limited to things.

On the other hand, in recent years, with the advent of high-density energy heat sources such as lasers and plasmas, the degree of freedom in materials has expanded, and it has become possible to build up Fe-based alloys that have relatively poor build-up properties.

By the way, conventionally known general Fe-based alloys can be roughly divided into (1) Fe-Cr-C alloys (Automotive Technology VO132
, No. 8.1978, p. 757), (2) Fe-
Cr-C-N i (Co) alloy (JP-A-58-15
4492@publication), (3) Fe-Cr-C-N + (
Co)-W(M0) based alloy (SAE, J775, JAN
88, p. 20).

[Problems to be Solved by the Invention] The above-mentioned conventional Fe-based alloys are particularly designed to be overlaid with a high-density energetic heat source, and generally have the following problems.

That is, although the alloy (1) above is the cheapest, it cannot be said to have sufficient properties for valve overlays, ie, toughness, corrosion resistance, wear resistance, etc.

The alloy of (2) above is either improved in toughness and corrosion resistance by adding Ni and/or CO, or has insufficient wear resistance and is expensive.

The alloy (3) above has improved wear resistance by adding W and/or Mo to the alloy (2), but is expensive. Note that Ni and/or CO also tends to suppress the decrease in toughness caused by the addition of W and/or Mo.

By the way, the valve face generally requires performance such as corrosion resistance, wear resistance, and fatigue strength.

The face of the intake valve is particularly required to have wear resistance, and the face of the exhaust valve is required to have particularly high fatigue strength and corrosion resistance at high temperatures.

A technical problem to be solved by the present invention is to provide an intake overlay engine valve that is inexpensive, has excellent toughness and wear resistance, and does not require extreme corrosion resistance.

[Means for Solving the Problems] The intake overlay engine valve of the present invention has a C: 1° 1 to 1
．． 9% by weight (hereinafter, % indicates weight%), Cr: 25~
33%, Mo: 3 to 8%, S+: 1°5% or less, Fe and unavoidable impurities: the remainder. It is characterized by having both.

The reason for limiting the above components will be explained below.

(C) C is partially dissolved in the Fe-Cr-Mo solid solution of the substrate to strengthen and harden the substrate, but most of the C is dissolved in Fe-Cr-Mo solid solution.
forms a double carbide mainly consisting of , and becomes a eutectic double carbide with the substrate solid solution. Therefore, C has the function of increasing the hardness of the alloy, improving the wear resistance, and lowering the melting point of the alloy.

When C is less than 1.1%, its effect is small, and when it exceeds 1.9%, double carbides increase and become hypereutectic.
Since double carbides crystallize as primary crystals, the toughness of the alloy decreases, which is not preferable.

For the above reasons, the amount of C added was limited to 1.1 to 1.9%.

(Cr) Cr constitutes a primary solid solution that forms a solid solution with FeSMo and becomes a matrix of the alloy. Moreover, a part of Cr combines with C together with Mo to form a double carbide mainly composed of Cr and Mo. That is, Cr, as a primary solid solution, increases oxidation resistance, corrosion resistance, and high-temperature strength, and also increases wear resistance through the formation of borocarbide.

If the content of Cr is less than 25%, the above-mentioned effects are poor, and if it is added in an amount of 33% or more, there is no effect of improving the above-mentioned effects, and the toughness of the alloy tends to decrease, which is not preferable.

For the above reasons, the amount of Cr added was limited to 25 to 33%.

(Mo) Mo is dissolved in the solid solution of the matrix to strengthen the alloy and at the same time improve the toughness of the alloy. It also combines with C along with Cr to form Cr and Mo double carbides, increasing the high temperature hardness of the alloy.
and '#4 has the function of improving abrasion resistance.

In particular, in the present invention, it has been found that by adding Mo, lumpy Mo-rich carbides are formed in addition to eutectic carbides, which significantly contributes to improving wear resistance.

If Mo is less than 3%, the amount of lumpy carbide is small and the improvement in wear resistance is insufficient, and if it is more than 8%, the amount of lumpy carbide is too much, resulting in a decrease in toughness and poor build-up properties. Furthermore, when Mo is 8% or more, there is also the problem that the aggressiveness towards the mating material increases.

For the above reasons, the amount of Mo added was limited to 3 to 8%.

(S i ) 3i is usually added as a deoxidizing agent, or
In the present invention, adding 1.5% or more of Sl reduces the toughness of the alloy.

For the above reasons, the amount of 3i added was limited to 1.5% or less.

The built-up portion of the built-up intake built-up engine valve of the present invention has a dendrite secondary arm spacing value (hereinafter referred to as DAS value) of 5 μm or less. This DAS value is a measure of the size of the overlay structure, that is, whether it is a coarse structure or a fine structure, and the smaller this value is, the finer the structure is. Therefore, when the DAS value exceeds 5 μm, the toughness decreases.

The above DAS value can be lowered by overlaying with a high-density energy heat source such as a laser or plasma.

When using the laser build-up method to make the DAS value 5 μm or less, the welding conditions are a laser output of 1.5 to 4.5 kW, a welding speed of 5 to 20 mm for 77 seconds, and a powder supply rate of 5 to 15 q/min. It is preferable. In addition, when using the plasma overlay method, the welding current is 100 to 130A, and the welding speed is 5.
It is preferable to carry out the welding under conditions of ~20 mm/sec and a powder supply rate of 5 to 15 Q/min.

[Function] The intake built-up engine valve of the present invention has excellent toughness and wear resistance because the composition of the built-up portion is specified and the DAS value is limited to 5 μm or less.

That is, due to the bonding of Cr and Mo with C, Cr, Mo
By-products mainly consisting of are formed, improving wear resistance. Moreover, Mo also forms massive Mo-rich carbides, which significantly improves wear resistance. Zarani, DASI
Because the overlay structure is fine due to the limitation of , it has excellent toughness.

[Example] The present invention will be explained below using examples.

1 having the composition shown in the table and excluding No. 10 and No. 21
Nine types of alloy powders were obtained by gas atomization.

Adjust the particle size of each powder to -250#, and use the overlay method shown in the table to make a valve material (cap diameter φ32 mm) made of 5UH3.
) was formed with a build-up part on the face surface to create a build-up engine valve for intake.

Note that the laser build-up method uses a laser output of 2.5kW.

The welding conditions were a welding speed of 9.5 mm/sec and a powder supply rate of 10 q/min. In addition, the plasma overlay method uses a plasma gas flow rate of 1.2'll/minζ welding current of 12OA, welding speed of 9
．． The welding conditions were 5 mm/sec and powder supply of 110 p/min.

The build-up structure and build-up properties of the build-up portion of the engine valve were investigated. The results are shown in the table.

In addition, the overlay structure is D by etching with Murakami reagent.
The AS value was measured and evaluated. In addition, build-up properties were evaluated based on wettability with the base material and bead shape.

Further, after forming a build-up part using the same 19 kinds of alloy powders as above on a plate-shaped base material made of 5UH3 by the build-up method shown in the table in the same manner as above, test screws were processed.

Regarding this test piece, Vickers hardness tester (load 10k)
A room temperature hardness test using a Vickers hardness tester (load: 1 kgf), a high temperature (600° C.) hardness test using a Vickers hardness tester (load: 1 kgf), and a Charpy impact test were conducted.

The results are shown in the table. The Charpy impact test was conducted using a notched test piece.

Furthermore, No. 10. having the composition shown in the table. and No. 2
Alloy No. 1 was melted in an argon gas atmosphere in an electric furnace and suction cast into a glass tube (φ4.8 mm) to form a built-up part. A similar valve material was overlaid on the face to create an overlay engine valve for intake.

Regarding the build-up portion of the engine valve, the build-up structure and build-up properties were investigated in the same manner as described above. The results are shown in the table.

Also, No. 10. and No. 21 alloy powder to 5UH
A bond and a test piece were fabricated using the oxygen-acetylene gas flame build-up method on a plate-shaped base material made of No. 3.

Regarding this test piece, Vickers hardness tester (load 10k)
qf), a high temperature (600° C.) hardness test using a Vickers hardness tester (load: 1 kgf), and a Charpy impact test were conducted in the same manner as described above. The results are shown in the table below.

In general, the wear resistance of engine valves with overlays made of alloys No. 1, No. 17 to No. 20, and separately manufactured 5t JH3 alloy valves without overlays were evaluated for wear resistance using a valve seat tester. . In this valve seat test, iron-based sintered valve seat material was used as the mating valve seat material, the test temperature was 270'C and 560'C, the test time was 8 hours, the load was 5kqf, and the number of strikes was 2158 times/min. It was conducted under the following conditions. The results are shown in FIG.

(evaluation> The results of each evaluation will be discussed below.

The valve face having a built-up part made of alloy No. 091 to No. 9 according to the present invention has a DAS value of 2.2 to 3 because the built-up part is formed using a high-density energy heat source.
．． It is as small as 8 μm. Therefore, despite using Fe-based alloy, the Charpy impact value is 0.6 kqf.
m/cm2 or more, and has excellent toughness. This performance is equivalent to or better than that of a conventional valve face in which a conventional alloy containing Go (NO921) is deposited using an oxygen-acetylene scum flame deposition method.

In addition, the valve face having built-up parts made of alloys No. 1 to No. 9 according to the present invention uses a high-density energy heat source to form the built-up parts, so Fe-based alloys are not used. Despite this, the build-up properties are good.

Furthermore, as is clear from the results shown in FIG. 1, the valve face with the built-up part made of the N011 alloy according to the present invention was made of a conventional alloy containing Co (No.

20> exhibits excellent wear resistance comparable to that of a valve face with a built-up part. As shown in Figure 2, which is a micrograph showing the metallographic structure of the built-up part of No. 1 alloy, the built-up part made of the alloy according to the present invention is composed of primary crystals (white parts in the figure). Either it is a eutectic butrite structure, or a lumpy Mo-rich carbide exists within the eutectic. This lumpy Mo
It is thought that the rich carbide (the large black part in the figure) significantly contributed to the improvement in wear resistance.

On the other hand, a comparative valve face having a built-up part made of an alloy has the following drawbacks.

No. 10 alloy has the same composition as No. 1 alloy, but
Since it is built up using the oxygen-acetylene scum flame build-up method, build-up properties are poor. Furthermore, the DAS value is large and the toughness is poor.

Alloy No. 11 has an excessively low Or content and therefore has poor oxidation resistance.

Alloy No. 12 has an excessively low Mo content and therefore has poor wear resistance.

Alloy No. 13 has an excessive MoC content, so it has poor build-up properties.

Alloy No. 14 has an excessively low C content and therefore has poor wear resistance.

Since alloy No. 15 has an excessive C content, it has poor build-up properties and poor toughness.

Alloy No. 16 has an excessive 3i content, so it is inferior in toughness.

Alloy No. 17 does not contain Mo, so it has poor wear resistance.

Alloy No. 18 also has poor wear resistance because it does not contain Mo.

Alloys No. 19 to No. 21 contain Ni, Co, W, etc., and are therefore expensive.

[Effects of the Invention] As detailed above, the intake build-up engine valve of the present invention has good build-up properties, toughness, and wear resistance of the built-up portion,
Moreover, it is inexpensive.

[Brief explanation of drawings]

FIG. 1 is a graph showing the measurement results of the amount of wear on the valve face using a valve seat tester, and FIG. 2 is a microscopic photograph showing the metal structure of the built-up portion of the valve face according to the present invention.

Claims (1)

[Claims] (1) C: 1.1 to 1.9% by weight, Cr: 25 to 33% by weight, Mo: 3 to 8% by weight, Si: 1.5% by weight or less,
An intake build-up engine valve having a build-up part on the valve face that is made up of the remainder of Fe and unavoidable impurities and has a dendrite secondary arm spacing value (DAS value) of 5 μm or less.