JPH0549802B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an engine valve for an internal combustion engine, and more particularly to an exhaust valve whose face performance is improved by surface treatment.

(Prior Art) Austenitic heat-resistant steel (for example, SUH31) is generally used for exhaust valves. However, in recent years, the usage conditions of internal combustion engines have tended to become more severe, and against this backdrop, it has become necessary to use the heat-resistant steel as a base material and apply stellite overlay to the face surface, which is the surface that contacts the valve seat. As a result, exhaust valves with improved wear resistance, heat resistance, etc. are increasingly being used.

(Problems to be Solved by the Invention) However, in the engine valves with the above-mentioned stellite overlay, the stellite itself is an expensive alloy based on cobalt (Co), and thin-walled overlay is difficult, resulting in a high cost per unit engine valve. In view of the fact that the amount used is large, there is a problem that it has to be extremely expensive.

The present invention is intended to solve the above-mentioned problems, and aims to provide an inexpensive exhaust valve while guaranteeing face surface performance equivalent to that of stellite overlays.

(Means for solving the problem) The above problem is solved by using austenitic heat-resistant steel as the base material, and using chromium (Cr) on the face surface.
10 to 60 wt%, carbon (C) 1 to 8 wt%, one or more of molybdenum (Mo), nickel (Ni), tungsten (W), boron (B), silicon (Si), Co, total 5 The solution is an exhaust valve formed of an alloy layer consisting of ~20wt%, the balance iron (Fe).

(Function) In the exhaust valve configured as above,
Cr combines with C to form carbide, which contributes to improving hardness, ie, wear resistance, and also serves to strengthen the matrix and increase heat resistance. However, if the content is less than 10wt%, the desired wear resistance and heat resistance cannot be secured, while if it exceeds 60wt%, alloying properties with the valve base material will deteriorate. %.

C combines with Cr, W, and Mo to form hard carbides and improves wear resistance, but if it is less than 1wt%, the desired effect cannot be obtained, while if it exceeds 8wt%, wear resistance decreases. Therefore, this was set at 1 to 8 wt%.

In addition, Mo, Ni, W, B, Si, and Co contribute to improving wear resistance by forming carbides, as well as improving heat resistance and corrosion resistance by strengthening the matrix.
If the total amount of one or more of them is less than 5 wt%, the desired effect cannot be obtained. On the other hand, if it exceeds 20wt%, the economic efficiency deteriorates, so this should be reduced to 5 to 20wt%.
%.

Therefore, in order to form an alloy with the above composition on the valve face surface, an alloy powder with the above composition is prepared in advance, this is thermally sprayed onto the face base surface, and then a laser beam, TIG arc, plasma arc, etc. The joint with the valve base material (face base) is partially alloyed by irradiation with a high-density energy medium, and finally, it is polished to the desired size and shape.

As a result, the hardness of the face surface is Hv400 ~
800, it is possible to ensure the same wear resistance, heat resistance, and corrosion resistance as conventional stellite overlays, and it also has improved bonding strength with the base material, making it an inexpensive exhaust valve with excellent overall face surface performance. can be obtained.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

Example 1 An alloy powder consisting of 20.0 wt% Cr, 3.0 wt% C, 10 wt% Ni, and the balance Fe was sprayed onto the face base of a valve body formed using SUH31 as a base material, and then the sprayed portion was sprayed. Laser irradiation, final
The face was polished to the desired size and shape.

FIG. 1 shows the main structure of the engine valve obtained as described above. In the same figure,
1 is an alloy layer according to the present invention formed on the face base surface 3 of the valve body 2;
This will constitute the following. The thickness of the alloy layer 1 is
It is about 0.2 to 0.6 mm at most.

On the other hand, an alloy having the same composition as above was separately formed on the surface of a test piece under the same thermal spraying conditions, and after polishing, this was subjected to a Bitkers hardness test, an Okoshi type rapid wear test, and a microscope test.

Example 2 Cr20.0wt%, C3.0wt%, Mo10.0wt%, balance Fe
This was sprayed onto the surface of a test piece formed using SUH31 as a base material, and after polishing, it was subjected to various tests similar to those in Example 1.

Comparative Example Stellite was overlaid on the surface of a test piece formed using SUH31 as a base material, and after polishing, it was subjected to a hardness test and an Ohgoe type rapid wear test.

The test results of Examples 1 and 2 and Comparative Examples will be explained below.

Figure 2 shows the results of the Okoshi type rapid abrasion test, and from this it can be seen that Examples 1 and 2 according to the present invention are approximately the same as or similar to the comparative example in which Stellite was deposited. It was confirmed that the abrasion resistance was slightly better than that of the conventional one. In addition, the hardness of Example 2 is higher than that of Example 1 (Example 1: Hv450-550, Example 2: Hv600-550).
700), and the abrasion resistance was also slightly superior to that of Example 2.

Figure 3 shows the microscopic structure of Example 1, and Figure 4 shows the microscopic structure of Example 1.
The figure shows the microscopic structure of Example 2. In these figures, the white part represents the Cr-based complex carbide, and the black part represents the matrix (Fe-Cr), but an almost uniform microstructure is obtained as a whole.

(Effects of the Invention) As explained above in detail, the exhaust valve according to the present invention has an Fe-Cr alloy formed on the face surface instead of the conventional stellite.
While ensuring the same face surface performance as Stellite, its relatively low material cost made it possible to create an inexpensive exhaust valve.

[Brief explanation of the drawing]

Fig. 1 is a side view showing a partial cross section of the main structure of the exhaust valve according to the present invention, and Fig. 2 shows the results of a wear test on a test piece manufactured using the same procedure as that of the present exhaust valve. A graph is shown in comparison with the results of a comparative example in which metallization was carried out, FIG. 3 is a micrograph showing an example of the metallographic structure of an engine valve according to the present invention, and FIG. 4 is a similar example showing another example of the metallographic structure. This is a microscopic photograph. 1... Alloy layer, 4... Face surface.

Claims (1)

[Claims] 1 The base material is austenitic heat-resistant steel, and the face is made of Cr10~60wt%, Cl~8wt%, Mo, Ni,
One or more of W, B, Si, Co, total 5
An exhaust valve for an engine characterized by being formed of an alloy layer consisting of ~20wt% and the balance Fe.