JPH01318709A - Manufacture of engine valve - Google Patents

Abstract

PURPOSE:To obtain an engine valve excellent in wear resistance by manufacturing an engine valve by cutting as well as integrally forming by a hot forging, etc. after the treatment of hot rolling, etc. with a betaTi alloy metal as a base metal and by executing nitriding at the specified temp. thereafter. CONSTITUTION:A betaTZi alloy metal consisting of Ti-3Al-8V-6Cr-4Mo-4Zr, Ti-15 V-3Al-3Sn-3Cr, etc. is taken as a base metal, after its hot rolling or solution treatment it is integrally formed by hot forging or cold forging or these combination and an engine valve is manufactured by executing specified cutting. Thereafter, a nitriding layer is formed by executing the nitriding serving for aging as well on the front face of the engine valve at the temp. range of 350-550 deg.C. The hardness of about Hv450 of the face is thus secured and the engine valve of excellent wear resistance is completed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an engine valve made of βTi alloy,
The present invention relates to a method for manufacturing an engine valve that is nitrided in a temperature range of 0° C. to 550° C. to form a nitrided layer on the entire surface to increase hardness and have excellent wear resistance.

[Conventional technology]

Normal engine valves are heat resistant! 4, and the specific gravity of the material is 7.8 to 8.0. On the other hand, for titanium alloy engine valves, the specific gravity of the material is approximately 4.5 to 4.7.
It weighs 60% less than heat-resistant steel, and has the advantage of increasing engine speed and increasing horsepower. However, its low hardness causes wear on the shaft end, seizing and galling of the shaft, and wear on the face. There are problems such as wear and tear. Measures have been taken to prevent wear on the shaft end surface, such as friction welding of Cr-Mo steel and brazing of Stellite tips.

Further, recently, a carburizing treatment method such as that disclosed in Japanese Patent Application Laid-Open No. 81-291959 has been proposed.

Furthermore, molybdenum thermal spraying is used as an effective surface treatment to prevent seizure of the shaft.

However, while face wear is not a problem in racing cars that are used for short periods of time, it is a concern in FFI cars that require no maintenance over long periods of time.Currently, the valve seat material is made to match the titanium alloy. Countermeasures have been taken, such as using copper-based sheet materials, but these are not sufficient.

Engine valves made of (α+β)-based Ti alloys have also been considered, but the Vickers hardness (hereinafter referred to as 1-1 V) is only about 330 (the face cannot be easily removed by wear-resistant surface treatments such as nitriding, carburizing, and plating). The current situation is that it is not possible to prevent surface wear.

[Problem to be solved by the invention]

As described above, in the prior art, since the engine valve is in the tlQ direction, even if an attempt is made to make the engine valve titanium, wear of the shaft end face, seizing and galling of the shaft portion, etc. occur. Furthermore, even if an (α+β) type Tj alloy is used, there is a problem in that the hardness is low and it is not possible to prevent wear on the face surface.

[Means to solve the problem]

As a result of various studies and tests to solve the above-mentioned problems, the inventors of the present application have found that the wear of the shaft end face and shaft portion of engine valves is reduced by hardness of about Hv300 to 330 (α+
β) type titanium alloy If a nitride layer is formed on the surface of the base material, sufficient wear resistance can be achieved, but the face surface requires even higher hardness, and a nitride layer is formed on the surface of the base material with Hv of about 300 to 330. If the hardness is too high (over 650 Hv), the seat surface of the iron-based sheet material with a current hardness of about 250 Hv will be damaged. It may cause scratches. Therefore, we considered using a βTi alloy which has a hardness of approximately 450 to 480 Hv if subjected to appropriate aging treatment. It has also been found that the βTi alloy itself is compatible with iron-based materials and has excellent wear resistance.

Therefore, the inventors of the present application have determined that Ti-3AuTi-3Au-
8V-6Cr-4, Ti-15V-3AI! , -33n
After hot rolling or solution treatment using a βTi alloy material consisting of -3Cr etc. as a base material, integral molding by hot forging, cold forging, or a combination thereof, cutting is performed to manufacture an engine valve, and then the engine valve is manufactured at 350℃~ The entire surface of the engine valve is subjected to nitriding treatment that also serves as aging in a temperature range of 550°C to form a nitrided layer, thereby increasing the hardness of the face surface H.
We have established a manufacturing method for engine valves that maintains v450 and improves wear resistance.

[For production]

As for the forming method used in the present invention, cold forging is the cheapest since the βTi alloy is highly deformable. In this case, after removing rolling scale by cutting or the like, oxidized scale is deposited at about 650° C., then lubricated with fluororesin or the like, and the valve head is formed by upsetting. Other forming methods include hot forging or a combination of hot and cold forging.

After forming, finishing cutting is performed, followed by a nitriding treatment that also serves as an aging process to fully form a nitrided layer to increase hardness and improve wear resistance.

Nitriding methods include gas nitriding, PVD1 io/nitriding, etc., but in the case of gas nitriding, the
The temperature reaches a high temperature of about 870° C., which causes bending in the shaft portion, making it unusable and undesirable.

On the other hand, PVD and ion nitriding treatments are preferable because the aging that also serves as nitriding can be performed at a low temperature of 350° C. to 550° C., resulting in cost reduction.

Taking these conditions into consideration, the processing temperature in the present invention is limited as follows.

If the treatment temperature is less than 350°C, the engine valve made of βTi alloy material will not age, but if it exceeds 550°C, it will soften due to overaging, making it impossible to maintain the appropriate hardness of around Hv450, and the wear resistance of the face surface will not be maintained. T! Since this is not preferable, the temperature of the nitriding treatment was limited to 350°C to 550°C.

[Example] As base material for engine valve, TiNia 5.00, Al1: 3.48, V: 8.0O1
Cr:5.77, Mo:3.80, Zr:3.82.0
:0.082, H:0.0059, N:0.015, F
A hot rolled wire rod of a βTi alloy having e: 0.13 (all percentages by weight) was integrally formed with a head part by hot forging, then cut and subjected to PVD nitriding treatment under the conditions shown in Table 1. For comparison, Ti-61, which is an (α+β)-based Ti alloy,
! Similar treatment was performed on the −4V base material.

(Margins below) Table 1 The cam (11, lifter ( 2), a retainer (3), a pulp spring (4), a pulp guide (5), a cylinder head (6), and a seat (7). (9) Set the edge/valve 0δ consisting of the head 00 with the face surface 0 [0], and install it in the engine intake system using methanol fuel.The engine rotation speed is 1000-5000 rpm, and the test time is 200 hours. The results of these tests are shown in Table 2.

As is clear from Table 2, if the βTi alloy base material (Nll 1.2.3), which is an example of the present invention, is nitrided in the temperature range of 350°C to 550°C, the nitriding result obtained It can be seen that the hardness of the face surface of Niasin pulp has increased, the wear resistance has been improved, and the amount of wear has increased significantly. On the other hand, even if the base material is a βTi alloy, the nitriding temperature is out of range (m 4.5 ), and even if the treatment temperature is appropriate, the base material is an (α+β) system Tj alloy (Kan 6). It is clear that the hardness of the face surface is low and the amount of wear is large, making it unsuitable for FFI, industry, and military applications that require long-term maintenance. In addition, βTi alloy is a (α+β) system Ti composite material with the same hardness even if the hardening is low.
Excellent wear resistance against iron-based sheet materials.

〔Effect of the invention〕

As described above, the present invention significantly improves the wear resistance of the face surface, which had been a problem with conventional Ti alloy F-1 valves, and eliminates wear on the shaft end, seizing and galling of the shaft, and provides a long-term non-slip valve. Since it can be applied to the edges/valves of mass-produced cars that require maintenance, it has the effect of greatly contributing to improving engine performance.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of a valve train for engine testing loaded with edge valves. In the figure,

Claims (1)

[Claims] βTi alloy material is used as the base material, hot rolled or solution treated, then integrally formed by hot forging, cold forging, or a combination thereof, and then cut to produce an engine valve, and then heated at a temperature of 350°C to 550°C. A method for manufacturing an engine valve, characterized in that the engine valve is nitrided to form a nitrided layer over the entire surface to increase hardness and improve wear resistance.