JPH04209913A - Manufacture of exhaust valve for large diesel engine - Google Patents

Abstract

PURPOSE:To obtain an exhaust valve of an expected property easily and efficiently with a press of small capacity ' by forming a forging rough part, concerning to a seat part, in a clad part and also protrusion-molding a part in an opposite side to the clad part, thereafter placing the clad part in a lower mold side by opening rotary forging to perform warm working. CONSTITUTION:An exhaust valve for a large Diesel engine has a clad part of high alloy rich in heat resistance and corrosion resistance in a seat part 1 relating to a main unit 2. Here, a forging rough part, corresponding to the seat part 1, is formed in a clad part and also protrusion-forming a part in an opposite side to the clad part formed. Thereafter, the clad part is placed in a lower mold side by opening rotary forging to perform warm working in a range of 950 to 850 deg.C within 5min further as necessary to apply required heat treatment. That is, the forging rough part concerning to the seat part 1 is formed in the clad part of arranging inconel 718 or the like and also protrusionmolding the part in the opposite side to the clad part. In this way, the warm working is limited to only the seat part 1 necessary for forging to reduce force required for work.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing an exhaust valve for a large diesel engine easily and efficiently using a small-capacity press.

(Prior Art) Diesel engines are generally used as the main engines of large ships, and in recent years, overhead valve type two-stroke diesel engines have become popular from the standpoint of fuel efficiency.

By the way, these overhead valves (exhaust valves) are usually manufactured from heat-resistant stainless steel, but because they operate in high-temperature and corrosive environments, parts that are easily damaged, such as the part that comes into contact with the cylinder head (seat part), are coated with CO base. The super superalloy is protected by welding overlay of the hard metal of the Ni-based superalloy to prevent wear of the part.

However, since the sheet portion is required to have not only wear resistance but also corrosion resistance and toughness, overlaying the CO-based superalloy with the Ni-based superalloy is insufficient.

Therefore, as a method to obtain desirable sheet properties,
One idea would be to arrange an alloy that has excellent heat resistance, corrosion resistance, and age hardenability in the sheet part, and then age harden this after forging. Further, in this case, it is desirable that the sheet portion has compressive residual stress. The reason for this is that during use, thermal stress is unavoidably generated in the valve body due to temperature distribution.

It is difficult to obtain the properties of the sheet portion as described in 2 only by the inherent characteristics of the material overlaid on the sheet portion, and it is also necessary to consider the imparting of characteristics by the manufacturing process. Exhaust valves have been manufactured based on similar ideas in the past, and one of them is Nimonic 80A (rNcF8).
An example of this is an exhaust valve manufactured by ``0A''. This is N
It utilizes the age hardening properties of CF 80A, and is
F30A is warm-forged and then age-hardened to improve corrosion resistance and
The objective is to obtain an exhaust valve with excellent wear resistance and toughness. Here, the purpose of warm forging is to impart strain energy, which promotes precipitation and makes it possible to obtain high hardness.

However, in the warm forging region, the deformation resistance of the workpiece is extremely high, so a large working force, that is, a large-capacity press is required to cause even slight deformation.

To avoid this, there is a method of forging the whole part by repeating partial forging instead of forging the parts that need to be processed all at once. According to this method, since the projected area of the part to be forged in the -th cycle is small, the required working force is naturally reduced.

However, with this method, it is difficult to perform uniform processing over the entire part because there are variations in forging each time, and the material cools during repeated partial forging and the deformation resistance changes every moment. It is. Furthermore, since the purpose of warm working is to impart strain energy at a relatively low temperature, once forging has started, even if the temperature of the workpiece decreases, it is not possible to reheat and forge it. For this reason, it goes without saying that the partial forging method is disadvantageous, but even if a large-capacity press is used, the workpiece is in close contact with the forging die over its entire surface, resulting in a significant temperature drop or similar disadvantages.

(Problems to be Solved by the Invention) The present invention has been made to solve the problems of the conventional methods described above, and it is possible to easily and efficiently obtain desired properties using a small-capacity press. It is an object of the present invention to provide a method for manufacturing an exhaust valve having the following.

(Means for Solving the Problems) In order to achieve the above object, the method for manufacturing an exhaust valve for a large diesel engine according to the present invention provides an exhaust valve having a high-alloy cladding portion with high heat resistance and corrosion resistance in the seat portion. In this method, a forged raw material portion corresponding to the seat portion is formed into a cladding portion, and a portion opposite to the cladding portion is formed into a protrusion, and then the cladding portion is formed into a lower die by open rotary forging. As a side, warm processing is performed within a range of 950 to 850°C for 5 minutes, and further heat treatment is performed as necessary.

That is, the method of the present invention is characterized by the following configuration.

■ Material selection In the method of the present invention, the following materials are used.

First, heat-resistant stainless steel is used for the exhaust valve body in consideration of price and marketability. For example, JIS 5UH31 or its equivalent.

Next, for the seat portion, an equivalent Ni-based bulky alloy such as Inconel 718 is used. This is because cladding by weld build-up is relatively easy, the hardness increases greatly due to aging treatment, and the effect of accelerating age hardening is large through relatively moderate warm working.

■ Shape of the forged raw material In the method of the present invention, the forged raw material portion corresponding to the seat portion is formed as a cladding portion in which the above-mentioned Inconel 718 etc. are arranged, and the opposite side of the cladding portion is formed as shown in Fig. 1 (A). As shown, protrusion molding is performed. This is to limit the warm working to only the sheet portion 1 that requires training and to reduce the force required for working. Note that 2 in FIG. 1(a) indicates the main body.

■Forging method The method of the present invention uses a rotary forging method. This is because in the rotary forging method, as shown in Figure 2, the upper die 3 and the workpiece 4 are machined in partial contact with each other, so the processing time is about 10 to 20 times that of a normal press. This is because it has the ability to process large exhaust valves with small-capacity rotary forging equipment. Furthermore, in the method of the present invention, this rotary forging process is performed in an open state without being closed, and as shown in FIG. 1 (b),
This causes burrs 5 to be generated in the processed portion. By doing so, it is possible to avoid insufficient pressing ability due to the high deformation resistance of the Inconel 718, and it is also possible to easily give the necessary amount of strain to the Inconel 718.

The area where warm processing is effective for the hardness of Inconel 718 after aging treatment and the relationship between temperature and deformation resistance of Inconel 718 are shown in FIGS. 3 and 4, respectively.

As can be seen from FIG. 3, the warm working area for Inconel 718 is close to the low temperature limit of the processable area. This region is a region in which forging cracks should be a concern in the case of normal press forging, or there is a margin for cracking in rotary forging. Therefore, rotary forging as in the present invention has an advantage.

In addition, the deformation resistance of Inconel 718 in this temperature range is
As can be seen from Figure 4, 55-65kg f/mm
2, which is extremely high. If you want to forge this using a normal press, you will need a capacity of about 8,000 tons, taking into account the projected area of the actual exhaust valve machining area, but if you use rotary forging as in the present invention, it is possible to forge about 500 tons. It is.

Next, FIG. 5 shows the die assembly for rotary forging during warm working.

In the method of the present invention, the forged raw material portion corresponding to the sheet portion formed with the cladding portion is protrusion-molded, and the corresponding upper die 3
The side recesses 6 allow local forging of only the necessary parts, which is effective in reducing machining force.

Furthermore, before forging, the lower mold 7 also contacts the workpiece 4 only through the seat portion 1, making partial contact, which is effective in suppressing the temperature drop of the workpiece 4.

Furthermore, another purpose of arranging the sheet portion l on the lower mold 7 side as in the present invention is to leave compressive residual stress in the sheet portion after completion. That is, when comparing the forming capacity of the upper die 3 and the lower die 7 of rotary forging, the forming capacity of the upper die 3 is higher. In other words, since more processing force is applied to the upper mold 3 side, the amount of processing heat generated on the upper mold 3 side increases, and a temperature difference occurs between the upper mold 3 side and the lower mold 7 side of the workpiece 4.

By the way, in the method of the present invention, the workpiece 4 is water-cooled immediately after warm working, if necessary, or at this time, the sheet part 1 is rapidly cooled from a lower temperature than other parts, so that the residual stress after cooling is This results in compressive stress.

As mentioned earlier, when the exhaust valve is in use, a temperature distribution occurs, with a temperature distribution of approximately 450°C at the seat and 500°C at the bottom of the valve.
~600°C. In addition, the valve body and Inconel 718
The linear expansion coefficient of each is 18Xlo-”/”C114
Since it is Since it is about 3X10-',
It is extremely important to apply compressive residual stress to the seat portion during warm forging, and it is no exaggeration to say that it affects the performance of the valve.

Next, the pattern of warm forging is shown in FIG. T1 in FIG. 6 is a solid solution treatment time of about 3 hours, and T2 is a warm forging time of less than 5 minutes (usually 30 seconds to 1 minute).

In the present invention, the temperature of warm forging is 950 to 850°C.
1. The reason why the time is set to within 5 minutes is to prevent precipitation of precipitates (δ phase) that do not contribute to age hardening. In addition,
Since rotary forging has a high processing capacity, it is possible to process Inconel 718 and heat-resistant stainless steel in a short time even though they are difficult-to-process materials as shown in FIG.

(Example) An example in which an exhaust valve is manufactured using the method of the present invention will be described below.

FIG. 7 is a sectional view of an exhaust valve mounted on an actual diesel engine after warm forging. Only the valve head portion is shown.

Inconel 718 and heat-resistant stainless steel have different deformation resistances, so if you simply upset Inconel 718, which has a high deformation resistance, it will hardly deform, and only the heat-resistant stainless steel will deform. Despite the difference in the amount of deformation between the two, there was no significant difference. The strain in the thickness direction and the strain in the radial direction of the main body and seat portion of the exhaust valve manufactured by the method of the present invention are shown in Table 1 below.

After the exhaust valve shown in FIG. 7 was subjected to age hardening treatment, a strain gauge was attached to the seat part and the residual stress was measured by the cutting method. The results are shown in Table 2 below. Note that T in Table 2 indicates the circumferential direction, and R indicates the radial direction.

Table 2 From Table 2 above, it can be seen that uniform and high compressive residual stress is applied to the sheet portion. This can be said to be the greatest feature of the method of the present invention.

Next, the results of hardness, corrosion resistance, and toughness (thermal shock resistance) after aging treatment are shown in Tables 3, 4, and 5, respectively. Both have good performance as exhaust valves for marine diesel engines.

Table 3 Tables 4 and 5 (Effects of the Invention) As explained above, according to the method of the present invention, an exhaust valve for large diesel engines having desirable properties can be
It is clear that it can be manufactured using a small capacity press.

[Brief explanation of the drawings] Fig. 1 is an explanatory diagram of the forged rough material used in the present invention, (a) is before processing, (b) is after processing, Fig. 2 is an explanatory diagram of the principle of rotary forging, and Fig. 3 is an explanatory diagram of the forged rough material used in the present invention. The figure shows the forging method and its processing range.
The figure shows the deformation resistance of Inconel 718, and Figure 5 shows the die set for rotary forging, where (a) shows the pattern before processing, (b) after processing, and Fig. 6 shows the pattern of warm forging. 7 are diagrams showing the cross-sectional shape of the exhaust valve. 11 is the seat part, 2 is the main body, 3 is the upper mold, and 7 is the lower mold. Patent applicant: Sumitomo Metal Industries, Ltd. Kawasaki Heavy Industries, Ltd.

Claims (1)

[Claims] (1) A method for manufacturing an exhaust valve having a high-alloy cladding portion with high heat resistance and corrosion resistance in the seat portion, in which the forged raw material portion corresponding to the seat portion is formed as the cladding portion, and the cladding portion and the cladding portion are The opposite side of the cladding part is then formed into a protrusion mold, and then open rotary forging is performed to form a 95mm piece with the cladding part as the lower die side.
A method for producing an exhaust valve for a large diesel engine, which comprises warm working at 0 to 8,500°C for 5 minutes or less, and further subjecting it to necessary heat treatment if necessary.