JP4414928B2 - Titanium alloy material for exhaust system parts having excellent workability, manufacturing method thereof, and exhaust device using the alloy material - Google Patents

Description

  The present invention relates to a titanium material used as an exhaust device for automobiles such as automobiles and motorcycles, and is exposed to a high temperature of 600 ° C. or higher as well as a main muffler part, and particularly requires heat resistance and oxidation resistance. It is related to a titanium alloy material that is lightweight and has excellent corrosion resistance, workability, heat resistance and oxidation resistance, and an exhaust device using this titanium alloy material, which can be used for parts such as exhaust manifolds, exhaust pipes and catalyst mufflers. .

  Titanium materials are used in automobile exhaust systems because they are lightweight but have high strength and good corrosion resistance. Combustion gases discharged from automobile and motorcycle engines are combined into one by an exhaust manifold and discharged from an exhaust port at the rear of the vehicle by an exhaust pipe. The exhaust pipe is divided into several parts to put a catalyst and a muffler (muffler) in the middle. In the present specification, the exhaust system is referred to as the exhaust system from the exhaust manifold to the exhaust pipe and the exhaust port.

  Currently, stainless steel with excellent corrosion resistance is mainly used as a material for such exhaust devices, but recently titanium has been used mainly in motorcycles from the viewpoint of weight reduction of vehicles. The material of titanium mufflers currently used is mostly JIS type 2 industrial pure titanium. The temperature of the exhaust gas is said to be about 700 ° C or higher, and pure titanium usually decreases in strength at a temperature of 600 ° C, but the muffler part is far from the exhaust gas outlet of the engine and touches the outside air. Therefore, it is rare that the temperature is 600 ° C. or higher, and even if the temperature is 600 ° C. or higher, it is not exposed to that temperature for a long time, and therefore pure titanium can be used sufficiently.

  However, in recent years, there has been a need to reduce the weight to a portion closer to the exhaust port of the engine, and a titanium alloy with higher high-temperature strength has been demanded.

  From the viewpoint of high strength at a high temperature of 600 ° C. or higher, a Ti-3Al-2.5V alloy or a Ti-6Al-4V alloy is suitable.

  Patent Document 1 proposes a titanium alloy having both cold workability and high temperature strength.

JP 2001-234266 A

  However, the Ti-3Al-2.5V alloy is too strong at room temperature and has poor formability, and cold work is possible, but it tends to cause ear cracks, and intermediate annealing is repeated many times. There was a problem that it was necessary and processing cost was high. Further, Ti-6Al-4V alloy is not suitable as an exhaust device material because it is difficult to cold work and cannot be made into a thin plate.

  On the other hand, the invention described in Patent Document 1 is a titanium alloy containing 0.5 to 2.3% by mass of Al. However, the elongation at room temperature is as small as less than 30%, and particularly a shape that requires stretch formability is required. It is difficult to process the exhaust system, and the degree of design freedom is limited.

  Accordingly, the present invention provides a titanium alloy material for exhaust system parts excellent in workability that can be used in parts such as an exhaust manifold, an exhaust pipe, and a catalyst muffler that are exposed to a high temperature around 600 ° C., a method for producing the same, and the alloy An object of the present invention is to provide an exhaust device using a material.

  The present inventors investigated the effect of impurity elements such as oxygen and Fe in order to improve the workability at room temperature, that is, the elongation of the Ti—Al binary titanium alloy. As a result, it has been found that the elongation at room temperature is greatly improved when the oxygen and Fe contents are below a certain value.

The present invention is based on such knowledge, and the gist thereof is as follows.
(1) It is characterized by containing Al: 0.4 to 2.3%, oxygen: 0.04% or less, Fe: 0.06% or less, and the balance being Ti and inevitable impurities. Titanium alloy material for exhaust system parts with excellent workability.
(2) By electron beam melting, it contains, by mass%, Al: 0.4 to 2.3%, oxygen: 0.04% or less, Fe: 0.06% or less, and the balance consisting of Ti and inevitable impurities. A method for producing a titanium alloy material for exhaust system parts having excellent workability, wherein the production is performed by adjusting the component composition.
(3) An exhaust system characterized in that any one or more parts of the exhaust manifold, the exhaust pipe, the catalyst, and the muffler are made of the titanium alloy material described in the above (1).

  According to the present invention, it is possible to manufacture and provide a titanium alloy material that is lightweight and has sufficient strength at high temperatures, good oxidation resistance at high temperatures, and good workability at room temperature. The weight reduction of exhaust devices for automobiles such as two-wheeled vehicles has greatly advanced, and industrial and environmental contributions are extremely remarkable.

  In general, plastic deformation of metallic materials is handled by slip deformation, but the slip system of titanium alloy with hexagonal close-packed structure is the number of slip systems necessary for deformation while maintaining continuous grain boundaries (five). Therefore, plastic deformation occurs due to twin deformation. Therefore, facilitating twinning deformation improves the workability of the titanium alloy. The titanium alloy in the present invention contains Al in an amount of 0.4 to 2.5% in order to obtain sufficient high-temperature strength and oxidation resistance, but Al suppresses twin deformation. Therefore, in order to obtain sufficient workability at room temperature, it is necessary to easily induce twin deformation. On the other hand, paying attention to the influence of oxygen and investigating its content and room temperature ductility, it was found that sufficient ductility can be obtained by setting the oxygen content to 0.04% or less. Oxygen is inevitably more than a certain level in consumable electrode arc melting, which is a general titanium material melting method, and it is difficult to stably reduce the oxygen content to 0.04% or less. In order to remove oxygen and other impurities adhering to the melting raw material at the time of melting, this can be achieved by using an electron beam melting method as a method for producing an alloy having a low oxygen content such as the titanium alloy of the present invention. Can do.

The titanium alloy of the present invention has the first requirements of high strength, particularly strength at 600 ° C. and good workability at room temperature, and oxidation resistance at 600 ° C. or higher. Estimated high temperature strength and room-temperature strength is 1.5 times the 0.2% proof stress at 600 ° C. for JIS2 kinds of industrial titanium, i.e. 55N / mm ² or more, a 0.2% yield strength at room temperature is 310N / mm ² or less And the elongation at room temperature is 30% or more. The standard of oxidation resistance is that the increase in oxidation is 8 g / m ² or less by heating at 600 ° C. for 200 hours.

  In the present invention according to claim 1, in mass%, Al: 0.4 to 2.3%, oxygen: 0.04% or less, Fe: 0.06% or less, and the balance is composed of titanium and inevitable impurities. It was set as the titanium alloy material for exhaust system parts characterized by this. The reasons for limiting the contents of Al, oxygen, and Fe are as follows.

This is because if the amount of Al added is less than 0.4%, the 0.2% proof stress at 600 ° C. does not become 55 N / mm ² or more. If it exceeds 2.3%, the 0.2% proof stress at room temperature is 310 N. This is because it exceeds / mm ² . This is because the elongation at room temperature does not become 30% or more when the oxygen content is more than 0.04%. Fe is useful as an element that suppresses the coarsening of crystal grains when used at a high temperature, but if the content is more than 0.06%, elongation at room temperature is suppressed and the elongation does not exceed 30%.

  In the present invention described in claim 2, it is specified that the electron beam melting method is used as the method for producing the titanium alloy material described in claim 1. Oxygen enters at a certain level or more in the consumable electrode type arc melting, which is the most common melting method of titanium, but the electron beam melting method can remove oxygen adhering to the melting raw material at the time of melting. The electron beam melting method was selected as a method for stably melting the titanium alloy.

  According to the third aspect of the present invention, the exhaust device is manufactured using the titanium alloy material according to the first aspect. Since the titanium alloy of the present invention has workability and weldability according to JIS type 2 industrial titanium, it can be melted, rolled and formed by a method according to JIS type 2 industrial titanium. The thin plate subjected to cold rolling annealing is bent into a tubular shape, TIG welded, and each part is welded to form an exhaust device.

  Hereinafter, an example is given and the composition and operation effect of the present invention are explained more concretely.

  A titanium alloy having the components shown in Table 1 was cast into an ingot of about 10 kg. The Fe content of the titanium alloy was adjusted according to the purity of the raw material. No. in Table 1 Nos. 1 to 7, 9, and 12 are obtained by electron beam melting. 8, 10, 11, 13, and 14 were produced by consumable electrode type vacuum arc melting. These were heated to 850 to 900 ° C. and hot-rolled to obtain a plate having a thickness of about 3.5 mm. After shot blasting and pickling, this was further cold-rolled to obtain a plate having a thickness of 1 mm. The obtained plate was annealed in a vacuum at 750 ° C. for 1 hour. A specimen of JIS No. 13B was cut out from these test materials, and a room temperature tensile test was performed. Moreover, the high temperature tensile test based on JISG0567 was done at 600 degreeC. In the high-temperature oxidation test, a test piece of 20 mm × 20 mm was polished with # 400 sandpaper on the surface and end face, then exposed to each temperature of 600 ° C. in the atmosphere for 200 hours, and the change in weight before and after the test was measured. The increase in oxidation per unit cross-sectional area was determined.

The measurement results are summarized in Table 1. In Table 1, no. 1 to No. 7 is an embodiment of the present invention described in claims 1 and 2. 0.2% proof stress both 600 ° C. is 1.5 times the JIS2 kinds of industrial titanium, ie at 55N / mm ² or more, a 0.2% yield strength at room temperature is 310N / mm ² or less, and at room temperature The elongation was 30% or more. As for oxidation resistance, the increase in oxidation by heating at 600 ° C. for 200 hours is 8 g / m ² or less, sufficient ductility at room temperature, sufficient yield strength at high temperature, and excellent oxidation resistance at high temperature.

  On the other hand, No. manufactured by consumable electrode type vacuum arc melting, which is the most common for melting titanium. In 8, 10, and 11, since the oxygen content exceeds the range of the present invention, the proof stress at 600 ° C. exceeds the target value, but the ductility at room temperature is less than 30% and does not have sufficient workability. In addition, No. having a large Fe content. 9 and 12 have a ductility at room temperature of less than 30% and do not have sufficient workability.

  Moreover, No. containing V 1.3% by mass or 2.5% by mass. 13 and no. No. 14 has a high yield strength at 600 ° C. and is excellent in terms of high-temperature strength, but its ductility at room temperature is insufficient.

  No. in Table 1 200 kg of the titanium alloy having the components shown in FIG. 6 was melted by electron beam melting, roughly forged at 1000 ° C. to a 300 mm square, and further forged at 900 ° C., and then a slab having a thickness of 100 mm was produced. Next, after hot rolling at 850 ° C. to obtain a plate having a thickness of 4 mm, it was cold-rolled to a thickness of 1 mm and heat-treated at 750 ° C. for 1 hour.

  The thin plate was cut out with a width of 120 mm to produce a welded tube with an outer diameter of 38 mm. After bending, a welded tube was manufactured by TIG welding. The manufacturing process of the welded pipe was the same as that of manufacturing using a thin plate according to JIS type 2 industrial titanium.

  When a 60 ° conical cone was pushed into the end of the welded tube and expanded to 1.3 times the initial diameter, no crack was generated in the welded portion, and the material had good spreading characteristics. Moreover, when this welded pipe was bent 90 ° with a radius of 90 mm, no cracks or wrinkles occurred.

  The titanium alloy material of the present invention has high strength at high temperature, good oxidation resistance, excellent ductility at room temperature, and easy to manufacture welded pipes as conventional pure titanium materials. In addition to the main muffler portion, it can be used for exhaust device members such as exhaust manifolds, exhaust pipes and catalyst mufflers.

Claims (3)

% By mass
Al: 0.4 to 2.3%,
Oxygen: 0.04% or less,
Fe: A titanium alloy material for exhaust system parts excellent in workability, characterized by containing 0.06% or less and the balance being Ti and inevitable impurities. By electron beam melting,
Al: 0.4 to 2.3%,
Oxygen: 0.04% or less,
A process for producing a titanium alloy material for exhaust system parts excellent in workability, characterized by comprising Fe: 0.06% or less and adjusting the composition to a component composition comprising the balance Ti and inevitable impurities.   An exhaust system, wherein one or more parts of an exhaust manifold, an exhaust pipe, a catalyst, and a muffler are made of the titanium alloy material according to claim 1.