JP4987609B2 - Heat-resistant titanium alloy for exhaust device member excellent in cold workability, manufacturing method thereof, and exhaust device member using the alloy - 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 not only to a main muffler (silencer) part but also to a high temperature of 700 ° C. or more, particularly heat resistance and acid resistance. TECHNICAL FIELD The present invention relates to a heat-resistant titanium alloy for exhaust device members excellent in cold workability suitable for members such as exhaust manifolds, exhaust pipes, catalyst mufflers, main mufflers and the like, a manufacturing method thereof, and exhaust device members using the alloys Is.

  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 in order to put a catalyst muffler and a main muffler (silencer) on the way. 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 700 ° C. or higher, Ti-3Al-2.5V alloy and Ti-6Al-4V alloy are suitable.

  Patent Document 1 proposes a titanium alloy that is excellent in high-temperature oxidation resistance and corrosion resistance.

  Patent Documents 2 and 3 describe inventions relating to heat-resistant titanium alloys suitable for applications that require characteristics in a high temperature range and cold workability, such as exhaust system parts.

  Patent Document 4 describes a titanium plate for an electrolytic Cu foil production drum made of an α single-phase titanium alloy containing Cu and a method for producing the same.

JP 2001-234266 A JP 2005-290548 A JP 2005-298970 A JP 2004-2953 A

  However, the Ti-3Al-2.5V alloy has too high strength at room temperature, poor molding processability, large oxidation increase at temperatures near 700 ° C., and cold working is possible. There was a problem that it was easy to generate an ear crack, and it was necessary to insert intermediate annealing many times, 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 for a muffler containing 0.5 to 2.3% by mass of Al, which is superior in heat resistance to pure titanium and has a cold workability equivalent to that of pure titanium. Although it is disclosed that the high-temperature tensile strength at 600 to 700 ° C. is lower than that of the Ti-3Al-2.5V alloy, it is less than 60%.

  The invention described in Patent Document 2 is an α-type titanium alloy in which an α phase containing 0.30 to 1.5% by mass of Al and 0.10 to 1.0% by mass of Si is 90% by volume or more, Or, it is an alloy containing 0.1 to 0.5% Nb, but these alloys also have a high temperature tensile strength at 600 ° C. lower than that of the Ti-3Al-2.5V alloy, which is less than 70%. Absent.

  Furthermore, the invention described in Patent Document 3 includes, by mass%, Cu of 0.8 to 1.8%, O of 0.18% or less, Fe of 0.30% or less, and 0.3% or less of impurities. The present invention relates to a heat-resistant titanium alloy containing or a heat-resistant titanium alloy containing 0.3 to 1.5% in total of at least one or more of Sn, Zr, Mo, Nb, and Cr. The titanium alloy of Patent Document 3 also has a high temperature tensile strength at 700 ° C. lower than that of the Ti-3Al-2.5V alloy, which is less than 70%.

  Accordingly, the present invention has high strength at high temperatures and excellent oxidation resistance and cooling that can be used for parts such as exhaust manifolds, exhaust pipes, catalyst mufflers, and main mufflers that are exposed to high temperatures of 600 ° C. or higher. It is an object of the present invention to provide a titanium alloy for exhaust system parts that can stably exhibit the workability, a manufacturing method thereof, and an exhaust device member using the alloy. In the present invention, the high temperature tensile strength at 700 ° C. is more than 70% of the high temperature strength of Ti-3Al-2.5V alloy, and the oxidation resistance at 700 ° C. is the same as that of the titanium alloy described in Patent Document 3. It is an object of the present invention to provide a heat-resistant titanium alloy for an exhaust device member excellent in cold workability, which is about the above, a manufacturing method thereof, and an exhaust device member using the alloy.

The invention described in Patent Document 4 relates to a titanium alloy containing, by mass%, 0.5 to 2.1% of Cu, 0.1% or less of O, and 0.04% or less of Fe. The component rules are the same except that the amount of Cu is different from that of the invention. However, the invention described in Patent Document 4, suppress the precipitation of the β-phase or Ti ₂ Cu, and the average crystal grain size is related to α single phase titanium alloy to less than 40 [mu] m, the Ti ₂ Cu precipitates of the present invention It is different from the technology that actively uses it. The use of the invention described in Patent Document 4 is a cathode drum for producing electrolytic Cu foil. The electrode is deposited on the surface of the drum in a copper sulfate solution while rotating the drum. It is for peeling Cu depositing Cu foil and manufacturing Cu foil continuously. Since the quality of the surface of the drum has a great influence on the quality of the deposited Cu, it is required that the average crystal grain size is a fine α-phase structure having a fine particle size of less than 40 μm and no second phase. The invention described in item 4 satisfies this. However, the invention described in Patent Document 4 does not provide an exhaust device member material that is excellent in cold workability and has excellent oxidation resistance and high temperature strength at 700 ° C.

In order to solve the above problems, the present invention is based on the following means.
(1) It is characterized by containing Cu: more than 2.1% to 4.5%, oxygen: 0.04% or less, Fe: 0.06% or less, and the balance being Ti and inevitable impurities. A heat-resistant titanium alloy for exhaust device members having excellent cold workability.
(2) The cold workability according to claim 1, wherein the titanium alloy further contains one or two of Sn and Zr in a mass percentage of 0.5 to 1.5% in total. Excellent heat-resistant titanium alloy for exhaust devices.
(3) The heat-resistant titanium alloy for exhaust device members having excellent cold workability according to claim 1 or 2, wherein one or two of Si and Nb are contained in a total amount of 0.5 to 1.5%. .
(4) In the titanium alloy plate manufacturing method manufactured through the steps of hot rolling, hot rolling annealing, cold rolling, intermediate annealing, and final annealing of the material, the component adjustment in the material is performed as described in (1) to (3) above. A method for producing a heat-resistant titanium alloy plate for an exhaust device member excellent in cold workability, wherein the final annealing is performed in a temperature range of 650 to 780 ° C. while adjusting to the component composition described in any of the above.
(5) An exhaust device member using the titanium alloy according to any one of (1) to (3).

  According to the present invention, it is possible to provide a heat-resistant titanium alloy for an exhaust device member that is lightweight, has a sufficient strength at high temperatures, and is excellent in cold workability, a manufacturing method thereof, and an exhaust device member using the alloy. Become. As a result, the weight reduction of exhaust devices of automobiles such as four-wheeled vehicles and two-wheeled vehicles has greatly progressed, and the contribution of industrial and environmental aspects is extremely remarkable.

  In order to solve the above problems, the present inventors have investigated in detail the effects of component elements on high temperature strength, high temperature oxidation resistance, and cold workability with respect to titanium, and as a result, a certain amount of Cu was added to titanium, and By suppressing the oxygen and iron contents below a certain value, the high temperature strength at 600-700 ° C is improved to more than half that of Ti-3Al-2.5V alloy without impairing cold workability and oxidation resistance. I found out that it is possible. The present invention has been made based on this finding.

  In the present invention according to claim 1 (hereinafter referred to as the present invention (1)), by mass%, more than 2.1% to 4.5% Cu, 0.04% or less oxygen, 0.06% or less A titanium alloy composed of Fe, the balance Ti and inevitable impurities was used.

Cu dissolves in titanium at a maximum of about 1.8%, and when Cu is added beyond that, a Ti ₂ Cu phase is formed. That is, the titanium alloy of the present invention is a two-phase alloy in which a Ti ₂ Cu phase is precipitated on α-Ti. This Ti ₂ Cu phase was initially thought to have an adverse effect on cold workability, but in practice it has been found that high temperature strength can be improved with little effect on cold rollability. It was.

Furthermore, in order to obtain a tensile strength of about 91 N / mm ² or more, which is 70% of the 700 ° C. tensile strength of the Ti-3Al-2.5V alloy targeted by the present invention, near 700 ° C., a certain level of Ti ₂ Cu or more. The amount of phase precipitation is necessary, and for that purpose, the amount of Cu needs to exceed 2.1%. On the other hand, the upper limit of the Cu addition amount is set to 4.5%. If Cu is added beyond this, the strength at room temperature increases too much and the cold workability is impaired.

  For this reason, in this invention, the range of Cu amount was made more than 2.1%-4.5%.

  Since the titanium alloy of the present invention (1) has a large amount of Cu added, the strength at room temperature is slightly higher than that of pure titanium. Here, in order to ensure sufficient cold workability, it is necessary to suppress as much as possible the content of elements that affect the cold workability. Oxygen suppresses twin deformation responsible for the cold workability of the titanium material, so that the cold workability deteriorates if the content is large. If the oxygen content is 0.04% or less, the influence on cold workability can be almost ignored.

Fe is a β-phase stabilizing element and generates a β-phase from room temperature to a high temperature range. If there is a β phase, Cu concentrates in a concentrated manner, affecting the amount of solid solution Cu and the amount of Ti ₂ Cu phase, and thus degrading cold workability and oxidation resistance. By making the content of Fe 0.06% or less, the formation of the β phase can be suppressed, and the concentration of Cu in the β phase can be prevented.

  Impurity elements are elements contained in normal titanium, such as nitrogen, carbon, Ni, Cr, and hydrogen. If the sum of these elements is less than 0.1%, the cold workability is not affected.

  Next, the invention described in claim 2 (hereinafter referred to as the present invention (2)) will be described. In the present invention (2), the alloy of the present invention (1) contains one or two of Sn and Zr in a total amount of 0.5 to 1.5%. This is intended to further improve the high temperature strength of the alloy of the present invention (1). Both Sn and Zr have a solid solution in the α phase to some extent, and have an effect of increasing the high temperature strength by superimposing with Cu. The lower limit of the content is the minimum amount necessary to improve the high-temperature strength in either case of single or composite addition, and the upper limit is the amount of addition that affects the workability if added beyond this. is there.

  The invention according to claim 3 (hereinafter referred to as the present invention (3)) intends to further improve the high temperature oxidation resistance of the alloy of the present invention (1). Both Si and Nb are dissolved in the α phase to some extent, and have the effect of improving high-temperature oxidation resistance. The lower limit of the content is the minimum amount required to improve high-temperature oxidation resistance in either case of single or composite addition, and the upper limit is an additive that affects the workability if added beyond this. Amount.

  When adding either Sn or Zr effective for improving high-temperature strength, or both, and Si or Nb effective for high-temperature oxidation resistance, or both, the respective addition ranges overlap. By doing so, the effects of both high temperature strength and high temperature oxidation resistance can be obtained.

  The present invention according to claim 4 (hereinafter referred to as the present invention (4)) relates to a method of manufacturing a thin plate used particularly as an automobile exhaust device member. It is a manufacturing method of the titanium alloy plate of this invention (1)-(3) characterized by performing final annealing in the temperature range of 650-780 degreeC.

This is a condition for obtaining a mixed structure of the α phase and the Ti ₂ Cu phase. Annealing above 790 ° C results in a two-phase structure of α and β phases, and high temperature oxidation resistance is impaired. Therefore, annealing below 790 ° C is necessary, but from the viewpoint of temperature control, it is set to 780 ° C or less. . When annealing is performed at a temperature lower than 650 ° C., sufficient recrystallization cannot be obtained and ductility becomes small. Therefore, the lower limit of the annealing temperature is set to 650 ° C.

  The present invention according to claim 5 (hereinafter referred to as the present invention (5)) is an exhaust device member manufactured using the titanium alloys of the present inventions (1) to (3). Here, the exhaust device refers to an exhaust manifold, an exhaust pipe, a catalyst muffler, a main muffler (silencer), and the like. 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. Cold-rolled and annealed thin plates can be bent or molded into a tubular shape or a box shape with an elliptical cross section, TIG welded, and each part can be welded to form an exhaust device pipe or casing. .

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

  Titanium alloys having the components shown in Table 1 were melted by vacuum arc melting and cast into ingots of about 10 kg. 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 770 ° C. for 5 hours. 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 700 degreeC. The high-temperature oxidation test involves polishing a 20 mm × 20 mm test piece with sandpaper # 400 on the surface and end face, and then exposing it to 700 ° C. or 800 ° C. in the atmosphere for 200 hours to change the weight before and after the test. Was measured, and the amount of increase in oxidation per unit cross-sectional area was determined. Further, the maximum height of a 90 mm square plate-like test piece pressed with a crease pressing force of 1 ton without pressing and pressing a spherical punch having a diameter of 20 mm was measured (Erichsen test). The lubricant used is graphite grease.

The measurement results are summarized in Table 1. In Table 1, no. 1 to No. 21 is an embodiment of the present invention according to claims 1 to 3. In any case, the tensile strength at 700 ° C. exceeds 70% of Ti-3Al-2.5V alloy, that is, 91.7 N / mm ² , the 0.2% proof stress at room temperature is 330 N / mm ² or less, and at room temperature. The elongation was 32% or more. In oxidation resistance, the increase in oxidation after heating at 700 ° C. for 200 hours was 31 g / m ² or less, and the increase in oxidation after heating at 800 ° C. for 200 hours was 57 g / m ² or less. Furthermore, in the Eriksen test, it has a sufficient overhanging property exceeding 9.5 mm, and has a workability sufficient to withstand the processing of an end cap of a muffler. That is, the titanium alloy of the present invention exhibits sufficient ductility and workability at room temperature, sufficient strength that can be compared with a Ti-3Al-2.5V alloy at high temperatures, and excellent oxidation resistance at high temperatures.

  On the other hand, the Cu content is less than the range of the present invention. No. 22 has no problem with ductility at room temperature, workability, and high-temperature oxidation resistance, but the high-temperature strength at 700 ° C. is less than 70% of the high-temperature strength of the Ti-3Al-2.5V alloy. Moreover, the content of Cu exceeds the range of the present invention. 23, the high-temperature strength at 700 ° C. is sufficient, but the ductility and processability at room temperature are poor, and it is difficult to process exhaust parts.

  No. In No. 24, the oxygen content exceeds 0.06%, the ductility at room temperature is less than 35%, the Erichsen value is low, and the processability is not sufficient. In addition, No. with a large Fe content. In No. 25, the increase in oxidation at 700 ° C. is larger than that of the conventional alloy and does not have sufficient high-temperature oxidation resistance.

  No. shown in Table 1. 2 and No. The final annealing conditions of the test material having 7 components were 600 ° C. 5 h, 690 ° C. 5 h, and 820 ° C. 5 h, 0.2% proof stress at room temperature, elongation, tensile strength at 700 ° C., 700 ° C. and 800 ° C. 200 h. The increase in oxidation during heating and the Erichsen value were measured.

  The results are shown in Table 2. The annealing temperature is lower than the temperature range described in the present invention (4). In 27 and 30, the elongation at room temperature is greatly reduced, the Erichsen value is low, and the ductility and workability at room temperature are insufficient. Moreover, No. whose annealing temperature is higher than the temperature range as described in this invention (4). In 29 and 32, it becomes a two-phase structure of α and β, and the high-temperature oxidation resistance deteriorates. On the other hand, No. of Table 1 which annealed in the temperature range of this invention (4). 1 to 21 and No. 2 in Table 2. 28 and 31 have sufficient ductility and workability at room temperature, sufficient high-temperature strength at 700 ° C, and sufficient high-temperature oxidation resistance at 700 ° C and 800 ° C.

  No. in Table 1 200 kg of the α-type titanium alloy having the components shown in FIG. 6 was melted by electron beam melting, roughly forged at 1000 ° C. to 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 subjected to heat treatment at 770 ° C. for 5 hours.

  The above thin plate is appropriately cut out to the required width to produce a welded tube having an outer diameter of 42.7 mm, 50.8 mm, and 60.5 mm, and an elliptical casing having a cross-sectional shape of a major axis of 100 mm and a minor axis of 69 mm is cut out of the same material. Exhaust devices used for exhaust manifolds, exhaust pipes, catalyst mufflers, main muffler (silencer) outer cylinders, inner cylinders, and interior parts. In manufacturing, when a 60 ° conical cone is pushed into the end of a welded pipe having an outer diameter of 42.7 mm and expanded to 1.3 times the initial diameter, the weld does not crack and has good spreading characteristics. At the same time, when the welded tube was bent 90 ° with a radius of 90 mm, no cracks or wrinkles occurred.

  The titanium alloy of the present invention has high strength at high temperatures and good high temperature oxidation resistance, and can stably exhibit excellent ductility and cold workability at room temperature. It is easy and can be used not only for main muffler parts of automobiles such as automobiles and motorcycles but also for exhaust device members such as exhaust manifolds, exhaust pipes and catalyst mufflers.

Claims (5)

% By mass
Cu: more than 2.1% to 4.5%,
Oxygen: 0.04% or less,
Fe: A heat-resistant titanium alloy for exhaust device members having excellent cold workability, characterized by containing 0.06% or less and the balance being Ti and inevitable impurities. The titanium alloy is further in mass%,
The heat-resistant titanium alloy for exhaust device members having excellent cold workability according to claim 1, comprising one or two of Sn and Zr in a total amount of 0.5 to 1.5%.   The heat-resistant titanium alloy for exhaust device members having excellent cold workability according to claim 1 or 2, wherein one or two of Si and Nb are contained in a total amount of 0.5 to 1.5%.   The component adjustment of the said raw material is any one of Claims 1-3 in the titanium alloy plate manufacturing method manufactured through the process of hot rolling of a raw material, hot rolling annealing, cold rolling, intermediate annealing, and final annealing. A method for producing a heat-resistant titanium alloy plate for an exhaust device member having excellent cold workability, wherein the final annealing is performed in a temperature range of 650 to 780 ° C.   An exhaust device member using the titanium alloy according to any one of claims 1 to 3.