JP2006213961A - alpha-beta TYPE TITANIUM ALLOY WHICH GIVES TOOL LONG LIFE AND CHIPS PARTIBILITY - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an α-β type titanium alloy which is easily hot-worked, and not only has superior machinability but also gives a tool the long life and excellent chips partibility. <P>SOLUTION: The α-β titanium alloy includes 0.01-0.5 mass% REM and 0.08-0.25 mass% C as essential components. The titanium alloy with the superior balance of strength and ductility further comprises 2.0-7.0% Al; 2.0-10% one or more elements among 5.0% or less V, 6.0% or less Cr, 2.5% or less Fe and 5.0% or less Mo, in total; and the balance Ti with impurities. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an α-β type titanium alloy excellent not only in forgeability and machinability but also in tool life and chip breaking property.

  α-β type titanium alloy is to adjust properties such as strength, ductility, fracture toughness and fatigue strength by coexisting α phase with hexagonal HCP structure and β phase with body centered cubic BCC structure. However, it is widely used as a material for machine structural parts. In particular, automotive parts such as connecting rods, intake / exhaust valves, suspension springs, and mufflers are promising to use titanium alloys from the viewpoint of weight reduction and fuel efficiency improvement. However, due to the characteristics of titanium, machinability is poor, and improvement of machinability is desired.

As a titanium alloy with improved machinability, for example, Japanese Patent Publication No. 6-99764 (Patent Document 1) discloses rare earth elements (REM) such as Sc and Y and S, Se, Te. A titanium alloy for connecting rods with improved machinability while suppressing deterioration of toughness and ductility by forming a granular compound by compounding elements such as JP-B-6-53902 (patent) Reference 2) describes a free-cutting titanium alloy to which B is added in order to improve machinability by adding REM and improve hot workability, and patent 2626344 (Patent Document 3) discloses a free-cutting component. As P and S, P and Ni, P, S and Ni, etc. are added, the machinability is reduced and the inclusions are refined, thereby improving the free machinability and reducing the hot workability and fatigue strength. Suppressed titanium alloy is described To have.
Japanese Patent Publication No. 6-99764 Japanese Patent Publication No. 6-53902 Japanese Patent No. 2626344

However, the method of improving the machinability with the REM compound or the P compound, the machinability is easily affected by the temperature and the cooling rate in the melting-forging process, and in order to obtain the desired inclusions, strict management in the manufacturing process In addition, the variation varies depending on the material shape and size. In addition, when a special element such as S or B is added in combination with REM, the chip cutting property generally decreases and the tool life is not necessarily improved, and chips are entangled with the tool during the cutting process, and the work surface of the work material There is a problem of deteriorating properties.
The present invention has been made in view of such a problem, and provides an α-β type titanium alloy that is easy to manufacture and has excellent tool life and chip breaking properties as well as machinability without impairing hot workability. The purpose is to do.

  Conventionally, when REM is added alone, machinability is remarkably improved, but hot workability is extremely deteriorated. Therefore, a technique of adding special elements such as B and S has been employed to prevent this. As described above, the chip breaking property is reduced, and the improvement of the tool life cannot always be expected, and the chips are entangled with the tool, which causes the processing surface properties of the work material to deteriorate. The present inventor made a detailed investigation of the cause of deterioration of hot workability by adding REM alone without adding special elements such as S and B. As a result, β-phase crystal grains in the β temperature range during hot working. Was found to be coarse. The present invention has been made on the basis of such knowledge, and during hot working, TiC is finely precipitated in the β temperature range, and the hot workability is ensured by suppressing the coarsening of β grains, and only REM. This improves the machinability and improves the tool life and the chip breaking property.

That is, the α-β type titanium alloy of the present invention contains 0.01 to 0.5 mass% REM and 0.08 to 0.25 mass% C as essential components. Hereinafter, the component unit may be simply indicated as “%”.
By adding 0.08 to 0.25% of C, TiC is finely precipitated during hot working in the β temperature range, thereby making the β phase crystal grains finer and deteriorating hot workability. Can be prevented. Further, the machinability can be improved by the action of REM, and the solid solution REM embrittles the matrix in the cutting temperature range (600 to 800 ° C.) of titanium, or a small amount of REM oxide. Although it is not clear whether (submicron to several microns) improves the strain concentration in the cutting part, REM has an effect of facilitating the generation and division of chips, and also improves the tool life.

In the α-β type titanium alloy, the alloy components include 0.01 to 0.5% REM, 0.08 to 0.25% C, and 2.0 to 7.0% Al in mass%. 5.0% or less of V, 6.0% or less of Cr, 2.5% or less of Fe, 5.0% or less of Mo or less of Mo or less of 5.0% in total, containing 2.0 to 10% in total, the balance A composition comprising Ti and impurities is preferable. By setting it as such a component, it can have the outstanding mechanical property.
The alloy component contains 1.0% or less of Si in place of a part of Ti, or further includes one or two of Zr of 5.0% or less and Sn of 5.0% or less in total. The composition may be 6.0% or less.

  Since the α-β type titanium alloy of the present invention contains 0.01 to 0.5 mass% REM and 0.08 to 0.25 mass% C, the machinability can be reduced without impairing hot workability. Excellent, and excellent tool life and chip separation regardless of cutting conditions. Moreover, it is sufficient to perform hot working in the β temperature range, and manufacturing is easy.

Hereinafter, the composition of the α-β type titanium alloy of the present invention will be described.
The α-β type titanium alloy of the present invention contains 0.01 to 0.5 mass% REM and 0.08 to 0.25 mass% C as essential components, and has a structure composed of a β phase and an α phase at room temperature. It is what you have.

  C is effective in improving the strength and finely precipitates as TiC in the β temperature range, so that the β phase crystal grains are refined, thereby improving the hot workability. If it is less than 0.08%, such an action is insufficient. On the other hand, if it exceeds 0.25%, coarse TiC that does not dissolve in the α phase at room temperature remains, and the mechanical characteristics deteriorate. For this reason, the lower limit of the C amount is 0.08%, preferably 0.10%, and the upper limit is 0.25%, preferably 0.20%.

  REM is effective in improving machinability. For this reason, REM is added in an amount of 0.01% or more, but if added over 0.5%, it is hot even if the β-phase crystal grains are refined by TiC precipitation. Workability deteriorates. Therefore, in the present invention, the lower limit of REM is set to 0.01%, preferably 0.05%, and the upper limit is set to 0.5%, preferably 0.45%.

  The α-β type titanium alloy of the present invention basically contains C and REM in the above ranges as essential components, but forms stable compounds with REM such as S, Se, Te and B. It is desirable not to include easily facile elements as much as possible. This is because, when these elements are added in combination, the REM bonds with these elements to form a stable compound, and thus the above-described effects of REM disappear.

  As a preferable composition of the α-β type titanium alloy of the present invention, in addition to the predetermined amounts of C and REM, Al: 2.0 to 7.0% is included, and V: 5.0% or less, Cr: 6 0,0% or less, Fe: 2.0% or less, Mo: 3.0% or less, or a total of 2.0 to 10%, with the remainder consisting of Ti and inevitable impurities Can do. This titanium alloy has a tensile strength (TS) of 740 MPa or more and an elongation (El) of 10% or more, and is suitable as a material for various mechanical structures. Hereinafter, the reason for component limitation will be described.

Al: 2.0 to 7.0%
Al is an α stabilizing element and is added to generate an α phase. If the Al content is less than 2.0%, the α-phase is generated too little, and sufficient strength is not exhibited, so that the target TS cannot be satisfied. For this reason, the lower limit of Al is set to 2.0%, preferably 2.2%. On the other hand, if the Al content exceeds 7.0% and becomes excessive, the ductility deteriorates and El becomes lower than the target value. Therefore, the upper limit of Al is set to 7.0%, preferably 6.0%.

V: 5.0% or less, Cr: 6.0% or less, Fe: 2.0% or less, Mo: 3.0% or less, or a total of 2.0 to 10%
These elements are β-stabilizing elements, and are added in a total amount of 2.0% or more, preferably 3.0% or more in order to form a β phase. These elements also have the effect of improving the strength, and if they are added in excess of the upper limit of each element or added in a total amount exceeding 10%, the deterioration of El is caused. In particular, when the amount of Fe becomes excessive, the aperture also decreases. For this reason, the upper limit of each element is prescribed as described above, and the upper limit of the total amount is 10%.

In addition to the basic element, the balance is composed of the remainder Ti and unavoidable impurities. In order to further improve the strength, (1) Si: 1.0% or less, (2) Zr: An element selected from each group of 5.0% or less and Sn: 5.0% or less in total of 6.0% or less can be contained alone or in combination.
If Si exceeds 1.0% and Zr and Sn each alone or in total exceeds 6.0%, the ductility deteriorates and El of 10% or more cannot be obtained. For this reason, the upper limit of each element of Si, Zr, and Sn and the total amount of Zr and Sn are regulated as described above.

In general, the titanium alloy of the above embodiment is subjected to hot forging mainly in the β temperature range and processed into a target shape, and then annealed. That is, a desired shape is formed in a temperature range of about 970 ° C. or higher, or in the case of a shape in which forging cracking is difficult to occur, hot forging is performed up to an α-β two-phase temperature range below that, After cooling once, annealing is performed for about 15 to 120 minutes at a temperature in the β phase region (about 970 ° C. or higher) or the α-β two phase region (about 700 to 970 ° C.). By this annealing, residual stress is removed and the morphology of the α phase and the grain size are adjusted. Cooling after annealing is not particularly limited, and may be allowed to cool, air cool (about 0.5 to 2 ° C./sec), or water cooled (5 ° C./sec or more), but residual stress is particularly problematic. In such a case, it is preferable to avoid water cooling.
Hereinafter, although the example of the α-β type titanium alloy of the present invention will be described more specifically, the present invention is not construed as being limited by the example.

  Titanium alloys having various components shown in Table 1 below were melted in vacuum to produce about 120 g of ingot. This ingot was heated to 1200 ° C. and hot forged, and further formed into a 25 mmφ round bar in the β temperature range (more than the β transformation point (Tβ)) with 1000 ° C. as the lower limit. Subsequently, annealing was carried out at 1050 ° C. × 2 hr, and allowed to cool. The reason why the annealing was performed at 1050 ° C. in the β phase region is to avoid the change of the amount of the primary α phase depending on the component and extract only the influence of the alloy element on the machinability.

A machinability test piece was collected from the sample thus obtained and cut under the following cutting conditions to examine the tool wearability and chip breaking property. Tool wear was evaluated by measuring the amount of wear (μm) on the tool flank. The chip breaking property was evaluated by randomly extracting chips after the cutting test and weighing them with an electronic balance to determine the number per 1 g of chips. These test results are shown in Table 2.
・ Cutting conditions
(1) Tool: H13A tip (made by Sandvik)
(2) Cutting speed: 100m / min
(3) Cutting feed and depth of cut Condition A: 0.10mm / rev, 0.5mm
Condition B: 0.15 mm / rev, 1.0 mm
(4) Cutting length: 50m
(5) Cutting oil: None

  From Table 2, in the invention examples (Sample Nos. 2, 6-8, 10-15) in which the C amount and the REM amount are within the scope of the present invention, the tool feedability is acceptable when the cutting feed / cutting amount condition is Condition A. The level is not more than 50 μm, and even in Condition B, the acceptable level is not more than 70 μm, so that the wear resistance of the tool is excellent and the tool life is excellent. In addition, the chip breaking property is 60 / g or more, which is an acceptable level in the condition A, and 80 pieces / g or more, which is also the acceptable level in the condition B, and an excellent chip dividing property is obtained regardless of the cutting conditions. It has been. On the other hand, even when an appropriate amount of REM is added, Sample No. 3 to which S has been added in combination has a tool wear property and chip breaking property that are acceptable in Condition B, but do not reach the acceptable level in Condition A, and cutting. Satisfactory results are not obtained depending on the conditions. In Sample No. 4 to which B was added in combination, satisfactory results were not obtained in both tool wear resistance and chip breaking property.

Claims (4)

  α-β type titanium alloy, which contains 0.01 to 0.5 mass% rare earth element and 0.08 to 0.25 mass% C as essential components, and is excellent in tool life and chip breaking properties. β-type titanium alloy. mass%
0.01-0.5% rare earth element,
0.08-0.25% C,
Containing 2.0-7.0% Al,
5.0% or less of V, 6.0% or less of Cr, 2.5% or less of Fe, and 5.0% or less of Mo or less of Mo or less of 5.0% in total, including 2.0 to 10% in total,
The α-β type titanium alloy according to claim 1, comprising the balance Ti and impurities.   The α-β titanium alloy according to claim 2, further comprising 1.0% or less of Si. The α-β type titanium alloy according to claim 2 or 3, further comprising 6.0% or less of 5.0% or less of Zr and 5.0% or less of Sn or 2 kinds in total.