JPH02217452A - Method for toughening near beta-type titanium alloy - Google Patents

Abstract

PURPOSE:To toughen the Near beta-type titanium alloy in an ultra highstrength level by successively executing specified solution heat treatment in different temp. range to the Near beta-type titanium alloy and thereafter subjecting the alloy to low temp. aging. CONSTITUTION:The Near beta-type titanium alloy is held to the one less than the beta transformation temp. to (the transformation temp. -15 deg.C) or above for 0.5 to 4hr and is thereafter cooled to a room temp. at >=0.5 deg.C/sec rate. In this way, the alpha phase having relatively coarse grains of about 100mum order is precipitated into the beta mother phase. Next, the alloy is furthermore held to (the betatransformation temp. -20 deg.C) or below to (the beta transformation temp. -100 deg.C) or above for 0.5 to 4hr and is thereafter cooled to a room temp. at >=5 deg.C/sec rate. In this way, the alpha phase having relatively coarse grains of about 10mum order is precipitated. The alloy after finished with the solution heat treatment is subjected to low temp. aging treatment and the alpha phase having fine grains of about 1mum order is precipitated to secure sufficient strength. In this way, the Near beta-type titanium alloy in which the precipitated alpha phase coexists with two kinds of relatively coarse grains and fine grains and having high roughness even in an ultra high-strength of >=140kg/mm<2> level or above can be obtd.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is directed to Ne
This invention relates to arβ type titanium mold 2F.

[Conventional technology]

In recent years, Ne as represented by Ti-10V-2Fe-3Al
It is attracting attention as a material for making arβ type titanium molds. This alloy is Ti-
It has higher strength and toughness than the α+β type titanium alloy represented by 6Af-4V, and has less alloy components than the β type titanium alloy, and has lower hot deformation resistance, so it has excellent constant molar forgeability. For this reason, it is expected to be an alternative material to Ti-6Al-4V in the field of aircraft body structural materials.

Such Near β type titanium mold 2F 13V-1 1
Similar to industrial β-type titanium alloys such as Cr-3A1, the metastable β phase remains through rapid cooling after solution treatment, and the fine grained α phase is precipitated in this β matrix by low-temperature aging, resulting in toughness. can.

The conventional near β-type titanium mold 2F method is carried out in a manner similar to the toughening method for β-type titanium alloys. A combination of quenching and two-stage low-temperature aging treatment was disclosed in "Applications with titanium metal" Nikkan Kogyo Shimbunsha (1983), and also complied with AMS standard 4.
983 has a two-stage solution treatment method in which the material is held at a temperature of -15 to 40°C, the β-transformation point, for 30 minutes or more, then cooled to room temperature by furnace cooling or air cooling, and then further heated and held in the same manner and then cooled to room temperature by water cooling. Disclosed.

[Problem to be solved by the invention]

If such conventional toughening methods for β-type titanium alloys were applied to the Ti-10V-2Fe-3Al, the practical tensile strength would be limited to about 130 kg f /3. When the above-mentioned toughening method reaches an extremely high strength state where the tensile strength exceeds 140 kg f7m, the toughness decreases significantly and the fracture toughness value (K + c value) reaches 100 kg f7m. /
m"" or less, and the tensile strength is 130 k from the toughness perspective.
This is because g f can be suppressed to about 7 m''.

The present invention was made in view of this situation, and
Excellent properties of β-type titanium alloy, especially 140kgf
Strengthening of the Near β type titanium alloy, which can secure an excellent fracture toughness value (K r c value) that can sufficiently fulfill its function as a structural material for aircraft bodies even at ultra-high strength levels exceeding 100% / am” The purpose is to provide a method.

(Means for solving the problem) Ti10V-2, a typical Near β type titanium alloy
Fe-3Aj! When toughening is performed by combining solution treatment and low-temperature aging treatment, the behavior is basically β
It is the same as type titanium alloy, and fine-grained α-phase precipitates during low-temperature aging in the matrix consisting of metastable β-phase that remains after rapid cooling after solution treatment. Increases strength. However, if the strength is too high (too high), the toughness will drop sharply as mentioned above.

The present inventors have been advised that uniform precipitation of fine α-phase is essential to ensure strength, and have continued to conduct intensive research on methods for improving toughness without imposing restrictions on the precipitation of this @fine α-phase. As a result, it was found that it is effective to precipitate two relatively coarse-grained α phases of different sizes into the β matrix during solution treatment before low-temperature aging treatment.

The present invention was made based on such knowledge, and is based on the Nea
The rβ type titanium alloy is below the β transformation point (β transformation point -15℃
) or above for 0.5 hours or more and 4 hours or less, then cooled to room temperature at a rate of 0.5°C/sec or more, and then further heated to (β transformation point - 20°C) or less, (β transformation point - 100℃
) to a temperature of 0.5 to 4 hours, cooled to room temperature at a rate of 5"07 seconds or more, and then subjected to low-temperature aging. The gist is how to

According to the toughening method of the present invention, a first relatively coarse-grained α phase of about 100 μm order is precipitated in the β matrix in the first stage solution treatment, and about 10 μm in size is precipitated in the second stage solution treatment. A second, relatively coarse-grained α phase of the order of magnitude precipitates in the β matrix. As a result, after the low-temperature aging treatment, a &1lva structure was formed in which these two relatively coarse-grained α phases with different sizes coexisted with the fine-grained α-phase on the order of 1 μm that precipitated during the low-temperature aging treatment, and the latter fine grained α phase coexisted. Sufficient strength is guaranteed by the grain α phase, and the former two types of relatively coarse grain α phase provide L 40 kgf/
High toughness is ensured even at ultra-high strength levels exceeding 3.5 cm.

Although the mechanism by which toughness is improved by two types of relatively coarse α phases of different sizes is not clear, the experimental data obtained by the present inventors all support this fact.

[For production]

The reasons for limiting the numerical values in the toughening method of the present invention will be explained below.

In the first stage solution treatment, a first relatively coarse-grained α phase on the order of about 100 μm is precipitated in the β matrix. If the heating temperature in this treatment is above the β transformation point, the α phase itself cannot be precipitated, and if it is lower than (β transformation point -15°C), the coarse α phase of the predetermined grain size cannot be precipitated. Also, toughness is insufficient after low temperature aging. Therefore, the heating temperature was set below the β-transformation point and above (β-transformation point -15°C).

Regarding the heating holding time, if it is less than 0.5 hours, the alpha phase will not be sufficiently precipitated, and if it is more than 4 hours, the precipitated alpha phase will grow and a coarse grained alpha phase of the predetermined grain size cannot be obtained. It was set as 4 hours.

Cooling after heating and holding is carried out at a rate of 0.5° C./sec or more, because if the temperature is less than 0.5° C./sec, the precipitated α phase will grow. If the cooling rate is 0.5° C./sec or more, the growth of the precipitated α phase can be suppressed, so there is no upper limit to the cooling rate.

In the second stage solution treatment, a second relatively coarse-grained α phase on the order of about 10 μm is precipitated in the β phase.

If the heating temperature in this treatment exceeds (β transformation point - 20°C), the precipitated α phase will be too coarse grained, and if the heating temperature is below (β transformation point 100°C), the precipitated α phase will be too fine grained, and eventually In this case, the toughness is also insufficient after low temperature aging treatment. Therefore, the heating temperature is below (β transformation point - 20℃), (β transformation point - 100℃
) and above.

The heating holding time and the cooling rate after heating holding are set to 0 for the same reason as the first stage solution treatment.
．． The cooling rate was 0.5°C/sec for 5 to 4 hours.

In addition, the low-temperature aging treatment after the solution treatment precipitates a fine grained α phase of approximately 1 μm order in the β matrix to ensure strength, and depending on the required strength, the 2NH
The process is carried out appropriately in a temperature range in which the relatively coarse-grained α phase of No. 4 does not disappear.

〔Example〕

Next, the effects of the present invention will be explained based on examples.

Ti-10V with the composition shown in Table 1 by vacuum arc melting
An ingot made of -2Fe-3Al with a diameter of 300 mm was melted, and this ingot was made into a thick plate with a width of 80M and a thickness of 40 mm by β forging and α10β forging. The β transformation point of this titanium alloy is 785°C.

After toughening the manufactured thick plates under various conditions, each thick plate was subjected to a tensile test and a fracture toughness test as specified in AM34983. The results are shown in Table 2 along with the processing conditions.

Laws 1 to 3 show the results when treated with the toughening method of the present invention, and in each case, i , i 0 kgf/m"
A tensile strength of over 130 kg f /1 m'' and a fracture toughness value (K+c value) of over 130 kg f /1 m'' are ensured.

On the other hand, No. 4 is a case where low-temperature aging treatment is performed after the two-stage solution treatment shown in AMS standard 4983, and the tensile strength reaches 140 kgf/1 shoe due to low-temperature aging treatment, but the fracture Toughness value is 100 kg r/van
"" L is too much, Nl17 is also a toughening treatment that is generally performed on β-type titanium alloys, but when the tensile strength is 145 kgf/1, the fracture toughness value is 80 kg f.
/wm"" is nothing more than that. In addition, although floors 5 and 6 are similar to the toughening method of the present invention, they are cases where the conditions are not met, and at an ultra-high strength level where the tensile strength exceeds 140 kg f /1 m'', sufficient fracture toughness is not achieved. However, the reason why the tensile strength is not sufficient in case 6 is that the holding time at the solution treatment temperature was long and the crystal grains of the β phase became coarse.

The toughening method of the present invention is based on the Ti10V-2 toughening method shown in the example.
Fe-3AI! , and α+β type titanium alloy and β
Nearβ has an intermediate structure with type titanium alloys.
Effective for both type titanium type metal tough alloy.

〔Effect of the invention〕

As is clear from the above explanation, the toughening method of the present invention can be applied to the Near β type titanium type gold tough alloy 140kgf/wt
Even when ultra-high strength exceeding a” is imparted, it is possible to ensure sufficient toughness to fulfill its function as a structural material for the aircraft body.
This contributes to reducing the weight and increasing the strength of β-type titanium-type gold tough alloys, etc., and ultimately aircraft.

Claims (1)

[Claims] 1. After holding the near β type titanium alloy at a temperature below the β transformation point and above (β transformation point -15°C) for 0.5 hours or more and 4 hours or less, 0.5°C/second or more After cooling to room temperature at a rate of
A method for toughening a Near β-type titanium alloy, which comprises cooling to room temperature at a rate of at least °C/second, and then subjecting it to low-temperature aging.