JP3118342B2 - Method of heating titanium and titanium alloy rolled material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for heating a raw material when hot working titanium and titanium alloy into rods, wires, pipes and the like.

[0002]

2. Description of the Related Art Titanium and titanium alloys are widely used in rods and wires, such as aircraft components, seawater ropes and eyeglass frames, because of their properties such as excellent corrosion resistance and high specific strength.

[0003] On the other hand, titanium has an extremely high oxidizing power, oxygen easily penetrates into the inside, and the oxidation hardened layer increases in a high temperature range. Therefore, the billet of the rolled material is hot
When rolled into wire or tube material, an oxidized hardened layer during heating remains after rolling. For this reason, the surface of the rolled material is removed by cutting or the like, but the remaining oxidized hardened layer causes the cutting tool to be broken or the material to be broken, resulting in extremely poor productivity. In addition, there is a problem that defects such as surface cracks of the product due to the oxidation hardened layer also occur.

For example, when a rolled material of a Ti-6A1-4V alloy is heated at 950 ° C. for 90 minutes only in a normal furnace for heating in a combustion atmosphere and then rod-rolled, an oxidized hardened layer of about 200 μm is formed on the surface of the rolled material. Generate. The thickness of the oxidation hardened layer is
In the case of the Ti-6A1-4V alloy, the thickness from the surface where the Hv is 400 or more in terms of the cross-sectional hardness, and in the case of titanium, the Hv is 300 or more is determined. When such a thick oxidation-hardened layer is formed, the cutting tool is damaged during the cutting after rolling.

In order to prevent surface oxidation during heating, Japanese Patent Publication No. 36-8163 describes a method of applying an antioxidant or water glass to a material surface in advance and heating the material surface.

[0006]

However, in this method, there is a problem that the applied antioxidant and water glass are easily peeled off locally, and further, the peeled off part becomes uneven in surface. In addition, since a step of applying an antioxidant to the material one by one and a step of removing the antioxidant after rolling are added, the production efficiency is extremely low.

In addition, there is a method in which the heating atmosphere is heated to a non-oxidizing atmosphere such as argon gas. However, in actual operation, it takes a long time to replace the inside of the heating furnace with the non-oxidizing atmosphere, and even if the replacement is performed, In addition, there is a problem that when the heating material is taken in and out, the air enters the heating furnace and does not become completely non-oxidized.

According to the present invention, titanium and a titanium alloy are made of a rod,
In the heating of a material at the time of hot working to a wire, a tube material, or the like, it is intended to suppress the formation of an oxidized hardened layer on the surface, perform heating with high production efficiency, and reduce the oxidized hardened layer of the rolled material.

[0009]

DISCLOSURE OF THE INVENTION The present inventors have proposed a method for heating a material when hot working titanium and a titanium alloy into a rod, a wire, a tube, or the like, while suppressing the formation of an oxidized hardened layer and producing the material. In order to perform highly efficient heating, the heating is divided into two stages, and in the primary heating, the combustion atmosphere is used up to the temperature range where the thickness of the oxidized hardened layer, which oxidizes but is not harmful to cutting after rolling, etc., does not increase. In the high-temperature region where the oxidation-hardened layer rapidly increases, heating is performed in an induction heating furnace under the condition that the thickness is equal to or less than the predetermined thickness of the oxidation-hardened layer. As a result, they have found that the oxidized hardened layer of the rolled material can be reduced.

The present invention is as follows. (1) after the primary heating of the rolled material of titanium and titanium alloys in a heating furnace of a combustion atmosphere, subsequently to a predetermined processing temperature by secondary heating in an induction heating furnace, the method of continuous heating, wherein the primary heating The heating is performed at a temperature equal to or lower than the temperature at which the thickness of the oxidation hardened layer on the surface starts to increase, and within a heating time predetermined according to the secondary heating temperature.

(2) In the heating of the rolled titanium material of the above (1), the primary heating temperature is 680 ° C. or less, and the heating time in the secondary heating is a time satisfying the expression (1); t ≦ [4800 / (T + 273)] ² (1) T: heating temperature (° C.) t: heating time (minutes).

(3) In the heating of the α + β type titanium alloy rolled material, the primary heating temperature is set to 780 ° C. or lower, and the heating time in the secondary heating is a time satisfying the expression (2); t ≦ [5900 / (T + 273) )] ² ··· ⁽²⁾ T: heating temperature (℃) t: heating time (minutes).

(4) For the β-type titanium alloy rolled material, the primary heating temperature is 780 ° C. or lower, and the heating time in the secondary heating is a time that satisfies the expression (3); t ≦ [5600 / (T + 273)] ² ... (3) T: Heating temperature (° C) t: Heating time (min)

[0014]

The present inventors have examined the relationship between the workability of the cutting work after rolling and the thickness of the oxidized hard layer on the surface of the rolled material. As a result, in order to perform machining with less damage to the cutting tool,
It has been found that the thickness of the oxidized hardened layer of the rolled material needs to be about 60 μm or less. In order to reduce the thickness of the oxidized hardened layer of the rolled material, the thickness of the oxidized hardened layer generated when the rolled material is heated may be reduced. Although there is a variation due to the rolling reduction of rolling, if the thickness of the oxidized hardened layer generated at the time of heating is at least 60 μm or less, the thickness of the oxidized hardened layer of the rolled material can be reduced to 60 μm or less. However,
In a continuous combustion atmosphere heating furnace usually used in industrial production, it is difficult to perform heating for a short time so that at least the thickness of the oxidation hardened layer is 60 μm or less.

The titanium alloy has a dense hexagonal crystal structure (α
There are three types: α-type alloy of phase: hcp), two-phase α + β-type alloy of α and body-centered cubic (β-phase: bcc) and β-type alloy. For α type, Ti-5A1-2.5Sn alloy, etc. For α + β type, Ti-6A1-4AV, Ti
Ti-3A1-8V-6Cr-4Mo-4Zr, Ti for β type such as -3A1-2.5V alloy
-15V-3Cr-3Sn-3A1 alloy, etc.

Therefore, titanium JIS 2 types, α-type Ti-5AI
-2.5Sn alloy, α + β type Ti-6AI-4V alloy and β type Ti-
Using 3AI-8V-6Cr-4Mo-4Zr alloy, we examined the effect of heating temperature and the formation of an oxidized hardened layer. However, it was found that the thickness of the oxidized hardened layer did not increase significantly. Further, it has been found that the thickness of the oxidation hardened layer of the α-type, α + β-type and β-type titanium alloys does not increase so much in a temperature range of about 780 ° C. or lower. This is because the oxidation resistance is improved as compared with titanium due to the alloy components Al, Sn, and Mo.

On the other hand, in order to hot-work titanium and titanium alloy into rods, wires and pipes, it is necessary to heat titanium to 700 ° C. or more and titanium alloy to 800 ° C. or more in view of its deformation resistance and deformability. desirable. Further, since it is not necessary to heat to a temperature of more than 950 ° C. for titanium and to more than 1250 ° C. for titanium alloy, and only to increase the thickness of the oxidized hardened layer, the upper limit of the desirable secondary heating temperature is 950 ° C. for titanium. For titanium alloys, 1250 ° C. is desirable.

In order to suppress the formation of the oxidation hardened layer during the heating of the material, heating at a low temperature can be considered, but the heating temperature required for processing is determined in consideration of the deformation resistance and deformability of the material. Things. Therefore, as described above, it is a possible measure to shorten the heating time, but it is difficult to heat for a short time in a continuous combustion atmosphere heating furnace usually used in a production process. On the other hand, a method of heating with an induction heating furnace from the beginning is also conceivable, but it is not necessarily effective in terms of manufacturing cost and production efficiency.

From these results, low-temperature and long-time primary heating is performed until a temperature range in which the thickness of the oxidized hardened layer, which is harmful to the cutting work after rolling, does not increase, and then the high-temperature range required for hot working is reduced to two. It has been found that the next heating reduces the thickness of the oxidized and cured layer by adjusting the heating time according to the heating temperature.

Next, in determining the secondary heating conditions, particularly the heating time, the relationship between the heating temperature and time and the thickness of the oxidized hardened layer in the hot working temperature range was investigated. Titanium JIS2
Species, α type Ti-5AI-2.5Sn alloy, α + β type Ti-6AI-4V alloy and β type Ti-3AI-8V-6Cr-4Mo-4Zr alloy,
After heating for 1 hour to a temperature at which the depth of the oxidation hardened layer does not increase as primary heating, 600 ° C. or less for titanium or 780 ° C. or less for titanium alloy,
Various heating was performed within 1 hour within the range of 0 to 1250 ° C., and the thickness of the oxidation hardened layer was examined. From the results, the heating time in the secondary heating satisfies the formula (1) for titanium, the formula (2) for α and α + β type titanium alloys, and the formula (3) for β type titanium alloys. It has been found that by setting the time, the thickness of the oxidation hardened layer can be reduced to 60 μm or less.

T ≦ [4800 / (T + 273)] ² ... (1) t ≦ [5900 / (T + 273)] ² ... (2) t ≦ [5600 / (T + 273)] ^2. Here, T is the heating temperature (° C.), and t is the heating time (minutes).

FIG. 1 shows the respective ranges of the secondary heating conditions of titanium and α, α + β type and β type titanium alloys. Here, although the β-type titanium alloy contains an oxidation resistance improving component of Al and Mo, the V-type titanium alloy conversely reduces the oxidation resistance.
, The oxidation resistance in the high temperature region is slightly inferior to that of the α and α + β type titanium alloys.

[0023]

[Examples] The thickness of the oxidized hardened layer after heating under various heating conditions using JIS 2 grade titanium materials and rolled billets (cross-sectional size: 106 × 106 mm) of various titanium alloys (in the case of titanium) Table 1 shows the results of an investigation of the cross-sectional hardness: Hv ≧ 300, and in the case of a titanium alloy, the thickness from the surface where Hv ≧ 400. Furthermore, after heating and rolling to roll a wire having a diameter of 11 mm, the results of skinning with a cutting depth of 0.1 mm using a round hole reverse die are also shown in Table 1. In addition, the primary heating time was all 60 minutes,
The secondary heating was performed in an induction heating furnace in the atmosphere.

[0024]

[Table 1]

In the present invention example, the oxidation hardened layer during heating was 60 μm.
m or less, and as a result, there was no tool breakage or the like even in the cutting work after rolling, which was favorable.

[0026]

According to the present invention, the oxidized layer at the time of heating can be reduced, as a result, the surface oxidized hardened layer of the rolled material can be suppressed, and the burden of subsequent cutting and the like can be reduced.
And high production efficiency is obtained, and the industrial effect is remarkable.

[Brief description of the drawings]

FIG. 1 is a graph showing a range of secondary heating conditions (temperature, time) of a titanium alloy.

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Akira Ishio 3434 Shimada, Omitsu-shi Nippon Steel Corporation Inside the Hikari Works (72) Inventor Yutaka Tadano 3434 Shimada, Oaza, Hikari-shi New Japan Inside the Hikari Works of Steel Corporation (72) Inventor Satoshi Yamamoto 3434 Shimada, Oaza, Nippon Steel Inside of the Hikari Works Nippon Steel Corporation (72) Inventor Tsuneshige Takahashi 3434 Shimada, Oaza, Nippon Steel Corporation (56) References JP-A-6-170410 (JP, A) JP-A-5-329510 (JP, A) JP-A-59-232612 (JP, A) JP-B-36-8163 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21B 45/00 B21B 3/00 C22F 1/18

Claims (4)

(57) [Claims] 1. A method for continuously heating a rolled material of titanium and a titanium alloy in a heating furnace in a combustion atmosphere, followed by a secondary heating in an induction heating furnace to a predetermined processing temperature. Titanium and titanium alloy rolling, wherein the primary heating is performed at a temperature equal to or lower than the temperature at which the thickness of the oxidation hardened layer on the surface starts to increase, and the secondary heating is performed within a predetermined heating time according to the heating temperature. How to heat the material. 2. The method according to claim 1, wherein the primary heating temperature is 68.
A method for heating a rolled titanium material, wherein the temperature is 0 ° C. or less and the heating time in the secondary heating is a time that satisfies the formula (1); t ≦ [4800 / (T + 273)] ² (1) T: heating temperature (° C.) t: heating time (minutes). 3. The method according to claim 1, wherein the primary heating temperature is 78.
Α and α + β-type rolled titanium alloy material, characterized in that the temperature is 0 ° C. or less and the heating time in the secondary heating is a time that satisfies the formula (2); t ≦ [5900 / (T + 273)] ^2. .. (2) T: heating temperature (° C.) t: heating time (minutes). 4. The method according to claim 1, wherein the primary heating temperature is 78.
A method for heating a rolled β-type titanium alloy material, characterized in that the temperature is 0 ° C. or less and the heating time in the secondary heating is a time satisfying the expression (3); t ≦ [5600 / (T + 273)] ^2. (3) T: heating temperature (° C.) t: heating time (minutes).