JPH0790524A - Batch annealing method for titanium strip - Google Patents

Abstract

PURPOSE:To produce products which are reduced in temp. difference due to coil parts and has uniform material characteristics in recrystallization annealing of a titanium strip. CONSTITUTION:The pressure in a bell type batch annealing furnace is reduced down to <=20hPa and thereafter gaseous argon is introduced therein and heating is started by restoring >= (atm. pressure +50hPa) positive pressure at the time of charging the coil of the titanium strip into this furnace and subjecting the titanium strip to recrystallization annealing. The titanium strip is subjected to soaking heating for >=4 hours in a range of 250 to 480 deg.C, and thereafter, the pressure in the furnace is again reduced clown to (20hPa and the gaseous argon is introduced therein. The soaking heating is executed by restoring >=(atm.+ 50QhPa) positive pressure, and thereafter, the strip is cooled in this gaseous atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a titanium strip batch annealing method in which a coil of titanium strip is charged into a bell-type batch annealing furnace and argon gas is introduced to carry out recrystallization annealing.

[0002]

2. Description of the Prior Art Titanium strips react easily with oxygen during annealing at high temperature, and due to a dense scale, coloring defects called temper color occur, which significantly impairs the appearance and causes a large degree of oxidation. It causes deterioration of the material. In addition, the titanium strip easily reacts with nitrogen and hydrogen, causing deterioration of the material. Therefore, conventionally, when carrying out the annealing of titanium strip, the coil of titanium strip is charged into a batch furnace, the inside of the furnace is evacuated to a pressure of about 10 ^-2 Pa, and then in or after vacuum evacuation. Argon gas is introduced for heating.

An example of such an annealing treatment method is as follows.
A titanium strip coil is charged into a batch furnace at atmospheric pressure, the furnace is evacuated, the pressure is reduced to 10 ^-2 Pa, the temperature rise is started, and argon gas is introduced after the material temperature reaches about 400 ° C. And heat soaking, and cooling with the argon gas filled (“Heat Treatment” Vol. 15 No. 6 (Dec. 1975)
Mon) P. 338-343), when charging titanium and a titanium alloy into a batch furnace and performing recrystallization annealing, the furnace is evacuated and the temperature rise is started to evaporate and heat until the material temperature falls within the range of 270-480 ° C. Then, an inert gas is introduced into the furnace, and the material temperature is 500 to 670 ° C. in the gas atmosphere.
To intermediate heating until the material temperature reaches 600 ° C. to 750 ° C. and then cooling in the gas atmosphere (JP-A-62-62).
No. 284054) is known.

[0004]

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention Heat Treatment 15 Vol. The methods disclosed in 338 to 343 and Japanese Patent Laid-Open No. 62-284054 are equipped with a dedicated furnace structure and an oil diffusion pump in order to load a titanium strip coil into a batch furnace and perform vacuum evacuation. Requires a large vacuum pump,
Not only is the equipment cost very expensive, but it also has the drawback of requiring time and effort for the daily maintenance of the vacuum exhaust equipment. Furthermore, heat transfer in a vacuum is only by radiation, the heat transfer efficiency is poor, and the temperature difference between the inside and outer peripheral edge of the coil of the titanium strip is large, and the conditions of heating and soaking depending on the coil portion are different, It was difficult to obtain a product with uniform material properties after annealing.

An object of the present invention is to utilize a bell-type batch annealing furnace having a high airtightness for recrystallization annealing of a titanium strip coil, and to reduce a temperature difference between coil portions to prevent temper color due to scale formation on the surface of the titanium strip. In addition, it is an object of the present invention to provide a method of batch annealing a titanium strip, which can obtain a product having uniform material properties.

[0006]

[Means for Solving the Problems] The present inventors have conducted various test studies in order to achieve the above object. As a result, a titanium strip coil was placed in a highly airtight bell-type batch annealing furnace used for annealing ordinary steel, and after depressurizing the furnace to a predetermined pressure, argon gas was introduced to replace it with air. After the start of heating, the temperature is raised to a predetermined temperature for uniform heating, the inside of the furnace is depressurized to 20 hPa or less again, and the argon gas is introduced again to exhaust the impurities inside the furnace to the outside of the furnace and to the titanium strip surface. The generation of temper color can be prevented, and by heating and soaking to a predetermined temperature in an argon gas atmosphere and then cooling in the gas atmosphere, thermal efficiency is improved as compared with heating in a vacuum, and the coil portion It was clarified that the temperature difference due to the above was small and a product of uniform material was obtained, and the present invention was reached.

That is, according to the first invention of the present application, when the titanium strip coil is charged into a bell-type batch annealing furnace and recrystallization annealing is performed, the pressure inside the furnace is reduced to 20 hPa or less, and then argon gas is introduced to the atmosphere. After returning to a positive pressure of +50 hPa or higher, heating is started, and soaking and heating are carried out for 4 hours or more in a material temperature range of 250 to 480 ° C., then the pressure inside the furnace is reduced to 20 hPa or lower, and then argon gas is introduced. The method is a batch annealing method for titanium strips, which is characterized by returning to a positive pressure of atmospheric pressure + 50 hPa or more, soaking and heating at a predetermined temperature, and then cooling in the gas atmosphere.

The second invention of the present application is that when the titanium strip coil is charged into a bell-type batch annealing furnace for recrystallization annealing, the pressure in the furnace is reduced to 20 hPa or less, and then argon gas is introduced. Heating is started by returning to a positive pressure of atmospheric pressure + 50 hPa or more, and soaking is performed for 4 hours or more in the material temperature range of 250 to 480 ° C. Argon gas is 10
After substituting in the range of up to 40 Nm ³ / Hr, the pressure inside the furnace is reduced to 20 hPa or lower again, and then argon gas is introduced to return the positive pressure to atmospheric pressure +50 hPa or higher, soaking at a predetermined temperature, and then heating the same. It is a batch annealing method for titanium strips, characterized by cooling in a gas atmosphere.

[0009]

The titanium strip according to the present invention means JI
Pure titanium specified in S H4600, 2 and 3 pure titanium, and 11 specified in JIS H4605, 12
Seed and 13 types of strips such as titanium-palladium alloy. The charging of the titanium strip coil into the bell-type batch annealing furnace according to the present invention is performed by charging the surface-cleaned titanium strip coil into the normal-pressure bell-type batch annealing furnace. Then, the pressure in the furnace is reduced to 20 hPa or less, and the air in the furnace is exhausted to the outside of the system. In this case, 20
At a pressure of hPa or higher, a large amount of oxygen remains in the furnace, which is a problem.

Then, argon gas was introduced, and the atmospheric pressure was +5.
After returning to a positive pressure of 0 hPa or higher and starting heating, the material temperature was soaked and heated in the range of 250 to 480 ° C. for 4 hours or more, and then the pressure in the furnace was reduced to 20 hPa or lower, and argon gas was introduced. Since it is returned to the positive pressure of atmospheric pressure + 50 hPa or more, the water and air adhering to the surface of the titanium strip coil and the surface of the metal material inside the furnace evaporate by heating,
It is discharged out of the system together with argon gas. At this time, if argon gas is introduced in the range of 10 to 40 Nm ³ / Hr during heating, discharge of evaporated water and air to the outside of the system is further promoted. In this case, if the material temperature is less than 250 ° C. and the soaking and heating is less than 4 hours, the evaporation of water and air adhering to the surface of the titanium strip coil and the surface of the metal material inside the furnace is insufficient, and 480 If the temperature exceeds ℃, an oxide film may be formed on the surface of the titanium strip coil. further,
When the input amount of argon gas is less than 10 Nm ³ / Hr,
The amount of evaporated water and air is not sufficiently discharged to the outside of the system.
When it exceeds Nm ³ / Hr, only the consumption of argon gas increases, the effect is saturated, and it is economically disadvantageous. Further, by reducing the pressure inside the furnace to 20 hPa or less again, the exhaust of evaporated water and air remaining in the atmosphere inside the furnace to the outside of the system is promoted. If it is 20 hPa or more, the effect is insufficient.

Next, argon gas is introduced again to return to a positive pressure of atmospheric pressure + 50 hPa or more, and uniform heating is performed at a predetermined temperature, for example, 600 to 750 ° C. In this case, if the atmosphere in the furnace is agitated by the circulation fan, the convection heat transfer is further promoted. Then, by cooling in the gas atmosphere, the heat transfer efficiency is poor and it is difficult to cool in a vacuum, but by cooling in argon gas until the material temperature becomes 200 ° C. or less, an oxide film called temper color is formed. It is possible to cool efficiently while preventing the above.

[0012]

【Example】

Example 1 JIS H460 having a plate thickness of 1.0 mm and a plate width of 1400 mm
The two types of pure titanium strip coils specified in 0 are loaded into a bell-type batch annealing furnace equipped with an exhaust system equipped with a rotary pump in the exhaust pipe, covered with an inner cover, and then depressurized to 10 hPa, Argon gas was introduced into the space, the pressure was returned to the positive pressure of atmospheric pressure + 50 hPa or more, and then a cover equipped with a heating device was covered to start heating. Then, the inner cover is filled with argon gas at 30 Nm ³ / H.
At the furnace atmosphere temperature of 400 ° C.
Heated for hours. Then, the introduction of argon gas into the inner cover was stopped, the inner pressure of the inner cover was reduced to 1 hPa, and the argon gas was introduced again to bring the atmospheric pressure to +50 h.
After returning to a positive pressure of Pa or higher, it is reheated to 680 ° C. and soaked for 15 hours. After that, heating is stopped and the cover with the heating device is removed. The atmosphere was cooled to 150 ° C. In this case, the temper color on the surface could be completely prevented, and the oxygen content in titanium was 50 ppm or less. Further, the variation in material temperature due to the coil portion was 5 ° C., and the difference in crystal grain size after annealing was within 0.5.

Example 2 JIS H460 having a plate thickness of 0.7 mm and a plate width of 1000 mm
The two types of titanium-palladium alloy strip coils specified in 0 are charged into a bell-type batch annealing furnace equipped with an exhaust system equipped with a rotary pump in an exhaust pipe, covered with an inner cover, and then decompressed to 10 hPa. After introducing argon gas into the furnace and returning it to a positive pressure of atmospheric pressure +50 hPa or more, heating was started by covering with a cover equipped with a heating device. Then, 40 argon gas is put in the inner cover.
Atmosphere temperature 3 in the furnace while charging with Nm ³ / Hr and replacing
Heated at 80 ° C. for 5 hours. Then, the supply of argon gas into the inner cover was stopped, the inner cover pressure was reduced to 1 hPa, and the argon gas was introduced again to return the positive pressure to atmospheric pressure + 50 hPa or more, and then reheated to 6
After heating to 50 ° C. and soaking and heating for 15 hours, heating was stopped, the cover equipped with the heating device was removed, the cooling cover was put on, and the mixture was cooled to 150 ° C. in an argon gas atmosphere. In this case, the temper color on the surface could be completely prevented, and the oxygen content in titanium was 50 ppm or less. Also, the variation in material temperature due to the coil portion is 6 ° C,
The difference in grain size after annealing was within 0.6.

Comparative Example JIS H460 having a thickness of 0.6 mm and a width of 1000 mm
The two types of pure titanium strip coils specified in 0 are charged into a batch furnace having an evacuation facility at atmospheric pressure, the inside of the furnace is evacuated, the pressure is reduced to 10 ^-2 Pa, and the temperature rise is started. 400
670 ° C by introducing argon gas when the temperature is raised to ℃
And soak for 5 hours, then in argon gas 2
Cooled to 00 ° C. In this case, the variation in material temperature due to the coil portion was 20 ° C., and the difference in crystal grain size after annealing was 1.2.

[0015]

As described above, according to the method of the present invention, in the recrystallization annealing of the titanium strip coil, it is possible to prevent the generation of an oxide film called temper color by replacing the argon gas, and to prevent the material temperature from changing depending on the coil portion. Variations can be suppressed and products of uniform quality can be obtained.

Claims (2)

[Claims] 1. When a coil of titanium strip is charged into a bell-type batch annealing furnace for recrystallization annealing, the inside of the furnace is set to 20.
After decompressing to hPa or less, introducing argon gas, returning to a positive pressure of atmospheric pressure + 50 hPa or more to start heating, and performing uniform heating for 4 hours or more in a material temperature range of 250 to 480 ° C., and then again in the furnace. The inside of the titanium strip is depressurized to 20 hPa or less, and then argon gas is introduced to return it to a positive pressure of atmospheric pressure + 50 hPa or more, soaking and heating at a predetermined temperature, and then cooling in the gas atmosphere. Batch annealing method. 2. When the coil of titanium strip is charged into a bell-type batch annealing furnace for recrystallization annealing, the inside of the furnace is set to 2
After reducing the pressure to 0 hPa or less, introducing argon gas, returning to a positive pressure of atmospheric pressure +50 hPa or more to start heating, and performing uniform heating for 4 hours or more in a material temperature range of 250 to 480 ° C. After substituting in the range of -40 Nm ³ / Hr, the pressure inside the furnace is reduced to 20 hPa or less,
Next, a batch annealing method for titanium strip, which comprises introducing argon gas to restore the positive pressure of atmospheric pressure + 50 hPa or more, soaking and heating at a predetermined temperature, and then cooling in the gas atmosphere.