JPS5837383B2 - Continuous annealing method for titanium and titanium alloy strips - Google Patents

Description

Detailed Description of the Invention The present invention provides titanium and titanium alloy strips (hereinafter abbreviated as titanium strips) hardened by cold rolling.
It relates to a method of annealing titanium without coloring due to oxidation and with a surface quality that is advantageous for use, especially titanium IJ.
This relates to a continuous annealing method that simultaneously forms a hardened layer on the surface of the tip.

Conventionally, titanium tubes are manufactured as welded tubes or seamless tubes, and welded tubes are manufactured by cutting a titanium strip into strips, then roll forming, and then performing, for example, TIG welding.

In many cases, the mechanical properties of the titanium materials used for these welded pipes are controlled primarily by controlling only the amount of oxygen, and these materials are generally referred to as industrially pure titanium.

However, if special corrosion resistance such as crevice corrosion is required, a titanium alloy containing a small amount of palladium may be used.

These titanium and titanium alloys are cold rolled into thin sheets, wound into coils, and often batch annealed in high vacuum, but may also be annealed in high purity inert gas.

All of these methods are aimed at preventing the reaction between titanium material and oxygen or nitrogen.

This conventional annealing method produces titanium strips that are free from oxidation-induced discoloration and have a uniform material quality. However, when this titanium strip is used as a raw material, for example, in the production of welded titanium tubes, the annealed titanium I-IJ tubes Because titanium is soft, surface scratches are easily formed during the forming process using forming rolls, straightening rolls, etc. As a result, these scratches remain on the surface of the manufactured welded titanium tubes, reducing the commercial value, and in general, titanium tubes are Because of their excellent corrosion resistance, they tend to become thinner, and the occurrence of such surface flaws is undesirable because it reduces the effective wall thickness.

In addition, titanium tubes are often used as heat transfer tubes for heat exchangers, but when assembling the heat exchanger, surface flaws may occur when the titanium tubes are stretched and inserted into tube sheets or buttress plates. It was something that could be granted.

From the above-mentioned viewpoints, this invention solves the problems of titanium l-IJ sprues treated by conventional annealing methods.
In other words, the present invention provides a continuous annealing method that solves the problem of easy surface flaws, and when continuously annealing a titanium strip after cold rolling in a gas atmosphere, the heating temperature is set to less than 650 to 750°C, and the atmosphere gas, 30
By using a mixed gas of argon and nitrogen, or both, containing ~100p of oxygen, the surface of the titanium coil after annealing is freed from oxygen and nitrogen without being colored by oxidation or nitridation. Either nitrogen,
This method is characterized by a continuous annealing method for a titanium strip in which a hardened layer is formed by dissolving both of them in solid solution, and this surface hardened layer makes it extremely difficult to generate surface flaws.

Note that in batch annealing, when gas is introduced, only the edges of the coil are hardened, but in continuous annealing, where the entire surface of the material is exposed to atmospheric gas, the reaction with the gas occurs uniformly over the entire surface, making it even more effective. It has the following.

Furthermore, when carrying out the continuous annealing method of the present invention, it is desirable that the hardness of the surface hardened layer formed on the titanium IJ spout after annealing is 240 to 350 in terms of Witzkers hardness; This is because if the hardness is less than 240, the formation of surface flaws cannot be suppressed, whereas if the hardness exceeds 350, the titanium strip itself tends to become brittle.

In addition, in the continuous annealing method of this invention, the heating temperature is set to 65
The reason for limiting the heating temperature to 0 to less than 750°C is that at a heating temperature of less than 650°C, a heating holding time of 1 minute or more is required to satisfactorily impart the desired mechanical properties, especially yield strength, to the titanium strip after annealing. If the heating retention time is long, it becomes necessary to increase the length of the heating furnace for high-efficiency operation, which is not only impractical but also increases equipment costs, and also reduces the hardened layer. Hardness is also low, on the other hand, 75
When the heating temperature is 0℃ or higher, nitrogen,
Alternatively, if a mixed gas of nitrogen and argon is used, the reaction of nitrogen to the titanium strip becomes rapid and violent, forming titanium nitride on the surface.
This is because the titanium nitride not only gives the titanium strip a yellow color but also reduces its ductility.

Similarly, the oxygen content in the atmospheric gas was increased from 30 to 100.
The reason why it is limited to ppffl is that if the content is less than 30 mm, a surface hardening layer sufficient to prevent surface flaw formation, that is, a surface hardening layer with a Witzkars hardness of 240 or more, is formed on the surface of the titanium strip. On the other hand, 1
This is because if the content exceeds 00 ppIll, the oxide formation on the surface of the titanium strip becomes significant and the titanium strip becomes colored.

Next, the method of the present invention will be explained using examples and comparing with comparative examples.

Example ASTM-B-26 plate thickness 0.6 rran after cold rolling
5 - Prepare grade 2 pure titanium coils, and while unwinding these coils, pass them continuously through a Matsufuru continuous annealing furnace so that the heating holding time is 30 seconds,
Annealing was performed under the operating conditions shown in Table 1.

In addition, in Table 1, Comparative Methods 1 to 6 are those in which the conditions marked with * among the operating conditions deviate from the conditions specified in the present invention.

In this way, we measured the Witzker's hardness on the surface and center of the thickness of pure titanium I-IJ tubes annealed under the operating conditions shown in Table 1, observed the surface coloration, and examined the results. It is also shown in Table 1.

As is clear from the results shown in Table 1, Comparative Methods 1 to 3 in which the oxygen content in the atmospheric gas was lower than the range of this invention, and the heating temperature was lower than the range of this invention. In Comparative Method 5, it is not possible to form the desired hardened surface layer, so the hardness of the surface area is insufficiently improved compared to the center part of the thickness of the strip, and the formation of surface flaws is prevented. Comparative method 4, in which the oxygen content in the atmospheric gas is higher than the range of this invention,
Similarly, in the case of Comparative Method 6, in which the heating temperature is higher than the range of the present invention, coloration occurs depending on the form of the oxide or nitride.

On the other hand, in Methods 1 to 6 of the present invention, a hardened layer with an appropriate hardness that is extremely hard to cause surface flaws is formed on the surface of the strip, and moreover, a hardened layer is formed on the surface of the strip and at the center of the thickness. The difference in hardness is also appropriate, and a strip in a good annealed state without coloring can be obtained.

These results can naturally be expected for, for example, a titanium alloy made by adding a small amount of palladium to pure titanium.

As mentioned above, according to the continuous annealing method of the present invention, an annealed state in which a colorless hardened surface layer is formed that is extremely resistant to surface flaws during the manufacture of welded titanium tubes or when assembling products thereof, etc. Titanium strip and titanium alloy strip
- Industrially advantageous effects such as the ability to continuously manufacture IJ chips at low cost are brought about.

Claims (1)

[Claims] 1 When continuously annealing titanium and titanium alloy strips after cold rolling in a gas atmosphere, the heating temperature was set to 65%.
0 to less than 750℃, and the atmospheric gas is 30 to 1oo
Annealing the coil with a gas containing ppm of oxygen and either argon or nitrogen, or a mixture of both, so as not to cause coloration due to oxidation and to form an arbitrary surface hardening layer. A continuous annealing method for titanium and titanium alloy strips characterized by: