JP2002180167A - Titanium band plate and its production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a titanium band plate which has small anisotropy in the coefficient of thermal expansion, and its production method. SOLUTION: The titanium band plate having small plane anisotropy in the coefficient of thermal expansion has a composition containing, by mass, <=0.05% Fe and Ni and Cr in the ranges satisfying the following inequality, and the balance substantially Ti, and has the average crystal grain size of >=30 μm. In its production method, a hot rolled steel plate is cold-rolled at a draft of >=50%: Fe+Ni+Cr<=0.1%; wherein, the elemental symbols denote the content (mass%) of each element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for producing heat
The present invention relates to a titanium strip used in an environment where occurrence of stress and strain due to in-plane anisotropy of a thermal expansion coefficient (a characteristic in which a thermal expansion coefficient differs between a rolling direction and a direction perpendicular thereto) is a problem.

[0002]

2. Description of the Related Art Titanium is used for various purposes as a consumer product such as watches, glasses and leisure goods, or as a material for chemical industrial equipment such as heat exchangers because of its light weight and extremely excellent corrosion resistance. .

[0003] Since these applications require formability, pure titanium for industrial use is mainly used. There are one to three types of industrial titanium specified in JIS H6400, and they are classified by the content of Fe and O (oxygen).

[0004] Among the above-mentioned applications, temperatures higher than normal temperature, especially 30
When a titanium plate is used in a high temperature environment of about 0 to 500 ° C., there is a problem that stress and strain are generated and deformed due to a difference in expansion degree depending on a direction of the titanium plate.

[0005] This problem is caused by the cold-rolled texture described later, and there is a difference in the thermal expansion coefficient between the rolling direction and the direction perpendicular to the rolling direction (the sheet width direction) in the production process of the titanium strip. The in-plane anisotropy of this coefficient of thermal expansion (hereinafter, referred to as
When the titanium plate is placed in a high-temperature environment, the amount of thermal expansion differs in the direction perpendicular to the rolling direction, which causes problems such as distortion of the flat material even at high temperatures. Inviting.

[0006] Titanium has a dense hexagonal crystal structure (HC
P), and the thermal expansion coefficient is known to be about 20% higher in the C-axis direction of the HCP structure than in the direction perpendicular to the C-axis (Materials Properties Handbook: Titanium All
oys, ASM International 1994). When a titanium strip is manufactured by ordinary cold rolling and recrystallization annealing, the C axis is oriented around a direction inclined about 35 degrees in the width direction from a direction perpendicular to the surface of the rolled sheet (hereinafter referred to as a rolling stable orientation). Form a cold rolled texture to accumulate.

As described above, if the coefficient of thermal expansion changes depending on the direction of the C axis, the C axis is aligned in a direction perpendicular to the plate surface.
It is considered that the production of titanium having a so-called basal-type cold-rolled texture can eliminate the anisotropy of the coefficient of thermal expansion. However, in order to produce a titanium strip having a basal-type texture, a method of performing cross-rolling instead of the generally performed one-way rolling is known [for example, Shinichi Nagashima, Iron and Steel (1
986), 314]. However, it is not possible to incorporate cross-rolling into the manufacturing process of the strip in the current mass production type production line, so the problem of the anisotropy of the thermal expansion coefficient of the titanium strip has not been solved, and the in-plane anisotropy is small. Development of a titanium plate having a thermal expansion coefficient is desired.

[0008]

An object of the present invention is to provide a titanium (hereinafter simply referred to as titanium) strip having a small in-plane anisotropy of thermal expansion coefficient and a method for producing the same.

[0009]

The present inventors conducted various experiments to obtain a titanium strip having a small in-plane anisotropy of the coefficient of thermal expansion.
As a result of the study, the following findings were obtained.

A) cold rolling titanium by a conventional method,
If recrystallization annealing is performed, a dense hexagonal C-axis is concentrated around the stable rolling direction and the in-plane isomerism increases, but the degree of thermal expansion coefficient increases by increasing the degree of integration of the C-axis in the stable rolling direction. Anisotropy can be reduced.

B) When recrystallization annealing is performed after cold rolling, crystal grains grow. At this time, the state of development of the recrystallization texture affects the anisotropy of the coefficient of thermal expansion, and the average recrystallized grain size. If it is less than 30 μm, the degree of integration of the C axis in the rolling stable direction cannot be increased, and the anisotropy of the thermal expansion coefficient becomes large. Therefore, the average recrystallized grain size needs to be 30 μm or more.

C) The working ratio in the cold rolling greatly affects the anisotropy of the coefficient of thermal expansion. If the total rolling reduction is less than 50%, when the crystal grains are grown by recrystallization annealing, The recrystallized grains do not become 30 μm or more, the variation of the accumulation direction of the C axis becomes large, and the degree of accumulation of the C axis centering on the stable rolling direction does not increase.

D) The chemical composition also has a great effect on the growth of crystal grains. When the Fe content exceeds 0.05%, precipitation of TiFe intermetallic compounds occurs in some regions. Is generated, and the growth of crystal grains is hindered, so that it is difficult to make the average crystal grain size 30 μm or more even when the rolling reduction in cold rolling is 50% or more.

E) Ni and Cr also inhibit the growth of crystal grains because they promote the formation of the β phase. If the total content of Fe, Ni and Cr exceeds 0.1%, it becomes industrially difficult to produce a titanium material having an average recrystallized grain size of 30 μm or more.

The present invention has been made based on such findings, and the gist is as follows.

(1) Fe in an amount of 0.05% by mass or less, Ni and Cr in a range satisfying the following formula, the balance being substantially Ti, and an average recrystallized grain size of 30 μm. A titanium strip having a small thermal expansion coefficient anisotropy as described above.

Fe + Ni + Cr ≦ 0.1% Here, the element symbol indicates the content (% by mass) of each element. (2) In% by mass, containing 0.05% or less of Fe, Ni and Cr are represented by the above formulas. Production of a titanium strip having low anisotropy in thermal expansion coefficient by cold rolling a hot rolled titanium sheet containing Ti to the extent that the content is satisfied and the balance substantially consisting of Ti at a total reduction of 50% or more, and then recrystallization annealing. Method.

Here, the average crystal grain size is determined according to JIS G05.
The particle size is determined by the cutting method specified in 52.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for defining the chemical composition, crystal grain size and manufacturing conditions of the titanium strip of the present invention will be described below. In addition, all the following% indications are mass%.

Chemical composition: Fe, Ni and Cr Fe is an element necessary for improving the strength of titanium, but when the content exceeds 0.05%, Ti is
Since precipitation of the Fe intermetallic compound is caused to hinder crystal growth, it is difficult to make the average crystal grain size 30 μm or more even when the rolling reduction in the cold rolling is 50% or more.
Therefore, the content of Fe is set to 0.05% or less. Desirably, it is 0.03% or less. The lower limit may be determined according to the reduction in economics due to the required strength and degree, and is not particularly limited, but is preferably 0.002% or more.

Ni and Cr are elements that are mixed in from the raw material, but basically exhibit the same behavior as iron. But F
If the total content of e, Ni and Cr exceeds 0.1%, crystal growth during annealing is hindered. Therefore, even if the rolling reduction in cold rolling is 50% or more, the average crystal grain size must be 30 μm or more. Becomes difficult. Therefore, Fe + Ni +
Cr ≦ 0.1%.

It is desirable that the amounts of Ni and Cr are as small as possible. However, from the viewpoint of economic effects, that is, from the viewpoint of suppressing an increase in raw material costs, the content of each is 0.002% or more.

The titanium strip of the present invention is an immiscible substance and titanium other than the above elements.

Average recrystallized particle size: Average recrystallized particle size is 30 μm
The reason for setting m or more is that if it is less than 30 μm, the degree of integration of the dense hexagonal C-axis in the rolling stable direction cannot be increased, and the anisotropy of the coefficient of thermal expansion cannot be reduced. The upper limit of the average crystal grain size is not particularly limited, but if it is too large, the smoothness of the surface is reduced.
It is preferably set to be not more than μm.

Next, the manufacturing method will be described.

The titanium strip of the present invention is obtained by cold rolling a hot rolled titanium sheet. In addition, the hot rolled sheet of titanium may be manufactured by a normal manufacturing method.

That is, sponge titanium and crushed scrap are mixed, pressed into briquettes, melted as electrodes, cast into ingots, bloomed by press, subjected to bulk rolling, and then hot-rolled by hot rolling. A plate is obtained. The hot rolled sheet is pickled with a nitric acid aqueous solution or the like and then subjected to cold rolling.

The reason why the total rolling reduction in the cold rolling is set to 50% or more is that if the total rolling reduction is less than 50%, the degree of C-axis integration in the stable rolling direction when crystal grains are grown by annealing. This is because the thermal expansion coefficient varies as a result of not becoming high. Desirably, it is 9% or less.

The annealing after the cold rolling may be performed under ordinary annealing conditions, for example, in a temperature range of 500 to 800.degree.
It may be held for several hours.

[0030]

EXAMPLES (Example 1) Small ingots having a thickness of 15 mm, a width of 50 mm, and a length of 100 mm having the 11 chemical compositions shown in Table 1 were produced by plasma melting in an argon arc.

[0031]

[Table 1] Each ingot was heated to 850 ° C. and hot rolled to a thickness of 5 mm. After annealing at 700 ° C., the oxide scale on the surface was removed by machining to obtain a hot-rolled sheet having a thickness of 4 mm for cold rolling. This hot rolled sheet was processed to a thickness of 1 mm by cold rolling. The titanium strip after cold rolling was subjected to recrystallization annealing in which the titanium strip was heated at 650 ° C. for 24 hours in an argon atmosphere.

From the titanium strip after recrystallization annealing, a test piece for measuring thermal expansion (width 2 mm, parallel to and perpendicular to the rolling direction)
5 mm in length) were collected. In addition, the crystal grain size at the center of the longitudinal section was measured by a cutting method.

The thermal expansion was measured between 20 ° C. and 500 ° C. The test piece was heated at a rate of 12 ° C./min, and the displacement was measured with a differential transformer at one end of the test piece to measure the coefficient of thermal expansion. The number of repetitions of the measurement was set to two times, and the average value was obtained. The results are shown in Table 1.

When the ratio of the coefficient of thermal expansion in the rolling direction and the rolling direction in the longitudinal direction is out of the range of the following expression, it is judged that the anisotropy is large. In the case of No., it was judged that the anisotropy was small, and was evaluated as ○. 0.95 ≦ coefficient of thermal expansion in the longitudinal direction / coefficient of thermal expansion in the width direction ≦ 1.
05 As is clear from Table 1, if the conditions specified in the present invention are satisfied, a titanium plate having small anisotropy in thermal expansion can be obtained.

(Embodiment 2) From the hot-rolled sheet after annealing used in Example 3, the thickness was 4 mm in the same manner as in Example 1.
Of cold rolled titanium plate was collected.

This titanium plate was cold-rolled to a thickness of 1 mm. At this time, a test plate was sampled at the time when each of the plate thicknesses shown in Table 2 was reached during rolling. Each of the sheets sampled during the cold rolling was machined to a sheet thickness of 1 mm in order to avoid the influence of the thickness difference during the test.

Each sample was annealed at 650 ° C. for 24 hours in an argon atmosphere. The cold reduction is calculated by the following equation.

Cold rolling reduction (%) = [(thickness before cold rolling−thickness after cold rolling) / thickness before cold rolling] × 100 Heat is applied from the annealed titanium strip in the same manner as in Example 1. Expansion measurement and crystal grain size measurement were performed. Table 2 also shows the results.

[0039]

[Table 2] The method of evaluating the results was the same as in Example 1. As is clear from Table 2, it is understood that a desired result cannot be obtained under the condition that the cold rolling reduction is less than 50%. This is considered to be because, when the cold rolling reduction is low, the strain accumulated in the material after cold rolling is small, so that the growth of crystal grains during annealing is delayed.

[0040]

According to the present invention, a titanium strip having a small anisotropy in thermal expansion coefficient can be obtained by utilizing a conventional manufacturing process.
An excellent effect is exhibited by using it as a member for a device used in a warm or high temperature environment.

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Claims (2)

[Claims] (1) Fe content of not more than 0.05% by mass,
Further, Ni and Cr are contained within a range satisfying the following formula,
The balance is substantially composed of Ti, and the average recrystallized grain size is 30 μm.
m or more, and a titanium strip used in a thermal expansion environment. Fe + Ni + Cr ≦ 0.1% Here, the element symbol indicates the content (% by mass) of each element. 2. The composition according to claim 1, comprising 0.05% by mass or less of Fe.
A hot-rolled titanium strip containing Ni and Cr in a range satisfying the following formula, and the balance substantially consisting of Ti, is subjected to a total rolling reduction of 50%.
A method for producing a titanium strip for use in a thermal expansion environment, comprising cold rolling and recrystallization annealing as described above. Fe + Ni + Cr ≦ 0.1% Here, the element symbol indicates the content (% by mass) of each element.