JPH1060528A - Production of high strength invar alloy sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means of producing invert alloy showing a sufficiently low thermal expansion coefficient even in a low temp. region from a room temp. to a liq. nitrogen temp. and furthermore having a high strength. SOLUTION: Invar alloy contg. <=0.10%, C, 0.35%, Si, <=1.0% Mn, 0.015% P, <=0.005% S, <=0.3% Cr, 35 to 37% Ni, 0 to 0.5% Mo, 0 to 0.05%V, 0.01 Al, 0 to 1.0% Mb, 0 to 0.005% B. <=0.005% N, and the valance Fe with inevitably impurities is subjected to rolling in which >=30% cumulative draft is secured at least in a temp. region except for a cold temp. regions less than the temp. T( deg.C) calculated by the formula of T( deg.C)=950+110×Nb(%)<1/2> +500×C(%).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an invar alloy plate having a sufficiently low coefficient of thermal expansion at room temperature or lower and a high strength.

[0002]

2. Description of the Related Art Fe-Ni based low thermal expansion invar alloys containing 34-45% (hereinafter, "%" representing a component ratio is referred to as "% by weight") of Ni have a temperature range from extremely low temperature to about 300 ° C. Because it shows a low coefficient of thermal expansion over a relatively wide temperature range,
In the past, taking advantage of this feature, it has been frequently used in tanks for liquefied natural gas transport vessels, shadow masks for large-sized televisions and cathode ray tubes for still images, IC lead frames, glass sealing materials, and the like. . The characteristics more strongly required for the above-mentioned invar alloy are the "temperature range used".
And "the degree of thermal expansion coefficient required for alloy members", but in the case of so-called "36Ni alloy" used for applications at room temperature or lower, the one developed especially to utilize a small thermal expansion coefficient Therefore, the “thermal expansion characteristic” is regarded as the most important characteristic.

The reason why the coefficient of thermal expansion of the Invar alloy is extremely small has been studied for a long time, and as a result, it has been reported that "Fe atoms transition to a magnetic moment and a large volume state at a low temperature. The spontaneous volume magnetostriction that has occurred has been considered to be due to the cancellation of thermal contraction. As described above, it has been concluded that the thermal expansion characteristic of the Invar alloy is governed by the magnetism of Fe atoms in the alloy, but this phenomenon itself has a part that has not been sufficiently elucidated.

It is known that reducing the content of alloying elements such as C, Si and Mn is effective in lowering the "coefficient of thermal expansion near room temperature" of an Invar alloy. 1.2 × 10 ^-6 / ℃ by minimizing the content
A very low thermal expansion coefficient of the stage can also be achieved.

[0005] However, such high-purity invar alloys are mostly used in a form having a wall thickness of less than 2 mm. Therefore, it is desired that the high-purity invar alloy has a strength sufficient to compensate for such a thickness. The strength at room temperature is about 20 to 40% lower than that of "9% Ni steel" or "SUS304 steel" used as the same low temperature material. Therefore, when an attempt is made to use the steel sheet as a thick steel sheet, in this case, there is a problem that the crystal grain size tends to increase in the manufacturing process, and the strength is further reduced.

However, it is possible to increase the strength of an Invar alloy by performing cold working or adding an alloy element, and for example, Co, Nb,
It is known that addition of C, Cr and the like is effective. For example, Japanese Patent Application Laid-Open No. 5-171357 discloses an example of an Fe-Ni-based invar alloy in which Nb is added to increase the strength.

However, as can be seen from the description in the "Example" section of JP-A-5-171357, even when an alloy element is added to increase the strength of an invar alloy, the strength of the invar alloy is actually increased. The cold working is an excellent method for increasing the strength and often depends on the cold working.

Heretofore, high strength invar alloys in which such strengthening measures have been taken have been applied only from room temperature such as shadow masks for televisions, lead frames for ICs, and core wires for power transmission. Most of ultra-thin plates and wires used in a temperature range of about ° C. have shapes which can be easily cold-worked.

However, considering the use as a thick steel plate, it is difficult to adopt a method of increasing strength by cold working in terms of manufacturing method and equipment, and other strengthening methods are employed. I have to do it. However, a high-strength method other than the cold-working method is applied, and a high thermal expansion coefficient of 1.5 × 10 ⁻⁶ / ° C or less in a temperature range of room temperature or less is maintained while maintaining high thermal expansion characteristics. A system for producing "invar alloys with increased strength" has not yet been established.

In view of the above, an object of the present invention is to exhibit a sufficiently low coefficient of thermal expansion even in a low temperature range from room temperature to liquid nitrogen temperature and to have a sheet thickness of about 10 mm which is not subjected to cold working. 0.2% yield strength of 35
The aim was to establish a means for producing an Invar alloy having a high strength of at least 0 MPa and a tensile strength of at least 500 MPa.

[0011]

Means for Solving the Problems The present inventor has made intensive studies to achieve the above object, and as a result, has obtained the following findings. a) To improve the strength of Invar alloy, C or Nb
Is a very effective and stable means, and the rolling in a temperature range equal to or higher than the warm rolling under specific conditions, ie, “T (° C.) = 950 + 110 × Nb (%) ^1/2 + 500 × C
(%) ", Cold rolling is required if combined with rolling｝ in a temperature range not lower than warm rolling where the cumulative rolling reduction below the temperature T (° C.) calculated by the formula below is 30% or more. And a sufficiently satisfactory strength can be ensured.

B) Further, by performing rolling in a temperature range equal to or higher than the warm rolling under the above specific conditions, the thermal expansion coefficient of the invar alloy in a low temperature range can be further reduced.
FIG. 1 is a graph showing the effect of the rolling temperature on the thermal expansion characteristics of a 0.004% C-0.13% Si-0.46% Mn-36% Ni alloy (T calculated by the above formula is 952 ° C.). . As can be seen from FIG. 1, the average thermal expansion coefficient from room temperature to liquid nitrogen temperature of the sheet material (9.5 mm thick) after annealing at 900 ° C. for 15 minutes is L direction (rolling direction) and C direction (rolling direction). Direction at right angles to both directions) exceeds 1.5 × 10 ^-6 / ° C, while 3.5 ° C in the temperature range below T (° C) calculated by the above equation.
When rolled to a thickness of mm (cumulative rolling reduction: 66%), L, C
In both directions, the coefficient of thermal expansion shows a small value.

Further, as can be seen from FIG. 1 described above, if warm rolling is performed in a temperature range of 400 ° C. or less, 1.0 × 10 ^−6.
/ ° C. as low as possible, and a sufficiently low coefficient of thermal expansion of 1.5 × 10 ⁻⁶ / ° C. or less even at 600 ° C. or more, which is more desirable from the viewpoint of productivity. it can. Moreover, it is clear that the dependence on the rolling direction is smaller than the dependence on the rolling temperature (in addition,
The hardness of these plates is 184 to 19 as measured by Vickers.
7, which is sufficiently higher than the hardness of 160 which is a standard of the tensile strength of 500 MPa, and the hardness has a small dependence on the rolling temperature.)

C) However, as described above, the addition of a strengthening element such as Nb generally adversely affects the hot workability of an Invar alloy. However, the disadvantage is to control the content of the strengthening element to be added within a specific range, and to reduce the P, S, Al, and N contents or to adjust the amount of B without adversely affecting the thermal expansion characteristics. Can be.

The present invention has been made based on the above findings, etc., "C: 0.10% or less, Si: 0.35% or less, Mn: 1.0% or less, P: 0.015% or less, S: 0.005% or less , Cr: 0.3% or less, Ni: 35 to 37%, Mo: 0 to 0.5%, V: 0 to 0.05%, Al: 0.01% or less, Nb: 0 to 1.0%, B: 0 to 0.005%, N: For an Invar alloy containing 0.005% or less and the balance consisting of Fe and unavoidable impurities, it is calculated by at least the following equation: T (° C.) = 950 + 110 × Nb (%) ^1/2 + 500 × C (%) By performing rolling to ensure a cumulative rolling reduction of 30% or more in a temperature range other than the cold range below T (° C.), a high-strength invar alloy plate exhibiting excellent thermal expansion characteristics at room temperature or lower can be obtained. That stable production can be achieved at low cost. " It is needless to say that the term “cold region” here is not a temperature region in the middle of cooling after heating or after heating, but a normal cold rolling temperature region performed on the alloy after cooling. .

[0016]

As described above, the present invention provides an invar alloy having a specific chemical composition only by rolling in a temperature range not lower than warm rolling, and has high strength and a low temperature range from room temperature to liquid nitrogen temperature. In the present invention, it is possible to stably provide an invar alloy plate exhibiting excellent thermal expansion characteristics.However, in the present invention, the reasons for limiting the chemical composition of the alloy and the manufacturing conditions of the plate material as described above together with the operation thereof will be described. It will be described in detail.

(A) Chemical composition of the alloy C: C is an element to be added because it is effective for increasing the strength of the Invar alloy. For this purpose, the C content in the alloy must be 0.015% or more. Is desirable (the strengthening effect appears even in a very small amount), but an excessive addition exceeding 0.10% adversely affects the excellent thermal expansion characteristics (low thermal expansion coefficient) of the alloy, so that the C content is 0.10%. It is determined as follows.

Si and Mn: Si and Mn are elements necessary as a deoxidizing agent at the time of melting the alloy, but if both are contained excessively, they adversely affect the thermal expansion characteristics of the alloy. Therefore,
The contents of Si and Mn were determined to be 0.35% or less and 1.0% or less, respectively.

P: P is an impurity element which significantly increases the susceptibility of the alloy to solidification cracking and welding cracking. If the content of P is 0.015% or less, the decrease in the yield of alloy materials due to the above-mentioned adverse effects will not be remarkable. Therefore, the upper limit of the P content is
It was determined to be 0.015%.

Cr: When the Cr content exceeds 0.3%, the adverse effect on the thermal expansion coefficient of the alloy becomes remarkable. Therefore, the Cr content was determined to be 0.3% or less.

Ni: Ni is the most important element that governs the thermal expansion characteristics of the alloy, and its thermal expansion coefficient can be minimized by adjusting its content to 35 to 37%. Therefore, Ni
The content was determined to be 35 to 37%.

Mo and V: Since Mo and V are both elements that deteriorate the thermal expansion characteristics of the alloy, the addition of these elements must be avoided. At least 0.5 for Mo content
% Or less, and the V content must be suppressed to 0.05% or less to ensure desired thermal expansion characteristics.

Al: Al is an element that deteriorates the hot workability of the alloy, and its content must be regulated from the viewpoint of hot workability. In particular, when the Al content exceeds 0.01%, the adverse effect on hot workability becomes remarkable, so the content is set to 0.01% or less.

Nb: Nb is an element effective for improving the strength of the alloy. Even if a strengthening effect can be obtained by adding C or rolling, it is desirable to add Nb as much as possible, if possible. On the other hand, in the alloy of the present invention, the Nb content was 1.0%.
If Nb is exceeded, the tendency of deterioration of the thermal expansion characteristic becomes conspicuous, so that Nb content exceeding 1.0% must be avoided. Therefore, the Nb content was set to 0 to 1.0%,
The preferred range is 0.15 to 1.0%.

S: S is an unavoidable impurity that is mixed in when the alloy of the present invention is melted, but is an element to be reduced as much as possible because it reduces the hot workability of the alloy. However, when the S content is reduced to 0.005% or less (preferably 0.001% or less), the decrease in the alloy material production yield due to the above-mentioned adverse effects becomes not significant.

N: N is an unavoidable impurity element that deteriorates the hot workability of the alloy. In the alloy of the present invention, if its content exceeds 0.005%, the tendency of the hot workability to deteriorate becomes remarkable. It has been determined that the N content should be reduced to 0.005% or less.

B: Since B has an effect of improving the hot workability of the alloy, it is effective to contain B in a range of up to 0.005% as necessary. However, if the content of B exceeds 0.005%, the coefficient of thermal expansion is significantly increased.
The content was determined to be 0 to 0.005%.

When melting the alloy of the present invention, Co or Cu
Etc. are often mixed as unavoidable impurity elements,
Even if these Co and Cu are contained as impurities, there is no particular problem as long as their contents are in the range of 0.1% or less.

(B) Sheet Material Manufacturing Conditions In the sheet material manufacturing method according to the present invention, at least “T (° C.) = 950 + 1
10 × Nb (%) ^1/2 + 500 × C (%) In a temperature range other than the cold range below the temperature T (° C.) calculated by the formula: Rolling in a temperature range equal to or higher than rolling). In this case, after performing the hot rolling at a temperature higher than the temperature T (° C.) to reduce the wall thickness to some extent, the above-described predetermined rolling is performed, and then, the cold rolling is further performed for further shape and surface adjustment. May be applied.

Incidentally, in the composition of the invar alloy targeted by the present invention, the recrystallization temperature during hot rolling is approximately 95%.
It is in the range of 0-1050 ° C. T calculated by the above equation
(° C.) correlates with this recrystallization temperature, and this temperature T
By rolling in a temperature range lower than (° C.), high strength can be effectively achieved. As can be seen from the above equation, as the content of C or Nb increases, the rolling temperature at which the strength of the Invar alloy is increased is extended to a higher temperature range.

However, in order to achieve the target strength level (0.2% yield strength of 350 MPa or more, tensile strength of 500 MPa or more) for the invar alloy sheet of the chemical composition according to the present invention, at least the cumulative temperature in the above temperature range is required. It is necessary to secure a rolling reduction of 30% or more.

In the invar alloy according to the present invention,
As described above, when “rolling with a cumulative rolling reduction of 30% or more in a temperature range lower than the temperature T (° C.)” is performed, a reduction in the thermal expansion coefficient is also achieved. In this case, by rolling at a temperature lower than 400 ° C., a thermal expansion coefficient of less than 1.0 × 10 ⁻⁶ / ° C. can be achieved. However, from the viewpoint of productivity, rolling at a temperature of 600 ° C. or higher is more practical. However, even in this case, a low coefficient of thermal expansion of 1.5 × 10 ⁻⁶ / ° C. or less is secured.

Hereinafter, the present invention will be described with reference to examples.

EXAMPLES First, invar alloys having the chemical compositions shown in Table 1 were melted and cast into ingots in a 25 kg vacuum induction furnace, and slabs having a thickness of 40 mm were formed by hot forging.

[0034]

[Table 1]

Next, each of the slabs was subjected to a heat treatment of "1150 ° C. × 1 hour" and then rolled to obtain a 12 mm thick plate. At this time, rolling was performed in two passes until the sheet thickness was reduced from 18 mm to 12 mm (cumulative rolling reduction of 3 mm).
In this embodiment, this two-pass rolling is particularly called “adjustment rolling”. And, in the adjustment rolling, the rolling temperature range is 50.
The temperature was kept within the range of ° C. Here,
For example, the rolling temperature of the adjusted rolling performed while controlling the rolling temperature range at 950 to 900 ° C. is 950 ° C., and the adjusted rolling temperature was changed depending on the applied alloy.

The cooling after rolling is performed by the following method: [rolling end temperature -100
[° C] to [room temperature] by spray cooling.
For comparison, a part of the sheet material was subjected to finish annealing at “900 ° C. × 15 minutes soaking” applied to the cold-rolled material.

Subsequently, for evaluation of the thermal expansion characteristics, a square bar test piece of “thickness 2 mm × width 5 mm × length 50 mm” was sampled in the L direction from the center of each rolled sheet thus obtained. And 2
The linear expansion from 0 ° C to -196 ° C was measured. And -1
The average coefficient of thermal expansion was calculated based on the measured value at 80 ° C to 20 ° C.

For evaluation of mechanical properties, a tensile test piece having a diameter of 6 mmφ × length of 40 mm was taken from each of the hot-rolled sheets, and was subjected to 0.2% yield strength in the L direction and tensile strength at room temperature. The strength was measured. The yield strength was measured at 0.8 × 10 ^-4 / s
At a strain rate of.

The results of these measurements (0.2% yield strength, tensile strength, average thermal expansion coefficient from 20 ° C. to −180 ° C.) are shown in Table 2 together with the sheet material production conditions.

[0040]

[Table 2]

From the results shown in Table 2, it can be seen that the coefficient of thermal expansion of the Invar alloy plate obtained in the comparative example which does not satisfy the conditions specified in the present invention exceeds 1.5 × 10 ^-6 / ° C. The invar alloy plate obtained by the means of the present invention, which is simple and does not cause extraordinary cost, although it does not have sufficiently satisfactory properties such as a 0.2% yield strength of less than 350 MPa. Can be confirmed to have excellent strength characteristics and thermal expansion characteristics, such as a high value of 0.2% yield strength exceeding 350 MPa and a low value of thermal expansion coefficient of 1.5 × 10 ⁻⁶ / ° C. or less. .

[0042]

As described above, according to the present invention, an invar alloy plate having excellent thermal expansion characteristics and high strength can be stably manufactured relatively easily regardless of the thickness of the plate. In addition, it is possible to provide a low-cost storage tank material or the like at a low cost, which is desirable, and has industrially useful effects.

[Brief description of the drawings]

[Figure 1] 0.004% C-0.13% Si-0.46% Mn-36.4% Ni-based invar
5 is a graph showing the effect of rolling temperature on the coefficient of thermal expansion of an alloy.

Claims (1)

[Claims] C. 0.10% or less by weight, Si: 0.35% or less, Mn: 1.0% or less, P: 0.015% or less, S: 0.005% or less, Cr: 0.3% or less, Ni: 35 to 37 %, Mo: 0 to 0.5%, V: 0 to 0.05%, Al: 0.01% or less, Nb: 0 to 1.0%, B: 0 to 0.005%, N: 0.005% or less, with the balance being Fe and inevitable 30% in the temperature range other than the cold range below the temperature T (° C.) calculated by the following equation
A method of producing a high-strength invar alloy sheet, characterized by applying a rolling process that ensures the above-mentioned cumulative rolling reduction. T (° C.) = 950 + 110 × Nb (%) ^1/2 + 500 × C (%)