JP2023003776A - Fe-Ni ALLOY AND METHOD FOR PRODUCING THE SAME - Google Patents

Abstract

To provide an Fe-Ni alloy that enables small and uniform residual stress during a process of annealing, particularly cooling, and can achieve fine precision in complicated processing of die frame material and the like.SOLUTION: An Fe-Ni alloy contains, in mass%, C: 0.01-0.05%, Ni: 30-45%, Si: 0.01-0.4%, Cr: 0.03-0.5%, Mn: 0.10-1.0%, Al: 0.001-0.10% or less, P: 0.005% or less, S: 0.005% or less, Mo: 0.01-0.1%, Cu: 0.01-0.5%, Ti: 0.1% or less, Co: 0.01-0.5%, Sn: 0.001-0.05%, and N: 0.001-0.005% as its key components, satisfying the relational expression (1), with the balance being Fe and inevitable impurities. 50≤-212×Si-140×Cr-578×Al-569×Ti+254×Mn+262×Mo+1550×Sn+14 (1).SELECTED DRAWING: Figure 1

Description

It relates to the Fe-Ni alloy used as a mold frame in the manufacture of organic EL panels. Even after complex processing and surface polishing, it is easy to ensure precision with little deformation. The target is an Fe--Ni alloy that contributes to yield improvement.

An Fe—Ni alloy containing 30 to 50% Ni is generally used as a material in the field of electronic materials, and is characterized by being able to control the thermal expansion coefficient by its chemical composition. An Fe—Ni alloy containing 36% Ni has a small coefficient of thermal expansion and excellent toughness, and is therefore used as a mold frame for manufacturing an organic EL panel. The frame material is precisely finished by complicated cutting and surface polishing, and strict management of processing accuracy, which affects the quality and yield of the panel, is carried out. In other words, dimensional changes due to cutting and polishing must be minimized.

This deformation is largely due to residual stress caused in the material manufacturing process. Residual stress occurs in various processes, among which the residual stress generated in the annealing process is large and it is important to reduce it.

Many previous inventions have been reported on alloys suitable for molds and their manufacturing methods, but there have been few reports on improvements in deformation that occurs during mold working. Patent Literature 1 reports a martensitic steel that retains strength and characteristics and a method for producing the same for use in molds for electronic display parts. However, this is an invention about a high-strength steel sheet, and the range of components such as Ni, Cr, and Mn is significantly different from that of the Fe—Ni alloy, which is the object of the present invention.

Further, Patent Document 2 reports a method of heat-treating a mold, but this also differs greatly from the Fe—Ni alloy in terms of component ranges such as Cr and Mn.

Thus, there is no report on molds using Fe--Ni alloys. Regarding Fe--Ni alloys, there are studies on thermal expansion characteristics and low-temperature characteristics, but there are no examples of studies on alloys and methods that can reduce or eliminate residual stress generated in the manufacturing process, especially the annealing process.

JP 2012-528943 A JP 2012-11619 A

An object of the present invention is to provide an Fe—Ni alloy that can reduce and uniformize the residual stress generated during the annealing process, especially during cooling, and that can obtain precise processing accuracy in applications where complex processing such as mold frame materials is performed. be.

In order to solve the above-mentioned problems faced by the prior art, the present invention focused mainly on the oxide film formed during annealing and cooling behavior, focusing on the effect of the component composition of the oxide film.

This is due to the fact that the following phenomenon has been observed. When Fe-36% Ni alloys were mass-produced and manufactured, it was found that even if the same size plate was annealed at the same temperature and under the same water cooling conditions, the warpage was clearly different. The size of the plate is 30mmt x 2000mm x 10000mm. A plate with a large warp needs to be corrected strongly, resulting in a large residual stress and complication. Small warpage is important. Test pieces of 30 mmt x 2000 mm x 100 mm were cut from these plates. Since they were made into small pieces, there is no difference in warpage between the two at this stage. The surface of this was ground by a milling machine by 6 mm, and the displacement (warping) was measured over the entire length at intervals of 100 mm with the end of the material as the origin. The largest displacement was in the center of the width, 9 mm for the plate with large warp and 5 mm for the small plate. If it is up to the intermediate level of this, the correction is mild and can be judged to be a clear improvement.

Subsequently, when a plate with good warpage was investigated, it was found that all of them were a specific ingot-making charge. Since the principal component is the same regardless of the magnitude of the warp, we have come to presume that other components have an effect. Furthermore, when we closely observed the behavior of heating, soaking, and cooling of a plate with small warp and a plate with large warp, we found that there was a difference in the grains of water vapor generated during water cooling, and that the grains of the plate with small warp were fine and uniform. . I figured this was what made the sled different.

In order to clarify what is the cause of this difference in water vapor droplets, the following oxidation experiments were carried out to compare the morphology and composition of scales. The test materials were cut out from two kinds of plates, a small warp plate and a large warp plate, as described above. All six surfaces were polished with #240 to a thickness of 200 μm or more, the oxide scale was completely removed, washed with water, degreased and dried, and subjected to an oxidation test. The test temperature was 960° C.×10 min, held in an air atmosphere, then allowed to cool, and the cross section was observed. As a result, although an oxide film containing Fe and Ni as main components was observed in both cases, it was found that the morphology was different. FIG. 1 shows the cross-sectional observation results after this heat treatment experiment. (a) with a small sled charge and (b) with a large sled charge. The small warp showed that the oxide scale was a little thick and had voids, while the large warp was fairly dense. When the composition was compared, good charges had high contents of Mn and Sn.

Considering that if the oxidized form can be made porous, the residual stress caused by water cooling can be reduced and made uniform, we investigated the effects of elements on the oxidized form. Various additive elements were added to the Fe-36% Ni alloy, and 10 kg of the alloy was melted in the laboratory. Si, Mn, Cr, Mo, Cu, Co, Al, Ti, and Sn were selected as additive elements. Each composition range was as shown in Table 1. 0.00 means no addition. The unit is wt %.

The obtained alloy ingot was hot forged to 10 mmt, then annealed at 1100° C., and then cold rolled to 4 mmt. A test material was cut out from this, the entire surface thereof was polished with #240, and subjected to an oxidation test at 1000° C. for 10 minutes while being allowed to cool. The reason for setting the temperature to 1000° C. is to clarify the difference in oxide scale. After that, cutting and embedding were performed, and the shape of the oxide film on the cross section was observed, and the number of voids was observed. Voids are observed with a field emission scanning electron microscope (JSM-7001F) at a magnification of 1000 to 3000, evaluated over a length of 50 μm, and observed for each composition image and TOPO image to ensure that they are voids. counted and evaluated. There was a portion where the scale was cracked due to the preparation of the sample. As a result, it was found that the number of voids increased as Sn increased, and the number of voids decreased as Al increased. The graph of FIG. 2 shows the effects of the amounts of Sn and Al on the number of voids in the oxide scale. When the number of voids was measured by the same method for the sample with good warpage observed in FIG. 1, 45 voids were found. It is thought that the introduction of voids to this extent will improve the performance. Further, it was found from the same evaluation that the elements that increase the number of voids are Mn and Mo, and the elements that decrease the number of voids are Si, Cr, and Ti.

In this way, it has been clarified that the number of pores in oxide scale is affected by the composition, but it is important to comprehensively understand the positive and negative effects of each element in order to stabilize the quality. Therefore, the relational expression (A) between the number of voids and the chemical composition was determined by performing multiple regression analysis on these results.
Number of voids (n) =
-212 x Si -140 x Cr -578 x Al -569 x Ti +254 x Mn +262 x Mo +1550 x Sn +14 (A)

FIG. 3 shows the relationship between the value of formula (A) and the measured number of voids. Although the variation is somewhat large when the number is small, the linearity is judged to be good. Since the number of voids changes greatly even when the content is small, we thought that it would be better to manage with a value that considers the lower limit of variation for stable management. If the number of voids in a plate with a good shape is 45 and the same level is assumed, the regression formula will be 70 or more. Since improvement was achieved with the number of voids of 45, it is presumed that a slightly smaller value would be sufficient. Regarding the validity and threshold value of this formula, it has been confirmed from an embodiment described later that 50 or more, not 70, is sufficient.
50 ≤ -212 x Si -140 x Cr -578 x Al -569 x Ti +254 x Mn +262 x Mo +1550 x Sn +14
…(1)

Furthermore, when the influence of B addition was investigated in the range up to 0.0050%, it was found that B also effectively introduces voids. It was also incorporated into the regression equation, and the equation was modified to (2). When B is contained, formula (2) is applied.
50 ≤ -212 x Si -140 x Cr -578 x Al -569 x Ti +254 x Mn +262 x Mo +1550 x Sn
+68000×B +14 …(2)

If the pores of the oxide scale are controlled in this way, the coefficient of thermal expansion will increase, though slightly, due to the effect of the additive element, but it is preferable to avoid this in consideration of its application to the frame material. The effects of most elements are known and increase the coefficient of thermal expansion when added, but the effect of Sn was unknown. For this reason, when the above laboratory melting material was used for measurement, the coefficient of thermal expansion at 30 to 100° C. was increased, and the amount of change per unit % of addition was 0.98. From this, the increase Δα _{30 to 100°C} (×10 ^-6 ) of the coefficient of thermal expansion at 30 to 100°C can be predicted by the following formula, and considering the application as a frame material, the increase should be 0.8 or less. is appropriate.
0.8 ≥ 0.89 x Si + 1.1 x Cr + 1.5 x Al + 0.86 x Ti + 0.7 x Mn + 0.53 x Mo + 0.98 x Sn
+0.26×Nb＋29.5×B …(3)

The alloy of the present invention was made through experiments as described above, and specifically, it is as follows. The alloys of the present invention are C: 0.001 to 0.05%, Ni: 30 to 45%, Si: 0.01 to 0.4%, Cr: 0.03 to 0.5 %, Mn: 0.10 to 1.0%, Al: 0.001 to 0.10%, P: 0.005% or less, S: 0.005% or less, Mo: 0.01 to 0.1% , Cu: 0.01-0.5%, Ti: 0.1% or less, Co: 0.01-0.5%, Sn: 0.001-0.05%, N: 0.001-0. 005% as a main component, satisfies the relational expression (1), and the balance is composed of Fe and unavoidable impurities.
50 ≤ -212 x Si -140 x Cr -578 x Al -569 x Ti +254 x Mn +262 x Mo +1550 x Sn +14
…(1)

In addition, Nb: 0.02 to 0.75%, B: 0.0005 to 0.0035%, any one or two of these satisfy the relational expression (2), and the balance is Fe and unavoidable An Fe—Ni alloy containing impurities is better.
50 ≤ -212 x Si -140 x Cr -578 x Al -569 x Ti +254 x Mn +262 x Mo +1550 x Sn
+68000×B +14 …(2)

Furthermore, it is more desirable that the alloy of the present invention be an Fe--Ni alloy that satisfies the formula (3) showing an increase in the thermal expansion coefficient from 30 to 100.degree.
0.8 ≥ 0.89 x Si + 1.1 x Cr + 1.5 x Al + 0.86 x Ti + 0.7 x Mn + 0.53 x Mo + 0.98 x Sn
+0.26×Nb＋29.5×B …(3)

Further provided is an Fe--Ni alloy plate having a thickness of 12.5 mm or more produced from the alloy of the present invention.

Further provided is a method for producing an Fe—Ni alloy. After hot-rolling the slab, it is made into a hot-rolled sheet, and the hot-rolled sheet is heat-treated and then spray-water cooled in a roller hearth-type cooling tank to reduce the residual stress and make it uniform. A method for producing an Fe—Ni alloy characterized by the following.

In the production method of the present invention, the heat treatment is preferably performed at a heat treatment temperature of 900 to 1000° C. and a holding time of 1 to 60 minutes.

In the manufacturing method of the present invention, in the roller hearth type cooling tank for spray cooling, a plurality of sprays are arranged vertically and horizontally on the upper and lower surfaces, and the hot rolling is performed at intervals of 200 to 400 mm in both the longitudinal direction and the width direction. It is preferable to arrange the nozzles so as to sufficiently cover the entire length and width of the plate.

It is a cross-sectional photograph after heat treatment experiment, (A) is a charge with a small warp, (B) is a charge with a large warp. 4 is a graph showing the effect of the amounts of Sn and Al on the number of voids in oxide scale in the Fe—Ni alloy of the present invention. 4 is a graph showing the relationship between the number of pores in oxide scale and a prediction regression equation in the Fe—Ni alloy of the present invention.

As described above, the Fe—Ni alloy according to the present invention contains C: 0.001 to 0.05%, Ni: 30 to 45%, Si: 0.01 to 0.4%, Cr : 0.03-0.5%, Mn: 0.10-1.0%, Al: 0.001-0.10%, P: 0.005% or less, S: 0.005% or less, Mo: 0.01 to 0.1%, Cu: 0.01 to 0.5%, Ti: 0.1% or less, Co: 0.01 to 0.5%, Sn: 0.001 to 0.05%, N: 0.001 to 0.005%, the balance being Fe and unavoidable impurities. The reasons for limiting each component composition as described above will be described below.

C: 0.001-0.05%
C is an element that contributes to solid-solution strengthening and also contributes to low-temperature stability of the structure. If it is less than 0.001%, sufficient strength as a mold cannot be obtained. However, if the content exceeds 0.05%, a large amount of carbides are formed, resulting in deterioration of toughness and fatigue resistance. Also, the coefficient of thermal expansion is increased. In particular, in order to obtain excellent strength, low-temperature properties, fatigue resistance and coefficient of thermal expansion, it is necessary to strictly limit the content of C. In the present invention, it is set to 0.001 to 0.05%. It is preferably 0.001 to 0.045%, more preferably 0.001 to 0.040%.

Ni: 30-45%
Ni is an important alloying element in controlling the thermal expansion coefficient of Fe—Ni alloys. The Ni content must be in the range of 30 to 45%. If the Ni content is out of this range, the coefficient of thermal expansion increases and the product becomes unusable. It is preferably 34-39%, preferably 35-37%.

Si: 0.01-0.4%
Si is an element effective as a deoxidizing agent and also for maintaining good weldability, and should be added in an amount of at least 0.01%. However, it is an element that forms a stable oxide film, and is an element that promotes densification of the oxide layer by annealing, and tends to make cooling uneven. Also, the upper limit is set to 0.4% in order to increase the coefficient of thermal expansion. Accordingly, in the present invention, the Si content is set to 0.01 to 0.4%, preferably 0.02 to 0.38%, more preferably 0.05 to 0.35%.

Cr: 0.03-0.5%
Cr is a solid-solution strengthening element that contributes to securing strength and further improves corrosion resistance. Therefore, addition of 0.03% or more is required. On the other hand, if the addition amount exceeds 0.5%, the coefficient of thermal expansion becomes high and the inherent low thermal expansion characteristic is lost. In addition, like Si, Cr is an element that stabilizes the oxide film. By forming a complex oxide film together with Si on the surface, Cr promotes the densification of the oxide film and promotes uniform cooling. Adversely affect. Therefore, in the present invention, the Cr content is added to 0.03 to 0.5%, preferably 0.04 to 0.40%, more preferably 0.05 to 0.5%. 35%.

Mn: 0.10-1.0%
Mn is a solid-solution strengthening element and is also an effective element as a deoxidizing agent. In addition, MnS is formed to promote fixation of S, thereby improving hot workability and weld crack resistance. Furthermore, it is an element that plays an important role in generating voids in the oxide scale and promoting uniform cooling. In order to obtain such effects, addition of 0.10% or more is necessary. However, if the Mn content exceeds 1.0%, the surface properties deteriorate, inclusions increase, the corrosion resistance deteriorates, and the thermal expansion coefficient increases. Therefore, in the present invention, the Mn content is limited to 0.10-1.0%. Preferably, it is 0.12-0.7%, more preferably 0.13-0.5%.

Al: 0.001-0.10%
Al is used as a deoxidizing agent, and when it is left in the alloy in an appropriate amount, it effectively forms a complex oxide film with antirust properties and helps ensure corrosion resistance in the atmosphere. For this purpose, addition of 0.001% or more is necessary. On the other hand, if the addition amount increases, the coefficient of thermal expansion increases and the weld penetration deteriorates. Furthermore, it promotes densification of oxide scale and adversely affects uniform cooling, so it is important to set the amount to an appropriate level. Therefore, the upper limit is regulated to 0.10%. It is preferably 0.002 to 0.050%, more preferably 0.003 to 0.020%.

P: 0.005% or less P deteriorates rust resistance and weldability, so it is desirable to reduce it as much as possible. Therefore, it is limited to 0.005% or less. The content is preferably 0.003% or less, more preferably 0.002% or less.

S: 0.005% or less If S exceeds 0.005%, hot workability is impaired and weld crack resistance is also deteriorated. Therefore, the S content is limited to 0.005% or less. It is preferably 0.002% or less, more preferably 0.001% or less.

Mo: 0.01-0.1%
Mo is an important element that not only contributes to the improvement of corrosion resistance, but also introduces voids into the oxide film during annealing. Therefore, it is necessary to add at least 0.01% or more. However, excessive addition leads to an increase in cost and increases the coefficient of thermal expansion, so the content should be 0.1% or less. It is preferably 0.02 to 0.09%, more preferably 0.02 to 0.07%.

Cu: 0.01-0.5%
Cu is F.C. C. C. It is an element that contributes to the improvement of phase stability and should be added in an amount of at least 0.01%. However, if it exceeds 0.5%, the coefficient of thermal expansion increases and the quality deteriorates. Therefore, in the present invention, Cu is regulated within the range of 0.01 to 0.50%. It is preferably 0.02 to 0.40%, more preferably 0.03 to 0.30%.

Ti: 0.1% or less Ti is a non-additive element, but may be mixed from raw materials. Therefore, it is necessary to suppress the contamination of Ti as much as possible. If it exceeds 0.1%, the increase in precipitates will lead to deterioration of corrosion resistance, and the coefficient of thermal expansion will increase, resulting in deterioration of quality. Furthermore, it promotes densification of the oxide film, which adversely affects uniform cooling. Therefore, in the present invention, the content of Ti is made as small as possible, and its upper limit is set at 0.1%. It is preferably 0.03% or less, more preferably 0.02% or less.

Co: 0.01-0.5%
Co, like Ni, keeps the thermal expansion coefficient of the Fe—Ni alloy low. C. C. It is an alloying element that stabilizes the phase. When an element is added to introduce voids into the oxide scale, the coefficient of thermal expansion increases, but like Ni, it is an effective element for suppressing this. Therefore, the content of at least 0.01% is essential. However, if it exceeds 0.5%, the machinability deteriorates, and even if the residual stress is suppressed, it becomes difficult to maintain quality during surface processing. Therefore, Co is regulated to 0.5% or less in the present invention. It is preferably 0.01 to 0.40% or less, more preferably 0.02 to 0.35%.

Sn: 0.001-0.05%
Sn is an important element that creates voids in the oxide film and uniforms cooling. Therefore, an addition of at least 0.001% is necessary. However, if it exceeds 0.05%, it lowers corrosion resistance and hot workability. Therefore, Sn is regulated within the range of 0.001 to 0.05%. It is preferably 0.002 to 0.040%, more preferably 0.005 to 0.035%.

N: 0.001 to 0.005%
N is a solid-solution-strengthening element that contributes to ensuring strength, and in order to obtain this effect, it is necessary to add at least 0.001% or more. However, if it is added excessively, it forms nitrides, which promotes the occurrence of surface defects and the occurrence of defects when welding. Therefore, the upper limit is set to 0.005%. It is preferably 0.001 to 0.004%, more preferably 0.001 to 0.003%.

B: 0.0005 to 0.0035%
B is a useful element that improves hot workability and contributes to uniform cooling by making the oxide film porous. Addition of at least 0.0005% is necessary to obtain this effect. However, an excessive addition tends to cause weld beads and solidification cracks in the manufacturing process, so the upper limit must be 0.0035%. Therefore, in the present invention, the B content must be strictly limited to 0.0005-0.0035%. It is preferably 0.0008 to 0.0030%, more preferably 0.0010 to 0.025%.

Nb: 0.02-0.75%
Nb is an element that effectively increases the strength of the Fe--Ni alloy, and is a useful element for increasing the rigidity and reducing the thickness of the frame material. This requires an addition of at least 0.02%. However, excessive addition increases the coefficient of thermal expansion and promotes the occurrence of weld cracks. Therefore, the upper limit is set to 0.75%. It is preferably 0.10 to 0.70%, more preferably 0.20 to 0.65%.

In the Fe—Ni alloy of the present invention, the balance other than the above components is iron (Fe) and unavoidable impurities. The Fe—Ni alloy of the present invention contains Fe as a main component.

50 ≤ -212 x Si -140 x Cr -578 x Al -569 x Ti +254 x Mn +262 x Mo +1550 x Sn +14
The number of voids in the oxide scale is affected by the composition, but there are positive and negative effects for each element, and comprehensive understanding is important for stabilizing the quality. This formula is obtained by performing multiple regression analysis of the influence of each element and sorting out the degree of contribution. Although it is an essential element for corrosion resistance and deoxidation treatment, if it is contained in a certain amount or more, the oxide scale becomes dense. In this case, it is necessary to add a certain amount of an element that introduces voids so that the value becomes 50 or more. It is preferably 75 or more, more preferably 95 or more. Moreover, when B is contained, an effect can be obtained by using a formula in which the evaluation of B (a term of +68000×B in the above formula) is added. In that case, the same threshold value of 50 is no problem.

0.8 ≥ 0.89 x Si + 1.1 x Cr + 1.5 x Al + 0.86 x Ti + 0.7 x Mn + 0.53 x Mo + 0.98 x Sn + 0.26 x Nb + 29.5 x B
This formula predicts the amount of increase Δα (×10 ^-6 ) in the coefficient of thermal expansion, and is intended for the coefficient of thermal expansion of 30 to 100° C. required for the frame material. Controlling the voids in the oxide scale slightly increases the coefficient of thermal expansion, but it is preferable to avoid it when considering application to the frame material. This makes it possible to mitigate the influence of a certain element with another element. This can be controlled by calculating Δα from the composition and making it 0.8 or less. It is appropriate to set it to preferably 0.6 or less, more preferably 0.5 or less, and still more preferably 0.4 or less.

The Fe—Ni alloy of the present invention is suitable as a material for molds and frames because it maintains a low coefficient of thermal expansion and is excellent in workability and production efficiency of alloy plates.

Heat treatment temperature: 900-1000°C, holding time: 1-60min
The purpose of the heat treatment is to soften the material hardened by hot rolling. If the temperature is less than 900° C., the softening is not sufficient, and if it is 1000° C. or more, the oxidation loss is large and the yield is reduced. In addition, the oxide scale becomes thicker and less uniform, resulting in difficulty in uniform cooling. Therefore, the heat treatment temperature is set to 900 to 1000.degree. Preferably 920-980°C, more preferably. It is 930-970°C.

The holding time can be appropriately selected according to the plate thickness, and holding for at least 1 minute is required for softening. On the other hand, if the holding time exceeds 60 minutes, the oxide scale becomes thicker and the uniformity is lowered. Therefore, it is set to 1 to 60 minutes. Preferably, it is 3-45 min, more preferably 5-30 min.

Next, examples of the present invention will be described, but the present invention is not limited to these examples as long as the gist of the present invention is not exceeded.
(1. Influence of Alloy Components on Evaluation of Properties)
The Fe—Ni alloy is produced by melting raw materials such as scrap and Ni in an electric furnace, and decarburizing the melt by blowing oxygen with AOD (Argon Oxygen Decarburization) and/or VOD (Vacuum Oxygen Decarburization). After that, Al and limestone are added for Cr reduction, and then limestone and fluorite _are added to form CaO-- _SiO.sub.2 --Al.sub.2O.sub.3--MgO--F system slag _on the molten alloy for deoxidation and desulfurization. A slab was manufactured by casting the molten alloy obtained by performing the above with a continuous casting machine. Its composition is shown in Table 2. After that, the slab was hot-rolled into a 30 mmt hot-rolled sheet. The size at this stage is 30mmt x 2000mm x 5000mm. This was subjected to heat treatment at 960° C.×10 min, followed by spray water cooling in a roller hearth type cooling tank to obtain a product.

This roller hearth-type cooling tank is equipped with a roller table equipped with multiple rollers for transporting the steel plate in the horizontal plane in the longitudinal direction, and multiple spray nozzles for cooling the upper and lower surfaces of the steel plate. . The cooling spray nozzles on the upper surface side of the steel plate are arranged vertically and horizontally to spray cooling water facing the upper surface of the steel plate. In the vertical direction (longitudinal direction of the steel sheet), the number is arranged so as to sufficiently cover the entire length of the steel sheet. A plurality of spray nozzles on the lower surface of the steel plate are also arranged vertically and horizontally so as to face the lower surface of the steel plate, similarly to the upper surface. Since the rollers are arranged on the lower surface of the steel plate and interfere with each other, by adjusting the arrangement intervals between the spray nozzles and the rollers, the spray nozzles are arranged vertically and horizontally at desired intervals as on the upper surface. The distance between the individual spray nozzles is preferably 200 to 400 mm, more preferably 250 to 350 mm, in both the width direction and the longitudinal direction, in order to perform necessary and sufficient cooling evenly. In this example, the intervals were 300 mm. The spray nozzles were for water, and the amount of water was 32 liters/min per nozzle. It was carried out in a process of quickly moving to the bottom of the spray, and cooling after the start of spraying while rocking so as not to cut off the water flow. The obtained alloys were evaluated as follows.

(1) Number of voids in oxide film
After the product was annealed, a test piece was taken, polished with #240 to 200 μm or more until the oxide scale was completely removed, washed with water and degreased, and subjected to an oxidation test at 1000° C. for 10 minutes and allowed to cool. After that, cutting and embedding were performed, and the number of voids in the oxide film on the cross section was measured. The measurement was carried out by observation with a field emission scanning electron microscope (JSM-7001F) at a magnification of 1000 to 3000. The composition image and the TOPO image were observed, and voids were counted and evaluated. The evaluation length is 50 μm, ×: less than 30 voids, Δ: 30 to less than 60 voids, ◯: 60 to less than 95 voids, ◎: 95 or more voids, They are also shown in Table 2.

(2) Evaluation of residual stress A test piece of 30 mmt x 2000 mm x 100 mm was cut out from the material after product annealing and used for evaluation. The surface of this was ground by a milling machine by 6 mm, and the displacement (warp) was measured over the entire width of 2000 mm at intervals of 100 mm with the end of the material as the origin. The grinding amount was constant at 1 mm per pass. It was evaluated by the maximum amount of displacement in the width direction. The maximum displacement (warp) after 6 mm grinding was evaluated as ×: 7 mm or more, Δ: 7 mm or more and less than 4 mm, ◯: 4 mm or more and less than 1 mm, and ◎: 1 mm or less.

(3) Strength After the surface of the annealed product was wet-polished to completely remove the oxide scale, the Vickers hardness was measured.

(4) Thermal expansion coefficient A test piece of 8 mmφ x 30 mm was sampled from the test material sampled from the material after product annealing. I made a measurement. Thermal expansion coefficient α _{30 to 100°C} at 30 to 100°C is evaluated by the ratio (α _{30 to 100°C} /α _standard ) to the standard value (α _standard = 1.35 × 10 ^-6 ), and the increase is small. is good. ×: 1.6 or more, Δ: 1.4 or more and less than 1.6, ◯: 1.3 or more and less than 1.4, ⊙: less than 1.3. In addition, since the evaluations (1) to (3) are prioritized in comparison with this evaluation, Example 14, which is x in this evaluation, is acceptable as an invention example.

Table 2 shows the evaluation results. No. 1, which is an example of the invention. 1 to 19, the number of voids in the oxide scale exceeded 30 in the measurement results, confirming the improvement. There is a good correlation between the measured number of voids and warpage, and it is considered that the threshold setting was appropriate. No. 1 to which Nb was added. Nos. 15-17 are about 10-20 HV higher in hardness than others. This is expected to increase the rigidity of the mold and make it thinner. Moreover, No. of B addition. The effect of Nos. 17 to 19 is remarkable, and a large effect can be obtained even with a very small amount.

No. in which the amount of Si exceeds the upper limit of the range. 20, and No. 20, in which the amounts of Cr and Al also exceed the range. In Nos. 21 and 22, the oxide scale is dense under the influence of each element, so the desired effect cannot be obtained. Therefore, warpage is large. No. In No. 23, the content of each element was specified, but the gap formula (1) was not satisfied, and as a result, the introduction of gaps was small, and the specified effect was not obtained. Also, No. In Nos. 24 to 26, since the contents of Mn, Mo and Sn are small, the effect is insufficient, and as a result the warpage cannot be suppressed.

(2. Examination of heat treatment after hot rolling)
Next, No. 1 subjected to hot rolling. For Nos. 3 and 17, instead of the heat treatment at 960° C.×10 min in the above experiment, the heat treatment was performed under the following conditions, and warpage was evaluated in the same manner as above. Table 3 shows the results.

No. in which either the heat treatment temperature or time is outside the scope of the present invention. 3-2, No. 3-3, No. 17-2, No. As a result, 17-3 had a large warpage.

The present invention relates to Fe—Ni alloys capable of reducing residual stress caused by cooling.In particular, the residual stress caused by cooling is reduced by forming a characteristic oxide film on the surface during the annealing process. This is a proposal for an Fe—Ni alloy plate that can be made small and uniform.

Claims (7)

In the following mass%, C: 0.01 to 0.05%, Ni: 30 to 45%, Si: 0.01 to 0.4% Cr: 0.03 to 0.5%, Mn: 0.10 to 1.0%, Al: 0.001 to 0.10% or less, P: 0.005% or less, S: 0.005% or less, Mo: 0.01 to 0.1%, Cu: 0.01 to 0.5%, Ti: 0.1% or less, Co: 0.01-0.5%, Sn: 0.001-0.05%, N: 0.001-0.005% as main components and satisfying the relational expression (1), the balance being Fe and unavoidable impurities.
50≦-212×Si-140×Cr-578×Al-569×Ti+254×Mn+262×Mo+1550×Sn+14 (1) Nb: 0.02 to 0.75%, B: 0.0005 to 0.0035%, containing either one or two, satisfying the relational expression (2), and the balance being Fe and unavoidable impurities The Fe—Ni alloy according to claim 1, characterized in that it consists of:
50≦-212×Si-140×Cr-578×Al-569×Ti+254×Mn+262×Mo+1550×Sn+68000×B+14 (2) 3. The Fe—Ni alloy according to claim 1, wherein the Fe—Ni alloy satisfies the relational expression (3) showing an increase in thermal expansion coefficient from 30 to 100.degree.
0.8 ≥ 0.89 x Si + 1.1 x Cr + 1.5 x Al + 0.86 x Ti + 0.7 x Mn + 0.53 x Mo + 0.98 x Sn + 0.26 x Nb + 29.5 x B … (3) An Fe—Ni alloy plate having a thickness of 12.5 mm or more, produced from the alloy according to any one of claims 1 to 3. The method for producing an Fe—Ni alloy according to any one of claims 1 to 3, wherein the slab is hot-rolled to form a hot-rolled sheet, and the hot-rolled sheet is heat-treated, followed by a roller hearth type A method for producing an Fe—Ni alloy characterized by reducing and uniformizing residual stress generated by applying spray water cooling in a cooling tank. 6. The method for producing an Fe—Ni alloy according to claim 5, wherein the heat treatment is performed under conditions of a heat treatment temperature of 900 to 1000° C. and a holding time of 1 to 60 minutes. In the roller hearth-type cooling tank for spray cooling, a plurality of sprays are arranged vertically and horizontally on the upper and lower surfaces, respectively, and the entire length and width of the hot-rolled sheet are sufficiently covered at intervals of 200 to 400 mm in both the longitudinal direction and the width direction. 7. The method for producing an Fe--Ni alloy according to claim 5 or 6, characterized in that the nozzles are arranged so as to cover.

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