Fe-ni alloy and method for producing the same

Abstract

Provided is an Fe-Ni alloy that can reduce residual stress generated during annealing, particularly during cooling, and that can achieve fine machining accuracy in applications in which complex machining is performed on a mold frame material or the like. The Fe-Ni alloy contains, by 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 to 0.5%, Sn: 0.001 to 0.05%, N: 0.001 to 0.005% as main components, satisfies the relational expression (1), and the balance is constituted by Fe and inevitable impurities. 50 ≤ -212 × Si - 140 × Cr - 578 × Al - 569 × Ti + 254 × Mn + 262 × Mo + 1550 × Sn + 14… (1).

Description

Technical Field

[0001] This invention relates to Fe-Ni alloys used as mold frames in the manufacture of organic EL panels. The object is a Fe-Ni alloy that exhibits minimal deformation and easily ensures precision even after complex processing and surface grinding, thereby contributing to improved panel quality and yield. Background Technology

[0002] Fe-Ni alloys containing 30-50% Ni are commonly used in the field of electronic materials, characterized by their ability to control the coefficient of thermal expansion through their chemical composition. Fe-Ni alloys containing 36% Ni, due to their low coefficient of thermal expansion and excellent toughness, are used as mold frames in the fabrication of organic EL panels. The frame material is precision-machined through complex cutting and surface grinding processes, with strict management of processing accuracy that affects panel quality and yield. That is, the dimensional changes caused by cutting and grinding must be minimized.

[0003] This deformation is largely caused by residual stress generated during the raw material preparation process. Residual stress is generated in various processes, among which the residual stress generated in the annealing process is the largest. Therefore, it is extremely important to reduce this part of the residual stress.

[0004] While many prior art inventions have been reported concerning alloys suitable for molds and their preparation methods, there are few reports on improvements to the deformation that occurs during mold processing. Patent Document 1, for use in molds for electronic display components, reports a martensitic steel that maintains strength and properties, and its preparation method. However, this invention concerns high-strength steel sheets, and the compositional ranges of Ni, Cr, Mn, etc., are significantly different from the Fe-Ni alloys that are the subject of this invention.

[0005] Furthermore, although a heat treatment method for the mold is reported in Patent Document 2, the composition range of Cr, Mn, etc. is quite different from that of the Fe-Ni alloy.

[0006] Thus, there are no reports on the use of Fe-Ni alloy molds. While studies have been conducted on the thermal expansion and low-temperature properties of Fe-Ni alloys, there are no examples of studies on alloys or methods for reducing or eliminating residual stress generated during the preparation process, particularly the annealing process.

[0007] Patent Document 1: Japanese Patent Application Publication No. 2012-528943,

[0008] Patent Document 2: Japanese Patent Application Publication No. 2012-11619. Summary of the Invention

[0009] The purpose of this invention is to provide an Fe-Ni alloy that reduces and unifies residual stress generated during annealing, especially during cooling, and enables fine machining accuracy in applications involving complex machining, such as mold frame materials.

[0010] In order to address the aforementioned issues of the prior art, this invention focuses on the oxide scale generated during annealing and the cooling behavior, and conducts repeated and in-depth research on the influence of the composition of the oxide scale.

[0011] This development stemmed from the observation that, during the mass production and preparation of Fe-36%Ni alloy, even when annealing plates of the same size under the same temperature and water-cooling conditions, significant differences in warpage were observed. The plates measured 30mm thick (mm) × 2000mm × 10000mm. Plates with large warpage, due to forceful straightening, exhibited high and complex residual stresses, making it difficult to maintain their shape when machined into frame materials. Importantly, plates with small warpage were selected. Test pieces measuring 30mm thick × 2000mm × 100mm were cut from these plates. Due to the small size, there was no difference in warpage between the two types at this stage. The surface of each piece was milled to 6mm, and displacement (warpage) was measured along its entire length at 100mm intervals, using the material end as the origin. The largest displacement was approximately in the center of the width, measuring 9mm in plates with large warpage and 5mm in plates with small warpage. Displacement below this level indicated mild straightening and could be considered a significant improvement.

[0012] Next, the plates with good warpage were investigated, and it was determined that they were all from specific ingot charges. Since the main components were the same regardless of the size of the warpage, it was speculated that components other than the main component had an effect. In addition, the heating-soaking-cooling behavior of plates with small and large warpages was carefully observed, and it was determined that the water vapor particles generated during water cooling were different; the water vapor particles in the plates with small warpage were finer and more uniform. This is considered to be the reason for the difference in warpage.

[0013] To clarify the cause of the difference in water vapor particles, the following oxidation experiment was conducted, and the morphology and composition of the oxide scale were compared. The test materials used were cut from two types of plates: one with small warping and the other with large warping. All six surfaces of these plates were ground with #240 (sandpaper) to a depth of at least 200 μm to completely remove the oxide scale. The plates were then washed, degreased, and dried before the oxidation test. The test temperature was 960℃ for 10 minutes in an atmospheric atmosphere, followed by cooling and cross-sectional observation. The results showed that the oxide scale was mainly composed of Fe and Ni, but their morphologies differed. The cross-sectional observation results after this heat treatment experiment are shown below. Figure 1(a) shows a charge with less warpage, and (b) shows a charge with more warpage. The side with less warpage has a slightly thicker oxide scale with gaps, while the side with more warpage is quite dense. Comparing the composition, a good charge is one with a high content of Mn and Sn.

[0014] If the oxide scale can be made porous, it is believed that the residual stress generated by water cooling can be reduced and made more uniform. The influence of elements on the oxide scale morphology was investigated. Various additive elements were added to Fe-36%Ni alloy, and laboratory melting was carried out in 10 kg. The additive elements selected were Si, Mn, Cr, Mo, Cu, Co, Al, Ti, and Sn. Their respective composition ranges are shown in Table 1. 0.00 means no addition. The unit is weight % (wt%).

[0015] Table 1

[0016]

[0017] The obtained alloy block was hot-forged to 10 mm, annealed at 1100 °C, and then cold-rolled to 4 mm. Samples were then taken from the prepared alloy plate, and the surface of the samples was thoroughly ground with #240 sandpaper for an oxidation test at 1000 °C for 10 minutes, followed by cooling. The temperature was set to 1000 °C to make the differences in oxide scale more apparent. The samples were then cut and embedded, and the morphology of the oxide scale in the cross-section was observed, along with the number of voids. Regarding voids, observation was performed using a field emission scanning electron microscope (JSM-7001F) at 1000–3000x magnification. Evaluation was conducted on a 50 μm length, with both compositional and TOPO images observed. Voids were counted and evaluated. Through sample adjustment, areas with oxide scale cracks were identified, but areas that could be avoided for stable evaluation were selected for observation. The results showed that increasing Sn increased the number of voids, while increasing Al decreased the number of voids. The effects of Sn and Al content on the number of pores in the oxide scale are shown in the figure. Figure 2 In the curve graph. For Figure 1 The well-warped sample observed in the study, when the number of voids was measured using the same method, yielded 45 voids. It was concluded that introducing this number of voids would improve the sample. Furthermore, the same evaluation was conducted, identifying Mn and Mo as the elements that increased the number of voids, and Si, Cr, and Ti as the elements that decreased it.

[0018] Thus, the number of voids in the oxide scale is clearly influenced by the composition, but each element has both positive and negative effects. Understanding the overall effect of each element is important for achieving quality stability. Therefore, by performing a multiple regression analysis on these results, the relationship between the number of voids and the chemical composition was derived (A).

[0019] Number of voids (n) = -212×Si-140×Cr-578×Al-569×Ti+254×Mn+262×Mo+1550×Sn+14…(A).

[0020] Figure 3 The relationship between the value of Equation (A) and the number of voids measured is shown. The deviation is slightly larger when the number of voids is small, but the linearity is good. Even within the range of low content, the number of voids can vary greatly. Therefore, it is considered that for stable management, it is advisable to manage with a value that takes into account the lower limit of deviation. The number of voids in a well-shaped plate is 45. If it is at the same level, it is 70 or more according to the regression equation. Since the number of voids is improved at 45, it is speculated that even a slightly smaller value is sufficient. Regarding the appropriateness and threshold of this equation, it is confirmed from the examples described later that 50 or more is sufficient instead of 70. Therefore, after modification, it becomes Equation (1).

[0021] 50≤-212×Si-140×Cr-578×Al-569×Ti+254×Mn+262×Mo+1550×Sn+14 …(1) .

[0022] Furthermore, the effect of adding B was studied within a range from a maximum of 0.0050%, and it was determined that B also effectively introduced gaps. Similarly, this was incorporated into the regression equation, which was then modified to (2). In the case of B, equation (2) was applied.

[0023] 50≤-212×Si-140×Cr-578×Al-569×Ti+254×Mn+262×Mo+1550×Sn+68000×B+14 …(2).

[0024] If the porosity of the oxide scale is controlled in this way, the coefficient of thermal expansion will still increase slightly due to the effects of the added elements. However, if considering its application in frame materials, this increase is preferable to avoid. The effects of almost all elements are known; their addition increases the coefficient of thermal expansion, but the effect of Sn is unclear. Therefore, measurements were performed using the aforementioned laboratory-melted material, and the results showed that the coefficient of thermal expansion increases from 30 to 100°C, with a change of 0.98 per unit percentage added. Thus, the increase in the coefficient of thermal expansion from 30 to 100°C is Δα. 30~100℃ (×10 -6 The following formula can be used to predict the amount, and if its application as a frame material is considered, an increase of less than 0.8 is appropriate.

[0025] 0.8≥0.89×Si+1.1×Cr+1.5×Al+0.86×Ti+0.7×Mn+0.53×Mo+0.98×Sn+0.26×Nb+29.5×B …(3).

[0026] The alloy of this invention was obtained through the experiment described above, as detailed below. The alloy of this invention is an Fe-Ni alloy, characterized in that it contains the following components by mass percentage: C: 0.001~0.05%, Ni: 30~45%, Si: 0.01~0.4%, Cr: 0.03~0.5%, Mn: 0.10~1.0%, Al: 0.001~0.10%, P: less than 0.005%, S: less than 0.005%, Mo: 0.01~0.1%, Cu: 0.01~0.5%, Ti: less than 0.1%, Co: 0.01~0.5%, Sn: 0.001~0.05%, N: 0.001~0.005%, satisfying the relation (1), and the balance consists of Fe and unavoidable impurities.

[0027] 50≤-212×Si-140×Cr-578×Al-569×Ti+254×Mn+262×Mo+1550×Sn+14…(1).

[0028] Furthermore, the preferred Fe-Ni alloy is one or two of the following: Nb: 0.02~0.75% and B: 0.0005~0.0035%, satisfying the relationship (2), and the balance being composed of Fe and unavoidable impurities.

[0029] 50≤-212×Si-140×Cr-578×Al-569×Ti+254×Mn+262×Mo+1550×Sn+68000×B+14…(2).

[0030] Furthermore, among the alloys of the present invention, a Fe-Ni alloy that satisfies formula (3) which represents an increase in the coefficient of thermal expansion of 30 to 100°C is more preferred.

[0031] 0.8≥0.89×Si+1.1×Cr+1.5×Al+0.86×Ti+0.7×Mn+0.53×Mo+0.98×Sn+0.26×Nb+29.5×B…(3).

[0032] In addition, an Fe-Ni alloy plate with a thickness of 12.5 mm or more prepared from the alloy of the present invention is also provided.

[0033] In addition, a method for preparing Fe-Ni alloys is also provided. The method for preparing Fe-Ni alloys is characterized by hot rolling a slab into a hot-rolled plate, heat-treating the hot-rolled plate, and then performing spray water cooling using a roller hearth-type cooling tank, thereby reducing and uniformizing the generated residual stress.

[0034] In the preparation method of the present invention, the heat treatment conditions are preferably: heat treatment temperature: 900~1000℃, holding time: 1~60 minutes.

[0035] In the preparation method of the present invention, it is preferable to arrange multiple sprayers longitudinally and transversely on the upper and lower surfaces of a spray-cooled roller furnace cooling tank, and to form a nozzle configuration that fully covers the entire length and width of the hot-rolled plate at intervals of 200-400 mm in either the length or width direction. Attached Figure Description

[0036] Figure 1 These are cross-sectional photographs after the heat treatment experiment. (A) shows the charge with small warpage, and (B) shows the charge with large warpage.

[0037] Figure 2 This is a graph showing the effect of Sn and Al content on the number of voids in the oxide scale of the Fe-Ni alloy of the present invention.

[0038] Figure 3 This is a graph showing the relationship between the number of voids in the oxide scale in the Fe-Ni alloy of the present invention and the predicted regression equation. Detailed Implementation

[0039] As described above, the Fe-Ni alloy involved in this invention has the following composition, comprising, by mass%, C: 0.001~0.05%, Ni: 30~45%, Si: 0.01~0.4%, Cr: 0.03~0.5%, Mn: 0.10~1.0%, Al: 0.001~0.10%, P: less than 0.005%, S: less than 0.005%, Mo: 0.01~0.1%, Cu: 0.01~0.5%, Ti: less than 0.1%, Co: 0.01~0.5%, Sn: 0.001~0.05%, N: 0.001~0.005%, with the balance consisting of Fe and unavoidable impurities. The reasons for limiting the composition as described above are explained below.

[0040] C: 0.001~0.05%

[0041] Carbon (C) is an element that contributes to solid solution strengthening and also to the low-temperature stability of the microstructure. If the content is below 0.001%, sufficient strength cannot be obtained as a mold. However, if the content exceeds 0.05%, a large amount of carbides are formed, resulting in deterioration of toughness and fatigue resistance. Furthermore, the coefficient of thermal expansion also increases. In particular, to obtain excellent strength, low-temperature properties, fatigue resistance, and coefficient of thermal expansion, the C content needs to be strictly limited. In this invention, it is set to 0.001~0.05%. Preferably, it is set to 0.001~0.045%, and more preferably, it is set to 0.001~0.040%.

[0042] Ni: 30~45%

[0043] Ni is an important alloying element in controlling the coefficient of thermal expansion of Fe-Ni alloys. The Ni content needs to be set within the range of 30-45%; outside this range, the coefficient of thermal expansion increases, making it unusable. Preferably, it is 34-39%, with a minimum of 35-37%.

[0044] Si: 0.01~0.4%

[0045] Si, as a deoxidizer, is an element effective in maintaining good weldability and needs to be added at least 0.01%. However, since it is an element that forms a stable oxide scale and promotes the densification of the oxide layer through annealing, it tends to cause uneven cooling. In addition, since it increases the coefficient of thermal expansion, the upper limit is set to 0.4%. Therefore, in this invention, the Si content is set to 0.01~0.4%, preferably 0.02~0.38%, and more preferably 0.05~0.35%.

[0046] Cr: 0.03~0.5%

[0047] Cr is a solid solution strengthening element, which helps ensure strength and provides good corrosion resistance. Therefore, it needs to be added at least 0.03%. On the other hand, if its addition exceeds 0.5%, the coefficient of thermal expansion becomes high, and the original low thermal expansion characteristic is lost. In addition, Cr, like Si, is also an element that stabilizes the oxide scale. By forming a composite oxide film with Si on the surface, it promotes the densification of the oxide scale, which has an adverse effect on uniform cooling. Therefore, in this invention, the content of Cr is set to 0.03~0.5%, preferably 0.04~0.40%, and more preferably 0.05~0.35%.

[0048] Mn: 0.10~1.0%

[0049] Mn is a solid solution strengthening element and also an effective deoxidizer. Furthermore, it forms MnS, promoting sulfur fixation and improving hot workability and resistance to weld cracking. In addition, it plays a crucial role in creating voids in the oxide scale, thus promoting uniform cooling. To achieve these effects, an addition of 0.10% or more is required. However, if the content exceeds 1.0%, excess Mn will deteriorate surface properties, increase inclusions, worsen corrosion resistance, and consequently increase the coefficient of thermal expansion. Therefore, in this invention, the Mn content is limited to 0.10% to 1.0%. Preferably, it is 0.12% to 0.7%, more preferably 0.13% to 0.5%.

[0050] Al: 0.001~0.10%

[0051] Al is used as a deoxidizer. If an appropriate amount remains in the alloy, it effectively forms a composite oxide film with anti-rust properties, helping to ensure corrosion resistance in the atmosphere. Therefore, an addition of 0.001% or more is required. On the other hand, if the amount added increases, the coefficient of thermal expansion becomes higher, and the weld penetration performance deteriorates. Furthermore, since promoting the densification of the oxide scale adversely affects uniform cooling, setting an appropriate amount is important. Therefore, the upper limit is specified as 0.10%. Preferably, it is set to 0.002~0.050%, more preferably 0.003~0.020%.

[0052] P: below 0.005%

[0053] Since phosphorus (P) deteriorates rust resistance and weldability, it is preferable to minimize its concentration. Therefore, it is limited to 0.005% or less. Preferably, it is set to 0.003% or less, and more preferably, it is set to 0.002% or less.

[0054] S: below 0.005%

[0055] If sulfur (S) exceeds 0.005%, it will impair hot workability and deteriorate resistance to weld cracking. Therefore, the sulfur content is limited to 0.005% or less. Preferably, it is set to 0.002% or less, and more preferably, it is set to 0.001% or less.

[0056] Mo: 0.01~0.1%

[0057] Mo not only helps improve corrosion resistance, but is also an important element for introducing porosity into the oxide scale during annealing. Therefore, it needs to be added at least 0.01%. However, excessive addition leads to increased costs and a larger coefficient of thermal expansion, so it needs to be set below 0.1%. Preferably, it is set at 0.02~0.09%, more preferably at 0.02~0.07%.

[0058] Cu: 0.01~0.5%

[0059] Cu is an element that helps improve the stability of the FCC phase, and at least 0.01% needs to be added. However, if it exceeds 0.5%, the coefficient of thermal expansion becomes high, and the quality deteriorates. Therefore, in this invention, Cu is limited to the range of 0.01% to 0.50%. Preferably, it is set to 0.02% to 0.40%, and more preferably, it is set to 0.03% to 0.30%.

[0060] Ti: below 0.1%

[0061] Ti is a non-added element, but it sometimes mixes in from the raw materials. Therefore, it is necessary to minimize the mixing of Ti. If it exceeds 0.1%, the increased precipitates will lead to deterioration of corrosion resistance, a higher coefficient of thermal expansion, and a decline in quality. In addition, it promotes the densification of the oxide scale, which has an adverse effect on uniform cooling. Therefore, in this invention, the Ti content is minimized as much as possible, and its upper limit is specified as 0.1%. Preferably, it is set to 0.03% or less, and more preferably, it is set to 0.02% or less.

[0062] Co: 0.01~0.5%

[0063] Like Ni, Co is an alloying element that maintains a low coefficient of thermal expansion in Fe-Ni alloys and stabilizes the FCC phase. If elements are added to introduce voids into the oxide scale, the coefficient of thermal expansion increases; however, like Ni, Co is an effective element for suppressing this increase. Therefore, a content of at least 0.01% is required. However, if it exceeds 0.5%, machinability decreases, and even with suppression of residual stress, it is difficult to maintain quality during surface finishing. Therefore, in this invention, Co is limited to 0.5% or less. Preferably, it is set to 0.01 to 0.40% or less, more preferably 0.02 to 0.35%.

[0064] Sn: 0.001~0.05%

[0065] Sn is an important element for creating voids in the oxide scale, thus ensuring uniform cooling. Therefore, at least 0.001% needs to be added. However, if it exceeds 0.05%, corrosion resistance decreases, reducing hot workability. Therefore, Sn is limited to the range of 0.001% to 0.05%. Preferably, it is set to 0.002% to 0.040%, more preferably to 0.005% to 0.035%.

[0066] N: 0.001~0.005%

[0067] Nitrogen (N) is a solid solution strengthening element that helps ensure strength; to achieve this effect, at least 0.001% needs to be added. However, excessive addition will form nitrides, promoting surface defects and contributing to defects during welding. Therefore, the upper limit is set at 0.005%. Preferably, it is set at 0.001~0.004%, more preferably at 0.001~0.003%.

[0068] B: 0.0005~0.0035%

[0069] Boron (B) is a useful element for improving hot workability and contributes to uniform cooling by making the oxide scale porous. To achieve this effect, at least 0.0005% needs to be added. However, since excessive addition can easily cause solidification cracking in the weld or during manufacturing, the upper limit needs to be set at 0.0035%. Therefore, in this invention, the B content needs to be strictly limited to 0.0005~0.0035%. Preferably, it is set to 0.0008~0.0030%, more preferably 0.0010~0.025%.

[0070] Nb: 0.02~0.75%

[0071] Nitrogen (Nb) is an element that effectively increases the strength of Fe-Ni alloys and is useful for achieving high rigidity and thin-walled structures in frame materials. Therefore, at least 0.02% needs to be added. However, excessive addition increases the coefficient of thermal expansion, thus promoting weld cracking. Therefore, the upper limit is set at 0.75%. Preferably, it is set at 0.10~0.70%, more preferably at 0.20~0.65%.

[0072] In the Fe-Ni alloy of the present invention, the balance other than the above-mentioned components is iron (Fe) and unavoidable impurities. In the Fe-Ni alloy of the present invention, Fe is contained as the main component.

[0073] 50≤-212×Si-140×Cr-578×Al-569×Ti+254×Mn+262×Mo+1550×Sn+14

[0074] The number of voids in the oxide scale is influenced by its composition, but each element has both positive and negative effects, and a comprehensive understanding is important for maintaining quality stability. This formula is derived by performing a multivariate regression analysis on the influence of each element and summarizing their contributions. While elements are necessary for corrosion resistance or deoxidation treatment, if they are present in a certain amount or more, the oxide scale will become denser. In this case, a certain amount of elements that introduce voids needs to be added to achieve a void count of 50 or more. Preferably, it is set to 75 or more, and more preferably 95 or more. Furthermore, in the case of containing B, the effect can be obtained by using a formula that includes an evaluation of B (adding a term of +68000×B to the above formula). In this case, a threshold of 50 is also acceptable.

[0075] 0.8 ≥ 0.89 × Si + 1.1 × Cr + 1.5 × Al + 0.86 × Ti + 0.7 × Mn + 0.53 × Mo + 0.98 × Sn + 0.26 × Nb + 29.5 × B

[0076] It is the predicted increase in the coefficient of thermal expansion Δα (×10). -6The formula is based on the coefficient of thermal expansion (CTE) required for use as a frame material, ranging from 30 to 100°C. While controlling the porosity of the oxide scale can slightly increase the CTE, this increase is preferable to avoid when considering its application as a frame material. Therefore, the influence of a particular element can be mitigated using other elements. This can be controlled by calculating Δα based on the composition and setting it to 0.8 or less. Preferably, it is 0.6 or less; more preferably, 0.5 or less; and even more preferably, 0.4 or less.

[0077] The Fe-Ni alloy of the present invention maintains a low coefficient of thermal expansion while exhibiting excellent machinability and production efficiency, making it suitable as a material for molds / frames.

[0078] Heat treatment temperature: 900~1000℃, holding time: 1~60 minutes

[0079] The purpose of heat treatment is to soften the material hardened by hot rolling. Softening is insufficient at temperatures below 900°C, while above 1000°C, oxidation loss is significant, leading to a lower yield. Furthermore, the oxide scale thickens, reducing uniformity and making uniform cooling more difficult. Therefore, the heat treatment temperature is set at 900–1000°C. Preferably, it is 920–980°C, and more preferably 930–970°C.

[0080] The holding time can be appropriately selected according to the plate thickness; for softening, it needs to be held for at least 1 minute. Conversely, if the holding time exceeds 60 minutes, the oxide scale becomes thicker, and uniformity decreases. Therefore, it is set to 1 to 60 minutes. Preferably, it is 3 to 45 minutes, and more preferably 5 to 30 minutes. Example

[0081] The embodiments of the present invention will be described next, but the present invention is not limited to these embodiments as long as it does not depart from its spirit.

[0082] (1. The influence of alloy composition on the evaluation of various properties)

[0083] In the preparation of Fe-Ni alloys, scrap iron, Ni, and other raw materials are melted in an electric furnace and decarburized through argon-oxygen decarburization (AOD) and / or vacuum oxygen decarburization (VOD) refining. Then, Al and limestone are added for Cr reduction, followed by the addition of limestone and fluorite to form a CaO-SiO2-Al2O3-MgO-F slag system on the molten alloy for deoxidation and desulfurization. The resulting molten alloy is then cast using a continuous casting machine to prepare slabs. The composition is shown in Table 2. The slabs are then hot-rolled to produce 30mmt hot-rolled plates. The dimensions at this stage are 30mmt × 2000mm × 5000mm. They are then heat-treated at 960℃ for 10 minutes, followed by spray water cooling in a roller bed cooling trough to produce the finished product.

[0084] This roller conveyor type cooling trough includes rollers and multiple spray nozzles for cooling the upper and lower surfaces of a steel plate. The rollers include multiple rollers for conveying the steel plate horizontally along its length. Multiple spray nozzles for cooling the upper surface of the steel plate are arranged longitudinally and transversely, spraying cooling water towards the upper surface. The number of nozzles sufficient to cover the entire width of the steel plate in the transverse direction (width direction) and sufficient to cover the entire length of the steel plate in the longitudinal direction (length direction). Similarly, multiple spray nozzles for the lower surface of the steel plate are arranged longitudinally and transversely towards the lower surface, just as on the upper surface. Since the rollers on the lower surface of the steel plate can cause interference, the spacing between the spray nozzles and the rollers is adjusted to achieve the desired longitudinal and transverse spacing, similar to the upper surface. For uniform and sufficient cooling, the spacing between the individual spray nozzles is preferably 200-400 mm in both the width and length directions, and particularly preferably 250-350 mm. In this embodiment, the process was carried out at 300mm intervals. The sprayer nozzles were water-based, with a water flow rate of 32 liters / minute per nozzle. The sprayer was quickly moved under the sprayer, and cooling was performed by continuously shaking the nozzle while the water flow was not interrupted after spraying began. The resulting alloy was evaluated as follows.

[0085] (1) Number of voids in the oxide scale

[0086] After annealing the finished product, samples were collected and their surfaces were thoroughly ground with #240 sandpaper to a depth of at least 200 μm until the oxide scale was completely removed. Following washing and degreasing, the samples were subjected to an oxidation test at 1000℃ for 10 minutes followed by cooling. Then, the samples were cut and embedded, and the number of voids in the oxide scale of the cross-section was determined. The determination was performed using a field emission scanning electron microscope (JSM-7001F) at magnifications of 1000–3000x. Compositional images and TOPO images were observed, and voids were counted and evaluated. The evaluation length was set to 50 μm, and the evaluation criteria were: ×: fewer than 30 voids; △: more than 30 but less than 60 voids; 〇: more than 60 but less than 95 voids; ◎: more than 95 voids. These results are recorded in Table 2.

[0087] (2) Evaluation of residual stress

[0088] 30mm × 2000mm × 100mm specimens were cut from the annealed material for evaluation. The specimens were milled to a surface thickness of 6mm. Displacement (warping) was measured across the entire 2000mm width at 100mm intervals, with the material end as the origin. The grinding amount was set to a fixed 1mm per pass. The maximum displacement in the width direction was used for evaluation. The maximum displacement (warping) after grinding 6mm was evaluated as follows: ×: 7mm or more, △: 7mm or more but less than 4mm, 〇: 4mm or more but less than 1mm, ◎: less than 1mm, and these values ​​are recorded in Table 2.

[0089] (3) Strength

[0090] The surface of the finished product after annealing was wet-ground to completely remove the oxide scale, and the Vickers hardness was measured and recorded in Table 2.

[0091] (4) Coefficient of thermal expansion

[0092] A sample measuring 8 mm φ × 30 mm l (mm length) was cut from the finished product after annealing. After stress-relief annealing at 960℃ for 10 minutes in a vacuum, the coefficient of thermal expansion was measured. The coefficient of thermal expansion α from 30 to 100℃ was determined. 30~100℃ With reference value (α) 基准 =1.35×10 -6 The ratio of α to 0. 30~100℃ / α 基准 Evaluation was conducted, with smaller samples being considered good. Evaluations of × (1.6 or higher), △ (1.4 or higher but lower than 1.6), 〇 (1.3 or higher but lower than 1.4), and ◎ (lower than 1.3) were recorded in Table 2. It should be noted that since evaluations (1) to (3) take precedence over this evaluation, example 14, which is × in this evaluation, is permissible as an inventive example.

[0093] Table 2

[0094]

[0095] The evaluation results are shown in Table 2. For invention examples 1-19, the number of voids in the oxide scale was measured to be over 30, confirming improvement. A good correlation was found between the number of voids and warpage, indicating that the threshold setting was appropriate. Examples 15-17 with added Nb showed a hardness increase of approximately 10-20 HV compared to the others. This increases the rigidity of the mold, making thinner wall thicknesses a possibility. Furthermore, the effect of adding B to examples 17-19 was significant; even trace amounts yielded substantial results.

[0096] Number 20, with Si content exceeding the upper limit, and numbers 21 and 22, with Cr and Al content exceeding the range, have dense oxide scales due to the influence of their respective elements, thus failing to achieve the specified effect. Therefore, warping is significant. Although number 23 has the specified content of each element, it does not meet the interstitial formula (1), resulting in insufficient interstitial introduction and failing to achieve the specified effect. In addition, numbers 24 to 26 have insufficient Mn, Mo, and Sn content, resulting in insufficient effect and failure to suppress warping.

[0097] (2. Research on heat treatment after hot rolling)

[0098] Next, for the hot-rolled samples 3 and 17, instead of the heat treatment of 960℃×10 minutes in the above experiment, the heat treatment was carried out under the following conditions, and the warpage was evaluated in the same way as above. The results are shown in Table 3.

[0099] Table 3

[0100]

[0101] If either the heat treatment temperature or time is outside of the present invention (as specified in numbers 3-2, 3-3, 17-2, and 17-3), the result is increased warpage.

[0102] This invention relates to Fe-Ni alloys that can reduce residual stress caused by cooling, and in particular to an Fe-Ni alloy plate that, during the annealing process, forms a characteristic oxide scale on the surface, thereby reducing and homogenizing the residual stress generated during cooling.

Claims

1. An Fe-Ni alloy, characterized in that, The main components are C: 0.01~0.05%, Ni: 30~45%, Si: 0.01~0.4%, Cr: 0.03~0.5%, Mn: 0.10~1.0%, Al: less than 0.001~0.10%, P: less than 0.005%, S: less than 0.005%, Mo: 0.01~0.1%, Cu: 0.01~0.5%, Ti: less than 0.1%, Co: 0.01~0.5%, Sn: 0.001~0.05%, and N: 0.001~0.005%, satisfying the relationship (1), with the balance consisting of Fe and unavoidable impurities. 50≤-212×Si-140×Cr-578×Al-569×Ti+254×Mn+262×Mo+1550×Sn+14…(1), The Fe-Ni alloy is obtained by heat treatment at a temperature of 900~1000℃ and a holding time of 1~60 minutes after hot rolling.

2. The Fe-Ni alloy according to claim 1, characterized in that, Containing any one or two of Nb (0.02-0.75%) and B (0.0005-0.0035%), satisfying relation (2), with the balance consisting of Fe and unavoidable impurities. 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, characterized in that, The relationship (3) that satisfies the increase in the coefficient of thermal expansion from 30 to 100℃ is satisfied: 0.8≥0.89×Si+1.1×Cr+1.5×Al+0.86×Ti+0.7×Mn+0.53×Mo+0.98×Sn+0.26×Nb+29.5×B…(3).

4. An Fe-Ni alloy plate, which is prepared from the alloy according to any one of claims 1 to 3, and has a thickness of 12.5 mm or more.

5. A method for preparing Fe-Ni alloy, which is the method for preparing Fe-Ni alloy according to any one of claims 1 to 3, characterized in that, The slab is hot-rolled to form a hot-rolled plate, which is then subjected to heat treatment at a temperature of 900~1000℃ for a holding time of 1~60 minutes. Subsequently, it is spray-cooled using a roller furnace cooling tank, thereby reducing and uniformizing the residual stress generated.

6. The method for preparing the Fe-Ni alloy according to claim 5, characterized in that, In the spray-cooled roller furnace cooling tank, multiple sprayers are arranged longitudinally and transversely on the upper and lower surfaces respectively, and the nozzles are arranged at intervals of 200~400mm in either the length or width direction to fully cover the entire length and width of the hot-rolled plate.

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