KR20040107158A - Fe-Ni-Co alloy having a low thermal expansion - Google Patents

Abstract

PURPOSE: To provide a Fe-Ni-Co base Kovar alloy having low thermal expansion capable of improving hot workability and microstructure stability by adding a trace of boron(B) to the alloy. CONSTITUTION: The Fe-Ni-Co base alloy having low thermal expansion contains 28 to 30 wt.% of nickel(Ni), 15.5 to 18.5 wt.% of cobalt(Co), 0.05 to 0.5 wt.% of silicon(Si), 0.1 to 0.5 wt.% of manganese(Mn), and impurities of 0.006 wt.% or less of phosphorus(P), 0.05 wt.% or less of carbon(C), 0.15 wt.% or less of chromium(Cr), 0.10 wt.% or less of aluminum(Al), 0.4 wt.% or less of molybdenum(Mo) and 0.01 wt.% or less of sulfur(S), wherein the Fe-Ni-Co base alloy additionally contains 0.001 to 0.006 wt.% of boron(B).

Description

Fe-Ni-Co alloy having a low thermal expansion}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low thermally expandable Kovar alloy material having excellent hot workability. In particular, the present invention can prevent surface defects from occurring during high temperature processing such as forging and hot rolling (wire rolling, sheet rolling, rolling rolling, etc.). It is related with the Fe-Ni-Co type low thermal expansion alloy containing boron (B).

Kovar alloys, commonly known as Fe-29Ni-17Co alloys, exhibit Invar alloy properties that hardly cause thermal expansion over a wide temperature range of -200 ° C to + 430 ° C.

In particular, COVA alloys can maintain low thermal expansion properties at significantly higher temperatures compared to iron (Fe) -nickel (Ni) -based tin alloys, and exhibit similar thermal expansion properties to glass such as alumina and borosilicates. Due to its excellent weldability, proper mechanical properties, and austenitic stability over a wide range, it is widely used in the sealing and sealing industry, the precision instrument industry, the vacuum tube industry, and the electronic communication industry based on glass-sealing applications. It is being applied, and its field of application is expanding.

However, COVA alloys must contain high composition of nickel (Ni) and cobalt (Co), and do not easily control impurities, so that cracks during work (forging of wire, sheet, rolling) Rupture, surface cracking, etc.) It is known that such cracks are mainly caused by high-temperature embrittlement embrittlement, and are mainly noticeable at 900 to 1,150 ^o C, which are susceptible to sulfides, oxides, and phosphides. It becomes inevitable.

In order to solve this problem, it is proposed to manage the impurity elements known to adversely affect the lower limit. For example, ASTM 15-98 and ASTM F1466, etc., limit the content of phosphorus (P) and sulfur (S) related to hot workability of COVA alloys, and at the same time, carbon (C) and aluminum ( Al, magnesium (Mg), zirconium (Zr), titanium (Ti), chromium (Cr), copper (Cu), molybdenum (Mo) and the like are also managed according to the use.

However, even in the case of the Koba alloy satisfying the alloy composition, it was not possible to completely prevent grain boundary embrittlement during high temperature hot working. Therefore, there is a need for a cobalt alloy having improved hot workability, but to date, there has been no suggestion on the improvement of hot workability in the case of the cobalt alloy composition, unlike in the case of other invar alloys (Publications 57-15656, Specials 57-35260, etc.). .

Therefore, the present invention is devised to obtain a Coba alloy with improved hot workability, the present invention is a grain boundary of impurity elements such as carbon (C), sulfur (S), phosphorus (P), oxygen (O), nitrogen (N) By preventing segregation of the furnace, it forms borides with these elements and aggregates preferentially at grain boundaries and other defects to become nuclei of crystals, and by adding a small amount of boron (B) to refine the grains and prevent grain embrittlement. An object of the present invention is to provide a Fe-Ni-Co-based low thermally expandable COVA alloy capable of improving hot workability and microstructure stability.

1 is an exemplary view of the surface bursting phenomenon according to the hot compression of Comparative Material 1 used in the present invention

2 is a comparative graph of hot workability according to the high temperature tension of a number of representative comparative materials 1, 2, 6, 7 and experimental materials 2, 3 used in the present invention

3 is a graph comparing the hot workability according to the S content of Comparative Materials 2 to 6 used in the present invention

Figure 4 is a reference diagram illustrating a 1050 ^o C tensile fracture surface of Comparative Material 1 used in the present invention

Figure 5 is a reference diagram illustrating a 1000 ^o C tensile fracture surface of Comparative Material 2 used in the present invention

Figure 6 is a reference diagram illustrating a 1000 ^o C tensile fracture surface of Experiment 3 according to an embodiment of the present invention

7 is a graph comparing the cross-sectional shrinkage rate according to the B content of the test materials 1 to 5 according to an embodiment of the present invention

Figure 8a and Figure 8b is a reference picture comparing the microstructure stability of Comparative Material 2 and Experimental Material 3 according to an embodiment of the present invention used in the present invention

In order to achieve the above object, the present invention is based on 28 to 30% by weight of nickel (Ni) and 15.5 to 18.5% by weight of cobalt (Co) 0.05 to 0.5% by weight of silicon (Si) and 0.1 to 0.5% by weight of manganese (Mn); As impurities, up to 0.006% by weight of phosphorus (P), up to 0.05% by weight of carbon (C), up to 0.15% by weight of chromium (Cr), up to 0.10% by weight of aluminum (Al) and 0.4% by weight Molybdenum (Mo) or less, in particular, sulfur (S) or less; Provided herein is a Fe-Ni-Co-based low thermally expandable alloy containing 0.001 to 0.006 wt% of boron (B).

Among the components constituting the alloy of the present invention, nickel (Ni) forms an abnormal α phase when its content is less than 28% by weight, resulting in poor microstructure stability and deterioration of hot workability. It is not preferable because the thermal expansion characteristics are impaired, and since the thermal expansion characteristics are lost when used at 30% by weight or more, it is preferable to limit the use range to 28 to 30% by weight.

Among the components constituting the alloy of the present invention, cobalt (Co) decreases microstructure stability and thermal expansion characteristics when used at 15.5 wt% or less, and when used at 18.5 wt% or more, it shows an undesirable thermal expansion curve shape. , 15.5 ~ 18.5% by weight of the ingredient limit is required.

In the case of silicon (Si), the effect of the oxide is suppressed, and the hot workability is improved as the content is increased, but when the content is 0.05 wt% or less, the effect is insignificant. It can be allowed to add in the range of 0.05% to 0.5% by weight.

In the case of the phosphorus (P), when the content is high, low melting point phosphide is formed at the grain boundary, so that cracking occurs easily and hot workability is deteriorated. This tendency becomes remarkable as the content increases, so it is preferable to use 0.006% by weight or less.

In the case of carbon (C), it is preferable to use it at 0.05% by weight or less, because it is easy to form carbide at a temperature of 1,000 ° C. or less when it contains 0.05% by weight or more, remarkably deteriorate hot workability and greatly increase the coefficient of thermal expansion. .

In the case of the chromium (Cr), excessively contained chromium (Cr) is not preferable because physical properties such as low thermal expansion characteristics and magnetic properties are impaired, it is preferable to limit to 0.15% by weight or less to reduce hot workability.

The aluminum (Al) is an element used as a deoxidizer, but if it contains 0.10% by weight or more, the cleanliness deteriorates, so it is preferable to limit it to 0.10% by weight or less.

Molybdenum (Mo) is preferably limited to 0.4% by weight or less because it improves the microstructure stability, but when contained in a large amount to increase the coefficient of thermal expansion and lower the hot workability.

In the case of manganese (Mn), the alloying element is important for improving the hot workability of the Fe-Ni-Co-based alloy, but when the amount is less than 0.1% by weight, the effect is small. It is preferable to limit the allowable range by weight%.

In the case of the sulfur (S), it is preferable to contain as small as possible as an element which rapidly lowers the hot workability of the Fe-Ni-Co-based alloy, and therefore it is necessary to limit it to 0.01% or less.

Boron (B) is the most important element required to improve the hot workability of the Fe-Ni-Co-based alloy in the present invention, carbon (C), sulfur (S), phosphorus (P), oxygen (O) ), And segregation of impurity elements such as nitrogen (N) to grain boundaries is prevented and borides are formed with these elements to reduce adverse effects. On the other hand, it directly aggregates directly to grain boundaries and other defects to become nuclei of crystals, and refines grains and prevents grain embrittlement, thereby improving hot workability. However, this action is insufficient at a content of less than 0.001% by weight, and shows a significant effect as the boron content increases to an appropriate level. In addition, the increase in the hot workability is reduced if the increase above the appropriate level, rather than adding more than 0.007% by weight of boron and intermetallic compound (M ₂ B), carbon (C), oxygen (O), nitrogen (N) It is preferable to limit the content to 0.006% by weight or less because various borides contained can reduce the hot workability.

Hereinafter, embodiments of the present invention will be described in detail.

EXAMPLE

Table 1 below compares a number of test materials 1 to 5 for Fe-Ni-Co-based alloys having the composition of the present invention, and Comparative Materials 1 to 1 for the Fe-Ni-Co-based alloys not belonging to the composition of the present invention. The chemical composition (wt%) of ash 7 is shown.

division Ni Co Si Mn C P S Cr Al Mo B Experiment 1 29.0 17.4 0.12 0.25 0.002 0.002 0.0011 0.01 0.006 0.001 0.0012 Experiment 2 28.9 17.2 0.11 0.27 0.004 0.002 0.0020 0.03 0.002 0.001 0.0021 Experiment 3 28.8 17.2 0.11 0.24 0.005 0.001 0.0022 0.01 0.007 0.002 0.0030 Experiment 4 29.3 16.9 0.10 0.28 0.003 0.002 0.0018 0.02 0.004 0.001 0.0047 Experiment 5 28.9 17.0 0.10 0.28 0.002 0.003 0.0025 0.02 0.004 0.001 0.0061 Comparative Material 1 28.9 17.2 0.01 0.02 0.003 0.002 0.0018 0.01 0.003 0.01 - Comparative Material 2 29.1 16.9 0.11 0.30 0.004 0.003 0.0012 0.02 0.004 0.002 - Comparative Material 3 29.4 17.3 0.09 0.27 0.002 0.001 0.0038 0.02 0.003 0.001 - Comparative Material 4 29.4 16.8 0.10 0.26 0.003 0.002 0.0055 0.01 0.006 0.001 - Comparative Material 5 28.7 17.1 0.12 0.25 0.005 0.003 0.0079 0.01 0.005 0.001 - Comparative Material 6 29.1 17.0 0.11 0.29 0.002 0.002 0.0178 0.02 0.002 0.002 - Comparative Material7 28.9 17.2 0.09 0.28 0.003 0.001 0.0022 0.02 0.004 0.31 -

The alloys of Table 1 were manufactured in an ingot using a 50 [kg] vacuum induction melting apparatus (VIM), and then hot-rolled to 13 [mm] sheet after 1200 [ ^o C / 2hr] heat treatment. Was prepared.

In the case of the high temperature tensile test, rod-shaped specimens having a diameter of 10 mm and a gauge length of 90 mm were used, and a gleebble tester was used at a temperature range of 900 ^° C to 1250 ^° C. It was done. During the test, the temperature was raised to 1220 [ ^o C] at the speed of 20 [ ^o C / sec] and maintained for 60 seconds, and then changed to the desired temperature at 10 [ ^o C / sec] and maintained at the deformation temperature for 30 seconds. Then, a high temperature tensile test was performed at a cross head speed of 10 [mm / sec].

On the other hand, in the case of the high temperature compression test, compression specimens having a particle diameter (φ) of 10 [mm] and a height (h) of 12 [mm] were used, and the experimental purpose was performed in the temperature range of 900 [ ^o C] ~ 1300 [ ^o C]. According to the strain rate and the strain was changed.

FIG. 1 illustrates the surface burst phenomenon observed when hot compressing Comparative Material 1 as an example of poor hot workability shown in Comparative Material of Table 1, according to temperature and processing rate, and a significant surface bursting even at a high temperature of 1200 ^° C. or higher. It can be seen that the phenomenon.

FIG. 2 is a graph showing the results of cross-sectional reduction of area of the high-temperature tensile test fracture surface of the comparative alloys 1, 2, 6, 7 and the test materials 2, 3 with respect to the respective alloys. As can be seen in 2, the experimental materials 2 and 3 to which boron (B) is added show superior hot workability improvement results when compared to comparative materials 1, 2, 6, and 7. In particular, compared to Comparative Material 1, it showed almost 6 times more hot workability at 1000 ^o C, and compared with Comparative Material 2, which improved the hot workability to the maximum by adding manganese (Mn) and controlling the sulfur (S) content. Even if the test material 2 and 3 according to the present invention it can be seen that far superior workability in the main hot working temperature range of 900 ^° C ~ 1050 ^° C.

Figure 3 is a graph comparing the hot workability according to the sulfur (S) content for a number of comparative materials 1 to 7, it can be seen that the hot workability is sensitively changed according to the sulfur (S) content and sulfur (S) content Shows that suppression of is essential for improving hot workability.

4 to 6 is a reference photograph comparing the tensile fracture surface tested in the vicinity of 1000 ^o C with respect to the above results in the comparative material and the test material, the comparative material 1 of Figure 4 is the case of 1050 ^o C fracture surface It shows significant hot grain boundary fracture with little tendency to ductility. In the case of the fracture surface of Comparative Material 2 (FIG. 5) in which the sulfur (S) compound was controlled by adding manganese (Mn), the grain boundary and intragranular fracture were mixed, but there was a tendency to improve the hot workability. In the case of the fracture surface (Fig. 6) of Test Material 3 added with), it shows the fracture surface of complete ductile fracture, which is not found at all at the same temperature. These results are simply examples of the fact that the grain boundary segregation of impurities is suppressed by the addition of boron (B) mentioned in the description of the present invention, thereby improving hot workability.

Figure 7 is a graph showing the change in hot workability (section shrinkage) according to the boron (B) content according to the temperature in the test materials 1 to 5 of the present invention with boron (B), the boron (B) content is increased As a result, the overall hot workability is improved, but from 0.0047% by weight or more, as the content of boron (B) increases, the hot workability gradually decreases.

On the other hand, in order to investigate the thermal expansion characteristics of the Fe-Ni-Co-based alloy in accordance with the present invention by processing a thermal expansion coefficient specimen having a shape of 10 [mm], particle diameter (φ) 3 [mm], the coefficient of thermal expansion (Differential Dilatometer) ) Was used to measure the coefficient of thermal expansion. In addition, the microstructure of the specimens heat treated under various conditions was examined to investigate the microstructure stability of the alloys.

The following Table 2 is a result of comparing the thermal expansion coefficient and microstructure stability of Experimental Materials 1 to 5 and Comparative Materials 1 to 6 of the present invention, the symbol ◎ indicates a very good microstructure stability, O is a microstructure A state of good stability is shown, Δ represents a state in which microstructure stability is relatively good, and X represents a state in which microstructure stability is poor.

division Thermal expansion coefficient α (30 ~ 400 ℃) (㎛ / m · ℃) Microstructure Stability Experiment 1 4.96 O Experiment 2 4.49 O Experiment 3 5.01 O Experiment 4 5.02 ◎ Experiment 5 5.02 ◎ Comparative Material 1 4.71 × Comparative Material 2 4.90 △ Comparative Material 3 4.92 △ Comparative Material 4 4.90 △ Comparative Material 5 4.93 △ Comparative Material 6 4.95 △ Comparative Material7 5.08 ◎

As can be seen from Table 2 above, in the case of Experimental Materials 1 to 5 of the present invention, the change of the coefficient of thermal expansion was hardly observed according to the addition of boron (B), and the results of the derived coefficient of thermal expansion were found to be the requirements of general COVA alloys. It can be seen that it is in the range of satisfying (4.6 ~ 5.2). In addition, in relation to the microstructure stability of the condition that is not observed to be a phase a abnormality, the test materials 1 to 5 of the present invention to which boron (B) was added have excellent microstructure stability rather than the comparative materials 1 to 6 except for the comparative material 7. Indicated.

Figure 8a and Figure 8b are each as compared to the comparative material 2 and microstructural stability of the test material 3 of the present ^{invention, 1000 [o C] / 30} [min] Microstructure of Comparative material 2 and the experimental material 3 of the heat-treated sample This is a comparison photo. Here, in the case of Comparative Material 2, many abnormal black phases of phase a were observed, whereas in Experimental Material 3 of the present invention, this tendency showed a stable microstructure in which the trend was significantly reduced.

According to the present invention, in the Fe-Ni-Co-based low thermally expandable alloy can improve the hot workability without lowering the thermal expansion characteristics, it is possible to reduce the surface defects during the production of the Coba alloy, thereby improving productivity It is possible to obtain the advantage that mass production at low cost is possible.

In addition, according to the present invention, it is possible to obtain an advantage such that the stability of the microstructure importantly required in the alloy can be improved.

Claims (1)

28 to 30 wt% nickel (Ni), 15.5 to 18.5 wt% cobalt (Co), 0.05 to 0.5 wt% silicon (Si), and 0.1 to 0.5 wt% manganese (Mn); As impurities, up to 0.006% by weight of phosphorus (P), up to 0.05% by weight of carbon (C), up to 0.15% by weight of chromium (Cr), up to 0.10% by weight of aluminum (Al) and 0.4% by weight Molybdenum (Mo) or less and 0.01% or less sulfur (S); Fe-Ni-Co-based low thermal expansion alloy, characterized in that it contains 0.001 to 0.006% by weight of boron (B).