JPH02233990A - Heat-resistant members and steel support members in heating furnaces - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a heat-resistant member whose main component is a composite sintered alloy block made of chromium carbide particles and an Fe-Cr alloy, and a heating furnace made of the heat-resistant member. Related to steel support members.

[Conventional technology]

Steel materials to be heated in the steel heating furnace (slabs, fillets 7 1, etc.)
For example, in a walking beam conhair type heating furnace, as shown in Fig. 2, a skinned button (10) is formed on a skinned pipe (20), which is a moving beam and a fixed beam. ), the higher alloy 'lA (ION i =
20C r-Fe series steel) and high co alloy tFfl
Heat-resistant alloys such as (50C o -20N i -Fe series steel) have been used.

Recently, the operating temperature of ζ heating furnaces has become higher, and high-temperature operations exceeding 1300'C are becoming common.As a measure to improve the material of skid buttons, ceramic particles (chromium carbide, silicon nitride, alumina, etc.) have been introduced. , heat-resistant metals such as metallic cobalt, Co alloys (UMCo50 etc.) {or high alloy steels (27Cr-17Ni-40Co-Fe)
The practical application of sintered materials (composite sintered alloys) having a mixed structure that is composite with This composite sintered alloy is intended to alleviate the fragility of single-phase ceramic sintered materials through the combined effect of ceramic particles and metal, and to ensure high-temperature properties superior to those of single-phase heat-resistant metal materials.

[Problem to be solved by the invention]

There are a wide variety of ceramics used in the above composite sintered alloy, but chromium carbide particles (Cr3Cz, etc.) are hard, high-strength, and thermally stable ceramics, so they can be composited with heat-resistant metals. By doing so, it should be possible to obtain a composite sintered alloy with excellent high-temperature properties. However, the high temperature strength of the composite sintered alloy is unexpectedly low; for example, Cr. Composite sintered alloys consisting of C2 chromium carbide particles and metallic cobalt can be used in high-temperature ranges exceeding 1300°C (Cr3Cz: approximately 1950°C, Co: approximately 1495°C), even though the constituent materials have high melting points (Cr3Cz: approximately 1950°C, Co: approximately 1495°C). For example, the compressive deformation resistance at 1350° C.) is low, and deformation easily occurs due to steel material loads.

In addition, although the composite sintered alloy has higher toughness than ceramic single-phase sintered materials, it cannot be used in applications where it is repeatedly subjected to impact from heavy steel materials such as skid buttons.
Damage such as chips and cracks often occurs.

In addition, in the case of a sintered alloy with a composite structure with heat-resistant steel,
When used in a high temperature range exceeding 1300°C, the oxidation resistance may decrease and the material may deteriorate significantly as a result.

The present invention has been made to solve the above-mentioned problems regarding composite sintered alloys.

[Means and effects for solving the problem] The heat-resistant member of the present invention comprises chromium carbide and Fe-C with an Fe content of 5 to 50% by weight.
A composite sintered alloy block having a uniform mixed structure with an r-alloy; a heat-resistant steel casing enclosing at least the circumference of the body excluding the top surface of the composite sintered alloy block; and a composite sintered alloy block made from the heat-resistant steel casing. The composite sintered alloy block, the metal intermediate layer, and the heat-resistant steel casing have a hot isostatic pressure sintering layer that is solid-state bonded to the contact interface between the composite sintered alloy block, the metal intermediate layer, and the heat-resistant steel casing. It is characterized by being a body.

The present invention will be explained in detail below.

The heat-resistant member of the present invention includes a composite sintered alloy block, a heat-resistant steel casing, and a metal intermediate layer interposed at the abutting interface between the two.

The composite sintered alloy block contains chromium carbide particles and Fe-
It is a sintered body having a uniform mixed structure with a Cr alloy, and its metal component (hereinafter also referred to as "base metal") is Fe-
The Cr alloy contains 5-50% by weight of Fe. The base metal of the composite sintered alloy block is Fe5-50% by weight.
The reason for using the Fe-Cr alloy is to ensure good sinterability and to give the composite sintered alloy a high melting point.

The composition, sinterability, and melting point of this base metal will be explained as follows.

In the sintering process of a sintering raw material powder mixture consisting of chromium carbide particles and metal powder, a diffusion solid solution of carbon from the chromium carbide particles to the metal component occurs, so the melting point of the base metal of the resulting sintered alloy is It is lower than before the binding process. In conventional composite sintered alloys whose base metal is cobalt metal, CO alloy, high NiCr alloy steel, etc., the melting point decreases significantly due to the diffusion and solid solution of carbon generated during the sintering process. The melting point of the sintered alloy obtained by combining C) with Cr3Cz carbide particles is approximately 1309°C. The reason why the high-temperature strength of conventional composite sintered alloys is unexpectedly low is because the melting point of the base metal is significantly lowered in this way.

The lack of high-temperature strength of the composite sintered alloy due to the lower melting point of the base metal can be improved by using metallic chromium (Cr) as the base metal. Since the temperature of the eutectic point (C: about 3.8%) of a binary alloy (eutectic type alloy) of chromium (melting point: about 1830°C) and carbon is about 1498°C, sintering This is because even if carbon is concentrated in solid solution during the process, its melting point will not fall below 1498°C. However, on the other hand, since the base metal (Cr) has a high melting point and low vapor pressure, it has low sinterability and has the disadvantage that sintering defects such as holes and cracks are likely to occur in the sintered alloy.

Therefore, in the present invention, a Fe-Cr alloy alloyed with 5 to 50% by weight of Fe is used as the base metal, thereby satisfying both the requirements of sinterability and ensuring a high melting point of the base metal. . The Fe-Cr binary alloy is a solid solution type alloy (Fe amount in the liquidus minimum part in contact with the solidus line: about 80% by weight, temperature: about 1
507°C), and the melting point of Cr (approximately 1830°C) gradually decreases as the amount of Fe is increased, and the sinterability improves accordingly. In the present invention, the lower limit of the amount of Fe added is set at 5% by weight (solidus temperature: approximately 1765°C, liquidus temperature:
The temperature was set at 1810°C to ensure the sinterability necessary to prevent pinholes and crack defects in the sintered body.
On the other hand, the reason why the upper limit was set at 50% (solidus temperature: about 1525°C, liquidus temperature: 1580"C) is because if it exceeds this, it will be difficult to ensure the high temperature strength of the sintered body. However, when the amount of Fe in the base metal increases, chromium carbide particles change to double carbides ((Cr, Fe) However, if the amount of Fe is limited to 50% by weight or less as described above, the phase change of the chromium carbide particles and the accompanying material deterioration can be substantially avoided.
A more preferable range of the amount of Fe is 10 to 40% by weight, which is determined from the viewpoints of ensuring the sinterability, high melting point and high strength of the alloy, and preventing a decrease in oxidation resistance due to changes in chromium carbide particles. .

The chromium carbide particles composited into the Fe-Cr alloy are Cr
．． C. , Cr7C3, Crz+C6, etc.
A mixture of two or more of these particles may be used. Moreover, the particle size may be, for example, 1 to 100 μm.

The proportion of chromium carbide particles in the composite sintered alloy block is arbitrary and may be determined depending on the use and required characteristics of the sintered alloy. For example, when used as a steel transport member in a heating furnace, the proportion of chromium carbide particles is preferably about 5% or more in order to ensure sufficient high-temperature strength to withstand the load of heavy steel materials. More preferably, it is 10% by weight or more.

However, if the proportion of chromium carbide particles becomes too high, the toughness tends to decrease as the relative proportion of the base metal decreases. In order to ensure good impact resistance, the proportion of chromium carbide particles is approximately 90% by weight.
The upper limit is preferably 80%, and more preferably 80%.

The heat-resistant steel casing enclosing the composite sintered alloy block functions as a protective member to prevent the composite sintered alloy block from being damaged, cracked, etc. due to impact. Heat-resistant steel, which is the material of the casing, refers to a steel material that can withstand the high-temperature oxidizing environment of the heat-resistant member of the present invention, such as S
US 310, US 304, US 310S, IIK, I
P, UMCo50, and other known alloy steels may be selected as appropriate.

The metal intermediate layer interposed at the interface between the composite sintered alloy block and the heat-resistant steel casing enclosing it prevents elements from diffusing into the composite sintered alloy block from the heat-resistant steel casing at high temperatures. It is a barrier layer. If the metal intermediate layer is omitted, when the metal is heated and maintained at a high temperature exceeding 13 oo'c, the chromium carbide particles in the composite sintered alloy will change to double carbide due to the diffusion of elements from the heat-resistant steel casing. Its oxidation resistance is significantly reduced. 130
In a temperature range exceeding 0°C, the change to double carbide progresses rapidly, and the accompanying material deterioration of the composite sintered alloy block is significant. Fe is mainly involved in this transformation of chromium carbide into double carbide. Therefore, in the present invention, a metal intermediate layer is provided at the interface between the two to prevent elements from diffusing into the composite sintered alloy block. Prevents deterioration. Further, the metal intermediate layer, which is the barrier layer, prevents the melting point of the composite sintered alloy block from decreasing (Fe diffusion solid solution concentration), and also contributes to maintaining a high melting point.

As the metal intermediate layer, nickel, chromium, nickel-chromium alloy, or the like is suitable. The layer thickness may be approximately 0.1 to 1 +r+m. This metal intermediate layer alleviates the difference in thermal expansion between the composite sintered alloy block and the heat-resistant steel casing, and prevents residual stress generated during the manufacturing process and peeling at the interface due to temperature changes during actual use. It has an effect.

FIG. 1 shows an example of the heat-resistant member of the present invention used as a steel support member in a heating furnace. (1) is a composite sintered alloy block, (3) is a heat-resistant casing that encloses the composite sintered alloy block (1), and (2) is a metal intermediate layer that is interposed as a barrier layer at the contact interface between the two. be. The composite sintered alloy block (1) has, for example, a cylindrical or truncated pyramid shape, and the periphery and bottom of the body are covered with a heat-resistant steel casing (3), and the top surface is covered with a casing (3) as a support surface for the heated steel material. 3
) is exposed. The heat-resistant member can be attached to the skid pipe by a simple and reliable method such as welding.

The heat-resistant member of the present invention comprising the composite sintered alloy block, the heat-resistant steel casing, and the metal intermediate layer serving as the barrier layer is manufactured by a hot isostatic pressing sintering method. That is, a mixture of chromium carbide powder and Fe-Cr alloy powder, which are the sintering raw materials for the composite sintered alloy block (1), and the casing (3
) and an intermediate layer (barrier layer) (2
) A metal intermediate layer material (sheet, foil, etc.) such as nickel or chromium is prepared, and the inner surface of the capsule is lined with the metal intermediate layer material, and then chromium carbide powder and Fe
After being filled with a uniform mixture of -Cr alloy powder, degassed and sealed, it is subjected to a hot isostatic pressure sintering process.

A mixture of chromium carbide powder and Fe-Cr powder, which is the raw material powder for sintering a composite sintered alloy block, is suitable for high-energy poles such as attritors due to its uniformity of mixing and dispersion and MA (mechanical alloying) effect. It is preferable to perform a mixing and pulverization process using a mill, and in that case, Fe
-Fe powder and Cr powder may be mixed and used instead of the -Cr alloy powder.

Instead of using a sheet, foil, or the like as the metal intermediate layer material, a lining of the metal intermediate layer material may be formed on the inner surface of the capsule by plating, thermal spraying, or the like. In addition, as described later, the sintered raw material powder mixture of the composite sintered alloy block is made into a compact by cold pressing, and then the compact is encapsulated in a capsule and hot isostatically pressed. When a tying step is performed, an appropriate clearance may be provided between the capsule and the powder compact, and the gap may be filled with a powdered metal intermediate layer material.

The hot isostatic pressure sintering process is performed at a temperature of approximately 1000 to 1300.
゜C1 pressurizing force approximately 1000-2000kgf/cff
This is achieved by holding for a suitable period of time (for example, 2 to 4 hours). Through the sintering process under pressure, a dense composite sintered alloy block without bottle holes etc. is formed, and the metal intermediate layer material/capsule is densified. A sintered body is formed in which the abutting surfaces of the capsules are solid phase bonded and have a bonded integral relationship. In addition, as another process for the sintering process, the raw powder mixture is filled into rubber, cold isostatic pressing is applied to form a compacted powder compact, which is then subjected to rough machining and then sealed in a capsule. Either hot isostatic pressure sintering is carried out, or the compact with rough machining is subjected to pressureless sintering in an inert atmosphere or hydrogen gas atmosphere or sintering under vacuum, and then It is also possible to take a step of sealing it in a capsule and subjecting it to hot isostatic pressure sintering. Cooling after the hot isostatic pressure sintering treatment may be performed by, for example, taking 24 hours to lower the temperature to room temperature.

In the above sintering process, carbon diffuses into the base metal from the chromium carbide constituting the composite sintered alloy block, but the melting point decrease due to this is small. Regardless of the blending ratio, the composite sintered alloy block formed has a high melting point exceeding approximately 1500°C and exhibits high compressive strength even at high temperatures exceeding 1300°C. In addition, since the composite sintering raw material powder mixture has good sinterability, the sintering temperature may be relatively low, and therefore high temperature sintering of around 1300°C is not particularly necessary. “Even when sintering is carried out at temperatures above C, the diffusion of elements from the capsule (heat-resistant steel) into the composite sintered alloy block is effectively targeted by the metal interlayer. Therefore, during the sintering process chromium There is no change in carbide particles to double carbide.

If the sintered body formed by the hot isostatic pressing sintering process is subjected to machining and the capsule material on the top side is removed, a composite sintered alloy block ( 1) and
A heat-resistant steel casing (
3) and a metal intermediate layer (2) interposed at the contact interface between them.

〔Example〕

Composite sintered alloy bronc raw material powder mixture, metal intermediate layer material,
and a heat-resistant steel capsule (cylindrical body) that becomes the casing.
A sintered body is obtained by hot isostatic pressing and sintering, and then machining is performed at key points to obtain a test heat-resistant member having the shape shown in FIG.

The left column of Table 1 shows the raw material composition of the test heat-resistant members.

Nα1-8 are invention examples, and Nα101-104 are comparative examples.

Comparative example no. Among 101 to 104, No. 101
and no. No. 102 is an example different from the invention example in that the metal intermediate layer material is omitted, Nα103 and No. No. 104 is an example that differs from the invention example in that a metal other than Fe-Cr (chromium for the former and cobalt for the latter) is used as the base metal of the composite sintered alloy block. The size of each test heat-resistant member is a composite sintered alloy block:
Φ100 x 150 1! (n++n), casing thickness: 10 mm (but bottom wall thickness: 20 mlI1).

(1) Raw materials (1) Composite sintered alloy block raw material powder Chromium carbide powder and base metal powder are mixed and ground in a high-energy ball mill to form a uniform mixed powder.

Chromium carbide average particle size: 27zm, base metal average particle size:
10 μm (2) Metallic intermediate layer material: metallic nickel sheet or metallic chromium sheet.

Thickness 1.0mm, (3) Capsule A cylinder made of heat-resistant steel a and b.

Heat-resistant steel a: 0. IC-27Cr-17N+ -40
Co-Fe (melting point 1390°C) Heat-resistant steel b: 0.05C-20Ni 25Cr-F
e (SUS310 equivalent material. Melting point: 1430°C) [■] Filling the inner surface of the sintered capsule with a composite sintered alloy raw material powder mixture with or without attaching a metal intermediate layer material (sheet),
After degassing and sealing, 1100°C x 1200kgf/c
I11×2HrO hot isostatic pressure sintering treatment was performed, and after the sintering treatment was completed, the temperature was lowered to room temperature over a period of 24 hours. The resulting sintered body was machined to remove the capsule material at the top to expose the top surface of the composite sintered alloy block, and the top surface was finished into a smooth surface.

(III) Quality test For each composite sintered alloy bronch of each test heat-resistant member, inspection for sintering defects (bottle holes, etc.), measurement of melting point, high temperature compressive strength (at. 1350°C), and oxidation resistance test. The results shown in the right column of Table 1 were obtained. In the table, "sintering defect" indicates the result of cutting and dividing a composite sintered alloy block in the radial direction and axial direction and observing the cut surface with a microscope.

In addition, "oxidation resistance" refers to the state of surface deterioration due to oxidation on the top surface of the composite sintered alloy block after an oxidation test in which each test heat-resistant member is held in an atmospheric furnace set at 1350°C for 48 hours. was determined by visual observation.

The ○ mark in the same column means "no oxidation", and the XX mark means "significant oxidation".

As shown in Table 1, Comparative Example No. 1 uses metallic chromium as the base metal. Although 103 has a high melting point, it is difficult to sinter, resulting in pinhole sintering defects, and as a result, its high-temperature compressive strength remains at a low level. Comparative example No. 1 using metallic cobalt as the base metal. 10
No. 4 has good soundness with no pinholes, etc., but the melting point of the base metal drops significantly and the high-temperature compressive strength is extremely low. On the other hand, invention example No. Nos. 1 to 8 have soundness without bottle holes etc. due to improved sinterability, and at the same time,
It has a high melting point of about 1500°C or more, and has excellent high temperature resistance. In addition, invention example No. 1 to B and comparative example No. A comparison with Nos. 101 and 102 reveals the significance of providing the heat-resistant member of the present invention with a metal intermediate layer. In other words, Nos. 101 and 1.02 have a high melting point and excellent high-temperature strength because they use a Fe-Cr alloy containing a suitable amount of Fe as the base metal, as in the invention example, but they cannot be exposed to an atmospheric furnace at 1350'C. Significant oxidation has occurred. On the other hand, in invention examples Nα1 to Nα8, almost no oxidation occurred even in the high temperature oxidizing atmosphere under the same conditions. This is Comparative Example No. 101, No. 102
(without metal intermediate layer), elements diffuse into the composite sintered alloy block from the heat-resistant steel casing due to the effect of high-temperature heating (
The change from chromium carbide particles to double carbide particles with low oxidation resistance progressed mainly due to Fe), whereas invention example No. 1 with a metal intermediate layer progressed. Nos. 1 to 8 show that the metal intermediate layer prevents elements from diffusing into the composite sintered alloy block, and as a result, the change of chromium carbide particles to double carbide is substantially prevented.

〔Effect of the invention〕

The heat-resistant member of the present invention has a composite sintered alloy block, which is the main member, which has high density and soundness, has a high melting point and excellent high-temperature strength, and does not cause material deterioration in high-temperature oxidizing atmosphere. It has a structure that is stable and protected from impact by a heat-resistant steel casing that tightly encloses the body, so it has high-temperature strength, high-temperature oxidation resistance,
It is suitable as a member for various uses that require impact resistance, especially as a member for conveying steel materials such as skid buttons in heating furnaces.
It has great effects on improving durability, reducing maintenance, and increasing the efficiency of I-mulberry furnaces.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the present invention, and FIG. 2 is a sectional view of a skid button in a heating furnace. 1: Composite sintered alloy block, 2: Metal intermediate layer 3: Heat-resistant steel casing, 10: Skid button, 20: Skid pipe.

Claims (1)

[Claims] 1. Chromium carbide and Fe with an Fe content of 5 to 50% by weight
- a composite sintered alloy block having a uniform mixed structure with a Cr alloy; a heat-resistant steel casing enclosing at least the periphery of the body except for the top surface of the composite sintered alloy block; and a composite sintered alloy block from the heat-resistant steel casing. and a metal intermediate layer that prevents element diffusion into the block, and hot isostatic pressing in which the abutting interfaces of the composite sintered alloy block, the metal intermediate layer, and the heat-resistant steel casing are solid phase welded. A heat-resistant member characterized by being a pressed sintered body. 2. A heated steel material supporting surface member for a heating furnace, which is made of the heat resistant member according to claim 1, and has the top surface of the composite sintered alloy block as a heated steel material supporting surface.