JP2802768B2 - Composite sintered alloy and steel support in heating furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a composite sintered alloy having a homogeneous mixed structure composed of chromium carbide particles and an Fe-Cr alloy, and a heating furnace made of the composite sintered alloy. The present invention relates to a steel support member.

[Conventional technology]

In a member for supporting a steel material (slab, billet, etc.) to be heated in a steel material heating furnace, for example, a walking beam conveyor type heating furnace, a skid pipe (20) which is a moving beam and a fixed beam is formed as shown in FIG. Skid buttons (10) (on which a steel material is supported on the top surface) are made of high alloy steel (10Ni-20Cr-Fe steel) or high Co alloy steel (50Co-20Ni-Fe steel). Heat resistant alloys have been used.

Recently, high temperature operation of heating furnace operation is progressing, and high temperature operation exceeding 1300 ° C is becoming popular, and as a measure to improve the material of skid buttons, ceramic (chromium carbide, silicon nitride, alumina, etc.) particles are Refractory metals such as metallic cobalt, Co alloys (such as UMCo50), or high alloy steels (0.
Practical use of a sintered material (composite sintered alloy) having a mixed structure combined with (1C-27Cr-17Ni-40Co-Fe system) has been attempted. This composite sintered alloy reduces the brittleness of the ceramic single-phase sintered material by the composite effect of the ceramic particles and the metal (hereinafter, also referred to as “base metal”), and has a high-temperature property that exceeds that of the heat-resistant metal single-phase material. It is intended to be secured.

[Problems to be solved by the invention]

The ceramics used in the above composite sintered alloys vary widely, but chromium carbide particles (such as Cr ₃ C ₂ ) are hard, high-strength, and have good thermal stability. It should be possible to obtain a composite sintered alloy having excellent high-temperature properties by forming a composite. However,
The high-temperature strength of the composite sintered alloy is unexpectedly low, for example,
The composite sintered alloy composed of Cr ₃ C ₂ chromium carbide particles and metallic cobalt has a high melting point (Cr ₃ C ₂ : about 1950 ° C, C
o: approx. 1495 ° C.), the resistance to compressive deformation in a high temperature range exceeding 1300 ° C. (for example, 1350 ° C.) is small, and deformation due to steel load is likely to occur. For this reason, when a composite sintered alloy is used as a skid button in a steel heating furnace, for example, in recent high-temperature operating conditions exceeding 1300 ° C., the service life can be improved, maintenance can be reduced, the operating efficiency can be improved, etc. Can not expect so much. Incidentally, in the case of a sintered alloy having a composite structure with heat-resistant steel, when used in a high temperature range exceeding 1300 ° C., the oxidation resistance may be lowered and the material may be significantly deteriorated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems relating to a composite sintered alloy.

[Means and actions for solving the problem]

The present invention is characterized in that in a composite sintered alloy composed of chromium carbide particles and a base metal, the base metal is an Fe-Cr alloy containing 5 to 50% by weight of Fe.

 Hereinafter, the present invention will be described in detail.

The Fe—Cr alloy constituting the base metal of the composite sintered alloy of the present invention is a solid solution type alloy (Fe of the liquidus line minimum portion in contact with the solidus line).
Amount: about 80% by weight, temperature: about 1507 ° C). The Fe-Cr
The Fe content in the alloy is set to 5 to 50% by weight because the composite sintered joint has a high melting point, ensures sufficient strength in the high temperature range, especially in the temperature range exceeding 1300 ° C, and has good sinterability. It is to guarantee. The composition, sinterability and melting point of this base metal will be described below.

In the sintering process of the sintering raw material powder mixture composed of the chromium carbide particles and the metal powder, since the diffusion of carbon from the chromium carbide particles to the metal is caused to form a solid solution, the melting point of the base metal of the obtained sintered alloy is reduced. It is lower than before the binding process. In conventional composite sintered alloys using metal cobalt, Co alloys, high NiCr alloy steels, etc. as base metals, the melting point drop due to the diffusion and solid solution of carbon generated in the sintering process is remarkable. For example, metallic cobalt (melting point: about 1495 ° C) The melting point of a sintered alloy obtained by compounding Cr and C ₃ C ₂ carbide particles is about 1309 ° C. The unexpectedly low high-temperature strength of the conventional composite sintered alloy is due to such a remarkable decrease in the melting point of the base metal.

The shortage of high-temperature strength of the composite sintered alloy accompanying the lowering of the melting point of the base metal can be improved by using metal chromium (Cr) as the base metal. Chromium (melting point: approx.
The temperature of the eutectic point (C: about 3.8% by weight) of a binary alloy (eutectic type alloy) of carbon at 1830 ° C) is about 1498 ° C. However, its melting point does not fall below 1498 ° C. However, on the other hand, since the base metal (Cr) has a high melting point and a low vapor pressure, there is a problem that sinterability is low and sintering defects such as pinholes and cracks easily occur in the sintered alloy.

Accordingly, the present invention provides a method of alloying 5 to 50% by weight of Fe.
-The Cr alloy is used as the base metal, which satisfies the requirements of both the sinterability and the high melting point of the base metal. In the present invention, the lower limit of the amount of Fe added is set to 5% by weight (solidus temperature: about 1765 ° C., liquidus temperature: 1810 ° C.)
This is to ensure the sinterability necessary to prevent pinholes and crack defects in the sintered body, while the other 50% by weight (solidus temperature: approx.
The upper limits of 1525 ° C. and the liquidus temperature of 1580 ° C. are because exceeding the upper limits makes it difficult to secure high-temperature strength of the sintered body. When the amount of Fe in the base metal increases, the chromium carbide particles change into double carbides (such as (Cr, Fe) ₃ C ₂ ), resulting in a decrease in oxidation resistance and deterioration in the properties of the sintered alloy material. 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 deterioration of the material accompanying the phase change are substantially avoided. More preferable range of the Fe amount defined from each aspect of securing the sinterability and high melting point and high strength of the Fe-Cr alloy, and preventing a decrease in oxidation resistance due to a change in chromium carbide particles is 10 to 40. % By weight.

The chromium carbide particles composited with the Fe-Cr alloy are Cr
_It may be ₃ C ₂ , Cr ₇ C ₃ , Cr ₂₃ C ₆ or the like, or may be a mixed particle of two or more of these. The particle size may be, for example, 1 to 100 μm.

The ratio of the chromium carbide particles in the composite sintered alloy is arbitrary, and may be determined according to the use and required characteristics of the sintered alloy. For example, in the application of a steel material conveying member in a heating furnace, the ratio of chromium carbide particles is set to about 5% by weight in order to secure sufficient high temperature strength to withstand the load of heavy steel material.
The content is preferably at least 10% by weight. However, if the ratio of chromium carbide particles is too high, the toughness tends to decrease as the relative ratio of matrix metal decreases, so in the case of skid buttons, it is necessary to prevent chips and cracks due to the impact of steel. In order to ensure high impact resistance, the proportion of chromium carbide particles is preferably up to about 80% by weight, more preferably 70% by weight.

The composite sintered alloy of the present invention comprises a chromium carbide powder and Fe-
It is manufactured by applying various known sintering methods, preferably a hot isostatic pressing sintering method, using a homogeneous mixed powder with a Cr alloy powder as a starting material. In preparing the sintering raw material powder mixture, a mixture of Fe powder and Cr powder may be used instead of the Fe-Cr alloy powder, in which case the uniformity of mixing / dispersion and MA (mechanical alloying) are used. From the viewpoint of effects, etc., it is preferable to carry out mixing and pulverization using a high energy ball mill such as an attritor. Hot isostatic pressing sintering involves mixing the raw material powder mixture into appropriate metal capsules (eg, mild steel, carbon steel,
(Stainless steel), degassed and sealed, and the temperature is about 10
This is achieved by maintaining the temperature at 00 to 1300 ° C. and the pressure of about 1000 to 2000 kg f / cm ² for an appropriate time (for example, 2 to 4 hours). Cooling after the completion of sintering may be performed, for example, by lowering to room temperature in 24 hours. In the above sintering process, the diffusion of carbon from chromium carbide to the matrix metal is caused by solid solution, but the drop in melting point is small, and as shown in Examples below, regardless of the mixing ratio of the chromium carbide particles, The resulting sintered alloy has a high melting point of about 1500 ° C. or higher, and exhibits high compressive strength even at high temperatures.

In addition, as another process of the sintering process, the raw material powder mixture is filled in rubber, cold isostatic pressing is applied to form a green compact, which is subjected to rough machining and sealed in a capsule. Hot isostatic pressing sintering, or a method of sintering a green compact subjected to rough machining at normal pressure in an inert atmosphere or a hydrogen gas atmosphere, or sintering under vacuum, In this case, a method of further sintering the sintered body by hot isostatic pressing or a method of subjecting the raw material powder mixture to hot pressing and sintering can be applied.

When the composite sintered alloy of the present invention is used, for example, as a steel support member in a heating furnace, the member does not necessarily need to be entirely the composite sintered alloy of the present invention, and the skid button shown in FIG. The lower half (11) of the side that comes into contact with the skid pipe (20), that is, the skid pipe (2
The part where sufficient cooling action by conduction heat transfer from (0) is exerted is a conventional heat-resistant alloy (eg, high Cr high Ni alloy steel), and the upper half (12) is formed of the composite sintered alloy of the present invention. May be done. The skid button is formed by welding or solid-phase joining of the composite sintered alloy block of the present invention to be the upper half (12) and the heat-resistant alloy block to be the lower half (11) separately prepared. It can be manufactured by the method of performing hot isostatic pressing and sintering by sealing the raw material powder of the composite sintered alloy or its green compact together with the heat-resistant alloy block in a capsule. You can also.

〔Example〕

The chromium carbide powder and the base metal powder are mixed and pulverized by a high energy ball mill, and the powder mixture (chromium carbide: average particle diameter 2 μm, metal powder average particle diameter: 10 μm) is filled into a mild steel capsule and degassed and sealed. subjected to hot isostatic pressure sintering, the temperature 1100 ° C., was sintered over a period of 2 hours under a pressure 1200 kg f / cm ^2, subjected to subsequent lowered to room temperature over a period of 24 hours試焼A bonded gold block (Φ100 × 150) was obtained.

Table 1 shows the component composition of each test sintered alloy. In the table, N
o.1 to 8 are invention examples using Fe-Cr alloy containing an appropriate amount of Fe as a base metal, No. 101 and No. 102 are comparative examples, No. 101 is metal chromium, No. 102 is metal cobalt Are base metals.

Sintering defects (pinholes, etc.) for each test sintered alloy
Inspection, melting point, measurement of high temperature compressive strength (at 1350 ° C.), and oxidation resistance test were performed, and the results shown in the right column of Table 1 were obtained. In the table, "sintering defect" indicates the result of cutting the composite sintered alloy block in the radial direction and the axial direction, and observing the cut surface with a microscope. Also, "Oxidation resistance"
After the oxidation test in which each of the test sintered alloy blocks was held in an atmosphere furnace set at 1350 ° C. for 48 hours, the state of surface deterioration due to oxidation was determined by visual observation. The ○ mark in the same column means that there is no oxidation.

As shown in Table 1, the sintered alloy (No. 101), which is a composite of chromium metal and chromium carbide, has a high melting point, but has low sinterability, so that the pin Holes and cracks have occurred and the high pressure compressive strength is also at a low level. Sintered alloy (No.102) using metallic cobalt (Co) as a base metal has no problem of sintering and has soundness without pinholes, but its melting point is as low as around 1310 ° C and high temperature. The compressive strength in the region is inferior. In contrast, Invention Examples Nos. 1 to 8 in which a Fe-Cr alloy containing 5 to 50% of Fe was used as a base metal and composited with chromium carbide, exhibited soundness without pinholes and cracks due to improved sinterability. And has a high melting point of about 1500 ° C. or higher, and has excellent strength in a high temperature range. It is also seen that the material has good oxidation resistance and can withstand use in a high-temperature oxidizing atmosphere.

[Effect of the Invention] The composite sintered alloy composed of the chromium carbide particles and the Fe-Cr alloy according to the present invention has soundness and high density without pinholes and cracks, and has a high melting point and a high temperature range. Since it does not lose high strength and has oxidation resistance at high temperatures, it is useful as a member requiring these various properties, especially as a steel support member such as a skid button in a heating furnace. Various effects such as improvement of performance, reduction of maintenance, and improvement of furnace operation efficiency are brought.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a steel material transport member in a heating furnace. 10: Skid button, 20: Beam (skid pipe).

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Bin Shinozaki 1-1-1, Nakamiya Oike, Hirakata City, Osaka Prefecture Inside the Hirakata Works of Kubota Iron Works Co., Ltd. (72) Inventor Hiroyuki Ran 1-1-1, Nakamiya Oike, Hirakata City, Osaka Prefecture No. 1 Kubota Iron Works Co., Ltd. Hirakata Works (56) References JP-A-1-263240 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C22C 29/06 C22C 32/00 C22C 1/05 C21D 1/00 116 F27D 3/00

Claims (2)

(57) [Claims] 1. A composite sintered alloy characterized by being a sintered body having a uniform mixed structure comprising chromium carbide particles and an Fe-Cr alloy containing 5 to 50% by weight of Fe. 2. A steel material supporting member for supporting a steel material to be heated in a heating furnace, wherein at least a top side of the steel material in contact with the steel material to be heated is made of the composite sintered alloy according to claim 1. Steel support members.