JP2001140031A - Heat resistant alloy for skid button - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a heat resistant alloy for the skid button of a slab heating furnace exhibiting excellent high temperature creep characteristics and oxidation resistance even under heating at >=1,300 deg.C and having a long service life. SOLUTION: By providing a heat resistant alloy for a skid button of a heating furnace with a composition containing <=0.2% C, <=1.0% Si, <=1.0% Mn, 0.1 to 2.0% Al, 25 to 35% Cr, 1.5 to 10% Mo, 0 to 0.05% W, 30 to 45% Co, <=5% Fe and 0 to 0.05% B or moreover containing one or more kinds among Nb, V, Ti and Ta by <=1% in total or furthermore containing one or more kinds among Ca, Y, Ce, Se, La, Nd and Pr by 0.0001 to 0.2% in total, and the balance substantially Ni, excellent high temperature creep characteristics, oxidation resistance or the like is imparted thereto.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a "heat-resistant alloy for a skid button of a heating furnace" which is excellent in high-temperature creep characteristics and oxidation resistance.

[0002]

2. Description of the Related Art In recent years, in the field of hot rolling of billets, equipment has been increased in size and speed has been increased in accordance with technological innovation in the steel industry, and cost competitiveness has been strongly improved by energy saving. Since it has become desirable, a walking beam furnace, which is advantageous in these respects, has been widely used as a heating furnace for billets.

In this walking beam furnace, a structure is employed in which a steel slab is sequentially moved from the entrance side to the exit side of the furnace by alternately arranged stationary and movable skid rails. A skid button is attached to each of these skid rails, and the billet is supported via the skid button. When the walking beam furnace is used, the skid button is placed under the condition that the upper part is in direct contact with the hot slab while the lower part is cooled through the skid pipe. .

The most important performance of such a skid button is a heat-resistant upper limit temperature determined from high-temperature strength and oxidation resistance. Because the lower part of the skid button is cooled, if the ambient temperature of the furnace is constant, the "skid height (that is, the distance from the cooling end)" and the "heat of the material constituting the skid button" Conductivity "
This determines the temperature of the upper surface of the skid button (the temperature of the surface in contact with the billet). In order to reduce the heat source unit of the heating furnace and to uniformly heat the steel slab, the higher the surface temperature of the skid button directly contacting the steel slab, in other words, the closer the surface temperature of the skid button to the furnace temperature, the better. The higher the height and the lower the thermal conductivity of the material, the better.However, since there is a design limit to the height of the skid button, the heating depends on the upper temperature limit of the skid button material. The maximum operating temperature of the furnace will be determined. Thus, the upper temperature limit of the skid button plays an important role in the characteristics of the heating furnace.

[0005] Therefore, with the development of a new technology that requires selection of a wide range of hot rolling conditions, the development of a skid button material having better high-temperature strength and oxidation resistance and a high heat-resistant upper limit temperature has been developed. Has been advanced.

[0006] Initially, Ni-base heat-resistant alloys (Ni-Cr-Fe-based alloys) were used as skid button materials. However, a material having higher high-temperature strength has been desired. A heat-resistant Co-based alloy (Co-Cr-Fe alloy: for example, UMC050 of the U.S. standard) has been introduced. The introduction of the Co-based heat-resistant cast alloy certainly improved the high-temperature strength of the skid button dramatically.

However, after that, heating for a long time
Under the actual use environment of a skid button subjected to repeated cooling load, a skid button made of a Co-based heat-resistant cast alloy is remarkably embrittled by precipitation of an intermetallic compound phase such as a σ phase, and the skid button deteriorates due to deformation (set). It has been found earlier that it is prone to damage and destruction such as cracking and chipping.

Therefore, "Co" is used as a material for skid buttons.
Co-Suppressed σ phase precipitation by increasing Ni content of base heat-resistant alloy
Cr-Ni-Fe alloys "have been developed (for example, see JP-A-63-1578).
No. 27, JP-A-60-190544, JP-A-10-36936, etc.) and the walking beam furnace can be heated up to about 1250 ° C., but embrittlement is suppressed. It is inevitable that the strength is reduced by the amount, and the occurrence of deformation (set) is a factor that hinders sufficient life extension.

On the other hand, recently, based on the establishment of a mechanical alloying technique, a fine refractory metal oxide (for example, Y ₂ O) is contained in a Ni—Cr—Co—Fe based austenitic matrix.
₃ ) Oxide dispersion-strengthened alloy containing) has been developed (see Japanese Unexamined Patent Publication (Kokai) No. 3-232945), which has attracted attention as a hearth material for a walking beam furnace capable of heating above 1300 ° C. However, this material does not have sufficient "oxidation resistance" and "repellent performance against scale" for skid buttons, which hinders life extension and also has a high susceptibility to heat embrittlement. When used as, there was a concern about the risk of damage due to repeated use of heating and cooling.

[0010] In addition to the above, a composite alloy in which ceramic particles are dispersed in a base material of a Cr-based powder metallurgy alloy (see JP-A-2-258947) or a Co-Cr-Ni-Fe alloy ( And the like have been developed as hearth materials for a walking beam furnace, but none of them have sufficiently high temperature strength and oxidation resistance for a skid button. I could not say.

In view of the above, an object of the present invention is to provide a skid button for a billet heating furnace which has excellent high-temperature creep characteristics and oxidation resistance even under heating at 1300 ° C. or more and has a long service life. It is to provide a heat-resistant alloy for use.

[0012]

In order to achieve the above object, the present inventors have investigated in detail the high-temperature creep characteristics, oxidation resistance, and reactivity with scale, particularly of a heat-resistant alloy for skid buttons. As a result, the following findings were obtained.

A) In a Co-Cr-Ni-Fe-based Co-Ni-based alloy, its high-temperature strength is greatly affected by the amounts of Mo and W added. Get higher. W is also an element that contributes to the increase in high-temperature strength. However, in the case of the Co-Ni-based alloy skid button to which W is added, when heated to 1250 ° C. or more, Fe falls between the scale and the scale dropped from the steel slab surface. -Forms a low-melting-point composite oxide of the W type and causes significant corrosion of the skid button itself.

B) In the skid button made of the Co—Ni-based alloy, if the addition of Fe is small, the drop in the impact value during long-term use tends to be suppressed, but Fe lowers the high-temperature strength. In order to achieve the desired high-temperature strength, it is necessary to regulate the Fe content after securing the required amounts of Co and Mo.

C) By the way, the oxidation resistance of the Co—Ni-based alloy becomes better as the Cr content increases. This is the surface
It is believed that this is because the Cr oxide works as a so-called oxidation-resistant protective film. However, 1300
In the ° C region, the Cr oxide becomes unstable, evaporating and decomposing, and does not work as a protective film. In addition, when the Cr content is too large, the formation of intermetallic compounds such as the σ phase by heating for a long time is promoted, and the susceptibility to embrittlement increases. d) In addition, Si has been known as an alloying component that improves oxidation resistance, and for simple gas oxidation in a heating furnace atmosphere, oxidation resistance increases with increasing Si content. Is an element that has been actively used for the purpose of improving oxidation resistance. This is because the contained Si is 1300 ° C
This is because it works as an oxidation-resistant surface film in the region. However, in the case of a skid button alloy, as in the case of W described above, if the content of Si is not suppressed, the low melting point of the Fe-Si system between the alloy and the scale dropped from the surface of the steel slab to be heated. A complex oxide (firelite) is formed, causing a problem that the skid button itself is significantly corroded.

E) On the other hand, Al also has the effect of improving the oxidation resistance of the Co—Ni-based skid button alloy, and even in a simple gas oxidation test in a heating furnace atmosphere, the oxidation resistance increases with increasing Al content. The improvement of the properties was observed, and 1300
Works as an excellent oxidation-resistant surface film in the ° C range. Moreover, Al does not show a behavior causing corrosion like Si in a reactivity test with scale, and is a very preferable element as an oxidation resistance improving component. However, if the Al content is too high, the high temperature strength of the alloy will be significantly reduced.

F) Furthermore, the Mn component, which is required as a deoxidizing / desulfurizing agent, also inhibits the formation of Cr oxide, which is an oxidation-resistant surface film, unless its content is regulated. This causes deterioration of the oxidation resistance of the Co-Ni based skid button alloy up to about 1200 ° C.

G) As described above, the high-temperature strength of the Co-Ni-based alloy skid button largely depends on the contents of Mo, W, Fe, etc. In order to further increase the strength, it is effective to add a grain boundary strengthening element such as Nb, V, Ti, or Ta.

H) Depending on the condition of transporting the billet, the protective oxide film on the skid button necessary to secure oxidation resistance is peeled off by contact between the billet and the skid button,
Oxidation may remarkably progress due to so-called erosion collision. Further, the protective oxide film on the skid button may peel off due to temperature fluctuations in the heating furnace, and the oxidation resistance may be deteriorated. All of these phenomena are caused by insufficient adhesion of the protective oxide film on the surface of the skid button. To improve the adhesion, it is effective to add a small amount of Ca or a rare earth element.

The present invention has been completed based on the above findings and the like, and provides a heat-resistant alloy for a heating furnace skid button having the following high-temperature creep characteristics and excellent oxidation resistance. (1) C: 0.2% or less (hereinafter,% representing the component ratio is referred to as% by weight), Si: 0.5% or less, Mn: 1.0% or less, Al: 0.1 to 2.0%, Cr: 25 to 35%, Mo : 1.5 to 10%, W: 0 to 0.05%, Co: 30 to 45%, Fe: 0 to 5%, B: 0 to 0.05%, and the balance consists of Ni and unavoidable impurities. Heat resistant alloy for heating furnace skid buttons with excellent high temperature creep characteristics and oxidation resistance. (2) C: 0.2% or less, Si: 0.5% or less, Mn: 1.0% or less, Al: 0.1 to 2.0%, Cr: 25 to 35%, Mo: 1.5 to 10%, W: 0 to 0.05%, Co : 30 to 45%, Fe: 0 to 5%, B: 0 to 0.05%, and one or more of Nb, V, Ti and Ta: 1% or less in total, with the balance being Ni and inevitable A heat-resistant alloy for a heating furnace skid button having excellent high-temperature creep characteristics and oxidation resistance, comprising an impurity. (3) C: 0.2% or less, Si: 0.5% or less, Mn: 1.0% or less, Al: 0.1 to 2.0%, Cr: 25 to 35%, Mo: 1.5 to 10%, W: 0 to 0.05%, Co : 30 to 45%, Fe: 0 to 5%, B: 0 to 0.05%, and at least one of Nb, V, Ti and Ta: 1% or less in total, and Ca, Y, Ce, Se, At least one of La, Nd and Pr: Furnace skid button excellent in high temperature creep characteristics and oxidation resistance, characterized by containing 0.0001 to 0.2% in total and the balance consisting of Ni and unavoidable impurities. For heat resistant alloys.

[0021]

The reason why the chemical composition of the heat-resistant alloy for a heating furnace skid button in the present invention is limited as described above, together with the function of each component element, will be described. A) C C is an element that contributes to the improvement of the creep strength, but tends to precipitate as Cr carbide at the grain boundaries during solidification or during long-term use. Therefore, the content of C is set to 0.2% or less in order to suppress the precipitation of Cr carbide at the grain boundaries and secure desired toughness and oxidation resistance.

B) Si In addition to deoxidizing the molten alloy, Si has a small content that improves the performance of the chromium oxide film formed on the skid button and improves the oxidation resistance. However, when the content exceeds 0.5%, the formation of a Fe-Si-based composite oxide, which is a low melting point compound, with the scale of the steel slab to be heated forms a significant progress of corrosion. Therefore, Si
The content was determined to be 0.5% or less.

C) Mn Mn is an effective element as a deoxidizing / desulfurizing agent. However, when the content of Mn exceeds 1.0%, the stability of chromium oxide, which is an oxidation-resistant film formed on the alloy, increases. Therefore, the Mn content is determined to be 1.0% or less because it inhibits the oxidation resistance of the alloy.

D) Al Al is an element indispensable for securing oxidation resistance at high temperatures. To secure good oxidation resistance at 1300 ° C. or more, Al is contained in 0.1% or more. There is a need.
However, an excessively high Al content significantly degrades the high-temperature strength of the alloy. Therefore, the Al content is set to 0.1 to 2.0% or less.

D) Cr Cr is an indispensable element for securing the oxidation resistance of the alloy at high temperatures. In order to ensure oxidation resistance for skid buttons at 1300 ° C or higher, the Cr content must be reduced.
Must be at least 25%. However, if the Cr content exceeds 35%, the precipitation of intermetallic compounds (such as the σ phase) and the precipitation of nitrides that adversely affect the ductility and toughness of the alloy will be promoted. Therefore, the Cr content was determined to be 25 to 35%.

E) Mo Mo is also an indispensable element in the alloy of the present invention.
This is an important element that controls the high-temperature creep strength described above. If the Mo content is less than 1.5%, the creep strength required for a skid button in a temperature range of 1250 ° C. or more cannot be secured. on the other hand,
If the Mo content exceeds 10%, the toughness decreases. Therefore, the Mo content was determined to be 1.5 to 10%.

F) WW, like Mo, is an element effective in increasing the high-temperature creep strength of the alloy. However, when the alloy is used at 1250 ° C. or more, the W content is similar. Even a very small amount forms a low-melting Fe-W composite oxide with the scale on the surface of the steel slab to be heated, causing an abnormal oxidation phenomenon (corrosion phenomenon). Therefore, W should be contained as needed in a range of 0.05% or less where the abnormal oxidation phenomenon is hardly conspicuous. Therefore, the W content is set to 0 to 0.05%.

G) Co Co stabilizes the austenitic matrix of the alloy,
In addition, it is an element having the function of increasing the melting point, and is an essential component for ensuring high-temperature strength in the alloy. And
To achieve the desired high-temperature strength for the alloy, the required amount of Mo
In addition to the addition and the restriction of Fe which adversely affects the high temperature strength, 30
It is necessary to secure a Co content of more than
When the content exceeds 45%, an embrittlement phase is formed.
Therefore, the Co content was determined to be 30 to 45%.

H) Fe Fe, when contained in a very small amount, has the effect of improving the ductility and toughness of the alloy and suppressing the decrease in impact value during long-term use, but the Fe content is 5%. Exceeding not only lowers the high-temperature strength of the alloy, but also lowers the impact value. Therefore, in order to ensure the desired high-temperature strength of the alloy and to eliminate the adverse effect on the impact properties, the required amount of
With the addition of Co and Mo, it is necessary to regulate the Fe content to 5% or less without lowering the high-temperature strength and impact value. Although the Fe content may be O, completely preventing the incorporation of Fe causes a significant increase in cost industrially. Therefore, it is preferable to control Fe in view of cost.

I) BB B is an element which exhibits an effect of improving the creep strength through the grain boundary strengthening action, and is therefore an element which is preferably added as necessary. Forming a melting point compound to lower the high temperature strength and toughness of the alloy. Therefore, when B is added, its content should be 0.05%
%, The B content is 0 to 0.05%.
%.

J) Nb, V, Ti, and Ta Nb, V, Ti, and Ta are elements that have the effect of strengthening grain boundaries and improving high-temperature strength. Therefore, further improvement in high-temperature strength is desired. If necessary, one or more of these may be added, but if contained in large amounts, the alloy becomes brittle due to the formation of intermetallic compounds, so that the content of these elements is 1% or less in total. I decided.

K) Ca, Se, Y, Ce, La, Nd and Pr Ca, Se, Y, Ce, La, Nd and Pr all improve the adhesion of the protective oxide film formed on the alloy surface. In order to prevent the protective oxide film from peeling off and to further improve the oxidation resistance, one or more of these elements are added as necessary, if necessary. Is 0 in total.
When the content is less than 0001%, the effect is not recognized. On the other hand, when the total content exceeds 0.2%, an oxide is formed during solidification of the alloy, and the toughness is reduced. Therefore, the contents of these elements are determined to be 0.0001 to 0.2% in total.

The heat-resistant alloy for a heating furnace skid button having the above-mentioned chemical composition according to the present invention may be manufactured by any means known as a method for manufacturing this kind of heat-resistant alloy.

Next, the present invention will be described in more detail with reference to Examples, but it goes without saying that the present invention is not limited by these Examples.

EXAMPLES First, using a 20 kg vacuum induction melting furnace, alloys having the chemical compositions shown in Table 1 were melted and cast into molds to prepare ingots having a diameter of 80 mmφ.

[0035]

[Table 1]

Next, “130” was added to each of the obtained ingots.
After heating and holding at 0 ° C. for 24 hours and air cooling ”, various test specimens were collected from each of these ingots and subjected to“ compression creep test ”and“ Charpy impact test ”under the following conditions. "," Oxidation test "and" Reactivity test with scale "were carried out. 1) Compression creep test Specimen dimensions: diameter 10 mmφ x length 15 mm, test temperature: 1300 ° C, test load: 2.0 kgf / mm ² , measurement item: creep deformation after 100 minutes (creep strain) amount). 2) Charpy impact test Specimen dimensions: 10mm high x 10mm wide x 55mm long with V notch, Aging condition of test specimen: a) As homogenized, b) 800 ° C x 300 hours aged material, c) Aged material at 900 ° C for 300 hours, test temperature: room temperature, test item: impact value. 3) Oxidation test Specimen dimensions: width 12.3 mm × length 15 mm × thickness 3 mm, test temperature: 1250 ° C, 1300 ° C and 1350 ° C, test atmosphere: 6% CO ₂ -20% H ₂ O-N ₂ (Bal ) (Simulated atmosphere of combustion in a heating furnace), test time: 25 hours, measurement item: weight loss (oxidative weight loss) = (initial weight-weight after descaling after test) / (surface area of initial test piece). 4) Reactivity test with scale Specimen dimensions: width 12.3mm x length 15mm x thickness 3mm, test method: embed the specimen in the scale of the heated steel piece taken from the heating furnace Holding, test temperature: 1250 ° C, 1300 ° C, and 1350 ° C, test atmosphere: 6% CO ₂ -20% H ₂ O-N ₂ (Bal) (simulated atmosphere of heating furnace combustion), test time: 25 hours, measurement items: Weight loss (reaction loss) = (initial weight-weight after descaling after test) / (surface area of initial test piece). The results of these tests are summarized in Table 2 below.

[0037]

[Table 2]

The following items are apparent from the results shown in Table 2. That is, the alloy of Comparative Example 1 has a low oxidation resistance to the atmosphere gas in the furnace and a high reactivity with the scale because the Al content is low. Further, since the contents of C and Fe are high, the impact value after aging (after use at a high temperature) is drastically reduced, and the oxidation resistance at 1250 ° C. is low due to the low Cr content. On the other hand, Comparative Example Alloy 2 has high reactivity with the scale due to the high Si content.

The alloy of Comparative Example 3 has a low oxidation resistance to the furnace atmosphere gas due to a high Mn content, and a low creep strength due to a low Mo content (ie, a low creep strength).
Large deformation strain). Furthermore, since the Co content is high, an embrittlement phase occurs, and the impact value after aging (after use at a high temperature) is low. Comparative Example Alloy 4 has a high reactivity with the scale due to a high W content, and the impact value after aging (after use at a high temperature) is remarkably reduced due to a high Mo and B content. In Comparative Example Alloy 5, the impact value after aging (after use at high temperature) was low due to the high Cr content. Also, the creep strength is low due to the low Co content.

The alloy of Comparative Example 6 had a low impact value after aging (after use at a high temperature) due to the high total content of Nb and V,
Also, the creep strength is low due to the large amount of Al. Comparative Example Alloy 7 has a low impact value after aging (after use at a high temperature) because of the high total content of Ti and Ta.

Although the alloy of Comparative Example 8 contains Ca, Se and Y, the total content thereof is small, so that the oxidation resistance to the atmosphere gas in the furnace is somewhat lower than that of Alloy 24 of the present invention. I understand. Comparative alloy 9 was made of Ce, Se, Y, Nd
After aging due to high total content of Pr and Pr (after high temperature use)
The impact value at is low.

The alloys of the present invention were compared with those of the comparative alloys.
Nos. 10 to 35 show excellent performance in all of the creep strength, impact value, oxidation resistance, and reactivity with scale, and are used as a heat-resistant alloy for skid buttons in a walking beam furnace. It can be determined that they are sufficiently satisfactory.

[0043]

As described above, according to the present invention, excellent high-temperature strength, oxidation resistance, and resistance to scale are exhibited even in a high-temperature range of 1300 ° C. or more, and the impact after high-temperature heating is obtained. An industrially useful effect such as the provision of a skid button material having a higher heat-resistant upper limit temperature can be realized, and a heat-resistant alloy with less characteristic deterioration can be provided.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshiro Anraku 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Inside Sumitomo Metal Industries, Ltd. (72) Inventor Yoshijun Sawaragi 4-chome, Kitahama, Chuo-ku, Osaka-shi, Osaka 5-33 No. Sumitomo Metal Industries Co., Ltd. (72) Inventor Kazuhisa Tanaka 1-3-1, Tsujido Shindai, Fujisawa-shi, Kanagawa Kanto Special Steel Co., Ltd.

Claims (3)

[Claims] [Claim 1] By weight percentage, C: 0.2% or less, Si: 0.5% or less, Mn: 1.0% or less, Al: 0.1 to 2.0%, Cr: 25 to 35%, Mo: 1.5 to 10%, W : 0 to 0.05%, Co: 30 to 45%, Fe: 0 to 5%, B: 0 to 0.05%, with the balance being Ni and unavoidable impurities, characterized by the high-temperature creep characteristics and Heat resistant alloy for heating furnace skid buttons with excellent oxidation resistance. 2. In a weight ratio, C: 0.2% or less, Si: 0.5% or less, Mn: 1.0% or less, Al: 0.1 to 2.0%, Cr: 25 to 35%, Mo: 1.5 to 10%, W : 0 to 0.05%, Co: 30 to 45%, Fe: 0 to 5%, B: 0 to 0.05%, and at least one of Nb, V, Ti and Ta: 1% or less in total A heat-resistant alloy for heating furnace skid buttons having excellent high-temperature creep characteristics and oxidation resistance, with the balance being composed of Ni and unavoidable impurities. 3. In a weight ratio, C: 0.2% or less, Si: 0.5% or less, Mn: 1.0% or less, Al: 0.1 to 2.0%, Cr: 25 to 35%, Mo: 1.5 to 10%, W : 0 to 0.05%, Co: 30 to 45%, Fe: 0 to 5%, B: 0 to 0.05%, and at least one of Nb, V, Ti and Ta: 1% or less in total and Ca , Y, Ce, Se, La, Nd and Pr: High temperature creep characteristics and oxidation resistance, characterized by containing 0.0001-0.2% in total and the balance consisting of Ni and unavoidable impurities. Excellent heat-resistant alloy for heating furnace skid buttons.