JPS6344814B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to hearth members such as hearth rails, hearth rollers, radiant tubes, etc., which are used at high temperatures of 1000° C. or higher and have excellent weld cracking resistance. Hearth rails, hearth rolls, etc. of steel ingot heating furnaces are
Since red-hot steel ingots weighing several tons to several tens of tons are transported, transported, and exposed to temperatures of 1000℃ or higher, these materials must have sufficient strength and oxidation resistance at high temperatures of 1000℃ or higher. It is necessary to have the following.
Currently, UMCo50 (30Cr−50Co−
Fe), 20Co (29Cr−20Ni−20Co−5W−2Nb−
Heat-resistant cast alloys containing a large amount of Co such as Fe) are used, but even the above cast alloys are not sufficient when used under harsh conditions such as hearth parts, and higher There is a need for the development of heat-resistant casting alloys for high-performance hearth components. Therefore, the present inventors have developed a hearth member that has superior high-temperature properties compared to UMCo50 or 20Co-based heat-resistant cast alloys, has excellent weld cracking resistance that does not cause microcracks during welding, and is also inexpensive. As a result of detailed investigation of the influence of various component elements for the purpose of development, we found that the cast alloy with the composition shown below has excellent strength and oxidation resistance in the high temperature range of 1000℃ or higher, and has excellent weld cracking resistance. It was confirmed that the material has excellent properties and is extremely suitable for use in hearth members. That is, the hearth member with excellent weld cracking resistance according to the present invention has (1) (C+N) in weight%: exceeding 0.20 to 1.50%;
Si: 2.50% or less, Mn: 2.50% or less, Ni: 15.0~
60.0%, Cr: 15.0-40.0%, W: 3.0-10.0%,
Contains Ti: 0.02~3.0%, Zr: 0.008~2.0%,
A hearth member with excellent weld cracking resistance, the remainder of which is essentially Fe. (2) In addition to the first invention composition, Co: 2.0% or less, Mo: 5.0% or less, Nb: 3.0% or less, Ta:
A hearth member with excellent weld cracking resistance, containing one or more elements selected from 3.0% or less, with the remainder being substantially Fe. (3) In addition to the first invention composition, REM: 2.0%
A hearth member having excellent weld cracking resistance, containing one or more elements selected from the following: Ca: 0.02% or less and Al: 4.0% or less, with the remainder being substantially Fe. (4) In addition to the first invention composition, B: 0.0001~
A hearth member with excellent weld cracking resistance, containing 0.05% Fe, with the remainder essentially consisting of Fe. It is characterized by the fact that The hearth member with excellent weld cracking resistance according to the present invention is obtained by designing an alloy by combining relatively inexpensive elements to obtain the best high temperature characteristics and weld cracking resistance, UMCo50 or
It has superior high-temperature strength, oxidation resistance, and creep strength compared to 20Co alloys, and also has excellent weld cracking resistance, making it extremely suitable for hearth components such as hearth rails, hearth rollers, and radiant tubes. It is something. Next, the reason for limiting the composition range (weight %) of the hearth member having excellent weld cracking resistance according to the present invention will be described below. (C+N): Exceeding 0.20 to 1.50% Both C and N are dissolved in the base, and Cr,
It is an extremely effective element that combines with W, Ti, and Zr to form fine carbides and/or nitrides and improves high-temperature strength, and the sum of both elements is 0.20.
It is necessary to contain it in excess of %. In this case, good high-temperature properties can be ensured even if N is not included, but if high-temperature tensile strength is particularly required, it is preferable to actively include N. As mentioned above, C and N are effective elements, but if they are included in large amounts, the toughness, weldability, etc. will decrease.
Limited to 1.50% or less. Si: 2.50% or less In addition to being necessary as a deoxidizing element during melting, it is an effective element for improving oxidation resistance and carburization resistance, and it is preferable to include it actively, but if it is included in a large amount, is produced because the high temperature strength decreases
Limited to 2.50% or less. Mn: 2.50% or less Mn is an effective element as a deoxidizing and desulfurizing refining agent during melting, but it is limited to 2.50% or less since oxidation resistance deteriorates if it is included in a large amount. Ni: 15.0 to 60.0% Ni is an effective element for stabilizing austenite and improving heat resistance, carburization resistance, and high-temperature strength, and must be contained at least 15.0%. The higher the amount of Ni, the more stable the austenite becomes, so it is better to include a larger amount, but in view of the balance with other components, it is limited to a range of 15.0 to 60.0%. Cr: 15.0-40.0% Cr is the most effective element for improving oxidation resistance at high temperatures, and must be contained at least 15.0%. However, if it is contained in a large amount, δ phase will be generated and the dazzling property will decrease.
It was limited to a range of 40.0%. W: 3.0 to 10.0% W is dissolved in the base and combined with C to form W-
It has the effect of producing C-based carbides and significantly improving high-temperature strength. This effect is more clearly observed when the amount is 3.0% or more, and the larger the amount, the better the effect, but on the other hand, the eyelids decrease, so the preferred range is 3.0%.
~10.0%. Ti: 0.02-3.0% Like W, Ti also forms a solid solution in the matrix and combines with C to form TC-based carbides, which has the effect of significantly improving high-temperature strength. Although this case has not been investigated theoretically, it has been experimentally confirmed that the synergistic effect with W is strong and high-temperature strength is significantly improved. This effect is observed when contained in a small amount, and the larger the amount, the better the effect, but on the other hand, the eyelids decrease, so the preferred range is 0.02 to 3.0%. Zr: 0.008~2.0% Zr is not only effective in improving oxidation resistance and strength at high temperatures, but also extremely effective in preventing the occurrence of microcracks during welding and improving weld cracking resistance. % or more. However, even if it is contained in a large amount, the effect is small and oxidation resistance begins to deteriorate, so it was limited to 2.0% or less. The above component composition ensures excellent strength, oxidation resistance, and weld cracking resistance in the high temperature range of 1000°C or higher, but the high temperature properties are further improved by further containing the following elements. One or more elements selected from Co: 2.0% or less, Mo: 5.0% or less, Nb: 3.0% or less, Ta: 3.0% or less. All of these elements are dissolved in the base to strengthen the base. At the same time, some of it precipitates as carbide, which is effective in improving high-temperature strength. However, even if it is contained in large amounts, its effect is small;
Rather, the eyelidness decreases, so the preferred range is
2.0% or less for Co, 5.0% or less for Mo, 3.0% or less for Nb, and 3.0% for Ta.
% or less. REM: 2.0% or less, Ca: 0.02% or less, Al: 4.0%
One or more elements selected from the following: All of these elements have a very high affinity for oxygen and are effective in improving oxidation resistance. However, even if it is contained in a large amount, the effect is small, and the eyelids will actually decrease, so the suitable range for each is limited.
REM (one or more rare earth elements)
2.0% or less for Ca, 0.02% or less for Ca,
For Al, it is 4.0% or less. B: 0.0001 to 0.05% It is an effective element for improving creep strength at high temperatures when contained in a small amount, but when contained in a large amount, it forms borides and deteriorates the tackiness.
Its preferred range is 0.0001-0.05%. Next, the characteristics of the hearth member having excellent weld cracking resistance according to the present invention will be explained in detail using examples. Example 1 UMCo50 alloy and 20Co alloy, which have been conventionally used as hearth member alloys of the present invention and comparative hearth member alloys, having the composition shown in Table 1 were melted and prepared based on JIS-G5121. A boat-shaped test piece was taken and various characteristic values were investigated.

【table】

[Table] Creep properties A creep test piece was taken from a boat-shaped test piece having the composition shown in Table 1, and was subjected to a creep property evaluation test for use as a hearth member. As an example of the results, Fig. 1 shows the life time until rupture under the conditions of temperature: 1100°C and load stress: 2 Kg/mm ² . As seen in the figure, the comparative example made of UMCo50 (sample material No. 6) broke in about 5 hours, and the material made of 20Co (sample material No. 7) broke in 80 hours. On the other hand, all of the samples according to the present invention have a rupture life of 90 hours or more. As described above, it was confirmed that the samples according to the present invention have extremely excellent creep properties at high temperatures of 1000°C or higher. High-temperature tensile properties A high-temperature tensile test piece was taken from a boat-shaped test piece having the composition shown in Table 1, and subjected to a high-temperature tensile property evaluation test as a hearth member. Figure 2 shows the tensile properties at a high temperature of 1100°C as an example of the results. As seen in the figure, the comparative example made of UMCo50 (sample material No. 6) had a tensile strength of 5.5 Kg/mm ² ,
Although the specimen according to the present invention exhibits an elongation of approximately 3.5%, the specimen according to the present invention exhibits a strength characteristic comparable to or greater than that of the comparative example made of a 20Co alloy (sample material No. 7). As described above, it was confirmed that the examples of the present invention have extremely excellent strength properties at high temperatures of 1000°C or higher. High-temperature oxidation resistance properties An oxidation resistance test piece was taken from a boat-shaped test piece having the composition shown in Table 1, and was subjected to an oxidation resistance evaluation test for use as a hearth member. Figure 3 shows an example of the results.
The figure shows the oxidation weight gain when exposed to a high temperature of 1200℃ for 100 hours. As seen in the figure, the comparative example showed relatively good high-temperature strength and creep properties.
The material made of 20Co alloy (sample material No. 7) showed a significantly large increase in weight due to oxidation, indicating that there was a problem in terms of oxidation resistance. On the other hand, all of the examples according to the present invention show an increase in oxidation weight equal to or less than that of the UMCo50 alloy. That is, in the case of the example of the present invention, the temperature is 1000°C.
It was confirmed that the material has excellent strength properties and oxidation resistance at the above-mentioned high temperatures, and is well-balanced for use as a hearth member. Weld cracking resistance properties As hearth parts require connection to the heating furnace body or cooling pipe, the weldability of the material itself,
In particular, one of the characteristics that should be provided is weld cracking resistance, which makes it difficult for microcracks to occur during welding. Therefore, test pieces for weld cracking resistance were taken from boat-shaped test pieces having the chemical compositions shown in Table 1, and butt welded with carbon steel in the manner shown in FIG. Thereafter, it was cut along the A-A' plane as shown in FIG. 4, and after polishing the same surface, microcracks in the B section were observed. Table 2 shows the welding conditions and the number of microcracks in the weld.

【table】

[Table] As shown in the same table, micro cracks occurred in the welds in both the comparative example made of UMCo50 alloy and the one made of 20Co alloy, but no weld cracks occurred in any of the inventive examples. However, it was confirmed that the weld cracking resistance was better than that of the comparative example. Example 2 0.2C-25Ni- having the component composition shown in Table 3
28Cr−6W−1.5Ti−0.09Zr series and 0.4C−30Ni−
The 34Cr-5W-0.3Ti-0.03Zr alloy for hearth members of the present invention was melted, No. A boat-shaped test pieces based on JIS-G5121 were taken, and various characteristic values were measured in the same manner as in Example 1. investigated.

【table】 The results are summarized in Table 4.

[Table] As shown in the table, the second invention example has higher high temperature strength than the first invention example, the third invention example has less oxidation weight gain, and the fourth invention example has a longer creep rupture life. clearly recognized. As described above, it was confirmed that the second to fourth invention examples had even better high-temperature characteristics than the first invention example. In addition, in both the first to fourth invention examples, no cracking was clearly observed during butt welding with carbon steel. As explained above, the hearth member according to the present invention has high-temperature strength at a high temperature of 1000°C or higher.
It has the same or better oxidation resistance than hearth members made of conventionally used 20Co alloys, and has the same or better oxidation resistance than hearth members made of UMCo50, and is less prone to weld cracking. As a hearth member, it is extremely well-balanced. Furthermore, since it does not contain a large amount of expensive Co, it is inexpensive and has the excellent effect of being able to fully meet recent demands for hearth members.

[Brief explanation of the drawing]

Figure 1 is a graph showing the creep rupture life time of the inventive example and the comparative example, Figure 2 is a graph showing the high temperature tensile strength, Figure 3 is a graph showing the oxidation weight gain, and Figure 4 is a graph showing the oxidation weight increase. FIG. 2 is a diagram showing a procedure for butt welding.

Claims (1)

[Claims] 1% by weight, (C+N): more than 0.20 to 1.50%,
Si: 2.50% or less, Mn: 2.50% or less, Ni: 15.0~
60.0%, Cr: 15.0-40.0%, W: 3.0-10.0%,
A hearth member containing Ti: 0.02 to 3.0%, Zr: 0.008 to 2.0%, and having excellent weld cracking resistance, the remainder being substantially Fe. 2 Weight% (C+N): over 0.20 ~ 1.50%,
Si: 2.50% or less, Mn: 2.50% or less, Ni: 15.0~
60.0%, Cr: 15.0-40.0%, W: 3.0-10.0%,
Ti: 0.02~3.0%, Zr: 0.008~2.0%, and Co:
2.0% or less, Mo: 5.0% or less, Nb: 3.0% or less,
Hearth member with excellent weld cracking resistance, containing one or more selected from Ta: 3.0% or less, with the remainder being substantially Fe. 3 Weight% (C+N): over 0.20 ~ 1.50%,
Si: 2.50% or less, Mn: 2.50% or less, Ni: 15.0~
60.0%, Cr: 15.0-40.0%, W: 3.0-10.0%,
Ti: 0.02~3.0%, Zr: 0.008~2.0%, and
REM: 2.0% or less, Ca: 0.02% or less, Al: 4.0%
A hearth member having excellent weld cracking resistance and containing one or more selected from the following, the remainder being substantially Fe. 4 Weight% (C+N): over 0.20 ~ 1.50%,
Si: 2.50% or less, Mn: 2.50% or less, Ni: 15.0~
60.0%, Cr: 15.0-40.0%, W: 3.0-10.0%,
Ti: 0.02~3.0%, Zr: 0.008~2.0%, B: 0.0001
A hearth member with excellent weld cracking resistance, containing ~0.05% Fe, with the remainder essentially consisting of Fe.