JPS6254179B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat-resistant casting alloy for hearths that has excellent strength, burn-out resistance, and oxidation resistance even at high temperatures of 1100°C or higher, as well as good weldability. Hearth materials used in soaking furnaces for steel ingots and firing furnaces for tiles, roof tiles, etc. are usually exposed to high temperatures of 1100°C or higher for long periods of time, so they have high strength and good hardening properties at high temperatures. In particular, properties such as durability and oxidation resistance are required. On the other hand, since connection with the heating furnace body or cooling pipe is required, weldability of the material itself is also one of the characteristics that must be provided. Currently, ceramic or UMCo50 is used for hearths.
(30%Cr-50%Co-Fe, Supertherm (27%
Cr-35%Ni-15%Co-5%W), MORE2 (30%
Super heat-resistant alloys such as Cr-50%Ni-15%W) have been used, but none of them satisfy all of the above characteristics. In other words, ceramic has insufficient cracking resistance due to thermal stress, UMCo50 is prone to weld cracking when welded to cooling pipes, and Supertherm and MORE2 have low melting points because they contain a large amount of C. Therefore, each material has its own disadvantages, such as the tendency to cause localized melting in areas that receive direct radiant heat from heat sources such as burners or heaters, so they are not necessarily suitable materials for hearths. No, no.
Therefore, in order to develop a material suitable for hearths, the present inventors conducted a detailed investigation into the effects of various component elements.As a result, a cast alloy with the composition shown below has higher high-temperature strength than conventional hearth materials. It was discovered that this material possesses excellent properties in terms of heat resistance, oxidation resistance, and weldability, and was confirmed to be an extremely suitable material for hearths. That is, the present invention provides (1) C+N: 0.20% or less, Si: 2.50% or less, Mn:
2.50% or less, Ni: over 30.0 ~ 60.0%, Cr: 15.0
~38.0%, Zr: 0.01~2.0%, W: 3.0~10.0%
is the basic component, and furthermore, Co: 25.0% or less,
A heat-resistant cast alloy containing one or more elements selected from Ti: 2.0% or less, Nb: 3.0% or less, Ta: 3.0% or less, and the remainder substantially consisting of Fe. (2) The composition of the first invention further contains one or more elements selected from RE: 2.0% or less, Al: 2.50% or less, Ca: 0.02% or less, and the remainder substantially consists of Fe. Heat-resistant casting alloy. (3) In addition to the first invention composition, B: 0.0001~
A heat-resistant cast alloy containing 0.05% Fe, with the remainder essentially consisting of Fe. (4) In addition to the first invention composition, one or more elements selected from RE: 2.0% or less, Al: 2.50% or less, Ca: 0.02% or less, and B:
It is a heat-resistant cast alloy containing 0.0001 to 0.05% of Fe, with the remainder essentially consisting of Fe. The cast alloy of the present invention has low C and N content to prevent deterioration of burn-out resistance and high-temperature oxidation resistance, contains a small amount of Zr to improve weldability, and has sufficient high-temperature strength at temperatures above 1100°C. In order to ensure that a relatively large amount of W is contained, σ
In order to prevent the formation of the above-mentioned σ phase in high Cr and high W alloys, which tend to generate phases, a large amount of Ni is added, and in order to further improve the high temperature strength.
It is a heat-resistant cast alloy that is characterized by containing an appropriate amount of an element selected from among Co, Ti, Nb, and Ta, and can solve all technical problems as a hearth material at once. Next, the reason for limiting the composition range of the cast alloy of the present invention will be described below. C + N: 0.20% or less C and N are effective elements for improving high-temperature strength, but on the other hand, they lower the melting point, so they are not preferable from the viewpoint of burnishing resistance, and they should be contained in large amounts because they also reduce oxidation resistance. I can't. Therefore, in order to find the appropriate amount of C+N, we conducted detailed experiments and found that if the total amount of C and N does not exceed 0.20%, the burn resistance and oxidation resistance will not deteriorate significantly. limited to. Si: 2.50% or less Si is an effective element as a deoxidizing rust refining agent during melting, as well as improving the flowability and oxidation resistance during casting.
At temperatures above 1150℃, Fe ₂ SiO ₂ with a low melting point is likely to be formed, and oxidation resistance deteriorates significantly.
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 because it deteriorates oxidation resistance when contained in large amounts. Cr: 15.0 to 38.0% 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
15.0-38.0% due to phase formation and decrease in toughness
limited to the range of Ni: Exceeding 30.0 to 60.0% Ni is an effective element for stabilizing austenite and improving heat resistance, carburization resistance, and high-temperature strength. To prevent phase formation,
In other words, in order to ensure phase stability at temperatures below 900°C, a high Ni content of over 30.0% was used. This phase stability at temperatures below 900°C is required when using the product as cast or because it passes through that temperature range during cooling. The higher the amount of Ni, the more stable the austenite becomes, so it is better to add a larger amount, but in view of the balance with other components, it is limited to a range of over 30.0% to 60.0%. Zr: 0.01-2.0% Zr is not only effective in improving oxidation resistance and strength at high temperatures, but also extremely effective in improving weldability, and must be contained at least 0.01%. However, if added in a large amount, the above effects will not be obtained and the oxidation resistance will deteriorate, so the amount was limited to 20% or less. W: 3.0 to 10.0% W is an element effective in improving strength particularly at high temperatures of 1100° C. or higher, and was set at 3.0% or more. However, even if it is contained in a large amount, its effect tends to be saturated and the cost increases, so it is limited to 10.0% or less. Co: 25.0% or less, Ti: 2.0% or less, Nb: 3.0%
Hereinafter, the alloy of the present invention contains one or more elements selected from Ta: 3.0% or less in order to reduce C and N as much as possible in order to improve burnout resistance and oxidation resistance, but on the other hand, it is difficult to ensure high temperature strength. As this became difficult, W, which is particularly effective in improving high-temperature strength, was included in the range of 3.0 to 10.0%, but high-temperature strength can be further ensured by containing appropriate amounts of the above elements alone or in combination. I made it possible to do this. However, even if it is contained in an amount more than necessary, the effect tends to be saturated and the cost will be high.
25.0% or less for Ti, 2.0% or less for Nb, 3.0% or less for Nb, and 3.0% for Ta.
% or less is suitable. Although Mo is also an element that contributes to improving high-temperature strength, it can also degrade oxidation resistance at high temperatures, so the above
It is preferable to select and add Co, Ti, Nb, and Ta. A cast alloy having the high-temperature strength, heat resistance, oxidation resistance, and weldability that is the object of the present invention can be obtained by combining the above-mentioned component compositions, but further excellent properties can be obtained by containing appropriate amounts of the following elements: is obtained. RE: 2.0% or less, Al: 2.50% or less, Ca: 0.02% or less. By containing a small amount of each of the above elements, oxidation resistance and burning resistance can be improved. However, all of them have a strong affinity with oxygen in the alloy, and if the amount is large, the cleanliness decreases, so for RE, it is less than 2.0%, for Al, it is less than 2.5%, and for Ca, it is less than 0.02%. is desirable. In addition, RE in this application refers to Y, La, Ce,
Indicates Sm and other rare earth elements. B: 0.0001 to 0.05% B can improve high temperature strength and creep strength by containing a small amount of B. However, in large amounts, borides are formed in the alloy,
Since high temperature strength decreases, a range of 0.0001 to 0.05% is desirable. Next, the characteristics of the cast alloy of the present invention will be explained in detail using examples. Examples The alloys of the present invention and comparative alloys having the compositions shown in Table 1 were melted and cast into No. A boat-shaped test pieces based on JIS G5121, and various characteristic values were investigated.

【table】

[Table] Test materials No. 1 to 8 are first invention casting alloys, No. 9, and 10.
is the second invention casting alloy, and No. 11 is the third invention casting alloy No.
12 is the fourth invention casting alloy No. 13, and 14 is the comparative casting alloy, Supertherm and UMCo50 respectively.
It is an alloy corresponding to Burning resistance
The wedge-shaped test piece shown in the figure was cut out and placed in an experimental furnace to investigate its resistance to burning. The temperature in the experimental reactor
After continuous heating at 1350°C for one month, the specimen was taken out and changes in dimensions were measured. The results are shown in Figure 2. As shown in the same figure, comparison casting alloys No. 13 (Supertherm) and No. 14
(UMCo50) has an extremely large dimensional change, that is, the shrinkage shrinkage length, whereas all of the cast alloys of the present invention show good shrinkage resistance with little dimensional change. High Temperature Strength Creep test pieces were cut out from the boat-shaped test pieces shown in Table 1 and used for testing. The test temperature was 1100℃ and
Two levels are set at 1200℃, and 1.0Kg/at 1100℃.
Loading stress of mm ² , 0.5Kg/mm ² at 1200℃
The time required for the test piece to break was measured by applying a stress of . The results are shown in Figure 3 (Test conditions: temperature
1100°C, stress 1.0Kg/mm ² ) as shown in Figure 4 (test conditions: temperature 1200°C, stress 0.5Kg/mm ² ). As seen in the same figure, compared to comparative casting alloys No. 13 and No. 14, the casting alloys of the present invention both have sufficiently long rupture lives despite having a lower C+N content. High-temperature oxidation resistance Oxidation test pieces were cut out from the test materials shown in Table 1 and used for testing. The test conditions were atmospheric heating at 1200°C for 200 hours, and the oxidation weight gain was measured after the test. The results are shown in Figure 5 (Test conditions: temperature 1200℃, time
200hr). As seen in the figure, Nos. 1 to 12 of the casting alloys of the present invention are Nos. 13 and 14 of the comparative casting alloys.
shows the same or lower oxidation weight gain compared to That is, it was confirmed that the cast alloy of the present invention has high-temperature oxidation resistance comparable to that of conventional heat-resistant cast alloys. Weldability Welding test pieces were cut out from the test materials shown in Table 1, and butt welded to carbon steel using the method shown in Figure 6. Then cut along the A-A' plane in Figure 6,
After polishing the same surface, microcracks in part B were observed. Second
The table shows the welding conditions and the number of microcracks in the weld.

[Table] As shown in the table, 7 micro-cracks occurred in the comparative cast alloy No. 13 and 3 micro-cracks occurred in No. 14, whereas no micro-cracks occurred in the cast alloy of the present invention. It was confirmed that it exhibited good weldability. As seen in the above examples, the casting alloy of the present invention is a conventional heat-resistant casting alloy (Supertherm,
Compared to UMCo50, etc.), it has higher burn resistance, high temperature strength,
It is a heat-resistant cast alloy with high practical value, as it has excellent high-temperature oxidation resistance and weldability, and can be manufactured at a relatively low cost.

[Brief explanation of the drawing]

Figure 1 shows the shrinkage test piece, where a is before the test,
b is a diagram showing the shape after the test, FIG. 2 is a diagram showing the shrinkability test results, FIGS. 3 and 4 are diagrams showing the creep test results, and FIG. 5 is a diagram showing the oxidation test results.
FIG. 6 shows a welding test method, in which a is a plan view and b is a cutaway view taken along the line A-A' in a.

Claims (1)

[Claims] 1 C+N: 0.20% or less, Si: 2.50% or less, Mn:
2.50% or less, Ni: over 30.0 ~ 60.0%, Cr: 15.0 ~
38.0%, Zr: 0.01-2.0%, W: 3.0-10.0% as basic components, further Co: 25.0% or less, Ti: 2.0%
A heat-resistant cast alloy containing one or more elements selected from the following: Nb: 3.0% or less, Ta: 3.0% or less, and the remainder substantially consisting of Fe. 2 C+N: 0.20% or less, Si: 2.50% or less, Mn:
2.50% or less, Ni: over 30.0 ~ 60.0%, Cr: 15.0 ~
38.0%, Zr: 0.01-2.0%, W: 3.0-10.0% as basic components, further Co: 25.0% or less, Ti: 2.0%
Below, one or more elements selected from Nb: 3.0% or less, Ta: 3.0% or less, and RE: 2.0
% or less, Al2.50% or less, Ca: 0.02% or less, and the remainder is substantially Fe. 3 C+N: 0.20% or less, Si: 2.50% or less, Mn:
2.50% or less, Ni: over 30.0 ~ 60.0%, Cr: 15.0 ~
38.0%, Zr: 0.01-2.0%, W: 3.0-10.0% as basic components, further Co: 25.0% or less, Ti: 2.0%
Below, one or more elements selected from Nb: 3.0% or less, Ta: 3.0% or less, and B:
A heat-resistant casting alloy containing 0.0001 to 0.05% of Fe, with the remainder essentially consisting of Fe. 4 C+N: 0.20% or less, Si: 2.50% or less, Mn:
2.50% or less, Ni: over 30.0 ~ 60.0%, Cr: 15.0 ~
38.0%, Zr: 0.01-2.0%, W: 3.0-10.0% as basic components, further Co: 25.0% or less, Ti: 2.0%
Below, one or more elements selected from Nb: 3.0% or less, Ta: 3.0% or less, and RE: 2.0
% or less, Al: 2.50% or less, Ca: 0.02% or less, and one or more elements selected from B:
A heat-resistant casting alloy containing 0.0001 to 0.05% of Fe, with the remainder essentially consisting of Fe.