JPH0118141B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an alloy for mesh belts in heating furnaces, and particularly to an alloy for mesh belts in heating furnaces that has excellent hot workability, heat resistance, and oxidation resistance, and is particularly suitable as a material for mesh belts, which are heating furnace parts that are highly processed. . Heat-resistant and oxidation-resistant steels are specified in JIS G 4311 (steel bars) and JIS G 4312 (steel plates).
There are SUH symbol and SUS symbol. Among them, SUH310, for example, is austenitic and is said to be mainly suitable for heat resistance and oxidation resistance. However, the Ni content is low,
During long-term use at high temperatures, there is a risk of precipitation of the σ phase and embrittlement, and the carburization resistance is poor, so although it is used in heat-resistant parts such as mesh belts for heating furnaces, its performance is not satisfactory. In addition, it is a heat-resistant alloy with improved heat resistance and oxidation resistance that prevents embrittlement even when used at high temperatures for long periods of time (product name: Alloy DS, see No. 7 in Table 1).
has also been developed. This alloy has excellent carburization resistance and has a small coefficient of thermal expansion, so it can be heated and
Although it can be said to be suitable for applications where cooling is frequently repeated, it has poor hot workability due to its high Si content, so it is not suitable for highly processed products such as the mesh belt for the heating furnace mentioned above. It has the following drawbacks. An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide a heat-resistant alloy that has excellent hot workability, heat resistance, and oxidation resistance. The mesh belt alloy for a heating furnace according to the present invention has, in weight percent, C (carbon): 0.01 to less than 0.15%, Si
(Silicon): over 0.1 ~ 2%, Mn (manganese): 0.3
~2%, Ni (nickel): over 35~45%, Cr (chromium): 18~less than 21%, B (boron): 0.0005~0.01
%, and Ca (calcium): 0.001-0.01%, Mg
Contains one or more of (magnesium): 0.001-0.04%, REM (rare earth element): 0.005-0.05%, and optionally Ti (titanium): 0.3%.
Below, Nb + Ta (niobium + tantalum): 0.3% or less,
It is characterized by containing one or more of the following: Zr (zirconium): 0.3% or less, V (vanadium): 0.3% or less, and the remainder consists of Fe and inevitable impurities. The reason for limiting each component range will be explained in detail below. Ni is a necessary element to create a stable austenite structure for long-term use at high temperatures and improve high-temperature strength. It is necessary to add This Ni addition increases the resistance to carburization and lowers the coefficient of thermal expansion as the amount of Ni increases. Therefore, it can be suitable as a material for mesh belts in heating furnaces where heating and cooling are frequently repeated.
is expensive, so the upper limit is set at 45%. Cr is an essential element for obtaining oxidation resistance and sulfidation resistance, and for this purpose it is necessary to add 18% or more. The addition of Cr can increase high-temperature strength, but excessive addition reduces oxidation resistance and sulfidation resistance, and also causes σ phase and embrittlement during long-term use at high temperatures. Therefore, in order to more reliably prevent such problems from occurring, the ratio should be less than 21%. Si is an element that is effective in increasing oxidation resistance, especially carburization resistance, and at the same time has an excellent deoxidizing effect. It is necessary to add more than %. This Si is preferably added to oxidation-resistant alloys, but this is because when examining the element distribution in the scale part, Si is concentrated near the boundary between the scale and the base, and the Si is concentrated near the boundary between the scale and the base. By improving adhesion, improving scale spalling resistance, and improving oxidation resistance. This improvement in oxidation resistance cannot be expected if the amount of Si added is too small, and it is necessary to exert a deoxidizing effect.
It is particularly preferable to add more than 1.0%.
This improvement in oxidation resistance increases significantly as the amount of Si increases, but when it exceeds 2%, the tendency for improvement in oxidation resistance becomes gradual. Furthermore, if the amount of Si added exceeds 2%, hot workability decreases, and if the steel is kept at a high temperature of 700 to 850° C. for a long time during use, it tends to form a σ phase at grain boundaries and become brittle. Therefore, the upper limit of Si is set to 2%. Mn produces dense scale together with Cr, and is an effective element to prevent scale spalling during heating and cooling, especially when used as a material for mesh belts in heating furnaces that are susceptible to heating and cooling. be. It is also an element that improves hot workability and has an excellent deoxidizing effect. Therefore, in order to exhibit these effects, it is necessary to add at least 0.3% or more. However, if added in excess, the oxidation resistance will be reduced, so the upper limit is set at 2%. C is an effective element for increasing high-temperature strength, refining grain size, and increasing scale adhesion, and for this purpose, it is necessary to add 0.01% or more. However, when the amount of C added increases, the amount of carbides (M ₂₃ C ₆ ) containing Cr increases at the grain boundaries, and along with this, the tendency to cause grain boundary oxidation increases, and the amount of carbides (M ₂₃ C ₆ ) increases. The generation of CO gas impairs hot workability, and there is an increased tendency for CO gas to be generated in the gap between the scale and the base, impairing the adhesion of the scale. Therefore, in order to more reliably prevent the occurrence of such problems, the upper limit of C is set to less than 0.15%. Since B eliminates grain boundary precipitation sites by filling vacancies at grain boundaries, B has the effect of delaying the precipitation of carbides (M ₂₃ C ₆ ) that are a cause of inhibiting hot workability. Therefore, hot workability, particularly workability at relatively low temperatures, is improved. It also has the effect of suppressing the formation of σ phase when held at high temperature for a long time. These effects are observed when added at 0.0005%, but when added in excess of 0.01%, low melting point eutectic is generated at grain boundaries, promoting grain boundary oxidation, resulting in a decrease in oxidation resistance. Therefore, B
shall be in the range of 0.0005 to 0.01%. When Ca, Mg, and REM are added in combination with B, hot workability is significantly improved. These elements are
In addition to exerting a strong desulfurization effect during the steelmaking process, it combines with impurity elements at grain boundaries to form a stable form.
It has the effect of cleaning grain boundaries and improves hot workability, especially on the high temperature side. Therefore, the above B
Together with the effect of adding , it improves hot workability over a wide range from low temperature to high temperature. moreover,
Ca, Mg, and REM significantly improve scale adhesion and contribute to increased oxidation resistance. In other words, these elements form a dense protective film at the boundary between the scale and the base and prevent the movement of C and N, suppressing the production of CO and _N2 gases that cause spalling, and reducing the scale. significantly improves adhesion. On the other hand, if the amount of Ca, Mg, or REM added is too large, a Ni-based metal compound with a low melting point will be formed, which will reduce hot workability, which is undesirable.In addition, excessive addition will cause internal oxidation along grain boundaries. progresses and oxidation resistance is impaired. Therefore, for the above reasons, the amount of Ca is 0.001 to 0.01%, Mg
One or more of these are added in an amount of 0.001 to 0.04% and an amount of REM of 0.005 to 0.05%. By fixing C, Ti, Nb + Ta, Zr, and V prevent the formation of carbides containing Cr (M ₂₃ C ₆ ) at grain boundaries, prevent embrittlement caused by this formation, and Although it is an effective element for preventing grain boundary oxidation along the lines and improving oxidation resistance, excessive addition is not preferable because it promotes the formation of the σ phase. Therefore, Ti, Nb+Ta,
If necessary, one or more of these Zr and V may be added within a range of 0.3% or less. Experimental Example Using a basic electric furnace, ingots having the respective chemical component ratios Nos. 1 to 10 shown in Table 1 were melted. At this time, Ca is Ni-5%Ca alloy, Mg is Ni-5%
Mg alloy and REM were each added as Mitsushi metal.

【table】

[Table] Next, the above ingot was soaked at 1200°C and then rolled and bloomed to form a 90 mm square billet. During this rolling, the temperature at the billet corner portions tends to drop, which tends to reduce workability, but Comparative Alloys 7, 8, and 10 in particular had significant cracking at the corner portions and exhibited low yields. Furthermore, Comparative Alloy 9 had slightly fewer corner cracks than Comparative Alloys 7, 8, and 10. On the other hand, in the alloys 1 to 6 of the present invention, corner cracks did not occur at all. Next, samples were taken from the billet, and test materials of 6.4 mm in diameter and 110 mm in length were cut out for each alloy and subjected to a tensile test using a Greeble type high-speed tensile tester to examine the quality of hot workability. The results are shown in FIG. As is clear from FIG. 1, alloys 1 and 2 of the present invention
All of these materials show particularly high ductility on the low-temperature side, and it was confirmed that mesh belts for heating furnaces, for example, can be easily processed at relatively low temperatures. Almost similar results were obtained for Invention Alloy 3, and it was found that First Invention Alloys 1 to 3 had excellent hot workability. It was also confirmed that the second invention alloys 4 to 6 (Figure 1 shows the results for alloy 4 as a representative) had excellent hot workability. In contrast, Comparative Alloy 7 had the poorest hot workability due to its high Si content. In addition, although Comparative Alloy 9 had improved hot workability due to the addition of B and was the best among Comparative Alloys 7 to 10, it still had considerably poorer hot workability than Invention Alloys 1 to 6. It was confirmed that it was on. Next, we conducted a continuous heating test in the atmosphere (test temperature: 1000°C) and measured the oxidation weight gain to examine the quality of the oxidation resistance. The result is the second
As shown in the figure. As is clear from FIG. 2, the alloys 1 and 2 of the present invention
All exhibited excellent oxidation resistance, with values comparable to Comparative Alloy 7. As mentioned above, Comparative Alloy 7 has poor hot workability, and is therefore not suitable for mesh belts in heating furnaces, which are heat-resistant parts that require a high degree of workability. Furthermore, almost similar results were obtained for Invention Alloy 3, and it was confirmed that All Invention Alloys 1 to 3 had excellent oxidation resistance. In addition, second invention alloys 4 to 6
(Figure 2 shows the results of 4 as a representative) was also confirmed to have excellent oxidation resistance. On the other hand, comparative alloys 8, 9, and 10 all obtained less favorable results in terms of oxidation resistance. Furthermore, we investigated changes in toughness due to long-term aging treatment. The results are shown in Table 2. In this test, a No. 4 test piece (2 mm, V-notch) specified in JIS Z 2202 was prepared, and the impact value was measured using a Sharpie impact tester.

[Table] As is clear from the results shown in Table 2, inventive alloys 1 to 6 and comparative alloys 8 and 9 all have relatively small decreases in toughness, while comparative alloy 7 has a high
Because of the Si content, the structure becomes unstable and the toughness is greatly reduced. Comparative Alloy 10 is high in Cr and low in Ni, so the σ phase is likely to occur, resulting in a large decrease in toughness. In this way, alloys 1 to 6 of the present invention have a lower Si content than comparative alloy 7, and also contain B and Ca.
By containing one or more of Mg and REM, and adding a small amount of one or more of Ti, Nb + Ta, Zr, and V to this, hot workability and oxidation resistance are improved. It has the advantage of being able to improve both toughness and toughness, and exhibiting excellent characteristics as a material for mesh belts in heating furnaces, which are heat-resistant parts that are highly processed, as well as minimizing the decrease in toughness caused by long-term aging treatment. It is equipped with As described above, according to the present invention, it is possible to obtain an alloy that has excellent hot workability, heat resistance, and oxidation resistance, and is particularly suitable as a material for mesh belts of heating furnaces, which are heat-resistant and oxidation-resistant parts that are highly processed. It can bring about very good effects.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between test temperature and area reduction rate using a Greeble-type high-speed tensile tester;
The figure is a graph showing the relationship between retention time and oxidation weight increase in a continuous heating test in the atmosphere.

Claims (1)

[Claims] 1 In weight%, C: 0.01 to less than 0.15%, Si: more than 1.0 to 2%, Mn: 0.3 to 2%, Ni: more than 35 to 45%,
Cr: 18 to less than 21%, B: 0.0005 to 0.01%, and
Ca: 0.001~0.01%, Mg: 0.001~0.04%,
REM: An alloy for a mesh belt of a heating furnace, characterized in that it contains one or more of 0.005 to 0.05%, and the balance consists of Fe and unavoidable impurities. 2 In weight%, C: 0.01 to less than 0.15%, Si: more than 1.0 to 2%, Mn: 0.3 to 2%, Ni: more than 35 to 45%,
Cr: 18 to less than 21%, B: 0.0005 to 0.01%, and
Ca: 0.001~0.01%, Mg: 0.001~0.04%,
REM: Contains one or more of 0.005-0.05%, Ti: 0.3% or less, Nb + Ta: 0.3
% or less, Zr: 0.3% or less, V: 0.3% or less, and the balance is Fe and inevitable impurities.