JPH05463B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention is suitable for skid rails, skid buttons, etc. that are attached to the upper surface of skid pipes provided as hearths in steel heating furnaces, etc. to directly support materials to be heated, and when applied to these. The present invention relates to a heat-resistant alloy for hearth members that exhibits excellent oxidation resistance and impact cracking resistance. <Prior art and its problems> Currently, heavy materials are processed at relatively high temperatures (1100
The mainstream heating furnaces for steel materials that require continuous heating to temperatures up to 1,250°C (approx. A support structure as illustrated in FIGS. 1 and 2 is employed in the section. That is, FIG. 1 shows a skid button 4 attached via a pedestal 3 to the top surface of a water cooling pipe 2 sealed with a heat insulating material 1 to prevent the adverse effects from the temperature inside the furnace, and FIG. A skid rail 6 is shown attached to the upper surface of a water cooling pipe 2 sealed with a material 1 via a support 5. Here, in any of the drawings, the reference numeral 7
indicates a heated material such as a slab. It goes without saying that the water cooling pipe 2 is for protecting the skid button 4 or the skid rail 6 from a high temperature atmosphere. As is clear from these drawings, the skid buttons and skid rails used as the hearth material of a heating furnace must support the weight of the material to be heated in a high-temperature atmosphere, and are subject to shocks caused by the movement of the material to be heated. Since it is also placed at the bottom, it is required to have sufficient strength and oxidation resistance at high temperatures. Therefore, conventionally, the hearth material
HS21 (American standard) material and UMCO50 (Belgian standard)
Co-based heat-resistant alloys such as steel, or heat-resistant cast steel such as SCH13 (JIS standard material, commonly used as hearth material for heating furnaces) were used. However, it has been pointed out that these conventional heat-resistant alloys used for hearth support members are susceptible to cracking and cracking due to thermal shock due to temperature fluctuations and mechanical shock due to load fluctuations, and also have poor strength. The limit temperature for use is approximately 1150°C, and when used in a higher temperature atmosphere, it is necessary to cool the member by means such as water cooling.
For this reason, current furnaces for heating steel materials have a structure in which the hearth components are cooled from the bottom, but this "cooling of the hearth components" can also cause skid marks on the heated materials. Therefore, it became necessary to take extra measures to prevent skid marks. Furthermore, even if hearth members are cooled from the bottom, the temperature at the top inevitably rises, and conventional hearth members made of heat-resistant alloys cannot prevent "cracking" or "settling" at the top. The problem with this issue also remained unresolved. For this reason, the inventors of the present invention have developed a method to first prevent "impact cracking" and "settling" of hearth members and to prevent skid marks on heated materials. We proposed a composite material for hearth parts in which ceramic particles are dispersed (Japanese Patent Application Laid-Open No. 60-200948, JP-A No. 61-41734).
issue). The above composite material proposed by the present inventors not only has excellent high-temperature strength and impact cracking resistance, but also has an extremely high heat insulation effect and has a thermal conductivity that is about 1/3 that of the matrix material alone. Therefore, even in the case of high-temperature heating when the material to be heated is steel, the temperature of the contact area with the material to be heated increases by about 40℃ compared to when using a hearth member made of a single metal. Therefore, it was highly effective in reducing skid marks. However, recent trends in the operation of heating furnaces indicate that the furnace temperature
High-temperature heating of 1250 to 1300°C is increasingly being carried out, and hearth members (supporting members for heated materials)
It is not uncommon for temperatures to reach over 1200℃,
At such high temperatures, even if the ceramic particle dispersed composite material proposed above is used, there is a concern that the strength will decrease and deformation will occur, and further improvement in impact cracking resistance is desired. I'm getting used to it. Furthermore, even when ceramic particle dispersed composites are used, the higher the amount of Co as a component of the matrix material, the better the compression creep resistance, but since Co is an expensive element,
There was a desire for an inexpensive matrix material with as little Co as possible. Therefore, the furnace temperature
Development of an inexpensive material for hearth components that maintains high strength and excellent impact cracking resistance even under severe operating temperatures of 1250 to 1300°C, and that can reduce skid marks without requiring excessive cooling. The current situation was that it was an urgent matter. <Means for Solving the Problems> From the above-mentioned viewpoints, the present inventors have developed a heat-resistant material for hearth members that exhibits excellent oxidation resistance, impact resistance, and strength that are sufficiently satisfactory even under high-temperature operation. In the course of this research, the inventors have proposed the above-mentioned ceramic particles, which have significantly superior properties than conventional materials for use as a hearth material for heating furnaces. It goes without saying that the dispersed ceramic particles greatly contribute to the high-temperature strength and impact cracking resistance of the "dispersed composite material," but the characteristics of the matrix material also have an extremely large influence, and the In order to further improve the above properties of particle-dispersed composites, it is absolutely necessary to develop matrix materials with even better high-temperature strength, oxidation resistance, and impact cracking resistance.'' Therefore, we are focusing on the relatively good high-temperature strength, oxidation resistance, and corrosion resistance of Co-based heat-resistant alloys, as well as further improving the strength of the alloys in high-temperature ranges and preventing cracking caused by thermal shock and mechanical shock. As a result of repeated research on ways to prevent this, we have come to the knowledge shown in (a) to (d) below. (a) This is a particular problem when used as a hearth component.
Impact cracking in Co-based heat-resistant alloys is caused by carbides, σ phase,
(b) However, this is largely due to the precipitation of intermetallic compounds, and it is essential to suppress these precipitations in order to improve the properties of Co-based heat-resistant alloys as hearth components. Reducing the amounts of C, Si, and Mn in the alloy is effective in preventing the precipitation of carbides and σ phase in Co-based heat-resistant alloys, and the above objectives can be fully achieved by suppressing the content of these elements below specific values. In addition, reducing the amounts of Si, Cr, Mo, and Mn is effective in suppressing the precipitation of intermetallic compounds in high-temperature ranges. Reducing the amounts of C, Si, Si, and Mn in the alloy has a very significant effect on suppressing the precipitation of carbides, σ phase, and intermetallic compounds without adversely affecting properties such as high temperature strength and oxidation resistance of the alloy. (d) By reducing the amounts of C, Si, and Mn in a Co-based heat-resistant alloy to below specific values, and carefully adjusting other components within specific ranges, oxidation resistance, high-temperature corrosion resistance, and high-temperature resistance can be improved. A heat-resistant alloy with excellent performance as a hearth member with good compressive creep strength and impact cracking resistance can be obtained, and when this is applied as a matrix (base material) of a ceramic particle dispersed composite material, it can be heated at temperatures of 1200 to 1300°C. It exhibits sufficiently excellent oxidation resistance, impact cracking resistance, and high-temperature compression creep strength even at moderately high temperatures.
Moreover, it is possible to obtain high-performance heat resistance for hearth members with good heat insulation properties. This invention was made based on the above knowledge, and it is based on the following: ``A heat-resistant alloy for a hearth member of a heating furnace, containing C: 0.1% or less (hereinafter, % representing the component ratio is % by weight); Si: 0.8% or less, Mn: 0.8% or less, Cr: 25-30%, Ni: 20-30%, Mo: 0.5-2%, Fe: 10-20%, P: 0.04% or less, S: 0.04% By having the following properties and the remainder being substantially made of Co, it not only has excellent high-temperature compressive strength, oxidation resistance, and corrosion resistance, but also has sufficient resistance to thermal shock and mechanical shock in high-temperature ranges. It also has impact cracking resistance that can withstand high temperatures, and has properties that can further improve its performance when applied as a matrix for composite materials for ceramic particle dispersion hearth components. It has the following. The reason why the proportions of each component in the heat-resistant alloy for hearth members of the present invention are numerically limited as described above is as follows. (a) C The C component has the effect of improving the creep strength of the alloy, but if its content exceeds 0.1%, it will form carbides and cause the alloy to become brittle, making it particularly disadvantageous as a matrix (material) material. Therefore, the C content was set at 0.1% or less. In addition, in the alloy composition according to the present invention, the effect of improving creep strength is sufficiently recognized even when the C content is extremely small. (b) Si Si element is a component that deoxidizes alloys and imparts oxidation resistance, but it is an important element that needs to be reduced as much as possible because if added in large amounts, it will form intermetallic compounds and cause a decrease in toughness. It is. Therefore, the upper limit is set at 0.8%, which is an acceptable amount to prevent impact cracking in high temperature ranges.
In particular, it was stipulated to be regulated below that value, but Si
The decrease in oxidation resistance that may occur due to a decrease in the content can be effectively avoided by carefully adjusting the alloy composition within the range defined in this invention. (c) Mn Mn is an effective component from the viewpoint of deoxidizing agent and desulfurizing agent for alloys, but its content is 0.8
The Mn content was limited to 0.8% or less since it would have a negative effect on high temperature strength if it exceeded 0.8%. (d) Cr Cr is an essential component to ensure good oxidation properties in the alloy, and is necessary to maintain sufficient heat resistance.
It is necessary to contain 25% or more, but since containing more than 30% will lead to deterioration of toughness, the Cr content is set at 25 to 30%. (e) Ni The Ni component has the effect of stabilizing the austenite in the alloy and ensuring oxidation resistance, but if its content is less than 20%, the desired effect cannot be obtained, especially when the Si content is However, the alloy system according to the invention causes considerable deterioration in oxidation resistance. On the other hand, the Ni content was limited to 20 to 30% because the oxidation resistance did not improve further even if the Ni content exceeded 30%. (f) Mo The Mo component has the effect of improving the high-temperature strength of the alloy, but if its content is less than 0.5%, the desired effect will not be obtained, while if it is contained in excess of 2%, the toughness will be reduced. There is a concern that this may have an adverse effect, especially when used as a matrix material for dispersing and compounding ceramic particles, as cracking may occur due to a decrease in toughness.
The Mo content was set at 0.5 to 2%. (g) Fe The Fe component has the effect of improving the high-temperature compression creep strength of the alloy, and is necessary to ensure the bonding properties when ceramic particles are dispersed and composited. If it is less than %, the desired effect cannot be obtained from the above action; on the other hand,
The Fe content was set at 10 to 20% because the above effects did not improve significantly even if the Fe content exceeded 20%. (h) P and S These are both impurity elements that are inevitably mixed in, and if any of them is contained in excess of 0.04%, it will have a negative effect on the strength, weldability, and toughness of the alloy. Each content 0.04%
Limited to the following. Note that the heat-resistant alloy of the present invention can be manufactured by melting and casting means, similar to conventional Co-based heat-resistant alloys. When producing a ceramic particle-dispersed composite material using the alloy as a matrix, it is desirable to employ the following method. That is, (i) As shown in FIG. 3, a mixture of the heat-resistant alloy powder and ceramic particles according to the present invention is put into a crucible 8 made of alumina or the like, and subjected to high frequency heating, etc. (the symbols in FIG. 3) 9 indicates a high-frequency induction coil), when the heat-resistant alloy is melted, the gap between the ceramic particles is sufficiently filled with the molten alloy by pressurizing it with a pressure piston 10 also made of alumina, and then the molten alloy is cooled. How to coagulate. (ii) An opening 11 at the bottom as shown in Figure 4.
and a compartment 13 having a gas venting hole 12 in the upper part is placed inside the refractory container 14,
First, the ceramic particles 15 are charged into the compartment 13, and then the heat-resistant alloy powder according to the present invention is charged around the compartment 13, and then these are heated to melt the heat-resistant alloy powder. to penetrate between the ceramic particles in the compartment 13 through the opening 11,
The method is then cooled and solidified. By the way, when a hearth member of a heating furnace is constructed from a ceramic particle-dispersed composite material whose matrix is the heat-resistant alloy according to the present invention, alumina (Al ₂ O ₃ ) is used as the ceramic to be uniformly dispersed.
High purity products are suitable, but other 3Al ₂ O ₃ and
Oxide ceramics such as 2SiO ₂ or ZrO ₂ ,
Carbide ceramics such as SiC or TiC, sialon, etc. can also be used. The average particle size of the particles is preferably 5 mmφ or less, and the amount incorporated into the matrix material is preferably about 50 to 75% by volume. Further, FIG. 5 is a schematic vertical cross-sectional view showing an example of a skid button for a heating furnace made of an alumina particle dispersed composite material, in which reference numeral 16 indicates alumina particles, 17 indicates a ceramic foam, and 18 indicates the present invention. A matrix (base material) made of such a heat-resistant alloy is shown. Next, the present invention will be specifically explained with reference to Examples. <Example> First, a Co-based heat-resistant alloy having the composition shown in Table 1 was melted by a conventional method, and alumina particles shown in Table 2 were prepared. Next, some of these heat-resistant alloys have a diameter of 90 mm.
A skid button with a length of 100 mm was cast, and the remaining heat-resistant alloy was cast using the method shown in Figure 4 [(ii) above].
Using the method described above, the alumina particles were uniformly dispersed and molded to produce skid buttons made of a ceramic (alumina) dispersed composite material of the same size.
The alumina particle filling rate of this composite material is approximately 60.
It was %. Next, each of these skid buttons should be acid resistant.

【table】

【table】

【table】

[Table] In addition to investigating the chemical resistance, compressive creep strength was measured using test pieces cut from skid buttons. In addition, "oxidation resistance" is evaluated by measuring the oxidation loss or oxidation gain when the skid button is heated to 1300℃ in the air and held for 40 hours, while "compressive creep strength" is evaluated at 1200℃, 1250℃ and oxidation gain. A stress of 2 Kgf/mm ² was applied to the test piece at each temperature of 1300°C and the amount of compressive creep strain was compared and evaluated after being held for 3 hours. Note that "oxidation weight loss" or "oxidation weight gain" refers to the weight change after a test piece is held in a heating furnace for a certain period of time and then taken out. That is, when a test piece is oxidized in a heating furnace and scale is formed on its surface, the weight of the test piece generally increases, and this is called "oxidation weight gain." On the other hand, when the scale generated in the heating furnace cracks and flakes off from the surface of the test piece during scale growth, the weight of the test piece decreases, and this is called "oxidation loss." A test piece in which an increase in weight due to oxidation was observed had no scale flaking off, and a test piece in which a weight loss due to oxidation was observed had scale flaking off.
Of course, it is possible that more scale will be generated after the scale has fallen off. In any case, a heat-resistant alloy with less oxidation loss or oxidation gain has excellent oxidation resistance. In this way, oxidation loss or weight gain can be a practical index that can very easily and accurately evaluate the oxidation resistance of a heat-resistant alloy in a heating furnace. We decided to conduct an evaluation. These results are shown in Table 3. From the results shown in Table 3, it is clear that
Co-based heat-resistant alloys are not only comparable to conventional alloys in terms of oxidation resistance and high-temperature compression creep strength even when used alone as skid buttons in heating furnaces, but also in the matrix of composite skid buttons in which alumina particles are dispersed. When used as a material (base material), it is clear that the resulting skid button exhibits superior oxidation resistance and high-temperature compression creep strength, surpassing conventional materials, and has sufficient strength even at high temperatures of 1300℃. I understand that. In particular, alloys E to H of the present invention have superior oxidation resistance compared to conventional alloy B. Furthermore, even if the amount of Co is reduced by increasing the amount of Ni and Fe, the high-temperature strength is not impaired, and therefore cost reduction is achieved by saving expensive Co. On the other hand, in the case of a Co-based alloy whose chemical composition does not meet the conditions specified in the present invention, even if it is used as a matrix of a composite material in which alumina particles are dispersed, the resulting skid button will be It can be confirmed that the performance expected of ceramic composite materials is not fully satisfied. Separately, the strength against mechanical impact at high temperatures was investigated for "materials f and j to which the alloy of the present invention was applied". The impact strength was measured using a drop weight test in which 50 specimens were prepared for each specimen and a 5 kg weight was dropped from a height of 4 meters under heating at 1200°C. In addition, the impact strength evaluation was performed based on the drop weight test results of a total of [50 specimens/1 material] by subjecting 10 specimens of the same material to each of 5 types of impact frequency tests from 1 to 5 times. Ivy. As a result, as shown in Figure 6, the "crack occurrence rate" calculated using the formula: crack occurrence rate (%) = number of cracked test specimens/10 specimens x 100 is 20% even after 5 impacts. On the other hand, when the same test was performed on the conventional alloy skid button B, the "crack occurrence rate" reached 50% even after about 5 impacts. <Effects of the Invention> As explained above, according to the present invention, it is possible to provide a low-cost heat-resistant alloy for hearth members having extremely excellent heat-resistant properties, and furthermore, it is possible to provide a ceramic particle composite matrix (base material). Sufficient strength even in the high temperature range of 1300℃ when used as a
A hearth member that exhibits oxidation resistance and impact cracking resistance, has excellent heat insulation properties, and is highly effective in suppressing skid marks has been realized, making it possible to further improve the performance and durability of heating furnaces. This brings about extremely useful industrial effects.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of essential parts showing an example of a hearth support structure of a heating furnace for heating steel materials, FIG. 1a is a front view thereof, and FIG. 1b is a cross-sectional view thereof. FIG. 2 is a schematic diagram of main parts showing another example of a hearth support structure of a heating furnace for heating steel materials. FIG. 3 is a schematic diagram showing an example of a method for manufacturing a ceramic particle composite material. FIG. 4 is a schematic diagram showing another example of a method for manufacturing a ceramic particle composite material. FIG. 5 is a schematic vertical cross-sectional view showing an example of a skid button for a heating furnace made of an alumina particle dispersed composite material. FIG. 6 is a graph showing the results of investigating the influence of the number of impacts on the crack occurrence rate for conventional materials and the alloy of the present invention. In the drawing, 1...Insulation material, 2...Water cooling pipe, 3...Pedestal, 4...Skid button, 5...
Support stand, 6... skid rail, 7... material to be heated (slab etc.), 8... crucible, 9... high frequency heating coil, 10... pressure piston, 11... opening, 1
2... Gas vent hole, 13... Compartment, 14... Refractory container, 15... Ceramic particles, 16...
Alumina particles, 17... Ceramic foam, 1
8...Heat-resistant alloy matrix.

Claims (1)

[Claims] 1 Containing chemical components: C: 0.1% or less, Si: 0.8% or less, Mn: 0.8% or less, Cr: 25-30%, Ni: 20-30%, Mo: 0.5-2%, Oxidation resistance and impact cracking resistance characterized by Fe: 10 to 20%, P: 0.04% or less, S: 0.04% or less (weight %), and the balance essentially consists of Co. A heat-resistant alloy for hearth parts with excellent properties. 2. The heat-resistant alloy for hearth members having excellent oxidation resistance and impact cracking resistance according to claim 1, which is used as a base material for particle-dispersed composite hearth members in which ceramic particles are uniformly dispersed.