High-temperature-resistant low-cost pad iron for heat treatment furnace and preparation method thereof

Abstract

The present application belongs to the technical field of heat treatment equipment, and particularly relates to a high-temperature-resistant low-cost backing iron for heat treatment furnace and a preparation method thereof. The high-temperature-resistant low-cost backing iron for heat treatment furnace in the technical scheme of the present application comprises the following components in mass percentage: C 0.35-0.50%, Si 2.0-3.0%, Mn≤0.7%, Cr 8.0-10.0%, and the balance is inevitable impurities and iron elements. The preparation method comprises manufacturing a backing iron mold, smelting raw materials, deoxidizing treatment, tapping, pouring and polishing products. Through excellent element content and proportioning, combined with an effective preparation method, the backing iron for heat treatment furnace with good high-temperature resistance is obtained.

Description

Technical Field

[0001] This invention belongs to the technical field of heat treatment equipment, specifically relating to a high-temperature resistant, low-cost heat treatment furnace pad and its preparation method. Background Technology

[0002] A heat treatment furnace is an electric or fuel-fired furnace used for heating furnace materials for heat treatment. Common heat treatment furnaces include box-type resistance furnaces, pit-type resistance furnaces, gas carburizing furnaces, and salt bath furnaces. Heat treatment furnaces have a wide temperature range and require uniform furnace temperature to avoid excessively high local temperatures. At the same time, strict furnace temperature control is required. Typically, the workpiece is placed in the furnace for high-temperature heat treatment.

[0003] Furnace shims are an indispensable and important component in heat treatment furnaces, frequently subjected to high temperatures, and are considered consumable parts. Ordinary materials have poor high-temperature resistance, are easily oxidized, and are prone to breakage after prolonged exposure to extreme temperatures. Currently, furnace shims are generally made of high-nickel, high-chromium 2520 austenitic heat-resistant steel (chemical composition: carbon C: ≤0.08, silicon Si: ≤1.00, manganese Mn: ≤2.00, sulfur S: ≤0.030, phosphorus P: ≤0.035, chromium Cr: 24.00~26.00, nickel Ni: 19.00~22.00), which is relatively expensive. Although they can withstand high-temperature heating to a certain extent, their high coefficient of thermal expansion, low thermal conductivity, and large heat absorption lead to decarburization and deformation. Deformation and burn-out of the shims cause workpieces to become unstable when placed on them, deforming along with the workpieces during heating. This is a major cause of workpiece deformation during heat treatment, so the shims must be replaced after a period of use. Summary of the Invention

[0004] The purpose of this invention is to address the above-mentioned technical problems by providing a high-temperature resistant, low-cost heat treatment furnace pad that has good high-temperature resistance and low production cost.

[0005] The high-temperature resistant, low-cost heat treatment furnace pad iron in the technical solution of this invention comprises the following components by mass percentage: C 0.35-0.50%, Si 2.0-3.0%, Mn≤0.7%, Cr 8.0-10.0%, with the balance being unavoidable impurities and iron.

[0006] Carbon can combine with alloying elements to form dispersed carbides, which precipitate and pin dislocations within the grains to strengthen the matrix, thereby enhancing and maintaining the material's performance over a long period. However, excessive carbon content can lead to a decrease in high-temperature oxidation resistance and mechanical properties.

[0007] Silicon can form a silicon-rich oxide layer. Under high temperature conditions, it combines with chromium and oxygen on the alloy surface to form an olivine structure. Its special lattice structure surrounds chromium atoms in a near-planar banded structure, which is conducive to the outward diffusion of chromium and at the same time hinders the diffusion of elements such as iron. The synergistic effect of chromium and iron enhances the high-temperature oxidation resistance and corrosion resistance of the alloy material.

[0008] Manganese typically accumulates on the surface of alloy materials at high temperatures, which helps prevent internal oxidation of the alloy and reduces cracks in the anti-oxidation layer caused by uneven stress due to internal oxidation. This is beneficial to the long-term high-temperature oxidation resistance of the alloy material. At the same time, it can fix harmful elements such as sulfur in the alloy material during the smelting process, thereby effectively reducing the tendency of heat-resistant steel to crack in subsequent forming processes, improving the yield of the product and reducing costs. In addition, the addition of manganese also improves the impact toughness of heat-resistant steel.

[0009] The present invention also provides a method for preparing the above-mentioned high-temperature resistant and low-cost heat treatment furnace pad, including manufacturing pad mold, raw material smelting, deoxidation treatment, tapping, casting and polishing the product.

[0010] Furthermore, the steps for manufacturing the pad mold include: resin sand molding, applying coating and then assembling the mold, and then baking at 150-200℃ for 2-3 hours.

[0011] Furthermore, the smelting temperature is 1550–1620℃.

[0012] Furthermore, after smelting, 0.08–0.1% of refining agent by weight of the molten steel is added.

[0013] Furthermore, during the deoxidation process, 0.08–0.1% of deoxidizer by weight of the molten steel is added, followed by nitrogen gas being introduced for tumbling deoxidation for 2–10 minutes.

[0014] Furthermore, the deoxidizer is one or more of aluminum wire, calcium silicon, calcium aluminum silicon, manganese, and rare earth silicon.

[0015] Furthermore, the deoxidizer is a mixture of silicon, aluminum, barium, calcium, and rare earth silicon in a mass ratio of 1–9:1–9. When rare earth silicon is used as a deoxidizer, it transforms sharp-angled oxides into spherical oxides, which can act as non-spontaneous crystallization nuclei to refine the grains. At the same time, it can also prevent brittle fractures in castings. When used in combination with silicon, aluminum, barium, and calcium, it can effectively reduce the oxygen content and improve the mechanical properties of the alloy material.

[0016] Furthermore, the tapping temperature is 1600–1620℃.

[0017] Furthermore, the iron mold is baked at 800-900℃ for 0.5-2.0h before pouring.

[0018] Furthermore, nitrogen is used for refining, and pouring begins at a temperature of 1560–1580°C for 30–70 seconds.

[0019] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0020] (1) This invention obtains heat treatment furnace pads with good high-temperature resistance by using excellent element content and ratio, combined with an effective preparation method.

[0021] (2) An appropriate amount of carbon can effectively strengthen the matrix;

[0022] (3) The appropriate amounts of silicon, chromium and iron work synergistically to enhance the high-temperature oxidation resistance and corrosion resistance of the alloy material.

[0023] (4) The appropriate amount of manganese element improves the long-term high-temperature oxidation resistance and impact toughness of alloy materials, while reducing the hot cracking tendency of heat-resistant steel and improving the yield of products.

[0024] (5) The preparation method of the high-temperature resistant and low-cost heat treatment furnace pad iron in the technical solution of the present invention is simple, efficient, easy to operate and low in cost. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of the pad mold in Example 1;

[0026] Figure 2 This is a cross-sectional view of the pad mold in Example 1;

[0027] Figure 3 This is a schematic diagram of the structure of the pad mold in Example 2;

[0028] Figure 4 This is a cross-sectional view of the pad mold in Example 2. Detailed Implementation

[0029] The technical solution of the present invention will be further described and illustrated below with reference to specific embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of helping to understand the present invention and are not intended to limit the specific scope of the present invention. Furthermore, the accompanying drawings used herein are merely for better illustrating the content disclosed in the present invention and do not limit the scope of protection. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used materials in the art, and the methods used in the embodiments are all conventional methods in the art.

[0030] Example 1

[0031] The method for preparing the shims for the heat treatment furnace in this embodiment includes the following steps:

[0032] (1) Select a suitable sand box, use resin sand to mold, make the cavity, brush the paint, close the box, and bake with 180° hot air for 2 hours to obtain the pad mold.

[0033] (2) The medium-frequency furnace is used to smelt the steel at 1590℃ with an element ratio of C 0.35%, Si 2.5%, Mn 0.6%, Cr 9.0%, and the balance being iron. 0.1% of the steel mass of the refining agent is added for refining and slag removal.

[0034] (3) Add 0.08% of deoxidizer (silicon, aluminum, barium, calcium and rare earth silicon in a mass ratio of 8:2) to the molten steel, pass nitrogen gas to roll and deoxidize for 5 minutes, bake the shim mold at 800℃ for 10 hours, pour the molten steel into the shim mold, tap the steel at 1620℃, use nitrogen gas to refine and cool it down, and pour it at 1570℃ for 50 seconds.

[0035] (4) After cooling, remove the casting, grind away the gates and risers to obtain the following: Figure 1-2 The heat treatment furnace with the structure shown uses a shim.

[0036] Example 2

[0037] The method for preparing the shims for the heat treatment furnace in this embodiment includes the following steps:

[0038] (1) Select a suitable sand box, use resin sand to mold, make the cavity, brush the paint, close the box, and bake with 180° hot air for 2 hours to obtain the pad mold.

[0039] (2) The medium-frequency furnace is used to smelt the steel at 1520℃ with an element ratio of C 0.45%, Si 3.0%, Mn 0.5%, Cr 8.5%, and the balance being iron. 0.08% of the steel mass of the refining agent is added for refining and slag removal.

[0040] (3) Add 0.08% of deoxidizer (silicon, aluminum, barium, calcium and rare earth silicon in a mass ratio of 7:3) to the molten steel, purge with nitrogen and roll for 8 minutes to deoxidize, bake the shim mold at 800℃ for 10 hours, pour the molten steel into the shim mold, tap the steel at 1620℃ and then pour it at 1570℃ for 50 seconds.

[0041] (4) After cooling, remove the casting, grind away the gates and risers to obtain the following: Figure 3-4 The heat treatment furnace with the structure shown uses a shim.

[0042] Example 3

[0043] The method for preparing the shims for the heat treatment furnace in this embodiment includes the following steps:

[0044] (1) Select a suitable sand box, use resin sand to mold, make the cavity, brush the paint, close the box, and bake with 180° hot air for 2 hours to obtain the pad mold.

[0045] (2) The medium-frequency furnace is used to smelt the steel at 1580℃ with an element ratio of C 0.35%, Si 2.5%, Mn 0.6%, Cr 9.0%, and the balance being iron. 0.08% of the steel mass of the refining agent is added for refining and slag removal.

[0046] (3) The shim mold is baked at 800℃ for 10 hours, the molten steel is poured into the shim mold, the steel is tapped at 1620℃ and then poured at 1570℃ for 50 seconds.

[0047] (4) After cooling, remove the casting, grind away the gates and risers to obtain the following: Figure 1-2 The heat treatment furnace with the structure shown uses a shim.

[0048] Example 4

[0049] The only difference between this embodiment and embodiment 1 is that in step (3), 0.08% by weight of silicon-aluminum-barium-calcium is added as a deoxidizer, and nitrogen gas is introduced to tumble and deoxidize for 5 minutes.

[0050] Example 5

[0051] The only difference between this embodiment and embodiment 1 is that in step (3), 0.08% of rare earth silicon by mass of molten steel is added as a deoxidizer, and nitrogen gas is introduced to tumble and deoxidize for 5 minutes.

[0052] Comparative Example 1

[0053] The only difference between this comparative example and Example 1 is that in step (2), an intermediate frequency furnace is used to smelt the material at 1580°C with an element ratio of C 0.2%, Si 2.5%, Mn 0.6%, Cr 9.0%, and the balance being iron.

[0054] Comparative Example 2

[0055] The only difference between this comparative example and Example 1 is that in step (2), an intermediate frequency furnace is used to smelt the material at 1580°C with an element ratio of C 0.60%, Si 2.5%, Mn 0.6%, Cr 9.0%, and the balance being iron.

[0056] Comparative Example 3

[0057] The only difference between this comparative example and Example 1 is that in step (2), a medium-frequency furnace is used to smelt the sample at 1580°C with an element ratio of 0.35% C, 1.0% Si, 0.6% Mn, 9.0% Cr, and the balance being iron.

[0058] Comparative Example 4

[0059] The only difference between this comparative example and Example 1 is that in step (2), an intermediate frequency furnace is used to smelt the sample at 1580°C with an element ratio of C 0.35%, Si 4.0%, Mn 0.6%, Cr 9.0%, and the balance being iron.

[0060] Comparative Example 5

[0061] The only difference between this comparative example and Example 1 is that in step (2), a medium-frequency furnace is used to smelt the sample at 1580°C with an element ratio of C 0.35%, Si 2.5%, Mn 0.8%, Cr 9.0%, and the balance being iron.

[0062] Comparative Example 6

[0063] The only difference between this comparative example and Example 1 is that in step (2), an intermediate frequency furnace is used to smelt the material at 1580°C with an element ratio of 0.35% C, 2.5% Si, 0.6% Mn, 7.0% Cr, and the balance being iron.

[0064] Comparative Example 7

[0065] The only difference between this comparative example and Example 1 is that in step (2), an intermediate frequency furnace is used to smelt the sample at 1580°C with an element ratio of 0.35% C, 2.5% Si, 0.6% Mn, 11.0% Cr, and the balance being iron.

[0066] The mechanical properties of the heat treatment furnace pads obtained in the above embodiments and comparative examples were tested after heat treatment (oil cooling at 1030℃ followed by oil cooling at 720℃). The test results are shown in Table 1.

[0067] Table 1 Performance Data of Pads for Heat Treatment Furnaces

[0068]

[0069]

[0070] Examples 1-2 yielded heat treatment furnace pads with good high-temperature resistance and mechanical properties. Example 3, lacking deoxidation, had excessively high oxygen content, easily generating porosity and leading to a decrease in the mechanical strength of the resulting heat treatment furnace pads. Examples 4-5 used a single deoxidizer, reducing the synergistic deoxidation effect, increasing the oxygen content in the system, and decreasing mechanical and high-temperature resistance properties. Comparative Example 1 used too little carbon, weakening the strengthening effect on the matrix, increasing the toughness of the resulting heat treatment furnace pads, but decreasing tensile and yield strength. Comparative Example 2 used too much carbon, causing the matrix to become brittle, significantly reducing elongation, and making it prone to fracture. Comparative Example 3 used too little silicon, reducing the product's thermal strength. Comparative Example 4 used too much silicon, causing the heat treatment furnace pads to become brittle and significantly reducing elongation. Comparative Example 5 used too much manganese, increasing tensile strength but decreasing ductility and toughness. Comparative Example 6 used too little chromium, resulting in poor high-temperature resistance and decreased high-temperature strength of the heat treatment furnace pads. Comparative Example 7 used too much chromium, causing the matrix to become brittle and poor high-temperature resistance.

[0071] Finally, it should be noted that the specific embodiments described herein are merely illustrative of the spirit of the invention and are not intended to limit the implementation of the invention. Those skilled in the art can make various modifications or additions to the described embodiments or use similar methods to replace them; it is neither necessary nor possible to exemplify all embodiments here. However, these obvious variations or modifications derived from the essential spirit of the invention still fall within the scope of protection of the invention, and interpreting them as any additional limitation would contradict the spirit of the invention.

Claims

1. A high-temperature resistant, low-cost shim for a heat treatment furnace, characterized in that, The composition includes the following components by mass percentage: C 0.35~0.45%, Si 2.5~3.0%, Mn≤0.7%, Cr 8.0~9.0%, with the balance being unavoidable impurities and iron. The method for preparing the high-temperature resistant, low-cost heat treatment furnace pad includes manufacturing pad molds, raw material smelting, deoxidation treatment, tapping, casting, and polishing the product. During deoxidation, 0.08-0.1% of deoxidizer by weight of molten steel is added, followed by nitrogen gas and tumbling deoxidation for 2-10 minutes. The deoxidizer is a mixture of silicon, aluminum, barium, calcium and rare earth silicon in a mass ratio of 1-9:1-9.

2. The high-temperature resistant, low-cost heat treatment furnace pad according to claim 1, characterized in that, The steps for manufacturing the pad mold include: resin sand molding, applying coating, assembling the mold, and then baking at 150~200℃ for 2~3 hours.

3. The high-temperature resistant, low-cost heat treatment furnace pad according to claim 1, characterized in that, The raw material melting temperature is 1550~1620℃.

4. The high-temperature resistant, low-cost heat treatment furnace pad according to claim 3, characterized in that, After the raw materials are smelted, 0.08~0.1% of refining agent by weight of molten steel is added.

5. The high-temperature resistant, low-cost heat treatment furnace pad according to claim 1, characterized in that, Before pouring, the shim mold is baked at 800~900℃ for 0.5~2.0h.

6. The high-temperature resistant, low-cost heat treatment furnace pad according to claim 1, characterized in that, Nitrogen gas is used for refining, and pouring begins at a temperature of 1560~1580℃, with a pouring time of 30~70s.

Images