Manufacturing method of iron pot and iron pot

Abstract

The application relates to the technical field of pots, and particularly provides a manufacturing method of an iron pot and the iron pot. The manufacturing method comprises the following steps: providing an iron pot blank, turning the surface of the iron pot blank to form a rough surface; heating the iron pot blank with the rough surface; combining a prefabricated complex bottom piece to the rough surface through high-pressure pressing to obtain a complex bottom semi-finished product with a complex bottom structure; and performing nitriding treatment on the complex bottom semi-finished product at a temperature lower than 520 DEG C to obtain an iron pot finished product. The manufacturing method can make the iron pot have excellent heat conduction and magnetic conduction performance and stainless steel-grade rust prevention ability, and can also eliminate the complicated maintenance of a traditional iron pot, thereby significantly prolonging the service life of the product.

Description

Technical Field

[0001] This application belongs to the field of cookware technology, specifically relating to a method for manufacturing an iron pot and the iron pot itself. Background Technology

[0002] Iron woks are a widely used cookware in Chinese cooking, known for their excellent heat conductivity and ability to enhance the flavor of stir-fries. To improve their compatibility with induction cooktops and their rust resistance, some iron wok products feature a multi-layered bottom structure combined with surface nitriding treatment, aiming to balance heat conductivity, magnetic conductivity, and corrosion resistance.

[0003] However, the existing methods for manufacturing iron pots have the following drawbacks: First, the bonding strength between the bottom layer and the pot body is insufficient, making it easy for the bottom to detach; second, the aluminum layer in the bottom layer structure is prone to softening or melting, causing the bottom of the pot to deform and the bottom layer to fall off; third, the existing process cannot guarantee the rust-proof performance of the iron pot while ensuring the stability of the bottom layer structure, which makes the iron pot require frequent maintenance and has a short service life. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this application proposes a method for manufacturing an iron pot and an iron pot in general, which is achieved through the following technical solution:

[0005] The first aspect of this application provides a method for manufacturing an iron pot, comprising: A cast iron pot blank is provided, and the surface of the cast iron pot blank is machined to form a rough surface; The iron pot blank with the rough surface is heated; The pre-made composite bottom sheet is bonded to the rough surface under high pressure to obtain a composite bottom semi-finished product with a composite bottom structure; The semi-finished product with the composite bottom is subjected to nitriding treatment at a temperature below 520°C to obtain the finished iron pot.

[0006] In one specific embodiment, the roughness of the rough surface is in the range of 1.2 μm to 4.0 μm.

[0007] In one specific embodiment, heating the iron pot blank with the roughened surface includes: The iron pot blank with the rough surface is heated to 420℃~450℃ by induction heating and kept at that temperature for 25~30 minutes, while the heating uniformity is controlled within ±3℃.

[0008] In one specific embodiment, the backing sheet is a multi-layer composite structure, which includes a magnetically conductive layer, a thermally conductive layer, a transition bonding layer and a food contact layer stacked sequentially. The magnetic conductive layer includes a ferritic stainless steel layer, and the thickness of the magnetic conductive layer is 0.8 to 1.5 mm. The thermally conductive layer comprises a high-purity aluminum layer or an aluminum alloy layer with an aluminum content of ≥99.5%, and the thickness of the thermally conductive layer is 3-4 mm; The transition bonding layer includes an aluminum-iron alloy layer, and the thickness of the transition bonding layer is 0.1 to 0.5 mm. The food contact layer includes at least one of a cold-rolled steel layer, a stainless steel layer, or a titanium alloy layer, and the thickness of the food contact layer is 0.5 to 1 mm.

[0009] In one specific embodiment, the step of bonding the pre-fabricated backing sheet to the rough surface under high pressure to obtain a composite backing semi-finished product with a composite backing structure includes: The iron pot blank and the bottom sheet are subjected to temperature treatment to maintain the temperature of the iron pot blank at 380℃~400℃ and preheat the temperature of the bottom sheet to 170℃~210℃. The temperature-treated iron pot blank and the bottom plate are placed in a high-pressure environment of 200MPa to 500MPa and pressed together for 28 to 45 seconds to form an Fe-Al intermetallic compound transition layer between the bottom plate and the iron pot blank. The iron pot blank with the Fe-Al intermetallic compound transition layer is cooled in stages, and the flatness of the cooled iron pot blank is tested so that the iron pot blank that meets the flatness condition is retained to obtain a multi-bottom semi-finished product with a multi-bottom structure.

[0010] In one specific embodiment, the segmented cooling of the iron pot blank having the Fe-Al intermetallic compound transition layer formed includes: First, the iron pot blank with the Fe-Al intermetallic compound transition layer is air-cooled to 180°C to 220°C, and then the air-cooled iron pot blank is water-cooled to room temperature.

[0011] In one specific embodiment, before the semi-finished product with a double bottom is nitrided at a temperature below 520°C to obtain the finished iron pot, the following steps are included: First, the composite bottom semi-finished product is subjected to ultrasonic degreasing cleaning at a temperature of 50-70°C for 10-20 minutes. The composite bottom semi-finished product after ultrasonic degreasing and cleaning is then rinsed with pure water. The semi-finished product with a composite bottom, after ultrasonic degreasing and rinsing with pure water, is dried at 80-120℃ to reduce the moisture content to ≤0.1%.

[0012] In one specific embodiment, the step of nitriding the semi-finished product with a double bottom at a temperature below 520°C to obtain the finished iron pot includes: The composite bottom semi-finished product is loaded into a nitriding furnace and subjected to gas nitriding treatment at a temperature below 520°C using an atmosphere containing active nitrogen atoms; the atmosphere includes ammonia or a mixture of ammonia and nitrogen, with ammonia accounting for not less than 4% of the volume. Under the conditions that the furnace pressure in the nitriding furnace is 0.005MPa to 0.1MPa and the decomposition rate of ammonia is 15% to 70%, the composite bottom semi-finished product is kept at a temperature for a preset time to form a dense nitriding anti-rust layer on the surface of the composite bottom semi-finished product; wherein, the preset time is 22 to 35 minutes. Then, the temperature is lowered to below 200°C according to a preset cooling rate, and then naturally cooled to room temperature to obtain the finished iron pot; wherein, the preset cooling rate is in the range of 1 to 6°C / min.

[0013] In one specific embodiment, after obtaining the finished iron pot, the following steps are included: The finished iron pot is dry polished to form a polished surface with a surface roughness of less than or equal to 0.8 μm.

[0014] The second aspect of this application provides an iron pot, which is made based on the above-described method for making an iron pot.

[0015] This application has at least the following beneficial effects: This application provides a method for manufacturing an iron pot and the iron pot itself. The method includes: providing an iron pot blank; machining the surface of the iron pot blank to form a rough surface; heating the iron pot blank with the rough surface; bonding a pre-made composite bottom sheet to the rough surface under high pressure to obtain a composite bottom semi-finished product; and subjecting the composite bottom semi-finished product to nitriding treatment at a temperature below 520°C to obtain the finished iron pot. This method enables the iron pot to combine excellent thermal conductivity and magnetic permeability with stainless steel-level rust resistance, while eliminating the cumbersome maintenance required for traditional iron pots and significantly extending the product's lifespan. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A schematic diagram of the manufacturing process of the iron pot provided in this embodiment; Figure 2 An overall sectional view of the iron pot provided for the embodiment; Figure 3 A partial cross-sectional view of the composite film provided for the embodiment.

[0018] Figure label: 1-Iron pot blank; 2-Replica film; 21-Stainless steel layer; 22-High-purity aluminum core layer; 23-Aluminum-iron alloy layer; 24-Cold-rolled steel layer. Detailed Implementation

[0019] This application provides a method for manufacturing an iron pot and an iron pot, which solves the problems of insufficient bonding strength between the bottom layer and the iron pot body in commercially available iron pots, which easily lead to bottom detachment, deformation, frequent maintenance, and short service life.

[0020] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0021] The following detailed descriptions will be provided through specific embodiments.

[0022] like Figure 1 , 2 As shown, one embodiment of this application provides a method for manufacturing an iron pot, including: 101: Provide an iron pot blank 1, and machine the surface of the iron pot blank 1 to form a rough surface.

[0023] The roughness of the roughened surface is in the range of 1.2 μm to 4.0 μm, preferably 2.0 μm. This roughness ensures sufficient mechanical interlocking force and contact area between the composite bottom sheet 2 and the iron pot blank 1, providing an ideal physical interface for atomic diffusion under high pressure, which is conducive to the formation of a continuous and dense Fe-Al intermetallic compound transition layer and significantly improves the bonding strength. At the same time, this range avoids stress concentration or poor local bonding caused by excessive surface roughness, and also prevents insufficient bonding force caused by excessive smoothness. By controlling the roughness within the above-mentioned preferred range, the shear strength of the composite bottom structure can stably reach above 65 MPa, and there is no detachment under thermal cycling test, further enhancing the durability and reliability of the product.

[0024] 102: Heat the iron pot blank 1 with a rough surface.

[0025] In one example, 102 "Heating the iron pot blank 1 with a rough surface" includes: heating the iron pot blank 1 with a rough surface to 420℃~450℃ using induction heating, and holding it at that temperature for 25~30 minutes, while controlling the heating uniformity within ±3℃.

[0026] The induction heating uses an induction coil wrapped around the outside of the pot body, with a frequency set between 10kHz and 30kHz. The power is adjusted according to the size of the pot body to ensure a uniform temperature rise at the bottom of the pot. Heating uniformity is monitored in real time by placing thermocouples at the center, edge, and middle of the bottom of the pot.

[0027] This application employs induction heating to heat the iron pot blank 1 to 420℃~450℃ and hold it at that temperature for 25~30 minutes. This effectively activates the molecular activity on the surface of the iron pot substrate, reduces the oxide layer, and forms a clean, highly active metal surface, providing ideal metallurgical bonding conditions for subsequent high-pressure pressing. Simultaneously, controlling the heating uniformity within ±3℃ ensures consistent temperature across the bottom of the pot, avoiding uneven bonding strength or thermal stress concentration caused by localized overheating or undercooling. This preferred heating process, synergistically with subsequent high-pressure pressing, facilitates the formation of a continuous, uniform, and defect-free Fe-Al intermetallic compound transition layer, thereby significantly improving the bonding strength of the composite bottom structure and the overall yield rate.

[0028] 103: The prefabricated composite bottom sheet 2 is bonded to the rough surface by high pressure to obtain a composite bottom semi-finished product with a composite bottom structure.

[0029] Among them, the composite bottom sheet 2 adopts a multi-layer composite structure with excellent thermal conductivity and magnetic conductivity. The composite bottom sheet 2 is permanently bonded to the iron pot blank 1 by high pressure pressing, so that the iron pot can be adapted to the high-frequency use scenario of Chinese stir-frying, while having good thermal conductivity and rust prevention performance.

[0030] Specifically, such as Figure 2 , 3 As shown, the multi-layer composite structure includes a magnetically conductive layer, a thermally conductive layer, a transition bonding layer, and a food contact layer stacked sequentially. The cooperation between the magnetically conductive layer, the thermally conductive layer, the transition bonding layer, and the food contact layer is used to achieve compatibility with induction cookers, uniform heat distribution, interface stress buffering, food safety, and wear resistance.

[0031] The magnetic conductive layer includes a ferritic stainless steel layer 21, preferably 430 series stainless steel, with a thickness of 0.8–1.5 mm. If the thickness of the magnetic conductive layer is less than 0.8 mm, the magnetic permeability decreases, resulting in insufficient power compatibility with the induction cooker; if the thickness is greater than 1.5 mm, it increases weight and cost. Therefore, setting the thickness of the magnetic conductive layer to 0.8–1.5 mm ensures that the permeability is stable at 800–1000, making it compatible with full-power induction cookers.

[0032] The heat-conducting layer comprises a high-purity aluminum layer (preferably 1060 / 1070 series) with an aluminum content ≥99.5% or an aluminum alloy layer, with a thickness of 3–4 mm. If the thickness of the heat-conducting layer is less than 3 mm, the heat conduction uniformity is insufficient, and the temperature difference at the bottom of the pot increases; if the thickness of the heat-conducting layer is greater than 4 mm, the thermal expansion of the aluminum core is too large, which can easily cause deformation of the bottom. Therefore, setting the thickness of the heat-conducting layer to 3–4 mm utilizes the high thermal conductivity of aluminum (238 W / (m·K)) to control the temperature difference at the bottom of the pot within ±3–4℃.

[0033] The transition bonding layer includes an aluminum-iron alloy layer 23, with a thickness of 0.1–0.5 mm. If the thickness of the transition bonding layer is less than 0.1 mm, it is difficult to effectively buffer interfacial thermal stress; if the thickness of the transition bonding layer is greater than 0.5 mm, brittle phases are easily generated, affecting the bonding strength. Therefore, setting the thickness of the transition bonding layer to 0.1–0.5 mm effectively buffers thermal stress and enhances interlayer bonding.

[0034] The food contact layer includes at least one of a cold-rolled steel layer 24, a stainless steel layer (preferably 304 / 316L), or a titanium alloy layer, and the thickness of the food contact layer is 0.5–1 mm. If the thickness of the food contact layer is less than 0.5 mm, the strength is insufficient and it is prone to wear; if the thickness of the food contact layer is greater than 1 mm, it increases the cost and affects heat conduction. Therefore, setting the thickness of the food contact layer in the range of 0.5–1 mm can balance food safety and wear resistance.

[0035] The synergistic combination of the above four thickness ranges enables the iron pot to maintain its lightweight design while achieving a bottom shear strength of ≥65MPa and withstanding 50 cycles of hot and cold without falling off. Its overall performance is significantly better than that of conventional products.

[0036] In one example, the stainless steel layer 21 is a 430 stainless steel layer 21 with a thickness of 1 mm, the high-purity aluminum core layer 22 is a 1070 high-purity aluminum core layer 22 with a thickness of 3.5 mm, the aluminum-iron alloy layer 23 has a thickness of 0.3 mm, and the cold-rolled steel layer 24 has a thickness of 0.7 mm. This set of thicknesses balances magnetic conductivity, thermal conductivity, bonding strength, and cost, and is the optimal matching value selected through numerous experiments in the embodiments of this application. It enables the composite bottom shear strength to reach 70 MPa, with no detachment after 60 thermal cycling tests, and a thermal conductivity of 92 W / (m·K).

[0037] This application achieves excellent induction cooker compatibility, uniform heat conduction, and structural reliability by sequentially layering a magnetic conductive layer, a heat-conducting layer, a transition bonding layer, and a food contact layer. Specifically, the magnetic conductive layer uses 0.8–1.5 mm thick stainless iron to ensure a stable magnetic permeability of 800–1000, making it compatible with full-power induction cookers; the heat-conducting layer uses a 3–4 mm thick high-purity aluminum core with a thermal conductivity of up to 238 W / (m·K), controlling the temperature difference at the bottom of the pot within ±3–4℃ and significantly improving the uniformity of heat distribution; the transition bonding layer is a 0.1–0.5 mm thick aluminum-iron alloy, effectively buffering thermal stress and enhancing interlayer bonding; the food contact layer is a 0.5–1 mm thick cold-rolled steel, ensuring food safety and wear resistance. This synergistic combination of thicknesses allows the iron pot to maintain a lightweight design while achieving a bottom shear strength ≥65 MPa and withstanding 50 cycles of hot and cold heating without detachment, demonstrating significantly superior overall performance compared to conventional products.

[0038] Among them, 103 "By bonding the pre-made composite sheet 2 to the rough surface under high pressure, a composite semi-finished product with a composite structure is obtained" includes: 1031: The iron pot blank 1 and the bottom plate 2 are subjected to temperature treatment to keep the temperature of the iron pot blank 1 at 380℃~400℃ and the temperature of the bottom plate 2 is preheated to 170℃~210℃ (preferably 190℃). 1032: The temperature-treated iron pot blank 1 and the bottom sheet 2 are placed in a high-pressure environment of 200MPa to 500MPa and pressed for 28 to 45 seconds to form an Fe-Al intermetallic compound transition layer between the bottom sheet 2 and the iron pot blank 1. 1033: The iron pot blank 1 with the Fe-Al intermetallic compound transition layer is cooled in sections, and the flatness of the cooled iron pot blank 1 is tested so that the iron pot blank 1 that meets the flatness condition is retained to obtain a composite bottom semi-finished product with a composite bottom structure.

[0039] This application demonstrates that by pressing the iron pot blank 1 and the bottom sheet 2 under a high pressure environment of 200MPa to 500MPa for 28 to 45 seconds, the mutual diffusion of interfacial atoms can be effectively promoted, forming a uniform, continuous and dense Fe-Al intermetallic compound transition layer.

[0040] Preferably, the iron pot blank 1 and the bottom sheet 2 are pressed together under a high pressure environment of 260MPa to 320MPa.

[0041] Preferably, the iron pot blank 1 and the bottom sheet 2 are pressed together under high pressure for 35 seconds.

[0042] The Fe-Al intermetallic compound transition layer has a thickness of 1–2 μm, which increases the bottom shear strength to over 65 MPa, far exceeding industry standards. Simultaneously, this high-pressure condition eliminates residual stress at the bonding surface, preventing the risk of bottom detachment during use. Subsequent segmented cooling and flatness testing (flatness ≤0.3 mm / 100 mm) further eliminates deformation caused by thermal stress, ensuring a flat bottom and perfect compatibility with flat-heating cooktops such as induction cookers, significantly improving product durability and user experience.

[0043] Furthermore, 1033 “segmented cooling of the iron pot blank 1 with the Fe-Al intermetallic compound transition layer” includes: first air cooling the iron pot blank 1 with the Fe-Al intermetallic compound transition layer to 180°C to 220°C, preferably 220°C, and then water cooling the air-cooled iron pot blank to room temperature.

[0044] This application first air-cools the pressed iron pot blank 1 to 180℃~220℃, and then water-cools it to room temperature. This segmented cooling method effectively controls the cooling rate and avoids excessive thermal stress caused by a sudden drop in temperature, thereby preventing pot deformation or cracking of the composite bottom interface. Compared with direct water cooling, air-cooling to 180℃~220℃ first allows the Fe-Al intermetallic compound transition layer to release internal stress evenly, and then water cooling quickly passes through the easily oxidized temperature zone, ensuring the stability of the composite bottom structure and improving production efficiency. Finally, the flatness of the pot bottom can be controlled within 0.3mm / 100mm, ensuring that the iron pot is heated evenly and does not shake when used on an induction cooker, significantly improving the dimensional accuracy of the product and the user experience.

[0045] 104: The semi-finished product with a double bottom is nitrided at a temperature below 520℃ to obtain the finished iron pot.

[0046] The process of "nitriding the semi-finished product at a temperature below 520°C to obtain the finished iron pot" includes a pretreatment step, specifically: First, the semi-finished composite base is subjected to ultrasonic degreasing cleaning at a temperature of 50–70°C for 10–20 minutes. Preferably, the cleaning temperature is 60°C and the time is 15 minutes. The semi-finished product after ultrasonic degreasing and cleaning is then rinsed with pure water. The semi-finished product with a composite bottom, after ultrasonic degreasing and rinsing with pure water, is dried at 80-120℃ to ensure a moisture content of ≤0.1%.

[0047] In one example, the ultrasonic degreasing cleaning is performed at a temperature of 60°C for 15 minutes, followed by drying at 100°C for 20 minutes. Preferably, the drying temperature is 100°C for 20 minutes.

[0048] Prior to low-temperature nitriding, this application involves sequentially subjecting the semi-finished composite bottom product to ultrasonic degreasing cleaning, pure water rinsing, and drying treatments. This process thoroughly removes surface oil, impurities, and residual moisture. Controlling the cleaning temperature to 50–70℃ and the time to 10–20 minutes ensures efficient degreasing while avoiding potential adverse effects on the composite bottom structure from excessively high temperatures or prolonged cleaning times. Strict control of the drying temperature (80–120℃) and moisture content (≤0.1%) ensures the surface to be nitrided is clean and dry. This pretreatment process provides ideal surface conditions for the subsequent nitriding reaction, facilitating the formation of a uniform, dense, and firmly bonded nitrided anti-rust layer, thereby significantly improving the rust resistance of the iron pot and the consistency of the nitrided layer quality.

[0049] Specifically, 104 "Nitriding the semi-finished product with a double bottom at a temperature below 520°C to obtain the finished iron pot" includes: The composite bottom semi-finished product is loaded into a nitriding furnace and subjected to gas nitriding treatment at a temperature below 520°C using an atmosphere containing active nitrogen atoms; the atmosphere includes ammonia or a mixture of ammonia and nitrogen, with ammonia accounting for not less than 4% of the volume.

[0050] The furnace can be heated to 410℃~460℃, preferably 430℃, according to a preset heating rate; wherein the preset heating rate is in the range of 1~10℃ / min. Preferably, a heating rate of 5℃ / min is used. The nitriding furnace contains nitrogen and ammonia gas, with a nitrogen to ammonia gas volume ratio of 18:1. Under the conditions of a furnace pressure of 0.005MPa to 0.1MPa and an ammonia decomposition rate of 15% to 70%, the composite bottom semi-finished product is kept at a temperature for a preset time to form a dense nitrided anti-rust layer on the surface of the composite bottom semi-finished product; wherein, the preset time is 22 to 35 minutes (preferably 27 minutes).

[0051] Preferably, the nitrogen to ammonia volume ratio is (10-25):1, the furnace pressure is 0.02-0.03 MPa, and the ammonia decomposition rate is 35%-45%, with the holding time being 8-12 hours to form a dense Fe3N nitriding anti-rust layer on the surface of the composite bottom semi-finished product. The nitriding furnace is a pit-type gas nitriding furnace, equipped with a circulating fan to ensure uniform atmosphere. The ammonia decomposition rate is monitored in real-time by a hydrogen probe or bubble bottle, and the ammonia flow rate is controlled by adjusting the flow rate.

[0052] Then, the temperature is lowered to below 200°C according to a preset cooling rate, followed by natural cooling to room temperature to obtain the finished iron pot; wherein, the preset cooling rate is in the range of 1 to 6°C / min. Preferably, the preset cooling rate is 3°C / min.

[0053] This application involves nitriding the semi-finished composite bottom at a temperature below 520°C, heating it to 430°C–450°C at a heating rate of 1–10°C / min, and holding it at this temperature for 22–35 minutes under furnace pressure of 0.01–0.05 MPa and an ammonia decomposition rate of 20%–60%. This effectively avoids the melting point (660°C) of the aluminum core in the composite bottom sheet 2, ensuring the integrity of the composite bottom structure without softening or detachment. Simultaneously, this process forms a uniform and dense Fe3N nitrided anti-rust layer on the surface of the semi-finished composite bottom, with a hardness reaching HV580–650, and exhibiting no rust spots after more than 3 hours of salt spray boiling test. By controlling the heating and cooling rates (1–6°C / min), cracking of the nitrided layer or loosening of the composite bottom caused by thermal shock is avoided. This method, while ensuring the firmness of the composite bottom, imparts stainless steel-level rust resistance to the iron pot, eliminating the cumbersome maintenance required for traditional iron pots and significantly extending the product's service life.

[0054] In one optional embodiment, the thickness of the nitrided anti-rust layer is 3 μm to 25 μm. Preferably, the thickness of the nitrided anti-rust layer is 5 μm to 15 μm, and the nitrided anti-rust layer includes a dense white bright layer with a thickness of 1 μm to 3 μm and a diffusion layer below it.

[0055] In an optional embodiment, the nitrided anti-rust layer comprises Fe4N phase and Fe3N phase, wherein the total content of Fe4N phase and Fe3N phase accounts for more than 60% of the mass of the nitrided anti-rust layer.

[0056] In one optional embodiment, the surface Vickers hardness of the nitrided rust-preventive layer is not less than HV450. Preferably, the surface Vickers hardness of the nitrided rust-preventive layer is HV550 to 700.

[0057] In an optional embodiment, the bonding force between the nitrided rust-preventive layer and the iron pot blank substrate is not less than 30N (scratch test Lc1 value); after the nitrided rust-preventive layer is boiled in 5% NaCl solution for not less than 3 hours, there are no rust spots on the surface, and the neutral salt spray test (GB / T 10125) time is not less than 96 hours.

[0058] Furthermore, after obtaining the finished iron pot, the process includes: Dry polishing is performed on the finished iron pot to form a polished surface with a surface roughness of less than or equal to 0.8 μm.

[0059] After the nitriding treatment yields the finished iron wok, it undergoes further dry polishing to achieve a surface roughness of no more than 0.8 μm. This treatment effectively removes surface dust, loose layers, and trace impurities from the nitrided layer, creating a smooth, dense, and uniform polished surface, significantly improving the wok's appearance and ease of cleaning. Simultaneously, reducing surface roughness helps minimize stain adhesion and the accumulation of corrosive media, further enhancing the rust-preventive effect of the nitrided layer and ensuring the wok maintains excellent corrosion resistance during long-term use. Furthermore, dry polishing avoids the residual moisture or chemical media that may be introduced by wet polishing, meeting the safety and hygiene requirements for food-grade cookware.

[0060] In summary, the preparation method of this application, through steps 101-104, forms a strong intermetallic compound transition layer between the composite bottom sheet 2 and the pot body, significantly improving the bonding strength and effectively avoiding the risk of bottom detachment during long-term use or alternating hot and cold periods. Secondly, the low-temperature nitriding treatment below 520℃ forms a dense and uniform nitrided anti-rust layer on the pot body surface while effectively avoiding the melting point of the aluminum core in the composite bottom sheet 2, ensuring the integrity of the composite bottom structure without deformation or detachment. This method combines excellent thermal conductivity and magnetic permeability with stainless steel-level rust resistance, making the iron pot compatible with various cooktops such as induction cookers and gas stoves, while eliminating the cumbersome maintenance of traditional iron pots and significantly extending the product's lifespan.

[0061] Another embodiment of this application provides an iron pot, which is manufactured based on the above-described method for making iron pots. This iron pot significantly outperforms conventional products in terms of heat conductivity, magnetic conductivity, rust prevention, bottom durability, and safety performance, as shown in the table below:

[0062] As can be seen, the thermal conductivity of this product reaches 85-95 W / (m·K), which is more than 38% higher than that of stainless steel multi-layer bottom pots. The temperature difference at the bottom of the pot is controlled within ±3-4℃, and the boiling time is shortened to 8-9 minutes, effectively reducing food scorching. The magnetic permeability is as high as 800-1000, and the power conversion efficiency is ≥92%, which is compatible with 1000-3500W full-power induction cookers, saving 5%-7% of energy. In terms of rust prevention, no rust spots are found after boiling in 5% salt water for more than 3 hours, and no rust is found after 90 days of environmental storage. The nitrided layer... With a hardness of HV580~650, its rust resistance is more than twice that of ordinary iron woks, eliminating the need for seasoning and maintenance. The shear strength of the composite bottom reaches 65~75MPa, far exceeding the industry standard (≥30MPa). It does not detach after 50 cycles of heat cycling from -20℃ to 200℃, and it does not deform after being impacted 30cm by a 500g steel ball. Its safety performance meets the requirements of GB4806.9. It does not deform after 30 minutes of continuous dry burning, and the handle temperature is ≤52℃. It is fully adapted to the high-frequency use scenarios of Chinese stir-frying, and its service life is extended by 3~5 years.

[0063] Note that the above description is merely a preferred embodiment and the technical principles employed in this application. Those skilled in the art will understand that this application is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of this application. Therefore, although this application has been described in detail through the above embodiments, this application is not limited to the above embodiments. Many other equivalent embodiments may be included without departing from the concept of this application, and the scope of this application is determined by the scope of the appended claims.

[0064] The above disclosures are only a few specific implementation scenarios of this application. However, this application is not limited to these. Any variations that can be conceived by those skilled in the art should fall within the protection scope of this application.

Claims

1. A method of making an iron pot, characterized by, include: A cast iron pot blank is provided, and the surface of the cast iron pot blank is machined to form a rough surface; The iron pot blank with the rough surface is heated; The pre-made composite bottom sheet is bonded to the rough surface under high pressure to obtain a composite bottom semi-finished product with a composite bottom structure; The semi-finished product with the composite bottom is subjected to nitriding treatment at a temperature below 520°C to obtain the finished iron pot.

2. The method of claim 1, wherein the iron pot is made of a material selected from the group consisting of cast iron, wrought iron, and steel. The roughness of the rough surface is in the range of 1.2 μm to 4.0 μm.

3. The method of claim 1, wherein the iron pot is made of a material selected from the group consisting of cast iron, wrought iron, and steel. The heating of the iron pot blank with the rough surface includes: The iron pot blank with the rough surface is heated to 420℃~450℃ by induction heating and kept at that temperature for 25~30 minutes, while the heating uniformity is controlled within ±3℃.

4. The method of claim 1, wherein the iron pot is made of a material selected from the group consisting of cast iron, carbon steel, and stainless steel. The backing sheet has a multi-layer composite structure, which includes a magnetic conductive layer, a thermal conductive layer, a transition bonding layer and a food contact layer stacked sequentially. The magnetic conductive layer includes a ferritic stainless steel layer, and the thickness of the magnetic conductive layer is 0.8 to 1.5 mm. The thermally conductive layer comprises a high-purity aluminum layer or an aluminum alloy layer with an aluminum content of ≥99.5%, and the thickness of the thermally conductive layer is 3-4 mm; The transition bonding layer includes an aluminum-iron alloy layer, and the thickness of the transition bonding layer is 0.1 to 0.5 mm. The food contact layer includes at least one of a cold-rolled steel layer, a stainless steel layer, or a titanium alloy layer, and the thickness of the food contact layer is 0.5 to 1 mm.

5. The method of claim 1, wherein the iron pot is made of a material selected from the group consisting of cast iron, carbon steel, and stainless steel. The process of bonding the pre-fabricated backing sheet to the rough surface under high pressure to obtain a composite backing semi-finished product with a composite backing structure includes: The iron pot blank and the bottom sheet are subjected to temperature treatment to maintain the temperature of the iron pot blank at 380℃~400℃ and preheat the temperature of the bottom sheet to 170℃~210℃. The temperature-treated iron pot blank and the bottom plate are placed in a high-pressure environment of 200MPa to 500MPa and pressed together for 28 to 45 seconds to form an Fe-Al intermetallic compound transition layer between the bottom plate and the iron pot blank. The iron pot blank with the Fe-Al intermetallic compound transition layer is cooled in stages, and the flatness of the cooled iron pot blank is tested so that the iron pot blank that meets the flatness condition is retained to obtain a multi-bottom semi-finished product with a multi-bottom structure.

6. The method of claim 5, wherein the iron pot is made of a material selected from the group consisting of cast iron, carbon steel, and stainless steel. The segmented cooling of the iron pot blank on which the Fe-Al intermetallic compound transition layer is formed includes: First, the iron pot blank with the Fe-Al intermetallic compound transition layer is air-cooled to 180°C to 220°C, and then the air-cooled iron pot blank is water-cooled to room temperature.

7. The method of claim 2, wherein the iron pot is made of a material selected from the group consisting of cast iron, carbon steel, and stainless steel. Before the semi-finished product with a double bottom is nitrided at a temperature below 520°C to obtain the finished iron pot, the following steps are included: First, the composite bottom semi-finished product is subjected to ultrasonic degreasing cleaning at a temperature of 50-70°C for 10-20 minutes. The composite bottom semi-finished product after ultrasonic degreasing and cleaning is then rinsed with pure water. The semi-finished product with a composite bottom, after ultrasonic degreasing and rinsing with pure water, is dried at 80-120℃ to reduce the moisture content to ≤0.1%.

8. The method for manufacturing an iron pot according to claim 1, characterized in that, The step of nitriding the semi-finished product with a double bottom at a temperature below 520°C to obtain the finished iron pot includes: The composite bottom semi-finished product is loaded into a nitriding furnace and subjected to gas nitriding treatment at a temperature below 520°C using an atmosphere containing active nitrogen atoms; the atmosphere includes ammonia or a mixture of ammonia and nitrogen, with ammonia accounting for not less than 4% of the volume. Under the conditions that the furnace pressure in the nitriding furnace is 0.005MPa to 0.1MPa and the decomposition rate of ammonia is 15% to 70%, the composite bottom semi-finished product is kept at a temperature for a preset time to form a dense nitriding anti-rust layer on the surface of the composite bottom semi-finished product; wherein, the preset time is 22 to 35 minutes. Then, the temperature is lowered to below 200°C according to a preset cooling rate, and then naturally cooled to room temperature to obtain the finished iron pot; wherein, the preset cooling rate is in the range of 1 to 6°C / min.

9. The method for manufacturing an iron pot according to claim 8, characterized in that, After obtaining the finished iron pot, the following is included: The finished iron pot is dry polished to form a polished surface with a surface roughness of less than or equal to 0.8 μm.

10. An iron pot, characterized in that, The iron pot is made according to the method of making an iron pot according to any one of claims 1-9.

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