Preparation method of coating-free hydrophobic low-carbon steel non-stick iron pan
By employing a two-stage heat treatment process and ethanol-nitric acid corrosion treatment on a low-carbon steel substrate, an uncoated hydrophobic non-stick iron pan was prepared, solving the coating problem of traditional non-stick iron pans and achieving high durability and low-cost industrial production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- XIAN TECH UNIV
- Filing Date
- 2026-01-27
- Publication Date
- 2026-05-05
AI Technical Summary
Existing non-stick iron pans have problems such as easy peeling and decomposition of the coating, release of harmful substances, poor durability, high production costs, and environmental pollution, making it difficult to achieve large-scale industrial promotion.
Using low-carbon steel as the base material, a uniform and dense micron-level rough grain boundary structure is formed through two-stage heat treatment and ethanol-nitric acid mixture corrosion treatment, achieving a coating-free hydrophobic effect.
It achieves high durability, safety, and low-cost production of uncoated non-stick iron pans, suitable for household cookware and other metal surface treatment fields.
Smart Images
Figure CN121970983A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of metal material surface modification technology and cookware manufacturing, specifically to a method for preparing an uncoated hydrophobic low-carbon steel non-stick iron pan. Background Technology
[0002] Iron woks have long been a common cooking utensil in households due to their advantages such as even heat conduction and the replenishment of iron needed by the human body. However, traditional iron woks have problems such as easy sticking and difficulty in cleaning. To solve this problem, the mainstream non-stick iron woks on the market use high-molecular materials such as polytetrafluoroethylene (PTFE) for surface coating. However, this type of non-stick coating has significant drawbacks: First, the coating is prone to peeling and decomposition during high-temperature cooking, releasing harmful chemicals and posing serious food safety risks, which are subject to strict food safety standards; second, the coating has poor durability, and the non-stick effect rapidly diminishes after long-term use, resulting in a short lifespan; third, the coating preparation process involves the volatilization of organic solvents, which pollutes the environment.
[0003] To break free from reliance on organic coatings, the field of materials science has begun exploring technological pathways to achieve natural non-stick effects through the manipulation of microstructures on metal surfaces, such as the preparation of superhydrophobic coatings and laser etching of micro / nano structures. However, these technologies suffer from high equipment investment, complex processes, and high production costs, making large-scale industrial application difficult.
[0004] Therefore, developing a simple, low-cost, safe, and environmentally friendly uncoated non-stick iron pan manufacturing technology has become a pressing technical challenge for the cookware industry. Summary of the Invention
[0005] This invention aims to overcome the problems of large equipment investment, complex processes, and high production costs in existing technologies, and provides a method for preparing an uncoated hydrophobic low-carbon steel non-stick iron pan.
[0006] To achieve the above objectives, the technical solution provided by this invention is as follows: A method for preparing an uncoated hydrophobic low-carbon steel non-stick pan, comprising the following steps: Step 1, Substrate Selection: Select a low-carbon steel cookware blank with a carbon content of ≤0.2% as the substrate; Step 2, Heat Treatment: The substrate described in Step 1 is subjected to a two-stage heat treatment: first, austenitization and heat preservation, then air cooling to room temperature, and finally low-temperature tempering. Step 3, Surface corrosion modification: Prepare an etching solution, which is a mixture of 96% ethanol and 4% nitric acid by volume. Under normal temperature conditions, immerse the substrate after heat treatment in step 2 in the etching solution to obtain a modified low-carbon steel non-stick iron pan.
[0007] Furthermore, in step two above, austenitization is carried out at 1000-1150℃ for 30 minutes.
[0008] Furthermore, in step two above, the sample is tempered at 300°C for 5 minutes.
[0009] Furthermore, in step three above, the room temperature is 25℃ and the soaking time is 10-15 seconds.
[0010] Furthermore, the low-carbon steel mentioned in step one above has a carbon content ≤ 0.2%, a sulfur content ≤ 0.025%, and a phosphorus content ≤ 0.028%.
[0011] Compared with the prior art, the advantages of the present invention are: 1. Substrate Selection: Low-carbon steel with a carbon content of ≤0.2% and impurity elements such as sulfur and phosphorus meeting the specified conditions is selected as the substrate. The selected substrate can reduce its interference with the uniformity of grain boundary corrosion, ensure the corrosion process is controllable, and at the same time take into account the corrosion resistance and mechanical performance requirements of the iron pot made from the substrate during the cooking process, avoiding deformation or corrosion failure during use; it is especially suitable for technical scenarios that achieve the intrinsic non-stick function of metal surface through microstructure control.
[0012] 2. Optimized Heat Treatment Process: A two-stage heat treatment process of "high-temperature austenitization + low-temperature tempering" is adopted to achieve precise control over the microstructure of the substrate. Specifically: In the first stage of heat treatment, the substrate microstructure is fully austenitized, laying the foundation for subsequent grain refinement and grain boundary optimization; then, the furnace door is opened and the substrate is cooled to room temperature by air cooling to promote grain refinement and prevent excessively large grains from affecting corrosion uniformity; the second stage of heat treatment involves placing the cooled substrate in a tempering device. This step promotes the precipitation of micro-cementite at the grain boundaries, improving the corrosion sensitivity and selectivity of the grain boundaries, creating conditions for the formation of a uniform and rough structure in subsequent surface corrosion, and providing structural support for achieving hydrophobic and non-stick properties.
[0013] 3. Surface Corrosion Modification: The ethanol-nitric acid mixed etching solution is formulated with a reasonable ratio. Immersing the heat-treated low-carbon steel substrate in the etching solution provided by this invention ensures the selective corrosion effect of the etching solution on the grain boundaries, while avoiding excessive corrosion of the substrate body. Through the selective corrosion effect of the etching solution on the grain boundaries, a uniform and dense micron-level rough grain boundary structure is formed on the surface of the substrate. This microstructure has excellent hydrophobic properties, thus significantly reducing the contact area between the substrate surface and the food in the iron pot prepared on the substrate, achieving a non-stick effect.
[0014] 4. The multiple steps of the present invention are optimized and combined in the following aspects: In step one, the present invention involves air cooling after high-temperature austenitization, which is equivalent to a normalizing treatment, resulting in a fine and uniform ferrite + pearlite (or bainite) microstructure, effectively refining the structure. Fine grains not only improve the strength and toughness of the material, but more importantly, the grain boundary length per unit area is greatly increased, providing corrosion points for subsequent corrosion. Through optimized heat treatment processes, the grain size and grain boundary state of the substrate are optimized, resulting in a substrate with significantly improved grain boundary corrosion sensitivity and selectivity. Such a substrate creates conditions for the formation of a uniform rough structure in subsequent surface corrosion processes, enhancing the ability to actively "design" weak points at grain boundaries that are easily attacked by specific corrosive solutions. The heat-treated substrate is then immersed in the designed corrosive solution provided by the present invention: an ethanol-nitric acid mixture. Nitric acid is the main corrosive agent, while ethanol plays a role in slow release, wetting, and potentially influencing polarization. This ratio of corrosive solution exhibits extremely high selectivity for grain boundaries. Corrosion occurs along dense, weakened grain boundaries, uniformly eroding them to form uniformly distributed micron-sized pits and trenches on the surface, with grains as units—a "uniform, dense micron-sized rough grain boundary structure." This uneven surface structure results in a wetting angle greater than 120° for water droplets, preventing them from adhering to the surface and causing them to eventually fall off. The material's microstructure is further optimized. The micron-sized rough grain boundary structure, constructed through physical means, is tightly bonded to the substrate, exhibiting high structural stability, excellent high-temperature resistance and wear resistance, and maintaining good hydrophobic and non-stick properties for a long time, significantly improving product lifespan and user experience.
[0015] 5. Simple Process, Easy to Industrialize and Promote: The preparation process of this invention uses conventional chemical reagents, with no emissions of toxic or harmful substances, and eliminates the need for complex coating processes, reducing environmental pollution and meeting the requirements of the national green manufacturing and sustainable development strategy. This invention employs conventional heat treatment equipment and a simple chemical corrosion process, eliminating the need for expensive specialized equipment (such as laser etching equipment, vacuum coating equipment, etc.). It has low technical barriers, requires minimal equipment investment, and its process parameters are easy to control, resulting in significantly lower production costs than existing technologies. It is not only suitable for iron cookware but can also be extended to various metal surface treatment fields requiring anti-sticking and anti-pollution properties, such as medical devices, food processing equipment, and mechanical parts made of stainless steel and low-carbon steel. The potential market size is enormous, the technology is highly scalable, and it possesses significant economic value and social benefits. Attached Figure Description
[0016] Figure 1 This is a microscopic morphology (SEM) image of the surface of the low-carbon steel substrate after etching treatment in Example 1. Figure 2 This is a microscopic morphology (SEM) image of the surface of the low-carbon steel substrate after corrosion treatment in Example 2. Figure 3 This is a contact angle test diagram of the surface of the low-carbon steel substrate before treatment in Example 1. Detailed Implementation
[0017] The technical solution of the present invention will be described in detail below with reference to specific embodiments. Example 1: This invention provides a method for preparing an uncoated hydrophobic low-carbon steel non-stick pan, comprising the following steps:
[0018] 1. Substrate Preparation: Commercially available low-carbon steel cookware blanks were purchased as the substrate. Composition testing confirmed that the carbon content was 0.15%, the sulfur content was 0.025%, and the phosphorus content was 0.028%, meeting the substrate selection requirements of this invention. The blanks were ultrasonically cleaned to remove surface oil and oxide scale, and then dried for later use.
[0019] 2. Heat treatment: Place the sample in a conventional resistance furnace, heat it to 1000℃, hold it for 30 minutes, then open the furnace door and air cool it to room temperature; then place the sample in a low-temperature tempering furnace, heat it to 300℃, hold it for 5 minutes, then remove it to promote the precipitation of micro cementite at the grain boundaries, optimize the grain size and grain boundary state, and finally cool it naturally to room temperature.
[0020] 3. Corrosion Treatment: Prepare the etching solution by mixing 96 mL of anhydrous ethanol with 4 mL of concentrated nitric acid (68% by mass) and placing the mixture in a corrosion-resistant glass container. Maintain the ambient temperature at 25°C. Immerse the heat-treated sample in the etching solution for 10 seconds, then quickly remove it and rinse the surface three times with deionized water to remove residual etching solution. Dry the sample with nitrogen gas to obtain an uncoated, hydrophobic, non-stick iron pan.
[0021] The performance of the uncoated hydrophobic nonstick iron pan prepared in Example 1 was tested: (1) Hydrophobicity test: The sample surface was tested using a contact angle tester, see [reference]. Figure 3 Ordinary materials have a contact angle of about 80°, which does not meet the hydrophobicity requirements (contact angle > 120°); after being processed by the process of this invention, the contact angle is greater than 120°. (2) Microscopic morphological observation: See Figure 1 Observation by scanning electron microscopy (SEM) revealed that the sample surface formed a uniform and dense micron-scale rough grain boundary structure with uniform grain size and no obvious excessive corrosion or uneven corrosion. (3) Non-stick performance verification: After the oil-free fried egg experiment, the egg can slide freely on the sample surface. After heating for 3 minutes, it is completely formed. After taking it out, there is no egg residue sticking to the sample surface. It can be completely cleaned by rinsing with water without the need for additional cleaning agents. After 15 consecutive oil-free fried egg experiments, the contact angle of the sample still remains at 122°, and the non-stick performance has not significantly decreased. (4) Corrosion resistance test: The sample was placed in a simulated humid kitchen environment (temperature 25℃, humidity 85%) for 30 days. There was no obvious rust on the surface, and the corrosion resistance met the requirements for daily use.
[0022] Example 2: The difference from Example 1 is that low-carbon steel with a carbon content of 0.18% was selected.
[0023] Performance testing: The contact angle of the sample surface obtained in Example 2 was 125°, see [link / reference]. Figure 2 SEM observation showed that the surface was rough and the structure was uniform; in the oil-free frying experiment, the fish skin was intact and undamaged, and there was no sticking. After cleaning, there were no residual stains on the surface; after 20 repeated cooking and cleaning, the non-stick and hydrophobic properties remained stable, proving that the process of the present invention has good repeatability and stability.
[0024] Under the same material conditions, samples that undergo only heat treatment without corrosion, while possessing the potential for selective corrosion, remain smooth metal and cannot achieve hydrophobic and non-stick properties. Furthermore, treating ordinary low-carbon steel without heat treatment with an etching solution results in corrosion occurring at random defects, inclusions, or areas of uneven structure. The resulting rough, chaotic, uncontrollable, and fragile structure may wear down quickly during cooking and also fails to guarantee a uniform non-stick effect.
[0025] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.
Claims
1. A method for preparing an uncoated hydrophobic low-carbon steel non-stick wok, characterized in that: Includes the following steps Step 1, Substrate Selection: Select a low-carbon steel cookware blank with a carbon content of ≤0.2% as the substrate; Step 2, Heat Treatment: The substrate described in Step 1 is subjected to a two-stage heat treatment: first, austenitization and heat preservation, then air cooling to room temperature, and finally low-temperature tempering. Step 3, Surface corrosion modification: Prepare an etching solution, which is a mixture of 96% ethanol and 4% nitric acid by volume. Under normal temperature conditions, immerse the substrate after heat treatment in Step 2 in the etching solution to obtain a modified low-carbon steel non-stick iron pan.
2. The method for preparing an uncoated hydrophobic low-carbon steel non-stick wok according to claim 1, characterized in that: In step two, austenitization is carried out at 1000-1150℃ for 30 minutes.
3. The method for preparing an uncoated hydrophobic low-carbon steel non-stick wok according to claim 2, characterized in that: In step two, the sample is tempered at 300°C for 5 minutes.
4. The method for preparing an uncoated hydrophobic low-carbon steel non-stick pan according to claim 3, characterized in that: In step three, the room temperature is 25°C, and the soaking time is 10-15 seconds.
5. The method for preparing an uncoated hydrophobic low-carbon steel non-stick pan according to claim 4, characterized in that: The low-carbon steel mentioned in step one has a carbon content ≤ 0.2%, a sulfur content ≤ 0.025%, and a phosphorus content ≤ 0.028%.