Preparation method of food-grade high-strength corrosion-resistant C30RE ultrahigh-nitrogen martensitic stainless steel cutter

Abstract

The invention belongs to the field of cutter manufacturing, and particularly relates to a preparation method of a food-grade high-strength corrosion-resistant C30RE ultrahigh-nitrogen martensitic stainless steel cutter. A food-grade high-strength corrosion-resistant C30RE ultrahigh-nitrogen martensitic stainless steel cast ingot is prepared through vacuum pressurization smelting, and a cutter base material which is high in purity, uniform in component and compact in structure is obtained through the processes of forging cogging, plate hot rolling, isothermal spheroidizing annealing and the like; through the processes of roll forging forming, mold pressing cooling quenching, subzero treatment, tempering treatment, stress relief annealing and the like, tool blanks in different shapes are obtained, martensite phase transformation in the tool blanks is promoted, quenching deformation is controlled, precipitated phases in the tool blank materials are promoted to be fine and dispersed out, the austenite content is reduced, and residual stress is reduced; the dimensional stability and obdurability matching of the cutter blank are improved; and finally preparing the food-grade high-strength corrosion-resistant C30RE ultrahigh-nitrogen martensitic stainless steel cutter with the functional attribute and the health attribute by virtue of the machining processes such as grinding and polishing, edging and the like.

Description

Technical Field

[0001] This invention belongs to the field of knife manufacturing, specifically a method for preparing food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel knives. It is especially suitable for knives in the food industry, and can take into account high sharpness, high corrosion resistance and non-toxic and harmless health properties. It can also be extended to the field of medical devices. Background Technology

[0002] Food-grade knives are primarily used for cutting various ingredients. During long-term use, they must be able to quickly and comfortably separate different types of ingredients, both soft and hard, while also withstanding the various corrosive environments encountered during the cutting process. In particular, they must not allow excessive leaching of harmful element ions after contact with food and must inhibit the growth of harmful microbial communities to avoid potential harm to the human body. This requires knives to possess excellent sharpness, durability, and corrosion resistance, and must also prioritize food-grade health attributes such as non-toxicity and harmlessness.

[0003] Currently, most food-grade knives, both domestically and internationally, focus more on functional attributes. German food-grade knives are particularly well-known, with brands such as Zwilling, Trident, and WMF. These brands use high-quality materials...

[0004] Martensitic stainless steels such as Cronidur30 and X50CrMoV15 are commonly used in the food industry. Japanese food industry knives mostly use ATS-34 and VG10, while American food industry knives typically use 440 series and 154CM steels. These foreign knives, after undergoing special metallurgical processes and appropriate heat treatment, achieve a hardness of 58-60 HRC, possessing good sharpness, durability, and corrosion resistance. In contrast, in my country, food industry knives typically use high-carbon, high-chromium martensitic stainless steels such as 7Cr17MoV and 9Cr18MoV. During actual production, these high-carbon, high-chromium martensitic stainless steels are prone to uneven composition and microstructure issues such as liquid carbides and network carbides. This results in poor strength-toughness matching, poor wear resistance, and reduced corrosion resistance, severely affecting quality stability and actual service life. Consequently, domestic knives lag significantly behind well-known foreign brands in terms of functional attributes.

[0005] Patent CN117305725A discloses a nitrogen-containing martensitic stainless steel, its smelting method, and stainless steel knives. The nitrogen content is 0.08–0.12%, with lax control over impurity elements, failing to meet the non-toxic requirements for food-grade knives. It only focuses on the hardness and machinability of conventional knives, failing to address the health and safety hazards of existing knives in the food sector. Patent CN116219288A discloses a nitrogen-containing martensitic stainless steel for knives and a smelting method for controlling and stabilizing nitrogen content. The nitrogen content is only 0.10–0.12%, and the total amount of impurity elements (such as As and Pb) is not controlled, failing to meet the health requirements for food-grade knives. Using recycled 3Cr13 material as raw material results in low purity, easily introducing impurities, and failing to meet national food safety standards. Patent CN115505851A discloses a high-hardness, high-nitrogen martensitic stainless steel knife material and its preparation method, with Ni content of 0-5.5% and Cu content of 0-3.5%. However, Ni and Cu are elements in food contact materials that require strict limits as they can potentially cause harm to the human body. The technical objective focuses solely on high hardness and does not address the total amount control of harmful elements (such as As, Sn, Sb, Bi, and Pb) in food-grade knives, thus failing to address the health risks of harmful element leaching during knife use. Patent CN113981317A discloses a nitrogen-containing martensitic stainless steel for knives and its manufacturing method, with a nitrogen content of only 0.05-0.15%. It also does not restrict elements such as Ni and Cu that may cause potential harm to the human body and does not consider the non-toxic and harmless health properties of food-grade knives. The processing method of "rapid cooling to the martensitic-austenitic two-phase region + reheating" results in a low hardness in the finished product, failing to meet the health requirements for knives in the food industry.

[0006] With the continuous improvement of living standards, people have paid increasing attention to the health attributes of knives used in the food industry in recent years. However, the existing knives and materials used in the food industry, both domestically and internationally, rarely address and fail to meet this requirement. Therefore, it is necessary to independently develop food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel as a material for knives in the food industry. Furthermore, by combining key technologies such as roll forging, die-pressing cooling quenching, cryogenic treatment and stress-relief annealing, as well as grinding, polishing, and sharpening, the development of food-grade knives that possess both functional and health attributes is of great significance for ensuring the quality of daily life and leading the way in the healthier use of knives in the food industry. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel knives, which solves the problems of insufficient functional and health properties of existing knives, and inability to meet the long-term cutting needs of different food ingredients in the food industry. The prepared food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel knives not only have good sharpness, durability and corrosion resistance, but also have food-grade health properties such as being non-toxic and harmless.

[0008] The technical solution of this invention is:

[0009] A method for preparing a food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tool. The base material of the cutting tool is a food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel alloy. The chemical composition, by weight percentage, ranges as follows: C: 0.20~0.50, N: 0.20~0.80, Cr: 13.0~16.0, Mo: 0.50~1.50, Mn: 0.10~0.60, Si: 0.30~0.80, RE: 0.002~0.030, Ni≤0.20, Cu≤0.20, Ti≤0.006, O≤0.0020, H≤0.0002, P≤0.015, S≤0.005, As+Sn+Sb+Bi+Pb≤0.0080, with the balance being Fe.

[0010] The preparation method of the food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tool includes the following steps:

[0011] Step 1: Vacuum pressure melting technology is used to prepare ingots with high purity, uniform composition, and dense structure;

[0012] Step 2: After high-temperature diffusion annealing, the ingot is homogeneously forged and hot-rolled to form the tool substrate;

[0013] Step 3: After hot rolling, the tool substrate is subjected to isothermal spheroidizing annealing to eliminate internal stress, improve segregation, and homogenize the microstructure;

[0014] Step 4: The hot-rolled tool substrate is roll-forged to obtain a tool blank with the initial tool morphology;

[0015] Step 5: After roll forging, the tool blank is subjected to die pressing and cooling quenching to promote martensitic phase transformation and obtain martensitic structure, and to control the deformation of the tool blank during the quenching process.

[0016] Step 6: After molding and cooling quenching, the tool blank is cryogenically treated in a cryogenic equipment to further reduce the content of residual austenite, improve the dimensional stability of the tool, and promote the precipitation of secondary precipitates after tempering.

[0017] Step 7: After cryogenic treatment, the tool blank is tempered to regulate its microstructure and properties;

[0018] Step 8: After tempering, the tool blank undergoes stress-relief annealing to significantly reduce the residual stress inside the tool blank.

[0019] Step 9: After annealing, the tool blank undergoes a series of processes including grinding, polishing, cleaning, and sharpening to obtain a finished tool body with a bright surface.

[0020] Step 10: Assemble the handle and the blade to obtain the finished knife.

[0021] The preparation method of the food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tool, in step 1, adopts vacuum pressure melting technology, and uses a vacuum pressure induction melting furnace to melt the cutting tool substrate. During the melting process, high-purity nitrogen gas is introduced at a pressure ≥7atm, and the mixture is stirred and kept for 3-5 minutes to carry out N alloying.

[0022] In the preparation method of the food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tool, in step 2, the ingot is heated to 1180-1260℃ for high-temperature diffusion annealing treatment, and the holding time is 1h / 100mm-2.5h / 100mm; the billet is opened using conventional forging method, and the final forging temperature is not lower than 950℃; after forging, the billet is heated to 1180-1220℃ and held for 1h / 100mm-2.5h / 100mm; thereafter, it is hot rolled in multiple passes to form a cutting tool blank of a set thickness, with a final rolling temperature of 900-950℃, and then air-cooled to room temperature after rolling.

[0023] In the preparation method of the food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tool, in step 3, the isothermal spheroidizing annealing temperature of the cutting tool substrate after hot rolling is 720-850℃, the holding temperature is 3-6h, and the furnace is cooled to room temperature.

[0024] In the preparation method of the food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tool, in step 4, the cutting tool substrate is heated at 1150℃±20℃ before roll forging and held at that temperature for 3 to 6 minutes. The cutting tool blank is then formed by roll forging according to the dimensions of different types of cutting tools and the edges are trimmed.

[0025] In the preparation method of the food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tool, in step 5, the quenching temperature of the cutting tool blank is 980-1030℃, the holding time is 2-6min, and the cooling circulating water is used for molding cooling.

[0026] In the preparation method of the food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tool, the specific parameters of the deep cryogenic treatment of the cutting tool blank in step 6 are as follows: cooling to -190℃ at a cooling rate of 0.5~1℃ / min, holding at the temperature for 2~20h, and then slowly heating to room temperature at a heating rate of 0.5~1℃ / min.

[0027] In the preparation method of the food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tool, in step 7, the cutting tool blank is immediately tempered after deep cooling. The tempering temperature is 200-500℃, the holding time is 3-6 hours, and then it is air-cooled to room temperature.

[0028] In the preparation method of the food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tool, in step 8, the cutting tool blank is immediately subjected to stress-relief annealing after tempering. The annealing temperature is 180-480℃, the holding time is 3h, and then it is furnace cooled to below 80℃ and air cooled to room temperature.

[0029] In the preparation method of the food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel knife, step 9 involves grinding and polishing the knife body using a single-sided grinding and polishing process, and then using a grinding wheel machine to perform coarse and fine edge sharpening on the ground and polished knife body.

[0030] The design concept of this invention is:

[0031] Vacuum pressure melting was used to prepare food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel ingots. Through forging, hot rolling, and isothermal spheroidizing annealing, a high-purity, uniformly composed, and densely structured tool substrate was obtained. Different shaped tool blanks were obtained through roll forging, die-pressing cooling quenching, cryogenic treatment, tempering, and stress-relief annealing. This process promoted martensitic phase transformation within the tool blanks and controlled quenching deformation. It also promoted the fine and dispersed precipitation of precipitates within the blank material, reduced austenite content, decreased residual stress, and increased dimensional stability and strength-toughness matching of the tool blanks. Finally, with grinding, polishing, and edge-sharpening processes, food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel tools with both functional and health-related properties were produced.

[0032] 1. Material Selection

[0033] Food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel has strictly limited content of elements such as Ni and Cu (Ni≤0.20%, Cu≤0.20%) that may cause potential harm to the human body. Furthermore, through the use of ultra-high purity raw materials, rare earth treatment (RE 0.002~0.030%), and vacuum pressure N alloying (ultra-high nitrogen 0.20~0.80%), the content of impurity elements (As+Sn+Sb+Bi+Pb≤0.0080%), residual elements, controlled elements, and gaseous elements can be strictly controlled to meet the health requirements of non-toxic and harmless knives in the food industry. Moreover, food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel is co-alloyed with C and N, which can produce a strong interstitial solid solution strengthening effect. In addition, it interacts with alloying elements such as Cr (13.0~16.0%) and Mo (0.50~1.50%) to effectively inhibit the formation of liquid carbides and network carbides. In addition, deep cryogenic treatment promotes the fine and dispersed precipitation of secondary precipitates during tempering, which has a strong precipitation strengthening effect. This ensures that knives for the food industry have high strength, high hardness, good wear resistance, corrosion resistance and appropriate impact toughness, thus possessing good sharpness, durability and corrosion resistance and other functional properties.

[0034] 2. Preparation method

[0035] A vacuum pressure induction melting furnace was used for melting. By adjusting the nitrogen partial pressure, food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel ingots with uniform composition, dense structure, and high purity were obtained. The ingots were heated to 1180–1260℃ for forging, with an initial forging temperature of 1080–1150℃ and a final forging temperature of 900–950℃. Subsequently, the ingots were hot-rolled to form tool substrates at 1100–1150℃, followed by isothermal spheroidizing annealing at 750–820℃. The annealed hot-rolled tool substrates were then roll-forged to obtain tool blanks with the initial tool morphology after blanking. The roll-forged tool blanks were then quenched (980–190℃). After being cooled by molding at 030℃, the blank is subjected to cryogenic treatment (-190℃). Then, the cryogenically cooled blank is tempered as soon as possible (200~500℃) to obtain a blank with a martensitic matrix, extremely low residual austenite content, and fine and dispersed precipitates. After tempering, the blank is further subjected to stress-relief annealing (180~480℃) to significantly reduce the residual stress inside the blank. After annealing, the blank is ground, polished, cleaned, and sharpened to obtain a finished blade with a bright surface. Finally, the shank and the blade are assembled to obtain a finished food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel blade with both functional and health properties.

[0036] The advantages and beneficial effects of this invention are:

[0037] 1. The food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel used in the knives of this invention is co-alloyed with C and N, which can produce a strong interstitial solid solution strengthening effect. It reacts with alloying elements such as Cr and Mo to effectively inhibit the formation of liquid carbides and network carbides. In addition, the deep cryogenic treatment promotes the fine and dispersed precipitation of secondary precipitates during tempering, which has a strong precipitation strengthening effect. This ensures that the knives in the food industry have high strength, high hardness, good wear resistance, corrosion resistance and appropriate impact toughness, so that the knives have good sharpness, durability and corrosion resistance and other functional properties.

[0038] 2. The food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel used in the knives of this invention has strictly limited the content of elements such as Ni and Cu that may cause potential harm to the human body in its chemical composition. Furthermore, by using ultra-high purity raw materials, rare earth treatment, and vacuum pressure N alloying technology, the content of impurity elements, residual elements, control elements, and gaseous elements is strictly controlled, so that the knives can meet the health requirements of non-toxic and harmless knives in the food industry.

[0039] 3. This invention employs vacuum pressure melting and N alloying technology, which can obtain food-grade, high-strength, corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel ingots with uniform composition, dense structure, and high purity, effectively solving the problem of N alloying in martensitic stainless steel. This technology is universally applicable and can be used for N alloying of high-nitrogen martensitic stainless steel and austenitic stainless steel.

[0040] 4. This invention employs techniques such as molding cooling quenching, deep cryogenic treatment, and stress-relief annealing, which effectively solves problems such as difficulty in controlling deformation during the quenching and cooling process of tool blanks, fine control of secondary precipitates during tempering, and excessive residual stress inside finished tools. It can significantly improve the quality stability and toughness matching of tools in the food industry, and avoid problems such as chipping, cracking, and rolling of the tool during actual use.

[0041] 5. This invention utilizes a complete processing technology, including pressure metallurgy, rare earth treatment, hot rolling of sheet metal, roll forging, die cooling, cryogenic treatment, tempering, stress-relief annealing, and grinding and polishing, to produce food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel knives. These knives possess excellent sharpness, durability, and corrosion resistance, as well as food-grade health attributes such as non-toxicity and harmlessness. Furthermore, the food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel substrate does not contain elements such as Ni and Cu that may cause potential harm to the human body. Therefore, it is not only suitable for manufacturing knives in the food industry but can also be extended to applications in fields such as medical devices where there is frequent contact with the human body and high health requirements. Attached Figure Description

[0042] Figure 1 Microstructure of food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tool substrate after hot rolling and annealing.

[0043] Figure 2 Microstructure of food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel tool blank after annealing.

[0044] Figure 3 This is a picture of a food-grade, high-strength, corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tool.

[0045] Figure 4 This is a comparison chart of the sharpness and durability of the ultra-high nitrogen martensitic cutting tool in Example 1 with high-end cutting tools from well-known domestic and foreign brands.

[0046] Figure 5 Comparison of local morphology after corrosion evaluation of the cutting edges of high-end cutting tools from different brands. Detailed Implementation

[0047] In specific implementation, the food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel knife base material of the present invention, by weight percentage, has the following alloy composition range: C: 0.20~0.50, N: 0.20~0.80, Cr: 13.0~16.0, Mo: 0.50~1.50, Mn: 0.10~0.60, Si: 0.30~0.80, RE: 0.002~0.030, Ni≤0.20, Cu≤0.20, Ti≤0.006, O≤0.0020, H≤0.0002, P≤0.015, S≤0.005, As+Sn+Sb+Bi+Pb≤0.0080, with the balance being Fe.

[0048] This invention relates to food-grade, high-strength, corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tools. These tools are manufactured using a complete processing technology encompassing pressure metallurgy, rare earth treatment, hot rolling of sheet metal, roll forging, die cooling, cryogenic treatment, tempering, stress-relief annealing, and grinding and polishing. The specific steps include:

[0049] (1) Pressure Melting: Molten steel is melted in a vacuum pressure induction melting furnace using high-purity carbon, ultra-high-purity iron, metallic chromium, metallic manganese, metallic silicon, and metallic molybdenum as alloying raw materials. The required high-purity raw materials are prepared according to the alloy composition requirements. After pre-deoxidation and Si and Mn alloying, high-purity nitrogen is introduced into the furnace, and the furnace pressure is adjusted to the target nitrogen partial pressure for N alloying. The target nitrogen partial pressure is maintained for 3-5 minutes. After N alloying, the superheat of the molten steel is adjusted to ΔT≤50℃, the bottom circulating cooling water switch of the mold is opened, and the nitrogen pressure in the melting chamber is kept constant. The equipment is rotated under nitrogen protection for ingot pouring and solidification.

[0050] (2) Homogeneous forging: The ingot is heated to 1180-1260℃ and subjected to high-temperature diffusion annealing. Subsequently, the oxide scale on the surface of the ingot is removed and forging is carried out, with a forging temperature range of 1150-950℃.

[0051] (3) Hot rolling of plate: Heat the forging billet to 1180~1220℃ and hold it for 1h / 100mm~2.5h / 100mm; then, control the total reduction and rolling passes, and roll the forging billet into a plate with a thickness of 3~6mm on a hot rolling mill. The final rolling temperature is 900~950℃, and the plate is air-cooled to room temperature after rolling.

[0052] (4) Isothermal spheroidizing annealing: The rolled sheet is subjected to isothermal spheroidizing annealing in the temperature range of 720 to 850℃ to eliminate the internal stress after rolling and to achieve uniform structure.

[0053] (5) Roll forging: The hot-rolled plate after being heated and annealed at 1150℃±20℃ is roll forged according to the blank size of different types of tools, and then the edges are cut to form tool blanks.

[0054] (6) Molding and cooling: Heat the tool blank to 980-1050℃, take it out and immediately put it into a molding press filled with circulating cooling water for molding and cooling to control the deformation of the tool blank.

[0055] (7) Cryogenic treatment: The molded and cooled tool blank is immediately placed into a cryogenic equipment for 2 to 20 hours of cryogenic treatment (interval time not exceeding 1 hour), and the cooling and heating rates of the cryogenic process are strictly controlled.

[0056] (8) Tempering treatment: The deep-cooled tool blanks are loaded into the furnace as soon as possible for tempering treatment. The tempering temperature is 200-500℃, the holding time is 3-6h, and then air-cooled to room temperature.

[0057] (9) Stress-relief annealing: The annealing temperature is 180-480℃ (20℃ lower than the tempering temperature), the holding time is 3-6h, then furnace cooling to below 80℃, and air cooling to room temperature.

[0058] (10) Grinding and polishing: The blade body is ground and polished using a single-sided grinding and polishing process. The blade body is then roughened and finely sharpened using a grinding wheel machine.

[0059] (11) Finished product assembly: Assemble the handle and the blade body to obtain the finished knife.

[0060] To make the technical solutions and advantages of the present invention clearer, a detailed description is provided below in conjunction with specific embodiments and accompanying drawings.

[0061] Example 1:

[0062] In this embodiment, the alloy composition of the food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel knife, by weight percentage, is: C 0.30%, N 0.45%, Cr 15.60%, Mo 1.00%, Mn 0.50%, Si 0.40%, RE(La) 0.0036%, Ni 0.07%, Cu 0.03%, Ti 0.004%, O 0.0018%, H 0.00015%, P 0.012%, S 0.003%, As+Sn+Sb+Bi+Pb=0.0045%, with the balance being Fe.

[0063] In this embodiment, the preparation process of the food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tool is as follows:

[0064] Molten steel was smelted in a vacuum pressure induction melting furnace. The alloying materials included high-purity carbon (99.99 wt%), ultra-high-purity iron (99.995 wt%), metallic chromium, metallic manganese, metallic silicon, and metallic molybdenum (chromium, manganese, silicon, and molybdenum all with a purity of 99.99 wt%). High-purity raw materials required for ingot casting were prepared according to the alloy composition requirements. High-purity carbon, ultra-high-purity iron, metallic chromium, and metallic molybdenum were placed in a magnesia crucible. After the alloying materials in the magnesia crucible were completely melted, metallic manganese and metallic silicon were added from the charging bin for Mn and Si alloying. After the melt was cleared, final deoxidation was performed. Then, high-purity rare earth metals (lanthanum with a total oxygen content of 180 ppm TO and a lanthanum content of 99.5 wt%) were added for rare earth treatment. High-purity nitrogen was introduced into the vacuum melting chamber by opening the nitrogen control valve, and the furnace pressure was adjusted to 0.7 MPa for N alloying. Stirring was intensified and maintained for 5 minutes. After N alloying is completed, the superheat of the molten steel is adjusted to 45℃. At this time, the bottom circulating cooling water switch of the mold is turned on to keep the nitrogen partial pressure in the furnace constant. The molten steel is poured steadily into the preheated ingot mold for 10 seconds. After pouring, the circulating cooling water continues to flow. After it is completely solidified, the water cooling system is turned off, and the ingot is demolded at high temperature to obtain food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel ingot.

[0065] The ingot was heated to 1200℃ and held for 4 hours for high-temperature homogenization diffusion annealing. The ingot was then forged into square bars with a cross-section of 120mm × 120mm within a temperature range of 1200–950℃ and air-cooled to room temperature. The square bars were then heated to 1200℃ and held for 1 hour before being hot-rolled on a rolling mill. After multiple passes, they were rolled into hot-rolled plates with dimensions of 5.0mm × 150mm × 1400mm and placed in a heat treatment furnace at a waiting temperature of 720℃ for isothermal spheroidizing annealing. After holding at this temperature for 5 hours, the plates were furnace-cooled to room temperature to relieve stress and homogenize the microstructure. Initial knife blanks for cleavers, slicing knives, kitchen knives, and fruit knives were obtained from the annealed hot-rolled plates. These blanks were heated in a heat treatment furnace at 1150℃ for 5 minutes, then roll-forged and trimmed on a rolling mill. The cutter blank, after roll forging and edge trimming, is heated to a quenching temperature of 980℃ and held for 5 minutes. It is then immediately removed and placed in a molding press equipped with circulating cooling water for molding cooling to control deformation. Next, it undergoes cryogenic treatment in a cryogenic chamber, with the cryogenic rate adjusted to cool to -190℃ at a rate of 0.75℃ / min. After holding at this temperature for 20 hours, the temperature is slowly increased to room temperature at a rate of 0.75℃ / min. Subsequently, the cryogenically cooled cutter blank is quickly placed in a tempering furnace, held at 500℃ for 4 hours, and then air-cooled to room temperature. Stress-relief annealing is then performed at 480℃, held for 4 hours, furnace-cooled to 60℃, and then air-cooled to room temperature. The stress-relief annealed cutter blank is then placed in a water grinder and polished to a bright blade using a single-sided polishing process. Finally, a grinding wheel is used to perform rough and fine edge sharpening on the polished blade. Finally, the handle is assembled with the sharpened blade to obtain a finished food-grade, high-strength, corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel knife.

[0066] like Figure 1 As shown in the optical micrograph of the annealed hot-rolled sheet, the precipitates in the microstructure of the annealed hot-rolled sheet are fine and dispersed.

[0067] like Figure 2 As shown in the scanning electron microscope image of the microstructure of the tool blank after tempering, the grains of the tool blank are fine, with a size of about 6 μm, and the fine secondary precipitates are uniformly distributed on its martensite matrix.

[0068] In this embodiment, the obtained food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tool is as follows: Figure 3 As shown in Table 1, the mechanical properties of the heat-treated tool blank samples from the embodiment were tested, and the test results are shown in Table 1.

[0069] Table 1 Mechanical properties of cutting tools used in the food industry both domestically and internationally.

[0070]

[0071]

[0072] As shown in Table 1, the hardness of the food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel in this embodiment is higher than that of brand-name knives in the food industry both domestically and internationally.

[0073] like Figure 4 and Figure 5 As shown, the results of the sharpness, durability, and corrosion resistance tests of food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel knives compared with those of domestic and foreign brand knives demonstrate that, compared with domestic and foreign brand knives, food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel knives possess excellent sharpness, durability, and corrosion resistance.

[0074] Example 2:

[0075] In this embodiment, the alloy composition of the food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tool, by weight percentage, is: C 0.42%, N 0.61%, Cr 14.30%, Mo 0.57%, Mn 0.25%, Si 0.31%, RE (La-Ce=1:1) 0.013%, Ni 0.05%, Cu 0.04%, Ti 0.005%, O 0.0016%, H 0.00010%, P 0.009%, S 0.004%, As+Sn+Sb+Bi+Pb=0.0037%, with the balance being Fe.

[0076] In this embodiment, the preparation process of the food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tool is as follows:

[0077] Molten steel was smelted in a vacuum pressure induction melting furnace. The alloying materials included high-purity carbon (99.99 wt%), ultra-high-purity iron (99.995 wt%), metallic chromium, metallic manganese, metallic silicon, and metallic molybdenum (chromium, manganese, silicon, and molybdenum all with a purity of 99.99 wt%). High-purity raw materials required for ingot casting were prepared according to the alloy composition requirements. High-purity carbon, ultra-high-purity iron, metallic chromium, and metallic molybdenum were placed in a magnesia crucible. After the alloying materials in the magnesia crucible were completely melted, metallic manganese and metallic silicon were added from the charging bin for Mn and Si alloying. After the melt was cleared, final deoxidation was performed. Then, high-purity rare earth metals (lanthanum and cerium mixed metal with a total oxygen content of 230 ppm TO and a lanthanum and cerium element content of 99.5 wt%) were added for rare earth treatment. High-purity nitrogen was introduced into the vacuum melting chamber by opening the nitrogen control valve, and the furnace pressure was adjusted to 0.8 MPa for N alloying. Stirring was intensified and maintained for 5 minutes. After N alloying is completed, the superheat of the molten steel is adjusted to 40℃. At this time, the bottom circulating cooling water switch of the mold is turned on to keep the nitrogen partial pressure in the furnace constant. The molten steel is poured steadily into the preheated ingot mold for 10 seconds. After pouring, the circulating cooling water continues to flow. After it is completely solidified, the water cooling system is turned off, and the ingot is demolded at high temperature to obtain food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel ingot.

[0078] The ingot was heated to 1220℃ and held for 3 hours for high-temperature homogenization diffusion annealing. The ingot was then forged into square bars with a cross-section of 120mm × 120mm within a temperature range of 1200–950℃ and air-cooled to room temperature. The square bars were then heated to 1180℃ and held for 1.5 hours before being hot-rolled on a rolling mill. After multiple passes, they were rolled into hot-rolled plates with dimensions of 5.0mm × 150mm × 1400mm and placed in a heat treatment furnace at a waiting temperature of 750℃ for isothermal spheroidizing annealing. After holding at this temperature for 6 hours, the plates were furnace-cooled to room temperature to relieve stress and homogenize the microstructure. Initial knife blanks for cleavers, slicing knives, kitchen knives, and fruit knives were obtained from the annealed hot-rolled plates. These blanks were heated in a heat treatment furnace at 1150℃ for 5 minutes, then roll-forged and trimmed on a rolling mill. The cutter blank, after roll forging and edge trimming, is heated to a quenching temperature of 1000℃ and held for 4 minutes. It is then immediately removed and placed in a molding press equipped with circulating cooling water for molding cooling to control deformation. Next, it undergoes cryogenic treatment in a cryogenic chamber, with the cryogenic rate adjusted to cool to -190℃ at a rate of 0.75℃ / min. After holding at this temperature for 20 hours, the temperature is slowly increased to room temperature at a rate of 0.75℃ / min. Subsequently, the cryogenically cooled cutter blank is quickly placed in a tempering furnace, held at 400℃ for 5 hours, and then air-cooled to room temperature. Stress-relief annealing is then performed at 420℃, held for 5 hours, furnace-cooled to 60℃, and then air-cooled to room temperature. The stress-relief annealed cutter blank is then placed in a water grinder and polished to a bright blade using a single-sided polishing process. Finally, a grinding wheel is used to perform rough and fine edge sharpening on the polished blade. Finally, the handle is assembled with the sharpened blade to obtain a finished food-grade, high-strength, corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel knife.

[0079] In this embodiment, the mechanical properties of the food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tool are as follows: tensile strength 2012MPa, hardness 60.5HRC.

[0080] Example 3:

[0081] In this embodiment, the alloy composition of the food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tool, by weight percentage, is: C 0.36%, N 0.52%, Cr 13.80%, Mo 1.25%, Mn 0.41%, Si 0.53%, RE(Ce) 0.012%, Ni 0.03%, Cu 0.05%, Ti 0.003%, O 0.0017%, H 0.00012%, P 0.008%, S 0.002%, As+Sn+Sb+Bi+Pb=0.0025%, with the balance being Fe.

[0082] In this embodiment, the preparation process of the food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tool is as follows:

[0083] Molten steel was smelted in a vacuum pressure induction melting furnace. The alloying materials included high-purity carbon (99.99 wt%), ultra-high-purity iron (99.995 wt%), metallic chromium, metallic manganese, metallic silicon, and metallic molybdenum (chromium, manganese, silicon, and molybdenum all with a purity of 99.99 wt%). High-purity raw materials required for ingot casting were prepared according to the alloy composition requirements. High-purity carbon, ultra-high-purity iron, metallic chromium, and metallic molybdenum were placed in a magnesia crucible. After the alloying materials in the magnesia crucible were completely melted, metallic manganese and metallic silicon were added from the charging bin for Mn and Si alloying. After the melt was cleared, final deoxidation was performed. Then, high-purity rare earth metals (cerium metal with a total oxygen content of 180 ppm TO and a cerium element content of 99.5 wt%) were added for rare earth treatment. High-purity nitrogen was introduced into the vacuum melting chamber by opening the nitrogen control valve, and the furnace pressure was adjusted to 1.0 MPa for N alloying. Stirring was intensified and maintained for 5 minutes. After N alloying is completed, the superheat of the molten steel is adjusted to 30°C. At this time, the bottom circulating cooling water switch of the mold is turned on to keep the nitrogen partial pressure in the furnace constant. The molten steel is poured steadily into the preheated ingot mold for 10 seconds. After pouring, the circulating cooling water continues to flow. After it is completely solidified, the water cooling system is turned off, and the ingot is demolded at high temperature to obtain food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel ingot.

[0084] The ingot was heated to 1240℃ and held for 3.5 hours for high-temperature homogenization diffusion annealing. The ingot was then forged into square bars with a cross-section of 120mm × 120mm within a temperature range of 1200–950℃ and air-cooled to room temperature. The square bars were then heated to 1190℃ and held for 2 hours before being hot-rolled on a rolling mill. After multiple passes, they were rolled into hot-rolled plates with dimensions of 5.0mm × 150mm × 1400mm and placed in a heat treatment furnace at a waiting temperature of 800℃ for isothermal spheroidizing annealing. After holding at this temperature for 4 hours, the plates were furnace-cooled to room temperature to relieve stress and homogenize the microstructure. Initial knife blanks for cleavers, slicing knives, kitchen knives, and fruit knives were obtained from the annealed hot-rolled plates. These blanks were heated in a heat treatment furnace at 1150℃ for 5 minutes, then roll-forged and trimmed on a rolling mill. The cutter blank, after roll forging and edge trimming, is heated to a quenching temperature of 1030℃ and held for 3 minutes. It is then immediately removed and placed in a molding press equipped with circulating cooling water for molding cooling to control deformation. Next, it undergoes cryogenic treatment in a cryogenic chamber, with the cryogenic rate adjusted to cool to -190℃ at a rate of 0.75℃ / min. After holding at this temperature for 20 hours, the temperature is slowly increased to room temperature at a rate of 0.75℃ / min. Subsequently, the cryogenically cooled cutter blank is quickly placed in a tempering furnace, held at 300℃ for 6 hours, and then air-cooled to room temperature. Stress-relief annealing is then performed at 370℃, held for 6 hours, furnace-cooled to 60℃, and then air-cooled to room temperature. The stress-relief annealed cutter blank is then placed in a water grinder and polished to a bright blade using a single-sided polishing process. Finally, a grinding wheel is used to perform rough and fine edge sharpening on the polished blade. Finally, the handle is assembled with the sharpened blade to obtain a finished food-grade, high-strength, corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel knife.

[0085] In this embodiment, the mechanical properties of the food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tool are as follows: tensile strength 1982MPa, hardness 60HRC.

[0086] The results of the embodiments show that the present invention successfully obtains food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tools with uniform composition, dense structure, high purity and excellent performance through a full-process processing technology including pressure metallurgy, rare earth treatment, hot rolling of plate, roll forging, die cooling, cryogenic treatment, tempering treatment, stress-relief annealing and grinding and polishing.

Claims

1. A method for preparing a food-grade, high-strength, corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tool, characterized in that, The base material of the knife is food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel alloy. The chemical composition, by weight percentage, ranges as follows: C: 0.20~0.50, N: 0.20~0.80, Cr: 13.0~16.0, Mo: 0.50~1.50, Mn: 0.10~0.60, Si: 0.30~0.80, RE: 0.002~0.030, Ni≤0.20, Cu≤0.20, Ti≤0.006, O≤0.0020, H≤0.0002, P≤0.015, S≤0.005, As+Sn+Sb+Bi+Pb≤0.0080, with the balance being Fe. The preparation method of the food-grade high-strength and corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tool includes the following steps: Step 1: Vacuum pressure melting technology is used to prepare ingots with high purity, uniform composition, and dense structure; Step 2: After high-temperature diffusion annealing, the ingot is homogeneously forged and hot-rolled to form the tool substrate; Step 3: After hot rolling, the tool substrate is subjected to isothermal spheroidizing annealing to eliminate internal stress, improve segregation, and homogenize the microstructure; Step 4: The hot-rolled tool substrate is roll-forged to obtain a tool blank with the initial tool morphology; Step 5: After roll forging, the tool blank is subjected to die pressing and cooling quenching to promote martensitic phase transformation and obtain martensitic structure, and to control the deformation of the tool blank during the quenching process. Step 6: After molding and cooling quenching, the tool blank is cryogenically treated in a cryogenic equipment to further reduce the content of residual austenite, improve the dimensional stability of the tool, and promote the precipitation of secondary precipitates after tempering. Step 7: After cryogenic treatment, the tool blank is tempered to regulate its microstructure and properties; Step 8: After tempering, the tool blank undergoes stress-relief annealing to significantly reduce the residual stress inside the tool blank. Step 9: After annealing, the tool blank undergoes a series of processes including grinding, polishing, cleaning, and sharpening to obtain a finished tool body with a bright surface. Step 10: Assemble the handle and the blade to obtain the finished knife.

2. The method for preparing food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tools according to claim 1, characterized in that, In step 1, vacuum pressure melting technology is used to melt the tool substrate using a vacuum pressure induction melting furnace. During the melting process, high-purity nitrogen gas is introduced at a pressure ≥7 atm, and the mixture is stirred and kept for 3 to 5 minutes to perform N alloying.

3. The method for preparing food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tools according to claim 1, characterized in that, In step 2, the ingot is heated to 1180-1260℃ for high-temperature diffusion annealing, with a holding time of 1h / 100mm to 2.5h / 100mm; the billet is opened using conventional forging methods, with a final forging temperature of not less than 950℃; after forging, the billet is heated to 1180-1220℃, with a holding time of 1h / 100mm to 2.5h / 100mm; thereafter, it is hot rolled in multiple passes to form a tool blank of a set thickness, with a final rolling temperature of 900-950℃, and then air-cooled to room temperature.

4. The method for preparing food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tools according to claim 1, characterized in that, In step 3, the isothermal spheroidizing annealing temperature of the hot-rolled tool substrate is 720-850℃, held for 3-6 hours, and then furnace cooled to room temperature.

5. The method for preparing food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tools according to claim 1, characterized in that, In step 4, the tool substrate is heated to 1150℃±20℃ before roll forging and held at that temperature for 3 to 6 minutes. The tool blank is then roll-forged according to the dimensions of different types of tools and the edges are trimmed.

6. The method for preparing food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tools according to claim 1, characterized in that, In step 5, the quenching temperature of the tool blank is 980-1030℃, the holding time is 2-6 minutes, and the molding cooling is carried out using cooling circulating water.

7. The method for preparing food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tools according to claim 1, characterized in that, In step 6, the specific parameters for the cryogenic treatment of the tool blank are as follows: cooling to -190℃ at a cooling rate of 0.5 to 1℃ / min, holding at that temperature for 2 to 20 hours, and then slowly heating to room temperature at a heating rate of 0.5 to 1℃ / min.

8. The method for preparing food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tools according to claim 1, characterized in that, In step 7, the tool blank is immediately tempered after deep cooling. The tempering temperature is 200-500℃, the holding time is 3-6 hours, and then it is air-cooled to room temperature.

9. The method for preparing food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tools according to claim 1, characterized in that, In step 8, the tool blank is immediately subjected to stress-relief annealing after tempering. The annealing temperature is 180-480℃, the holding time is 3 hours, and then it is furnace cooled to below 80℃ and air cooled to room temperature.

10. The method for preparing food-grade high-strength corrosion-resistant C30RE ultra-high nitrogen martensitic stainless steel cutting tools according to claim 1, characterized in that, In step 9, the blade body is polished using a single-sided polishing process, and the polished blade body is rough-sharpened and fine-sharpened using a grinding wheel machine.

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