A cryogenic treatment technique for reducing temper brittleness susceptibility of chromium-containing stainless steel

Abstract

This invention provides a heat treatment method and chromium-containing stainless steel products for reducing temper brittleness of chromium-containing stainless steel, comprising: austenitizing and quenching the chromium-containing stainless steel; pre-tempering the quenched chromium-containing stainless steel at 420-460°C; warm forging the pre-tempered chromium-containing stainless steel at 620-680°C; cryogenic treatment the warm-forged chromium-containing stainless steel at -201°C to -191°C; and finally tempering the cryogenically treated chromium-containing stainless steel after restoring it to room temperature, thereby obtaining chromium-containing stainless steel products with low temper brittleness. This application sequentially performs austenitizing, oil quenching, tempering-warm forging combined treatment, cryogenic treatment, and final tempering on forged chromium-containing stainless steel, overcoming the problem of existing chromium-containing stainless steel easily developing 475°C brittleness when tempered near 450°C, improving the impact toughness of chromium-containing stainless steel, effectively weakening the brittleness sensitivity of chromium-containing stainless steel, while maintaining high strength and good low-temperature toughness.

Description

Technical Field

[0001] This invention relates to the field of heat treatment technology for metallic materials, specifically to a heat treatment method for reducing the temper brittleness of chromium-containing stainless steel and chromium-containing stainless steel products. Background Technology

[0002] Martensitic-ferritic stainless steels possess excellent corrosion resistance and high strength, making them widely used in critical structural components in aerospace, shipbuilding, and energy industries, such as fasteners, blades, and shaft parts. To achieve superior overall mechanical properties, this type of steel typically requires quenching and tempering (quenching + high-temperature tempering).

[0003] However, chromium-containing stainless steel exhibits a significant decrease in impact toughness, known as "475℃ brittleness," when heated for extended periods or slowly cooled within the 450–550℃ temperature range. Studies show that 475℃ brittleness is caused by the amplitude-modulated decomposition of chromium atoms within the ferrite at this temperature, forming a chromium-rich α′ phase. This phase, along with the parent phase, causes lattice distortion and internal stress, leading to a sharp decrease in toughness. This brittleness is closely related to the chromium content in the steel: the higher the chromium content, the more prone it is to brittleness, and the brittleness-sensitive temperature range shifts towards higher temperatures, while the heating time required for brittleness to occur is shorter. 475℃ brittleness occurs in all types of stainless steel, including ferritic stainless steels (such as 1Cr17) ​​and martensitic-ferritic stainless steels (such as 1Cr13, 2Cr13, 1Cr17Ni2, and 1Cr17Ni3). This brittleness cannot be eliminated by rapid cooling and is a unique structural defect of stainless steel. In actual production, tempering processes around 450℃ are very common. How to weaken or avoid the adverse effects of 475℃ brittleness on material properties is a key technical challenge to improve the service safety of 1Cr17Ni2 steel.

[0004] Currently, to mitigate the 475℃ brittleness of chromium-containing stainless steel, methods typically involve avoiding the sensitive temperature range (e.g., tempering above 550℃ or below 400℃) or strictly limiting the holding time. However, both methods have limitations: high-temperature tempering significantly reduces material strength; low-temperature tempering cannot adequately eliminate quenching stress; and shortening the time makes it difficult to ensure microstructure uniformity. Cryogenic treatment, as a novel process, has been applied to improve the dimensional stability and wear resistance of mold steel and bearing steel, but research on reducing the 475℃ tempering brittleness sensitivity of chromium-containing stainless steel (such as 1Cr17Ni2 steel) has not been reported. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a heat treatment method and chromium-containing stainless steel products to reduce the temper brittleness of chromium-containing stainless steel. The aim is to overcome the tendency of existing chromium-containing stainless steel to develop 475℃ brittleness when tempered at around 450℃, improve the impact toughness of chromium-containing stainless steel, effectively weaken the brittleness sensitivity of chromium-containing stainless steel, and maintain the high strength and good low-temperature toughness of chromium-containing stainless steel.

[0006] In a first aspect, embodiments of this application provide a heat treatment method for reducing the temper brittleness of chromium-containing stainless steel, comprising: Chromium-containing stainless steel is subjected to austenitizing treatment and quenching. The quenched chromium-containing stainless steel is pre-tempered at a temperature of 420–460℃. The pre-tempered chromium-containing stainless steel is subjected to warm forging at a temperature of 620–680°C. The chromium-containing stainless steel after warm forging is subjected to deep cryogenic treatment at a temperature of -201℃ to -191℃. After cryogenic treatment, chromium-containing stainless steel is restored to room temperature and then subjected to final tempering to obtain chromium-containing stainless steel products with low temper brittleness.

[0007] Optionally, the cryogenic treatment holding time is 120 min to 2880 min.

[0008] Optionally, the cryogenic treatment holding time is 480 min to 720 min.

[0009] Optionally, before the warm forging treatment of chromium-containing stainless steel, the process further includes: heating the pre-tempered chromium-containing stainless steel to 620-680°C in the furnace and holding it at that temperature for 8-15 minutes.

[0010] Optionally, the holding time for the pre-tempering treatment is 50–65 min; Optionally, the final tempering treatment is performed at a temperature of 440–460°C for a holding time of 20–40 minutes.

[0011] Optionally, the austenitizing treatment involves heating the chromium-containing stainless steel to 1000–1040°C and holding it for 120–160 minutes. Optionally, the quenching is oil quenching; Optionally, the warm forging process is a multi-pass forging process with a cumulative deformation of 80% to 85%.

[0012] Optionally, the chromium-containing stainless steel is a martensitic-ferritic stainless steel or a ferritic stainless steel, with a chromium content ≥13%.

[0013] Optionally, the chromium-containing stainless steel is 1Cr17Ni2 steel, 1Cr13 steel, or 2Cr13 steel.

[0014] Optionally, the chemical composition of 1Cr17Ni2 steel is as follows (mass fraction): C 0.11-0.17%, Si ≤0.8%, Mn ≤0.8%, P ≤0.03%, S ≤0.025%, Cr 16-18%, Ni 1.5-2.5%, with the balance being Fe and unavoidable impurities.

[0015] 10. A chromium-containing stainless steel product, characterized in that it is prepared by the method according to any one of claims 1 to 9, wherein the content of chromium-rich α′ phase in the microstructure of the product after tempering at 450°C is lower than that of the comparative product without cryogenic treatment.

[0016] Secondly, embodiments of this application provide a chromium-containing stainless steel product prepared using a heat treatment method that reduces the temper brittleness of chromium-containing stainless steel. After tempering at 450°C, the chromium-rich α′ phase content in the microstructure of the chromium-containing stainless steel product is lower than that of the comparative product without cryogenic treatment.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention promotes the full transformation of retained austenite to martensite by precisely controlling cryogenic treatment parameters, while effectively regulating the distribution of residual stress, homogenizing the stress state of the microstructure, and suppressing the amplitude-modulated decomposition of chromium atoms, thereby reducing the 475℃ temper brittleness sensitivity of stainless steel. Specifically, this invention employs a process chain of pre-tempering, warm forging, cryogenic treatment, and final tempering. The synergistic effect of pre-tempering and warm forging alters the precipitation kinetics of chromium during subsequent tempering, and cryogenic treatment further stabilizes the microstructure, thus suppressing 475℃ brittleness. Taking chromium-containing stainless steel, including 1Cr17Ni2 steel, as an example, this method significantly reduces the impact toughness loss after tempering at 450℃ (the 475℃ brittleness-sensitive range), while maintaining a tensile strength ≥1200MPa, increasing the low-temperature impact energy at -60℃ to over 60J, and improving the uniformity of the microstructure. Compared with traditional quenching and tempering treatments and single tempering processes, this invention effectively weakens the 475℃ temper brittleness sensitivity of stainless steel while significantly improving the yield strength of the material. Attached Figure Description

[0018] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0019] Figure 1 This is a schematic flowchart of a heat treatment method for reducing temper brittleness of chromium-containing stainless steel according to an embodiment of this application.

[0020] Figure 2This is a schematic diagram of the process flow of a heat treatment method for reducing the temper brittleness of chromium-containing stainless steel according to an embodiment of this application.

[0021] Figure 3 Scanning electron microscope (SEM) image of the microstructure of 1Cr17Ni2 steel after treatment in Example 4 of the heat treatment method for reducing temper brittleness of chromium-containing stainless steel provided in an embodiment of this application.

[0022] Figure 4 Scanning electron microscope (SEM) image of the microstructure of 1Cr17Ni2 steel after treatment in Comparative Example 1, which is part of the heat treatment method for reducing temper brittleness of chromium-containing stainless steel provided in an embodiment of this application.

[0023] Figure 5 Scanning electron microscope (SEM) image of the microstructure of 1Cr17Ni2 steel after treatment in Comparative Example 3, which is part of the heat treatment method for reducing temper brittleness of chromium-containing stainless steel provided in an embodiment of this application.

[0024] Figure 6 The XRD patterns of 1Cr17Ni2 steel treated by Comparative Example 1 and Examples 1-6 of the present invention in the heat treatment method for reducing temper brittleness of chromium-containing stainless steel provided in an embodiment of this application.

[0025] Figure 7 Transmission electron microscopy (TEM) images of 1Cr17Ni2 steel treated in Examples 3 and 4 of the heat treatment method for reducing temper brittleness of chromium-containing stainless steel provided in an embodiment of this application.

[0026] Figure 8 Transmission electron microscopy (TEM) image and high-resolution image of 1Cr17Ni2 steel after treatment in Example 4 of the heat treatment method for reducing temper brittleness of chromium-containing stainless steel provided in an embodiment of this application.

[0027] Figure 9 The strain field diagrams of 1Cr17Ni2 steel treated by Comparative Example 1 and Examples 1-6 of the present invention after being processed by geometric phase analysis in the heat treatment method for reducing the temper brittleness of chromium-containing stainless steel provided in an embodiment of this application are shown.

[0028] Figure 10 The image shows a transmission dark field image of 1Cr17Ni2 steel after treatment in Comparative Example 3 and the corresponding EDS surface scan of Cr element in the heat treatment method for reducing temper brittleness of chromium-containing stainless steel provided in an embodiment of this application.

[0029] Figure 11 The transmission dark field image and the corresponding EDS surface scan of Cr element of 1Cr17Ni2 steel after treatment in the heat treatment method for reducing temper brittleness of chromium-containing stainless steel provided in an embodiment of this application. Figure 12The transmission dark field image and the corresponding EDS surface scan of Cr element of 1Cr17Ni2 steel after treatment in the heat treatment method for reducing temper brittleness of chromium-containing stainless steel provided in an embodiment of this application. Figure 13 The transmission dark field image and the corresponding EDS surface scan of Cr element of 1Cr17Ni2 steel after treatment in Example 4 of the heat treatment method for reducing temper brittleness of chromium-containing stainless steel provided in an embodiment of this application. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0031] When a quantity, concentration, or other value or parameter is described as a range, preferred range, or preferred upper and lower limits, it should be understood that it is equivalent to specifically disclosing any range by combining any pair of upper or preferred values ​​with any lower or preferred values, regardless of whether the range is specifically disclosed. Unless otherwise stated, the numerical range values ​​listed herein include the endpoints of the range and all integers and fractions within that range.

[0032] Unless otherwise stated, all percentages, parts, ratios, etc. in this document are by weight.

[0033] The materials, methods, and embodiments described herein are exemplary and should not be construed as limiting unless otherwise stated.

[0034] Unless otherwise specified, all raw materials or reagents in the following embodiments can be obtained through commercial purchases or prepared using conventional methods in the art.

[0035] This embodiment uses, as follows: Figure 1 The heat treatment method shown reduces the temper brittleness of chromium-containing stainless steel. Figure 2 Heat treatment, forging, and cryogenic treatment methods to improve the temper brittleness sensitivity of 1Cr17Ni2 steel at 475℃. Heat treatment methods to reduce temper brittleness in chromium-containing stainless steel include: S1, austenitizing and quenching of chromium-containing stainless steel; S2, pre-tempering the quenched chromium-containing stainless steel at a temperature of 420-460℃. S3 involves warm forging pre-tempered chromium-containing stainless steel at a temperature of 620–680°C. S4 involves subjecting warm-forged chromium-containing stainless steel to cryogenic treatment at temperatures ranging from -201℃ to -191℃. S5 involves restoring the cryogenically treated chromium-containing stainless steel to room temperature and then performing a final tempering treatment to obtain chromium-containing stainless steel products with low temper brittleness.

[0036] This invention uses 1Cr17Ni2 steel as an example for detailed explanation. However, the method of this invention, based on the inhibitory effect of cryogenic treatment on the decomposition of chromium, can also be extended to other chromium-containing stainless steels (such as 1Cr17, 1Cr13, 2Cr13, 1Cr17Ni3, etc.). Those skilled in the art, based on the teachings of this invention, can adjust the process parameters to a range suitable for the corresponding steel grade without creative effort. The 1Cr17Ni2 steel used in this invention has the following chemical composition by mass fraction: C 0.11–0.17%, Si ≤0.8%, Mn ≤0.8%, P ≤0.03%, S ≤0.025%, Cr 16–18%, Ni 1.5–2.5%, with the balance being Fe and unavoidable impurities. The initial sample used is a cylinder with a diameter of 100 mm × 100 mm. In the following embodiments, the austenitizing temperature is 1030℃ and the holding time is 140 min (the allowable range of this invention is 1000~1040℃, 120 min~160 min), the warm forging temperature is 650℃ (the allowable range is 620~680℃), the cumulative deformation of warm forging is 80% (the allowable range is 80%~85%, corresponding to a side length of 34~39 mm for the finished product cross section), and the tempering treatment is 450℃ for 60 min (the allowable range is 50~65 min) followed by furnace heating to 650℃ for 10 min (the allowable range is 620~680℃, 8~15 min).

[0037] Example 1:

[0038] Using a 3-ton free forging machine, it can forge forgings up to 5 tons. The billet diameter is 100mm, the finished square bar is 38mm, and the corresponding deformation is 80%.

[0039] (1) Polish the surface of a sample with a diameter of 100 mm and a length of 100 mm to remove rust and oxide scale until the metal luster is exposed.

[0040] (2) Clean the polished surface with alcohol to remove stains and blow dry.

[0041] The specific operations for heat treatment, forging, and cryogenic processes are as follows: (1) Heat the muffle furnace to 1030℃. After the temperature reaches the specified temperature (1030℃), put in the cleaned 1Cr17Ni2 steel and keep it at that temperature for 140 minutes.

[0042] (2) Immediately perform oil quenching (oil temperature is room temperature).

[0043] (3) Set the muffle furnace temperature to 450℃. After the temperature reaches the specified temperature (450℃), put the oil-quenched 1Cr17Ni2 steel into the furnace and hold it for 60 minutes. Then, raise the furnace temperature to 650℃ and hold it for 10 minutes. At this temperature, perform multi-pass elongation forging with a cumulative deformation of 80% (the side length of the elongated section is about 38 mm). After forging, oil cool to room temperature. The specific operation is that the finished side length of the warm-forged elongated square bar is 38 mm. The reduction amount in each warm-forging elongation process is about 5 mm. After 13 forging passes, put it into the oil bath for quenching to room temperature and then take it out.

[0044] (4) Take out the 1Cr17Ni2 steel that has been cooled to room temperature by warm forging oil, and cut the forged 1Cr17Ni2 steel into square bars with a length of 10mm, a width of 10mm and a height of 100mm using a wire cutting device.

[0045] (5) Immerse the cut 1Cr17Ni2 steel in liquid nitrogen at -196℃ for 120 minutes, then remove it and allow it to naturally return to room temperature in the air.

[0046] (6) After cryogenic treatment, the sample was placed in a muffle furnace at 450℃ for 30 minutes for tempering and then oil cooled.

[0047] Example 2:

[0048] Using a 3-ton free forging machine, it can forge forgings up to 5 tons. The billet diameter is 100mm, the finished square bar is 38mm, and the corresponding deformation is 80%.

[0049] (1) Polish the surface of a sample with a diameter of 100 mm and a length of 100 mm to remove rust and oxide scale until the metal luster is exposed.

[0050] (2) Clean the polished surface with alcohol to remove stains and blow dry.

[0051] The specific operations for heat treatment, forging, and cryogenic processes are as follows: (1) Heat the muffle furnace to 1030℃. After the temperature reaches the specified temperature (1030℃), put in the cleaned 1Cr17Ni2 steel and keep it at that temperature for 140 minutes.

[0052] (2) Immediately perform oil quenching (oil temperature is room temperature).

[0053] (3) Set the muffle furnace temperature to 450℃. After the temperature reaches the specified temperature (450℃), put the oil-quenched 1Cr17Ni2 steel into the furnace and hold it for 60 minutes. Then, raise the furnace temperature to 650℃ and hold it for 10 minutes. At this temperature, perform multi-pass elongation forging with a cumulative deformation of 80% (the side length of the elongated section is about 38 mm). After forging, oil cool to room temperature. The specific operation is that the finished side length of the warm-forged elongated square bar is 38 mm. The reduction amount in each warm-forging elongation process is about 5 mm. After 13 forging passes, put it into the oil bath for quenching to room temperature and then take it out.

[0054] (4) Take out the 1Cr17Ni2 steel that has been cooled to room temperature by warm forging oil, and cut the forged 1Cr17Ni2 steel into square bars with a length of 10mm, a width of 10mm and a height of 100mm using a wire cutting device.

[0055] (5) Immerse the cut 1Cr17Ni2 steel in liquid nitrogen at -196℃ for 240 minutes, then remove it and allow it to naturally return to room temperature in the air.

[0056] (6) After cryogenic treatment, the sample was placed in a muffle furnace at 450℃ for 30 minutes for tempering and then oil cooled.

[0057] Example 3:

[0058] Using a 3-ton free forging machine, it can forge forgings up to 5 tons. The billet diameter is 100mm, the finished square bar is 38mm, and the corresponding deformation is 80%.

[0059] (1) Polish the surface of a sample with a diameter of 100 mm and a length of 100 mm to remove rust and oxide scale until the metal luster is exposed.

[0060] (2) Clean the polished surface with alcohol to remove stains and blow dry.

[0061] The specific operations for heat treatment, forging, and cryogenic processes are as follows: (1) Heat the muffle furnace to 1030℃. After the temperature reaches the specified temperature (1030℃), put in the cleaned 1Cr17Ni2 steel and keep it at that temperature for 140 minutes.

[0062] (2) Immediately perform oil quenching (oil temperature is room temperature).

[0063] (3) Set the muffle furnace temperature to 450℃. After the temperature reaches the specified temperature (450℃), put the oil-quenched 1Cr17Ni2 steel into the furnace and hold it for 60 minutes. Then, raise the furnace temperature to 650℃ and hold it for 10 minutes. At this temperature, perform multi-pass elongation forging with a cumulative deformation of 80% (the side length of the elongated section is about 38 mm). After forging, oil cool to room temperature. The specific operation is that the finished side length of the warm-forged elongated square bar is 38 mm. The reduction amount in each warm-forging elongation process is about 5 mm. After 13 forging passes, put it into the oil bath for quenching to room temperature and then take it out.

[0064] (4) Take out the 1Cr17Ni2 steel that has been cooled to room temperature by warm forging oil, and cut the forged 1Cr17Ni2 steel into square bars with a length of 10mm, a width of 10mm and a height of 100mm using a wire cutting device.

[0065] (5) Immerse the cut 1Cr17Ni2 steel in liquid nitrogen at -196℃ for 480 minutes, then remove it and allow it to naturally return to room temperature in the air.

[0066] (6) After cryogenic treatment, the sample was placed in a muffle furnace at 450℃ for 30 minutes for tempering and then oil cooled.

[0067] Example 4:

[0068] Using a 3-ton free forging machine, it can forge forgings up to 5 tons. The billet diameter is 100mm, the finished square bar is 38mm, and the corresponding deformation is 80%.

[0069] (1) Polish the surface of a sample with a diameter of 100 mm and a length of 100 mm to remove rust and oxide scale until the metal luster is exposed.

[0070] (2) Clean the polished surface with alcohol to remove stains and blow dry.

[0071] The specific operations for heat treatment, forging, and cryogenic processes are as follows: (1) Heat the muffle furnace to 1030℃. After the temperature reaches the specified temperature (1030℃), put in the cleaned 1Cr17Ni2 steel and keep it at that temperature for 140 minutes.

[0072] (2) Immediately perform oil quenching (oil temperature is room temperature).

[0073] (3) Set the muffle furnace temperature to 450℃. After the temperature reaches the specified temperature (450℃), put the oil-quenched 1Cr17Ni2 steel into the furnace and hold it for 60 minutes. Then, raise the furnace temperature to 650℃ and hold it for 10 minutes. At this temperature, perform multi-pass elongation forging with a cumulative deformation of 80% (the side length of the elongated section is about 38 mm). After forging, oil cool to room temperature. The specific operation is that the finished side length of the warm-forged elongated square bar is 38 mm. The reduction amount in each warm-forging elongation process is about 5 mm. After 13 forging passes, put it into the oil bath for quenching to room temperature and then take it out.

[0074] (4) Take out the 1Cr17Ni2 steel that has been cooled to room temperature by warm forging oil, and cut the forged 1Cr17Ni2 steel into square bars with a length of 10mm, a width of 10mm and a height of 100mm using a wire cutting device.

[0075] (5) Immerse the cut 1Cr17Ni2 steel in liquid nitrogen at -196℃ for 720 minutes, then remove it and allow it to naturally return to room temperature in the air.

[0076] (6) After cryogenic treatment, the sample was placed in a muffle furnace at 450℃ for 30 minutes for tempering and then oil cooled.

[0077] Example 5:

[0078] Using a 3-ton free forging machine, it can forge forgings up to 5 tons. The billet diameter is 100mm, the finished square bar is 38mm, and the corresponding deformation is 80%.

[0079] (1) Polish the surface of a sample with a diameter of 100 mm and a length of 100 mm to remove rust and oxide scale until the metal luster is exposed.

[0080] (2) Clean the polished surface with alcohol to remove stains and blow dry.

[0081] The specific operations for heat treatment, forging, and cryogenic processes are as follows: (1) Heat the muffle furnace to 1030℃. After the temperature reaches the specified temperature (1030℃), put in the cleaned 1Cr17Ni2 steel and keep it at that temperature for 140 minutes.

[0082] (2) Immediately perform oil quenching (oil temperature is room temperature).

[0083] (3) Set the muffle furnace temperature to 450℃. After the temperature reaches the specified temperature (450℃), put the oil-quenched 1Cr17Ni2 steel into the furnace and hold it for 60 minutes. Then, raise the furnace temperature to 650℃ and hold it for 10 minutes. At this temperature, perform multi-pass elongation forging with a cumulative deformation of 80% (the side length of the elongated section is about 38 mm). After forging, oil cool to room temperature. The specific operation is that the finished side length of the warm-forged elongated square bar is 38 mm. The reduction amount in each warm-forging elongation process is about 5 mm. After 13 forging passes, put it into the oil bath for quenching to room temperature and then take it out.

[0084] (4) Take out the 1Cr17Ni2 steel that has been cooled to room temperature by warm forging oil, and cut the forged 1Cr17Ni2 steel into square bars with a length of 10mm, a width of 10mm and a height of 100mm using a wire cutting device.

[0085] (5) Immerse the cut 1Cr17Ni2 steel in liquid nitrogen at -196℃ for 1440 min, then remove it and allow it to naturally return to room temperature in the air.

[0086] (6) After cryogenic treatment, the sample was placed in a muffle furnace at 450℃ for 30 minutes for tempering and then oil cooled.

[0087] Example 6:

[0088] Using a 3-ton free forging machine, it can forge forgings up to 5 tons. The billet diameter is 100mm, the finished square bar is 38mm, and the corresponding deformation is 80%.

[0089] (1) Polish the surface of a sample with a diameter of 100 mm and a length of 100 mm to remove rust and oxide scale until the metal luster is exposed.

[0090] (2) Clean the polished surface with alcohol to remove stains and blow dry.

[0091] The specific operations for heat treatment, forging, and cryogenic processes are as follows: (1) Heat the muffle furnace to 1030℃. After the temperature reaches the specified temperature (1030℃), put in the cleaned 1Cr17Ni2 steel and keep it at that temperature for 140 minutes.

[0092] (2) Immediately perform oil quenching (oil temperature is room temperature).

[0093] (3) Set the muffle furnace temperature to 450℃. After the temperature reaches the specified temperature (450℃), put the oil-quenched 1Cr17Ni2 steel into the furnace and hold it for 60 minutes. Then, raise the furnace temperature to 650℃ and hold it for 10 minutes. At this temperature, perform multi-pass elongation forging with a cumulative deformation of 80% (the side length of the elongated section is about 38 mm). After forging, oil cool to room temperature. The specific operation is that the finished side length of the warm-forged elongated square bar is 38 mm. The reduction amount in each warm-forging elongation process is about 5 mm. After 13 forging passes, put it into the oil bath for quenching to room temperature and then take it out.

[0094] (4) Take out the 1Cr17Ni2 steel that has been cooled to room temperature by warm forging oil, and cut the forged 1Cr17Ni2 steel into square bars with a length of 10mm, a width of 10mm and a height of 100mm using a wire cutting device.

[0095] (5) Immerse the cut 1Cr17Ni2 steel in liquid nitrogen at -196℃ for 2880 min, then remove it and allow it to naturally return to room temperature in the air.

[0096] (6) After cryogenic treatment, the sample was placed in a muffle furnace at 450℃ for 30 minutes for tempering and then oil cooled.

[0097] Example 7:

[0098] Using a 3-ton free forging machine, it can forge forgings up to 5 tons. The billet diameter is 100mm, the finished square bar is 38mm, and the corresponding deformation is 80%.

[0099] (1) Polish the surface of a sample with a diameter of 100 mm and a length of 100 mm to remove rust and oxide scale until the metal luster is exposed.

[0100] (2) Clean the polished surface with alcohol to remove stains and blow dry.

[0101] The specific operations for heat treatment, forging, and cryogenic processes are as follows: (1) Heat the muffle furnace to 1000℃. After the temperature reaches the specified temperature (1000℃), put in the cleaned 1Cr17Ni2 steel and keep it at that temperature for 160 minutes.

[0102] (2) Immediately perform oil quenching (oil temperature is room temperature).

[0103] (3) Set the muffle furnace temperature to 420℃. After the temperature reaches the specified temperature, put the oil-quenched 1Cr17Ni2 steel into the furnace and hold it for 65 minutes. Then, raise the furnace temperature to 680℃ and hold it for 15 minutes. At this temperature, perform multi-pass elongation forging with a cumulative deformation of 82% (the side length of the elongated section is about 38 mm). After forging, oil cool to room temperature. The specific operation is that the finished side length of the warm-forged elongated square bar is 38 mm. The reduction amount in each warm-forging elongation process is about 5 mm. After 13 forging passes, put it into the oil bath for quenching to room temperature and then take it out.

[0104] (4) Take out the 1Cr17Ni2 steel that has been cooled to room temperature by warm forging oil, and cut the forged 1Cr17Ni2 steel into square bars with a length of 10mm, a width of 10mm and a height of 100mm using a wire cutting device.

[0105] (5) Immerse the cut 1Cr17Ni2 steel in liquid nitrogen at -201℃ for 480 minutes, then remove it and allow it to naturally return to room temperature in the air.

[0106] (6) After cryogenic treatment, the sample was placed in a muffle furnace at 440℃ for 20 minutes for tempering and then oil cooled.

[0107] Example 8:

[0108] Using a 3-ton free forging machine, it can forge forgings up to 5 tons. The billet diameter is 100mm, the finished square bar is 38mm, and the corresponding deformation is 80%.

[0109] (1) Polish the surface of a sample with a diameter of 100 mm and a length of 100 mm to remove rust and oxide scale until the metal luster is exposed.

[0110] (2) Clean the polished surface with alcohol to remove stains and blow dry.

[0111] The specific operations for heat treatment, forging, and cryogenic processes are as follows: (1) Heat the muffle furnace to 1040℃. After the temperature reaches the specified temperature (1040℃), put in the cleaned 1Cr17Ni2 steel and keep it at that temperature for 120 minutes.

[0112] (2) Immediately perform oil quenching (oil temperature is room temperature).

[0113] (3) Set the muffle furnace temperature to 460℃. After the temperature reaches the specified temperature (460℃), put the oil-quenched 1Cr17Ni2 steel into the furnace and hold it for 50 minutes. Then, raise the furnace temperature to 620℃ and hold it for 8 minutes. At this temperature, perform multi-pass elongation forging with a cumulative deformation of 82% (the side length of the elongated section is about 38 mm). After forging, oil cool to room temperature. The specific operation is that the finished side length of the warm-forged elongated square bar is 38 mm. The reduction amount in each warm-forging elongation process is about 5 mm. After 13 forging passes, put it into the oil bath for quenching to room temperature and then take it out.

[0114] (4) Take out the 1Cr17Ni2 steel that has been cooled to room temperature by warm forging oil, and cut the forged 1Cr17Ni2 steel into square bars with a length of 10mm, a width of 10mm and a height of 100mm using a wire cutting device.

[0115] (5) Immerse the cut 1Cr17Ni2 steel in liquid nitrogen at -191℃ for 720 minutes, then remove it and allow it to naturally return to room temperature in the air.

[0116] (6) After cryogenic treatment, the sample was placed in a muffle furnace at 460℃ for 40 minutes for tempering and then oil cooled.

[0117] Example 9:

[0118] Using a 3-ton free forging machine, it can forge forgings up to 5 tons. The billet diameter is 100mm, the finished square bar is 38mm, and the corresponding deformation is 80%.

[0119] (1) Polish the surface of a sample with a diameter of 100 mm and a length of 100 mm to remove rust and oxide scale until the metal luster is exposed.

[0120] (2) Clean the polished surface with alcohol to remove stains and blow dry.

[0121] The specific operations for heat treatment, forging, and cryogenic processes are as follows: (1) Heat the muffle furnace to 1030℃. After the temperature reaches the specified temperature (1030℃), put in the cleaned 1Cr13 steel and hold for 140 minutes.

[0122] (2) Immediately perform oil quenching (oil temperature is room temperature).

[0123] (3) Set the muffle furnace temperature to 450℃. After the temperature reaches the specified temperature (450℃), put the oil-quenched 1Cr13 steel into the furnace and hold it for 60 minutes. Then, raise the furnace temperature to 650℃ and hold it for 10 minutes. At this temperature, perform multi-pass elongation forging with a cumulative deformation of 80% (the side length of the elongated section is about 38 mm). After forging, oil cool to room temperature. The specific operation is that the finished side length of the warm-forged elongated square bar is 38 mm. The reduction amount in each warm-forging elongation process is about 5 mm. After 13 forging passes, put it into the oil bath for quenching to room temperature and then take it out.

[0124] (4) Take out the 1Cr13 steel that has been cooled to room temperature by warm forging oil, and cut the forged 1Cr13 steel into square bars with a length of 10mm, a width of 10mm and a height of 100mm using a wire cutting device.

[0125] (5) Immerse the cut 1Cr13 steel in liquid nitrogen at -196℃ for 720 minutes, then remove it and allow it to naturally return to room temperature in the air.

[0126] (6) After cryogenic treatment, the sample was placed in a muffle furnace at 450℃ for 30 minutes for tempering and then oil cooled.

[0127] Example 10:

[0128] Using a 3-ton free forging machine, it can forge forgings up to 5 tons. The billet diameter is 100mm, the finished square bar is 38mm, and the corresponding deformation is 80%.

[0129] (1) Polish the surface of a sample with a diameter of 100 mm and a length of 100 mm to remove rust and oxide scale until the metal luster is exposed.

[0130] (2) Clean the polished surface with alcohol to remove stains and blow dry.

[0131] The specific operations for heat treatment, forging, and cryogenic processes are as follows: (1) Heat the muffle furnace to 1000℃. After the temperature reaches the specified temperature (1000℃), put in the cleaned 2Cr13 steel and keep it at that temperature for 140 minutes.

[0132] (2) Immediately perform oil quenching (oil temperature is room temperature).

[0133] (3) Set the muffle furnace temperature to 450℃. After the temperature reaches the specified temperature (450℃), put the oil-quenched 2Cr13 steel into the furnace and hold it for 60 minutes. Then, raise the furnace temperature to 650℃ and hold it for 10 minutes. At this temperature, perform multi-pass elongation forging with a cumulative deformation of 80% (the side length of the elongated section is about 38 mm). After forging, oil cool to room temperature. The specific operation is that the finished side length of the warm-forged elongated square bar is 38 mm. The reduction amount in each warm-forging elongation process is about 5 mm. After 13 forging passes, put it into the oil bath for quenching to room temperature and then take it out.

[0134] (4) Take out the 2Cr13 steel that has been cooled to room temperature by warm forging oil, and cut the forged 2Cr13 steel into square bars with a length of 10mm, a width of 10mm and a height of 100mm using a wire cutting device.

[0135] (5) Immerse the cut 2Cr13 steel in liquid nitrogen at -196℃ for 720 minutes, then remove it and allow it to naturally return to room temperature in the air.

[0136] (6) After cryogenic treatment, the sample was placed in a muffle furnace at 450℃ for 30 minutes for tempering and then oil cooled.

[0137] Comparative Example 1: Steps (1) to (4) are the same as in Examples 1 to 6. After forging, the oil is cooled to room temperature, but no deep cryogenic treatment is performed. Instead, the oil is directly tempered at 450°C for 30 minutes and then cooled.

[0138] Comparative Example 2: Using a 3-ton free forging machine, it can forge forgings up to 5 tons. The billet diameter is 100mm, the finished square bar is 38mm, and the corresponding deformation is 80%.

[0139] (1) Polish the surface of a sample with a diameter of 100 mm and a length of 100 mm to remove rust and oxide scale until the metal luster is exposed.

[0140] (2) Clean the polished surface with alcohol to remove stains and blow dry.

[0141] The specific operations for heat treatment, forging, and cryogenic processes are as follows: (1) Heat the muffle furnace to 1030℃. After the temperature reaches the specified temperature (1030℃), put in the cleaned 1Cr17Ni2 steel and keep it at that temperature for 140 minutes.

[0142] (2) Immediately perform oil quenching (oil temperature is room temperature).

[0143] (3) Set the muffle furnace temperature to 450℃. After the temperature reaches the specified temperature (450℃), put the oil-quenched 1Cr17Ni2 steel into the furnace and hold it for 60 minutes. Then, raise the furnace temperature to 650℃ and hold it for 10 minutes. At this temperature, perform multi-pass elongation forging with a cumulative deformation of 80% (the side length of the elongated section is about 38 mm). After forging, oil cool to room temperature. The specific operation is that the finished side length of the warm-forged elongated square bar is 38 mm. The reduction amount in each warm-forging elongation process is about 5 mm. After 13 forging passes, put it into the oil bath for quenching to room temperature and then take it out.

[0144] (4) Take out the 1Cr17Ni2 steel that has been cooled to room temperature by warm forging oil, and cut the forged 1Cr17Ni2 steel into square bars with a length of 10mm, a width of 10mm and a height of 100mm using a wire cutting device.

[0145] (5) The cut 1Cr17Ni2 steel was placed in a muffle furnace at 450℃ and held for 30 minutes for tempering treatment, and then oil cooled.

[0146] (6) After tempering, 1Cr17Ni2 steel is immersed in liquid nitrogen at -196℃ for 720 minutes and then taken out and allowed to recover to room temperature naturally in the air.

[0147] Comparative Example 3: (1) Use an angle grinder and sandpaper to grind the surface with a diameter of 100mm and a length of 100mm to remove rust, oxide film and other substances until the surface is shiny.

[0148] (2) Clean the polished surface with alcohol to remove the stains, and then dry it with a hair dryer.

[0149] (3) Austenitizing the 1Cr17Ni2 steel sample: heating to 1030℃ in a muffle furnace, holding for 140 min, and then oil quenching.

[0150] (4) The oil-quenched sample was kept at 450℃ for 160 min for tempering, and then oil-quenched to room temperature.

[0151] Comparative Example 4: (1) Use an angle grinder and sandpaper to grind the surface with a diameter of 100mm and a length of 100mm to remove rust, oxide film and other substances until the surface is shiny.

[0152] (2) Clean the polished surface with alcohol to remove the stains, and then dry it with a hair dryer.

[0153] (3) Austenitizing the 1Cr17Ni2 steel sample: heating to 1030℃ in a muffle furnace, holding for 140 min, and then oil quenching to room temperature.

[0154] (4) The oil-quenched sample was kept at 600℃ for 160 min for tempering, and then oil-quenched to room temperature.

[0155] Comparative Example 5: Using a 3-ton free forging machine, it can forge forgings up to 5 tons. The billet diameter is 100mm, the finished square bar is 38mm, and the corresponding deformation is 80%.

[0156] (1) Polish the surface of a sample with a diameter of 100 mm and a length of 100 mm to remove rust and oxide scale until the metal luster is exposed.

[0157] (2) Clean the polished surface with alcohol to remove stains and blow dry.

[0158] The specific operations for heat treatment, forging, and cryogenic processes are as follows: (1) Heat the muffle furnace to 1030℃. After the temperature reaches the specified temperature (1030℃), put in the cleaned 1Cr17Ni2 steel, hold for 140 minutes, and immediately oil quench to room temperature.

[0159] (2) The oil-quenched sample was directly heated to 650°C in the furnace and held for 60 minutes. At this temperature, a multi-pass drawing forging with a cumulative deformation of 80% was carried out. After forging, the sample was oil-cooled to room temperature.

[0160] (3) Take out the 1Cr17Ni2 steel that has been cooled to room temperature by warm forging oil, and cut the forged 1Cr17Ni2 steel into square bars with a length of 10mm, a width of 10mm and a height of 100mm using a wire cutting device.

[0161] (4) Immerse the cut sample in liquid nitrogen at -196℃ for 720 min, then remove it and allow it to naturally return to room temperature in the air.

[0162] (5) The cut 1Cr17Ni2 steel was placed in a muffle furnace at 450℃ and held for 30 minutes for tempering treatment, and then oil cooled.

[0163] Comparative Example 6: (1) Polish the surface of a sample with a diameter of 100 mm and a length of 100 mm to remove rust and oxide scale until the metal luster is exposed.

[0164] (2) Clean the polished surface with alcohol to remove stains and blow dry.

[0165] The specific operations for heat treatment, forging, and cryogenic processes are as follows: (1) Heat the muffle furnace to 1030℃. After the temperature reaches the specified temperature (1030℃), put in the cleaned 1Cr17Ni2 steel, hold for 140 minutes, and immediately oil quench to room temperature.

[0166] (2) Set the temperature of the muffle furnace to 450℃, put the oil-quenched sample into the furnace, keep it at the temperature for 60 minutes, then raise the temperature to 650℃ and keep it at the temperature for 10 minutes, and then take it out and cool it to room temperature.

[0167] (3) Take out the 1Cr17Ni2 steel that has been cooled to room temperature by warm forging oil, and cut the forged 1Cr17Ni2 steel into square bars with a length of 10mm, a width of 10mm and a height of 100mm using a wire cutting device.

[0168] (4) Immerse the cut sample in liquid nitrogen at -196℃ for 720 min, then remove it and allow it to naturally return to room temperature in the air.

[0169] (5) The cut 1Cr17Ni2 steel was placed in a muffle furnace at 450℃ and held for 30 minutes for tempering treatment, and then oil cooled.

[0170] Comparative Example 7: Using a 3-ton free forging machine, it can forge forgings up to 5 tons. The billet diameter is 100mm, the finished square bar is 38mm, and the corresponding deformation is 80%.

[0171] (1) Polish the surface of a sample with a diameter of 100 mm and a length of 100 mm to remove rust and oxide scale until the metal luster is exposed.

[0172] (2) Clean the polished surface with alcohol to remove stains and blow dry.

[0173] The specific operations for heat treatment, forging, and cryogenic processes are as follows: (1) Heat the muffle furnace to 1030℃. After the temperature reaches the specified temperature (1030℃), put in the cleaned 1Cr17Ni2 steel, hold for 140 minutes, and immediately oil quench to room temperature.

[0174] (2) The oil-quenched sample was directly heated to 650°C in the furnace and held for 60 minutes. At this temperature, a multi-pass drawing forging with a cumulative deformation of 80% was carried out. After forging, the sample was oil-cooled to room temperature.

[0175] (3) Take out the 1Cr17Ni2 steel that has been cooled to room temperature by warm forging oil, and cut the forged 1Cr17Ni2 steel into square bars with a length of 10mm, a width of 10mm and a height of 100mm using a wire cutting device.

[0176] (4) Immerse the cut sample in liquid nitrogen at -196℃ for 720 min, then remove it and allow it to naturally return to room temperature in the air.

[0177] The following performance tests were conducted on the 1Cr17Ni2 steels from Examples 1-8 and Comparative Examples 1-7, which underwent cryogenic insulation: Impact toughness: Impact toughness test: The impact absorption energy at room temperature is tested according to GB / T 229~2020 "Metallic Materials Charpy Pendulum Impact Test Method", using a U-notch specimen and a 2mm pendulum hammer blade.

[0178] Hardness test: Vickers hardness tester was used, the test force was 200g, the holding time was 10s, 10 points were tested for each sample and the average value was taken.

[0179] Tensile strength testing: Tensile strength, yield strength, and elongation after fracture were tested according to GB / T 228.1~2010 "Metallic materials, tensile testing—Part 1: Tests at room temperature". An electronic universal testing machine was used. The specimens were circular with a diameter of 5 mm and a gauge length of 25 mm. The average value of the test results from three identically treated specimens was calculated. Microstructure characterization: Cr elemental distribution analysis was performed using transmission electron microscopy (TEM) and its associated energy dispersive spectroscopy (EDS) to assess the degree of amplitude modulation decomposition.

[0180] The test results are shown in Table 1.

[0181] Table 1 Test Results

[0182] As shown in Table 1: Compared to Comparative Example 1, which did not undergo cryogenic treatment, the cryogenic treatment process used in each embodiment of the present invention resulted in an elongation of over 15% for 1Cr17Ni2 steel after tempering at 450℃. This indicates that cryogenic treatment effectively suppressed the chromium modulated decomposition during final tempering at 450℃, thereby reducing the sensitivity to tempering brittleness at 475℃. Combined with... Figures 3 to 5 The comparison of tissues under scanning electron microscopy (SEM) showed that the control sample 1 (which did not undergo cryogenic treatment) was significantly different. Figure 4 The tissue is coarse and the carbide distribution is uneven, while Example 4, which uses the complete process of the present invention, has a coarse tissue. Figure 3 ) exhibits finer, more uniformly dispersed carbides, and at the same time, the microstructure of retained austenite transformed into martensite is observed, Comparative Example 3 ( Figure 5 The presence of coarse precipitates is evident; the side-by-side comparison of the three figures intuitively verifies the significant effect of the process of this invention on tissue refinement and homogenization, providing a structural basis for improving elongation.

[0183] Compared to Comparative Example 2, which employed traditional quenching and tempering treatment, the embodiments of the present invention, while maintaining a tensile strength of not less than 1213 MPa, increased the -60°C low-temperature impact energy from 40 J (Comparative Example 2) to a maximum of 80.6 J (Example 3). This demonstrates that the method of the present invention enables the material to possess both high strength and excellent low-temperature toughness, thanks to the synergistic effect of pre-tempering + warm forging + deep cryogenic treatment on the regulation of chromium precipitation behavior. Combined with... Figure 7 and Figure 8 Transmission electron microscopy (TEM) and high-resolution microstructure images show that the 1Cr17Ni2 steel processed by the present invention has formed fibrous structure, nano carbides, high-density dislocation network and fine twinned martensite structure. This fine microstructure enables the material to maintain excellent plastic deformation capacity while obtaining high strength (≥1200MPa), and confirms the microstructural root of the synergistic improvement of strength and toughness at the microscale.

[0184] The cryogenic treatment time has a significant impact on the final properties of the material. Within the scope defined by this invention, when the cryogenic time is 120 min (Example 1), the impact energy at -60°C is 57.2 J; when extended to 720 min (Example 4), its tensile strength reaches 1255.5 MPa, elongation is 17.12%, and the impact energy at -60°C is 63.4 J; when further extended to 2880 min (Example 6), the impact energy at -60°C decreases to 48.0 J. For example, Figure 6 The XRD diffraction patterns showed that the peak broadening and peak shift characteristics in Example 1 (cryogenic treatment for 120 min) differed significantly from those in Example 4 (cryogenic treatment for 720 min). This indicates that the crystal defect density and lattice distortion state after short-time cryogenic treatment have not yet reached their optimal levels, which is detrimental to the stabilization of the microstructure during subsequent tempering. Meanwhile, Figure 9 The geometric phase analysis (GPA) strain field diagrams show that Comparative Example 1 exhibits a significant strain concentration region, while the strain field distribution of the samples subjected to cryogenic treatment (such as Examples 1-6) is relatively uniform, strongly demonstrating the effect of cryogenic treatment on stress homogenization. These results indicate that excessively short cryogenic times (e.g., 120 min) lead to insufficient stress control and inadequate microstructure optimization, failing to effectively constrain the diffusion behavior of chromium atoms; while excessively long cryogenic times (e.g., 2880 min) easily generate microcracks and coarseen nano-carbide precipitation, thus reducing the low-temperature toughness of the material.

[0185] To further verify the suppression effect of the present invention on the α′ phase, scanning electron microscopy (SEM) was performed. Figure 3-5 XRD Figure 6 TEM Figure 7-8 ) and GPA strain field ( Figure 9 Based on the characterization of tissues and structures, further analysis was conducted using TEM-EDS (...). Figures 10-13The results show that: Comparative Example 3 (conventional tempering) contains obvious coarse chromium-rich carbide precipitates; Comparative Example 7 shows nano-sized chromium-rich carbide precipitates and Cr element segregation regions; Comparative Example 1 (without cryogenic treatment) also contains nano-sized chromium-rich carbide precipitates, and the Cr distribution is significantly uneven. In contrast, although Example 4 (complete process) also has nano-sized chromium-rich carbide precipitates, the Cr element distribution is relatively uniform, and no significant component segregation was observed. These results confirm that the synergistic effect of pre-tempering, warm forging, and cryogenic treatment can effectively suppress chromium decomposition, thereby weakening the microstructural induction factors of 475℃ brittleness.

[0186] This application achieves multi-stage synergistic suppression of chromium atom dispersion through an organic combination of pre-tempering (420-460℃ to form a uniform pre-distribution of chromium atoms, avoiding subsequent segregation), warm forging (620-680℃ to form a fibrous structure and high-density dislocation network, combined with the dispersed precipitation of nanoscale carbides), and cryogenic treatment (promoting the full transformation of retained austenite and changing the stress field to stabilize the microstructure). During final tempering (450℃), due to the uniform pre-distribution and the increased diffusion channels provided by dislocations, chromium atoms tend to precipitate uniformly and dispersedly, thereby weakening the brittle crack initiation path. Compared with the untreated sample, after 720 min of cryogenic treatment, the -60℃ low-temperature impact energy increased from 43 J to 63.4 J. Figure 10 The TEM-EDS results further confirmed that the Cr distribution in the complete process of the present invention (Example 4) was relatively uniform, while the comparative examples all showed different degrees of Cr segregation signals, which proved the significant suppression effect of the present invention on amplitude modulation decomposition, significantly weakened the tempering brittleness at 475℃ and revealed the synergistic mechanism.

[0187] This application, through the high-density dislocations and refined lath martensite structure introduced by cryogenic treatment, increases the elongation to over 17% while maintaining tensile strength ≥1200MPa and yield strength ≥1100MPa. This overcomes the contradiction between strength and plasticity in traditional quenching and tempering processes, achieving a synergistic improvement in both strength and toughness. Figures 3 to 9 The multi-scale characterization results (from macroscopic microstructure, phase composition, fine structure to microscopic strain distribution) constitute a complete chain of evidence, systematically proving that the process of the present invention achieves an excellent match between strength and low-temperature toughness through microstructure refinement, full transformation of retained austenite, and stress homogenization.

[0188] Scanning electron microscopy revealed that samples subjected to cryogenic treatment (especially 720 min and above) exhibited finer lath martensite and a more uniform and dispersed distribution of carbides, with significantly better microstructure uniformity than samples without cryogenic treatment and those subjected to traditional quenching and tempering.

[0189] The cryogenic treatment in this application is carried out in a liquid nitrogen environment, which has high temperature control accuracy, is easy to operate, and the parameters such as austenitization (1000~1040℃), holding time (120min~160min), warm forging (620~680℃), tempering holding (50~65min), and holding after heating (8~15min) can all achieve the expected results within a wide range. It is easy to integrate into existing heat treatment production lines, and is environmentally friendly with strong process controllability.

[0190] In summary, this invention organically combines pre-tempering, warm forging, and cryogenic treatment, utilizing the synergistic effect of these three processes to suppress chromium amplitude decomposition (i.e., suppress the formation of chromium-rich α′ phase). This effectively reduces the material's sensitivity to temper brittleness at 475℃ and achieves a synergistic improvement in high strength and excellent low-temperature toughness, providing an effective technical solution for the manufacturing of key components in aerospace, shipbuilding, and other fields.

[0191] This invention overcomes the problem of 475°C brittleness in existing chromium-containing stainless steel when tempered at around 450°C by organically combining pre-tempering, warm forging and deep cryogenic treatment. It improves the impact toughness of chromium-containing stainless steel, effectively weakens the brittleness sensitivity of chromium-containing stainless steel, and maintains the high strength and good low-temperature toughness of chromium-containing stainless steel.

[0192] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A heat treatment method for reducing temper brittleness of chromium-containing stainless steel, characterized in that, include: Chromium-containing stainless steel is subjected to austenitizing treatment and quenching. The quenched chromium-containing stainless steel is pre-tempered at a temperature of 420–460℃. The pre-tempered chromium-containing stainless steel is subjected to warm forging at a temperature of 620–680°C. The chromium-containing stainless steel after warm forging is subjected to deep cryogenic treatment at a temperature of -201℃ to -191℃. After cryogenic treatment, chromium-containing stainless steel is restored to room temperature and then subjected to final tempering to obtain chromium-containing stainless steel products with low temper brittleness.

2. The method according to claim 1, characterized in that, The cryogenic treatment duration is 120 min to 2880 min.

3. The method according to claim 2, characterized in that, The cryogenic treatment duration is 480 min to 720 min.

4. The method according to claim 1, characterized in that, Before the warm forging treatment of chromium-containing stainless steel, the process also includes: heating the pre-tempered chromium-containing stainless steel to 620-680°C in the furnace and holding it at that temperature for 8-15 minutes.

5. The method according to claim 1, characterized in that, The holding time for the pre-tempering treatment is 50–65 min.

6. The method according to claim 1, characterized in that, The final tempering treatment is performed at a temperature of 440–460°C for a holding time of 20–40 minutes.

7. The method according to claim 1, characterized in that, The austenitizing treatment involves heating the chromium-containing stainless steel to 1000–1040°C and holding it for 120–160 minutes. The quenching is oil quenching; The warm forging process involves multiple forging passes with a cumulative deformation of 80% to 85%.

8. The method according to claim 1, characterized in that, The chromium-containing stainless steel is a martensitic-ferritic stainless steel or a ferritic stainless steel, with a chromium content ≥13%.

9. The method according to claim 8, characterized in that, The chromium-containing stainless steel is 1Cr17Ni2 steel, 1Cr13 steel, or 2Cr13 steel.

10. A chromium-containing stainless steel product, characterized in that, The product prepared by the method according to any one of claims 1 to 9 has a lower content of chromium-rich α′ phase in its microstructure after tempering at 450°C than that of the comparative product without cryogenic treatment.

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