Forging process for eliminating twinned carbides in high nitrogen stainless steel bearing ring

Abstract

The application discloses a forging process method for eliminating twinned carbide of high-nitrogen stainless steel bearing ring, and relates to the technical field of metal material forging.The forging process method comprises the following steps: S1, a preheating stage: when the furnace temperature is greater than or equal to 600 DEG C, a blank of the high-nitrogen stainless steel bearing ring is loaded, and preheating is performed for 30-40 minutes; S2, a low-temperature holding stage: the blank is rapidly heated to 840-860 DEG C, and holding is performed for 90-150 minutes; S3, a high-temperature holding stage: the blank is rapidly heated to 1120-1140 DEG C, and holding is performed for 80-100 minutes; and S4, a blank preparation stage: the blank after high-temperature holding is discharged from the furnace, and is sequentially subjected to upsetting, blind hole punching, piercing and core rod hole expanding to obtain a ring-shaped blank with a wall thickness of S0.The forging process method controls the heating temperature, holding time, deformation amount and cooling mode after forging of the blank, so that twinned carbide generation in the forging process of the high-nitrogen stainless steel is inhibited.

Description

Technical Field

[0001] This invention relates to the field of metal material forging technology, specifically to a forging process method for eliminating forging twin carbides in high-nitrogen stainless steel bearing rings. Background Technology

[0002] With the increasing use of aviation, aerospace, and ship equipment in harsh environments such as marine salt spray and rainforest heat and humidity, traditional stainless steel bearings are unable to meet the environmental adaptability requirements such as corrosion resistance, damp heat resistance, and high temperature resistance, often resulting in premature failure and severely restricting the use of equipment.

[0003] A high-nitrogen stainless steel, 40Cr15Mo2VN, has a nitrogen content of 0.2wt% and is typically used as a fully quenched stainless bearing steel. This design solves the problem of large eutectic carbides forming during the smelting and solidification processes of 9Cr18 and 9Cr18Mo steels, which leads to poor performance. By reducing carbon and increasing nitrogen, its corrosion resistance can be greatly improved. After heat treatment, the carbides are small in size and uniformly distributed, allowing the high-nitrogen stainless bearing steel to achieve a balance between high strength and a certain toughness reserve, while also possessing good wear resistance and heat resistance. It is widely used in corrosion-resistant environments such as aviation, aerospace, and shipbuilding.

[0004] High-nitrogen stainless steel 40Cr15Mo2VN, as a new type of bearing material, has many advantages, but its forging temperature range is narrow (about 100-150℃) and its metal plasticity is poor. During the forging process, carbides are easily generated along the twin boundaries (twin carbides). Twin carbides are a relatively serious structural defect. Their presence will seriously reduce the bearing performance and may lead to premature failure and unexpected fracture of parts.

[0005] In recent years, as this material has become increasingly larger and more diverse, multiple batches of forgings have exhibited excessive twin carbides after annealing in production practice. Current technologies typically improve material plasticity by extending the holding time or increasing the heating temperature. Other methods employ multi-pass, small-deformation forging, but these are inefficient and fail to suppress twin carbides.

[0006] Therefore, there is an urgent need for a method that can accurately match heating parameters with deformation processes to eliminate twinned carbides. Summary of the Invention

[0007] The purpose of this invention is to propose a forging process method to eliminate twin carbides in the forging of high-nitrogen stainless steel bearing rings. By controlling the heating temperature, holding time, deformation amount and post-forging cooling method of the blank, the formation of twin carbides during the forging process of high-nitrogen stainless steel can be suppressed.

[0008] The technical solution adopted in this invention is a forging process method for eliminating twinned carbides in the forging of high-nitrogen stainless steel bearing rings, comprising the following steps:

[0009] S1. Preheating stage: When the furnace temperature is ≥600℃, the blank containing the high-nitrogen stainless steel bearing ring is preheated for 30min~40min.

[0010] S2, Low-temperature heat preservation stage: The blank is rapidly heated to 840℃~860℃ and held for 90min~150min;

[0011] S3, High-temperature heat preservation stage: The blank is rapidly heated to 1120℃~1140℃ and held for 80min~100min;

[0012] S4. Blanking stage: After the blank is heated to high temperature, it is taken out of the furnace and then subjected to upsetting, blind hole punching, piercing and mandrel expansion in sequence to obtain an annular blank with a wall thickness of S0.

[0013] S5. Return to furnace and heat preservation stage: Return the ring-shaped blank to the furnace and heat it rapidly to 1120℃~1140℃, and keep it at that temperature for 20min~30min.

[0014] S6. Rolling and expanding stage: The annular blank after being kept warm in the furnace is rolled and expanded to obtain an annular forging with a wall thickness of S, where S0≥1.5S.

[0015] S7. Cool the rolled and expanded annular forgings with water mist.

[0016] As a preferred embodiment, the high-nitrogen stainless steel bearing ring is made of 40Cr15Mo2VN.

[0017] As a preferred embodiment, the water mist cooling is completed on a spray conveyor belt, and the surface temperature of the cooled forging is 300℃~400℃.

[0018] As a preferred embodiment, the low-temperature insulation stage rapidly heats the blank to 850°C;

[0019] The high-temperature heat preservation stage rapidly raises the temperature of the blank to 1130°C;

[0020] During the reheating and heat preservation stage, the annular blank is rapidly heated to 1130°C.

[0021] As a preferred option, the ratio of the holding times for the three stages—low-temperature holding stage, high-temperature holding stage, and reheating holding stage—is 12:9:2.

[0022] As a preferred option, the final forging temperature in both the billet preparation stage and the rolling expansion stage is ≥900℃.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] This invention effectively suppresses twinned carbides in the forging microstructure of high-nitrogen stainless steel 40Cr15Mo2VN bearing rings by segmented heating and heat preservation control, two-stage deformation distribution during billet preparation and rolling, and rapid cooling with water mist after forging. The elimination of twinned carbides avoids microstructural defects and can significantly improve the fatigue resistance of the bearing. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a flowchart of the forging process method of the present invention;

[0027] Figure 2 This is a temperature curve diagram of the heating process of the present invention. Detailed Implementation

[0028] The present invention will now be described in detail through exemplary embodiments. However, it should be understood that, without further description, elements, structures, and features in one embodiment may be advantageously incorporated into other embodiments.

[0029] It should be noted that, unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "a," "an," or "the," etc., used in the specification and claims of this patent application do not express a limitation on quantity, but rather indicate the presence of at least one; the terms "first," "second," and "third," as used herein, should not be considered as a limitation on the order of components, but are merely for distinguishing different components; the terms "comprising," "including," etc., indicate that the elements or objects preceding "comprising" or "including" encompass the elements or objects listed following "comprising" or "including" and their equivalents, but do not exclude other elements or objects having the same function.

[0030] To more clearly describe the forging process for eliminating twinned carbides in high-nitrogen stainless steel bearing rings, the following is a summary: Figure 1-2 Description of the embodiment:

[0031] A forging process for eliminating twinned carbides in high-nitrogen stainless steel bearing rings includes the following steps:

[0032] S1. Preheating stage: When the furnace temperature is ≥600℃, the blank containing the high-nitrogen stainless steel bearing ring is preheated for 30min~40min.

[0033] S2, Low-temperature holding stage: The blank is rapidly heated to 840℃~860℃ (using a box-type resistance furnace or gas furnace, the heating rate is generally above 100℃ / hour, or even reaches 200℃ / hour), and held for 90min~150min.

[0034] S3, High-temperature heat preservation stage: The blank is rapidly heated to 1120℃~1140℃ and held for 80min~100min;

[0035] S4. Billet making stage: After the billet is heated to high temperature, it is taken out of the furnace and then subjected to upsetting, blind hole punching, piercing and mandrel expansion in sequence to obtain an annular billet with a wall thickness of S0; the final forging temperature of the billet making stage is ≥900℃.

[0036] S5. Return to furnace and heat preservation stage: Return the ring-shaped blank to the furnace and heat it rapidly to 1120℃~1140℃, and keep it for 20min~30min.

[0037] S6. Rolling and Expanding Stage: The annular blank after being kept warm in the furnace is rolled and expanded to obtain an annular forging with a wall thickness of S, where S0≥1.5S; the final forging temperature of the rolling and expanding stage is ≥900℃.

[0038] S7. The rolled and expanded annular forgings are cooled by water mist on a spray conveyor belt. After cooling, the temperature drops rapidly from over 900℃ to 300℃~400℃.

[0039] The core points of this invention are: firstly, the high-temperature holding temperature and the holding time at each stage have been appropriately reduced; secondly, the deformation amount in the final forging pass has been controlled, with the rolling-expansion ratio ensuring it is greater than 1.5; and thirdly, a rapid cooling method using post-forging mist cooling. At temperatures of 1120℃ and lower, the diffusion rate of carbon and alloying elements is slow, requiring a long holding time (more than 120 minutes) to preferentially nucleate and precipitate carbides at high-energy grain boundaries. This is a typical grain boundary segregation and precipitation pattern. Carbides grow along the interface direction, possibly related to minimizing interface energy or element diffusion channels. A sufficiently large rolling-expansion ratio / deformation amount allows the forging to be fully forged through, facilitating the breaking up of coarse twinned carbides formed during the holding process. Rapid cooling corresponds to slow cooling. Since the post-forging temperature is still above 900℃, if the cooling rate is too slow, carbon atoms may still diffuse sufficiently, providing enough time for segregation to the grain boundaries.

[0040] To facilitate understanding and implementation of the present invention, a more specific and detailed embodiment is provided below using the forging process of 40Cr15Mo2VN as an example.

[0041] Example 1

[0042] S1. Preheating stage: The blank of high-nitrogen stainless steel bearing ring is put into the furnace at a furnace temperature of 600℃ and preheated for 30 minutes.

[0043] S2, Low-temperature heat preservation stage: The blank is rapidly heated to 840℃ and held for 90 minutes;

[0044] S3, High-temperature heat preservation stage: The blank is rapidly heated to 1120℃ and held for 80 minutes;

[0045] S4. Billet making stage: After the billet is heated to high temperature, it is taken out of the furnace and then subjected to upsetting, blind hole punching, piercing and mandrel expansion in sequence to obtain an annular billet with a wall thickness of S0; the final forging temperature of the billet making stage is 900℃.

[0046] S5, Reheating and Heating Stage: Return the ring-shaped blank to the furnace and heat it rapidly to 1120℃, then hold it for 25 minutes.

[0047] S6. Rolling and Expanding Stage: The annular blank after being kept warm in the furnace is rolled and expanded to obtain an annular forging with a wall thickness of S, where S0 = 1.5S; the final forging temperature of the rolling and expanding stage is 900℃.

[0048] S7. After rolling, for finished ring forgings with qualified dimensions, water mist cooling is performed on a spray conveyor belt, and the temperature drops rapidly from over 900℃ to 300℃.

[0049] Example 2

[0050] S1. Preheating stage: The blank of high-nitrogen stainless steel bearing ring is put into the furnace at a furnace temperature of 600℃ and preheated for 30 minutes.

[0051] S2, Low-temperature heat preservation stage: The blank is rapidly heated to 850℃ and held for 120 minutes;

[0052] S3, High-temperature heat preservation stage: The blank is rapidly heated to 1130℃ and held for 90 minutes;

[0053] S4. Billet making stage: After the billet is heated to high temperature, it is taken out of the furnace and then subjected to upsetting, blind hole punching, piercing and mandrel expansion in sequence to obtain an annular billet with a wall thickness of S0; the final forging temperature of the billet making stage is 900℃.

[0054] S5. Return to furnace and heat preservation stage: Return the ring-shaped blank to the furnace and heat it rapidly to 1130℃, and keep it at that temperature for 20 minutes.

[0055] S6. Rolling and Expanding Stage: The annular blank after being kept warm in the furnace is rolled and expanded to obtain an annular forging with a wall thickness of S, where S0 = 1.5S; the final forging temperature of the rolling and expanding stage is 900℃.

[0056] S7. After rolling, for finished ring forgings with qualified dimensions, water mist cooling is performed on a spray conveyor belt, and the temperature drops rapidly from over 900℃ to 350℃.

[0057] Example 3

[0058] S1. Preheating stage: The blank of high-nitrogen stainless steel bearing ring is put into the furnace at a furnace temperature of 600℃ and preheated for 35 minutes.

[0059] S2, Low-temperature heat preservation stage: The blank is rapidly heated to 860℃ and held for 150 minutes;

[0060] S3, High-temperature heat preservation stage: The blank is rapidly heated to 1140℃ and kept at that temperature for 100 minutes;

[0061] S4. Billet making stage: After the billet is heated to high temperature, it is taken out of the furnace and then subjected to upsetting, blind hole punching, piercing and mandrel expansion in sequence to obtain an annular billet with a wall thickness of S0; the final forging temperature of the billet making stage is 900℃.

[0062] S5. Return to furnace and heat preservation stage: Return the ring-shaped blank to the furnace and heat it rapidly to 1140℃, and keep it at that temperature for 30 minutes.

[0063] S6. Rolling and Expanding Stage: The annular blank after being kept warm in the furnace is rolled and expanded to obtain an annular forging with a wall thickness of S, where S0 = 1.6S; the final forging temperature of the rolling and expanding stage is 900℃.

[0064] S7. After rolling, the finished ring forgings with qualified dimensions are cooled by water mist on a spray conveyor belt. After cooling, the temperature drops rapidly from over 900℃ to 320℃.

[0065] From July 2023 to 2024, a total of 221 batches of 40Cr15Mo2VN forgings were produced using the process of this invention. Except for a few batches where twin carbides were generated due to abnormal heating furnace, no parts were scrapped due to twin carbides, and the forging microstructure qualification rate was close to 100%. Compared with the 83 batches produced using the existing process from January to July 2023 (14 batches had twin carbides, accounting for 16.87%), the twin carbides defect rate was reduced from 16.87% to nearly 0%, achieving significant technological progress.

[0066] The forging process provided by this invention can be widely applied to the mass production of bearing rings and other annular forgings made of high-nitrogen stainless steel (especially 40Cr15Mo2VN and its equivalents), which is of great significance for improving the fatigue life and reliability of high-end bearings. This process has moderate equipment requirements and can be implemented on existing forging production lines, possessing good industrial practicality and application value.

[0067] The parts not described in detail in the above embodiments are existing technologies.

[0068] It should be noted that although the present invention has been described through the above embodiments, the present invention may have many other embodiments. Without departing from the spirit and scope of the present invention, those skilled in the art can obviously make various corresponding changes and modifications to the present invention, but all such changes and modifications should fall within the scope of protection of the appended claims and their equivalents.

Claims

1. A forging process method for eliminating forging twinned carbides in high-nitrogen stainless steel bearing rings, wherein the high-nitrogen stainless steel bearing rings are made of 40Cr15Mo2VN, characterized in that... The forging process includes the following steps: S1. Preheating stage: When the furnace temperature is ≥600℃, the blank containing the high-nitrogen stainless steel bearing ring is preheated for 30min~40min. S2, Low-temperature heat preservation stage: The blank is rapidly heated to 840℃~860℃ and held for 90min~150min; S3, High-temperature heat preservation stage: The blank is rapidly heated to 1120℃~1140℃ and held for 80min~100min; S4. Blanking stage: After the blank is heated to high temperature, it is taken out of the furnace and then subjected to upsetting, blind hole punching, piercing and mandrel expansion in sequence to obtain an annular blank with a wall thickness of S0. S5. Return to furnace and heat preservation stage: Return the ring-shaped blank to the furnace and heat it rapidly to 1120℃~1140℃, and keep it at that temperature for 20min~30min. S6. Rolling and expanding stage: The annular blank after being kept warm in the furnace is rolled and expanded to obtain an annular forging with a wall thickness of S, where S0≥1.5S. S7. Cool the rolled-out annular forgings with water mist. The final forging temperature in both the billet preparation stage and the rolling and expanding stage is ≥900℃. After water mist cooling, the temperature of the finished ring forging drops rapidly from above 900℃ to 300℃~400℃.

2. The forging process method for eliminating twinned carbides in high-nitrogen stainless steel bearing rings according to claim 1, characterized in that: The water mist cooling is completed on a spray conveyor belt, and the surface temperature of the cooled forging is 300℃~400℃.

3. The forging process for eliminating twinned carbides in high-nitrogen stainless steel bearing rings according to claim 1, characterized in that: The low-temperature heat preservation stage rapidly raises the temperature of the blank to 850°C; The high-temperature heat preservation stage rapidly raises the temperature of the blank to 1130°C; During the reheating and heat preservation stage, the annular blank is rapidly heated to 1130°C.

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