CN113416832B - High-strength-toughness complex-phase heat treatment method for aeroengine bearing - Google Patents

Abstract

The invention discloses a high-strength and high-toughness complex phase heat treatment method for an aircraft engine bearing, which comprises the following steps of: according to the size of the inner diameter and the outer diameter of the bearing ring, the bearing ring is subjected to preheating treatment before austenitizing, the bearing ring is uniformly immersed into a high-temperature salt bath furnace for austenitizing after preheating, and the austenitizing structure is uniform by controlling the austenitizing temperature and time; immersing the bearing ring subjected to austenitizing in a low-temperature salt bath furnace for isothermal quenching, and controlling the bainite content in a specified interval range by controlling the isothermal quenching temperature and time; and putting the bearing ring into a tempering furnace for tempering treatment. The high-toughness complex-phase heat treatment method for the bearing of the aircraft engine realizes quantitative regulation and control of the proportion of the martensite-bainite complex-phase structure by controlling complex-phase heat treatment process parameters, thereby optimizing the heat treatment structure and improving the toughness of the matrix.

Description

High-strength and toughness complex heat treatment method for aero-engine bearings

technical field

The invention relates to a bearing manufacturing technology, in particular to a high-strength and toughness complex-phase heat treatment method for an aero-engine bearing.

Background technique

Aero-engine bearings are used to support the core rotor system of the engine. Their service conditions are extremely harsh, requiring high speed, high precision, high load capacity and high reliability. They are the key components to ensure the long-life service of aero-engines. The bearing consists of inner and outer rings, rolling elements and cages. Among them, the ring is the core component of the bearing, and its weight and manufacturing cost account for 60% to 70% of the bearing. Its performance directly determines the bearing life and reliability, and is the core of bearing manufacturing. How to obtain high-strength and tough bearing rings to ensure reliable service in extreme working conditions of bearings is a cutting-edge topic that is highly valued in the field of international bearing science and technology.

The main material of aero-engine bearing rings is 8Cr4Mo4V, which is a typical high-temperature bearing steel. In order to ensure its high-temperature hardness and high dimensional stability, the heat treatment process of martensitic quenching and multiple high-temperature tempering is usually used. However, under the existing traditional process, the content of ductile phase paralysate is very small, and the ratio of tissue strength and toughness is poor, which makes it difficult to ensure long-life service of bearings in extremely harsh working environments, which has seriously hindered the development of aviation equipment manufacturing.

SUMMARY OF THE INVENTION

The main purpose of the present invention is to provide a high-strength and toughness complex heat treatment method for aero-engine bearings, which aims to improve the strength and toughness of the matrix.

In order to achieve the above purpose, the present invention provides a high-strength and toughness complex heat treatment method for aero-engine bearings, comprising the following steps:

According to the inner and outer diameter of the ring, the bearing ring is preheated before austenitization. After preheating, the ring is evenly immersed in a high-temperature salt bath furnace for austenitization. By controlling the austenitization temperature and time Make the austenitized structure uniform;

The austenitized bearing ring is immersed in a low-temperature salt bath furnace for isothermal quenching, and the bainite content is controlled within the specified range by controlling the isothermal quenching temperature and time;

Place the bearing ring in a tempering furnace for tempering.

Preferably, when the ferrule is evenly immersed in a high-temperature salt bath furnace for austenitizing treatment, the austenitizing temperature T _A =T _Ac3 +k _T T _Ac1 , and the austenitizing time t _A =[(Dd)/ 1mm]·T _A /T _Ac1 ,

Among them, D and d are the outer diameter and inner diameter of the ring, respectively, T _Ac1 is the starting temperature of the austenitizing transformation of the bearing material, T _Ac3 is the end temperature of the austenitizing transformation of the bearing material, and k _T is the austenitizing transformation. Temperature correction coefficient, k _T is 0.25～0.28.

Preferably, when preheating the bearing ring, the preheating time is related to the size of the ring, and the preheating temperature is 200°C to 350°C.

Preferably, the bearing ring preheating time is t ₁ , t ₁ =t ₀ (Dd)/d, t ₀ is the initial preheating time of the ring, and t ₀ is 20min˜30min.

Preferably, after the step of immersing the austenitized bearing ring in a low-temperature salt bath furnace for isothermal quenching, it further includes:

After the isothermal quenching process is completed, quench the bearing ring into the oil tank and stir it evenly. After the salt on the surface of the ring is condensed and crystallized, take it out and put it into warm water to wash and dry.

Preferably, when the austenitized bearing ring is immersed in a low-temperature salt bath furnace for isothermal quenching, the isothermal quenching temperature T _B is:

T _B =[1+k _B d/(Dd)]T _Ms ,

Among them, T _Ms is the starting point of martensitic transformation of the bearing material, k _B is the correction coefficient of the isothermal quenching temperature, and k _B is 0.05 to 0.1.

Preferably, the isothermal quenching time t _B is related to the inner and outer diameters of the ferrule and the isothermal quenching temperature, and the numerical control is:

t _A =t ₂ [(Dd)/d]·[T _Ms /(T _B −T _Ms )],

Among them, t ₂ is the initial time of isothermal quenching, and t ₁ is 150min-180min.

Preferably, when the bearing ring is put into a tempering furnace for tempering treatment, the tempering temperature is 535-550° C., and the cycle is repeated three times.

Preferably, the content of the quenched retained austenite is controlled between 20% and 30%, and the tempered retained austenite is controlled to be less than 4%.

Preferably, when the austenitized bearing ring is immersed in a low-temperature salt bath furnace for isothermal quenching, the bainite content is controlled between 5% and 50%.

The high-strength and toughness complex heat treatment method for aero-engine bearings proposed by the present invention has the following beneficial effects:

(1) By introducing preheating treatment before austenitization, the heat treatment deformation and stress of the ferrule can be reduced, and austenitizing by high-temperature salt bath method can reduce the uneven heating of the ferrule and improve the structure. performance uniformity;

(2) By reasonably controlling the austenitizing time and temperature, the austenitizing parameters can be accurately matched with the size and material properties to ensure that the austenitizing structure is uniform and controllable;

(3) Based on the size and material characteristics of the bearing ring, on the one hand, by controlling the isothermal quenching time and temperature, the bainite content is controlled within the specified range, and the bainite division effect on the grains is used to obtain fine laths structure, which increases the effect of structure refinement; on the other hand, the introduction of appropriate bainite can make the content of parasite in the specified range, and the decomposition of appropriate parasite during high-temperature tempering increases the dislocation density after tempering, increasing Dislocation strengthening effect, which promotes the simultaneous improvement of strength and toughness;

(4) Based on the optimized complex heat treatment process window, the entire process flow of complex heat treatment is accurately designed and planned, which ensures the heat treatment efficiency and quality of bearing products, and the final microstructure is regulated through quantitative control of complex ratio and process planning. state, thereby significantly improving the strength and toughness of aero-engine bearing rings.

Description of drawings

FIG. 1 is a schematic flow chart of a preferred embodiment of the high-strength-toughness multiphase heat treatment method for aero-engine bearings of the present invention.

The realization, functional characteristics and advantages of the present invention will be further described with reference to the accompanying drawings in conjunction with the embodiments.

Detailed ways

It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

Referring to FIG. 1, in this preferred embodiment, a high-strength and toughness complex heat treatment method for aero-engine bearings includes the following steps:

Step S10, according to the inner and outer diameters of the ferrule, preheat the bearing ferrule before austenitizing, and after preheating, evenly immerse the ferrule in a high-temperature salt bath furnace for austenitization, and control the austenitization by controlling the austenitization process. The temperature and time make the austenitizing structure uniform (the austenitizing temperature is related to the bearing material, and the austenitizing time is related to the bearing material and size);

Step S20, the austenitized bearing ring is immersed in a low-temperature salt bath furnace for isothermal quenching, and the bainite content is controlled within a specified range by controlling the isothermal quenching temperature and time;

Step S30, putting the bearing ring into a tempering furnace for tempering treatment.

The traditional austenitizing method uses resistance furnace or vacuum furnace heating, which leads to slow heat conduction, uneven heating and poor structure uniformity. In step S10, austenitizing is performed by using a high-temperature salt bath furnace, thereby reducing the uneven heating of the ferrule and improving the uniformity of the structure and properties.

In step S10, when the ferrule is evenly immersed in a high-temperature salt bath furnace for austenitizing treatment, the austenitizing temperature T _A =T _Ac3 +k _T T _Ac1 , and the austenitizing time t _A =[(Dd) /1mm]·T _A /T _Ac1 ,

Among them, D and d are the outer diameter and inner diameter of the ring, respectively, T _Ac1 is the starting temperature of the austenitizing transformation of the bearing material, T _Ac3 is the end temperature of the austenitizing transformation of the bearing material, and k _T is the austenitizing transformation. Temperature correction coefficient, k _T is 0.25～0.28.

The austenitizing parameters used in the prior art are single fixed, and the size and material properties of the ferrule are not considered, which seriously affects the stability and uniformity of the heat treatment structure of the component. In this example, both the time and temperature of austenitization take into account the size and material properties of the ferrule.

In step S10, when preheating the bearing ring, the preheating time is related to the size of the ring, and the preheating temperature is 200°C to 350°C.

Specifically, the bearing ring preheating time is t ₁ , t ₁ =t ₀ (Dd)/d, t ₀ is the initial preheating time of the ring, and t ₀ is 20min-30min.

Further, after step S20, it also includes:

Step S21, after the isothermal quenching process is completed, the bearing ring is quickly quenched into the oil tank and stirred evenly.

In step S20, when the austenitized bearing ring is immersed in a low-temperature salt bath furnace for isothermal quenching, the isothermal quenching temperature T _B is:

T _B =[1+k _B d/(Dd)]T _Ms ,

Among them, T _Ms is the starting point of martensitic transformation of the bearing material, k _B is the correction coefficient of the isothermal quenching temperature, and k _B is 0.05 to 0.1.

In step S20, the time t _B of isothermal quenching is related to the inner and outer diameters of the ferrule and the isothermal quenching temperature, and the numerical control is:

t _A =t ₂ [(Dd)/d]·[T _Ms /(T _B -T _Ms )]

Among them, t ₂ is the initial time of isothermal quenching, and t ₁ is 150min-180min. Under this process condition, the bainite content can be strictly controlled within the specified range to ensure that the ratio of martensite and bainite complex structure meets the requirements.

Because the key to complex heat treatment is to control the content of martensite and bainite, the ratio of martensite to bainite will directly determine the performance of the final component, and an unsuitable mape complex structure may even cause serious performance problems. deterioration. In this embodiment, according to the different sizes and material properties of the ferrule, the time and temperature of austempering are precisely controlled, and the bainite content is controlled within a specified range.

In step S30, when the bearing ring is put into a tempering furnace for tempering treatment, the tempering temperature is 535-550° C., the cycle is repeated three times, and the tempering time is 2 hours each time.

Specifically, the content of the quenched retained austenite (that is, the retained austenite content after step S20 ) is controlled between 20% and 30%, and the tempered retained austenite (that is, the retained austenite after step S30 ) is controlled between 20% and 30%. content) is controlled below 4%. When the austenitized bearing ring is immersed in a low-temperature salt bath furnace for isothermal quenching, the bainite content is controlled between 5% and 50%.

The following specifically takes a certain type of bearing made of 8Cr4Mo4V bearing steel as an example (the outer diameter of the outer ring is 120mm, and the inner diameter is 102mm) as an example to describe the process in detail:

(1) Uniform austenitization of the structure

According to the inner and outer diameter of the ring, the bearing ring should be preheated for 5 minutes before austenitizing, and the preheating temperature is 300 °C. Then, the ferrule is evenly immersed in a high-temperature salt bath furnace for austenitization. The T _Ac1 and T _Ac3 of the 8Cr4Mo4V material are 820 ℃ and 874 ℃ respectively. Based on the design formula of the austenitizing isothermal temperature and isothermal time, the calculated austenitizing temperature range is 1079 ℃～1104 ℃, and the austenitizing isothermal time is 24min, the austenitization temperature was set to 1088 °C, and the austenitization isothermal time was set to 24min.

(2) Precise control of quenching by complex phase structure

The austenitized bearing ring is immersed in a low-temperature salt bath furnace, and the T _Ms of the 8Cr4Mo4V material is taken as 161 °C. According to the starting point of martensitic transformation of the bearing material and the dimensional characteristics of the ring, the austempering temperature and time are used to design the formula , the temperature range of the calculated isothermal quenching is 206℃～252℃, the time range is 47min～114min, the isothermal quenching temperature is set to 236℃, and the isothermal quenching time is set to 60min. After the isothermal quenching process is completed, the bearing ring is quickly quenched into a large oil tank and fully stirred. After the salt on the surface of the ferrule has condensed and crystallized, take it out and wash it in warm water and dry it.

(3) The organization is uniformly tempered

The bearing rings are evenly loaded into the high temperature tempering furnace. During the process, it is necessary to ensure that the temperature in the tempering furnace is uniform, and the temperature is set to 550 ℃, and the cycle is repeated three times.

The technical effect of the obtained bearing ring and the traditional martensitic heat treatment bearing ring was compared, and it was found that the bainite content of the 8Cr4Mo4V bearing ring of this embodiment was 13%, and the average lath size decreased from 1.95 μm to 1.06 μm. The size is reduced by 45.6%; the average dislocation density is increased from 3.6×10 ¹⁵ /m ² to 5.4×10 ¹⁵ /m ² , and the dislocation density is increased by 50%. At the same time, the results of mechanical properties test showed that the tensile strength increased from 2143MPa to 2248MPa, and the impact energy increased from 56J to 93J. This shows that: by introducing an appropriate amount of bainite, the structure can be effectively refined and dislocations can be increased, thereby realizing the improvement of the strength and toughness of aero-engine bearings.

The high-strength and toughness complex heat treatment method for aero-engine bearings proposed by the present invention has the following beneficial effects:

(1) By introducing preheating treatment before austenitization, the heat treatment deformation and stress of the ferrule can be reduced, and austenitizing by high-temperature salt bath method can reduce the uneven heating of the ferrule and improve the structure. performance uniformity;

(2) By reasonably controlling the austenitizing time and temperature, the austenitizing parameters can be accurately matched with the size and material properties to ensure that the austenitizing structure is uniform and controllable;

(3) Based on the size and material characteristics of the bearing ring, on the one hand, by controlling the isothermal quenching time and temperature, the bainite content is controlled within the specified range, and the bainite division effect on the grains is used to obtain fine laths structure, which increases the effect of structure refinement; on the other hand, the introduction of appropriate bainite can make the content of parasite in the specified range, and the decomposition of appropriate parasite during high-temperature tempering increases the dislocation density after tempering, increasing Dislocation strengthening effect, which promotes the simultaneous improvement of strength and toughness;

(4) Based on the optimized complex heat treatment process window, the entire process flow of complex heat treatment is accurately designed and planned, which ensures the heat treatment efficiency and quality of bearing products, and the final microstructure is regulated through quantitative control of complex ratio and process planning. state, thereby significantly improving the strength and toughness of aero-engine bearing rings.

The above are only preferred embodiments of the present invention, and are not intended to limit the scope of the present invention. Any equivalent structural transformation made by using the contents of the description and drawings of the present invention, or directly or indirectly applied to other related technical fields, are the same. Included in the scope of patent protection of the present invention.

Claims (9)

1. A high-strength and toughness complex-phase heat treatment method for an aircraft engine bearing is characterized by comprising the following steps:

according to the size of the inner diameter and the outer diameter of the bearing ring, the bearing ring is subjected to preheating treatment before austenitizing, the bearing ring is uniformly immersed into a high-temperature salt bath furnace for austenitizing after preheating, and the austenitizing structure is uniform by controlling the austenitizing temperature and time;

immersing the bearing ring subjected to austenitizing in a low-temperature salt bath furnace for isothermal quenching, and controlling the bainite content in a specified interval range by controlling the isothermal quenching temperature and time;

putting the bearing ring into a tempering furnace for tempering treatment;

when the ferrule is evenly immersed into a high-temperature salt bath furnace for austenitizing treatment, the austenitizing temperature T is_A＝T_Ac3+k_TT_Ac1Time t of austenitization_A＝[(D-d)/1mm]·T_A/T_Ac1，

Wherein D and D are respectively the outer diameter and the inner diameter of the ferrule，T_Ac1Is the austenitizing transformation starting temperature, T, of the bearing material_Ac3The austenite transformation end temperature, k, of the bearing material_TFor austenitizing temperature correction coefficient, k_T0.25 to 0.28.

2. The complex-phase heat treatment method for the high strength and toughness of the bearing of the aircraft engine as claimed in claim 1, wherein when the bearing ring is subjected to the preheating treatment, the preheating time is related to the size of the ring, and the preheating temperature is 200-350 ℃.

3. The high-toughness complex-phase heat treatment method for the aero-engine bearing as claimed in claim 2, wherein the preheating time of the bearing ring is t₁，t₁＝t₀(D-d)/d，t₀For preheating the ferrule for an initial time t₀Is 20min to 30 min.

4. The method for the complex-phase heat treatment of the high strength and toughness of the aero-engine bearing as set forth in claim 1, wherein the step of immersing the austenitized bearing ring in a low-temperature salt bath furnace for isothermal quenching further comprises the steps of:

after the isothermal quenching process is finished, quenching the bearing ring into an oil tank and uniformly stirring, taking out the bearing ring after the salt on the surface of the ring is condensed and crystallized, and washing and drying the bearing ring in warm water.

5. The high-strength and high-toughness complex-phase heat treatment method for the aero-engine bearing as claimed in claim 1, wherein when the bearing ring after austenitizing is immersed in a low-temperature salt bath furnace for isothermal quenching, the temperature T of isothermal quenching is_BComprises the following steps:

T_B＝[1+k_Bd/(D-d)]T_Ms，

wherein, T_MsIs the martensite transformation starting point, k, of the bearing material_BIs an austempering temperature correction coefficient, k_B0.05 to 0.1.

6. The aeroengine bearing high toughness complex phase heat as claimed in claim 5Treatment method, characterized in that the time t of austempering_BThe numerical control is related to the inner and outer diameter sizes of the ferrule and the isothermal quenching temperature as follows:

t_B＝t₂[(D-d)/d]·[T_Ms/(T_B-T_Ms)]，

wherein, t₂Initial time of isothermal quenching, t₂Is 150 min-180 min.

7. The high-strength and high-toughness complex-phase heat treatment method for the aero-engine bearing as claimed in claim 1, wherein when the bearing ring is placed into a tempering furnace for tempering treatment, the tempering temperature is 535-550 ℃, and the cycle is carried out for three times.

8. The high-toughness complex-phase heat treatment method for the aeroengine bearing as claimed in claim 1, wherein the content of the quenched retained austenite is controlled to be between 20% and 30%, and the content of the tempered retained austenite is controlled to be below 4%.

9. The high-toughness complex-phase heat treatment method for the aero-engine bearing according to any one of claims 1 to 8, wherein when the bearing ring after austenitizing is immersed in a low-temperature salt bath furnace for isothermal quenching, the bainite content is controlled to be between 5% and 50%.

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