Heat treatment method for obtaining equilibrium structure of 18CrNiMo7-6 carburized and quenched steel forge piece

Abstract

The invention discloses a heat treatment method for obtaining an equilibrium structure of a 18CrNiMo7-6 carburized and quenched steel forge piece, which comprises the following steps: A1, preheating treatment: putting the 18CrNiMo7-6 carburized and quenched steel forge piece into an effective heating area of an electric heating heat treatment furnace, heating to 700 DEG C at the speed of less than or equal to 100 DEG C per hour, and preserving heat for H1, after heat preservation is finished, heating to 950 DEG C at the speed of 120 DEG C per hour; a2, heat preservation treatment is conducted, heat preservation is conducted at 950 DEG C for H2, the forge piece is pulled out of the electric heating heat treatment furnace through a trolley and air-cooled till the surface temperature of the forge piece reaches 580-630 DEG C, the forge piece is pulled into the electric heating heat treatment furnace through the trolley in time, a furnace door is closed, then the forge piece is heated to 690 DEG C, heat preservation is conducted for H3; and A3, cooling treatment is conducted, specifically, after furnace cooling is conducted to 500 DEG C at the speed smaller than or equal to 25 DEG C per hour, the forge piece is discharged out of the furnace and And it can be ensured that the forge piece obtains an equilibrium-state structure, the structure is uniform, and stable performance of a product in the follow-up procedure is ensured.

Description

Technical Field

[0001] The invention relates to the technical field of post-forging heat treatment of forgings, and in particular to a heat treatment method for obtaining an equilibrium structure of a 18CrNiMo7-6 carburized and quenched steel forging. Background Art

[0002] Planetary gears and sun gears made of 18CrNiMo7-6 carburized and quenched steel are important components of wind power gearboxes. With the vigorous development of onshore and offshore wind power, the megawatt level is gradually increasing, and the technical level requirements for planetary gears and sun gear forgings are getting higher and higher, especially the requirements for the organization of the forgings after pretreatment. The equilibrium organization must be obtained to ensure the stability of the product's performance in subsequent processes and ensure the high-speed, economical and safe operation of the gearbox products. Ordinary normalizing + tempering cannot obtain the equilibrium organization F+P (a mixed organization of ferrite and cementite), so it is urgent to develop a heat treatment method that completely solves this technical problem. Summary of the invention

[0003] In order to solve certain technical problems existing in the prior art, the purpose of this application is to provide a heat treatment method for 18CrNiMo7-6 carburized and quenched steel forgings to obtain an equilibrium state structure, which can ensure that the forgings obtain an equilibrium state structure and the structure is uniform, thereby ensuring the stable performance of the product in subsequent processes.

[0004] In order to solve the above existing technical problems, the purpose of this application is achieved by adopting the following technical solutions:

[0005] A heat treatment method for obtaining an equilibrium structure of a 18CrNiMo7-6 carburized and quenched steel forging, comprising the following steps:

[0006] A1. Preheating treatment: put the 18CrNiMo7-6 carburized and quenched steel forging into the effective heating area of ​​the electric heating heat treatment furnace, heat it to 700℃ at a speed of less than or equal to 100℃ per hour, and keep it warm for H1. After the end of the warming, heat it to 950℃ at a speed of 120℃ per hour to make the structure of the 18CrNiMo7-6 carburized and quenched steel forging fully austenitized;

[0007] A2. Insulation treatment: Insulation at 950℃ for H2 time. The trolley pulls the forging out of the electric heating heat treatment furnace and air cools it until the surface temperature of the forging reaches 580-630℃. The trolley promptly pulls the forging into the electric heating heat treatment furnace, closes the furnace door, and then heats it to 690℃ for H3 time to ensure the transformation of the organization and obtain a sufficient and uniform equilibrium organization.

[0008] A3. Cooling treatment: After cooling to 500℃ at a temperature of 25℃ or less per hour, air cool the forgings out of the furnace to avoid the formation of upper bainite structure.

[0009] Preferably, in step A1, H1=0.25-0.5h / effective cross-sectional dimension of the part for every 100mm.

[0010] Preferably, in step A2, H2=2.5-3.0h / effective cross-sectional dimension of the part for every 100mm.

[0011] Preferably, in step A2, H3=5.0-6.0h / effective cross-sectional dimension of the part for every 100mm.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] The present invention adopts the above technical scheme to air-cool the 18CrNiMo7-6 carburized quenched steel forging after forging, slowly heat up during preheating treatment, and quickly heat up after the first heat preservation, so as to ensure that the forging can be fully austenitized; during the heat preservation treatment, quickly cool after the second heat preservation, and then perform the third heat preservation for a long time, so that the forging obtains a refined and uniform equilibrium state structure; controlling the cooling rate during the cooling treatment can avoid obtaining an upper bainite structure; it can ensure that the forging obtains an equilibrium state structure, and the structure is uniform, so as to ensure the stable performance of the product in subsequent processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a process flow chart of the present invention;

[0015] Figure 2 This is the equilibrium tissue map obtained after adopting the present invention. DETAILED DESCRIPTION

[0016] Below, the present application is further described in conjunction with the accompanying drawings and specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form a new embodiment.

[0017] In the description of the present application, it should be understood that the terms "up", "down", "left", "right", etc., indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present application.

[0018] The terms "first", "second", etc. in this application are used to distinguish similar objects, and are not used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application can be implemented in an order other than those illustrated or described here, and the objects distinguished by "first", "second", etc. are generally of one type, and the number of objects is not limited. For example, the first object can be one or more. In addition, "and / or" in the specification and claims represents at least one of the connected objects, and the character " / " generally indicates that the objects associated with each other are in an "or" relationship.

[0019] like Figure 1 As shown, a heat treatment method for obtaining an equilibrium structure of a 18CrNiMo7-6 carburized and quenched steel forging includes the following steps:

[0020] A1. Preheating treatment: put the 18CrNiMo7-6 carburized and quenched steel forging into the effective heating area of ​​the electric heating heat treatment furnace, heat it to 700℃ at a speed of less than or equal to 100℃ per hour, and keep it warm for H1=0.25~0.5h / 100mm of the effective cross-sectional size of the part. After the end of the warming, heat it to 950℃ at a speed of 120℃ per hour to make the structure of the 18CrNiMo7-6 carburized and quenched steel forging fully austenitized.

[0021] A2. Insulation treatment: Insulation at 950℃, the insulation time is H2 = 2.5~3.0h / effective cross-sectional size of the part for every 100mm. The trolley pulls the forging out of the electric heating heat treatment furnace and air cools it until the surface temperature of the forging reaches 580~630℃. The trolley promptly pulls the forging into the electric heating heat treatment furnace, closes the furnace door, and then heats it to 690℃ for insulation. The insulation time is H3 = 5.0~6.0h / effective cross-sectional size of the part for every 100mm, to ensure the transformation of the organization and obtain a sufficient and uniform equilibrium organization;

[0022] A3. Cooling treatment: Cool the forgings in the furnace at a temperature of 25°C per hour or less to 500°C, then air cool them out of the furnace.

[0023] Avoid the formation of upper bainite structure.

[0024] It can ensure that the forging obtains a balanced structure and a uniform structure, ensuring the stable performance of the product in subsequent processes. Figure 2 As shown, the equilibrium state organization is uniform and the product performance is stable.

[0025] The above-mentioned implementation modes are only preferred implementation modes of the present application and cannot be used to limit the scope of protection of the present application. Any non-substantial changes and substitutions made by technicians in this field on the basis of the present application shall fall within the scope of protection required by the present application.

Claims

1. A heat treatment method for obtaining an equilibrium structure of a 18CrNiMo7-6 carburized and quenched steel forging, characterized in that: The following steps are involved: A1. Preheating treatment: put the 18CrNiMo7-6 carburized and quenched steel forging into the effective heating area of ​​the electric heating heat treatment furnace, heat it to 700℃ at a speed of less than or equal to 100℃ per hour, and keep it warm for H1. After the end of the warming, heat it to 950℃ at a speed of 120℃ per hour to make the structure of the 18CrNiMo7-6 carburized and quenched steel forging fully austenitized; A2. Insulation treatment: Insulation at 950℃ for H2 time. The trolley pulls the forging out of the electric heating heat treatment furnace and air cools it until the surface temperature of the forging reaches 580-630℃. The trolley promptly pulls the forging into the electric heating heat treatment furnace, closes the furnace door, and then heats it to 690℃ for H3 time to ensure the transformation of the organization and obtain a sufficient and uniform equilibrium organization. A3. Cooling treatment: After cooling to 500℃ at a temperature of 25℃ or less per hour, air cool the forgings out of the furnace to avoid the formation of upper bainite structure.

2. The heat treatment method for obtaining an equilibrium structure of a 18CrNiMo7-6 carburized and quenched steel forging according to claim 1, characterized in that: In the step A1, H1=0.25-0.5h / effective cross-sectional dimension of the part for every 100mm.

3. The heat treatment method for obtaining an equilibrium structure of a 18CrNiMo7-6 carburized and quenched steel forging according to claim 1, characterized in that: In the step A2, H2=2.5-3.0h / effective cross-sectional dimension of the part for every 100mm.

4. The heat treatment method for obtaining an equilibrium structure of a 18CrNiMo7-6 carburized and quenched steel forging according to claim 1, characterized in that: In the step A2, H3=5.0-6.0h / effective cross-sectional dimension of the part for every 100mm.

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