Multi-heating-number hammer forging process for improving mixed crystals of small-specification A-100 steel die forging

Abstract

According to the multi-heating-number hammer forging process for improving the mixed crystals of the small-specification A-100 steel die forging, the deformation rate, the forging temperature gradient and the deformation amount of each heating number are accurately controlled, the sufficiency and uniformity of dynamic recrystallization are effectively promoted, the mixed crystal phenomenon is fundamentally avoided, the forged piece is made to have a complex shape, and meanwhile the quality of the forged piece is improved. The steel plate has a uniform and fine grain structure and excellent comprehensive mechanical properties, and relates to the field of forging. The hammer forging process comprises a blank making stage and a die forging stage, the total forging heating number of the blank making stage and the die forging stage is larger than or equal to three times, and in the blank making stage, the deformation rate is 5-8 m / s, and the deformation amount of the first heating number is 30%-80%; if the forging heating number of the blank manufacturing stage is larger than or equal to 2, the deformation of the subsequent heating number is 10%-30%; in the die forging stage, the deformation rate is 4-9 m / s, and the deformation of the first heating number is 30%-60%; and if the forging heating number of the die forging stage is larger than or equal to 2, the deformation of the subsequent heating number is smaller than or equal to 20%.

Description

Technical Field

[0001] This invention relates to the field of forging, specifically to a multi-fire hammer forging process for improving the mixed crystal structure of small-sized A-100 steel die forgings. Background Technology

[0002] A-100 steel is an ultra-high strength, secondary hardening martensitic alloy steel. It is widely used in the aerospace field, where there are stringent requirements for high strength, high toughness, and environmental resistance. It has become an indispensable key material in modern aviation equipment and is widely used in important components such as aircraft landing gear and engine housings.

[0003] In the production of A-100 steel forgings, the forging process plays a decisive role in the grain structure and mechanical properties of the forgings. Due to the high deformation resistance of A-100 steel and the narrow forging process window, traditional forging processes face severe challenges. For large-sized forgings (weighing over 650 kg), in order to control grain size, existing technologies (such as the scheme disclosed in CN117620060A) typically employ multi-pass forging, and avoid grain coarsening by gradually reducing the heating temperature in each pass and controlling the deformation amount in a single pass to 15%–30%, thereby achieving grain refinement while ensuring forming.

[0004] However, the aforementioned technical solutions applicable to large-size forgings present new and difficult-to-solve technical problems when applied to small-size die forgings (weighing 100 kg or less). While small-size die forgings using multi-pass hammer forging have lower impact deformation resistance, the increased number of passes and higher heating temperatures mean that incomplete dynamic recrystallization can easily occur in insufficiently deformed areas if the deformation per pass is not properly controlled. This results in a "mixed-grain" structure within the forging, containing both coarse and fine grains. This mixed-grain phenomenon significantly reduces the uniformity and stability of the forging's mechanical properties, severely impacting product reliability and service life.

[0005] Existing technologies for large-sized parts focus on addressing the overall coarse grain problem, but do not address, and cannot address, the unique challenge of localized grain mixing in multi-stage forging of small-sized parts. Therefore, there is an urgent need in the field for a forging process specifically designed for small-sized A-100 steel forgings that can effectively avoid grain mixing while increasing the number of forging stages to ensure the filling and forming of complex shapes, thus ensuring that the forgings achieve a uniform, fine-grained microstructure and excellent overall mechanical properties. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a multi-stage hammer forging process for improving the mixed grain structure of small-sized A-100 steel die forgings. This process effectively promotes the sufficiency and uniformity of dynamic recrystallization by precisely controlling the deformation rate, forging temperature gradient and deformation amount of each stage, fundamentally avoiding the occurrence of mixed grain phenomenon, so that the forgings can obtain complex shapes while having a uniform and fine grain structure and excellent comprehensive mechanical properties.

[0007] The technical solution adopted by the present invention to solve its technical problem is: to improve the multi-fire hammer forging process of mixed crystals for small-sized A-100 steel die forgings, wherein the weight of the forging is no more than 100kg, the hammer forging process includes two stages: billet preparation and die forging, and the total number of forging fires in the two stages of billet preparation and die forging is greater than or equal to 3, the forging temperature of the first fire is 1040~1080℃, and the forging temperature of the subsequent fires is 20~100℃ lower than the forging temperature of the first fire;

[0008] In the billet preparation stage: the deformation rate is 5-8 m / s, and the deformation amount in the first forging pass is 30%-80%; if the forging passes in the billet preparation stage are greater than or equal to 2, the deformation amount in subsequent passes is 10%-30%.

[0009] Die forging stage: the deformation rate is 4 to 9 m / s, and the deformation amount of the first forging is 30% to 60%; if the forging stages have more than or equal to 2 forging times, the deformation amount of subsequent forging times is less than or equal to 20%.

[0010] Furthermore, the deformation amount in the first firing during the billet preparation stage is 40% to 60%.

[0011] Furthermore, in the first heating stage of billet preparation: the furnace is preheated to 800±15℃; then the billet at room temperature is loaded into the furnace and kept warm to make the temperature inside and outside the billet uniform; finally, the billet is heated to 1040~1080℃ with the furnace and kept warm to complete the austenitization process.

[0012] Furthermore, in the first heating stage of die forging: first, the heating furnace is heated to 800±15℃; then, the billet formed in the billet preparation stage at room temperature is loaded into the furnace and kept at a constant temperature to make the internal and external temperatures of the billet uniform; finally, the billet is heated to the set temperature with the furnace and kept at a constant temperature to complete the austenitization process.

[0013] Furthermore, the billet preparation and die forging stages each require two heat passes.

[0014] The beneficial effects of this invention are: it effectively suppresses uneven grain growth, promotes complete and uniform dynamic recrystallization, resulting in a more uniform microstructure in the formed forgings, free from mixed grain phenomena, and improving the mechanical properties of the forgings. Furthermore, while ensuring microstructure and properties, this invention allows for multi-pass forming, reducing reliance on large deformation in a single pass, making the forming of complex-shaped small forgings easier, and improving die life and production efficiency. Attached Figure Description

[0015] Figure 1 This is the crystal phase diagram of forging 1;

[0016] Figure 2 This is the crystal phase diagram of forging 2;

[0017] Figure 3 This is the crystal phase diagram of forging 3;

[0018] Figure 4 This is the crystal phase diagram of forging 4. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] like Figure 1 , Figure 2 As shown, the present invention provides an improved multi-stage hammer forging process for small-sized A-100 steel die forgings with mixed crystals. The weight of the forging is no more than 100 kg. The hammer forging process includes two stages: billet preparation and die forging. The total number of forging stages in the billet preparation and die forging stages is greater than or equal to three. The forging temperature of the first forging stage is 1040–1080 °C, and the forging temperature of subsequent forging stages is 20–100 °C lower than the forging temperature of the first forging stage. In the billet preparation stage, the deformation rate is 5–8 m / s, and the deformation amount of the first forging stage is 30%–80%. If the number of forging stages in the billet preparation stage is greater than or equal to two, the deformation amount of subsequent forging stages is 10%–30%. In the die forging stage, the deformation rate is 4–9 m / s, and the deformation amount of the first forging stage is 30%–60%. If the number of forging stages in the die forging stage is greater than or equal to two, the deformation amount of subsequent forging stages is less than or equal to 20%.

[0021] This invention addresses the mixed grain defect in multi-pass hammer forging of small-sized A-100 steel by introducing deformation rate as a core control parameter. Combined with specific temperature gradients and deformation distribution, this creates a dedicated process window suitable for hammer forging small parts. Through a strategy of "low-temperature, high-speed" deformation (subsequent passes with cooling and high deformation rates), it effectively suppresses uneven grain growth, promotes complete and uniform dynamic recrystallization, and results in a more uniform microstructure in the forgings, free from mixed grain phenomena, thus improving the mechanical properties of the forgings. Furthermore, this invention allows for multi-pass forming while ensuring microstructure and properties, reducing reliance on large deformation amounts in a single pass, making the forming of complex-shaped small forgings easier, and improving die life and production efficiency.

[0022] In this invention, preferably, the deformation amount of the first firing in the billet-making stage is 40% to 60%. A deformation amount of 40% to 60% in the first firing during the billet-making stage can more effectively break down the original as-cast state or coarse grains, generating a large number of fine, uniform new grains, thus laying an excellent initial microstructure foundation for the entire forging.

[0023] To better control the grain size of the forgings, the first heating stage of the billet preparation process of this invention preferably adopts the following process: First heating stage of billet preparation: The furnace is preheated to 800±15℃; then, the billet at room temperature is loaded into the furnace and held at that temperature to homogenize the temperature inside and outside the billet; finally, the billet is heated with the furnace to 1040~1080℃ and held at that temperature to complete the austenitization process. First heating stage of die forging: The furnace is first heated to 800±15℃; then, the initial billet formed in the billet preparation stage at room temperature is loaded into the furnace and held at that temperature to homogenize the temperature inside and outside the initial billet; finally, the initial billet is heated with the furnace to the set temperature and held at that temperature to complete the austenitization process. The holding times mentioned above can be calculated experimentally or using existing relevant calculation formulas. These will not be elaborated upon here.

[0024] Example 1: Forging 1 is made of A-100 steel, with billet dimensions of φ300mm×150mm and a weight of 85Kg. Forging 1 undergoes a total of 4 forging passes, including 2 passes in the billet preparation stage and 2 passes in the die forging stage. The hammer forging process of forging 1 is as follows:

[0025] Step 1, First heating stage of billet preparation: First, heat the furnace to 800±15℃; then load the billet at room temperature into the furnace and keep it at that temperature to make the temperature inside and outside the billet uniform; finally, heat the billet to 1080℃ with the furnace and keep it at that temperature to complete the austenitization process.

[0026] Step 2, First firing of billet: The billet is drawn to 235mm×210mm×210mm in one pass, with a deformation amount of 30% and a deformation rate of 5m / s;

[0027] Step 3, Second heating stage of billet preparation: The hot billet after the first heating is loaded into the furnace and heated to 1040℃ and held at that temperature to complete the austenitization process.

[0028] Step 4, Second forging: The billet is drawn twice to 220mm×200mm×235mm, with a deformation amount of 10% and a deformation rate of 5m / s. After forging, it is air-cooled to obtain the initial billet.

[0029] Step 5, First heating stage of die forging: First, heat the furnace to 800±15℃; then load the billet at room temperature into the furnace and keep it at that temperature to make the temperature inside and outside the billet uniform; finally, heat the billet to 1040℃ with the furnace and keep it at that temperature to complete the austenitization process.

[0030] Step 6, First forging: Die forging the initial billet, controlling the deformation amount to be 30% and the deformation rate to be 4m / s;

[0031] Step 7, Second Heating Stage of Die Forging: The hot billet is loaded into the furnace and heated to 1040℃ and held at that temperature;

[0032] Step 8, Second forging: The initial billet is forged again with a deformation amount of 10% and a deformation rate of 4m / s. After forging, it is air-cooled to obtain forging 1.

[0033] Step 9, Heat treatment: After normalizing and high-temperature tempering, the forging 1 is air-cooled to room temperature. The normalizing temperature is 900℃ and the high-temperature tempering temperature is 680℃.

[0034] Example 2:

[0035] Forging 2 is made of A-100 steel, with a billet size of φ300mm×150mm and a weight of 85Kg. Forging 2 undergoes a total of 4 forging passes, including 2 passes in the billet preparation stage and 2 passes in the die forging stage. The hammer forging process for forging 2 is as follows:

[0036] Step 1, First heating stage of billet preparation: First, heat the furnace to 800±15℃; then load the billet at room temperature into the furnace and keep it at that temperature to make the temperature inside and outside the billet uniform; finally, heat the billet to 1060℃ with the furnace and keep it at that temperature to complete the austenitization process.

[0037] Step 2, First firing of billet: The billet is drawn to 180mm×155mm×380mm in one pass, with a deformation amount of 60% and a deformation rate of 6m / s;

[0038] Step 3, Second heating stage of billet preparation: The hot billet after the first heating is loaded into the furnace and heated to 1020℃ and held at that temperature to complete the austenitization process.

[0039] Step 4, Second forging: The billet is drawn twice to 150mm×150mm×470mm, with a deformation amount of 20% and a deformation rate of 6m / s. After forging, it is air-cooled to obtain the initial billet.

[0040] Step 5, First heating stage of die forging: First, heat the furnace to 800±15℃; then load the billet at room temperature into the furnace and keep it at that temperature to make the temperature inside and outside the billet uniform; finally, heat the billet to 1020℃ with the furnace and keep it at that temperature to complete the austenitization process.

[0041] Step 6, First forging: Die forging the initial billet, controlling the deformation amount to 45% and the deformation rate to 7m / s;

[0042] Step 7, Second Heating Stage of Die Forging: The hot billet is loaded into the furnace and heated to 1020℃ and held at that temperature;

[0043] Step 8, Second forging: The initial billet is forged again with a deformation amount of 15% and a deformation rate of 6m / s. After forging, it is air-cooled to obtain forging 2.

[0044] Step 9, Heat treatment: After normalizing and high-temperature tempering, the forging 2 is air-cooled to room temperature. The normalizing temperature is 900℃ and the high-temperature tempering temperature is 680℃.

[0045] Example 3:

[0046] Forging 3 is made of A-100 steel, with a billet size of φ300mm×150mm and a weight of 85Kg. Forging 3 undergoes a total of 4 forging passes, including 2 passes in the billet preparation stage and 2 passes in the die forging stage. The hammer forging process for forging 3 is as follows:

[0047] Step 1, First heating stage of billet preparation: First, heat the furnace to 800±15℃; then load the billet at room temperature into the furnace and keep it at that temperature to make the temperature inside and outside the billet uniform; finally, heat the billet to 1040℃ with the furnace and keep it at that temperature to complete the austenitization process.

[0048] Step 2, First firing of billet: The billet is drawn to 140mm×100mm×750mm in one pass, with a deformation amount of 80% and a deformation rate of 8m / s;

[0049] Step 3, Second heating stage of billet preparation: The hot billet after the first heating is loaded into the furnace and heated to 1020℃ and held at that temperature until the austenitization process is completed.

[0050] Step 4, Second forging: The billet is drawn twice to 130mm×75mm×1080mm, with a deformation amount of 30% and a deformation rate of 8m / s. After forging, it is air-cooled to obtain the initial billet.

[0051] Step 5, First heating stage of die forging: First, heat the furnace to 800±15℃; then load the billet at room temperature into the furnace and keep it at that temperature to make the temperature inside and outside the billet uniform; finally, heat the billet to 940℃ with the furnace and keep it at that temperature to complete the austenitization process.

[0052] Step 6, First forging: Die forging the initial billet, controlling the deformation amount to 60% and the deformation rate to 9m / s;

[0053] Step 7, Second Heating Stage of Die Forging: The hot billet is loaded into the furnace and heated to 940℃ and held at that temperature;

[0054] Step 8, Second forging: The initial billet is forged again with a deformation amount of 20% and a deformation rate of 9m / s. After forging, it is air-cooled to obtain forging 3.

[0055] Step 9, Heat treatment: After normalizing and high-temperature tempering, the forging 3 is air-cooled to room temperature. The normalizing temperature is 900℃ and the high-temperature tempering temperature is 680℃.

[0056] Comparative example:

[0057] Forging 4 is made of A-100 steel, with a billet size of φ300mm×150mm and a weight of 85Kg. Forging 4 undergoes a total of 4 forging processes, including 2 forging stages in the billet preparation stage and 2 forging stages in the die forging stage. Forging 4 adopts a conventional multi-forging process.

[0058] Samples were taken from forgings 1, 2, 3, and 4, and their grain micrographs are shown below. Figure 1 , Figure 2 , Figure 3 and Figure 4 The grain size and mechanical properties are shown in the table below:

[0059]

[0060] As can be seen from the table above and the accompanying drawings, the forging formed by the method of the present invention achieves a grain size of grade 8, and the forging structure is more uniform with no mixed grain phenomenon.

Claims

1. An improved multi-stage hammer forging process for small-sized A-100 steel die forgings with mixed crystal structure, wherein the weight of the forging is no more than 100 kg, and the hammer forging process includes two stages: billet preparation and die forging, and the total number of forging stages is greater than or equal to 3. The method is characterized by... The forging temperature of the first forging is 1040-1080℃, and the forging temperature of subsequent forgings is 20-100℃ lower than that of the first forging. In the billet preparation stage: the deformation rate is 5-8 m / s, and the deformation amount in the first forging pass is 30%-80%; if the forging passes in the billet preparation stage are greater than or equal to 2, the deformation amount in subsequent passes is 10%-30%. Die forging stage: the deformation rate is 4 to 9 m / s, and the deformation amount of the first forging is 30% to 60%; if the forging stages have more than or equal to 2 forging times, the deformation amount of subsequent forging times is less than or equal to 20%.

2. The multi-stage hammer forging process for improving mixed grain structure in small-sized A-100 steel forgings as described in claim 1, characterized in that, The deformation amount in the first firing during the billet preparation stage is 40% to 60%.

3. The multi-stage hammer forging process for improving mixed-grained crystals in small-sized A-100 steel forgings as described in claim 1, characterized in that, The first heating stage of billet preparation: First, preheat the furnace to 800±15℃; then load the billet at room temperature into the furnace and keep it warm to make the temperature inside and outside the billet uniform; finally, heat the billet to 1040~1080℃ with the furnace and keep it warm to complete the austenitization process.

4. The multi-stage hammer forging process for improving mixed grain structure in small-sized A-100 steel forgings as described in claim 1, characterized in that, The first heating stage of die forging: First, the heating furnace is heated to 800±15℃; then, the billet formed in the billet preparation stage at room temperature is loaded into the furnace and kept at a constant temperature to make the temperature inside and outside the billet uniform; finally, the billet is heated to the set temperature with the furnace and kept at a constant temperature to complete the austenitization process.

5. The multi-stage hammer forging process for improving mixed grain structure in small-sized A-100 steel forgings as described in claim 1, characterized in that, The billet preparation and die forging stages each require two heat passes.

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