Novel heat treatment process for special alloy bar

Abstract

The invention belongs to the technical field of metal material manufacturing, and relates to a novel heat treatment process of a special alloy bar, which comprises the following steps: firstly, carrying out two-stage homogenization treatment on the bar to eliminate composition segregation, carrying out heat preservation at 1000-1100 DEG C for 2.0-4.0 hours at the first stage, and carrying out heat preservation at 1100-1200 DEG C for 2.0-4.0 hours at the second stage; then heating to an austenitizing temperature range of 850-950 DEG C, and keeping for 1.0-2.0 hours; then oil-cooling quenching treatment is carried out, and rapid cooling is carried out to form a specific microscopic structure; after quenching, immediately immersing into a salt bath with the temperature of 200-300 DEG C, and preserving heat for 10.0-30.0 minutes, so as to adjust the structure and reduce the internal stress; then induction heating tempering treatment is conducted, the tempering temperature ranges from 500 DEG C to 650 DEG C, the tempering time ranges from 1.0 h to 3.0 h, at least one tempering period is included, and the period temperature and the period time are independently adjustable; and finally air-cooling to room temperature. The grain size of the treated bar is controlled to be 10-20 microns, the tensile strength is over 2000 MPa, the yield strength is over 1800 MPa, the impact energy at the temperature of minus 40 DEG C is not lower than 40 J, and the high-strength and high-toughness anti-fatigue structural part is suitable for manufacturing high-strength, high-toughness and anti-fatigue structural parts such as aerospace vehicle parts.

Description

Technical Field

[0001] The present invention belongs to the technical field of heat treatment of metal materials, and particularly relates to a new heat treatment process for special alloy bars. Background Art

[0002] In the current field of materials science, special alloy bars have attracted much attention due to their excellent mechanical properties and wide application potential. However, with the development of technology and the continuous improvement of industrial requirements, the performance requirements for special alloy bars are also getting higher and higher. Traditional heat treatment processes often face many challenges when dealing with such alloys.

[0003] On the one hand, composition segregation and non-uniform microstructure are inevitable problems in traditional heat treatment processes. These problems not only affect the mechanical properties of alloy bars but also limit their applications in high-precision and high-reliability fields. On the other hand, excessive internal stress is also a thorny problem in traditional heat treatment processes, which may cause cracks and deformation in alloy bars during processing and use, reducing their fatigue life. To overcome these difficulties, researchers have been constantly exploring new heat treatment processes. However, existing improvement schemes often have deficiencies such as complex processes, high costs, or limited effects. Therefore, there is an urgent need for a new heat treatment process for special alloy bars to achieve fine control of the microstructure and optimization of the properties of alloy bars.

[0004] The new heat treatment process needs to be able to eliminate composition segregation and homogenize the microstructure; at the same time, it also needs to be able to control the austenitization process to ensure that the microstructure is completely transformed into austenite; during quenching, rapid cooling is required to form a specific microstructure; in addition, it is necessary to adjust the microstructure and reduce internal stress through subsequent treatment steps, and finally obtain special alloy bars with high strength, high toughness, and good fatigue resistance. Such a new heat treatment process will provide strong support for the manufacture of high-precision and high-reliability structural components.

[0005] Patent document CN 116814931 A discloses a quenching and tempering heat treatment method for 42CrMo connecting rods. This patent realizes one-time quenching and tempering through processes such as segmented heating, holding, cooling, and oil bath cooling, and precisely controls the austenitization process of workpieces, so that the tensile strength and plasticity indexes are matched. This method does not require repeated heat treatment, can effectively reduce production costs and cycles, and at the same time controls oxidation, decarburization, and deformation, improving product quality. However, this process has a complex process flow, extremely strict requirements for parameters such as heating rate, holding time, cooling rate, and transfer time, relies on high-precision equipment and an automated control system, has a high operation difficulty, is easily affected by the environment and equipment stability during actual promotion, and has high management requirements.

[0006] Patent document CN 116656935 A discloses a heat treatment method for improving the low-temperature impact toughness of large-sized 42CrMo steel forgings. This patent uses rapid cooling, segmented heat preservation, and strictly controls the water cooling and oil cooling processes, finely regulating the parameters of each process, significantly improving the low-temperature impact toughness of large-sized steel forgings at -20°C. This method shortens the production cycle, reduces costs, and does not require additional adjustment of alloy components, with the process being economical and efficient. However, the cooling rate and parameter control in each stage of this patent are extremely demanding, with high requirements for the temperature control and circulation systems of the water tank and oil tank, precise control of the workpiece transfer time, a complex operation process, and high requirements for equipment and on-site management levels, resulting in risks in industrial application and promotion.

[0007] Although traditional manufacturing methods can improve the strength and toughness of alloy bars to a certain extent, it is difficult to achieve the optimization of both low-temperature impact toughness and high fatigue life simultaneously. The present invention aims to achieve fine regulation of the microstructure of special alloy bars and improve their comprehensive mechanical properties by optimizing homogenization treatment, austenitization, quenching, salt bath treatment, and precisely controlling the tempering process, so as to meet the requirements of high-strength, high-toughness, and fatigue-resistant materials in the field of high-end equipment manufacturing. Summary of the Invention

[0008] The present invention aims to overcome the deficiencies of the prior art and provide a new heat treatment process for special alloy bars. By precisely controlling the process parameters, the alloy microstructure is uniformly refined to form an ultrafine equiaxed crystal structure, thereby achieving the simultaneous improvement of the high strength and high toughness of special alloy bars. The process flow of the present invention is simple and efficient, can be implemented on conventional industrial equipment, has high production efficiency, and excellent industrial application prospects.

[0009] The present invention is achieved through the following technical solutions:

[0010] A new heat treatment process for special alloy bars, comprising the following steps:

[0011] Step 1: Perform homogenization treatment on the special alloy bar to eliminate composition segregation;

[0012] Step 2: Heat the bar after homogenization treatment to the austenitization temperature range and hold for a period of time to completely austenitize the structure;

[0013] Step 3: Perform oil quenching treatment on the austenitized bar to rapidly cool and form a specific microstructure;

[0014] Step 4: Immediately immerse the quenched bar in a salt bath for short-time heat preservation to adjust the structure and reduce internal stress;

[0015] Step 5: Perform induction heating tempering treatment on the bar after salt bath treatment to precisely control the tempering temperature and time and adjust its hardness and toughness;

[0016] Step 6: Air-cool the bar after tempering treatment to room temperature to obtain the required mechanical properties.

[0017] Furthermore, a new heat treatment process for special alloy bars, the homogenization treatment temperature is 1000 - 1100 °C for 2.0 - 4.0 h, and then at 1100 - 1200 °C for 2.0 - 4.0 h.

[0018] Furthermore, a new heat treatment process for special alloy bars, the austenitizing temperature range is 850 - 950 °C, and the holding time is 1.0 - 2.0 h.

[0019] Furthermore, a new heat treatment process for special alloy bars, the temperature of the salt bath is 200 - 300 °C, and the holding time is 10.0 - 30.0 min.

[0020] Furthermore, a new heat treatment process for special alloy bars, the induction heating tempering treatment includes at least one tempering cycle, the temperature and time of each tempering cycle are independently adjustable, the tempering temperature range is 500 - 650 °C, and the time is 1.0 - 3.0 h.

[0021] Furthermore, a new heat treatment process for special alloy bars, the induction heating tempering treatment includes two tempering cycles. In the first stage, high-frequency rapid tempering is carried out, with a frequency of 20 - 60 kHz to rapidly heat the surface of the bar, so as to form an ultrafine grain strengthening layer on the surface; in the second stage, it is switched to medium-frequency induction heating, with a frequency of 5 - 20 kHz to perform through-heat treatment on the core of the bar to optimize the toughness of the core.

[0022] Furthermore, a new heat treatment process for special alloy bars, the chemical composition of the special alloy bar includes carbon (C): 0.34% - 0.38%, silicon (Si): 0.17% - 0.37%, manganese (Mn): 0.50% - 0.80%, sulfur (S): ≤0.035%, phosphorus (P): ≤0.035%, chromium (Cr): 0.90% - 1.20%, nickel (Ni): 3.0% - 3.3%, molybdenum (Mo): 0.15% - 0.25%, and the rest are iron and unavoidable impurities.

[0023] Furthermore, a new heat treatment process for special alloy bars, the special alloy bar after being treated by the heat treatment process has a specific microstructure. The microstructure of the special alloy bar shows a gradient distribution. The microstructure of the surface high-frequency quenching zone is ultrafine-grained equiaxed grains, with a grain size of 5 - 10 μm and a martensite content of ≥90%; the grain size in the transition zone is 10 - 15 μm, and the dislocation density gradient decreases; the microstructure of the core medium-frequency tempering zone is equiaxed grains and a small amount of retained austenite, with a grain size of 15 - 20 μm.

[0024] Furthermore, a new heat treatment process for special alloy bars. After the special alloy bars undergo this heat treatment process, their tensile strength reaches above 2000 MPa and their yield strength reaches above 1800 MPa.

[0025] Furthermore, a new heat treatment process for special alloy bars. After the special alloy bars undergo this heat treatment process, they have good low-temperature impact toughness, and the impact energy at -40 °C is not less than 40 J.

[0026] The method of this patent has the following beneficial effects compared with the prior art:

[0027] 1. The present invention adopts two-stage homogenization treatment to effectively eliminate composition segregation, homogenize the microstructure of the bars, and lay a foundation for subsequent heat treatment processes. In contrast, traditional homogenization treatment often fails to completely eliminate segregation, resulting in uneven local properties of the material and affecting service reliability.

[0028] 2. Oil quenching is used for rapid cooling to form an ultrafine microstructure, combined with short-time salt bath heat preservation to adjust the microstructure and release internal stress, so as to balance high strength and high toughness. Traditional quenching processes may lead to quenching cracks or excessive internal stress, while this method effectively reduces deformation and improves low-temperature impact toughness through salt bath buffering.

[0029] 3. Induction heating tempering is adopted, allowing multiple tempering cycles to be independently adjustable to achieve precise microstructure control. The grain size of the alloy bars is controlled within 10 - 20 μm, forming a uniform and fine equiaxed microstructure without macroscopic defects. Traditional processes are difficult to form such fine grain microstructures, resulting in a decrease in the plasticity and toughness of the material. In contrast, traditional tempering methods have poor controllability and are difficult to optimize the matching of strength and toughness, affecting the fatigue performance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Shows the process flow chart of the present invention;

[0031] Figure 2 Shows the heat treatment process diagram of Example 1;

[0032] Figure 3 Shows the microstructure morphology photo of Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] The present invention will be described in detail below with reference to the drawings and specific embodiments. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several changes and improvements can still be made. These all fall within the protection scope of the present invention.

[0034] Example 1

[0035] A new heat treatment process for special alloy bars, and the specific steps are as follows:

[0036] Homogenization treatment: Heat the special alloy bar to 1020 °C, hold for 2.5 h, then raise the temperature to 1120 °C and continue to hold for 3.0 h to fully eliminate composition segregation;

[0037] Austenitization treatment: Heat the homogenized bar to the austenitization temperature range of 860 °C and hold for 1.2 h to fully austenitize the structure;

[0038] Oil quenching: Perform oil quenching treatment on the austenitized bar to achieve rapid cooling and form a specific microstructure;

[0039] Salt bath short-time holding: Immediately immerse the quenched bar in a salt bath at 210 °C and hold for 12.0 min to regulate the microstructure and effectively reduce internal stress;

[0040] Induction heating tempering: Perform induction heating tempering treatment on the bar after salt bath treatment. This step includes at least one tempering cycle, and the temperature and holding time of each tempering cycle can be independently adjusted. The tempering temperature is 520 °C and the holding time is 1.5 h to precisely control the hardness and toughness of the bar;

[0041] The first-stage high-frequency rapid tempering, with a frequency of 35 kHz, rapidly heats the surface of the bar to form an ultrafine grain strengthening layer on the surface; the second stage switches to medium-frequency induction heating, with a frequency of 12 kHz, to perform through-heat treatment on the core of the bar to optimize the toughness of the core.

[0042] New heat treatment process for alloy bars. The chemical composition of the special alloy bar includes carbon (C): 0.36%, silicon (Si): 0.27%, manganese (Mn): 0.65%, sulfur (S): 0.020%, phosphorus (P): 0.020%, chromium (Cr): 1.05%, nickel (Ni): 3.15%, molybdenum (Mo): 0.20%, and the rest is iron and unavoidable impurities.

[0043] Air cooling: Air cool the tempered bar to room temperature to finally obtain the required mechanical properties.

[0044] After the special alloy bar is treated by the above heat treatment process, its microstructure is ultrafine grain equiaxed structure, and the grain size is 10 μm; in terms of mechanical properties, its tensile strength reaches 2000 MPa, yield strength reaches 1800 MPa, and the low-temperature impact energy at -40 °C is 40 J.

[0045] The steps of Examples 2 to 9 are the same as those of Example 1. For the composition, process and properties of the special alloy steel in each specific example, refer to Tables 1 to 3.

[0046] The microstructure of the special alloy bars prepared through the above Examples 1-9 shows a gradient distribution. The structure in the surface high-frequency quenching zone is ultrafine-grained equiaxed crystals with a grain size of 5-10 μm and a martensite content of ≥90%; the grain size in the transition zone is 10-15 μm, and the dislocation density gradient decreases; the structure in the core intermediate-frequency tempering zone is equiaxed crystals and a small amount of retained austenite with a grain size of 15-20 μm.

[0047] Table 1 Chemical composition of the special alloy steel in each example

[0048] Example Carbon (C) Silicon (Si) Manganese (Mn) Sulfur (S) Phosphorus (P) Chromium (Cr) Nickel (Ni) Molybdenum (Mo) Iron (Fe) Example 1 0.360 0.27 0.65 0.020 0.020 1.05 3.15 0.20 The rest Example 2 0.350 0.19 0.70 0.030 0.030 0.95 3.20 0.17 The rest Example 3 0.370 0.32 0.55 0.010 0.025 1.10 3.05 0.23 The rest Example 4 0.340 0.35 0.80 0.035 0.030 1.20 3.30 0.15 The rest Example 5 0.380 0.25 0.60 0.025 0.020 0.90 3.10 0.25 The rest Example 6 0.365 0.17 0.75 0.015 0.035 1.00 3.25 0.18 The rest Example 7 0.355 0.30 0.52 0.030 0.010 1.15 3.00 0.22 The rest Example 8 0.375 0.22 0.68 0.020 0.020 0.98 3.18 0.16 The rest Example 9 0.345 0.29 0.78 0.032 0.030 1.08 3.28 0.21 The rest

[0049] Table 2 Processes in each example

[0050]

[0051] Table 3 Properties in each example

[0052]

[0053] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A new heat treatment process for special alloy bars, characterized in that, The process includes the following steps: Step 1: Homogenization treatment. The special alloy bar is subjected to homogenization treatment to eliminate compositional segregation. Step 2: Austenitization. The homogenized bar is heated to the austenitization temperature range and held for a period of time to fully austenitize the structure. Step 3: Oil quenching. The austenitized bar is subjected to oil quenching treatment to rapidly cool and form a specific microstructure. Step 4: Salt bath treatment. The quenched bar is immediately immersed in a salt bath for short-term heat preservation to adjust the structure and reduce internal stress. Step 5: Tempering treatment. The bar after salt bath treatment is subjected to induction heating tempering treatment to precisely control the tempering temperature and time and adjust its hardness and toughness. Step 6: Air cooling. The bar after tempering treatment is air cooled to room temperature to obtain the required mechanical properties.

2. The novel heat treatment process for a special alloy bar according to claim 1, characterized in that, The temperature of the homogenization treatment is 1000 - 1100 °C, held for 2.0 - 4.0 h, and then held at 1100 - 1200 °C for 2.0 - 4.0 h.

3. A novel heat treatment process for a special alloy bar according to claim 1, characterized in that, The austenitization temperature range is 850 - 950 °C, and the holding time is 1.0 - 2.0 h.

4. A novel heat treatment process for a special alloy bar according to claim 1, characterized in that, The temperature of the salt bath is 200 - 300 °C, and the heat preservation time is 10.0 - 30.0 min.

5. A novel heat treatment process for a special alloy bar according to claim 1, characterized in that, The induction heating tempering treatment includes at least one tempering cycle, and the temperature and time of each tempering cycle are independently adjustable. The tempering temperature range is 500 - 650 °C, and the time is 1.0 - 3.0 h.

6. A novel heat treatment process for a special alloy bar according to claim 1, characterized in that, The induction heating tempering treatment includes two tempering cycles. In the first stage, high-frequency rapid tempering is carried out. The frequency of 20 - 60 kHz is used to rapidly heat the surface of the bar, so that a superfine grain strengthening layer is formed on the surface. In the second stage, it is switched to medium-frequency induction heating, and the frequency of 5 - 20 kHz is used to perform through-heat treatment on the core of the bar to optimize the toughness of the core.

7. A novel heat treatment process for a special alloy bar according to claim 1, characterized in that, The chemical composition of the special alloy bar includes carbon (C): 0.34% - 0.38%, silicon (Si): 0.17% - 0.37%, manganese (Mn): 0.50% - 0.80%, sulfur (S): ≤0.035%, phosphorus (P): ≤0.035%, chromium (Cr): 0.90% - 1.20%, nickel (Ni): 3.0% - 3.3%, molybdenum (Mo): 0.15% - 0.25%, and the rest is iron and unavoidable impurities.

8. A novel heat treatment process for a special alloy bar according to claim 1, characterized in that, After being treated by the heat treatment process, the special alloy bar has a specific microstructure morphology. The microstructure of the special alloy bar shows a gradient distribution. The microstructure of the surface high-frequency quenching zone is superfine-grained equiaxed crystals, the grain size is 5 - 10 μm, and the martensite content is ≥90%. The grain size of the transition zone is 10 - 15 μm, and the dislocation density gradient decreases. The microstructure of the core medium-frequency tempering zone is equiaxed crystals and a small amount of retained austenite, and the grain size is 15 - 20 μm.

9. A novel heat treatment process for a special alloy bar according to claim 1, characterized in that, After the special alloy bar is treated by the heat treatment process, its tensile strength reaches more than 2000 MPa, and its yield strength reaches more than 1800 MPa.

10. A novel heat treatment process for a special alloy bar according to claim 1, characterized in that, After the special alloy bar is treated by the heat treatment process, it has good low-temperature impact toughness, and the impact energy of the core at -40 °C is not less than 40 J.

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