Special steel precision bar and preparation method thereof

Abstract

The present invention relates to the technical field of special steels and provides a special steel precision bar and a preparation method thereof. The special steel precision bar is composed of the following raw materials in weight percentage: C 0.4% to 0.5%, Mn 1.2% to 1.4%, Cr 8% to 10%, Mo 0.4% to 0.6%, Ni 0.5% to 0.7%, V 0.6% to 0.8%, Ti 0.9% to 1.1%, Si 0.2% to 0.4%, with the remainder being Fe and unavoidable impurities, wherein the ratio of (C+V+Ti):Cr is 0.19 to 0.3:1. This technical solution solves the problem of insufficient hardness of special steel precision bars in related technologies.

Description

Technical Field

[0001] The present invention relates to the technical field of special steel, and in particular to a special steel precision bar and a preparation method thereof. Background Art

[0002] In today's era of rapid development of high-end manufacturing, special steel precision bars, as key basic materials, their performance and quality play a decisive role in equipment operation and product quality in many fields.

[0003] However, as the industry develops towards high-end and precision, the existing special steel precision bars still have some shortcomings in hardness. Insufficient hardness will bring many hazards to the use of the bars. For example, in the field of mechanical processing, if the hardness of special steel bars used to manufacture cutting tools and molds is insufficient, the cutting tools will wear out rapidly during the cutting process, resulting in reduced processing accuracy, poor surface quality of the workpiece, and even inability to perform normal cutting processing; the mold is prone to deformation, collapse and other problems, shortening the service life of the mold and increasing production costs.

[0004] In the existing technology, the hardness of the rod is improved by optimizing the alloy composition design, such as adding alloy elements such as chromium, molybdenum, and vanadium, but the degree is limited, and there is a problem of unbalanced alloy composition. Although the addition of some elements can improve the hardness, it has a certain impact on other properties of the rod. How to accurately control the content of each element to ensure that the hardness is effectively improved while maintaining a balance of other key properties is a major challenge.

[0005] Therefore, it is necessary to propose a special steel precision bar and a preparation method thereof, which can improve the hardness of the bar while taking into account other key properties. Summary of the Invention

[0006] The present invention provides a special steel precision bar and a preparation method thereof, which solves the problem of insufficient hardness of special steel precision bars in related technologies.

[0007] The technical solution of the present invention is as follows: The present invention proposes a special steel precision bar, which is composed of the following raw materials in weight percentage: C 0.4%~0.5%, Mn 1.2%~1.4%, Cr 8%~10%, Mo 0.4%~0.6%, Ni 0.5%~0.7%, V 0.6%~0.8%, Ti 0.9%~1.1%, Si 0.2%~0.4%, and the balance is Fe and unavoidable impurities, wherein (C+V+Ti):Cr=0.19~0.3:1.

[0008] As a further technical solution, the (C+V+Ti):Cr=0.24.

[0009] The present invention also provides a method for preparing a special steel precision bar, which is used to prepare the special steel precision bar, comprising the following steps:

[0010] S1, mixing the raw materials according to the component ratio, smelting and casting to obtain an ingot;

[0011] S2, the ingot is homogenized and preheated and then forged to obtain a forged rod;

[0012] S3. The forged rod is subjected to solution treatment, quenching and aging treatment to obtain a special steel precision rod.

[0013] As a further technical solution, in step S1, the vacuum degree of the smelting is 1~1.2 Pa, preferably 1 Pa, and the casting temperature is 1500~1600℃, for example, it can be 1500℃, 1510℃, 1520℃, 1530℃, 1540℃, 1550℃, 1560℃, 1570℃, 1580℃, 1590℃, 1600℃, preferably 1550℃.

[0014] As a further technical solution, in step S2, the homogenization treatment is performed twice, and the temperature and holding time of the first homogenization treatment are different from the temperature and holding time of the second homogenization treatment.

[0015] In the present invention, the homogenization treatment of the special steel precision bar is carried out twice, and the temperature and time of the two times are different. Since the diffusion rate and diffusion activation energy of different elements in steel are different, the diffusion characteristics of different elements can be optimized through two homogenization treatments with different parameters; the grains can also be made finer and more uniform. The refined grain structure can increase the number of grain boundaries, and the grain boundaries can hinder the movement of dislocations, thereby improving the strength of the special steel precision bar.

[0016] As a further technical solution, the temperature of the first homogenization treatment is less than the temperature of the second homogenization treatment, and the holding time of the first homogenization treatment is greater than the holding time of the second homogenization treatment.

[0017] In the component system of the special steel precision bar of the present invention, elements such as carbon, manganese, chromium, molybdenum, nickel, vanadium, titanium, and silicon play a synergistic role in a specific ratio. Based on this component ratio, during the homogenization treatment of the special steel precision bar, the first homogenization treatment at a lower temperature and for a longer time can cause atoms to diffuse slowly in a relatively stable environment, especially for some elements with low diffusion activation energy, a preliminary uniform distribution can be achieved. The subsequent second homogenization treatment at a higher temperature and for a shorter time can accelerate the diffusion process of elements that did not diffuse sufficiently in the first treatment and require higher energy to diffuse effectively (such as strong carbide-forming elements such as titanium and vanadium). By adopting this method of first slow and then fast, first low temperature and then high temperature, a uniform distribution of various elements in the steel is achieved, component segregation is reduced, the uniformity of the components of the special steel precision bar is improved, and the strength of the special steel precision bar is thereby improved.

[0018] In the present invention, during the homogenization treatment of special steel precision bars, the first low-temperature and long-time treatment can change the original grain structure of the ingot to a certain extent, prompting the grains to begin to refine and stabilize; the second high-temperature and short-time treatment can, on the one hand, further refine the grains, and on the other hand, due to the short high-temperature time, effectively inhibit the excessive growth of the grains. These two treatments cooperate with each other to enable the special steel precision bars to obtain a fine and uniform grain structure, thereby further improving the strength of the special steel precision bars.

[0019] As a further technical solution, the temperature of the first homogenization treatment is 1000~1150℃, for example, it can be 1000℃, 1030℃, 1050℃, 1080℃, 1100℃, 1120℃, 1150℃, preferably 1100℃; the temperature of the second homogenization treatment is 1200~1250℃, for example, it can be 1200℃, 1210℃, 1220℃, 1230℃, 1240℃, 1250℃, preferably 1250℃.

[0020] As a further technical solution, the holding time of the first homogenization treatment is 8 to 10 hours, for example, it can be 8.0 hours, 8.5 hours, 9.0 hours, 9.5 hours, 10.0 hours, and preferably 9.0 hours; the holding time of the second homogenization treatment is 5 to 7 hours, for example, it can be 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, and preferably 6 hours.

[0021] As a further technical solution, in step S2, the preheating temperature is 1100~1150℃, for example, it can be 1100℃, 1110℃, 1120℃, 1130℃, 1140℃, 1150℃, preferably 1150℃, and the time is 3~5h, for example, it can be 3.0h, 3.2h, 3.5h, 3.8h, 4.0h, 4.2h, 4.5h, 4.8h, 5.0h, preferably 4h; the hammering frequency of the forging is 100 times / min.

[0022] As a further technical solution, in step S3, the solid solution temperature is 1000~1050℃, for example, it can be 1000℃, 1010℃, 1020℃, 1030℃, 1040℃, 1050℃, and preferably 1020℃; the time is 2~3h, for example, it can be 2h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h, 3.0h, and preferably 2.5h.

[0023] As a further technical solution, in step S3, the quenching medium is water, and the temperature of the medium is 25-35°C, for example, it can be 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, preferably 30°C.

[0024] As a further technical solution, the diameter of the forged rod is 50-60 mm, preferably 50 mm.

[0025] As a further technical solution, the aging treatment temperature is 400-450°C, for example, 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, preferably 450°C, and the time is 5-6h; for example, 5.0h, 5.1h, 5.2h, 5.3h, 5.4h, 5.5h, 5.6h, 5.7h, 5.8h, 5.9h, 6.0h, preferably 5.0h.

[0026] The working principle and beneficial effects of the present invention are:

[0027] In the present invention, in the component system of special steel precision bars, carbon is an important element that affects the hardness of steel, and an appropriate carbon content can significantly improve the strength and hardness of steel; vanadium, titanium, and chromium combine with carbon to form carbides with higher hardness, which are evenly distributed in the steel matrix, play a role of dispersion strengthening, effectively hinder the movement of dislocations, and thus greatly improve the hardness of the bars; by precisely controlling the ratio of (C+V+Ti) to Cr within a range of 0.19 to 0.3:1, an optimal synergistic effect is achieved between the elements, and the quantity and distribution of carbides formed by carbon, vanadium, and titanium are more reasonable, which cooperate with the carbides formed by chromium and the solid solution strengthening effect of chromium, thereby further improving the hardness of the special steel precision bars. DETAILED DESCRIPTION

[0028] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0029] Example 1

[0030] A special steel precision bar composed of the following raw materials in weight percentage: C 0.4%, Mn 1.2%, Cr 8%, Mo 0.4%, Ni 0.5%, V 0.6%, Ti 0.9%, Si 0.2%, and the balance being Fe and unavoidable impurities;

[0031] A method for preparing special steel precision bars comprises the following steps:

[0032] S1. Mix the raw materials according to the component ratio, smelt them at a vacuum degree of 1 Pa, and cast them at 1550°C to obtain an ingot;

[0033] S2. After the ingot is homogenized, it is heated to 1150°C and preheated for 4 hours before forging at a hammering frequency of 100 times / min to obtain a forged rod with a diameter of 50 mm;

[0034] S3. After the forged bar is solution-treated at 1020℃ for 2.5h, it is quenched with water as the quenching medium at a temperature of 30℃ and aged at 450℃ for 5h to obtain special steel precision bars;

[0035] The homogenization treatment includes the following process: the ingot is heated to 1250°C and kept at this temperature for 15 hours, and then cooled to room temperature.

[0036] Example 2

[0037] A special steel precision bar composed of the following raw materials in weight percentage: C 0.45%, Mn 1.3%, Cr 9%, Mo 0.5%, Ni 0.6%, V 0.7%, Ti 1.0%, Si 0.3%, and the balance being Fe and unavoidable impurities;

[0038] A method for preparing special steel precision bars comprises the following steps:

[0039] S1. Mix the raw materials according to the component ratio, smelt them at a vacuum degree of 1 Pa, and cast them at 1550°C to obtain an ingot;

[0040] S2. After the ingot is homogenized, it is heated to 1150°C and preheated for 4 hours before forging at a hammering frequency of 100 times / min to obtain a forged rod with a diameter of 50 mm;

[0041] S3. After the forged bar is solution-treated at 1020℃ for 2.5h, it is quenched with water as the quenching medium at a temperature of 30℃ and aged at 450℃ for 5h to obtain special steel precision bars;

[0042] The homogenization treatment includes the following process: the ingot is heated to 1250°C and kept at this temperature for 15 hours, and then cooled to room temperature.

[0043] Example 3

[0044] A special steel precision bar composed of the following raw materials in weight percentage: C 0.5%, Mn 1.4%, Cr 10%, Mo 0.6%, Ni 0.7%, V 0.8%, Ti 1.1%, Si 0.4%, and the balance being Fe and unavoidable impurities;

[0045] A method for preparing special steel precision bars comprises the following steps:

[0046] S1. Mix the raw materials according to the component ratio, smelt them at a vacuum degree of 1 Pa, and cast them at 1550°C to obtain an ingot;

[0047] S2. After the ingot is homogenized, it is heated to 1150°C and preheated for 4 hours before forging at a hammering frequency of 100 times / min to obtain a forged rod with a diameter of 50 mm;

[0048] S3. After the forged bar is solution-treated at 1020℃ for 2.5h, it is quenched with water as the quenching medium at a temperature of 30℃ and aged at 450℃ for 5h to obtain special steel precision bars;

[0049] The homogenization treatment includes the following process: the ingot is heated to 1250°C and kept at this temperature for 15 hours, and then cooled to room temperature.

[0050] Example 4

[0051] Compared with Example 2, the difference of Example 4 is that a special steel precision bar is composed of the following raw materials in weight percentage: C 0.4%, Mn 1.3%, Cr 10%, Mo 0.5%, Ni 0.6%, V 0.6%, Ti 0.9%, Si 0.3%, and the balance is Fe and unavoidable impurities.

[0052] Example 5

[0053] Compared with Example 2, the difference of Example 5 is that a special steel precision bar is composed of the following raw materials in weight percentage: C 0.5%, Mn 1.3%, Cr 8%, Mo 0.5%, Ni 0.6%, V 0.8%, Ti 1.1%, Si 0.3%, and the balance is Fe and unavoidable impurities.

[0054] Example 6

[0055] Compared with Example 2, Example 6 is different in that the homogenization process is different. In this example, the homogenization process includes the following process: heating the ingot to 1100° C. and keeping the temperature for 15 hours, and then cooling to room temperature.

[0056] Example 7

[0057] Compared with Example 2, Example 7 is different in that the homogenization process is different. In this example, the homogenization process includes the following process: the ingot is first heated to 1100°C and kept warm for 9 hours, then heated to 1250°C and kept warm for 6 hours, and then cooled to room temperature.

[0058] Example 8

[0059] Compared with Example 2, Example 8 is different in that the homogenization process is different. In this embodiment, the homogenization process includes the following process: the ingot is first heated to 1100°C and kept warm for 6 hours, then heated to 1250°C and kept warm for 9 hours, and then cooled to room temperature.

[0060] Example 9

[0061] Compared with Example 2, Example 9 is different in that the homogenization process is different. In this embodiment, the homogenization process includes the following process: the ingot is first heated to 1100°C and kept warm for 7.5 hours, then heated to 1250°C and kept warm for 7.5 hours, and then cooled to room temperature.

[0062] Example 10

[0063] Compared with Example 2, Example 10 is different in that the homogenization process is different. In this embodiment, the homogenization process includes the following process: the ingot is first heated to 1250°C and kept warm for 6 hours, then heated to 1100°C and kept warm for 9 hours, and then cooled to room temperature.

[0064] Example 11

[0065] Compared with Example 2, Example 11 is different in that the homogenization process is different. In this embodiment, the homogenization process includes the following process: the ingot is first heated to 1250°C and kept warm for 9 hours, then heated to 1100°C and kept warm for 6 hours, and then cooled to room temperature.

[0066] Example 12

[0067] Compared with Example 2, Example 12 is different in that the homogenization process is different. In this embodiment, the homogenization process includes the following process: the ingot is first heated to 1250°C and kept warm for 7.5 hours, then heated to 1100°C and kept warm for 7.5 hours, and then cooled to room temperature.

[0068] Comparative Example 1

[0069] Compared with Example 2, the difference of Comparative Example 1 is that a special steel precision bar is composed of the following raw materials in weight percentage: C 0.45%, Mn 1.3%, Cr 14%, Mo 0.5%, Ni 0.6%, V 0.7%, Ti 1.0%, Si 0.3%, and the balance is Fe and unavoidable impurities.

[0070] Comparative Example 2

[0071] Compared with Example 2, the difference of Comparative Example 2 is that a special steel precision bar is composed of the following raw materials in weight percentage: C 0.45%, Mn 1.3%, Cr 5%, Mo 0.5%, Ni 0.6%, V 0.7%, Ti 1.0%, Si 0.3%, and the balance is Fe and unavoidable impurities.

[0072] Comparative Example 3

[0073] Compared with Example 2, the difference of Comparative Example 3 is that a special steel precision bar is composed of the following raw materials in weight percentage: C 0.45%, Mn 1.6%, Cr 9%, Mo 0.5%, Ni 0.6%, V 0.7%, Ti 1.0%, Si 0.3%, and the balance is Fe and unavoidable impurities.

[0074] Comparative Example 4

[0075] Compared with Example 2, the difference of Comparative Example 4 is that a special steel precision bar is composed of the following raw materials in weight percentage: C 0.45%, Mn 1.3%, Cr 9%, Mo 0.5%, Ni 0.3%, V 0.7%, Ti 1.0%, Si 0.6%, and the balance is Fe and unavoidable impurities.

[0076] Experimental Example 1

[0077] The special steel precision bars prepared in Examples 1 to 5 and Comparative Examples 1 to 4 were tested for Vickers hardness according to the test method specified in GB / T 4340.1-2024 “Vickers hardness test for metallic materials - Part 1: Test method”.

[0078] The test results are shown in Table 1:

[0079] Table 1 Performance test results of special steel precision bars prepared in Examples 1 to 5 and Comparative Examples 1 to 4

[0080]

[0081] It can be seen from Table 1 that when the content of each element meets the range requirements and when (C+V+Ti):Cr=0.19~0.3:1, the hardness of special steel precision bars can be improved.

[0082] Experimental Example 2

[0083] The special steel precision bars prepared in Example 2 and Examples 6 to 12 were tested for tensile strength according to the test method specified in GB / T 228.1-2021 "Tensile Test of Metallic Materials Part 1: Room Temperature Test Method".

[0084] The test results are shown in Table 2:

[0085] Table 2 Performance test results of special steel precision bars prepared in Example 2 and Examples 6 to 12

[0086]

[0087] It can be seen from Table 2 that when the ingot is homogenized twice, and the temperature of the first homogenization treatment is less than the temperature of the second homogenization treatment, and the holding time of the first homogenization treatment is greater than the holding time of the second homogenization treatment, the strength of the special steel precision bar can be improved.

[0088] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A special steel precision bar, characterized in that: The invention is composed of the following raw materials in weight percentage: C 0.4%-0.5%, Mn 1.2%-1.4%, Cr 8%-10%, Mo 0.4%-0.6%, Ni 0.5%-0.7%, V 0.6%-0.8%, Ti 0.9%-1.1%, Si 0.2%-0.4%, and the balance is Fe and unavoidable impurities, wherein (C+V+Ti):Cr=0.19-0.3:1; The method for preparing the special steel precision bar comprises the following steps: S1, mixing the raw materials according to the component ratio, smelting and casting to obtain an ingot; S2, the ingot is homogenized and preheated and then forged to obtain a forged rod; S3, the forged rod is subjected to solution treatment, quenching and aging treatment to obtain a special steel precision rod; In step S2, the homogenization treatment is performed twice, the temperature of the first homogenization treatment is 1000-1150°C, the temperature of the second homogenization treatment is 1200-1250°C, the holding time of the first homogenization treatment is 8-10 hours, and the holding time of the second homogenization treatment is 5-7 hours.

2. The method for preparing a special steel precision bar according to claim 1, characterized in that: In step S1, the vacuum degree of the smelting is 1-1.2 Pa, and the temperature of the casting is 1500-1600°C.

3. The method for preparing a special steel precision bar according to claim 1, characterized in that: In step S2, the preheating temperature is 1100-1150°C for 3-5 hours; the forging hammering frequency is 100 times / minute.

4. The method for preparing a special steel precision bar according to claim 1, characterized in that: In step S3, the temperature of the solid solution is 1000-1050° C., and the time is 2-3 hours.

5. The method for preparing a special steel precision bar according to claim 1, characterized in that: In step S3, the quenching medium is water, and the temperature of the medium is 25-35°C.

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