Special steel precision bar and preparation method thereof

Abstract

The invention relates to the technical field of special steel, and provides a special steel precision bar and a preparation method thereof.The special steel precision bar is composed of, by weight, 0.4%-0.5% of C, 1.2%-1.4% of Mn, 8%-10% of Cr, 0.4%-0.6% of Mo, 0.5%-0.7% of Ni, 0.6%-0.8% of V, 0.9%-1.1% of Ti, 0.2%-0.4% of Si and the balance Fe and inevitable impurities, and the ratio of (C + V + Ti) to Cr is (0.19-0.3): 1. According to the technical scheme, the problem that the hardness of the special steel precision bar is insufficient in the related technology is solved.

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 special steel bars used to manufacture cutting tools and molds are not hard enough, the cutting tools will wear out quickly during the cutting process, resulting in reduced processing accuracy and 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 problem.

[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 other key properties into consideration. 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 the special steel precision bar in the related art.

[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 for preparing the special steel precision bar described above, comprising the following steps: S1. Mix the raw materials according to the component ratio, and after smelting and casting, obtain an ingot; S2. Subject the ingot to homogenization treatment and preheating, and then perform forging to obtain a forged bar; S3. Subject the forged bar to solution treatment, quenching and aging treatment to obtain the special steel precision bar.

[0010] As a further technical solution, in step S1, the vacuum degree of the smelting is 1 to 1.2 Pa, preferably 1 Pa, and the casting temperature is 1500 to 1600 °C, for example, it can be 1500 °C, 1510 °C, 1520 °C, 1530 °C, 1540 °C, 1550 °C, 1560 °C, 1570 °C, 1580 °C, 1590 °C, 1600 °C, preferably 1550 °C.

[0011] As a further technical solution, in step S2, the homogenization treatment is carried out in two times, and the temperature and holding time of the first homogenization treatment are different from those of the second homogenization treatment.

[0012] In the present invention, the homogenization treatment of the special steel precision bar is carried out in two times, and the temperature and time of the two times are different. Due to the differences in the diffusion rate and diffusion activation energy of different elements in the steel, through the homogenization treatment with two different parameters, the diffusion characteristics of different elements can be optimized; it can also make the grains 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, improving the strength of the special steel precision bar.

[0013] As a further technical solution, the temperature of the first homogenization treatment < the temperature of the second homogenization treatment, and the holding time of the first homogenization treatment > the holding time of the second homogenization treatment.

[0014] In the composition 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 specific proportions. On the basis of this composition ratio, during the homogenization treatment of the special steel precision bar, the first homogenization treatment at a relatively low temperature for a long time can enable 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. Subsequently, the second homogenization treatment at a higher temperature for a shorter time can accelerate the diffusion process of those elements (such as strong carbide-forming elements like titanium and vanadium) that did not diffuse sufficiently during the first treatment and require higher energy for effective diffusion. By such a way of first slow then fast, first low temperature then high temperature, the uniform distribution of various elements in the steel is realized, the composition segregation is reduced, the uniformity of the composition of the special steel precision bar is improved, and thus the strength of the special steel precision bar is enhanced.

[0015] In the present invention, during the homogenization treatment of the special steel precision bar, the first low-temperature and long-time treatment can, to a certain extent, change the original grain structure of the ingot, promote the grains to start to refine and tend to be stable; 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. The cooperation of these two treatments can enable the special steel precision bar to obtain a fine and uniform grain structure, further enhancing the strength of the special steel precision bar.

[0016] As a further technical solution, the temperature of the first homogenization treatment is 1000 - 1150 °C, for example, it can be 1000 °C, 1030 °C, 1050 °C, 1080 °C, 1100 °C, 1120 °C, 1150 °C, and preferably 1100 °C; the temperature of the second homogenization treatment is 1200 - 1250 °C, for example, it can be 1200 °C, 1210 °C, 1220 °C, 1230 °C, 1240 °C, 1250 °C, and preferably 1250 °C.

[0017] As a further technical solution, the holding time of the first homogenization treatment is 8 - 10 h, for example, it can be 8.0 h, 8.5 h, 9.0 h, 9.5 h, 10.0 h, and preferably 9.0 h; the holding time of the second homogenization treatment is 5 - 7 h, for example, it can be 5 h, 5.5 h, 6 h, 6.5 h, 7 h, and preferably 6 h.

[0018] As a further technical solution, in step S2, the temperature of the preheating is 1100~1150°C, for example, it can be 1100°C, 1110°C, 1120°C, 1130°C, 1140°C, 1150°C, preferably 1150°C, 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 per minute.

[0019] As a further technical solution, in step S3, the temperature of the solution treatment is 1000~1050°C, for example, it can be 1000°C, 1010°C, 1020°C, 1030°C, 1040°C, 1050°C, preferably 1020°C; 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, preferably 2.5h.

[0020] 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.

[0021] As a further technical solution, the diameter of the forged bar is 50~60mm, preferably 50mm.

[0022] As a further technical solution, the temperature of the aging treatment is 400~450°C, for example, it can be 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, preferably 450°C, and the time is 5~6h; for example, it can be 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.

[0023] The working principle and beneficial effects of the present invention are as follows: In the present invention, in the composition system of the special steel precision bar, carbon is an important element affecting the hardness of the steel. An appropriate carbon content can significantly improve the strength and hardness of the steel; vanadium, titanium, and chromium combine with carbon to form carbides with higher hardness, which are evenly distributed in the steel matrix and play a role of dispersion strengthening, effectively hindering the movement of dislocations, thereby greatly improving the hardness of the bar; by precisely controlling the ratio of (C+V+Ti) to Cr at 0.19~0.3:1, the best synergistic effect is achieved among the elements, and the quantity and distribution of the carbides formed by carbon and vanadium and titanium are more reasonable, and they cooperate with the carbides formed by chromium and the solution strengthening effect of chromium to further improve the hardness of the special steel precision bar. Detailed implementation manners

[0024] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present invention.

[0025] Embodiment 1 A special steel precision bar is composed of the following raw materials by 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 is Fe and inevitable impurities; A method for preparing a special steel precision bar includes the following steps: S1. Mix the raw materials according to the component ratio, smelt at a vacuum degree of 1 Pa, and after casting at 1550 °C, obtain an ingot; S2. After the ingot is subjected to homogenization treatment, heat it to 1150 °C, preheat for 4 h, and then perform forging. The hammering frequency of forging is 100 times / min to obtain a forged bar with a diameter of 50 mm; S3. After the forged bar is solution-treated at 1020 °C for 2.5 h, quench it with water as the quenching medium. The temperature of the medium is 30 °C, and perform aging treatment at 450 °C for 5 h to obtain the special steel precision bar; Among them, the homogenization treatment includes the following process: heat the ingot to 1250 °C, hold for 15 h, and cool to room temperature.

[0026] Embodiment 2 A special steel precision bar is composed of the following raw materials by 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 is Fe and inevitable impurities; A method for preparing a special steel precision bar includes the following steps: S1. Mix the raw materials according to the component ratio, smelt at a vacuum degree of 1 Pa, and after casting at 1550 °C, obtain an ingot; S2. After the ingot is subjected to homogenization treatment, heat it to 1150 °C, preheat for 4 h, and then perform forging. The hammering frequency of forging is 100 times / min to obtain a forged bar with a diameter of 50 mm; S3. After the forged bar is solution-treated at 1020 °C for 2.5 h, quench it with water as the quenching medium. The temperature of the medium is 30 °C, and perform aging treatment at 450 °C for 5 h to obtain the special steel precision bar; Among them, the homogenization treatment includes the following process: heating the ingot to 1250 °C, holding for 15 h, and then cooling to room temperature.

[0027] Example 3 A special steel precision bar is composed of the following raw materials by 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 is Fe and unavoidable impurities; A preparation method of a special steel precision bar includes the following steps: S1. Mix the raw materials according to the component ratio, smelt under a vacuum degree of 1 Pa, and after casting at 1550 °C, an ingot is obtained; S2. After the ingot is subjected to homogenization treatment, it is heated to 1150 °C, preheated for 4 h, and then forged. The hammering frequency of forging is 100 times / min, and a forged bar with a diameter of 50 mm is obtained; S3. After the forged bar is solution-treated at 1020 °C for 2.5 h, it is quenched with water as the quenching medium, the temperature of the medium is 30 °C, and aged at 450 °C for 5 h, thus obtaining the special steel precision bar; Among them, the homogenization treatment includes the following process: heating the ingot to 1250 °C, holding for 15 h, and then cooling to room temperature.

[0028] Example 4 Compared with Example 2, the difference in Example 4 is that a special steel precision bar is composed of the following raw materials by 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.

[0029] Example 5 Compared with Example 2, the difference in Example 5 is that a special steel precision bar is composed of the following raw materials by 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.

[0030] Example 6 Compared with Example 2, the difference in Example 6 is that the homogenization treatment process is different. In this example, the homogenization treatment includes the following process: heating the ingot to 1100 °C, holding for 15 h, and then cooling to room temperature.

[0031] Example 7 Compared with Example 2, Example 7 is different in that the homogenization process is different. In this example, the homogenization process includes the following steps: The ingot is first heated to 1100 °C and held for 9 h, then heated to 1250 °C and held for 6 h, and then cooled to room temperature.

[0032] Example 8 Compared with Example 2, Example 8 is different in that the homogenization process is different. In this example, the homogenization process includes the following steps: The ingot is first heated to 1100 °C and held for 6 h, then heated to 1250 °C and held for 9 h, and then cooled to room temperature.

[0033] Example 9 Compared with Example 2, Example 9 is different in that the homogenization process is different. In this example, the homogenization process includes the following steps: The ingot is first heated to 1100 °C and held for 7.5 h, then heated to 1250 °C and held for 7.5 h, and then cooled to room temperature.

[0034] Example 10 Compared with Example 2, Example 10 is different in that the homogenization process is different. In this example, the homogenization process includes the following steps: The ingot is first heated to 1250 °C and held for 6 h, then heated to 1100 °C and held for 9 h, and then cooled to room temperature.

[0035] Example 11 Compared with Example 2, Example 11 is different in that the homogenization process is different. In this example, the homogenization process includes the following steps: The ingot is first heated to 1250 °C and held for 9 h, then heated to 1100 °C and held for 6 h, and then cooled to room temperature.

[0036] Example 12 Compared with Example 2, Example 12 is different in that the homogenization process is different. In this example, the homogenization process includes the following steps: The ingot is first heated to 1250 °C and held for 7.5 h, then heated to 1100 °C and held for 7.5 h, and then cooled to room temperature.

[0037] Comparative Example 1 Compared with Example 2, Comparative Example 1 is different in that a special steel precision bar is composed of the following raw materials in weight percentages: 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.

[0038] Comparative Example 2 Compared with Example 2, the difference in Comparative Example 2 is that a special steel precision bar is composed of the following raw materials by 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 inevitable impurities.

[0039] Comparative Example 3 Compared with Example 2, the difference in Comparative Example 3 is that a special steel precision bar is composed of the following raw materials by 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 inevitable impurities.

[0040] Comparative Example 4 Compared with Example 2, the difference in Comparative Example 4 is that a special steel precision bar is composed of the following raw materials by 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 inevitable impurities.

[0041] Experimental Example 1 For the special steel precision bars prepared in Examples 1 to 5 and Comparative Examples 1 to 4, the Vickers hardness of the samples was tested according to the test method specified in GB / T 4340.1-2024 "Metallic materials - Vickers hardness test - Part 1: Test method".

[0042] The test results are shown in Table 1: Table 1 Performance test results of special steel precision bars prepared in Examples 1 to 5 and Comparative Examples 1 to 4

[0043] As can be seen from Table 1, when the content of each element meets the range requirements and when (C + V + Ti):Cr = 0.19 to 0.3:1, the hardness of the special steel precision bar can be improved.

[0044] Experimental Example 2 For the special steel precision bars prepared in Example 2 and Examples 6 to 12, the tensile strength of the samples was tested according to the test method specified in GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature".

[0045] The test results are shown in Table 2: Table 2 Performance test results of special steel precision bars prepared in Example 2 and Examples 6 to 12

[0046] As can be seen from Table 2, when the ingot is subjected to two homogenization treatments, and the temperature of the first homogenization treatment < the temperature of the second homogenization treatment, and the holding time of the first homogenization treatment > the holding time of the second homogenization treatment, the strength of the special steel precision bar can be improved.

[0047] The above are only the 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 principle of the present invention shall be included within the protection scope 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 inevitable impurities, wherein (C+V+Ti):Cr=0.19~0.3:

1.

2. A method for preparing a special steel precision bar, used for preparing the special steel precision bar according to claim 1, characterized in that: The following steps are involved: S1, mixing the raw materials according to the component ratio, smelting and casting to obtain an ingot; S2, the ingot is forged after being homogenized and preheated 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.

3. The method for preparing a special steel precision bar according to claim 2, 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.

4. The method for preparing a special steel precision bar according to claim 2, characterized in that: In step S2, the homogenization treatment is performed twice, and the temperature and the holding time of the first homogenization treatment are different from the temperature and the holding time of the second homogenization treatment.

5. The method for preparing a special steel precision bar according to claim 4, characterized in that: The temperature of the first homogenization treatment is less than the temperature of the second homogenization treatment, and the heat preservation time of the first homogenization treatment is greater than the heat preservation time of the second homogenization treatment.

6. The method for preparing a special steel precision bar according to claim 5, characterized in that: The temperature of the first homogenization treatment is 1000-1150°C, and the temperature of the second homogenization treatment is 1200-1250°C.

7. The method for preparing a special steel precision bar according to claim 5, characterized in that: The heat preservation time of the first homogenization treatment is 8 to 10 hours, and the heat preservation time of the second homogenization treatment is 5 to 7 hours.

8. The method for preparing a special steel precision bar according to claim 2, characterized in that: In step S2, the preheating temperature is 1100-1150°C for 3-5 hours; the hammering frequency of the forging is 100 times / minute.

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

10. The method for preparing a special steel precision bar according to claim 2, 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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