Processing method of high-speed tool steel

Abstract

The invention provides a machining method of high-speed tool steel, and relates to the technical field of high-speed tool steel preparation.The machining method of the high-speed tool steel comprises the steps that a steel ingot is heated, and the heated steel ingot is forged through an upsetting and drawing treatment process; in the heating process, the temperature is increased to a first preset temperature in a sectional type temperature increasing mode, heat preservation is carried out for a first preset time, then the temperature is decreased to a second preset temperature, heat preservation is carried out for a second preset time, then the temperature is increased to a third preset temperature, and heat preservation is carried out for a third preset time. According to the machining method of the high-speed tool steel, optimization of the internal organization structure of the high-speed tool steel and elimination of internal stress of the high-speed tool steel are facilitated, the cooling procedure is set in the heating process to adjust the temperature gradient of a steel ingot and reduce thermal stress, heat preservation is conducted to ensure that the internal temperature of the steel ingot is uniform, and forging is conducted through the upsetting and drawing treatment process. And defects and cracks in the steel ingot can be eliminated, so that the required mechanical property and internal structure can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of high-speed tool steel preparation, and particularly relates to a processing method for high-speed tool steel. Background Art

[0002] High-Speed Steel (HSS) is a tool and die material containing about 25% of high-carbon and high-alloy elements such as W, Mo, Cr, V, Si, Al, Co, etc. It has characteristics such as high hardness, high wear resistance, high hot hardness, and strict carbide requirements. Due to its excellent hot hardness, wear resistance, and anti-tempering softening ability, it is widely used in high-temperature and high-load scenarios such as cutting tools and dies. The performance of high-speed tool steel depends to a large extent on its microstructure, which is directly affected by the heat treatment process and forging technology during the preparation process.

[0003] Traditional methods for preparing high-speed tool steel usually involve simple heating and holding processes to achieve the expected microstructure transformation and performance optimization. However, this single heat treatment mode often makes it difficult to precisely control the temperature distribution and phase transformation process inside the ingot, easily leading to problems such as uneven microstructure, large differences in hardness distribution, and thermal stress concentration, thus affecting the mechanical properties and service life of the final product. Summary of the Invention

[0004] In view of this, the present invention aims to propose a processing method for high-speed tool steel to improve the performance of high-speed tool steel.

[0005] To achieve the above object, the technical solution of the present invention is realized as follows:

[0006] A processing method for high-speed tool steel, the method comprising:

[0007] Heating the ingot, and during the heating process, first heating it to a first preset temperature in a segmented heating manner, holding for a first preset time, then cooling to a second preset temperature, holding for a second preset time, and then heating to a third preset temperature, holding for a third preset time;

[0008] Forging the heated ingot using a upsetting and drawing process.

[0009] Further, the length of the ingot is between 1250 mm and 1350 mm, and the diameter of the ingot is between φ490 mm and φ510 mm.

[0010] Further, heating the steel ingot to the first preset temperature and maintaining the temperature for the first preset time includes: heating the steel ingot to a temperature between 800°C and 900°C and maintaining the temperature for a time between 2h and 3h, and then heating it to the first preset temperature and maintaining the temperature for the first preset time; wherein, the first preset temperature is between 1180°C and 1200°C; the first preset time is between 6h and 8h.

[0011] Further, the second preset temperature is between 840°C and 860°C, and the second preset time is between 1.5h and 2h; and / or, the third preset temperature is between 1120°C and 1130°C, and the third preset time is between 5h and 6h.

[0012] Further, the upsetting and drawing process adopts an upsetting and drawing process of two-upsetting and two-drawing.

[0013] Further, the upsetting and drawing process of two-upsetting and two-drawing includes: during the first upsetting and drawing process, the first upsetting length is 35% - 45% of the total length of the steel ingot, and then it is laid down and drawn to a length between 950mm and 1050mm; during the second upsetting and drawing process, the second upsetting length is 25% - 35% of the total length of the steel ingot, and then it is drawn to the preset length.

[0014] Further, tempering is carried out before the second upsetting and drawing process, the tempering temperature is between 1120°C and 1130°C, and the holding time is between 1.5h and 2h.

[0015] Further, during the second upsetting and drawing process, during the drawing process, it is flattened in two directions that are mutually perpendicular by 90°, and the flattening size should reach a width-to-thickness ratio between 2.0 and 2.2.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] In the processing method of high-speed tool steel of the present invention, a segmented heating method is adopted during the heating process before forging, and multiple heat preservation stages are set. This heating method helps to accurately control the temperature and time of the steel ingot, thereby optimizing its internal organizational structure. Heating to the first preset temperature and maintaining the temperature, this stage is to preheat the steel ingot, eliminate its internal stress, and prepare for the subsequent heating process. Cooling to the second preset temperature and maintaining the temperature, wherein the cooling process is to adjust the temperature gradient of the steel ingot, especially the temperature of the core of the steel ingot, which can preferably reduce the thermal stress of the core of the steel ingot, and the heat preservation is to ensure the uniform temperature inside the steel ingot. Heating to the third preset temperature and maintaining the temperature is to make the steel ingot reach the austenitizing temperature range and the ideal deformation temperature range, so as to obtain the required organizational structure during the subsequent forging process.

[0018] During the upsetting and drawing process, through upsetting, a billet with a sufficiently large diameter can be obtained, increasing the forging ratio, which helps to eliminate internal defects and cracks in the ingot and break down carbides to the greatest extent. The drawing process elongates the ingot axially under compressive stress, thereby changing its shape and size.

[0019] The length of the ingot is limited to be between 1250 mm and 1350 mm, and the diameter of the ingot is between φ490 mm and φ510 mm to ensure uniform heating. Larger ingot sizes may result in non-uniform temperature distribution during the heating process, especially in the central part of the ingot, which is not conducive to obtaining uniform mechanical properties. Also, the appropriate size of the ingot ensures an appropriate height-to-diameter ratio (2.5 - 2.7) during subsequent upsetting, which can better prevent the ingot from bending during upsetting. Therefore, designing an appropriate ingot size is beneficial to ensuring that the temperature inside and outside the ingot can reach the required level and facilitating the subsequent upsetting production of the ingot.

[0020] If the volume of the ingot is large, it takes longer to heat it to the required temperature, and the energy consumption will also increase accordingly. Moreover, larger ingot sizes require forging equipment with a larger tonnage to meet the pressure requirements during the forging process, and it may even be more difficult to obtain uniform mechanical properties during the forging and heat treatment processes. The size of the ingot also affects its internal microstructure. If the ingot size is too large, internal defects such as cracks and inclusions are more likely to occur during the cooling process.

[0021] In addition, during the segmented heating process, in the first stage, the temperature is raised to the range between 800 °C and 900 °C to preheat the ingot, eliminate internal stress, and prepare for the subsequent heating process. Limiting the holding time is to ensure uniform temperature inside the ingot and eliminate the thermal stress generated during the preheating process and the phase transformation process.

[0022] In the second stage, the temperature is raised to the range between 1180 °C and 1200 °C. The purpose is to make the ingot reach the austenitizing temperature range so as to obtain the required microstructure during the subsequent forging process. During the austenitizing process, the holding time should be long enough to ensure full transformation of the internal structure of the ingot.

[0023] After the segmented heating is completed, the temperature is lowered to the second preset temperature. This is a very crucial process. The temperature range is limited to between 840 °C and 860 °C, and the holding time is limited to between 1.5 h and 2 h. The purpose is to adjust the temperature distribution in the core of the ingot so that both the core temperature and the surface temperature are in the plastic deformation range before forging, in order to prepare for the subsequent upsetting and drawing treatment process.

[0024] Then, the temperature is raised to the third preset temperature, and the temperature range is limited between 1120°C and 1130°C. Since the heat is transferred from the outside to the inside during the heating process, the temperature of the core of the ingot rises more slowly than the surface temperature. During this heating process, the surface temperature is mainly controlled. Due to the extremely strict temperature requirements during forging, too high core temperature is prone to cracking defects during forging. Therefore, this heating step is coordinated with the previous cooling step to make the core temperature and the surface temperature uniform, which can effectively prevent core cracking defects during forging, thus facilitating the improvement of the quality of the ingot during forging.

[0025] The upsetting and drawing process of two-upsetting and two-drawing is an effective forging method suitable for the forging of high-speed tool steel, aiming to improve the internal structure and mechanical properties of the steel through multiple upsetting and drawing.

[0026] For the first upsetting, the total length of the ingot after upsetting is limited to 35% - 45%. The purpose is to increase the cross-sectional area of the ingot by applying compressive stress, eliminate possible internal pores, cracks and other defects, and improve its internal structure and carbide distribution.

[0027] On the basis of the first upsetting, the length after drawing is limited between 950 mm and 1050 mm. Through the drawing process, the ingot is elongated along the axial direction, further improving its internal structure and mechanical properties, and preparing for the subsequent upsetting and drawing process.

[0028] The ingot after the first drawing is subjected to the second upsetting. After upsetting again, the target length is limited to 25% - 35% of the total length of the ingot, which can further eliminate internal defects, refine grains, and provide a suitable shape and size for the final drawing process.

[0029] On the basis of the second upsetting, the final drawing length is limited to obtain the high-speed tool steel ingot material with the required shape and size, while ensuring that its internal structure and mechanical properties meet the requirements.

[0030] During the upsetting and drawing process of high-speed tool steel, tempering is a key heat treatment process. It can eliminate forging stress, improve the stability and machining performance of the ingot, refine grains, thereby improving its mechanical properties and fatigue resistance. Through tempering treatment, it can also make it more in line with the requirements of subsequent processing and use, achieving the purpose of adjusting the mechanical properties such as hardness and toughness of the ingot. When tempering between two upsetting and drawing processes, the tempering temperature is limited between 1120°C and 1130°C, aiming to eliminate the stress generated during forging and avoid excessive softening of the ingot. And the holding time is limited between 1.5 h and 2 h, which is conducive to the effective adjustment of the internal structure and stress state of the ingot.

[0031] During the second forging extension process, the ingot will be flattened twice, and the directions of the two flattenings should be perpendicular to each other (90°). After the first flattening, the width and thickness of the ingot will change. Subsequently, the second flattening is carried out in a direction perpendicular to the first one to further adjust its shape and size.

[0032] It is specified that the flattened ingot should reach a certain width-to-thickness ratio, that is, the ratio of width to thickness is limited between 2.0 and 2.2. The main purpose is to further improve its internal structure and mechanical properties by changing the shape of the ingot. By flattening in two perpendicular directions, the stress and structure inside the ingot can be more evenly distributed, thus improving the overall performance of the ingot.

[0033] Reaching a certain width-to-thickness ratio is also helpful for the stability and reliability during subsequent processing and use. For example, in machining, an ingot with an appropriate width-to-thickness ratio can more easily obtain the required shape and dimensional accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0035] Figure 1 It is a photograph of the carbide non-uniformity of Ingot No. 1 according to the embodiment of the present invention;

[0036] Figure 2 It is a photograph of the carbide non-uniformity of Ingot No. 2 according to the embodiment of the present invention;

[0037] Figure 3 It is a photograph of the carbide non-uniformity of Ingot No. 3 according to the embodiment of the present invention;

[0038] Figure 4 It is a photograph of the carbide non-uniformity of Ingot No. 4 according to the embodiment of the present invention;

[0039] Figure 5 It is a photograph of the carbide non-uniformity of Ingot No. 5 according to the embodiment of the present invention;

[0040] Figure 6 It is a photograph of the maximum carbide particle size of Ingot No. 1 according to the embodiment of the present invention;

[0041] Figure 7 It is a photograph of the maximum carbide particle size of Ingot No. 2 according to the embodiment of the present invention;

[0042] Figure 8 It is a photograph of the maximum carbide particle size of Ingot No. 3 according to the embodiment of the present invention;

[0043] Figure 9A photograph of the maximum carbide particle size of the No. 4 ingot according to the embodiments of the present invention;

[0044] Figure 10 A photograph of the maximum carbide particle size of the No. 5 ingot according to the embodiments of the present invention. Detailed implementation manners

[0045] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments may be combined with each other.

[0046] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0047] Although the processing methods of traditional high-speed tool steels meet the requirements of industrial applications to a certain extent, in the context of pursuing higher performance, more stable quality, and lower-cost production, in order to improve the performance of high-speed tool steels, in recent years, researchers have begun to explore more complex and refined heat treatment processes.

[0048] Among them, the segmented heating technique, as an innovative heat treatment strategy, can more effectively control the phase transformation kinetics inside the ingot by performing heat preservation treatments for different times in different temperature ranges, promote the uniform precipitation and refinement of carbides, thereby optimizing the microstructure of the steel. In addition, the segmented heating also helps to reduce thermal stress, avoid cracks in the ingot during the heating process, and improve the overall quality of the material.

[0049] In terms of forging, the upsetting and drawing process has become an important link in the preparation of high-speed tool steels because it can significantly improve the density and uniformity of the material. Through the upsetting and drawing process, the grain size can be further refined, the strength and toughness of the material can be improved, and it also helps to eliminate internal defects generated during the heat treatment process, such as pores, inclusions, etc.

[0050] This embodiment relates to a processing method of high-speed tool steel, which combines the segmented heating heat treatment with the upsetting and drawing forging process, aiming to precisely control heating, heat preservation, cooling, reheating, and subsequent forging treatments to achieve fine control of the microstructure of high-speed tool steel, thereby improving the comprehensive mechanical properties and service performance of high-speed tool steel.

[0051] The processing method of the high-speed tool steel in this embodiment mainly includes step S101 and step S102.

[0052] Step S101: Heat the ingot. During the heating process, first use the segmented heating method to heat to the first preset temperature and hold for the first preset time, then cool to the second preset temperature and hold for the second preset time, and then heat to the third preset temperature and hold for the third preset time.

[0053] Step S102, forging the heated ingot by using the upsetting and drawing process.

[0054] As a preferred embodiment, in step S101, the length of the ingot is between 1250 mm and 1350 mm, such as 1250 mm, 1270 mm, 1300 mm, 1325 mm, 1350 mm, etc., and the diameter of the ingot is between φ490 mm and φ510 mm, such as φ490 mm, φ500 mm, φ510 mm, etc.

[0055] As a preferred embodiment, in step S101, heating the ingot to a temperature between 800 °C and 900 °C, such as 800 °C, 8250 °C, 850 °C, 880 °C, 900 °C, etc., and keeping it at this temperature for a time between 2 h and 3 h, such as 2 h, 2.5 h, 3 h, etc., and then heating it to the first preset temperature, and the holding time is the first preset time.

[0056] In a preferred embodiment, the first preset temperature is between 1180 °C and 1200 °C, such as 1180 °C, 1190 °C, 1200 °C, etc., and the first preset time is between 6 h and 8 h, such as 6 h, 7 h, 8 h, etc.

[0057] As a preferred embodiment, in step S101, the second preset temperature is between 840 °C and 860 °C, such as 840 °C, 845 °C, 850 °C, 855 °C, 860 °C, etc., and the second preset time is between 1.5 h and 2 h, such as 1.5 h, 1.6 h, 1.75 h, 1.8 h, 2 h, etc.

[0058] As a preferred embodiment, in step S101, the third preset temperature is between 1120 °C and 1130 °C, such as 1120 °C, 1122 °C, 1125 °C, 1128 °C, 1130 °C, etc., and the third preset time is between 5 h and 6 h, such as 5 h, 5.2 h, 5.5 h, 5.8 h, 6 h, etc.

[0059] As a preferred embodiment, in step S102, the upsetting and drawing process adopts the two-upsetting and two-drawing upsetting and drawing process.

[0060] As a preferred embodiment, the two-upsetting and two-drawing upsetting and drawing process includes: in the first upsetting and drawing process, the first upsetting length is 35% - 45% of the total length of the ingot, such as 35%, 40%, 45%, etc., and then it is laid down and drawn to a length between 950 mm and 1050 mm, such as 950 mm, 970 mm, 1000 mm, 1020 mm, 1050 mm, etc.

[0061] During the second upsetting and drawing process, the length of the second upsetting is 25% - 35% of the total length of the ingot, such as 25%, 30%, 35%, etc., and then it is drawn to a preset length. Taking the specification φ320 after blooming as an example, the length after drawing, that is, the preset length, is between 2600 mm and 3400 mm, such as 2600 mm, 2800 mm, 3000 mm, 3200 mm, 3400 mm, etc.

[0062] As a preferred embodiment, tempering is carried out before the second upsetting and drawing process. The tempering temperature is between 1120 °C and 1130 °C, such as 1120 °C, 1122 °C, 1125 °C, 1128 °C, 1130 °C, etc., and the holding time is between 1.5 h and 2 h, such as 1.5 h, 1.6 h, 1.7 h, 1.9 h, 2 h, etc.

[0063] As a preferred embodiment, during the second upsetting and drawing process, the drawing process is flattened in two directions that are perpendicular to each other by 90°. The flattened size should reach a width-to-thickness ratio between 2.0 and 2.2.

[0064] The processing method of the high-speed tool steel in this embodiment, by setting a reasonable heating process and forging process, has few defects and cracks inside the prepared ingot and has excellent mechanical properties.

[0065] Next, the processing method of the high-speed tool steel in this embodiment will be described in detail with reference to specific embodiments.

[0066] Take 5 ingots, numbered 1 to 5, with a length dimension of 1250 mm and a diameter of φ500 mm.

[0067] Ingot No. 1:

[0068] Heat Ingot No. 1 to a temperature of 800 °C, hold for 2.5 h, then raise the temperature to 1200 °C, hold for 7 h, then lower the temperature to 860 °C, hold for 1.5 h, and continue to raise the temperature to 1120 °C, hold for 5.5 h.

[0069] The length of the first upsetting is 45% of the total length of the ingot, draw it to a length of 950 mm, temper at a temperature of 1120 °C, hold for 1.5 h, and then the length of the second upsetting is 35% of the total length of the ingot, draw it to a length of 950 mm.

[0070] Ingot No. 2:

[0071] Heat Ingot No. 2 to a temperature of 800 °C, hold for 2.5 h, then raise the temperature to 950 °C, hold for 7 h, and continue to raise the temperature to 1120 °C, hold for 1.5 h.

[0072] The length of the first upsetting is 45% of the total length of the ingot, which is drawn out to a length of 950 mm, tempered at a temperature of 1120 °C for 1.5 h, and then the length of the second upsetting is 35% of the total length of the ingot, which is drawn out to a length of 950 mm.

[0073] Ingot No. 3:

[0074] Heat Ingot No. 3 to a temperature of 800 °C and hold for 2.5 h, then raise the temperature to 1120 °C and hold for 5.5 h.

[0075] The length of the first upsetting is 45% of the total length of the ingot, which is drawn out to a length of 950 mm, tempered at a temperature of 1120 °C for 1.5 h, and then the length of the second upsetting is 35% of the total length of the ingot, which is drawn out to a length of 950 mm.

[0076] Ingot No. 4:

[0077] Heat Ingot No. 1 to a temperature of 1200 °C and hold for 2.5 h, then cool down to 860 °C and hold for 1.5 h, and continue to raise the temperature to 1120 °C and hold for 5.5 h.

[0078] The length of the first upsetting is 45% of the total length of the ingot, which is drawn out to a length of 950 mm, tempered at a temperature of 1120 °C for 1.5 h, and then the length of the second upsetting is 35% of the total length of the ingot, which is drawn out to a length of 950 mm.

[0079] Ingot No. 5:

[0080] Heat Ingot No. 1 to a temperature of 800 °C and hold for 2.5 h, then raise the temperature to 1200 °C and hold for 7 h, then cool down to 860 °C and hold for 1.5 h, and continue to raise the temperature to 1120 °C and hold for 5.5 h.

[0081] The length of the first upsetting is 45% of the total length of the ingot, which is drawn out to a length of 950 mm.

[0082] For the prepared Ingots No. 1 - 5, tests on carbide non-uniformity, maximum carbide particle size, heat treatment hardness and flexural strength are carried out, and the test results are shown in Table 1.

[0083] Table 1:

[0084]

[0085] Analysis of the data in Table 1 shows that for ingots No. 2 and No. 3, since there is no cooling step set during the heating process, the ultrasonic flaw detection results, carbide non-uniformity, maximum carbide particle size, heat treatment hardness, flexural strength, etc. of ingot No. 1 are all better than those of ingots No. 2 and No. 3. Although ingot No. 4 has a cooling step, it does not adopt a segmented heating method, and the performance of ingot No. 1 in all aspects is better than that of No. 4 steel.

[0086] Although ingot No. 5 adopts the heating process of this embodiment, due to the use of a single upsetting and drawing process and no tempering, the performance of ingot No. 1 in all aspects is also better than that of ingot No. 5.

[0087] 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 processing method of high-speed tool steel, characterized in that, The method includes: heating the ingot, and during the heating process, first raising the temperature to a first preset temperature in a segmented heating manner, holding for a first preset time, then lowering the temperature to a second preset temperature, holding for a second preset time, and then raising the temperature to a third preset temperature, holding for a third preset time; forging the heated ingot by using a upsetting and drawing process.

2. The processing method of high-speed tool steel according to claim 1, wherein: the length of the ingot is between 1250 mm and 1350 mm, and the diameter of the ingot is between φ490 mm and φ510 mm.

3. The processing method of high-speed tool steel according to claim 2, wherein, The manner of raising the temperature to the first preset temperature in a segmented heating manner and holding for the first preset time includes: heating the ingot to a temperature between 800 °C and 900 °C, holding for a time between 2 h and 3 h, and then raising the temperature to the first preset temperature, and the holding time is the first preset time; wherein, the first preset temperature is between 1180 °C and 1200 °C. The first preset time is between 6 h and 8 h.

4. The processing method of high-speed tool steel according to claim 3, wherein: the second preset temperature is between 840 °C and 860 °C, and the second preset time is between 1.5 h and 2 h; and / or, the third preset temperature is between 1120 °C and 1130 °C, and the third preset time is between 5 h and 6 h.

5. The processing method of high-speed tool steel according to any one of claims 2-4, wherein: the upsetting and drawing process adopts a two-upsetting and two-drawing upsetting and drawing process.

6. The processing method of high-speed tool steel according to claim 5, characterized in that, The two-upsetting and two-drawing upsetting and drawing process includes: during the first upsetting and drawing process, the first upsetting length is 35% - 45% of the total length of the ingot, and then it is laid down and drawn to a length between 950 mm and 1050 mm; during the second upsetting and drawing process, the second upsetting length is 25% - 35% of the total length of the ingot, and then it is drawn to a preset length.

7. The processing method of high-speed tool steel according to claim 6, wherein: tempering is carried out before the second upsetting and drawing process, the tempering temperature is between 1120 °C and 1130 °C, and the holding time is between 1.5 h and 2 h.

8. The processing method of high-speed tool steel according to claim 6, wherein: during the second upsetting and drawing process, during the drawing process, it is flattened in two directions that are mutually perpendicular by 90°, and the flattened size should reach a width-to-thickness ratio between 2.0 and 2.2.

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