Alloy tool steel for internal hexagonal wrench and preparation method of alloy tool steel

Abstract

The invention discloses alloy tool steel for an internal hexagonal wrench and a preparation method of the alloy tool steel, and belongs to the field of alloy tool steel. The alloy tool steel comprises the following chemical components in percentage by weight: 0.66%-0.70% of [C], 0.95%-1.15% of [Si], 0.55%-0.75% of [Mn], 0.85%-0.95% of [Cr], 0.11%-0.18% of [Ni], 0.12%-0.20% of [V], 0.010%-0.025% of [Al], less than or equal to 0.025% of [P], less than or equal to 0.020% of [S] and the balance of Fe and inevitable impurities. The smelting method comprises the procedures of converter smelting, LF refining, RH vacuum treatment, small square billet continuous casting, casting billet finishing, casting billet heating, wire rod rolling and wire rod controlled cooling, the produced steel is stable in component, the hot-rolled wire rod decarburization control level is high, and various performance requirements of users are met.

Description

Technical Field

[0001] The present invention belongs to the field of alloy tool steels, and particularly relates to an alloy tool steel for hexagon socket wrenches and a preparation method thereof. Background Art

[0002] At present, common steel grades used for making hexagon socket wrenches include 40Cr, SAE6145, SAE6150, 60CrV, SUP11, etc., and a relatively common specification is S6mm. Among them, the hardness of the S6mm hexagon socket wrench made of conventional steel grades such as SAE6150, 60CrV, and SUP11 according to the national standard "GB / T5356 Hexagon Socket Wrenches" is 52HRC - 56HRC, and the minimum test torque is 52N.m. The hardness of the S6mm hexagon socket wrench produced with the high-grade steel grade S2 is 58 - 60HRC, and the minimum test torque is about 74N.m. However, since S2 contains 0.4 - 0.5% of the precious alloy Mo, the cost is relatively high.

[0003] In practical applications, with the continuous improvement of the strength of hexagon socket screws, the hexagon socket wrenches produced according to the national standard GB / T5356 have problems of insufficient hardness and torque during the process of tightening or loosening hexagon socket screws. However, using S2 hexagon socket wrenches has a relatively high cost. Therefore, it is necessary to develop a new low-cost alloy tool steel with performance between conventional steel grades and the high-grade steel grade S2. Summary of the Invention

[0004] Aiming at the problems of insufficient hardness and poor torque of the hexagon socket wrenches made of existing common steel grades during the process of tightening or loosening high-strength hexagon socket screws, the present invention provides an alloy tool steel for hexagon socket wrenches and a preparation method thereof through composition design, process flow, and control of key parameters, which can reduce the production cost of steel, ensure stable steel composition, high decarburization control level of hot-rolled wire rods, and the hardness and torque of the processed products reach or even exceed the performance level of "GB / T5356 Hexagon Socket Wrenches".

[0005] The present invention provides an alloy tool steel, and its chemical composition is as follows by weight percentage: [C] 0.66% - 0.70%, [Si] 0.95% - 1.15%, [Mn] 0.55% - 0.75%, [Cr] 0.85% - 0.95%, [Ni] 0.11% - 0.18%, [V] 0.12% - 0.20%, [Al] 0.010% - 0.025%, [P] ≤ 0.025%, [S] ≤ 0.020%, and the rest is Fe and inevitable impurities.

[0006] Preferably, its chemical composition by weight percentage is: [C] 0.66% - 0.68%, [Si] 0.95% - 1.05%, [Mn] 0.60% - 0.70%, [Cr] 0.85% - 0.95%, [Ni] 0.11% - 0.15%, [V] 0.15% - 0.20%, [Al] 0.015% - 0.025%, [P] ≤ 0.015%, [S] ≤ 0.010%, and the rest is Fe and inevitable impurities.

[0007] More preferably, its chemical composition by weight percentage is: [C] 0.67% - 0.68%, [Si] 1.02% - 1.05%, [Mn] 0.64% - 0.65%, [Cr] 0.90% - 0.95%, [Ni] 0.12% - 0.13%, [V] 0.17% - 0.18%, [Al] 0.015% - 0.025%, [P] ≤ 0.015%, [S] ≤ 0.010%, and the rest is Fe and inevitable impurities.

[0008] The hardness of the hex key wrench processed from the steel type provided by the present invention is 56HRC - 58HRC, the test torque is not less than 65 N·m, and its performance is between that of conventional steel types and high - grade steel type S2. Compared with steel type S2, since S2 contains 0.4 - 0.5% of precious alloy Mo, its cost is relatively high; the steel type of the present invention has a relatively low cost.

[0009] In view of the high - hardness and high - torque requirements of the alloy tool steel for hex key wrenches, and comprehensively considering the cost of the steel type, the reasons for its composition design are as follows: Carbon is a key element affecting the strength and hardness of steel. When the carbon content is low, the hardness of the steel is relatively low. In the present invention, carbon forms cementite (F C) or other alloy carbides (such as VC, C etc.) with iron, significantly improving the hardness and strength of the steel. Preferably, the content of [C] in the present invention is controlled between 0.67% and 0.68%.

[0010] The solubility of silicon in α - Fe is as high as 15%. By distorting the crystal lattice, it greatly improves the strength of ferrite (each 1% Si increases the yield strength by about 80 - 100 MPa), significantly improving the elastic limit and strength of the steel; Si strongly inhibits the formation of cementite (F C), delays the precipitation and aggregation of carbides during tempering (improving the tempering resistance), makes the carbides refined and evenly distributed, and maintains good toughness; when combined with chromium, etc., silicon can improve antioxidant, corrosion - resistant, heat - resistant and other properties; when the content of Si is high, the risk of decarburization of hot - rolled wire rods is large, and when the content of Si is low, the strength and hardness are insufficient. Therefore, preferably, the content of [Si] in the present invention is controlled between 1.02% and 1.05%.

[0011] Manganese can improve the hardenability and strength of steel, weaken and eliminate the adverse effects of sulfur. However, excessive Mn will affect the torsional properties of the material. In the present invention, the content of [Mn] is preferably controlled between 0.64% and 0.65%.

[0012] Chromium can significantly improve the hardenability of steel, inhibit the pearlite transformation, and form high-hard carbides in combination with carbon, etc. (Fe, Cr or C (hardness 1500 - 1800HV), thereby improving the strength and hardness of the material. In the present invention, it is preferably 0.85% - 1.0%. [Cr] 0.90% - 0.95%.

[0013] Nickel can improve the plasticity and toughness of steel, which is especially helpful for high-carbon steel. In the present invention, the content of [Ni] is preferably 0.12% - 0.13%.

[0014] Vanadium can refine the austenite grains and prevent the grains from growing prematurely; it can significantly improve the hardenability of steel, improve the strength and toughness, form composite high-hard carbides with carbon and chromium, and increase the hardness and wear resistance. In the present invention, the content of [V] is preferably 0.17% - 0.18%.

[0015] Aluminum As a key element for deoxidation, it has the function of refining grains and improving the impact toughness. However, when the content of aluminum is too high, it will have an adverse effect on the high-temperature strength and toughness of the material. In the present invention, the content of [Al] is preferably 0.015% - 0.025%.

[0016] Surface decarburization of alloy tool steel hot-rolled wire rods will have a fatal impact on the hardness of the material after quenching and tempering. Years of production practice have shown that the finishing method of the billet, the heating process, and the wire rod controlled cooling process all have an important impact on the wire rod. Therefore, for alloy tool steel wire rods used to make internal hexagonal wrenches, reasonable design is required from both the composition and process aspects to meet the requirements of high hardness and high torque of the product.

[0017] Furthermore, for the alloy tool steel for internal hexagonal wrenches of the present invention, the present invention also provides its preparation process, including converter smelting, LF refining, RH vacuum treatment, small billet continuous casting, billet finishing, billet heating, wire rod rolling, wire rod controlled cooling, etc. The specific operations are as follows: (1) Converter smelting The converter is charged according to the weight ratio of 80% hot metal and 20% scrap. Requirements for hot metal are: [Si]: 0.50% - 0.80%, [P] ≤ 0.10%, [S] ≤ 0.030%. The composition of harmful residual elements in raw materials shall be strictly controlled, and it is prohibited for harmful residual elements to exceed the standard. The temperature is 1300 - 1400°C. High-carbon tapping operation is adopted at the end of smelting. The tapped steel [C] is greater than 0.05%, the tapped steel [P] is less than 0.015%, the tapping temperature is greater than 1600°C, the tapping time is 4 - 6 minutes. The ladle shall be ensured clean, there shall be no slag on the ladle bottom, and it is prohibited to use a black ladle. New ladles and ladles after medium repair must be baked according to regulations before being put into use. When about 1 / 4 of the tapping is completed, deoxidizer, alloy, carburizer and slag materials are added respectively. Double-block operation is adopted at the end of tapping. After the tapping is completed, the molten steel is lifted to LF for refining.

[0018] (2)LF refining

[0019] Samples are taken before the molten steel enters the LF station. After the molten steel enters the station, argon is blown throughout the process. Adjust according to the tumbling situation of the molten steel, and adjust the argon stirring intensity in a timely manner. When adding carbon and alloy to adjust the composition, the argon stirring can be appropriately increased. After maintaining this stirring intensity for 1 - 2 minutes, the stirring flow rate is adjusted down. In the early stage of refining, Al pellets and silicon carbide are used for deoxidation and desulfurization. In the middle and late stages, silicon carbide is used to protect the slag, that is, a small amount of silicon carbide is evenly added to the slag surface to ensure that the slag surface is in a reducing atmosphere. In the middle stage, other alloy components are adjusted to the target value according to the LF inlet sample, and the temperature is adjusted in place. Control the production rhythm well. The normal LF refining time is 30 - 45 minutes.

[0020] (3)RH vacuum treatment

[0021] After the molten steel reaches the RH station, the ladle is lifted to the vacuum tank, and cyclic vacuum pumping starts. The lifting gas argon is controlled at 80 - 120 Nm 3 / h. After the vacuum degree is less than 120 Pa, keep the pressure for 15 - 20 minutes and then break the vacuum. Take a sample of the molten steel. According to the analysis result of the sample, the Al content is adjusted by feeding aluminum wire, and then 50 - 100 meters of calcium wire is fed for modification treatment. After soft blowing for 15 - 20 minutes, the molten steel is lifted to the continuous casting for casting.

[0022] (4)160 mm×160mm billet continuous casting

[0023] Before continuous casting starts, the tundish baking temperature is greater than 1100 °C. After the tundish stops baking, argon is flushed into it for 3 - 5 minutes. After casting starts, the molten steel surface in the tundish is protected throughout the process. For the first layer in contact with the molten steel during protected casting, an alkaline covering agent is used, and for the second layer, carbonized rice husk ash is used. There is no exposed molten steel on the tundish surface. The tundish is cast using an integral nozzle, and the casting superheat is controlled at 20 - 30 °C. The temperature of the first ladle is not greater than 1507 °C, the temperature of the second ladle is not greater than 1502 °C, and the temperature of the continuous casting ladle is not greater than 1497 °C. After each furnace of casting is completed, slag is left in the ladle. The temperature difference of the first cooling water return is controlled at 5 - 10 °C, and the secondary cooling water specific flow rate is 0.20 L / kg. The mold and final electromagnetic stirring are started. The mold electromagnetic stirring current is 280 - 300 A, and the frequency is 2.4 - 2.8 Hz; the final electromagnetic stirring current is 370 - 390 A, and the frequency is 5.2 - 5.8 HZ; soft reduction is applied at the solidification end. The small billets are slowly cooled in a pit. The temperature when entering the pit is greater than 500 °C, and they can only be taken out of the pit after the heat preservation time is greater than 48 hours.

[0024] (5)Billet finishing

[0025] The 160 mm×160mm billets are finished and then subjected to surface quality flaw detection.

[0026] (6) Billet heating

[0027] The 160 mm×160mm billets are heated at a low temperature in the high-speed wire rod heating furnace.

[0028] (7)Wire rod rolling

[0029] The billets are rolled into wire rods through rough rolling, medium rolling, pre-finishing rolling, and finishing rolling and then enter the coiler. The finishing rolling temperature is 880 °C - 920 °C, and the temperature when exiting the finishing mill is not greater than 1000 °C.

[0030] (8)Wire rod controlled cooling

[0031] Strictly control the wire rod spinning temperature. After spinning, controlled cooling is carried out, and finally, it is coiled, packed, and stored in the warehouse, etc.

[0032] Furthermore, in the step (5), the finishing method for the 160 mm×160mm billets is chamfering + magnetic particle flaw detection, and the chamfer width is 10 - 15 mm.

[0033] Furthermore, in the step (6), the first heating temperature is 700 - 800 °C, the second heating temperature is 920 - 990 °C, the soaking temperature is 1005 - 1055 °C, the heating time is 80 - 110 minutes, and the rolling start temperature is 900 - 950 °C.

[0034] Furthermore, in the step (8), the wire rod spinning temperature is controlled at 750 - 780 °C.

[0035] The present invention designs the alloy tool steel composition based on the ultimate product requirements, and also establishes a production process consisting of a converter - LF refining - RH vacuum treatment - billet continuous casting - billet finishing - billet heating - billet rolling - wire rod controlled cooling. The cross-section of the continuous-cast billet in the present invention is preferably 160 mm x 160 mm. Surface decarburization of the wire rod is effectively controlled through a rational billet finishing method, a suitable heating process, and strict control of the spinning temperature, ensuring that the surface hardness of the hexagonal wrench is not affected by decarburization.

[0036] The beneficial effects of the present invention are as follows: the hot rolled wire rod is shot blasted, spheroidized annealed, pickled and drawn into a fine wire. After that, various specifications of hexagonal wrenches are made according to GB / T5356-hexagonal wrench standard. The typical specification is S6mm. Take the 96mm hexagonal wrench as an example. The surface hardness is 56HRC-58HRC. Under the torque test conditions of 65N.M, the hexagonal wrench does not show any permanent deformation that affects its use. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is the microstructure diagram of the decarburized layer of the hot-rolled wire rod in Example 1.

[0038] Figure 2 This is the microstructure diagram of the decarburized layer (22.37 μm) of the hot-rolled wire rod in Example 2.

[0039] Figure 3 Microstructure diagram of the decarburized layer (24.25 μm) of the hot-rolled wire rod in Example 3.

[0040] Figure 4 This is the microstructure diagram of the decarburized layer (56.1 μm) of the hot-rolled wire rod of Comparative Example 11.

[0041] Figure 5 This is the microstructure diagram of the decarburized layer (66.87 μm) of the hot-rolled wire rod of Comparative Example 12.

[0042] Figure 6 This is the microstructure diagram of the decarburized layer (50.74 μm) of the hot-rolled wire rod of Comparative Example 13. DETAILED DESCRIPTION

[0043] The present invention is further described below in conjunction with a production example of an alloy tool steel for hexagonal wrenches and a preparation method thereof, wherein conditions not defined herein are conventional conditions.

[0044] Example 1

[0045] (1) Converter smelting

[0046] The converter is charged according to the weight ratio of 110 tons of hot metal and 28 tons of scrap steel. The hot metal has [Si] 0.62%, [P] 0.058%, [S] 0.025%, and the temperature is 1347°C. At the end of smelting, the tapped steel has [C] 0.10%, [P] 0.010%, the tapping temperature is 1628°C, and the tapping time is 5 min. The ladle must be ensured clean, without slagging at the bottom, and it is strictly prohibited to use a black ladle. New ladles and ladles after medium repair must be baked according to regulations before being put into use. 30 s after tapping, 60 kg of aluminum blocks are added respectively. After adding the aluminum blocks, 1520 kg of ferrosilicon, 600 kg of high-carbon ferromanganese, 3500 kg of high-carbon ferrochrome, 350 kg of ferrovanadium, 110 kg of nickel plates are added. Then 600 kg of carburizer is added, and finally 550 kg of lime and 320 kg of slag-making agent are added. At the end of tapping, a slide plate and a slag stopper are used for slag blocking. After the tapping is completed, the molten steel is lifted to LF for refining.

[0047] (2)LF refining

[0048] Before the molten steel enters the LF station for refining, samples are taken. After the molten steel enters the station, argon is blown throughout the process and adjusted according to the tumbling situation of the molten steel. Appropriately adjust the argon stirring intensity in a timely manner. When adding carbon and alloys to adjust the composition, the argon stirring can be appropriately increased. After maintaining this stirring intensity for 1 - 2 min, the stirring flow rate is then reduced. When the molten steel enters the refining station, 50 kg of Al pellets and 80 kg of silicon carbide are used for deoxidation and desulfurization. After smelting for 15 min, silicon carbide is used to maintain the slag, that is, a small amount of silicon carbide is evenly added to the slag surface to ensure a reducing atmosphere on the slag surface. According to the analysis results of the samples taken when entering the station, alloys are supplemented respectively, and the temperature is adjusted to 1580°C. The argon stirring intensity throughout the LF refining process is 72 L / min. Control the production rhythm well. The LF refining time is 30 - 45 minutes.

[0049] (3)RH vacuum treatment

[0050] After the molten steel reaches the RH station, the ladle is lifted to the vacuum chamber, and the circulation vacuum pumping starts. The lifting gas argon is controlled at 90 Nm 3 / h. After the vacuum degree reaches 67 Pa, it is kept under pressure for 20 min and then the pressure is released. 100 m of calcium wire is fed for modification treatment. After soft blowing for 20 min, the molten steel is lifted to the continuous casting for pouring.

[0051] (4)160 mm×160mm billet continuous casting

[0052] Before continuous casting starts, the tundish baking temperature is greater than 1100 °C. After the tundish stops baking, argon is flushed into it for 3 - 5 minutes. After casting starts, protective casting is carried out on the entire surface of the tundish molten steel level. The first layer in contact with the molten steel for protective casting uses an alkaline covering agent, and the second layer uses carbonized rice husk ash. There is no exposed molten steel on the tundish surface. The tundish is cast using an integral nozzle, and the casting superheat is controlled at 20 - 30 °C. The temperature of the first ladle is not greater than 1507 °C, the temperature of the second ladle is not greater than 1502 °C, and the temperature of the continuous casting ladle is not greater than 1497 °C. After each furnace of casting is completed, slag is left in the ladle. The temperature difference of the first cooling water return is controlled at 5 - 10 °C, the secondary cooling water specific flow rate is 0.20 L / kg, the mold and final electromagnetic stirring are started. The mold electromagnetic stirring current is 280 - 300 A, and the frequency is 2.4 - 2.8 Hz; the final electromagnetic stirring current is 370 - 390 A, and the frequency is 5.2 - 5.8 HZ; soft reduction is adopted at the solidification end. The small billet is slowly cooled in a pit. The temperature when entering the pit is greater than 500 °C, and it can only be taken out of the pit after the heat preservation time is greater than 48 hours.

[0053] (5)Billet finishing

[0054] The 160 mm×160 mm billets are chamfered, and the chamfer width is 10 - 15 mm, and then surface magnetic particle flaw detection is carried out.

[0055] (6)Billet reheating

[0056] The 160 mm×160 mm billets are reheated at low temperature in the high-speed wire rod reheating furnace. The first heating temperature is 780 °C, the second heating temperature is 960 °C, the soaking temperature is 1030 °C, the heating time is 100 minutes, and the rolling start temperature is 940 °C.

[0057] (7)Wire rod rolling

[0058] The billets are rolled into wire rods through rough rolling, medium rolling, pre-finishing rolling, and finishing rolling and enter the laying head. The finishing rolling temperature is 900 °C, and the temperature when leaving the finishing mill is 980 °C.

[0059] (8)Wire rod controlled cooling

[0060] Strictly control the laying head temperature of the wire rod. The laying head temperature of the wire rod is controlled at 770 °C. After laying head, controlled cooling is carried out, and finally it is coiled, packed, and stored in the warehouse, etc.

[0061] In Example 2 and Example 3, as well as Comparative Examples 1 - 10, the chemical composition of the alloy tool steel for internal hexagonal wrenches is adjusted. The specific chemical composition is shown in Table 1, and the smelting process is basically the same as that of Example 1.

[0062] Comparative Example 11

[0063] In this comparative example, the chemical composition of the alloy tool steel for internal hexagonal wrenches is the same as that of Example 1. In the smelting process, the chamfering process in step (6) of Example 1 is deleted, and other conditions are the same as those of Example 1.

[0064] Comparative Example 12

[0065] In this comparative example, the chemical composition of the alloy tool steel for the hexagon socket wrench is the same as that in Example 1. In the smelting process, the heating process in step (7) of Example 1 is adjusted as follows: the first heating temperature is 780°C, the second heating temperature is 1050°C, the soaking temperature is 1100°C, the heating time is 100 minutes, and the rolling start temperature is 1000°C; other conditions are the same as those in Example 1.

[0066] Comparative Example 13

[0067] In this comparative example, the chemical composition of the alloy tool steel for the hexagon socket wrench is the same as that in Example 1. In the smelting process, the wire laying temperature in step (9) of Example 1 is adjusted to 830°C, and other conditions are the same as those in Example 1.

[0068] The melting components of the examples and comparative examples of the present invention are shown in Table 1. For convenient comparison, the cast billets of the examples and comparative examples are all arranged to produce Ø8mm wire rods. After the wire rods are shot blasted, spheroidized annealed, pickled, and drawn into fine wires, the subsequent process is to manufacture hexagon socket wrenches according to the hexagon socket wrench standard of GB / T5356, taking the typical specification S6mm The 96mm hexagon socket wrench is taken as an example for comparative analysis, and the specific data are shown in Table 2.

[0069] Figures 1-6 They are respectively the microstructures of the decarburized layers of the hot-rolled wire rods of Examples 1 to 3 and Comparative Examples 11 to 13.

[0070] Table 1 Melting components of the examples and comparative examples (wt / %)

[0071] Table 2 Performance parameters of the examples and comparative examples

[0072] From the data in the above tables, it can be seen that the performance indicators of the examples fully meet the predetermined performance indicator requirements, that is, the surface hardness is 56HRC - 58HRC, and under the torque test condition of 65N·m, no permanent deformation affecting its use occurs in the hexagon socket wrench. However, the process of the comparative examples is somewhat inappropriate, resulting in a relatively deep decarburization of the hot-rolled wire rods, and some even have complete decarburization. During the production process of the fine wires, the surface decarburization of the wire rods cannot be completely eliminated, which will cause the surface hardness of the final product, that is, the hexagon socket wrench, to be low. Although it still meets the hexagon socket wrench standard of GB / T5326 during the torque test, it does not meet the performance expectation requirements of product development.

[0073] Unless otherwise specified, the raw materials and equipment used in the present invention are common raw materials and equipment in the art; the methods used in the present invention are conventional methods in the art unless otherwise specified. The above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification made to the above embodiments based on the technical essence of the present invention is included within the protection scope of the present invention.

Claims

1. An alloy tool steel, characterized in that, The chemical composition of the alloy tool steel is as follows by weight percentage: [C] 0.66% - 0.70%, [Si] 0.95% - 1.15%, [Mn] 0.55% - 0.75%, [Cr] 0.85% - 0.95%, [Ni] 0.11% - 0.18%, [V] 0.12% - 0.20%, [Al] 0.010% - 0.025%, [P] ≤ 0.025%, [S] ≤ 0.020%, and the balance is Fe and unavoidable impurities.

2. The alloy tool steel according to claim 1, characterized in that, The chemical composition of the alloy tool steel is as follows by weight percentage: [C] 0.66% - 0.68%, [Si] 0.95% - 1.05%, [Mn] 0.60% - 0.70%, [Cr] 0.85% - 0.95%, [Ni] 0.11% - 0.15%, [V] 0.15% - 0.20%, [Al] 0.015% - 0.025%, [P] ≤ 0.015%, [S] ≤ 0.010%, and the balance is Fe and unavoidable impurities.

3. The preparation method of the alloy tool steel according to claim 1 or 2, characterized in that, The preparation method includes converter smelting, LF refining, RH vacuum treatment, bloom continuous casting, bloom finishing, bloom heating, wire rod rolling, and wire rod controlled cooling processes; among them, in the converter smelting process: requirements for hot metal: [Si]: 0.50% - 0.80%, [P] ≤ 0.10%, [S] ≤ 0.030%; high-tap-carbon operation is adopted at the end of smelting, the [C] in tapped steel is greater than 0.05%, the [P] in tapped steel is less than 0.015%, the tapping temperature is greater than 1600 °C, and the tapping time is 4 - 6 min; deoxidizer, alloy, carburizer, and slag materials are respectively added starting at about 1 / 4 of the tapping time, double-block operation is adopted at the end of tapping, and the molten steel is lifted to LF for refining after the end of tapping.

4. The preparation method of the alloy tool steel according to claim 3, characterized in that, The RH vacuum treatment process: The lifting gas is controlled at 80 - 120 Nm 3 / h. After the vacuum degree is less than 120 Pa, keep the pressure for 15 - 20 minutes and then break the vacuum. Take a molten steel sample. According to the analysis results of the sample, adjust the Al content by feeding aluminum wire, and then feed 50 - 100 meters of calcium wire for modification treatment. After soft blowing for 15 - 20 minutes, lift the molten steel to continuous casting for casting.

5. The preparation method of the alloy tool steel according to claim 3, characterized in that, In the bloom continuous casting process: the tundish baking temperature is greater than 1100 °C before continuous casting starts, argon gas is flushed into the tundish for 3 - 5 min after the tundish stops baking, protective casting is carried out throughout the surface of the tundish molten steel level after starting casting, the casting superheat is controlled at 20 - 30 °C, the temperature of the first ladle is not greater than 1507 °C, the temperature of the second ladle is not greater than 1502 °C, the temperature of the continuous casting ladle is not greater than  1497 °C, and steel slag is left in the ladle after each furnace casting ends; the size of the bloom is 160 mm × 160 mm.

6. The preparation method of the alloy tool steel according to claim 3, characterized in that, The bloom finishing is carried out by chamfering and magnetic particle flaw detection in sequence.

7. The preparation method of the alloy tool steel according to claim 6, characterized in that, The width of the chamfer is 10 - 15 mm.

8. The preparation method of the alloy tool steel according to claim 3, characterized in that, In the bloom heating: low-temperature heating is carried out in a high-speed wire heating furnace, the first heating temperature is 700 - 800 °C, the second heating temperature is 920 - 990 °C, the soaking temperature is 1005 - 1055 °C, the heating time is 80 - 110 minutes, and the rolling start temperature is 900 - 950 °C.

9. The preparation method of the alloy tool steel according to claim 3, characterized in that, In the wire rod rolling process: the bloom is rolled into a wire rod through rough rolling, intermediate rolling, pre-finishing rolling, and finishing rolling and enters the laying head machine, the finishing rolling temperature is 880 °C - 920 °C, and the temperature leaving the finishing mill is not greater than 1000 °C; in the wire rod controlled cooling process: the laying head temperature of the wire rod is 750 - 780 °C.

10. Use of the alloy tool steel according to claim 1 or 2 in the machining and manufacturing of hexagon socket wrenches, characterized in that, The hardness of the internal hexagonal wrench is greater than or equal to 56 HRC, and the test torque is not less than 65 N·m.

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