Steel wire rod for manufacturing alloy tools having high fatigue life and high impact resistance and use thereof

Abstract

The present invention relates to a steel wire rod for manufacturing alloy tools, which has a long fatigue life and high impact resistance, and its use. The chemical composition of the steel is, by weight, 0.83-0.92% [C], 2.30-2.60% [Si], 0.40-0.80% [Mn], 0.70-1.05% [Cr], 1.31-1.61% [Ni], 0.14-0.30% [V], 0.025-0.060% [Al], [P]≦0.025%, S≦0.020%, and the balance being Fe and unavoidable impurities. The steel wire rod for manufacturing alloy tools obtained by the present invention is suitable for manufacturing driver bits, screwdrivers, hex wrenches, and other products that require a long fatigue life and high impact resistance. It has a hardness of 60-62 HRC, a fatigue life of 30,000 cycles or more, and an impact resistance of 60 seconds or more.

Description

[Technical Field]

[0001] The present invention relates to the field of steel material production, and more particularly to a steel wire rod for manufacturing alloy tools having a long fatigue life and high impact resistance, and its use. [Background technology]

[0002] In modern industry, screw tightening systems are specialized machinery used for semi-automated and fully automated screw tightening, combining driver bits (such as screwdrivers and hex wrenches) with electric and pneumatic tools to form a complete tool. Among these, driver bits, bit bits, driver tools, and other tools are required to have high hardness, high torque, high impact resistance, and long fatigue life because they come into direct and close contact with the screws. They are also consumables that need to be replaced after a certain period of use.

[0003] Currently, the highest-grade screwdriver bit material commonly used in the industry is S2M, with a chemical composition of 0.66-0.72% C, 0.85-1.10% Si, 0.40-0.55% Mn, 0.15-0.30% Cr, 0.10-0.20% Ni, 0.38-0.45% Mo, and 0.15-0.25% V. Taking the widely used T25 x 57mm finished screwdriver bit as an example, after the standard hardening (first hardening the entire bit to martensite) and tempering process, the tool hardness is 58-60 HRC, but no data is available on fatigue life or impact resistance.

[0004] CN202310995781.1 discloses a high-strength, high-wear-resistant alloy tool steel and its smelting method, which has a chemical composition, by weight, of [C] 0.70%-0.76%, [Si] 1.40%-1.60%, [Mn] 0.50%-0.80%, [Cr] 1.00%-1.20%, [Ni] 0.20%-0.26%, [V] 0.14%-0.20%, [Al] 0.020%-0.040%, [P] ≤ 0.025%, [S] ≤ 0.020%, and the balance Fe and unavoidable impurities. This steel is based on 60Si2CrV, with an increased carbon content and some Ni added. It is essentially a spring steel design concept. Compared to S2M, it is a different steel system. The heat treatment method and final product performance are not disclosed, resulting in an incomplete invention and lack of comparability. CN202011060372.5 discloses a high-strength, tough alloy tool steel wire rod with a chemical composition of 0.60-0.90 wt.% C, 1.00-3.00 wt.% Si, 0.45-1.00 wt.% Mn, 0.45-1.00 wt.% Cr, and 0.20-0.60 wt.% Mo, as well as a method for manufacturing the same. The steel of this invention first undergoes a quenching and tempering process to convert the entire wire to martensite, after which it has a Rockwell hardness of 58-62 HRC and a twist angle per unit length of 10-15° / mm, and is believed to have excellent resistance to torsional fracture. However, the torsion angle per unit length describes high-toughness alloy tool steel wire rods, not the tools manufactured from them. In fact, the torsion (fracture) angle is closely related to the structural design of the tool. Furthermore, torsion fracture performance is related to torsional strength and impact resistance. A single torsion (fracture) angle cannot fully explain the issue, especially for automated machinery, where impact resistance is important. Generally, the invention fails to address the fatigue life and impact resistance of the material, making it difficult to compare. Furthermore, the steel's composition range is too broad, resulting in significant variations in performance between different component combinations, and some combinations may not achieve the performance described in the invention. Conventional alloy tool steel, S2M, contains approximately 0.4% Mo, which significantly improves hardenability and quench hardenability. However, the hot-rolled wire rod structure forms abnormal structures such as martensite, making it prone to brittle fracture and expensive.Most conventional alloy tool steels do not have the requirements for fatigue life and impact resistance, and even if they do have a fatigue life, it does not exceed 10,000 cycles, and impact resistance has not been a requirement until now.Long fatigue life and impact resistance are necessary to meet the requirements for no or reduced downtime of equipment in the Industry 4.0 era.

[0005] As industrial automation enters the new 4.0 era, there is a demand for further improvements in work efficiency, and screw tightening systems must operate continuously for long periods of time or minimize the number of stops. Furthermore, as the range of applications for high-strength screws continues to expand, there is a strong demand for improved service life for tools such as screwdriver bits. Therefore, qualitative improvements are required in performance aspects such as hardness, impact resistance, and fatigue life. Summary of the Invention

[0006] In response to the shortcomings of the prior art, the present invention aims to provide a steel wire rod for use in the manufacture of alloy tools, which has a long fatigue life and high impact resistance, and uses thereof. The steel wire rod for use in the manufacture of alloy tools, obtained through the composition design of the present invention, is subjected to a spheroidizing annealing process to manufacture tools such as driver bits, and then subjected to bainite isothermal quenching and tempering treatment. The finally tempered driver bits, drivers, hex wrenches, etc., meet the requirements for a long fatigue life and high impact resistance, having a hardness of 60-62 HRC, a fatigue life of 30,000 cycles or more in fatigue tests, and an impact resistance of 60 seconds or more.

[0007] In order to achieve the above object, the present invention uses the following technical means.

[0008] The present invention combines the process principles of bainite isothermal quenching and tempering to design a high-carbon, high-silicon, nickel-rich alloy tool steel with the following composition by weight: [C] 0.83%~0.92%, [Si] 2.30%~2.60%, [Mn] 0.40%~0.80%, [Cr] 0.70%~1.05%, [Ni] 1.31%~1.61%, [V] 0.14%~0.30%, [Al] 0.025%~0.060%, [P]≦0.025%, [S]≦0.020%, and the balance being Fe and unavoidable impurities.

[0009] Preferably, the chemical components are, in weight percentage, [C] 0.86% to 0.90%, [Si] 2.31% to 2.45%, [Mn] 0.40% to 0.60%, [Cr] 0.75% to 0.95%, [Ni] 1.31% to 1.41%, [V] 0.18% to 0.24%, [Al] 0.025 to 0.050%, [P] ≦ 0.025%, [S] ≦ 0.015%, with the balance being Fe and unavoidable impurities.

[0010] Products such as driver bits, screwdrivers, and hex wrenches made from the material obtained by the present invention have extremely strict requirements for final hardness, torque, twist angle, fatigue life, impact resistance, etc. Composition is an important factor that affects the final performance of the product, and when designing chemical compositions, certain performance is influenced not only by a single element but also by multiple elements at the same time, so it is necessary to consider the rational design of multiple elements depending on the product's application.

[0011] The reasons for the component design of the present invention are as follows.

[0012] [C] is the most effective element for improving the strength and hardness of steel, and has a significant solid solution strengthening effect. A low carbon content results in low steel hardness and poor wear resistance, but too much carbon can form large carbides. In the steel of the present invention, carbon also serves to lower the bainite transformation temperature (Bs). The bainite isothermal transformation is below the nose of the bainite transformation curve, resulting in a low Bs temperature and good performance. However, too much carbon makes nucleation of bainite difficult, lengthening the inoculation period and slowing the bainite transformation rate. Therefore, a low Bs temperature and a low bainite transformation rate are in conflict. Therefore, the carbon content must be appropriate, and in the present invention, the carbon content is preferably 0.86% to 0.90%.

[0013] [Si] can significantly improve the elastic limit, yield point, and strength of steel. When a certain amount of silicon is added to tempered steel, silicon combines with chromium, molybdenum, etc. to improve performance such as oxidation prevention, corrosion resistance, and heat resistance. Silicon also acts as a conventional deoxidizer, partially replacing aluminum for deoxidation. Silicon in the steel of the present invention can also suppress the formation of cementite during the cooling process and inhibit the decomposition of C in supercooled austenite. However, if the silicon content is too high, a hard oxide layer will form on the steel surface, reducing coating ability, and the strengthening effect of Si will become significant. If the silicon content is too high, the steel will become more brittle. Therefore, the silicon content in the present invention is preferably 2.31% to 2.45%.

[0014] [Mn] can improve the strength of steel, eliminate the adverse effects of sulfur, significantly improve the hardenability of steel, and improve the hot workability of steel. Mn is an austenite-forming element and can lower the cementite precipitation start temperature. Too high a Mn content is disadvantageous and may cause the formation of a banded structure. In the present invention, the Mn content is preferably 0.40% to 0.60%.

[0015] [Cr] is one of the basic elements of wear-resistant materials, and can significantly improve the strength, hardness and wear resistance of steel, as well as improve the oxidation resistance and corrosion resistance of steel. Alloy tool steel generally contains about 0.20% Cr, and since the present invention needs to improve wear resistance, the present invention preferably contains 0.75% to 0.95% Cr.

[0016] [Ni] expands the austenite phase region, forms an infinite solid solution, does not form carbides, improves the strength of steel, improves solid solution strengthening and hardenability, and can also improve the corrosion resistance of steel. Nickel mainly improves the plasticity and toughness of low-alloy steel. Since nickel is a scarce resource, in the present invention, the content is preferably 1.31% to 1.41%.

[0017] [V] refines the crystal grains of the structure, improves strength and toughness, forms carbides with carbon, and can improve hydrogen corrosion resistance under high temperature and pressure. Alloy tool steels generally contain about 0.20% V, and in the present invention, the V content is preferably 0.18% to 0.24%.

[0018] [Mo] significantly improves hardenability and hardenability, but can cause the hot-rolled wire rod to form abnormal structures such as martensite, making it prone to brittle fracture and expensive. Adding Mo to the present invention would result in a different steel system. In this invention, under the premise of high carbon, high Si, and high Ni, adding Mo would double the risk of brittle fracture in the hot-rolled wire rod and may prevent the structure from being manufactured normally. Therefore, Mo is not added to the present invention.

[0019] [Al] is an important deoxidizing element, refining crystal grains and improving impact toughness. Aluminum also has oxidation prevention and corrosion resistance, and when used in combination with chromium and silicon, it can significantly improve the high-temperature non-scaling properties and high-temperature corrosion resistance of steel. Furthermore, since Al does not dissolve in cementite and significantly delays its formation, in the steel of the present invention, aluminum not only increases the cementite formation temperature but also accelerates the formation of bainite. Therefore, the aluminum content must be appropriately controlled, and in the present invention, it is preferably 0.025% to 0.050%.

[0020] [P] and [S] are generally harmful elements in steel, but in the present invention, the contents of [P]≦0.025% and [S]≦0.015% are preferred.

[0021] For the steel wire rod for manufacturing alloy tools having a long fatigue life and high impact resistance, the present invention further provides a wire rod manufacturing process including converter smelting, LF refining, RH vacuum treatment, continuous bloom casting, high temperature diffusion and blooming, finishing of rolled billet, heating of billet, wire rod rolling, and controlled cooling of wire rod, and the specific steps are as follows:

[0022] (1) Converter smelting The converter is charged with 80% to 85% molten pig iron and 15% to 20% steel scrap by weight, and a high-carbon drawing operation is used at the end of the smelting process, with the tapping [C] exceeding 0.07% and the tapping [P] less than 0.015%, the tapping time being 4 to 6 minutes, the tapping temperature exceeding 1600°C, and from 30 seconds after tapping, aluminum cake, alloys (e.g., silicomanganese, ferrosilicon, ferrovanadium, high-carbon ferrochrome, nickel-iron), and general recarburizer balls are added. Lime and furnace additives are added to the tapping slag material, and tapping is completed using a double slag blocking operation using a slide plate and a slag blocking cone. The molten steel is then transported by crane to the LF for refining.

[0023] (2)LF refining Sampling is performed before the LF refining process. In the early stages of refining, calcium carbide, silicon carbide, or aluminum granules are used for deoxidation and desulfurization. Lime and fluorite (cryolite) are added in appropriate amounts depending on the slag fluidity. In the early stages of refining, aluminum wire is added in appropriate amounts depending on the Al content of the molten steel, with only one addition allowed to ensure the target aluminum content in the finished product. In the intermediate and later stages, silicon carbide is used for slag protection, i.e., small amounts of silicon carbide are uniformly added to the slag surface to ensure a reducing atmosphere. In the intermediate stages, other alloy elements are adjusted to target values ​​based on the LF process sample, controlling them accordingly and reducing compositional fluctuations, and the temperature is adjusted appropriately. The casting furnace temperature is set to 1559°C to 1599°C, and the continuous casting furnace temperature is set to 1529°C to 1569°C. Refining is performed throughout the refining process with stirring by small amounts of argon gas injected.

[0024] (3) RH vacuum treatment After the molten steel reaches the RH stage, the ladle is lifted into the vacuum vessel, and the vacuum circulation suction is started. The lifting gas is supplied at 80-120 Nm 3 / h, and after the vacuum level falls below 133 Pa, the pressure is maintained for 20 minutes before the vacuum is released, and 100 to 300 meters of calcium wire is added for modification treatment, and after 20 to 40 minutes of soft blowing, the molten steel is transferred by crane to the continuous casting process for casting. The temperature of the casting furnace is controlled at 1504°C to 1534°C, and the temperature of the continuous casting furnace is controlled at 1479°C to 1509°C.

[0025] (4) Continuous bloom casting Before starting continuous casting, the firing temperature of the tundish is set to over 1100°C. After stopping the firing of the tundish, argon gas is flowed inside for 3 to 5 minutes. After starting casting, the liquid surface of the tundish is protected throughout the entire casting process. The tundish is cast using an integrated casting nozzle, and the casting superheat is controlled to 20°C to 30°C. After casting in each furnace is completed, steelmaking slag is left in the ladle. The continuous casting drawing speed is controlled to 0.80 m / min, the return water temperature difference of the primary cooling water is controlled to 4°C to 6°C, the secondary cooling water flow rate is controlled to 0.20 L / kg, the crystallizer and terminal electromagnetic stirrer are operated, and the crystallizer's electric stirring parameters are set to 290 to 310 A, with a target of 300 A, and a frequency of 1.8 to 2.2 Hz, with a target of 2.0 Hz, and the terminal electromagnetic stirring parameters are set to 290 to 310 A, with a target of 300 A, and a frequency of 5.8 to 6.2 Hz, with a target of 6.0 Hz. The bloom is slowly cooled in a pit, and the temperature when it is placed in the pit is set to over 500°C. It can be removed from the pit after being kept at this temperature for at least 48 hours.

[0026] (5) Blowing and rolling production The 300mm x 325mm cast billets are subjected to high-temperature diffusion for a long time in a 51m long heating furnace, with the heating temperature set to 1220℃~1270℃. After the long-term high-temperature diffusion, they are rolled through 10 stands and then bloomed into 160mm x 160mm rolled billets. The collection temperature of the rolled billets is set to 400℃~500℃, and after rolling, they are stacked and cooled in a wind-protected manner.

[0027] (6) Finishing of rolled billets A 160mm x 160mm rolled billet is finished and peeled, with the peeling depth on one side set to 2mm, and surface flaw detection is performed.

[0028] (7) Heating of rolling billet A 156mm x 156mm rolling billet is heated in a high-speed wire heating furnace at a heating temperature of 1150°C to 1200°C for a heating time of 100 to 150 minutes, and at a rolling start temperature of 1050°C to 1100°C.

[0029] (8) Wire rod rolling The rolled billet is rolled into a wire rod through rough rolling, intermediate rolling, preliminary finish rolling, and finish rolling, and then sent to the discharge device. The rolling temperature of the finish rolling is 900°C to 950°C, and the temperature of the finish rolling mill is 970°C or higher.

[0030] (9) Cooling control of wire rod The wire is discharged at a temperature of 900 to 940°C. After discharge, the wire is cooled in a controlled manner, with rapid cooling in the first half and cooling in the cover in the second half. The temperature when entering the cover is 550 to 600°C, and the temperature when leaving the cover is less than 490°C.

[0031] (10) The wire is wound, packed, and stored in the warehouse.

[0032] The subsequent heat treatment steps of the wire are specifically as follows.

[0033] Furthermore, the wire rod of the present invention needs to be transformed into a hexagonal wire rod through spheroidizing annealing and pickling / drawing at a wire mill, and the annealing process is 765°C x 12 hours. The purpose of annealing is to facilitate the subsequent drawing and machining.

[0034] Furthermore, the wire rod of the present invention is modified into a hexagonal wire rod, which is then machined to produce tools such as driver bits, drivers, and hexagonal wrenches, and then subjected to bainite isothermal quenching and tempering treatment, where the austenitizing temperature is 900°C to 910°C, the heating time is 80 to 90 minutes, the salt bath quenching temperature is 300°C to 310°C (the quenching medium is salt), the isothermal time is 55 to 65 minutes, the tempering temperature is 280°C to 290°C, and the tempering time is 55 to 65 minutes.

[0035] The quenching temperature for bainite isothermal quenching is below the nose point of the bainite transformation curve. The lower the Bs point, the lower the nose point and the better the overall performance. To reduce Bs, the carbon content must be significantly increased. However, too much carbon leads to excessive cementite formation during quenching, which significantly impacts fatigue life and impact resistance. Therefore, the silicon content must be increased. Silicon inhibits the formation of cementite during cooling, forming lower bainite, which is suitable for high toughness. High nickel contributes to better toughness. Tools used for screwdrivers, drivers, and hex wrenches require tempering after bainite isothermal quenching. Tempering relieves residual stress in the steel and improves its toughness.

[0036] Compared with the prior art, the present invention has the following beneficial effects: By rationally designing the components, the Bs temperature of the material is lowered, and the material of the present invention is subjected to bainite isothermal quenching below the nose of the bainite transformation curve. After tempering, the driver bits, screwdrivers, and hex wrenches meet the requirements for high fatigue life and high impact resistance, i.e., they have a hardness of 60-62HRC, a fatigue life of more than 30,000 cycles, and an impact resistance of more than 60 seconds. [Brief explanation of the drawings]

[0037] [Figure 1] 1-1 shows the metal structure and the decarburized layer of Example 1, and FIG. 1-2 shows the metal structure. [Figure 2]The diagrams show the fracture location and appearance of a T25 x 57 mm finished driver bit in an impact resistance test, with Figure 2-1 showing fracture in the rod section and Figure 2-2 showing fracture in the head section. [Figure 3] This shows the full-function torque life tester and model number for T25 x 57 mm finished driver bits. [Figure 4] This shows the impact resistance test equipment for a finished driver bit of T25 x 57 mm. DETAILED DESCRIPTION OF THE INVENTION

[0038] The present invention will be described in more detail below in conjunction with examples of steel wire rods for manufacturing alloy tools having a long fatigue life and high impact resistance. Conditions not limited here are general conditions. The T25 x 57 mm finished driver bit is merely an example, and driver bits with other different head types and lengths have similar performance, all of which can achieve excellent hardness, fatigue life, and impact resistance.

[0039] Example 1 (1) Converter smelting The converter was charged with 102 tons of molten pig iron and 27 tons of scrap steel by weight, the molten pig iron [Si] was 0.65%, [P] was 0.060%, [S] was 0.022%, the temperature was 1348°C, the tapping temperature was 1629°C, the tapping time was 5 min, and 30 seconds after tapping, 120 kg of aluminum blocks were added. After adding the molten steel block, 3,400 kg of ferrosilicon, 660 kg of silicomanganese, and 1,756 kg of high-carbon ferrochrome are added, followed by 800 kg of recarburizer, and finally 550 kg of lime and 310 kg of chemical slag agent.At the end of tapping, slag blocking is performed using a slide plate and slag blocking cone, and after tapping is complete, the molten steel is transported by crane to the LF for refining.

[0040] (2)LF refining The temperature inside the LF furnace was set to 1503°C. Samples were taken before the refining process. During the refining process, 180 kg of calcium carbide was used for deoxidation and desulfurization. After 15 minutes of refining, silicon carbide was used to protect the slag. That is, a small amount of silicon carbide was uniformly added to the slag surface to ensure that the slag surface was in a reducing atmosphere. Based on the results of the sample analysis during the process, 692 kg of ferrosilicon, 161 kg of silicomanganese, 253 kg of high-carbon ferrochromium, 100 kg of ferrovanadium, and 300 kg of nickel plate were added, and the temperature was adjusted to 1571°C. The stirring intensity of argon gas was 70 L / min throughout the refining process.

[0041] (3) RH vacuum treatment After the molten steel reaches the RH stage, the ladle is lifted into the vacuum vessel, and the vacuum circulation suction is started. The lifting gas is supplied at 100 Nm 3 / h, and after the vacuum level falls below 80 Pa, the pressure is maintained for 20 minutes before the vacuum is released. 200 meters of calcium wire is added to carry out a modification treatment, and after 20 minutes of soft blowing, the molten steel is transferred by crane to the continuous casting process for casting.

[0042] (4) Continuous bloom casting Before continuous casting, the tundish firing temperature was set to over 1100°C. After casting began, the tundish surface was protected throughout the entire casting process. The tundish was cast using an integrated casting nozzle, the casting superheat was controlled at 20-30°C, and the initial temperature was set to 1475°C. After each casting, steelmaking slag was left in the ladle. The continuous casting withdrawal speed was controlled at 0.80 m / min, the primary cooling water return water temperature difference was controlled at 5.55°C, and the secondary cooling water flow rate was controlled at 0.20 L / kg. The crystallizer and terminal electromagnetic stirrer were operated. The crystallizer's electric stirring parameter current was set at 300 A with a target frequency of 2.0 Hz, and the terminal electromagnetic stirring parameter current was set at 300 A with a frequency of 6.0 Hz. The bloom was slowly cooled in the pit, and the temperature when entering the pit was set at over 500°C. After 48 hours of incubating, it could be removed from the pit.

[0043] (5) Blowing and rolling production The 300mm x 325mm cast billets are subjected to high-temperature diffusion for a long time in a 51m long heating furnace, with the heating temperature set to 1230-1250°C. After the long-term high-temperature diffusion, they are rolled through 10 stands and then bloomed into 160mm x 160mm rolled billets. The collection temperature of the rolled billets is set to 450°C-460°C, and after rolling, they are stacked to cool, away from the wind.

[0044] (6) Finishing of rolled billets A 160mm x 160mm rolled billet is finished and peeled, with the peeling depth on one side set to 2mm, and surface flaw detection is performed.

[0045] (7) Heating of rolling billet A 156mm x 156mm rolling billet is heated in a high-speed wire heating furnace, the heating temperature is 1160°C to 1190°C, the heating time is 135 minutes, and the rolling start temperature is 1060°C to 1090°C.

[0046] (8) Wire rod rolling The rolled billet is rolled into a wire rod through rough rolling, intermediate rolling, preliminary finish rolling, and finish rolling, and then sent to the discharge device. The rolling temperature of the finish rolling is 920°C to 930°C, and the temperature of the finish rolling mill is 1000°C or higher.

[0047] (9) Cooling control of wire rod The wire is discharged at a temperature of 915°C, and cooled after discharge in a controlled manner, with rapid cooling in the first half and cooling in the cover in the second half. The temperature when entering the cover is 565°C, and the temperature when leaving the cover is less than 480°C.

[0048] (10) The wire is wound, packed, and stored in the warehouse.

[0049] (11) The wire rod is spheroidized and annealed at the wire mill, and then the wire rod is converted into a hexagonal wire rod through pickling and drawing. The annealing process is at 765°C for 12 hours.

[0050] (12) The wire is converted into hexagonal wire and then machined. The resulting driver bits are subjected to bainite isothermal quenching and tempering treatment, with an austenitizing temperature of 905°C, a heating time of 82 minutes, a quenching temperature of 305°C, an isothermal time of 60 minutes, and a tempering temperature of 285°C, a tempering time of 60 minutes. The fatigue life test value of the model T25 x 57 mm driver bits was an average of 35,000 cycles, the average holding time in the impact resistance test was 72 seconds, the torsional fracture location in the test was in the head, and the fracture opening was flat. Other test values ​​are as shown in Table 2.

[0051] Figure 1-1 shows the decarburized layer of a T25 x 57 mm driver bit with 0 mm of decarburization, and Figure 1-2 shows the metal structure of a T25 x 57 mm driver bit.

[0052] Example 2 The wire manufacturing process was the same as in Example 1, but the components were slightly adjusted within the preferred ranges of the present invention. The specific components are as shown in Table 1, and the wire manufacturing process was the same as steps (1) to (12) of Example 1.

[0053] In Example 2, the torsional fracture in the fatigue life and impact resistance tests of the product was located in the head, the fracture site was flat, and the performance was normal. The fatigue life test value of the model T25 x 57 mm driver bit was 33,000 times on average, the average hold time in the impact resistance test was 69 seconds, the torsional fracture in the test was located in the head, and the fracture site was flat. Other test values ​​are as shown in Table 2.

[0054] Example 3 The wire manufacturing process was the same as in Example 1, but the components were slightly adjusted within the preferred ranges of the present invention. The specific components are as shown in Table 1, and the wire manufacturing process was the same as steps (1) to (12) of Example 1.

[0055] In Example 3, the torsional fracture in the fatigue life and impact resistance tests of the product was located in the head, the fracture site was flat, and the performance was normal. The fatigue life test value of the model T25 x 57 mm driver bit was 38,000 times on average, the average hold time in the impact resistance test was 70 seconds, the torsional fracture in the test was located in the head, and the fracture site was flat. Other test values ​​are as shown in Table 2.

[0056] Example 4 The wire manufacturing process was the same as in Example 1, but the components were slightly adjusted within the preferred ranges of the present invention. The specific components are as shown in Table 1, and the wire manufacturing process was the same as steps (1) to (12) of Example 1.

[0057] In Example 4, the torsional fracture in the fatigue life and impact resistance tests of the product was located in the head, the fracture site was flat, and the performance was normal. The fatigue life test value of the model T25 x 57 mm driver bit was 41,000 times on average, the average hold time in the impact resistance test was 77 seconds, the torsional fracture in the test was located in the head, and the fracture site was flat. Other test values ​​are as shown in Table 2.

[0058] (Comparative Example 1) Comparative Example 1 uses the same wire rod manufacturing process as Example 1, but the carbon content is reduced to 0.80% based on Example 1, with the remaining components remaining unchanged. The specific components are listed in Table 1. The wire rod manufacturing process is the same as steps (1) through (11) of Example 1, with the heat treatment parameters fine-tuned based on the chemical components. (The heat treatment temperature is based on the Ac3 and Bs points of the steel. If the components of the comparative example differ significantly, the Ac3 and Bs points will vary significantly, and the heat treatment parameters must be adjusted to ensure smooth production of the finished driver bit. Using the same temperature as Example 1 would result in an insufficient austenitizing temperature, which would prevent the carbon and alloy from fully converting to austenite, resulting in significantly lower hardness after quenching.) The austenitizing temperature for the bainite isothermal quenching in Comparative Example 1 is 927°C, the quenching temperature is 330°C, and the tempering temperature is 285°C.

[0059] In Comparative Example 1, the carbon content was low, resulting in a high Ms temperature, a slight decrease in hardness after bainite isothermal quenching and tempering, and a certain decrease in fatigue life and impact resistance test value. The torsional fracture location in the impact resistance test was at the head, and the fracture opening was oblique. The specific test values ​​are as shown in Table 2.

[0060] (Comparative Example 2) Comparative Example 2 has the same wire rod manufacturing process as Example 1, but the Si content is reduced to 2.05% based on Example 1, and the other components remain unchanged. The specific components are as shown in Table 1. The wire rod process is the same as steps (1) to (11) of Example 1, and the heat treatment parameters are fine-tuned based on the chemical components. The austenitizing temperature of bainite isothermal quenching is 887°C, the quenching temperature is 306°C, and the tempering temperature is 285°C.

[0061] In Comparative Example 2, the low Si content reduced the effect of suppressing the formation of cementite during the cooling process, resulting in a slight decrease in hardness after bainite isothermal quenching and tempering, and a certain decrease in fatigue life and impact resistance test values. In the impact resistance test, the torsional fracture position was at the head, and the fracture opening was oblique. The specific test values ​​are as shown in Table 2.

[0062] (Comparative Example 3) Comparative Example 3 has the same wire rod manufacturing process as Example 1, but the Ni content is reduced to 1.10% based on Example 1, with the rest remaining unchanged. The specific components are as shown in Table 1. The wire rod process is the same as steps (1) to (11) of Example 1, with the heat treatment parameters fine-tuned based on the chemical components. The austenitizing temperature of the bainite isothermal quenching is 905°C, the quenching temperature is 316°C, and the tempering temperature is 285°C.

[0063] In Comparative Example 3, the Ni content was low, so the fatigue life and impact resistance test values ​​were significantly reduced. The torsional fracture position in the impact resistance test was in the head portion, and the fracture opening was an oblique fracture. The specific test values ​​are as shown in Table 2.

[0064] Comparative Example 4 Comparative Example 4 has the same wire rod manufacturing process as Example 1, but the carbon content is increased to 0.96% based on Example 1, and the other components remain unchanged. The specific components are as shown in Table 1. The wire rod process is the same as steps (1) to (11) of Example 1, and the heat treatment parameters are fine-tuned based on the chemical components. The austenitizing temperature of the bainite isothermal quenching is 885°C, the quenching temperature is 287°C, and the tempering temperature is 290°C.

[0065] In Comparative Example 4, the carbon content was high, resulting in a low Bs temperature. As a result, the hardness after bainite isothermal quenching and tempering was significantly improved. However, the fatigue life and impact resistance test values ​​were significantly reduced. The torsional fracture in the impact resistance test was located in the rod portion, and the fracture opening was oblique. The specific test values ​​are as shown in Table 2.

[0066] (Comparative Example 5) Comparative Example 5 has the same wire rod manufacturing process as Example 1, but the Si content is increased to 2.72% based on Example 1, with the rest remaining unchanged. The specific components are as shown in Table 1. The wire rod process is the same as steps (1) to (11) of Example 1, with the heat treatment parameters fine-tuned based on the chemical components. The austenitizing temperature of the bainite isothermal quenching is 920°C, the quenching temperature is 305°C, and the tempering temperature is 290°C.

[0067] In Comparative Example 5, the Si content was high, resulting in high hardness after spheroidizing annealing, which was unfavorable for drawing manufacturing. Although the hardness after bainite isothermal quenching and tempering was significantly improved, the fatigue life and impact resistance test values ​​were somewhat reduced. In the impact resistance test, the torsional fracture position was in the rod portion, and the fracture opening was oblique. The specific test values ​​are as shown in Table 2.

[0068] (Comparative Example 6) Comparative Example 6 has the same wire rod manufacturing process as Example 1, but the Cr content is reduced to 0.40% based on Example 1, and the other components remain unchanged. The specific components are as shown in Table 1. The wire rod process is the same as steps (1) to (11) of Example 1, and the heat treatment parameters are fine-tuned based on the chemical components. The austenitizing temperature of bainite isothermal quenching is 907°C, the quenching temperature is 337°C, and the tempering temperature is 285°C.

[0069] In Comparative Example 6, the hardness after bainite isothermal quenching and tempering was significantly improved, but the fatigue life and impact resistance test values ​​were somewhat reduced. The torsional fracture position in the impact resistance test was in the head portion, and the fracture opening was oblique. The specific test values ​​are as shown in Table 2.

[0070] (Comparative Example 7) The wire rod manufacturing process was the same as in Example 1, but a comparative test was conducted using a conventional S2M material. The wire rod process was the same as steps (1) to (10) of Example 1. The wire rod annealing process was 750°C for 10 hours, with the austenitizing temperature of bainite isothermal quenching being 865°C, the quenching temperature being 385°C, and the tempering temperature being 230°C. Due to the low carbon content, the Bs temperature was very high, and the hardness after bainite isothermal quenching and tempering was only 59.1 HRC on average. The fatigue life and impact resistance were significantly different from those of the Examples, but the fracture opening of the torsional fracture in the impact resistance test was flat, indicating a tough fracture.

[0071] The chemical compositions of the examples and comparative examples of the present invention are shown in Table 1. Table 2 shows the performance test data for a finished screwdriver bit T25 x 57 mm, including hardness, torque, maximum twist angle, 13.3 NM static torque fatigue life, and impact resistance test data, as well as the location and appearance of the fracture. The specific location and appearance of the fracture are shown in Figure 2.

[0072] Table 1: Chemical composition table for Examples and Comparative Examples [Table 1]

[0073] Table 2 Tool performance test data using a finished driver bit T25 x 57 mm as an example [Table 2]

[0074] remarks: (1) Fatigue life test, torque, and maximum torsion angle were tested using the PB-6010 full-function torque life tester, as shown in Figure 3. The fatigue life test was performed in a forward / reverse rotation mode under the set torque conditions (the torque in this test was 13.3NM), and the finished driver bit was rotated until it broke. The torque and maximum torsion angle were measured using a one-way torsion mode, and the data tested by the equipment was read. (2) The impact resistance test method is shown in Figure 4, and the specific method is as follows: A screw is fixed, and a power tool with a finished screwdriver bit is clamped. The power is turned on and the screw begins to be tightened using the maximum torque (205 N.M). The finished screwdriver bit continues to be subjected to shear stress until it finally breaks. Considering the duration from when the finished screwdriver bit is subjected to force until it breaks, the longer the duration, the better. (3) Hardness test: It was carried out in accordance with GB / T230.1-2018 (Test method for Part 1 of Rockwell hardness test for metallic materials).

[0075] Figure 1 shows the metal structure and decarburized layer of Example 1, and Figure 2 shows the fracture location and appearance of a 25 x 57 mm completed driver bit in an impact resistance test. Figure 2-1 shows fracture in the rod part of a 25 x 57 mm driver bit, and Figure 2-2 shows fracture in the head part of a 25 x 57 mm driver bit.

[0076] The tools manufactured from the alloy tool manufacturing steel wire rod having high fatigue life and high impact resistance described in the present invention have significant advantages in hardness, fatigue life, torsional impact resistance, etc., and can be effectively applied in the field of hardware tools such as driver bits, screwdrivers, and hex wrenches, thereby improving the technical level of the hardware tool industry and having very important practical significance.

[0077] Unless otherwise specified, the raw materials and equipment used in the present invention are those commonly used in this field, and the methods used in the present invention are those commonly used in this field, unless otherwise specified. The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications made to the above examples based on the technical concept of the present invention are within the scope of protection of the present invention.

Claims

1. The chemical components are, in weight percentage, [C] 0.83% to 0.92%, [Si] 2.30% to 2.60%, [Mn] 0.40% to 0.80%, [Cr] 0.70% to 1.05%, [Ni] 1.31% to 1.61%, [V] 0.14% to 0.30%, [Al] 0.025% to 0.060%, [P] ≦ 0.025%, [S] ≦ 0.020%, with the balance being Fe and unavoidable impurities. A steel wire rod for manufacturing alloy tools, having a long fatigue life and high impact resistance, characterized by:

2. The chemical components of the steel wire rod are, in weight percentage, [C] 0.86% to 0.90%, [Si] 2.31% to 2.45%, [Mn] 0.40% to 0.60%, [Cr] 0.75% to 0.95%, [Ni] 1.31% to 1.41%, [V] 0.18% to 0.24%, [Al] 0.025% to 0.050%, [P] ≦ 0.025%, [S] ≦ 0.015%, and the balance being Fe and unavoidable impurities.

2. The steel wire rod for manufacturing alloy tools having a long fatigue life and high impact resistance according to claim 1.

3. Steel wire rods are used in the manufacture of alloy tools.

3. Use of the steel wire rod having a long fatigue life and high impact resistance for manufacturing alloy tools according to claim 1 or 2.

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