Steel wire rod for manufacturing alloy tools with high fatigue life and high impact resistance, and its use

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 belongs to the field of steel material manufacturing, and specifically relates to a steel wire rod for manufacturing alloy tools having high fatigue life and high impact resistance, and its use.

Background Art

[0002] In modern industries, a screw tightening system is mechanical equipment specialized for semi-automatic and fully automatic screw tightening, which combines a driver bit (such as a driver, hex key, etc.) and tools such as electric and pneumatic tools to form a complete tool. Among them, tools such as driver bits, batch bits, and drivers are in direct and close contact with screws, so high hardness, high torque, high impact resistance, and high fatigue life are required. They are consumables and need to be replaced after being used for a certain period.

[0003] Currently, the material of the highest grade driver bit widely used in the industry is S2M, and its chemical composition is designed to be [C] 0.66 - 0.72%, [Si] 0.85 - 1.10%, [Mn] 0.40 - 0.55%, [Cr] 0.15 - 0.30%, [Ni] 0.10 - 0.20%, [Mo] 0.38 - 0.45%, [V] 0.15 - 0.25% in weight percentage. Taking the widely used finished product driver bit of T25×57mm as an example, after undergoing the normal quenching (first, quenching all into martensite) and tempering process, the tool hardness is 58 - 60HRC, and no data regarding fatigue life and impact resistance can be found.

[0004] CN202310995781.1 discloses a high-strength and high-wear-resistant alloy tool steel and a method for smelting the same, with chemical composition by weight percentage being [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%, with the remainder being Fe and unavoidable impurities. This is essentially a spring steel design idea based on 60Si2CrV with increased carbon content and some Ni added, and is a different steel type compared to S2M. The heat treatment method and the performance of the final product are not disclosed, the invention is incomplete, and it is not comparable. CN202011060372.5 discloses a high-toughness alloy tool steel wire rod and a method for manufacturing the same, with chemical composition of C: 0.60~0.90 wt.%, Si: 1.00~3.00 wt.%, Mn: 0.45~1.00 wt.%, Cr: 0.45~1.00 wt.%, and Mo: 0.20~0.60 wt.%. The steel of this invention is considered to have excellent torsional fracture resistance, with a Rockwell hardness of 58~62 HRC and a torsion angle of 10~15° / mm per unit length, after undergoing a quenching and tempering process to convert the entire material to martensite. However, the subject described by the torsional angle per unit length is high-toughness alloy tool steel wire, not the tools manufactured from it. In reality, the torsional (fracture) angle is closely related to the structural design of the tool, and torsional fracture performance is related to torsional strength and impact resistance. Single torsional (fracture) angle data cannot fully explain the problem, and impact resistance is particularly important for automated machinery. Generally, the present invention does not consider the fatigue life and impact resistance of the material, making it uncomparable. Furthermore, the range of steel components in the present invention is too broad, resulting in significant differences in the performance of each component combination, 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 hardening. The hot-rolled wire structure forms abnormal structures such as martensite, making it prone to brittle fracture and expensive.Most conventional alloy tool steels lacked requirements for fatigue life and impact resistance, or if they did, they never exceeded 10,000 cycles, and impact resistance requirements were previously absent. High fatigue life and impact resistance are necessary to meet the requirements of Industry 4.0, which aim for zero or reduced equipment downtime.

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

[0006] In response to the shortcomings of the prior art, the present invention aims to provide a steel wire rod for manufacturing alloy tools that has high fatigue life and high impact resistance, and its use. The steel wire rod for manufacturing alloy tools obtained by the composition design of the present invention undergoes a spheroidizing annealing process to manufacture tools such as screwdriver bits, and then undergoes bainite isothermal quenching and tempering treatment. The final tempered screwdriver bits, screwdrivers, hex wrenches, etc., meet the requirements for high fatigue life and high impact resistance, possessing characteristics such as a hardness of 60-62 HRC, a fatigue life of 30,000 cycles or more in fatigue tests, and impact resistance of 60 seconds or more.

[0007] To achieve the above objective, the present invention employs the following technical means.

[0008] This invention combines the process principles of bainite isothermal quenching and tempering to design the composition of a high-carbon, high-silicon, nickel-rich alloy tool steel, with the following weight percentages: [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%, with the remainder being Fe and unavoidable impurities.

[0009] Preferably, the chemical composition is, by weight percentage, [C] 0.86%~0.90%, [Si] 2.31%~2.45%, [Mn] 0.40%~0.60%, [Cr] 0.75%~0.95%, [Ni] 1.31%~1.41%, [V] 0.18%~0.24%, [Al] 0.025%~0.050%, [P] ≤ 0.025%, [S] ≤ 0.015%, with the remainder being Fe and unavoidable impurities.

[0010] Products such as screwdriver bits, screwdrivers, and hex wrenches manufactured from the materials obtained by this invention have extremely stringent requirements regarding final hardness, torque, helix angle, fatigue life, and impact resistance. The composition is a crucial factor that affects the final performance of the product, and in designing the chemical composition, certain performance is influenced not only by one element but also by multiple elements simultaneously. Therefore, it is necessary to consider the rationalization of multiple elements depending on the application of the product.

[0011] The reasons for the component design of this invention are as follows:

[0012] [C] is the most effective element for improving strength and hardness in steel, exhibiting a significant solid solution strengthening effect. Low carbon content results in low steel hardness and poor wear resistance, but excessively high content leads to the formation of large carbides. Furthermore, in the steel of the present invention, carbon can also lower the bainite transformation temperature Bs. Bainite isothermal transformation occurs below the nose point of the bainite transformation curve, resulting in a low Bs temperature and good performance. However, excessively high carbon content makes bainite nucleation difficult, prolonging the inoculation period and reducing the bainite transformation rate. Therefore, there is a contradiction between a low Bs temperature and the bainite transformation rate. In other words, carbon must have an appropriate content, which in the present invention 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, the silicon combines with chromium, molybdenum, etc., improving properties such as oxidation prevention, corrosion resistance, and heat resistance. Furthermore, silicon can be used as a commonly used deoxidizing agent, partially replacing aluminum in deoxidation. In addition, silicon in the steel of the present invention can 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 is formed on the steel surface, reducing its coating ability, and the strengthening effect of the Si element becomes more pronounced. If the content is too high, the brittleness of the steel increases. Therefore, in the present invention, the silicon content 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. As an austenite-forming element, Mn can lower the cementite precipitation initiation temperature. Too high a Mn content is disadvantageous, as it may lead to the formation of a striped structure. In this invention, the Mn content is preferably 0.40% to 0.60%.

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

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

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

[0018] [Mo] significantly improves hardenability and hardenability, but the hot-rolled wire rod structure forms abnormal structures such as martensite, making it prone to brittle fracture, and it is also expensive. Adding Mo to the present invention results in a different steel type system. In the present invention, under the premise of high carbon, high Si, and high Ni, adding Mo doubles the risk of brittle fracture of the hot-rolled wire rod, and there is a possibility that the structure cannot be manufactured normally. Therefore, Mo is not added in the present invention.

[0019] [Al] is an important element for deoxidation, refining the crystal grains and improving impact toughness. Furthermore, aluminum has antioxidant and corrosion-resistant properties, and when used in combination with chromium and silicon, it can significantly improve the high-temperature scale-free and high-temperature corrosive properties of steel. In addition, since Al does not dissolve in cementite and significantly delays cementite formation, in the steel of the present invention, aluminum not only raises the cementite formation temperature but also accelerates bainite formation. For this reason, it is necessary to appropriately control the aluminum content, which in the present invention is preferably 0.025% to 0.050%.

[0020] [P] and [S] are generally harmful elements in steel, but in this invention, [P] ≤ 0.025% and [S] ≤ 0.015% are preferred.

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

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

[0023] (2) LF Refining Before the LF refining process, samples are taken. In the initial stages of refining, deoxidation and desulfurization are performed using calcium carbide, silicon carbide, or aluminum granules. Appropriate amounts of lime and fluorite (cryocrystal) are added in appropriate amounts according to the fluidity of the slag. In the initial stages of refining, an appropriate amount of aluminum wire is added according to the Al content in the molten steel, with only one addition permitted to ensure the target aluminum content of the finished product. In the intermediate and later stages, silicon carbide is used to protect the slag; that is, a small amount of silicon carbide is uniformly added to the slag surface to ensure that the slag surface is in a reducing atmosphere. In the intermediate stage, other alloy components are adjusted to target values ​​based on the LF process sample, controlled according to the target components, and the variation in components is reduced while the temperature is appropriately adjusted. The temperature of the casting furnace is set to 1559°C to 1599°C, and the temperature of the continuous casting furnace is set to 1529°C to 1569°C. Refining is carried out throughout the entire refining process while stirring is performed by blowing in small amounts of argon gas.

[0024] (3) RH vacuum treatment After the molten steel reaches the RH process, the ladle is lifted into the vacuum chamber, and vacuum circulation suction is initiated, with the lifting gas flowing at 80-120 Nm. 3Control it to / h. After the vacuum degree becomes less than 133 Pa, keep the pressure for 20 min to release the vacuum. Add a 100 - 300 - meter lutetium wire for modification treatment. After soft blowing for 20 - 40 min, transfer the molten steel to the continuous casting process by crane for casting. Control the temperature of the casting furnace at 1504 °C - 1534 °C and control the temperature of the continuous casting furnace at 1479 °C - 1509 °C.

[0025] (4) Continuous casting of bloom Before starting the casting by continuous casting, make the baking temperature of the tundish exceed 1100 °C. After stopping the baking of the tundish, flow argon gas into it for 3 - 5 min. After starting the casting, perform the casting while protecting the liquid surface of the tundish throughout the whole process. Cast the tundish with an integral casting nozzle. Control the casting superheat degree at 20 °C - 30 °C. After the casting of each furnace is completed, leave steelmaking slag in the ladle. Control the drawing speed of continuous casting at 0.80 m / min, control the return water temperature difference of the primary cooling water at 4 °C - 6 °C, control the secondary cooling water volume at 0.20 L / kg. Operate the crystallizer and the electromagnetic stirring device at the end. Set the electric stirring parameter current of the crystallizer at 290 - 310 A, with the target being 300 A, set the frequency at 1.8 - 2.2 Hz, with the target being 2.0 Hz. Set the electric stirring parameter current of the electromagnetic stirring device at the end at 290 - 310 A, with the target being 300 A, set the frequency at 5.8 - 6.2 Hz, with the target being 6.0 Hz. Slowly cool the bloom in the pit, make the temperature when putting it into the pit exceed 500 °C, and after heat preservation for 48 hours or more, it can be taken out from the pit.

[0026] (5) Block rolling production Let the 300 mm × 325 mm casting billet undergo long - time high - temperature diffusion in a heating furnace with a total length of 51 m. Set the heating temperature at 1220 °C - 1270 °C. After long - time high - temperature diffusion, through 10 - stand rolling, perform block rolling into a 160 mm × 160 mm rolling billet. Set the collection temperature of the rolling billet at 400 °C - 500 °C. After rolling, stack and cool it while avoiding wind.

[0027] (6) Finishing of the rolling billet Finish rolling a 160 mm × 160 mm rolling billet, perform peeling with a peeling depth of 2 mm on one side, and conduct surface flaw detection.

[0028] (7) Heating of the rolling billet Heat a 156 mm × 156 mm rolling billet in a high-speed wire heating furnace, with the heating temperature being 1150°C to 1200°C, the heating time being 100 to 150 minutes, and the rolling start temperature being 1050°C to 1100°C.

[0029] (8) Wire rolling Roll the rolling billet into a wire through rough rolling, medium rolling, preliminary finishing rolling, and finishing rolling, and send it to a discharging device. The rolling temperature of the finishing rolling is 900°C to 950°C, and the temperature of the finishing rolling mill is 970°C or higher.

[0030] (9) Cooling control of the wire Set the discharging temperature of the wire to 900°C to 940°C, control the cooling after discharging, cool rapidly in the first half, and cool inside the cover in the second half. The temperature when entering the cover is 550°C to 600°C, and the temperature when exiting the cover is less than 490°C.

[0031] (10) Coil the wire, package it, and store it in a warehouse.

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

[0033] Furthermore, it is necessary to modify the wire of the present invention into a hexagonal wire through spheroidizing annealing and pickling drawing in a fine wire factory, and the annealing process is 765°C × 12 h. The purpose of annealing is to facilitate subsequent drawing and machining.

[0034] Furthermore, after modifying the wire of the present invention into a hexagonal wire, it is machined to manufacture tools such as screwdriver bits, screwdrivers, and hex wrenches, and then subjected to bainite isothermal quenching and tempering. Here, the austenitizing temperature is set to 900°C to 910°C, the heating time to 80 to 90 minutes, the salt bath quenching temperature to 300°C to 310°C (the quenching medium is salt), the isothermal time to 55 to 65 minutes, the tempering temperature to 280°C to 290°C, and the tempering time to 55 to 65 minutes.

[0035] The quenching temperature for isothermal bainite quenching is below the nose point of the bainite transformation curve. A lower Bs point results in a lower nose point and superior overall performance. To reduce Bs, it is necessary to significantly increase the carbon content. However, if the carbon content is too high, too much cementite is formed during quenching, which greatly affects fatigue life and impact resistance. Therefore, it is necessary to increase the Si content. Silicon suppresses the formation of cementite during the cooling process, forming a lower bainite suitable for high toughness, and high Ni can contribute to the material having better toughness. For tools such as screwdriver bits, screwdrivers, and hex wrenches, the tools must be tempered after isothermal bainite quenching. The tempering process can release residual stress in the steel and improve the toughness of the steel.

[0036] Compared to conventional technology, the present invention has the following beneficial effects. By rationally designing the composition, the Bs temperature of the material is reduced, and the material of the present invention undergoes isothermal quenching of bainite below the nose point of the bainite transformation curve. After tempering, the driver bits, drivers, and hex wrenches meet the requirements for high fatigue life and high impact resistance, namely, they have a hardness of 60-62 HRC, a fatigue life of 30,000 cycles or more, and impact resistance of 60 seconds or more. [Brief explanation of the drawing]

[0037] [Figure 1] Figure 1-1 shows the metallographic structure and decarburized layer of Example 1, with Figure 1-1 showing the decarburized layer and Figure 1-2 showing the metallographic structure. [Figure 2]Figure 2-1 shows the fracture location and appearance of a finished T25 x 57 mm screwdriver bit during an impact resistance test. Figure 2-2 shows the fracture of the rod portion. [Figure 3] This shows the full-function torque life tester and model number for a T25 x 57mm finished screwdriver bit. [Figure 4] This shows the impact resistance testing equipment for a finished screwdriver bit measuring T25 x 57 mm. [Modes for carrying out the invention]

[0038] The present invention will be described in more detail below in combination with examples of steel wire rods for manufacturing alloy tools having high fatigue life and high impact resistance. Conditions not limited herein are general conditions. The T25×57mm finished screwdriver bit is merely illustrative, and screwdriver bits of other different head types and lengths will have similar performance, all of which will also have excellent hardness, fatigue life and impact resistance.

[0039] (Example 1) (1) Converter smelting The converter was charged with 102 tons of molten iron and 27 tons of scrap steel by weight, with the molten iron [Si] content set to 0.65%, [P] to 0.060%, and [S] to 0.022%, the temperature set to 1348°C, the tapped steel [C] content at the end of smelting set to 0.16%, the tapped steel [P] content set to 0.012%, the tapping temperature set to 1629°C, the tapping time set to 5 min, and 120 kg of aluminum blocks were added 30 seconds after tapping. After adding Mublock, 3400 kg of ferrosilicon, 660 kg of silicomanganese, and 1756 kg of high-carbon ferrochrome are added, followed by 800 kg of carburizing agent. Finally, 550 kg of lime and 310 kg of chemical slag agent are added. At the end of tapping, slag blocking is performed using a slide plate and slag blocking cone. After tapping is complete, the molten steel is transferred to the LF by crane for refining.

[0040] (2) LF Refining The furnace temperature of the LF was set to 1503°C, a sample was taken before the refining process, and in the refining process, deoxidation and desulfurization were performed using 180 kg of calcium carbide, and 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, and based on the results of the sample analysis of the process, 692 kg of ferrosilicon, 161 kg of silicomanganese, 253 kg of high-carbon ferrochrome, 100 kg of ferrovanadium, and 300 kg of nickel plate were added respectively, the temperature was adjusted to 1571°C, and the stirring intensity with argon gas was set to 70 L / min throughout the entire refining process.

[0041] (3) RH vacuum treatment After the molten steel reaches the RH process, the ladle is lifted into the vacuum chamber, vacuum circulation and suction are started, and the lifting gas is 100 Nm³ 3 The pressure is controlled to / h, and after the vacuum level drops below 80 Pa, the pressure is held for 20 minutes, then the vacuum is released. A 200-meter calcium wire is added for modification, followed by 20 minutes of soft blowing. Finally, the molten steel is transferred by crane to the continuous casting process for casting.

[0042] (4) Continuous casting of Bloom Before starting continuous casting, the tundish firing temperature is set to over 1100°C. After casting begins, the liquid surface of the tundish is protected throughout the entire process. The tundish is cast using an integrated casting nozzle, the casting superheating is controlled to 20-30°C, the initial temperature is set to 1475°C, and after casting is completed in each furnace, steelmaking slag is left in the ladle. The continuous casting withdrawal speed is controlled to 0.80 m / min, the primary cooling water return temperature difference is controlled to 5.55°C, the secondary cooling water volume is controlled to 0.20 L / kg, the crystallizer and the terminal electromagnetic stirring device are operated, the crystallizer's electric stirring parameter current is set to 300 A with a target of 2.0 Hz, and the terminal electromagnetic stirring parameter current is set to 300 A with a frequency of 6.0 Hz. The bloom is slowly cooled in a pit, the temperature when placed in the pit is set to over 500°C, and it can be removed from the pit after being kept warm for 48 hours or more.

[0043] (5) Blowing rolling production A 300mm x 325mm cast billet is heated to a high temperature for an extended period in a 51m long heating furnace, with the heating temperature set to 1230-1250°C. After prolonged high-temperature diffusion, it undergoes rolling through 10 stands to be divided and rolled into 160mm x 160mm rolled billets. The rolled billets are collected at a temperature of 450-460°C, and after rolling, they are stacked and cooled away from airflow.

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

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

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

[0047] (9) Cooling control of wires The wire discharge temperature is set to 915°C, and cooling is controlled after discharge. The first half is rapidly cooled, and the second half is cooled inside the cover. The temperature when entering the cover is 565°C, and the temperature when exiting the cover is less than 480°C.

[0048] (10) The wires are bundled, wound, packaged, and stored in the warehouse.

[0049] (11) The wire is modified into hexagonal wire through spheroidizing annealing and pickling drawing at a wire refining factory, with the annealing process being 765°C for 12 hours.

[0050] (12) After modifying the wire into hexagonal wire, the manufactured driver bits are subjected to bainite isothermal quenching and tempering, with the austenitizing temperature set to 905°C for 82 minutes, the quenching temperature to 305°C for 60 minutes, the tempering temperature to 285°C for 60 minutes. The fatigue life test value for the driver bit of model T25×57mm was an average of 35,000 cycles, the holding time for the impact resistance test was an average of 72 seconds, the torsional fracture location in the test was in the head, the fracture opening was flat, and other test values ​​are shown in Table 2.

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

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

[0053] In Example 2, the torsional fracture location in the fatigue life and impact resistance tests of the product was in the head section, the fracture surface was flat, and the performance was normal. The fatigue life test value for the driver bit with model number T25×57mm was an average of 33,000 cycles, the holding time for the impact resistance test was an average of 69 seconds, the torsional fracture location in the test was in the head section, the fracture surface was flat, and other test values ​​are as shown in Table 2.

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

[0055] In Example 3, the torsional fracture location in the fatigue life and impact resistance tests of the product was in the head section, the fracture surface was flat, and the performance was normal. The fatigue life test value for the driver bit with model number T25×57mm was an average of 38,000 cycles, the holding time for the impact resistance test was an average of 70 seconds, the torsional fracture location in the test was in the head section, the fracture surface was flat, and the other test values ​​are as shown in Table 2.

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

[0057] In Example 4, the torsional fracture location in the fatigue life and impact resistance tests of the product was in the head section, the fracture surface was flat, and the performance was normal. The fatigue life test value for the driver bit with model number T25×57mm was an average of 41,000 cycles, the holding time for the impact resistance test was an average of 77 seconds, the torsional fracture location in the test was in the head section, the fracture surface was flat, and other test values ​​are shown in Table 2.

[0058] (Comparative Example 1) Comparative Example 1 uses the same wire manufacturing process as Example 1, but the carbon content is reduced to 0.80% based on Example 1, with the rest remaining unchanged. The specific components are shown in Table 1. The wire manufacturing process is the same as steps (1) to (11) of Example 1, with fine-tuning of the heat treatment parameters based on the chemical composition (the heat treatment temperature is based on the Ac3 and Bs points of the steel grade. If the difference in the components of the comparative example is large, the change between the Ac3 and Bs points will be large, and it will be necessary to adjust the heat treatment parameters to ensure the smooth production of the finished driver bits. If the same temperature as Example 1 is used, the austenitization temperature will be insufficient, the carbon and alloy will not completely change to austenite, and a significant reduction in hardness after quenching will occur). The austenitization temperature for bainite isothermal quenching in Comparative Example 1 is 927°C, the quenching temperature is 330°C, and the tempering temperature is 285°C.

[0059] Comparative Example 1, due to its low carbon content, had a high Ms temperature, resulting in a slight decrease in hardness after bainite isothermal quenching and tempering, a certain degree of decrease in fatigue life and impact resistance test values, and the torsional fracture location in the impact resistance test was in the head portion, with an oblique fracture. The specific test values ​​are shown in Table 2.

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

[0061] Comparative Example 2, due to its low Si content, had a reduced effect in suppressing cementite formation during the cooling process. As a result, the hardness after bainite isothermal quenching and tempering decreased slightly, and the fatigue life and impact resistance test values ​​decreased to some extent. In the impact resistance test, the torsional fracture location was in the head portion, and the fracture opening was oblique. The specific test values ​​are shown in Table 2.

[0062] (Comparative Example 3) Comparative Example 3 uses the same wire 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 shown in Table 1. The wire manufacturing process is the same as steps (1) to (11) of Example 1, with fine-tuning of the heat treatment parameters based on the chemical composition. The austenitizing temperature for bainite isothermal quenching is 905°C, the quenching temperature is 316°C, and the tempering temperature is 285°C.

[0063] Comparative Example 3, due to its low Ni content, showed a significant decrease in fatigue life and impact resistance test values. In the impact resistance test, the torsional fracture location was in the head section, and the fracture was oblique. The specific test values ​​are shown in Table 2.

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

[0065] Comparative Example 4, due to its high carbon content, had a lower Bs temperature and significantly improved hardness after bainite isothermal quenching and tempering. However, its fatigue life and impact resistance test values ​​decreased significantly. In the impact resistance test, the torsional fracture occurred in the rod section, and the fracture was oblique. The specific test values ​​are shown in Table 2.

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

[0067] Comparative Example 5, due to its high Si content, exhibited high hardness after spheroidizing annealing, which was unfavorable for drawing. Although its hardness improved significantly after bainite isothermal quenching and tempering, its fatigue life and impact resistance test values ​​decreased to some extent. In the impact resistance test, the torsional fracture occurred in the rod section, and the fracture was oblique. The specific test values ​​are shown in Table 2.

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

[0069] Comparative Example 6 showed a significant improvement in hardness after bainite isothermal quenching and tempering, but the fatigue life and impact resistance test values ​​decreased to some extent. In the impact resistance test, the torsional fracture location was in the head portion, and the fracture opening was oblique. The specific test values ​​are shown in Table 2.

[0070] (Comparative Example 7) The wire manufacturing process is the same as in Example 1, but a comparative test is conducted using conventional S2M material. The wire process is the same as steps (1) to (10) of Example 1. The wire annealing process is 750°C for 10 hours, the austenitization temperature for bainite isothermal quenching is 865°C, the quenching temperature is 385°C, and the tempering temperature is 230°C. Due to the low carbon content, the Bs temperature is very high, and the hardness after bainite isothermal quenching and tempering is only 59.1 HRC on average. There is a significant difference in fatigue life and impact resistance compared to the example, but the fracture surface in torsional fracture in the impact resistance test is flat, indicating a tough fracture.

[0071] The chemical components of the examples and comparative examples of the present invention are shown in Table 1. Table 2 shows the performance detection data for each component tested using a finished driver bit T25×57mm as an example, including hardness, torque, maximum helix angle, 13.3NM static torque fatigue life, and impact resistance test data, as well as the location and appearance of the torsional fracture. The specific location and appearance of the torsional fracture are shown in Figure 2.

[0072] Table 1: Chemical composition table of examples and comparative examples [Table 1]

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

[0074] remarks: (1) Fatigue life tests, torque, and maximum twist angle were performed 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 set torque conditions (the torque for this test was 13.3 NM), rotating until the finished screwdriver bit broke. Torque and maximum twist angle were measured in a unidirectional twisting mode, twisting until breakage, and the data tested by the instrument was read. (2) The impact resistance test method is as shown in Figure 4, and the specific method is as follows: A screw is fixed, and a power tool having a finished screwdriver bit is clamped. The power is turned on and the screw is tightened using the maximum torque (205 N.M). The finished screwdriver bit is subjected to shear stress and eventually breaks. Considering the duration from when the finished screwdriver bit is subjected to force until it breaks, a longer duration is preferable. (3) Hardness test: The test was performed in accordance with GB / T230.1-2018 (Test method for Part 1 of the 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 the finished T25×57mm screwdriver bit in an impact resistance test. Figure 2-1 shows the fracture at the rod portion of the T25×57mm screwdriver bit, and Figure 2-2 shows the fracture at the head portion of the T25×57mm screwdriver bit.

[0076] Tools manufactured from the steel wire rod for alloy tool manufacturing, which has high fatigue life and high impact resistance as described in the present invention, have remarkable advantages in performance such as hardness, fatigue life, and torsional impact resistance. They can be effectively applied to the field of hardware tools such as screwdriver bits, screwdrivers, and hex wrenches, improving the technological level of the hardware tool industry and having very important practical significance.

[0077] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the art, and unless otherwise specified, the methods used in this invention are all common methods in the art. The above are merely preferred embodiments of the invention and do not limit the invention, and any modifications made to the above embodiments based on the technical concept of the invention are all within the scope of protection of the invention.

Claims

1. The chemical composition, by weight percentage, is as follows: [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%, with the remainder being Fe and unavoidable impurities. A steel wire rod for manufacturing alloy tools, characterized by high fatigue life and high impact resistance.

2. The chemical composition of the steel wire is, by 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 remainder being Fe and unavoidable impurities. Steel wire rod for manufacturing alloy tools having high fatigue life and high impact resistance as described in feature 1.

3. Steel wire is used in the manufacture of alloy tools. The use of steel wire rods for manufacturing alloy tools having high fatigue life and high impact resistance as described in feature 1 or 2.

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