Steel wire rod for the production of alloyed tools with high fatigue life and high impact strength, and its application

Abstract

The present invention belongs to the field of steel materials and discloses a steel wire rod for producing alloyed tools with high fatigue life and high impact toughness, as well as its application. The chemical composition of the steel is, in weight percent, 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. The steel wire rod for the production of alloyed tools obtained by the invention is suitable for the production of screwdriver tips, turning tools and Allen keys with requirements for high fatigue life and high impact toughness and has the following properties: hardness of 60 ~ 62 HRC, fatigue life of at least 30,000 cycles and an impact toughness of at least 60 seconds.

Description

Technical area

[0001] The present invention belongs to the field of production of steel materials and particularly relates to a steel wire rod for producing alloyed tools with high fatigue life and high impact toughness and its application. Background technology

[0002] In modern industry, screw fastening systems are mechanical devices specifically designed for semi-automatic and fully automatic screw tightening. They consist of a screwdriver tip (screwdriver, Allen wrench, etc.) and electrically or pneumatically operated tools combined to form a complete tool system. The focus here is on the tools in direct contact with the screw, such as screwdriver heads, tips, and turning tools. These must exhibit high hardness, high torque, high impact resistance, and a long fatigue life. These are wear parts that must be replaced after a certain period of use.

[0003] The most commonly used and highest quality grade for screwdriver tips in the industry today is S2M. Its chemical composition, by weight percentage, is as follows: [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%, and [V] 0.15-0.25%. Using a commonly used finished screwdriver tip T25*57mm as an example, the tool hardness after conventional quenching (full martensite formation) and subsequent tempering is 58-60 HRC. Fatigue life and impact toughness data are not available.

[0004] CN202310995781.1 A high-strength, wear-resistant alloy tool steel and its melting process discloses the chemical composition, measured in mass percent, as follows: [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 consisting of Fe and unavoidable impurities. The alloy is based on the steel type 60Si2CrV with increased carbon content and an addition of nickel; Essentially, it is a spring steel concept. Compared to S2M, this represents a different steel system. Neither heat treatment processes nor final product properties were disclosed; the invention is therefore incomplete and lacks comparability. CN202011060372.5 A high-strength and tough alloy tool steel wire and its manufacturing process discloses the chemical composition: C: 0.60~0.90 wt.-%, Si: 1.00-3.00 wt%, Mn: 0.45-1.00 wt%, Cr: 0.45-1.00 wt%, Mo: 0.20-0.60 wt%. The steel of the present invention is produced by fully martensite formation followed by tempering. The Rockwell hardness is between 58-62 HRC and the torsion angle per unit length is 10-15° / mm, thus exhibiting excellent torsional fracture toughness. However, the object described by the torsion angle per unit length is high-strength and count-alloyed tool steel wire, not the tool made from it. In fact, the torsion (fracture) angle is very closely related to the structural design of the tool, and the torsional fracture toughness is also related to the torsional strength and impact resistance. The data of a single torsion (break) angle cannot fully explain the problem, especially in automated machines, impact resistance is essential.Overall, this invention lacks information on the fatigue life of the material and its impact toughness; therefore, comparability is not possible. Furthermore, the specified composition range of the steel according to the invention is very broad, whereby different combinations of components can lead to significant differences in performance, and some combinations may not achieve the properties described in the invention. S2M in conventional alloyed tool steels contains approximately 0.4% molybdenum (Mo). The element Mo significantly increases the hardness and hardness after quenching. In hot-rolled steel wires, the microstructure is prone to the formation of martensite or other abnormal microstructures with brittle fracture behavior; moreover, the costs for these are very high.Conventional alloyed tool steels generally do not have fatigue life or impact toughness requirements. Even if fatigue requirements exist—these rarely exceed ten thousand cycles—impact toughness requirements are not yet known. High fatigue life and impact toughness are necessary to meet the requirements of machines in the Industry 4.0 era with uninterrupted or minimally interrupted operation.

[0005] As industrial automation enters the new era of Industry 4.0, it is necessary to further increase work efficiency. Screw fastening systems must operate for extended periods with little to no downtime. At the same time, the application range of high-strength screws is continuously expanding, which is why the service life of tools such as screwdriver bits urgently needs to be improved. Qualitative improvements in hardness, impact resistance, and fatigue life are required. Content of the invention

[0006] To overcome the deficiencies of the prior art, the present invention aims to provide a steel wire rod for the production of alloyed tools with high fatigue life and high impact toughness, and its application. The alloyed tool steel wire rod obtained through targeted composition design is subjected to bainitic isothermal quenching and tempering after spheroidizing to produce tools such as screwdriver tips. The screwdriver tips, turning tools, hex wrenches, etc. produced after tempering meet the requirements for high fatigue life and high impact toughness with the following properties: hardness of 60 ~ 62 HRC, a fatigue life in the fatigue test of no less than 30,000 cycles, and an impact toughness of at least 60 seconds.

[0007] To achieve the above-mentioned objectives, the present invention uses the following technical solution: The present invention combines the principle of bainitic isothermal quenching and tempering to develop the composition of a high carbon, high silicon and nickel rich alloy tool steel, which is as follows by weight percentage: [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 balance being Fe and unavoidable impurities.

[0008] Preferably, the chemical composition, measured in mass percent, is as follows: [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.

[0009] The materials produced within the scope of this invention, which are used to manufacture screwdriver tips, rotary tools, Allen keys, and similar products, are subject to extremely stringent requirements regarding final hardness, torque, twist angle, fatigue life, and impact strength. The composition represents a decisive factor for the final product properties. When designing the chemical composition, a particular property is significantly influenced not only by a single element but by several elements simultaneously. Therefore, it is necessary to consider a rationalized design of multiple elements according to the intended use of the product. Reason for the composition design of the present invention:

[0010] [C] is the most effective element for increasing the strength and hardness of steel, with a pronounced solution-hardening effect. At low carbon contents, the steel exhibits low hardness and poor wear resistance, while too high a content leads to the formation of large carbide blocks. Furthermore, carbon in the steel described in the present invention lowers the bainite transformation temperature Bs. Isothermal bainite transformation occurs below the inflection point of the bainite transformation curve; at low Bs temperatures, the overall properties are improved. However, too high a carbon content makes bainite nucleation difficult, prolongs the incubation time, and reduces the bainite transformation rate.Thus, there is a contradiction between a low Bs temperature and the rate of bainite transformation, which is why the carbon content must have a suitable value, with a content of 0.86% ~ 0.90% being preferred in the present invention.

[0011] [Si] can significantly improve the elastic limit, yield strength, and strength of steel. By adding a certain amount of silicon to quenched and tempered steel, silicon, in combination with chromium, molybdenum, and other elements, can improve oxidation resistance, corrosion resistance, and heat resistance. Silicon also serves as a common deoxidizer, partially replacing aluminum in deoxidation. In addition, silicon in the present steel has an inventive effect on inhibiting the formation of cementite during the cooling process and preventing the decomposition of carbon in supercooled austenite. However, a high silicon content also leads to the formation of a hard oxide layer on the steel surface, which impairs the coating ability. At the same time, the strengthening effect of the element Si is significant; however, too high a content increases the brittleness of the steel.Therefore, in the present invention, a content of 2.31% ~ 2.45% is preferred.

[0012] [Mn] can increase the strength of steel, mitigate and eliminate the harmful effects of sulfur, significantly improve the hardenability of steel, and optimize the hot-working properties of steel. As an austenite-forming element, Mn can lower the temperature at which cementite begins to precipitate. However, an excessively high manganese content is disadvantageous because, on the one hand, it leads to the formation of a band-like microstructure; a content of 0.40 ~ 0.60% is preferred in the present invention.

[0013] Cr is one of the fundamental elements of wear-resistant materials, significantly improving the strength, hardness, and wear resistance of the steel, while also increasing its oxidation and corrosion resistance. In alloy tool steels, the Cr content is typically about 0.20%. To increase wear resistance, the present invention prefers a Cr content of 0.75~0.95%.

[0014] [Ni] expands the austenite phase region, forms an infinite solid solution without generating carbides, increases the strength of the steel, acts as a solution hardener, and improves hardenability. At the same time, it can also improve the corrosion resistance of the steel. Nickel mainly serves to increase plasticity and toughness in low-alloy steels. Since nickel is a relatively scarce resource, a content of 1.31% to 1.41% is preferred in the present invention.

[0015] [V] can improve grain refinement of the microstructure, thereby increasing strength and toughness. It forms carbides with carbon and can improve hydrogen corrosion resistance under high temperatures and high pressures. In alloyed tool steels, the vanadium content is typically about 0.20%, with the present invention preferably having a content of 0.18% to 0.24%.

[0016] [Mo] significantly increases hardenability and quenchability. The microstructure of hot-rolled steel wires is prone to martensite formation and other abnormal microstructures that can lead to brittle fractures, and the cost is very high. If molybdenum is also added in the present invention, a different steel system is created. Under conditions of high carbon, silicon, and nickel content, the addition of molybdenum leads to an exponentially increased risk of brittle fractures in hot-rolled wire blanks, potentially making regular production of the microstructure impossible. Therefore, molybdenum is not added in the present invention.

[0017] [Al] serves as a crucial element for deoxidation, while simultaneously refining grain size and increasing impact toughness. Aluminum also possesses antioxidant and corrosion-resistant properties. In combination with chromium and silicon, it can significantly improve the high-temperature spalling resistance and high-temperature corrosion resistance of the steel. Furthermore, aluminum is insoluble in cementite, which greatly retards the formation of cementite.

[0018] Therefore, aluminum in the steel described here not only increases the formation temperature of cementite but also accelerates the formation of bainite. For this reason, appropriate control of the aluminum content is required, with a content of 0.025% to 0.050% being preferred in the present invention.

[0019] [P] and [S] are generally harmful elements in steel, and in the present invention a content of [P] ≤ 0.025% and [S] ≤ 0.015% is preferred.

[0020] With respect to the steel wire rod for producing alloyed tools with high fatigue life and high impact toughness, the present invention further provides a wire rod manufacturing process comprising the following steps: converter melting, LF refining, RH vacuum treatment, continuous casting of large billets, billet opening by high-temperature diffusion, billet rolling, heating of rolled blanks, rolling of wire rods, cooling control of wire rods, etc., the specific steps being as follows: (1) Converter melting

[0021] The converter is charged with a weight ratio of 80-85% pig iron and 15-20% steel scrap. At the end of the melting process, a high-carbon operation is performed, with the carbon content of the steel [C] exceeding 0.07% and the phosphorus content [P] below 0.015%. The tapping time is 4-6 minutes, and the tapping temperature exceeds 1600°C. Starting 30 seconds after the start of tapping, aluminum ingots and alloys (such as silicomanganese, ferrosilicon, ferrovanadium, high-carbon chromium, and ferronickel) are added, along with common carbonizing agents in spheroidal form. Lime and furnace protective agents are added to the slag buildup during the tapping phase. After tapping is complete, the slag is covered using a combination of a slide rail and a slag stop cone. The liquid metal is then lifted into the LF furnace for further processing. (2) LF finishing

[0022] Sampling is conducted before entering the LF refining process. In the initial refining phase, deoxidation and desulfurization are carried out using calcium carbide, silicon carbide, or aluminum granules. Depending on the flowability of the slag, appropriate amounts of limestone and fluorite (cryolite) are added in several batches. Depending on the aluminum content of the molten steel before refining, an appropriate amount of aluminum wire may be added once to ensure the target aluminum content of the final product. In the middle to late phases, silicon carbide is used for slag maintenance by adding small, uniform amounts to the slag surface to ensure a reducing atmosphere.In the middle phase, other alloying elements are adjusted to the target values ​​using the LF run-in samples to control the target composition, minimize fluctuations, and adjust the temperature accordingly. The initial pouring temperature is between 1559 °C and 1599 °C, and between 1529 °C and 1569 °C for continuous pouring. A low argon stirring gas supply is used throughout the refining process. (3) RH vacuum treatment

[0023] After the liquid steel arrives at the RH station, the ladle is lifted into the vacuum chamber to begin cyclic vacuuming. The gas supply is adjusted to 80 ~ 120 Nm 3 / h. Once the vacuum pressure drops below 133 Pa, the pressure is maintained for 20 minutes before the vacuum is broken. Subsequently, 100 to 300 meters of calcium wire are introduced for modification. After a soft-blowing process of 20 to 40 minutes, the liquid steel is lifted to the continuous casting hanger and prepared for pouring. The temperature control during commissioning of the casting furnace is in the range of 1504 to 1534 °C, while the temperature control of the continuous casting furnace is between 1479 to 1509 °C. (4) Continuous casting of large billets

[0024] Before the start of continuous casting, the ladle is preheated to a temperature of over 1100°C. After preheating, the ladle is flushed with argon for 3 to 5 minutes. During casting, the steel surface is continuously protected by a protective coating. The ladle uses a full-mold casting process, with superheat during casting controlled at 20 to 30°C. After each casting, the steel residue remains in the ladle. The continuous drawing speed is controlled at 0.80 m / min, the temperature difference of the return cooling water in the first cooling zone is 4 to 6°C, and the cooling water volume ratio in the second cooling zone is 0.20 L / kg. The crystallizer and final electromagnetic stirring are activated; The parameters for electromagnetic stirring in the crystallizer are current of 290 ~ 310 A (target value: 300 A) and frequency of 1.8 ~ 2.2 Hz (target value: 2.0 Hz).For final electromagnetic stirring, currents of 290 to 310 A (target: 300 A) and frequencies of 5.8 to 6.2 Hz (target: 6.0 Hz) apply. Large billets undergo slow cooling in the pit furnace; the initial temperature is above 500 °C, and the holding time in the furnace is at least 48 hours before removal from the furnace. (5) Commissioning of billet production

[0025] A 300 mm × 325 mm cast ingot undergoes prolonged high-temperature diffusion in a 51 m long furnace. The heating temperature ranges from 1220 to 1270 °C. After the prolonged high-temperature diffusion, rolling takes place over ten rolling stands, during which the cast ingot is opened up into a 160 mm × 160 mm billet. The billet temperature during collection is between 400 °C and 500 °C. After rolling, it is stacked and cooled in a wind-protected area. (6) Refining of rolled blanks

[0026] A rolled part measuring 160 mm × 160 mm undergoes a precise peeling operation, with a peeling depth of 2 mm on one side. Subsequently, a surface inspection for defects is carried out. (7) Heating of rolled blanks

[0027] A rolled billet measuring 156 mm × 156 mm is heated in a wire rod heating furnace. The heating temperature is between 1150 and 1200 °C, the heating time is 100 and 150 minutes, and the initial rolling temperature is between 1050 and 1100 °C. (8) Rolling of wire rods

[0028] After rough rolling, intermediate rolling, pre-finish rolling, and fine rolling, the billet is rolled into wire rod and then transferred to the stretching machine. The temperature during fine rolling is 900°C to 950°C, and the exit temperature from the fine rolling machine is not lower than 970°C. (9) Cooling control of wire rods

[0029] The wire drawing temperature is 900-940°C. After drawing, a controlled cooling process takes place, with the front section being rapidly cooled and the rear section entering a cooling cover. The entry temperature into the cover is 550-600°C; the exit temperature from the cover is below 490°C. (10) The wire rod is wound into coils, packaged and stored.

[0030] The subsequent heat treatment steps for wire rods are as follows: Furthermore, the wire rods of the present invention must undergo ball annealing and pickling in a fine wire mill, as well as drawing and forming treatments into hexagonal bars. The annealing process is carried out at 765 °C for 12 hours. The purpose of annealing is to facilitate subsequent drawing and machining.

[0031] Furthermore, after forming into hexagonal bars, the wire rod of the present invention is mechanically processed to produce tools such as screwdriver tips, turning tools, and Allen keys. These tools are then subjected to an isothermal bainite quenching and tempering process. The austenitizing temperature is 900~910°C, the heating time is 80~90 minutes, the salt bath quenching temperature is 300~310°C (the quenching medium is salt), and the isothermal time is 55~65 minutes. The tempering temperature is 280~290°C, with a tempering time of 55~65 minutes.

[0032] The quenching temperature during isothermal quenching of bainite is below the nose point of the bainite transformation curve. The lower the Bs point, and thus the nose point, the better the overall properties. To lower the Bs point, the carbon content must be significantly increased. However, too high a carbon content leads to the formation of excessive cementite during quenching, which severely affects fatigue life and impact toughness. Therefore, it is necessary to increase the silicon content, as silicon inhibits the formation of cementite during the cooling process, thus promoting a high-strength and tough lower bainite structure. At the same time, a high nickel content contributes to improving the toughness of the material. Tools such as screwdriver tips, turning tools, and Allen keys require tempering after isothermal bainite quenching.Tempering serves to reduce the residual stresses present in the steel and to increase the toughness of the steel.

[0033] Compared to the prior art, the advantageous effects of the present invention include: through a suitable composition, the Bs temperature of the material has been lowered; the material of the invention undergoes isothermal quenching from bainite below the nose point of the bainitic transformation curve. The screwdriver tips, turning tools, hex wrenches, etc. produced after tempering meet the requirements for high fatigue life and high impact toughness with the following properties: hardness of 60 ~ 62 HRC, a fatigue life in the fatigue test of no less than 30,000 cycles, and an impact toughness of at least 60 seconds. Illustration of the attached drawings Fig.1 shows the metallographic structure and the decarburization layer according to Example 1. Fig. Figure 2 shows the fracture point and the impact resistance test appearance of a finished screwdriver tip with dimensions T25*57 mm. Fig. 3 shows the T25*57 mm finished screwdriver tip, the fully functional torque life testing machine and the model. Fig. 4 shows the testing machine for impact resistance testing of the finished screwdriver tip T25*57 mm. Specific embodiments

[0034] The present invention will be explained in more detail below using an example of a steel wire rod for the production of alloyed tools with high fatigue life and high impact toughness. Conditions not specified are considered standard conditions. The T25*57 mm finished screwdriver tip serves only as an example; other screwdriver tips with different tip types and lengths exhibit equivalent performance and also achieve excellent hardness, fatigue life, and impact toughness. Example 1(1) Converter melting

[0035] The converter is filled according to the weight ratio of 102 tons of liquid steel to 27 tons of scrap. The liquid steel has the following composition: [Si] 0.65%, [P] 0.060%, [S] 0.022% at a temperature of 1348 °C. At the end of the melting process, the carbon content in the steel [C] is 0.16%, the phosphorus content [P] 0.012%, and the outlet temperature is 1629 °C. The discharge time is 5 minutes; starting 30 seconds after the start of discharge, 120 kg of aluminum ingots are added one after the other. Following the addition of the aluminum ingots, 3400 kg of ferrosilicon, 660 kg of ferromanganese, and 1756 kg of high-carbon ferrochrome follow. Then, 800 kg of carbonizing agent are added, followed by 550 kg of lime and 310 kg of slag former. At the end of the run-out, a slide plate and a slag stop cone are used to retain the slag.After the run-out is complete, the liquid steel is lifted into the LF furnace for refining. (2) LF finishing

[0036] The temperature of the LF furnace is 1503°C. A sample is taken before entering the refining section. 180 kg of carbide is used for desulfurization and deoxidation at the refining section entrance. After 15 minutes of melting, silicon carbide is used for slag maintenance by adding a small, even amount to the slag surface to ensure a reducing atmosphere. Based on the analysis results of the entry sample, 692 kg each of ferrosilicon, 161 kg of ferromanganese, 253 kg of high-carbon chromium iron, 100 kg of ferrovanadium, and 300 kg of nickel sheet are added. The temperature is set to 1571°C. An argon stirring intensity of 70 L / min is maintained throughout the refining process. (3) RH vacuum treatment

[0037] After the liquid steel arrives at the RH station, the ladle is lifted into the vacuum chamber to begin cyclic vacuuming. The gas supply is set to 100 Nm 3 / h. Once the vacuum pressure drops below 80 Pa, the pressure is maintained for 20 minutes before the vacuum is broken. Then, 200 meters of calcium wire are introduced for modification. After a 20-minute soft-blowing process, the liquid steel is lifted to the continuous casting hanger and prepared for pouring. (4) Continuous casting of large billets

[0038] Before the start of continuous casting, the ladle is preheated to a temperature of over 1100°C. During casting, a continuous protective coating is applied to the steel surface within the ladle. The ladle uses a full-mold casting process, with superheat during casting controlled between 20°C and 30°C. The initial temperature of the first batch is 1475°C. After each casting, the steel residue remains in the ladle. The drawing speed is controlled at 0.80 m / min. The temperature difference of the return cooling water in the first cooling zone is 5.55°C, and the cooling water volume ratio of the second cooling zone is 0.20 L / kg. The crystallizer and final electromagnetic stirring are activated; the parameters for the electromagnetic stirring in the crystallizer are a current of 300 A and a frequency of 2.0 Hz. The current of 300 A and a frequency of 6.0 Hz apply to the final electromagnetic stirring.Large billets undergo slow cooling in the pit furnace; the initial temperature is above 500 °C and the holding time in the furnace is at least 48 hours before removal from the furnace. (5) Commissioning of billet production

[0039] A 300 mm × 325 mm cast ingot undergoes prolonged high-temperature diffusion in a 51 m long furnace. The heating temperature is between 1230 and 1250 °C. After the prolonged high-temperature diffusion, rolling takes place over ten rolling stands, during which the cast ingot is opened up into a 160 mm × 160 mm billet. The billet temperature during collection is between 450 and 460 °C. After rolling, the billet is stacked and cooled in a wind-protected area. (6) Refining of rolled blanks

[0040] A rolled part measuring 160 mm × 160 mm undergoes a precise peeling operation, with a peeling depth of 2 mm on one side. Subsequently, a surface inspection for defects is carried out. (7) Heating of rolled blanks

[0041] A rolled billet measuring 156 mm × 156 mm is heated in a wire rod heating furnace. The heating temperature is between 1160 and 1190 °C, the heating time is 135 minutes, and the initial rolling temperature is between 1060 and 1090 °C. (8) Rolling of wire rods

[0042] After rough rolling, intermediate rolling, pre-finish rolling, and fine rolling, the billet is rolled into wire rod and then transferred to the stretching machine. The temperature during fine rolling is 920 °C to 930 °C, and the exit temperature from the fine rolling machine is 1000 °C. (9) Cooling control of wire rods

[0043] The wire drawing temperature is 915°C. After drawing, a controlled cooling process takes place, with the front section being rapidly cooled and the rear section entering a cooling enclosure. The entry temperature into the enclosure is 565°C; the exit temperature from the enclosure is below 480°C.

[0044] (10) The wire rod is wound into coils, packaged and stored.

[0045] (11) The wire rods of the present invention are subjected to ball annealing and pickling in a fine wire mill, as well as drawing and forming treatment into hexagonal bars, the annealing process being carried out at 765 °C * 12 hours.

[0046] (12) After forming the wire rod into hexagonal bars, it is machined. The resulting screwdriver tips are subjected to isothermal quenching and tempering from bainite. The austenitizing temperature is 905°C, the heating time is 82 minutes; the quenching temperature is 305°C, the isothermal time is 60 minutes; the tempering temperature is 285°C, and the tempering time is 60 minutes. The T25*57mm model screwdriver tip has an average fatigue life of 35,000 cycles, and the average impact test duration is 72 seconds. The fracture occurs at the head, and the fracture cross-section is uniform. Further test results are shown in Table 2.

[0047] Fig. 1-1 shows the decarburization layer of the screwdriver tip T25*57 mm, with no decarburization (0 mm); Fig. 1-2 shows the metallographic structure of the screwdriver tip T25*57 mm. Example 2

[0048] The wire rod is produced using the same method as in Example 1. Within the preferred range of the present invention, the composition is slightly adjusted. The exact composition is listed in Table 1. The wire rod production process corresponds to steps (1) - (12) of Example 1.

[0049] In the fatigue life and impact resistance test of the product in Example 2, the fracture location is at the head, the fracture is smooth, and the performance is normal. The screwdriver tip of the T25*57mm model has an average fatigue life of 33,000 cycles in the fatigue test, and the average impact resistance test duration is 69 seconds. The fracture occurs at the head, and the fracture cross-section is smooth. Other test results are shown in Table 2. Example 3

[0050] The wire rod is produced using the same method as in Example 1. Within the preferred range of the present invention, the composition is slightly adjusted. The exact composition is listed in Table 1. The wire rod production process corresponds to steps (1) - (12) of Example 1.

[0051] In the fatigue life and impact resistance test of the product in Example 3, the fracture location is at the head, the fracture is smooth, and the performance is normal. The screwdriver tip of the T25*57 mm model has an average fatigue life of 38,000 cycles, and the average impact resistance test duration is 70 seconds. The fracture occurs at the head, and the fracture cross-section is smooth. Other test results are shown in Table 2. Example 4

[0052] The wire rod is produced using the same method as in Example 1. Within the preferred range of the present invention, the composition is slightly adjusted. The exact composition is listed in Table 1. The wire rod production process corresponds to steps (1) - (12) of Example 1.

[0053] In the fatigue life and impact resistance test of the product in Example 4, the fracture location is at the head, the fracture is smooth, and the performance is normal. The screwdriver tip of the T25*57 mm model has an average fatigue life of 41,000 cycles, and the average impact resistance test duration is 77 seconds. The fracture occurs at the head, and the fracture cross-section is smooth. Other test results are shown in Table 2. Comparison example 1

[0054] In Comparative Example 1, the wire rod manufacturing process is the same as in Working Example 1, except that the carbon content in Working Example 1 was reduced to 0.80%, while the other components remained unchanged; the exact compositions are listed in Table 1. The wire rod manufacturing process follows steps (1) to (11) of Working Example 1; the heat treatment parameters are fine-tuned according to the chemical composition (the heat treatment temperature is based on the Ac3 and Bs points of the steel). Due to the significant differences in the composition of the Comparative Example, Ac3 and Bs points change significantly, so the heat treatment parameters must be adjusted to ensure smooth production of the finished screwdriver tip.Using the same temperature as in Example 1 leads to adverse effects, as the austenitizing temperature is insufficient and carbon and alloying elements are not completely converted into austenite. After quenching, the hardness is significantly lower. For the isothermal quenching of bainite in Comparative Example 1, the austenitizing temperature is 927 °C, the quenching temperature is 330 °C, and the tempering temperature is 285 °C.

[0055] In Comparative Example 1, the low carbon content leads to a high Ms temperature; after isothermal quenching and tempering of the bainite, the hardness decreases slightly, and the fatigue life and impact toughness values ​​show a slight decline. The fracture point in the impact toughness test is located at the head, and the fracture exhibits a wedge-shaped fracture surface. The detailed test results are listed in Table 2. Comparison example 2

[0056] In Comparative Example 2, the wire rod manufacturing process was the same as in Example 1, except that the silicon content in Example 1 was reduced to 2.05%, while the remaining components remained unchanged; the exact compositions are listed in Table 1. The wire rod manufacturing process followed the same procedure as steps (1)-(11) in Example 1; based on the chemical composition, the heat treatment parameters were fine-tuned: the austenitizing temperature for isothermal quenching of bainite was 887 °C, the quenching temperature was 306 °C, and the tempering temperature was 285 °C.

[0057] In Comparative Example 2, the low Si content leads to reduced inhibition of cementite formation during the cooling process. After isothermal quenching and tempering of the bainite, the hardness decreased slightly, and the fatigue life and impact toughness values ​​showed a slight decrease. The fracture point in the impact toughness test is located at the head, and the fracture exhibits a wedge-shaped fracture surface. The detailed test results are listed in Table 2. Comparison example 3

[0058] In Comparative Example 3, the wire rod manufacturing process was the same as in Example 1, except that the nickel content in Example 1 was reduced to 1.10%, while the remaining components remained unchanged; the exact compositions are listed in Table 1. The wire rod manufacturing process followed the same procedure as steps (1)-(11) in Example 1; based on the chemical composition, the heat treatment parameters were fine-tuned: the austenitizing temperature for isothermal quenching of bainite was 905 °C, the quenching temperature was 316 °C, and the tempering temperature was 285 °C.

[0059] In Comparative Example 3, due to the low Ni content, significant reductions in impact strength and impact toughness are observed. The fracture point in the impact strength test is located at the head, and the fracture exhibits a wedge-shaped fracture surface. The detailed test results are listed in Table 2. Comparison example 4

[0060] In Comparative Example 4, the wire rod manufacturing process was the same as in Example 1, except that the carbon content in Example 1 was increased to 0.96%, while the other components remained unchanged; the exact compositions are listed in Table 1. The wire rod manufacturing process followed the same procedure as steps (1)-(11) in Example 1; based on the chemical composition, the heat treatment parameters were fine-tuned: the austenitizing temperature for isothermal quenching of bainite was 885 °C, the quenching temperature was 287 °C, and the tempering temperature was 290 °C.

[0061] In Comparative Example 4, the high carbon content and low Bs temperature lead to a significant increase in hardness after isothermal quenching and tempering from bainite, but the fatigue life and impact toughness values ​​show a slight decrease. The fracture site in the impact toughness test is located on the shank, and the fracture exhibits a wedge-shaped fracture surface. The detailed test results are listed in Table 2. Comparison example 5

[0062] In Comparative Example 5, the wire rod manufacturing process was the same as in Example 1, except that the silicon content in Example 1 was increased to 2.72%, while the other components remained unchanged; the exact compositions are listed in Table 1. The wire rod manufacturing process followed the same procedure as steps (1)-(11) in Example 1; based on the chemical composition, the heat treatment parameters were fine-tuned: the austenitizing temperature for isothermal quenching of bainite was 920 °C, the quenching temperature was 305 °C, and the tempering temperature was 290 °C.

[0063] In Comparative Example 5, the high Si content allows for high hardness after ball annealing, which is detrimental to drawing and forming treatments. Isothermal quenching and tempering of the bainite lead to a significant increase in hardness, but the fatigue life and impact toughness values ​​show a slight decrease. The fracture point in the impact toughness test is located on the shank, and the fracture exhibits a wedge-shaped fracture surface. The detailed test results are listed in Table 2. Comparison example 6

[0064] In Comparative Example 6, the wire rod manufacturing process was the same as in Example 1, except that the chromium content in Example 1 was reduced to 0.40%, while the other components remained unchanged; the exact compositions are listed in Table 1. The wire rod manufacturing process followed the same procedure as steps (1)-(11) in Example 1; based on the chemical composition, the heat treatment parameters were fine-tuned: the austenitizing temperature for isothermal quenching of bainite was 907 °C, the quenching temperature was 337 °C, and the tempering temperature was 285 °C.

[0065] Isothermal quenching and tempering of bainite in Comparative Example 6 lead to a significant increase in hardness, but the fatigue life and impact toughness values ​​show a slight decrease. The fracture point in the impact toughness test is located at the head, and the fracture exhibits a wedge-shaped fracture surface. The detailed test results are listed in Table 2. Comparison example 7

[0066] The wire rod is manufactured using the same process as in Example 1, except that conventional S2M material is used for the comparative test. The wire rod manufacturing process corresponds to steps (1) - (10) of Example 1. The wire rod is annealed at 750 °C for 10 hours. The austenitizing temperature for isothermal quenching of bainite is 865 °C, with the quenching temperature being 385 °C and the tempering temperature being 230 °C. Due to the low carbon content, the Bs temperature is very high.

[0067] After isothermal quenching and tempering of the bainite, the average hardness is only 59.1 HRC. Compared to the example, there are significant differences in fatigue life and impact toughness. However, the fracture surface shows a smooth fracture in the impact toughness test, which can be classified as a ductile fracture.

[0068] The chemical compositions of the working examples and comparative examples of the present invention are shown in Table 1. Table 2 contains the test results of various performance parameters measured on the finished screwdriver tip T25*57 mm, including hardness, torque, maximum twist angle, static fatigue life at 13.3 N·m torque, impact resistance test data, fracture location, and external appearance. The exact fracture locations and external appearance are shown in Fig. 2 shown. Table 1 Chemical composition of the working examples and comparative examples C Si Mn P S Cr Ni V Al Mon Example 1 0.88 2.33 0.5 0.012 0.007 0.8 1.33 0.19 0.042 0 Example 2 0.89 2.35 0.49 0.008 0.005 0.81 1.33 0.22 0.032 0 Example 3 0.89 2.35 0.51 0.009 0.008 0.79 1.32 0.19 0.039 0 Example 4 0.88 2.38 0.49 0.011 0.006 0.83 1.33 0.2 0.041 0 Comparison example 1 0.80 2.33 0.45 0.012 0.008 0.85 1.33 0.2 0.043 0 Comparison example 2 0.89 2.05 0.49 0.013 0.009 0.8 1.33 0.19 0.032 0 Comparison example 3 0.87 2.34 0.48 0.011 0.007 0.81 1.10 0.18 0.021 0 Comparison example 4 0.96 2.33 0.49 0.009 0.009 0.8 1.34 0.21 0.035 0 Comparison example 5 0.89 2.72 0.5 0.01 0.008 0.81 1.33 0.2 0.038 0 Comparison example 6 0.88 2.35 0.49 0.011 0.007 0.4 1.34 0.21 0.035 0 Comparison example 7 0.7 1.01 0.44 0.014 0.005 0.2 0.14 0.17 0.032 0.42 Table 2: Performance test data with finished screwdriver tip T25*57 mm as an example hardness torque Maximum angle of rotation (°) T25 * 57 mm fatigue life test (10,000 cycles) T25 * 57 mm impact resistance test (HRC) (kgf.cm)) Time (seconds) Fracture point and appearance Example 1 61.0 258 220 3.5 72 Fracture on the head + even fracture Example 2 61.1 260 214 3.3 69 Fracture on the head + even fracture Example 3 61.2 260 215 3.8 70 Fracture on the head + even fracture Example 4 61.1 259 228 4.1 77 Fracture on the head + even fracture Comparison example 1 60.1 245 152 1.3 44 Fracture on the head + even fracture Comparison example 2 60.3 244 154 1.1 45 Fracture on the head + even fracture Comparison example 3 59.7 239 126 0.7 39 Fracture on the head + even fracture Comparison example 4 62.8 259 110 0.3 25 Fracture on the shaft + even fracture Comparison example 5 62.2 268 102 0.3 22 Fracture on the shaft + even fracture Comparison example 6 60.0 238 148 0.6 36 Fracture on the head + even fracture Comparison example 7 59.1 238 158 0.4 21 Fracture on the head + even fracture Note: (1) The fatigue life tests, torque and maximum twist angle were carried out on the fully functional torque life testing machine PB-6010, see Fig. 3; the fatigue life test was conducted under specified torque conditions (the torque used for this test is 13.3 N m) in bidirectional operation until the finished screwdriver tip broke; the torque and maximum twist angle were tested in the one-way rotation mode, rotated until breakage, and the data obtained from the device was read. (2) The test method for impact resistance is Fig.4. The specific procedure is as follows: The screw is fixed, a power tool with a finished screwdriver tip is clamped, the power is turned on, and screw tightening begins using the maximum torque (205 N m). The finished screwdriver tip is continuously subjected to shear stress until it finally breaks. The time from the start of the load to the fracture of the finished screwdriver tip is evaluated; a longer time is considered better. (3) Hardness test: Conducted in accordance with GB / T230.1-2018 (Metallic materials - Rockwell hardness test - Part 1: Test methods).

[0069] Fig. 1 shows the metallographic structure and the decarburization layer according to embodiment 1; Fig. Figure 2 shows the fracture point and the impact resistance test appearance of a finished screwdriver tip with dimensions T25*57 mm. Fig.2-1 shows the smooth fracture at the head of the screwdriver tip T25*57 mm; Fig. 2-2 shows the smooth fracture on the shaft of the screwdriver tip T25*57 mm.

[0070] The tool described in the present invention, made of a steel wire rod for alloy tools with high fatigue life and high impact toughness, exhibits significant advantages in terms of hardness, fatigue life, and torsional shock resistance. It can be effectively used in the fields of screwdriver tips, screw tools, and Allen wrenches, contributing to raising the technical level of the hardware tool industry, which is of great practical significance.

[0071] The raw materials and equipment used in the present invention are, unless expressly stated otherwise, conventional raw materials and equipment in the relevant field; the methods employed in the invention are, unless expressly stated otherwise, conventional methods in the relevant field. The above statements represent merely preferred embodiments of the invention and are not to be construed as limiting the invention. Any modifications to the above embodiments based on the technical essence of the present invention are within the scope of the invention. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] CN 202310995781.1

[0004] CN 202011060372.5

[0004] GB 230.1-2018

[0068]

Claims

[1] Steel wire rod for the production of alloyed tools with high fatigue life and high impact strength, characterized by that the chemical composition of the steel wire rod 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 balance being Fe and unavoidable impurities. [2] Steel wire rod for the production of alloyed tools with high fatigue life and high impact strength according to claim 1, characterized by that the chemical composition of the steel wire rod by weight percentage is as follows: [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 balance being Fe and unavoidable impurities. [3] Use of a steel wire rod according to claim 1 or 2 for the production of alloyed tools with high fatigue life and high impact strength, characterized by that the steel wire rod is used for the production of alloyed tools.

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