Wire rod for non-quenched and tempered fastener, production method of wire rod and fastener

Abstract

The invention relates to a steel wire rod for a non-quenched and tempered fastener, a production method of the steel wire rod and the fastener, and the steel wire rod is characterized in that through component design, an element B is added on the basis of strengthening elements such as carbon, silicon and manganese, so that excellent hardenability and plasticity of steel are guaranteed; the tensile strength of the steel wire rod obtained through the production process of converter smelting, LF refining, bloom continuous casting, cogging, steel wire rod rolling and offline salt bath of the steel wire rod is 1050-1250 MPa, and the percentage reduction of area is 65-70%; the steel wire rod is subjected to drawing and cold heading to produce the fastener, thermal refining can be omitted, the technical requirements of the 12.9-grade fastener can be met, and the production cost and the carbon emission are effectively reduced.

Description

Technical Field

[0001] This invention relates to a wire rod for non-quenched and tempered fasteners, its production method, and the fastener itself, belonging to the technical field of steelmaking. Background Technology

[0002] In fastener production, spheroidizing annealing and quenching and tempering are energy-intensive, carbon-emitting, and inefficient processes. Therefore, non-quenched and tempered wire rods for fasteners have always been a hot demand in the fastener industry. Non-quenched and tempered wire rods possess high strength and high ductility. They are then drawn to further enhance strength while maintaining good ductility. The good ductility maintained after drawing primarily ensures the smoothness of subsequent cold heading. Fasteners made from non-quenched and tempered wire rods through drawing and cold heading meet technical requirements, and the spheroidizing annealing and quenching and tempering processes are omitted during fastener production.

[0003] Currently, the main technical approach for non-quenched and tempered fastener wire rods is to increase the content of strengthening elements such as carbon, manganese, and chromium, and then add elements such as Nb and V for microalloying. Simultaneously, low-temperature rolling and precise cooling processes are used to refine the grain size and control the microstructure transformation, thereby improving the strength and plasticity of the wire rod. However, the precise control of low-temperature rolling and post-rolling cooling places extremely stringent requirements on the rolling mill's capacity, operator skill, and cooling process. Furthermore, non-quenched and tempered fastener wire rods are currently mainly used for producing fasteners of grade 10.9 and below; there are few reports on their use for fasteners of grade 12.9 and above.

[0004] Patent application number 202410969478.9 discloses a 12.9 grade non-quenched and tempered hot-rolled high-carbon cold-heading steel wire rod and its manufacturing method. The material is produced using a high C-Si-Mn-Cr-Mo composition and a controlled rolling and cooling process. The chemical composition and mass percentages include C: 0.72~0.76%, Si: 0.20~0.35%, Mn: 0.60~0.90%, Cr: 0.34~0.42%, Mo: 0.10~0.30%, P≤0.015%, S≤0.015%, with the remainder being Fe and unavoidable impurities. The wire rod has a wire drawing temperature of ≥940℃. After online molten salt isothermal phase transformation treatment, the wire rod is cooled to the pearlite phase region of 510~560℃ at a cooling rate of ≥38℃ / s to carry out isothermal phase transformation. The microstructure of the wire rod includes tempered pearlite with a volume percentage of ≥93%, and the remainder is ferrite and fused pearlite. The wire rod can achieve a tensile strength of 1165~1215MPa, a reduction of area of ​​53~58%, and mechanical fluctuation of ≤28MPa. However, the main technical problems of this patent application are: (1) The high carbon content increases the strength of the wire rod but reduces the plasticity of the steel. Its reduction of area is only 53~58%, which is not conducive to the production of parts with large cold heading deformation and is prone to cold heading cracking; (2) The addition of Mo and Cr alloying elements increases the production cost. Summary of the Invention

[0005] To address the aforementioned problems, this invention discloses a wire rod for non-heat-treated fasteners, its manufacturing method, and the fastener itself. The specific technical solution is as follows: A non-heat-treated fastener wire rod, the chemical composition of which, by mass percentage, includes: C 0.18~0.24%, Si 0.15~0.25%, Mn 1.30~1.60%, P≤0.015%, S≤0.010%, Cr≤0.10%, Mo≤0.03%, B 0.0010~0.0025%, Ti 0.05~0.10%, Al 0.020~0.045%, N≤0.007%, with the remainder being Fe and unavoidable impurities.

[0006] The method for producing the aforementioned non-quenched and tempered fastener wire rods employs a production process of converter smelting - LF refining - large billet continuous casting - billet preparation - wire rod rolling - offline salt bath wire rod production. The wire rod rolling process is as follows: the initial rolling temperature is 930~960℃, the finishing rolling inlet temperature is 900~930℃, and the wire rod extrusion temperature is 880~900℃. The offline salt bath process for the wire rod: the temperature of the salt bath liquid in the salt tank is 350~400℃, and the salt bath time is 180~205 seconds.

[0007] Furthermore, in the converter smelting process: the converter tapping temperature is 1600-1650℃, the converter final slag basicity is 3.5-4.0, and the bottom blowing argon pressure in the ladle is 0.40-0.60MPa.

[0008] Furthermore, in the LF refining process: the basicity of the refining slag is 3.5-4.0, and the argon gas soft stirring time is 15-20 minutes.

[0009] Furthermore, in the large billet continuous casting process: the cross-sectional dimensions of the continuously cast billet are 300mm×390mm, the casting speed is 0.70±0.2m / min, and the water content in the secondary cooling zone is 0.42±0.2L / kg.

[0010] Furthermore, the billet-making process involves rolling a large square billet into a (140~160) mm × (140~160) mm square billet, with the billet being heated at a temperature of 1180~1220℃ and for a heating time of 150-210 min.

[0011] Furthermore, in the wire rod rolling process: the billet heating temperature is 1040~1080℃, and the inlet section roller speed is 0.3~0.5m / s; the Stellmore cooling line does not close the heat preservation cover, turns on the first four fans, and the fan air volume is 100%. The wire rod is collected into coils by the collecting drum and waits for offline salt bath.

[0012] Furthermore, the offline salt bath process for the wire rod involves: the rolled wire rod being fed clockwise through a straightening roller conveyor into a heating furnace, where the heating temperature is 910~980℃, the heating time is 8-10 min, the carbon potential inside the furnace is 0.19±0.01%, and the wire rod feeding speed is 3.0~3.5 m / min; after heating, the wire rod is immersed in a salt bath solution in a salt tank, the salt bath solution having a weight ratio of 40% KNO3 and 60% NaNO3.

[0013] The wire rod produced by the above-described method for producing wire rods for non-heat-treated fasteners has a tensile strength of 1050~1250MPa and a reduction of area of ​​65~70%; the tensile strength fluctuation range of the same coil of the wire rod is ≤20MPa.

[0014] Furthermore, the wire rod is directly drawn at room temperature after pickling and phosphating, without softening or spheroidizing treatment. After drawing, the tensile strength of the wire rod is 1250~1500MPa. The reduction rate of the wire rod during drawing is 10~75%, and the reduction rate is calculated as [(cross-sectional area of ​​the wire rod before drawing - cross-sectional area of ​​the wire rod after drawing) / cross-sectional area of ​​the wire rod before drawing]*100%.

[0015] The fasteners produced by the above-mentioned cold heading of wire rod have the following properties: tensile strength ≥1250MPa, yield strength ≥1125MPa, hardness ≥39HRC, meeting the performance requirements of grade 12.9 fasteners.

[0016] The beneficial effects of this invention are: This invention, by designing the strengthening elements such as carbon, silicon, and manganese content, adds elements such as boron and titanium to ensure the steel has good hardenability. Simultaneously, a suitable production process is used to obtain wire rods with high strength, good plasticity, and excellent consistency throughout. After drawing, the wire rod has a tensile strength of 1250~1500MPa and a reduction of area of ​​55~65%. Parts obtained from the drawn and cold-headed wire rods do not require heat treatment and can meet the requirements of grade 12.9 fasteners, effectively reducing production costs and meeting environmental protection requirements.

[0017] The metallographic structure of the wire rod obtained by this invention is bainitic, and the tensile strength and plasticity of the wire rod are significantly improved. The tensile strength of the wire rod is further improved by drawing, while maintaining good plasticity, which can meet the requirements of cold heading deformation. Attached Figure Description

[0018] Figure 1 The metallographic structure of the wire rod obtained in Example 1; Figure 2 The metallographic structure of the wire rod obtained in Comparative Example 2; Figure 3 The metallographic structure of the wire rod obtained in Comparative Example 3; Figure 4 The metallographic structure of the wire rod obtained in Comparative Example 4 is shown. Detailed Implementation

[0019] The present invention is further illustrated by the following embodiments: The present invention can be better understood from the following embodiments. However, those skilled in the art will readily understand that the specific material ratios, process conditions, and results described in the embodiments are for illustrative purposes only and should not, and will not, limit the present invention as described in detail in the claims.

[0020] This invention provides wire rods for non-heat-treated fasteners, the chemical composition of which, by mass percentage, is: C 0.18~0.24%, Si 0.15~0.25%, Mn 1.30~1.60%, P≤0.015%, S≤0.010%, Cr≤0.10%, Mo≤0.03%, B 0.0010~0.0025%, Ti 0.05~0.10%, Al 0.020~0.045%, N≤0.007%, with the remainder being Fe and unavoidable impurities.

[0021] This invention improves the plasticity and cold heading properties of wire rod by designing lower carbon and silicon contents. To compensate for the loss of solid solution strengthening of the wire rod by carbon and silicon, a higher Mn content is designed; at the same time, the addition of boron improves the hardenability of the wire rod; the addition of titanium (Ti) fixes nitrogen in the steel to form TiN, preventing the formation of BN, thus allowing boron to fully play its role in improving hardenability.

[0022] Carbon (C) is the most basic and cheapest strengthening element in steel, but as the carbon content increases, the plasticity of wire rod decreases, reducing the cold heading performance of the steel. Therefore, in this invention, the carbon content is controlled at 0.18~0.24%.

[0023] Silicon (Si) is a strengthening and deoxidizing element in steel, but excessive silicon can reduce the cold heading performance of wire rod. In this invention, the silicon content is controlled at 0.15~0.25%.

[0024] Manganese (Mn) is a strengthening element in steel, which can improve the strength and hardenability of steel. However, excessive manganese will reduce the plasticity of steel. In this invention, the manganese content is controlled at 1.30~1.60%.

[0025] P and S are impurity elements in steel. Their segregation at grain boundaries causes grain boundary embrittlement, thereby reducing the strength and plasticity of the steel. In addition, S and Mn elements form MnS, which can reduce the solid solution strengthening effect of Mn. In this invention, the phosphorus content is controlled below 0.015% and the sulfur content is controlled below 0.010%.

[0026] Cr is a strengthening element in steel, but too much Cr can significantly increase the stability of austenite, leading to a longer bainite transformation time, which is not conducive to wire rod salt bath production. This invention controls the chromium content to Cr≤0.10%.

[0027] Mo can improve the strength and hardenability of steel, but it can significantly prolong the bainite transformation time, which is detrimental to wire rod salt bath production. This invention controls the molybdenum content to below 0.03%.

[0028] Ti can form fine TiC and TiN in steel, preventing boron (B) from forming BN with nitrogen, thus allowing B to improve hardenability. However, excessive Ti content can coarsen TiN and TiC, which is detrimental to cold heading. This invention controls the titanium content to 0.05~0.10%.

[0029] Boron (B) can improve the hardenability of steel, thereby increasing its strength. However, adding excessive amounts of boron will cause it to form a "boron phase" at grain boundaries, reducing the steel's plasticity. This invention controls the boron content to be between 0.0010% and 0.0025%.

[0030] Al is a deoxidizing element in steel, effectively removing oxygen and improving its cleanliness. Additionally, it can react with nitrogen to form AlN, which refines the grain size. In this invention, the aluminum content is controlled between 0.020% and 0.045%.

[0031] Nitrogen (N) can reduce the plasticity of steel, affecting its cold heading properties. High nitrogen content can also coarsen AlN and TiN, hindering fine-grain strengthening and cold heading deformation. In this invention, the nitrogen content is controlled below 0.007%.

[0032] During the production process, the heating temperature for wire rod rolling is 1040~1080℃, the initial rolling temperature is 930~960℃, the finishing rolling inlet temperature is 900~930℃, the wire drawing temperature is 880~900℃, the inlet section roller speed is 0.3~0.5m / s, the Stellmore cooling line does not close the heat insulation cover, and the first four fans are turned on with a fan air volume of 100%.

[0033] The heating temperature of the offline salt bath is 910~980℃, the wire release speed is 3.0~3.5m / min, the temperature of the salt bath liquid in the salt tank is 350~400℃, and the salt bath time is 180~205 seconds.

[0034] The cross-sectional dimensions of the continuous casting billet in the large billet continuous casting process are 300mm×390mm. Before the wire rod is rolled, the large billet needs to be cut into (140~160)mm×(140~160)mm billets, and the billet heating temperature is 1180~1220℃.

[0035] Example 1

[0036] This embodiment provides a method for producing wire rods for non-quenched and tempered fasteners, which adopts a production process of converter smelting-LF refining-large billet continuous casting-billing-wire rod rolling-wire rod offline salt bath.

[0037] The converter tapping temperature is 1600℃, the converter final slag basicity is 3.8, and the ladle bottom-blowing argon pressure is 0.5MPa. The LF refining slag basicity is 3.7, and the argon soft stirring time is 15min. Large square billet continuous casting is adopted, with a billet cross-section of 300mm×390mm, a casting speed of 0.70m / min, and a secondary cooling zone water content of 0.42L / kg.

[0038] Large billets are heated and rolled into square billets. The heating temperature of the large billets is 1180℃, and the heating time is 160 minutes. The cross-section of the square billets is 140mm×140mm. The square billets are then heated and rolled into wire rods. The wire rods undergo coiling, Stellmore cooling, and collection into coils using a collecting drum. The billet heating temperature is 1040℃, the initial rolling temperature is 930℃, and the finishing mill entry temperature is 900℃. The wire rod coiling temperature is 880℃, and the entry section roller speed is 0.5m / s. The Stellmore cooling line does not close the insulation cover and the first four fans are turned on at 100% airflow. The wire rods are collected into coils by the collecting drum and await offline salt bath treatment.

[0039] The resulting rolled coil is fed clockwise, and a single coil enters the heating furnace through the straightening roller conveyor. The heating temperature is 910℃, the heating time is 10min, the carbon potential in the furnace is 0.20%, and the coil feeding speed is 3.0m / min. After heating, the coil enters the salt bath, where the salt bath temperature is 350℃ and the salt bath time is 205 seconds.

[0040] Comparative Example 1 The preparation process of the wire rod is the same as in Example 1. The wire rod is collected into coils by a winding drum and awaits offline salt bath treatment.

[0041] The resulting rolled coil is fed clockwise, and a single coil enters the heating furnace through the straightening roller conveyor. The heating temperature is 890℃, the heating time is 5 minutes, the carbon potential in the furnace is 0.15%, and the coil feeding speed is 6 m / min. After heating, the coil enters the salt bath, where the salt bath temperature is 410℃ and the salt bath time is 100 seconds.

[0042] Example 2

[0043] This embodiment provides a method for producing wire rods for non-quenched and tempered fasteners, which adopts a production process of converter smelting-LF refining-large billet continuous casting-billing-wire rod rolling-wire rod offline salt bath.

[0044] The converter tapping temperature was 1630℃, the converter final slag basicity was 3.5, and the ladle bottom-blowing argon pressure was 0.4MPa. The LF refining slag basicity was 3.5, and the argon soft stirring time was 18min. Large square billet continuous casting was adopted, with a billet cross-section of 300mm×390mm, a casting speed of 0.68m / min, and a secondary cooling zone water content of 0.44L / kg.

[0045] Large billets are heated and rolled into square billets. The heating temperature of the large billets is 1200℃, and the heating time is 150min. The cross-section of the square billets is 150mm×150mm. The square billets are heated and rolled into wire rods. The wire rods are then coiled after being coiled, cooled in Stellmore, and collected in a coiling drum. The billet heating temperature is 1060℃, the initial rolling temperature is 945℃, and the finishing mill inlet temperature is 915℃. The wire rod coiling temperature is 890℃, and the inlet section roller speed is 0.4m / s. The Stellmore cooling line does not close the insulation cover and the first four fans are turned on at 100% airflow. The wire rods are collected in coils in the coiling drum and await offline salt bath treatment.

[0046] The resulting rolled coil is fed clockwise, and a single coil enters the heating furnace through the straightening roller conveyor. The heating temperature is 950℃, the heating time is 9 minutes, the carbon potential in the furnace is 0.19%, and the coil feeding speed is 3.2 m / min. After heating, the coil enters the salt bath, where the salt bath temperature is 380℃ and the salt bath time is 192 seconds.

[0047] Comparative Example 2 The preparation process of the wire rod is the same as in Example 2. The wire rod is collected into coils by a winding drum and awaits offline salt bath treatment.

[0048] The resulting rolled coil is fed clockwise, and a single coil enters the heating furnace through the straightening roller conveyor. The heating temperature is 900℃, the heating time is 7 minutes, the carbon potential in the furnace is 0.15%, and the coil feeding speed is 4.3 m / min. After heating, the coil enters the salt bath, where the salt bath temperature is 420℃ and the salt bath time is 140 seconds.

[0049] Example 3

[0050] This embodiment provides a method for producing wire rods for non-quenched and tempered fasteners, which adopts a production process of converter smelting-LF refining-large billet continuous casting-billing-wire rod rolling-wire rod offline salt bath.

[0051] The converter tapping temperature was 1650℃, the converter final slag basicity was 4.0, and the ladle bottom-blowing argon pressure was 0.6MPa. The LF refining slag basicity was 4.0, and the argon soft stirring time was 20min. Large square billet continuous casting was adopted, with a billet cross-section of 300mm×390mm, a casting speed of 0.72m / min, and a secondary cooling zone water content of 0.40L / kg.

[0052] Large billets are heated and rolled into square billets. The heating temperature of the large billets is 1220℃, and the heating time is 210 minutes. The cross-section of the square billets is 160mm×160mm. The square billets are then heated and rolled into wire rods. The wire rods undergo coiling, Stellmore cooling, and collection into coils using a collecting drum. The billet heating temperature is 1080℃, the initial rolling temperature is 960℃, and the finishing mill entry temperature is 930℃. The wire rod coiling temperature is 900℃, and the entry section roller speed is 0.3m / s. The Stellmore cooling line does not close the insulation cover and the first four fans are turned on at 100% airflow. The wire rods are collected into coils by the collecting drum and await offline salt bath treatment.

[0053] The resulting rolled coil is fed clockwise, and a single coil enters the heating furnace through the straightening roller conveyor. The heating temperature is 980℃, the heating time is 8 minutes, the carbon potential in the furnace is 0.18%, and the coil feeding speed is 3.5 m / min. After heating, the coil enters the salt bath, where the salt bath temperature is 400℃ and the salt bath time is 180 seconds.

[0054] Comparative Example 3 The preparation process of the wire rod is the same as in Example 3. The wire rod is collected into coils by a winding drum, without any subsequent salt bath process.

[0055] Comparative Example 4 (SCM435) The process involves converter smelting, LF refining, large billet continuous casting, billet preparation, and wire rod rolling to produce 12mm SCM435 wire rod. The converter tapping temperature is 1620℃, the final slag basicity is 3.2, and the bottom-blowing argon pressure in the ladle is 0.5MPa. The LF refining slag basicity is 3.8, and the argon soft stirring time is 12min. Large billet continuous casting is used, with a billet cross-section of 300mm×390mm, a casting speed of 0.75m / min, and a secondary cooling zone water content of 0.38L / kg.

[0056] Large billets are heated and rolled into square billets. The heating temperature of the large billets is 1220℃, and the heating time is 210 minutes. The cross-section of the square billets is 160mm × 160mm. The square billets are then heated and rolled into wire rods. The wire rods undergo coiling, Stellmore cooling, and collection into coils using a coiling drum. The billet heating temperature is 1080℃, the initial rolling temperature is 960℃, and the finishing mill inlet temperature is 870℃. The wire rod coiling temperature is 880℃, and the inlet section roller speed is 0.25m / s. The Stellmore cooling system is operated with the insulation cover and fan closed. The wire rods are collected into coils using a coiling drum, without any subsequent salt bath process.

[0057] The SCM435 wire rod obtained in Comparative Example 4 is a commonly used wire rod for 12.9 grade fasteners. The wire rod needs to undergo drawing-spheroidizing annealing-drawing-cold heading-quenching and tempering treatment to obtain fasteners that can meet the technical requirements of 12.9 grade fasteners.

[0058] The chemical composition of the wire rods obtained in Examples 1-3 and Comparative Examples 1-4 is shown in Table 1.

[0059] Table 1

[0060] Table 2 shows the metallographic structure and mechanical properties of the wire rods obtained in Examples 1-3 and Comparative Examples 1-4. The metallographic structure of the wire rods obtained in Examples 1-3 is bainitic; the tensile strength of the wire rods obtained in Examples 1-3 is 1050-1250 MPa, the reduction of area is 65-70%, and the tensile strength fluctuation range within the same coil is 15-20 MPa. The metallographic structure of the wire rods obtained in Comparative Examples 1-2 is bainitic + ferrite, the metallographic structure of the wire rod obtained in Comparative Example 3 is ferrite + pearlite, and the metallographic structure of the wire rod obtained in Comparative Example 4 is bainitic + martensite. In Comparative Examples 1-2, the short salt bath time or high salt bath temperature led to the appearance of ferrite in the metallographic structure, resulting in a decrease in the tensile strength of the wire rods, which does not meet the requirements of the wire rods obtained in this invention. The metallographic structure and mechanical properties of the wire rods obtained in Comparative Examples 3-4 do not meet the requirements of this invention.

[0061] Table 2

[0062] The wire rods obtained in Examples 1-3 and Comparative Examples 1-3 were directly drawn. The wire rod obtained in Comparative Example 4 had poor plasticity and could not be directly drawn to achieve a 40% reduction in area; it required a drawing-spheroidizing annealing-drawing process. Referring to Table 3, the wire rods obtained in Examples 1-3 had a tensile strength of 1250-1500 MPa and a reduction in area of ​​55-65% after drawing. The wire rods obtained in Comparative Examples 1-2 had a tensile strength of 1150-1180 MPa and a reduction in area of ​​67-68% after drawing; the tensile strength of the wire rods obtained in Examples 1-2 after drawing was lower than the requirements of this invention. The wire rod obtained in Comparative Example 3 had a tensile strength of 750 MPa and a reduction in area of ​​62% after drawing, which was also lower than the requirements of this invention. The wire rod obtained in Comparative Example 4 also had a tensile strength lower than the requirements of this invention after drawing-spheroidizing annealing-drawing.

[0063] The wire rods obtained in Examples 1-3 and Comparative Examples 1-2 were drawn and cold-headed to form fasteners, and their mechanical properties were measured. The wire rods obtained in Comparative Examples 3-4 were drawn and cold-headed to form fasteners, and then the fasteners were subjected to quenching and tempering treatment. The quenching and tempering process was as follows: 850℃, holding for 30 min, oil quenching; tempering temperature was 480℃, and tempering time was 120 min. The mechanical properties of the fasteners obtained from the quenched and tempered wire rods of Comparative Examples 3-4 were tested. The test results are shown in Table 4.

[0064] Table 3

[0065] Table 4

[0066] The fasteners produced from the wire rods obtained in Examples 1-3 after drawing and cold heading exhibit the following properties: tensile strength ≥1250MPa, yield strength ≥1125MPa, and hardness ≥39HRC. These properties are superior to those of the fasteners produced from the wire rods obtained in Comparative Example 4 after drawing-spheroidizing annealing-drawing-cold heading-quenching and tempering treatment, as well as the fasteners produced from the wire rods obtained in Comparative Example 3 after drawing-cold heading-quenching and tempering treatment.

[0067] Those skilled in the art will understand that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0068] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A wire rod for non-quenched and tempered fasteners, characterized by, The chemical composition includes, in mass percentage: C 0.18-0.24%, Si 0.15-0.25%, Mn 1.30-1.60%, P≤0.015%, S≤0.010%, Cr≤0.10%, Mo≤0.03%, B 0.0010-0.0025%, Ti 0.05-0.10%, Al 0.020-0.045%, N≤0.007%, and the rest is Fe and inevitable impurities.

2. A method of producing the non-hardened fastener wire rod as claimed in claim 1, characterized by, The production process comprises converter smelting-LF refining-bulb continuous casting-billet rolling-wire rod rolling-off-line salt bath, The billet rolling process has an opening rolling temperature of 930-960℃ and a finish rolling inlet temperature of 900-930℃; the wire rod spinning temperature is 880-900℃; The wire rod rolling-off-line salt bath process has a salt bath liquid temperature in the salt tank of 350-400℃ and a salt bath time of 180-205 seconds.

3. The method of producing a wire rod for non-quenched and tempered fasteners according to claim 2, characterized by, The converter smelting process has a converter tapping temperature of 1600-1650℃ and a converter final slag basicity of 3.5-4.0; the ladle bottom argon blowing pressure is 0.40-0.60 MPa.

4. The method of producing a wire rod for non-quenched and tempered fasteners according to claim 2, characterized by, The LF refining process has a refining slag basicity of 3.5-4.0 and an argon soft stirring time of 15-20 min.

5. The method of producing a wire rod for non-heat-treated fasteners according to claim 2, characterized by, The bulb continuous casting process has a continuous casting billet cross section specification of 300mm×390mm, a pulling speed of 0.70±0.2 m / min, and a two-cooling zone specific water consumption of 0.42±0.2 L / kg.

6. The method of producing a wire rod for non-heat-treated fasteners according to claim 5, characterized by, The blooming process rolls the bulb into (140-160) mm×(140-160) mm square billets, and the bulb heating temperature is 1180-1220℃ and the heating time is 150-210 min.

7. The method of producing a wire rod for non-heat-treated fasteners according to claim 6, characterized by, The wire rod rolling process has a square billet heating temperature of 1040-1080℃ and an entry section roller speed of 0.3-0.5 m / s; the Stelmor cooling line does not close the heat preservation cover, the first four air fans are opened, the fan air volume is 100%, the wire rod is collected into a coil through a coil collecting drum, and waits for off-line salt bath.

8. The method of producing a wire rod for non-heat-treated fasteners according to claim 7, characterized by, The wire rod rolling-off-line salt bath process has the rolled wire rod put on the wire in a clockwise direction and enter a heating furnace through a straightening roller, the heating temperature is 910-980℃, the heating time is 8-10 min, the carbon potential in the furnace is 0.19±0.01%, and the wire rod wire laying speed is 3.0-3.5 m / min; the wire rod after heating is immersed in the salt bath liquid in the salt tank, and the salt bath liquid composition has a weight ratio of 40% KNO3 and 60% NaNO3.

9. Wire rod produced by the method of claims 2-8 for non-heat treated fasteners, characterized in that, The wire rod tensile strength is 1050-1250 MPa, and the reduction of area is 65-70%; the tensile strength fluctuation range of the wire rod is ≤20 MPa.

10. The rod as claimed in claim 9, characterized in that The wire rod is directly drawn at normal temperature after pickling and phosphorization without softening or spheroidizing treatment, the tensile strength of the wire rod after drawing is 1250-1500 MPa, and the wire rod drawing reduction of area is 10-75%, the reduction of area=[(wire rod cross section area before drawing-wire rod cross section area after drawing) / wire rod cross section area before drawing]*100%.

11. Fastener produced from the wire rod cold upsetting according to claim 10, characterized in that, The performance of the fastener is: tensile strength ≥ 1250 MPa, yield strength ≥ 1125 MPa, hardness ≥ 39HRC, which meets the performance requirements of the 12.9 grade fastener.

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