A wire rod for non-quenched and tempered fastener, a production method thereof, and a fastener

Abstract

The present application relates to a kind of non-tempered fastener wire rod and its production method and fastener, wire rod is added B element on the basis of carbon, silicon, manganese and other strengthening elements by composition design, ensure that steel has excellent hardenability and plasticity;Using the production process of converter smelting-LF refining-bulb continuous casting-billet breaking-wire rod rolling-wire rod off-line salt bath, the tensile strength of the wire rod obtained is 1050~1250MPa, the reduction of area is 65~70%;The fastener produced by wire rod drawing, cold heading can omit quenching and tempering treatment, that is, it can meet the technical requirements of 12.9 grade fastener, effectively reduce production cost and carbon emission.

Description

TECHNICAL FIELD

[0001] The present application relates to a non-quenched fastener wire rod and its production method and fastener, belonging to the technical field of steelmaking. BACKGROUND

[0002] In the fastener production process, spheroidizing annealing and quenching and tempering treatment are high-energy-consuming, high-carbon-emission and low-efficiency production processes, so non-quenched fastener wire rods have been a hot demand in the fastener industry. The non-quenched fastener wire rod has the characteristics of high strength and high plasticity, and then the strength is further improved through drawing, while the plasticity is maintained. The wire rod maintains good plasticity after drawing, mainly to provide guarantee for subsequent cold heading deformation. The non-quenched fastener wire rod obtained by drawing and cold heading meets the technical requirements, and the spheroidizing annealing and quenching and tempering treatment are omitted in the fastener production process.

[0003] At present, the main technical route of the non-quenched fastener wire rod is to improve the content of carbon, manganese and chromium and other strengthening elements, and add Nb and V for micro-alloying; at the same time, low-temperature rolling and precise cooling process are matched to refine the grain and control the metallographic structure transformation, so as to improve the strength and plasticity of the wire rod. However, the low-temperature rolling and precise cooling control after rolling are extremely harsh on the rolling capacity of the rolling mill, the operation level and the cooling process. In addition, the current non-quenched fastener wire rod is mainly used for producing fasteners below 10.9 grade, and there are few reports on non-quenched wire rods for fasteners of 12.9 grade and above.

[0004] The patent application with the patent application number 202410969478.9 discloses a 12.9-grade non-quenched and tempered hot-rolled high-carbon cold heading steel wire rod and a manufacturing method thereof. The wire rod is produced by using a high C-Si-Mn-Cr-Mo composition and a controlled rolling and controlled cooling process line, and the chemical composition and mass percentage includes 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%, and the rest is Fe and inevitable impurities. The wire rod drawing temperature is ≥940℃, and after on-line molten salt isothermal phase change treatment, the wire rod is cooled to the pearlite phase region of 510-560℃ at a cooling rate of ≥38℃ / s for isothermal phase change, and the wire rod microstructure includes ≥93% of tempered pearlite in volume percentage, and the rest is ferrite and molten broken pearlite cold heading steel wire rod, so that the wire rod can reach a tensile strength of 1165-1215MPa, a reduction of area of 53-58%, and a mechanical fluctuation of ≤28MPa in the same circle. However, the patent application has the following main technical problems: (1) the carbon content is high, which increases the strength of the wire rod while reducing the plasticity of the steel, and the reduction of area is only 53-58%, which is not conducive to the production of cold heading parts with large deformation and is prone to cold heading cracking; (2) Mo and Cr alloy elements are added, which increases the production cost. SUMMARY

[0005] In order to solve the above problems, the present application discloses a non-quenched fastener wire rod and its production method and fastener, and the specific technical scheme is as follows:

[0006] A non-quenched fastener wire rod, 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.

[0007] The method for producing the above-mentioned non-quenched fastener wire rod adopts a production process of converter smelting-LF refining-bulb continuous casting-billet breaking-wire rod rolling-wire rod offline salt bath,

[0008] The wire rod rolling process: the opening rolling temperature is 930-960℃, and the finish rolling inlet temperature is 900-930℃; the wire rod drawing temperature is 880-900℃;

[0009] The wire rod offline salt bath process: the salt bath liquid temperature in the salt tank is 350-400℃, and the salt bath time is 180-205 seconds.

[0010] Further, the converter smelting process: converter tapping temperature 1600-1650℃, converter final slag basicity 3.5-4.0, ladle bottom argon blowing pressure 0.40-0.60MPa.

[0011] Further, the LF refining process: refining slag basicity 3.5-4.0, argon soft stirring time 15-20min.

[0012] Further, the bloom continuous casting process: continuous casting billet cross section specification 300mm×390mm, drawing speed 0.70±0.2m / min, two cold zone specific water consumption 0.42±0.2L / kg.

[0013] Further, the cogging process: the bloom is rolled into (140~160)mm×(140~160)mm square billet, bloom heating temperature 1180~1220℃, heating time 150-210min.

[0014] Further, the wire rod rolling process: square billet heating temperature 1040~1080℃, entry section roller speed 0.3~0.5m / s; Stelmor cooling line does not close the heat preservation cover, opens the first four air blowers, blower air volume 100%, the wire rod is collected into a coil through the coil collecting drum, and waits for offline salt bath.

[0015] Further, the wire rod offline salt bath process: the rolled wire rod is unwound clockwise and enters the heating furnace through the straightening roller, heating temperature 910~980℃, heating time 8-10min, furnace carbon potential 0.19±0.01%, wire rod unwinding speed 3.0~3.5m / min; the wire rod after heating is immersed in the salt bath liquid in the salt tank, and the salt bath liquid composition weight ratio is 40% KNO3 and 60% NaNO3.

[0016] The wire rod produced by the above method for producing the non-quenched fastener wire rod, the tensile strength of the wire rod is 1050~1250MPa, the reduction of area is 65~70%; the tensile strength fluctuation range of the wire rod is ≤20MPa.

[0017] Further, the wire rod is directly drawn after pickling and phosphating without softening or spheroidizing treatment, the tensile strength of the wire rod after drawing is 1250~1500MPa, the area reduction of the wire rod after drawing is 10~75%, the area reduction = [(wire rod cross-sectional area before drawing-wire rod cross-sectional area after drawing) / wire rod cross-sectional area before drawing]*100%.

[0018] The fastener produced by the wire rod cold heading has the performance of tensile strength ≥1250MPa, yield strength ≥1125MPa, hardness ≥39HRC, and meets the performance requirement of 12.9 grade fastener.

[0019] The beneficial effects of the present application are:

[0020] The present application adds B and Ti elements on the basis of designing the content of strengthening elements such as carbon, silicon and manganese, so that the steel has good hardenability, and meanwhile, the reasonable production process is matched, so that the obtained wire rod has the characteristics of high strength, good plasticity and excellent wire rod consistency. After drawing processing, the tensile strength of the wire rod is 1250-1500MPa, and the reduction of area is 55-65%; the part obtained by drawing processing and cold heading of the wire rod does not need quenching and tempering treatment, and can meet the requirement of 12.9 grade fastener, so that the production cost is effectively reduced and the environmental protection requirement is met.

[0021] The metallographic structure of the wire rod obtained by the present application is bainite, and the tensile strength and plasticity of the wire rod are obviously improved; the tensile strength of the wire rod is further improved by drawing, and the plasticity is good, so that the requirement of cold heading deformation can be met. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The metallographic structure of the wire rod obtained by the present application is bainite, and the tensile strength and plasticity of the wire rod are obviously improved; the tensile strength of the wire rod is further improved by drawing, and the plasticity is good, so that the requirement of cold heading deformation can be met.

[0023] Figure 2 The metallographic structure of the wire rod obtained by the present application is bainite, and the tensile strength and plasticity of the wire rod are obviously improved; the tensile strength of the wire rod is further improved by drawing, and the plasticity is good, so that the requirement of cold heading deformation can be met.

[0024] Figure 3 The metallographic structure of the wire rod obtained by the present application is bainite, and the tensile strength and plasticity of the wire rod are obviously improved; the tensile strength of the wire rod is further improved by drawing, and the plasticity is good, so that the requirement of cold heading deformation can be met.

[0025] Figure 4 The metallographic structure of the wire rod obtained by the present application is bainite, and the tensile strength and plasticity of the wire rod are obviously improved; the tensile strength of the wire rod is further improved by drawing, and the plasticity is good, so that the requirement of cold heading deformation can be met. DETAILED DESCRIPTION

[0026] The present application is further illustrated by the following examples: according to the following examples, the present application can be better understood. However, it is easy for those skilled in the art to understand that the specific material ratio, process conditions and results described in the examples are only used to illustrate the present application, and should not and will not limit the present application described in detail in the claims.

[0027] The application provides a wire rod for non-tempered fasteners, which has a chemical composition in mass percentage of 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.

[0028] The application improves the plasticity and cold heading performance of the wire rod by designing a lower carbon content and silicon content. In order to compensate for the loss of solid solution strengthening of carbon and silicon on the wire rod, a higher Mn content is designed; B element is added to improve the hardenability of the wire rod; Ti element is added to solidify nitrogen in the steel to form TiN and prevent the formation of BN, so that B fully plays a role in improving the hardenability.

[0029] C is the most basic and cheapest strengthening element in steel, but as the carbon content increases, the plasticity of the wire rod will deteriorate, reducing the cold heading performance of the steel. Therefore, the carbon content in the application is controlled at 0.18-0.24%.

[0030] Si is a strengthening element and a deoxidizing element in steel, but too much silicon will reduce the cold heading performance of the wire rod. The silicon content in the application is controlled at 0.15-0.25%.

[0031] Mn is a strengthening element in steel, which can improve the strength and hardenability of the steel, but too much manganese will reduce the plasticity of the steel. The manganese content in the application is controlled at 1.30-1.60%.

[0032] P and S are impurity elements in steel, which are segregated at the grain boundary to make the grain boundary brittle, thereby reducing the strength and plasticity of the steel; in addition, S and Mn elements generate MnS, which can reduce the solid solution strengthening effect of Mn. The phosphorus content in the application is controlled at 0.015% or less, and the sulfur content is controlled at 0.010% or less.

[0033] Cr is a strengthening element in steel, but too much Cr element can significantly improve the stability of austenite, leading to an extension of the bainite transformation time, which is not conducive to the production of wire rod in a salt bath. The chromium content in the application is controlled at Cr≤0.10%.

[0034] Mo can improve the strength and hardenability of the steel, but it can significantly extend the bainite transformation time, which is not conducive to the production of wire rod in a salt bath. The molybdenum content in the application is controlled at 0.03% or less.

[0035] Ti can form fine TiC and TiN in the steel, avoid B element and N forming BN in the steel, so that B element plays a role in improving the hardenability. But too high Ti will make TiN and TiC coarsen, which is not conducive to cold heading deformation. The titanium content is controlled at 0.05-0.10% in the application.

[0036] B can improve the hardenability of the steel to achieve the purpose of improving the strength, but excessive boron element will form "boron phase" at the grain boundary, reducing the plasticity of the steel. The boron content is controlled at 0.0010-0.0025% in the application.

[0037] Al is a deoxidizing element in the steel, which can effectively remove oxygen in the steel and improve the cleanliness of the steel. In addition, AlN can be formed with nitrogen to refine the grain. The aluminum content is controlled at 0.020-0.045% in the application.

[0038] N can cause the plasticity of the steel to deteriorate, affect the cold heading performance of the steel, and high nitrogen content can make AlN and TiN coarsen, which is not conducive to fine grain strengthening and cold heading deformation. The nitrogen content is controlled at less than 0.007% in the application.

[0039] In the production process, the heating temperature of the wire rod rolling is 1040-1080℃, the opening rolling temperature is 930-960℃, the finish rolling inlet temperature is 900-930℃, the wire drawing temperature is 880-900℃, the entry section roller speed is 0.3-0.5m / s, the Stelmor cooling line does not close the heat preservation cover, and the first four fans are opened, and the fan air volume is 100%.

[0040] The heating temperature of the offline salt bath is 910-980℃, the wire drawing speed is 3.0-3.5m / min, the salt bath liquid temperature in the salt bath is 350-400℃, and the salt bath time is 180-205 seconds.

[0041] The cross section specification of the continuous casting billet in the bloom continuous casting process is 300mm×390mm, and the bloom needs to be broken down to (140-160)mm×(140-160)mm square billet before wire rod rolling, and the breaking down heating temperature is 1180-1220℃.

[0042] Example 1

[0043] The embodiment provides a production method of a wire rod for non-quenched fasteners, which adopts a production process of converter smelting-LF refining-bloom continuous casting-breaking down-wire rod rolling-wire rod offline salt bath.

[0044] The converter tapping temperature is 1600℃, the converter final slag basicity is 3.8, and the ladle bottom argon blowing pressure is 0.5MPa. The LF refining slag basicity is 3.7, and the argon soft stirring time is 15min. The bloom continuous casting is adopted, the continuous casting blank cross section size is 300mm×390mm, the pulling speed is 0.70m / min, and the two cooling area specific water consumption is 0.42L / kg.

[0045] The bloom is heated and rolled into a bloom, the bloom heating temperature is 1180℃, the heating time is 160min, and the bloom cross section is 140mm×140mm. The bloom is heated and rolled into a rod, the rod is collected into a coil through wire drawing, Stelmor cooling and coil collecting drum. The bloom heating temperature is 1040℃, the rolling starting temperature is 930℃, and the finishing rolling inlet temperature is 900℃; the rod wire drawing temperature is 880℃, and the inlet section roller speed is 0.5m / s; the Stelmor cooling line does not close the heat preservation cover, the first four air blowers are opened, and the air blower air volume is 100%. The rod is collected into a coil through the coil collecting drum, and waits for off-line salt bath.

[0046] The obtained rolling coil is put on line clockwise, a single rod passes through the straightening roller to enter the heating furnace, the heating temperature is 910℃, the heating time is 10min, the carbon potential in the furnace is 0.20%, and the rod putting on line speed is 3.0m / min; the rod passes through the heating to enter the salt bath, the salt bath liquid temperature in the salt bath is 350℃, and the salt bath time is 205s.

[0047] Comparative Example 1

[0048] The rod preparation process is consistent with that of Example 1. The rod is collected into a coil through the coil collecting drum, and waits for off-line salt bath.

[0049] The obtained rolling coil is put on line clockwise, a single rod passes through the straightening roller to enter the heating furnace, the heating temperature is 890℃, the heating time is 5min, the carbon potential in the furnace is 0.15%, and the rod putting on line speed is 6m / min; the rod passes through the heating to enter the salt bath, the salt bath liquid temperature in the salt bath is 410℃, and the salt bath time is 100s.

[0050] Example 2

[0051] The example provides a production method of a non-tempered fastener rod, adopting a production process of converter smelting-LF refining-bloom continuous casting-blooming-rod rolling-off-line salt bath.

[0052] The converter tapping temperature is 1630℃, the converter final slag basicity is 3.5, and the ladle bottom argon blowing pressure is 0.4MPa. The LF refining slag basicity is 3.5, and the argon soft stirring time is 18min. The bloom continuous casting is adopted, the continuous casting blank cross section size is 300mm×390mm, the pulling speed is 0.68m / min, and the two cooling area specific water consumption is 0.44L / kg.

[0053] The bloom is heated and rolled into a bloom, the heating temperature of the bloom is 1200℃, the heating time is 150 min, and the cross section of the bloom is 150mmx150mm. The bloom is heated and rolled into a wire rod, the wire rod is collected into a coil through wire drawing, Stelmor cooling and collecting drum. The heating temperature of the bloom is 1060℃, the open rolling temperature is 945℃, and the finish rolling inlet temperature is 915℃; the wire rod wire drawing temperature is 890℃, and the entry section roller speed is 0.4m / s; the Stelmor cooling line does not close the heat preservation cover, and the first four fans are opened, and the fan air volume is 100%. The wire rod is collected into a coil through the collecting drum, and waits for offline salt bath.

[0054] The obtained rolling coil is put on line clockwise, a single wire rod enters the heating furnace through the straightening roller, the heating temperature is 950℃, the heating time is 9min, the carbon potential in the furnace is 0.19%, and the wire rod unwinding speed is 3.2m / min; the wire rod enters the salt tank after heating, the temperature of the salt bath liquid in the salt tank is 380℃, and the salt bath time is 192 seconds.

[0055] Comparative Example 2

[0056] The preparation process of the wire rod is consistent with that of Example 2. The wire rod is collected into a coil through the collecting drum, and waits for offline salt bath.

[0057] The obtained rolling coil is put on line clockwise, a single wire rod enters the heating furnace through the straightening roller, the heating temperature is 900℃, the heating time is 7min, the carbon potential in the furnace is 0.15%, and the wire rod unwinding speed is 4.3m / min; the wire rod enters the salt tank after heating, the temperature of the salt bath liquid in the salt tank is 420℃, and the salt bath time is 140 seconds.

[0058] Example 3

[0059] The present embodiment provides a production method of a non-quenched fastener wire rod, which adopts a production process of converter smelting-LF refining-bloom continuous casting-breaking-wire rod rolling-wire rod offline salt bath.

[0060] The converter tapping temperature is 1650℃, the converter final slag basicity is 4.0, and the ladle bottom argon blowing pressure is 0.6MPa. The LF refining slag basicity is 4.0, and the argon soft stirring time is 20min. The bloom continuous casting is adopted, the cross section size of the continuous casting billet is 300mmx390mm, the withdrawal speed is 0.72m / min, and the specific water consumption of the secondary cooling zone is 0.40L / kg.

[0061] The bloom is heated and rolled into a bloom, the heating temperature of the bloom is 1220℃, the heating time is 210min, and the cross section of the bloom is 160mmx160mm. The bloom is heated and rolled into a wire rod, the wire rod is collected into a coil through wire drawing, Stelmor cooling and a collecting reel. The heating temperature of the bloom is 1080℃, the starting rolling temperature is 960℃, and the entry temperature of the finishing rolling is 930℃; the wire drawing temperature of the wire rod is 900℃, and the entry speed of the entry section is 0.3m / s; the Stelmor cooling line is not closed, the first four fans are opened, and the air volume of the fans is 100%. The wire rod is collected into a coil through the collecting reel, and waits for offline salt bath.

[0062] The obtained rolling coil is unwound clockwise, a single wire rod enters the heating furnace through a straightening roller, the heating temperature is 980℃, the heating time is 8min, the carbon potential in the furnace is 0.18%, and the wire rod unwinding speed is 3.5m / min; the wire rod enters the salt tank after heating, the temperature of the salt bath liquid in the salt tank is 400℃, and the salt bath time is 180s.

[0063] Comparative Example 3

[0064] The preparation process of the wire rod is consistent with that of Example 3. The wire rod is collected into a coil through a collecting reel, and no subsequent salt bath process is performed.

[0065] Comparative Example 4 (SCM435)

[0066] A 12mm specification SCM435 wire rod is produced by adopting converter smelting-LF refining-bloom continuous casting-breaking-wire rod rolling. The converter tapping temperature is 1620℃, the converter final slag basicity is 3.2, and the ladle bottom argon blowing pressure is 0.5MPa. The LF refining slag basicity is 3.8, and the argon soft stirring time is 12min. The bloom continuous casting is adopted, the cross section specification of the continuous casting billet is 300mmx390mm, the withdrawal speed is 0.75m / min, and the specific water consumption of the secondary cooling zone is 0.38L / kg.

[0067] The bloom is heated and rolled into a bloom, the heating temperature of the bloom is 1220℃, the heating time is 210min, and the cross section of the bloom is 160mmx160mm. The bloom is heated and rolled into a wire rod, the wire rod is collected into a coil through wire drawing, Stelmor cooling and a collecting reel. The heating temperature of the bloom is 1080℃, the starting rolling temperature is 960℃, and the entry temperature of the finishing rolling is 870℃; the wire drawing temperature of the wire rod is 880℃, and the entry speed of the entry section is 0.25m / s; the Stelmor cooling closes the heat preservation cover and the fan. The wire rod is collected into a coil through the collecting reel, and no subsequent salt bath process is performed.

[0068] The SCM435 wire rod obtained in Comparative Example 4 is a commonly used 12.9 grade fastener wire rod, and the wire rod needs to be subjected to drawing-spheroidizing annealing-drawing-cold heading-heat treatment to obtain a fastener that can meet the technical requirements of the 12.9 grade fastener.

[0069] The chemical compositions of the wire rods obtained in Examples 1-3 and Comparative Examples 1-4 are shown in Table 1.

[0070] Table 1

[0071]

[0072] Table 2 shows the metallographic structures 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 bainite. 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 fluctuation range of the tensile strength of the same circle is 15-20 MPa. The metallographic structure of the wire rods obtained in Comparative Examples 1-2 is bainite + 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 bainite + martensite. The ferrite structure appears in the metallographic structure of the wire rods obtained in Comparative Examples 1-2 due to the short salt bath time or high salt bath temperature, which leads to the decrease of the tensile strength of the wire rods and does not meet the requirements of the wire rods obtained in the present application. The metallographic structure and mechanical properties of the wire rods obtained in Comparative Examples 3-4 do not meet the requirements of the present application.

[0073] Table 2

[0074]

[0075] The wire rods obtained in Examples 1-3 and Comparative Example 1-3 are directly drawn; the wire rod obtained in Comparative Example 4 has poor plasticity and cannot be directly drawn to achieve a reduction of 40%, and needs to be drawn, spheroidizing annealed and drawn. As shown in Table 3, the tensile strength of the wire rods obtained in Examples 1-3 after drawing is 1250-1500 MPa, and the reduction of area is 55-65%. The tensile strength of the wire rods obtained in Comparative Examples 1-2 after drawing is 1150-1180 MPa, and the reduction of area is 67-68%. The tensile strength of the wire rods obtained in Comparative Examples 1-2 after drawing is lower than the requirements of the present application. The tensile strength of the wire rod obtained in Comparative Example 3 after drawing is 750 MPa, and the reduction of area is 62%. The tensile strength of the wire rod obtained in Comparative Example 3 after drawing is lower than the requirements of the present application. The tensile strength of the wire rod obtained in Comparative Example 4 after drawing, spheroidizing annealing and drawing is also lower than the requirements of the present application.

[0076] The wire rods obtained in Examples 1-3 and Comparative Example 1-2 are drawn and cold headed into fasteners, and the mechanical properties of the fasteners are measured. The wire rods obtained in Comparative Examples 3-4 are drawn and cold headed into fasteners, and then the fasteners are quenched and tempered. The quenching and tempering process is as follows: 850℃, holding for 30 min, oil quenching; tempering temperature is 480℃, and tempering time is 120 min. The mechanical properties of the fasteners obtained from the wire rods of Comparative Examples 3-4 after quenching and tempering are detected. The detection results are shown in Table 4.

[0077] Table 3

[0078]

[0079] Table 4

[0080]

[0081] The fastener produced by drawing, cold heading of the wire rod of Examples 1-3 has a tensile strength of ≥1250 MPa, a yield strength of ≥1125 MPa, and a hardness of ≥39 HRC, which is superior to the mechanical properties of the fastener produced by drawing-spheroidizing annealing-drawing-cold heading-tempering of the wire rod of Comparative Example 4, and the mechanical properties of the fastener produced by drawing-cold heading-tempering of the wire rod of Comparative Example 3.

[0082] As will be understood by those familiar with the art, the terms used herein have meanings commonly used in the art unless otherwise defined. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0083] Based on the above ideal embodiments according to the present application, the relevant personnel can make various changes and modifications without deviating from the technical idea of the present application according to the above description. The technical scope of the present application is not limited to the contents of the specification, and must be determined by the scope of the claims.

Claims

1. A method of producing wire rod for non-quenched fasteners, characterized in that, The chemical composition of the non-heat-treated fastener wire rod, 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; The specific method for producing wire rods for non-quenched and tempered fasteners is a process of converter smelting - LF refining - large billet continuous casting - billet preparation - wire rod rolling - offline salt bath production of wire rods. 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.

2. The method of producing a wire rod for non-quenched and tempered fasteners according to claim 1, characterized by, The converter smelting process is as follows: the converter tapping temperature is 1600-1650℃, the converter final slag basicity is 3.5-4.0, and the bottom blowing argon pressure of the ladle is 0.40-0.60MPa.

3. The method of producing a wire rod for non-quenched and tempered fasteners according to claim 1, characterized by, The LF refining process involves a refining slag basicity of 3.5-4.0 and an argon-assisted soft stirring time of 15-20 minutes.

4. The method of producing a wire rod for non-heat-treated fasteners according to claim 1, characterized by, The large billet continuous casting process has the following characteristics: 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.

5. The method of producing a wire rod for non-heat-treated fasteners according to claim 4, characterized by, The billet rolling process involves rolling a large square billet into a (140~160) mm × (140~160) mm square billet. The heating temperature of the large square billet is 1180~1220℃, and the heating time is 150-210 min.

6. The method of producing a wire rod for non-heat-treated fasteners according to claim 5, characterized by, The wire rod rolling process is as follows: 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, the first four fans are turned on, the fan air volume is 100%, and the wire rod is collected into coils by the collecting drum and waits for offline salt bath.

7. The method of producing a wire rod for non-heat-treated fasteners according to claim 6, characterized by, 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 at a temperature of 910-980℃ for 8-10 minutes, with a carbon potential of 0.19±0.01% and a wire rod feeding speed of 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.

8. Wire rod produced by the method of any one of claims 1 to 7, characterized in that The wire rod has a tensile strength of 1050~1250MPa and a reduction of area of ​​65~70%; the tensile strength of the same coil of wire rod fluctuates within a range of ≤20MPa.

9. The rod as claimed in claim 8, characterized in that 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%.

10. Fastener produced from the wire rod cold upsetting according to claim 9, 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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