Annealing-free cold heading steel for large deformation workpieces and its preparation method and application

Abstract

The present invention discloses an annealing-free cold heading steel for workpieces with large deformation, a preparation method and an application thereof, and relates to the technical field of steel production. The area reduction rate of the cold heading wire in the cold working deformation process is ≥70%; the pearlite content in the metallographic structure of the cold heading wire is ≤5wt%, the hardness is 48-55HRB, and the strength-to-yield ratio is 0.60-0.75. By controlling the low pearlite content, low hardness and low yield-to-strength ratio of the cold heading wire, the smooth production of workpieces with large deformation (area reduction rate ≥70%) in the cold heading process is achieved, and no annealing treatment is required in the project, no additional energy consumption is generated, and the production cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of steel production, and in particular to an annealing-free cold heading steel for a workpiece with a large deformation amount, and a preparation method and application thereof. Background Art

[0002] Cold heading steel is a kind of steel suitable for cold heading process manufacturing. It mainly produces various standard parts, such as rivets, bolts, pins and nuts, as well as non-standard special-shaped parts, by utilizing the plastic deformation of metal at room temperature. It is widely used in industries such as automobiles, shipbuilding, equipment manufacturing, electronics, home appliances, bicycles, tools, light steel structures and construction, and has wide application value.

[0003] The process of producing various parts by cold heading generally uses cold heading steel wire, which is deformed by cold drawing, cold drawing or cold rolling to form a workpiece of corresponding shape. The greater the deformation of the cold heading process, the higher the performance requirements of the wire. The existing cold heading wire has a very large deformation amount and a fast deformation speed during the deformation process of the cold heading process, so it is easy to produce a large work hardening phenomenon. It often needs to be annealed before it can be smoothly processed and formed. Otherwise, it is easy to crack and mismatch the structure and performance during the cold heading process. However, annealing increases the energy consumption of the product production process and increases production costs.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The object of the present invention is to provide an annealing-free cold heading steel for a workpiece with a large deformation amount, and a preparation method and application thereof.

[0006] The present invention is achieved in that:

[0007] In the first aspect, the present invention provides an annealing-free cold heading steel for workpieces with large deformation, wherein the surface reduction rate of the cold heading wire during the cold working deformation process is ≥70%; the pearlite content in the metallographic structure of the cold heading wire is ≤5wt%, the hardness is 48-55HRB, and the strength-to-yield ratio is 0.60-0.75.

[0008] In a second aspect, the present invention provides a method for preparing cold heading steel as described in any of the aforementioned embodiments, comprising smelting raw materials in proportion to obtain molten steel, then continuously casting the molten steel to obtain a steel billet, and then rolling the steel billet to obtain a cold heading wire.

[0009] In a third aspect, the present invention provides a use of a cold heading steel as in any of the aforementioned embodiments or a cold heading steel prepared by a preparation method as in any of the aforementioned embodiments in preparing a workpiece with a reduction rate of ≥70% during a cold working deformation process.

[0010] The present invention has the following beneficial effects:

[0011] The present invention provides an annealing-free cold heading steel for workpieces with large deformation, a preparation method and an application thereof. By controlling the low pearlite content, low hardness and low yield strength ratio of the cold heading wire, the smooth production of workpieces with large deformation (reduction of area ≥ 70%) in the cold heading process is achieved, and no annealing treatment is required in the project, no additional energy consumption is generated, and the production cost is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0013] Figure 1 A metallographic image of the edge region of the annealing-free cold heading steel for a workpiece with a large deformation amount provided in Example 1 of the present invention;

[0014] Figure 2 A metallographic image of the central area of ​​the annealing-free cold heading steel for a workpiece with a large deformation amount provided in Example 1 of the present invention;

[0015] Figure 3 The metallographic diagram of the large deformation workpiece provided in Example 1 of the present invention after cold working of the annealing-free cold heading steel;

[0016] Figure 4 This is a metallographic diagram of a workpiece with large deformation after cold working with annealing-free cold heading steel provided in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0018] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0019] Cold heading steel is a general term for steel suitable for cold heading process manufacturing, but according to its different forms during the processing, it can generally be divided into cold heading wire and cold heading workpiece. Cold heading wire is a product obtained by smelting, continuous casting and rolling of steel, while cold heading workpiece is a variety of standard workpieces or non-standard workpieces formed by cold heading wire through cold heading process, such as screws, pins and nuts.

[0020] Therefore, it can be understood that the chemical composition of cold heading wire and cold heading workpiece should be the same. The two are only different in morphological structure, and the organizational properties are hereditary and continuous.

[0021] In order to prepare cold-forged workpieces with large deformation from existing cold-forged wire, it is usually necessary to anneal the cold-forged wire to meet the processing requirements of the cold-forging process with large deformation. However, the annealing process will increase energy consumption and thus increase production costs. In order to solve the above problems, the inventors propose the following solution.

[0022] In the first aspect, the present invention provides an annealing-free cold heading steel for workpieces with large deformation, wherein the surface reduction rate of the cold heading wire during the cold working deformation process is ≥70%; the pearlite content in the metallographic structure of the cold heading wire is ≤5wt%, the hardness is 48-55HRB, and the strength-to-yield ratio is 0.60-0.75.

[0023] The cold heading steel provided by the present invention can meet the above-mentioned performance requirements without annealing treatment. By controlling the low pearlite content, low hardness and low yield strength ratio of the cold heading wire, the smooth production of workpieces with large deformation (reduction rate ≥ 70%) in the cold heading process is achieved. In addition, no annealing treatment is required in the project, no additional energy consumption is required, and the production cost is reduced.

[0024] The above-mentioned annealing-free cold heading wire should also meet the following requirements to ensure the smooth progress of the cold heading process.

[0025] In an optional embodiment, the DS inclusion of the cold-headed wire is ≤1.0, and the grain size of the ferrite is 10-30 μm. The evaluation standard for DS inclusion is GB / T 10561-2005.

[0026] By controlling the inclusions of the cold heading wire within the above range, the cold heading steel provided by the present invention has a higher purity, which is beneficial to ensuring the quality of the workpiece obtained by processing and deforming the cold heading wire during the cold heading process.

[0027] By controlling the ferrite grain size within the above range, the uniformity of plastic deformation of cold heading wire can be ensured, while avoiding the increase of deformation resistance caused by too fine grain size. It is conducive to ensuring the smooth processing and deformation of cold heading wire, without the need for annealing of cold heading wire, ensuring the product performance of cold heading workpiece while reducing production costs and energy consumption.

[0028] Preferably, the aspect ratio of the cross section of the cold heading wire after cold working deformation is ≥4.

[0029] Preferably, the diameter of the cold-headed wire is 5.5-20 mm.

[0030] In some embodiments, the diameter of the cold heading wire and the aspect ratio of the cross section after deformation are controlled to ensure that the cold heading wire meets the large deformation standard after deformation. It should be noted that the cold heading steel provided by the present invention can be applied to the cold heading process with large deformation, and therefore, it is also applicable to the cold heading process with small deformation that has relatively low performance requirements for the cold heading steel.

[0031] In an optional embodiment, the elemental composition of the cold heading steel includes, by mass percentage, C: 0.01-0.08wt%, Si: 0.01-0.05wt%, Mn: 0.1-0.5wt%, Al: 0.015-0.045wt%, Cu≤0.20wt%, As≤0.040wt%, Sn≤0.028wt%, P≤0.025wt%, S≤0.015wt% and N≤0.005wt%, with the balance being Fe and unavoidable impurities.

[0032] Preferably, the Cu, As and Sn elements in the cold heading steel satisfy: Cu+3As+8Sn≤0.22%.

[0033] By controlling the element composition of the cold heading steel within the above range, it is beneficial to ensure the excellent microstructure and performance of the cold heading wire, meet the smooth progress of the large deformation cold heading process, and at the same time minimize the impurity inclusions in the cold heading steel.

[0034] In a second aspect, the present invention provides a method for preparing cold heading steel as described in any of the aforementioned embodiments, comprising smelting raw materials in proportion to obtain molten steel, then continuously casting the molten steel to obtain a steel billet, and then rolling the steel billet to obtain a cold heading wire.

[0035] In an alternative embodiment, the raw materials include molten iron and scrap steel.

[0036] Preferably, in order to ensure that the element composition of the cold heading steel meets the above range and thus ensure the overall performance of the cold heading steel, the element composition of the molten iron and scrap steel both meet the following requirements: Cu≤0.04wt%, As≤0.03wt%, Sn≤0.02wt%.

[0037] In an optional embodiment, the smelting process includes primary smelting and refining. The primary smelting process includes smelting molten iron and scrap steel to obtain molten steel, while removing some impurities in the molten steel to reduce the difficulty of subsequent refining.

[0038] Refining includes adding slag to the molten steel obtained from primary refining for refining, and the time of adding slag includes the steel-out process after the primary refining is completed and after the molten steel arrives at the refining furnace. Preferably, the time of adding slag after the molten steel arrives at the refining furnace is generally the initial stage of refining, that is, after the molten steel is completely in the refining furnace, before the start of refining and / or when the refining starts.

[0039] Preferably, the mass ratio of the slag added during the steel tapping process to the mass ratio of the slag added after the molten steel arrives at the refining furnace is 2.5 to 5. Adding slag during the steel tapping process can promote early slagging, thereby improving the slag's ability to adsorb inclusions, which is conducive to obtaining cold heading steel with less impurities and high purity.

[0040] Preferably, the slag is added during the steel tapping process when the steel tapping amount reaches 40-60% of the total steel melt mass. For example, when 1 / 2 of the steel is tapped, slag can be added to the steel melt.

[0041] Preferably, in order to control the contents of various components in the molten steel obtained by refining, especially the contents of Si and N elements, and avoid excessive contents of the two elements, the refining time is controlled to be 20 to 40 minutes.

[0042] Preferably, in order to ensure that the composition of the cold heading steel is controlled within the required range, and at the same time ensure that the performance and impurity inclusions of the cold heading steel also meet the composite requirements, if the ladle used in the refining process has previously produced steels with Si content ≥ 0.6% and high-alloy steels, such as steels with Cr and Mo content ≥ 1%, then the ladle needs to strengthen the removal of residual steel and slag to reduce the residual components in the ladle on the composition fluctuation and performance impact of the cold heading steel.

[0043] In an optional embodiment, during the continuous casting process, the superheat of the molten steel before solidification is 15-40° C., the continuous casting adopts a constant drawing speed, and the fluctuation of the molten steel level in the crystallizer is ≤3 mm.

[0044] By controlling the superheat and liquid level fluctuation range during the continuous casting process, the microstructure of the steel billet obtained by continuous casting is made more stable, which is conducive to the smooth progress of the subsequent rolling process.

[0045] In an optional embodiment, the steel billet obtained by continuous casting is heated before rolling, and the heating process ensures that the temperature of each part of the steel billet is uniform.

[0046] Since the head of the billet is rolled first and then the tail of the billet is rolled in sequence before it is rolled after being heated, the tail of the billet has a longer waiting time for rolling, which may easily lead to different temperatures between the head and tail of the billet during rolling, resulting in poor structural uniformity of the billet. Therefore, preferably, the temperature of the tail of the heated billet is 15 to 25°C higher than the temperature of the head.

[0047] In an optional embodiment, during the rolling process, the rough rolling inlet temperature is 920-1020°C, the finishing rolling inlet temperature is 900-950°C, and the wire drawing temperature is 850-900°C; the cooling rate of the cold-headed wire obtained after wire drawing is 0.1-0.5°C / s.

[0048] By controlling the parameters of the rolling process within the above range, it is beneficial to ensure that the metallographic structure of the cold heading wire obtained by rolling is mainly composed of ferrite, contains a very small amount of pearlite (≤5wt%), and the ferrite grains are between 10 and 30μm. The organizational structure is uniform and more suitable for cold heading processing technology with large deformation. It also saves the annealing step of the cold heading process and reduces processing costs.

[0049] In a third aspect, the present invention provides a use of a cold heading steel as in any of the aforementioned embodiments or a cold heading steel prepared by a preparation method as in any of the aforementioned embodiments in preparing a workpiece with a reduction rate of ≥70% during a cold working deformation process.

[0050] Example 1

[0051] The present embodiment provides an annealing-free cold heading steel for a workpiece with a large deformation amount, wherein the element composition thereof, by mass percentage, includes C: 0.04wt%, Si: 0.02wt%, Mn: 0.25wt%, Al: 0.025wt%, Cu: 0.02%, As: 0.004%, Sn: 0.004%, P: 0.008%, S: 0.002% and N: 0.0035wt%, and the remainder is Fe and unavoidable impurities.

[0052] This embodiment also provides a method for preparing the above-mentioned annealing-free cold heading steel for large deformation workpieces, comprising the following steps:

[0053] S01. Smelting

[0054] The molten iron and scrap steel are charged into a furnace for primary smelting to obtain molten steel. The element composition of the molten iron satisfies: Cu: 0.02wt%, As: 0.002wt% and Sn: 0.002wt%. The element composition of the scrap steel satisfies: Cu: 0.01wt%, As: 0.003wt% and Sn: 0.001wt%.

[0055] After the initial refining is completed, steel is tapped. When 1 / 2 of the steel is tapped, 800 kg of slag is added to the molten steel. After the molten steel is completely in the refining furnace, another 200 kg of slag is added and refining begins. The refining time is 30 minutes. After the refining is completed, refined molten steel is obtained. The composition of the refined molten steel meets the composition requirements of cold heading steel.

[0056] S02, continuous casting

[0057] The refined molten steel obtained in step S01 is continuously cast to obtain a steel billet. During the continuous casting process, the superheat of the molten steel before solidification is controlled to be 25°C, the continuous casting adopts a constant drawing speed of 1.2m / min, and the fluctuation of the molten steel level in the crystallizer is ±1mm.

[0058] S03, rolling

[0059] The billet is heated and then rolled to obtain a cold headed wire rod. The temperature of the tail of the heated billet is 20°C higher than that of the head.

[0060] During the rolling process, the rough rolling inlet temperature is 950°C, the finishing rolling inlet temperature is 920°C, and the wire drawing temperature is 880°C; the cooling rate of the cold-headed wire obtained after wire drawing is 0.2°C / s, and the diameter of the cold-headed wire obtained by rolling is 6.5mm.

[0061] The edge area and the center area of ​​the cold-headed wire prepared in this embodiment were respectively corroded with nitric acid alcohol solution and then observed under a metallographic microscope to obtain the following Figure 1 and Figure 2 The results are shown. Figure 1 and Figure 2 It can be seen that the cold-headed wire obtained in this embodiment has uniform structure at all places, and the metallographic picture shows mainly ferrite, the pearlite content is 2.3%, the inclusion DS rating is 0.5, and the surface reduction rate of the cold-headed wire in the annealing-free deformation process reaches 78.3%.

[0062] Example 2

[0063] The present embodiment provides an annealing-free cold heading steel for a workpiece with a large deformation amount, wherein the element composition thereof, by mass percentage, includes C: 0.04wt%, Si: 0.02wt%, Mn: 0.22wt%, Al: 0.025wt%, Cu: 0.02%, As: 0.004%, Sn: 0.004%, P: 0.008%, S: 0.002% and N: 0.0035wt%, and the remainder is Fe and unavoidable impurities.

[0064] This embodiment also provides a method for preparing the above-mentioned annealing-free cold heading steel for large deformation workpieces, comprising the following steps:

[0065] S01. Smelting

[0066] The molten iron and scrap steel are charged into a furnace for primary smelting to obtain molten steel. The element composition of the molten iron satisfies: Cu: 0.02wt%, As: 0.002wt% and Sn: 0.002wt%. The element composition of the scrap steel satisfies: Cu: 0.01wt%, As: 0.003wt% and Sn: 0.001wt%.

[0067] After the initial refining is completed, steel is tapped. When 1 / 2 of the steel is tapped, 820 kg of slag is added to the molten steel. After the molten steel is completely in the refining furnace, another 180 kg of slag is added and refining begins. The refining time is 25 minutes. After the refining is completed, refined molten steel is obtained. The composition of the refined molten steel meets the composition requirements of cold heading steel.

[0068] S02, continuous casting

[0069] The refined molten steel obtained in step S01 is continuously cast to obtain a steel billet. During the continuous casting process, the superheat of the molten steel before solidification is controlled to be 25°C, the continuous casting adopts a constant drawing speed of 1.3m / min, and the fluctuation of the molten steel level in the crystallizer is ≤3mm.

[0070] S03, rolling

[0071] The billet is heated and then rolled to obtain a cold headed wire rod. The temperature of the tail of the heated billet is 15°C higher than the temperature of the head.

[0072] During the rolling process, the rough rolling inlet temperature was 980°C, the finishing rolling inlet temperature was 950°C, and the wire drawing temperature was 870°C; the cooling rate of the cold-headed wire obtained after wire drawing was 0.2°C / s, and the diameter of the cold-headed wire obtained by rolling was 7.5mm.

[0073] The cold-headed wire obtained in this embodiment has uniform structure at all places, mainly ferrite, pearlite content is 2.1%, DS inclusion rating is 0.5, the average grain size is 25 μm, and the area reduction rate in annealing-free cold working is 79.2%.

[0074] Comparative Example 1

[0075] This comparative example provides a cold heading steel, whose element composition and preparation method are similar to those of Example 1, except that the refining time of step S01 is 80 min, resulting in a Si content of 0.07 wt % in the cold heading steel provided in this comparative example.

[0076] Comparative Example 2

[0077] This comparative example provides a cold heading steel, whose elemental composition and preparation method are similar to those of Example 1, with the only difference being step S01. After the primary refining is completed, steel is tapped, and only 200 kg of slag is added to the molten steel when 1 / 2 of the steel is tapped. After the molten steel is completely in the refining furnace, 800 kg of slag is added and refining begins, resulting in atmospheric stirring and slag melting during the refining process, violent slag-steel reaction, and increased inclusion size.

[0078] After testing, the DS rating of the cold-headed wire obtained in this comparative example reaches 2.0, and the surface reduction rate of the annealing-free cold working is 50%.

[0079] Comparative Example 3

[0080] This comparative example provides a cold heading steel, whose elemental composition and smelting method are similar to those of Example 1, and the only difference is that in the S02 step, the superheat of the molten steel before solidification is 40°C, and there is a certain segregation in the core of the steel billet.

[0081] After testing, the inclusion rating of the cold-headed wire obtained in this comparative example is DS2.0, and the surface reduction rate of the cold working without annealing is 45%.

[0082] Comparative Example 4

[0083] This comparative example provides a cold heading steel, whose element composition and smelting and continuous casting methods are similar to those of Example 1, and the only difference is that in step S03, the finishing rolling inlet temperature is 850°C.

[0084] According to the test, the surface reduction rate of the cold heading wire obtained in this comparative example without annealing cold working is 62%.

[0085] Test Example 1

[0086] The cold-headed wires prepared in Examples 1 to 2 and Comparative Examples 1 to 4 were subjected to microstructure and performance analysis. The analysis used cross-sections to prepare metallographic samples, and the proportions of each phase were statistically analyzed after corrosion, and the inclusions were rated, and the results shown in Table 1 were obtained.

[0087] Table 1 Organization properties and inclusion rating of cold heading steel

[0088]

[0089]

[0090] The cold-headed wires prepared in Examples 1 to 2 and Comparative Examples 1 to 4 were subjected to tensile mechanical property tests at room temperature, and the results shown in Table 2 were obtained.

[0091] Table 2 Mechanical properties of cold heading steel

[0092] Tensile strength(MPa) Yield strength(MPa) Sectional shrinkage (%) Yield strength ratio (%) Example 1 333.3 213.0 78.3 0.64 Example 2 329.5 211.2 79.2 0.64 Comparative Example 1 340.8 257.6 69.5 0.76 Comparative Example 2 310.2 201.5 50.1 0.65 Comparative Example 3 305.2 201.5 45.1 0.65 Comparative Example 4 340.2 261.2 62.2 0.77

[0093] It can be seen from Table 1 and Table 2 that the metallographic structure of the cold heading steel provided by the embodiment of the present invention is mainly ferrite, and contains a very small amount of pearlite. While ensuring that it has a certain strength, the yield strength ratio is moderate, the cross-sectional shrinkage rate is high, and it can meet the large deformation requirements of the cold heading process. However, due to the increase in refining time in Comparative Example 1, the Si content in the molten steel increases, and exists in the ferrite in the form of solid solution, the tensile strength increases significantly, and the cross-sectional shrinkage rate decreases. Due to the violent reaction of slag steel in the refining process and the high DS rating of inclusions in Comparative Example 2, the cold working reduction rate is greatly reduced. Due to the high overheating of continuous casting in Comparative Example 3, there is a certain segregation in the core of the billet, the pearlite content increases, and the inclusion rating is DS2.0, and the reduction in cold working reduction rate is further increased. Comparative Example 4 adopts low-temperature rolling, the pearlite content increases slightly, the strength increases, and the cross-sectional shrinkage rate decreases.

[0094] Test Example 2

[0095] The cold-forged wires prepared in Examples 1 to 2 and Comparative Examples 1 to 4 were processed by the same cold-forging process to prepare cold-worked workpieces, and the processing conditions were recorded as shown in Table 3.

[0096] Among them, the main parameters of the cold heading process are as follows: the cold working area reduction rate is ≥70%, and the aspect ratio of the cross section after cold working deformation is ≥4.

[0097] Table 3 Cold working properties of cold heading steel

[0098] Annealing conditions Processing Example 1 no Uncracked Example 2 no Uncracked Comparative Example 1 no The overall structure is hard and cracked Comparative Example 2 no The deformation of the inclusions and the steel matrix is ​​inconsistent, forming holes and causing cracks Comparative Example 3 no Inclusions and organization aggregation work together to cause cracking Comparative Example 4 no Cracking

[0099] It can be seen from Table 3 that the cold heading steel provided by the embodiment of the invention can meet the production requirements of the cold heading process with a large deformation amount. After cold working, the structure is uniformly elongated and there are fewer hard knots in the structure. Figure 3 As shown, during the cold heading process, no annealing operation is required, and the obtained workpiece is of excellent quality without cracking. However, due to the increase in refining time in Comparative Example 1, the Si content in the molten steel increases, so the cold heading wire obtained has more hard knots in the structure after cold working, such as Figure 4 As shown, cracking occurs due to excessive hardness of the core during continued drawing, making it difficult to meet the cold heading process requirements for large deformation. In Comparative Example 2, due to the violent reaction of slag steel during the refining process and the high DS rating of inclusions, the deformation of the inclusions and the matrix during cold working is inconsistent, forming holes and causing cracking. In Comparative Example 3, due to the high overheating of continuous casting, there is a certain segregation in the core of the billet, resulting in cracking during cold working. Comparative Example 4 uses low-temperature rolling, which slightly increases the pearlite content and strength, and cracking occurs during cold working.

[0100] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An annealing-free cold heading steel for workpieces with large deformation, characterized in that: The area reduction rate of the cold heading wire in the cold working deformation process is ≥70%; the pearlite content in the metallographic structure of the cold heading wire is ≤5wt%, the hardness is 48-55HRB, and the yield strength ratio is 0.60-0.

75.

2. The cold heading steel according to claim 1, characterized in that: The DS inclusion of the cold heading wire is ≤1.0, and the grain size of the ferrite is 10-30 μm; Preferably, the aspect ratio of the cross section of the cold heading wire after cold working deformation is ≥4; Preferably, the diameter of the cold-headed wire is 5.5-20 mm.

3. The cold heading steel according to claim 1, characterized in that: The element composition of the cold heading steel includes, by mass percentage, C: 0.01-0.08wt%, Si: 0.01-0.05wt%, Mn: 0.1-0.5wt%, Al: 0.015-0.045wt%, Cu≤0.20wt%, As≤0.040wt%, Sn≤0.028wt%, P≤0.025wt%, S≤0.015wt% and N≤0.005wt%, with the remainder being Fe and unavoidable impurities; Preferably, the elements Cu, As and Sn in the cold heading steel satisfy: Cu+3As+8Sn≤0.22%.

4. A method for preparing cold heading steel according to any one of claims 1 to 3, characterized in that: The method comprises smelting raw materials in proportion to obtain molten steel, then continuously casting the molten steel to obtain steel billets, and then rolling the steel billets to obtain the cold heading wire rod.

5. The preparation method according to claim 4, characterized in that: The raw materials include molten iron and scrap steel; Preferably, the element compositions of the molten iron and the scrap steel satisfy the following conditions: Cu≤0.04wt%, As≤0.03wt%, Sn≤0.02wt%.

6. The preparation method according to claim 4, characterized in that: The smelting process includes primary smelting and refining; The refining includes adding slag to the molten steel obtained by primary refining for refining, and the slag is added during the steel tapping process after the primary refining is completed and after the molten steel reaches the refining furnace; Preferably, the ratio of the mass of the slag added during the steel tapping process to the mass of the slag added after the molten steel reaches the refining furnace is 2.5 to 5; Preferably, the slag is added during the steel tapping process when the steel tapping amount reaches 40-60% of the total molten steel mass; Preferably, the refining time is 20 to 40 minutes.

7. The preparation method according to claim 4, characterized in that: During the continuous casting process, the superheat of the molten steel before solidification is 15-40° C., the continuous casting adopts a constant drawing speed, and the fluctuation of the molten steel liquid level in the crystallizer is ≤3mm.

8. The preparation method according to claim 4, characterized in that: The step of heating the steel billet obtained by continuous casting before rolling; Preferably, the tail temperature of the heated billet is 15-25° C. higher than the head temperature.

9. The preparation method according to claim 8, characterized in that: During the rolling process, the rough rolling inlet temperature is 920-1020°C, the finishing rolling inlet temperature is 900-950°C, and the wire drawing temperature is 850-900°C; the cooling rate of the cold-headed wire obtained after the wire drawing is 0.1-0.5°C / s.

10. Use of the cold heading steel as claimed in any one of claims 1 to 3 or the cold heading steel produced by the production method as claimed in any one of claims 4 to 9 in producing workpieces with a reduction ratio of ≥ 70% during cold working deformation.

Images