Non-quenched and tempered steel wire rod and production method and application thereof

Abstract

The invention belongs to the technical field of ferrous metallurgy, and particularly relates to a non-quenched and tempered steel wire rod and a production method and application thereof. The production method comprises the following steps that a continuous casting large square billet is subjected to initial rolling and cogging treatment to obtain a small square billet, and the small square billet is prepared into a non-quenched and tempered steel wire rod; the initial rolling and cogging treatment comprises heating and rolling. The grain size of the non-quenched and tempered steel wire rod is larger than or equal to 10 grades, full decarburization is avoided, and the total decarburization depth is detected to be within 0.05 mm; the dimensional tolerance ranges from-0.15 mm to 0.15 mm; the yield strength is 520 MPa or more, the tensile strength is 800 MPa-950 MPa, the percentage elongation after fracture is 17% or more, and the percentage reduction of area is 50% or more.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron and steel metallurgy, and particularly relates to a non-quenched and tempered steel wire rod and its production method and application. Background Art

[0002] Non-quenched and tempered steel refers to adding elements with strong carbide-forming characteristics such as V, Nb, Ti, etc. to medium carbon steel. During the controlled cooling process after hot rolling, elements such as V, Nb, Ti, etc. will precipitate as carbon / nitrides in ferrite and pearlite, playing a strengthening role, enabling it to reach the strengthening level after quenching and tempering of medium carbon steel, thus eliminating the quenching and tempering treatment and simplifying the process. Non-quenched and tempered steel not only saves energy, significantly shortens the production cycle, but also avoids deformation and cracking caused by quenching, effectively improving product quality and reducing manufacturing costs. Therefore, non-quenched and tempered steel is widely used as bars in manufacturing industries such as automobiles.

[0003] However, due to deficiencies such as insufficient strength and toughness matching, poor cold working performance, and high composition sensitivity of non-quenched and tempered steel, its application scope as wire rod is limited. Summary of the Invention

[0004] To solve the above problems, the present invention provides a non-quenched and tempered steel wire rod and its production method and application to solve at least one aspect of the above technical problems.

[0005] The present invention is achieved through the following technical solutions:

[0006] In a first aspect, the present invention provides a production method of a non-quenched and tempered steel wire rod, including the following steps:

[0007] The continuous casting bloom is processed by primary rolling to obtain a small bloom, and the small bloom is used to prepare the non-quenched and tempered steel wire rod;

[0008] The primary rolling and blooming treatment includes heating and rolling;

[0009] During the heating, the heating temperature of the preheating section is controlled at 690°C - 710°C; the furnace temperature of the first heating section is 950°C - 1050°C; the furnace temperature of the second heating section is 1180°C - 1230°C; the soaking section is 1190°C - 1220°C, and the total heating time is 420 min - 450 min;

[0010] During the rolling, the starting rolling temperature is 1180°C - 1210°C, the final rolling temperature is 1000°C - 1080°C, and the sawing temperature is controlled not to be lower than 550°C.

[0011] In some possible implementation manners, preparing the continuous casting bloom includes the following steps:

[0012] The molten steel is continuously cast to obtain a continuous casting bloom, and it is stacked and cooled for more than 24 hours.

[0013] In some possible implementation manners, the preparation of the continuous casting bloom includes the following steps:

[0014] The molten iron is smelted in a converter, refined by LF, and then refined by VD to obtain molten steel.

[0015] The molten steel is continuously cast to obtain the continuous casting bloom.

[0016] In some possible implementation manners, in the converter smelting, 1.25 kg / t to 1.43 kg / t of synthetic slag materials are added for slag making, the tapping temperature is ≥1580 °C; slag tapping is adopted.

[0017] In some possible implementation manners, the synthetic slag material is MJ-55 produced by Henan Rongjin High Temperature Materials Co., Ltd.

[0018] In some possible implementation manners, in the converter smelting, the P content in the tapped steel is below 0.009% and the S content is below 0.015%.

[0019] In some possible implementation manners, in the converter smelting, at least one of aluminum blocks, silicomanganese alloys, medium-carbon ferrochromium, and vanadium-nitrogen alloys is added during the tapping process.

[0020] In some possible implementation manners, in the LF refining, the refining time is 40 min or more, the white slag holding time is 30 min or more, the total slag amount for slag making is controlled at 10 kg / t to 12 kg / t, after the molten steel temperature reaches 1590 °C to 1600 °C, a nitrogen alloy wire is fed to increase nitrogen, the composition is finely adjusted according to the target composition of the non-quenched and tempered steel wire rod, and the basicity is controlled at 4.0 to 5.0.

[0021] In some possible implementation manners, in the VD refining, the refining time is 30 min or more, the vacuum holding time is 15 min or more, nitrogen gas is blown in a circulating manner during the vacuum treatment process, and the soft blowing argon time is controlled at 20 min to 30 min after breaking the vacuum. In this case, since a certain amount of nitrogen content will be removed during the vacuum treatment process, nitrogen is increased by blowing nitrogen in a circulating manner during the vacuum treatment process, which can ensure the relative stability of the nitrogen content in the steel; the soft blowing argon time is controlled after breaking the vacuum, so that inclusions have sufficient floating and removal time, improving the cleanliness of the molten steel.

[0022] In some possible implementation manners, in the continuous casting, the casting speed is below 0.70 m / min, preferably 0.65 m / min to 0.70 m / min; the superheat is below 20°C, preferably 12°C to 18°C; the specific water consumption for secondary cooling in continuous casting is 0.33 L / kg to 0.37 L / kg; during the casting process, the liquid level in the mold and the stopper rod stroke are controlled stably, and the liquid level fluctuation is controlled within ±5 mm. It should be noted that the operations and relevant material dosages not mentioned in the continuous casting are conventional in the art and are not particularly limited in the present invention; however, as an example, in some examples, soft reduction technology is adopted for the straightening machine to reduce the central segregation and central porosity of the billet; the parameters of the electromagnetic stirring in the mold are 250 A and 2.5 Hz to promote the floating of inclusions and increase the equiaxed crystals of the continuous casting bloom; the parameters of the electromagnetic stirring at the end of solidification are 250 A and 8.0 Hz.

[0023] In some possible implementation manners, the stacking cooling time is 24 h to 30 h.

[0024] In some possible implementation manners, the cross-sectional size of the continuous casting bloom is (345 mm to 355 mm) × (425 mm to 435 mm).

[0025] In some possible implementation manners, the primary rolling and blooming treatment specifically includes the following steps:

[0026] After descaling, heating, rolling, and heat preservation of the bloom, a small bloom is obtained.

[0027] Among them, the descaling and heat preservation are conventional technologies and conditions in the art and are not particularly limited in the present invention.

[0028] In some possible implementation manners, the steps of preparing the non-quenched and tempered steel wire rod from the small bloom include:

[0029] After grinding the small bloom, it undergoes soaking treatment, descaling treatment, horizontal-vertical alternating continuous rolling, sizing, wire laying, cooling, coiling, and finished product pickling to obtain the non-quenched and tempered steel wire rod.

[0030] In some possible implementation manners, the small bloom is a cube with a side length of 150 mm ± 0.5 mm and a fillet radius of 25 mm or less.

[0031] In some possible implementation manners, in the grinding, the grinding process uses a grinding wheel type skin peeling machine to grind the steel billet (i.e., the small bloom), where the grinding depth of the billet surface is 1.0 mm ± 0.2 mm and the grinding width of the billet corner is 10.0 mm ± 0.2 mm; after the steel billet is ground, flaw detection is carried out, and a magnetic particle flaw detector is used to check the surface quality of the ground steel billet to ensure normal surface quality of the steel billet.

[0032] In some possible implementation manners, in the homogenizing heat treatment, the temperature of the preheating section is below 850°C, the temperature of the soaking section is 1180°C to 1220°C, and the total heating time is 140 min to 160 min.

[0033] In some possible implementation manners, in the horizontal-vertical alternating continuous rolling, the finishing rolling temperature is below 960°C, preferably 950°C to 960°C.

[0034] In some possible implementation manners, in the horizontal-vertical alternating continuous rolling, the rough and medium rolling and pre-finishing rolling mills adopt temperature-controlled rolling at 952°C, and the finishing rolling mill adopts two-phase zone controlled rolling at 825°C; after rolling, it is cooled through the Stelmor controlled cooling line, and the fan and the heat preservation cover are closed; after the controlled cooling is completed, the wire rod leaves the controlled cooling line and enters the PF line for normal flow, and a protective outer package is put on when it is cooled to 55°C.

[0035] In some possible implementation manners, in the reducing and sizing, the reducing and sizing temperature is below 845°C.

[0036] In some possible implementation manners, in the wire laying, the wire laying temperature is below 845°C, preferably 835°C to 840°C.

[0037] In some possible implementation manners, in the cooling, it is controlled and cooled by the Stelmor air cooling line.

[0038] In some possible implementation manners, in the coiling, the roller table rotation speed is 20 rpm to 30 rpm.

[0039] In some possible implementation manners, the non-quenched and tempered steel wire rod is composed of the following mass fractions:

[0040] C: 0.32% to 0.40%, Mn: 1.30% to 1.55%, Si: 0.20% to 0.30%, Cr: 0.10% to 0.30%, Al: 0.010% to 0.030%, V: 0.05% to 0.12%, Ti: 0.010% to 0.030%, N: 0.012% to 0.022%, P ≤ 0.020%, S ≤ 0.004%, and the balance is iron and inevitable impurities.

[0041] In some possible implementation manners, the non-quenched and tempered steel wire rod is composed of the following components by mass fraction:

[0042] C: 0.37% to 0.38%, Mn: 1.42% to 1.43%, Si: 0.26% to 0.28%, Cr: 0.19% to 0.20%, Al: 0.017% to 0.018%, V: 0.09% to 0.10%, Ti: 0.020% to 0.021%, N: 0.019% to 0.020%, P: 0.011% to 0.012%, S: 0.003% to 0.004%, the balance being iron and unavoidable impurities.

[0043] In some possible implementation manners, the non-quenched and tempered steel wire rod is composed of components with the following mass fractions:

[0044] C: 0.37%, Mn: 1.42%, Si: 0.28%, Cr: 0.19%, Al: 0.018%, V: 0.09%, Ti: 0.021%, N: 0.019%, P: 0.012%, S: 0.004%, the balance being iron and unavoidable impurities.

[0045] In some possible implementation manners, the non-quenched and tempered steel wire rod is composed of components with the following mass fractions:

[0046] C: 0.38%, Mn: 1.43%, Si: 0.26%, Cr: 0.20%, Al: 0.017%, V: 0.09%, Ti: 0.020%, N: 0.019%, P: 0.012%, S: 0.003%, the balance being iron and unavoidable impurities.

[0047] In a second aspect, the present invention provides a non-quenched and tempered steel wire rod produced by a production method of the non-quenched and tempered steel wire rod provided by the present invention, with a diameter of 16 mm to 22 mm.

[0048] In a third aspect, the present invention provides an application of the non-quenched and tempered steel wire rod provided by the present invention in the field of automotive manufacturing technology.

[0049] A non-quenched and tempered steel wire rod and a production method thereof provided by the present invention, compared with the prior art, have at least the following beneficial technical effects:

[0050] (1) The production method of the non-quenched and tempered steel wire rod provided by the present invention involves subjecting the continuously cast bloom to primary rolling and blooming (secondary blooming) followed by grinding, and then performing subsequent treatments, which can significantly reduce the surface defects of the product; grinding can remove the scabs, cracks, pinholes, pockmarks, sand holes, and non-metallic inclusions on the surface of the small bloom, as well as defects such as indentations with a depth greater than 1.5 mm and cracks with a depth greater than 0.2 mm, making the surface of the small bloom smooth and providing a billet with good surface quality for subsequent treatments. The yield strength of the non-quenched and tempered steel wire rod produced by the production method is above 520 MPa, the tensile strength is 800 MPa - 950 MPa, and the elongation after fracture is above 17%.

[0051] (2) The grain size of the non-quenched and tempered steel wire rod provided by the present invention is ≥ 10 grades, there is no complete decarburization, and the total decarburization depth is detected within 0.05 mm; the dimensional tolerance is -0.15 mm - 0.15 mm; the yield strength is above 520 MPa, the tensile strength is 800 MPa - 950 MPa, the elongation after fracture is above 17%, and the reduction of area is above 50%. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the technical solutions in the embodiments of the present drawings or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following-described drawings are only some embodiments of the present drawings. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0053] Figure 1 It is the metallographic structure diagram (1000X) of the non-quenched and tempered steel wire rod produced by the production method of a non-quenched and tempered steel wire rod in Embodiment 1 of the present invention;

[0054] Figure 2 It is the control effect diagram (100X) of the decarburized structure of the non-quenched and tempered steel wire rod produced by the production method of a non-quenched and tempered steel wire rod in Embodiment 1 of the present invention.

[0055] The realization, functional features, and advantages of the present drawings will be further described in combination with the embodiments with reference to the drawings. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0056] In order to make the purpose, technical solutions, and advantages of the present invention clearer, the following will describe and explain the present invention in combination with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Based on the embodiments provided by the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0057] Obviously, the following description is only some examples or embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, the present invention can also be applied to other similar scenarios. In addition, it can also be understood that although the efforts made in such a development process may be complex and lengthy, for those of ordinary skill in the art related to the content disclosed in the present invention, some design, manufacturing, or production changes based on the technical content disclosed in the present invention are only conventional technical means and should not be understood as the content disclosed in the present invention being insufficient.

[0058] However, there will be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters are omitted and repeated descriptions of actually identical structures are omitted. This is to avoid the following description becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the following description is provided for those skilled in the art to fully understand the present invention and is not intended to limit the subject matter recited in the claims.

[0059] If there is no special description, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions, and all technical features and optional technical features of the present invention can be combined with each other to form new technical solutions.

[0060] The following is further illustrated with specific embodiments. Operations not mentioned in the production method of the non-quenched and tempered steel wire rod involved in the embodiments can be carried out using conventional production operations in the art and will not be specifically described and recorded in the embodiments of the present application.

[0061] Example 1

[0062] Example 1 provides a production method of a non-quenched and tempered steel wire rod, and the target composition of the non-quenched and tempered steel wire rod is as follows:

[0063] C: 0.37%, Mn: 1.42%, Si: 0.28%, Cr: 0.19%, Al: 0.018%, V: 0.09%, Ti: 0.021%, N: 0.019%, P: 0.012%, S: 0.004%, and the balance is iron and inevitable impurities.

[0064] The steps are as follows:

[0065] S1. Continuously cast the molten steel to obtain a continuously cast bloom and stack-cool it for 30 h;

[0066] S1.1. The preparation steps of the molten steel are as follows:

[0067] S1.1.1. Obtain 122 t of hot metal and 29 t of scrap steel to make the hot metal for smelting. After the hot metal is smelted in a converter, refined by LF, and refined by VD, molten steel is obtained.

[0068] Among them, during the converter smelting process, bottom blowing nitrogen stirring is carried out throughout the process. 500 kg of lime and 200 kg of synthetic slag materials are added to make slag. The tapping temperature is 1618 °C; slag blocking tapping is adopted; the tapping carbon content is 0.05%, the P content is 0.009%, and the S content is 0.015%; aluminum blocks, ferrosilicon manganese alloy, medium-carbon ferrochrome and vanadium-nitrogen alloy are added during the tapping process to adjust the composition.

[0069] During LF refining, silicon carbide and a small amount of aluminum grains are used for diffusion deoxidation; the holding time of the refined white slag is about 25 min, the total slag amount is controlled at 10 kg / ton of steel, and nitrogen alloy wires are fed to increase nitrogen after the molten steel temperature reaches 1590 °C. The composition is slightly adjusted according to the target composition, and the target basicity control is 4.0.

[0070] During VD refining, the refining time is 32 min, the vacuum holding time is 15 min, nitrogen is blown in a circulating manner during the vacuum treatment process, and the soft blowing argon time is controlled at 22 min after breaking the vacuum.

[0071] S1.2. Continuous casting of molten steel: A 350×430 rectangular billet continuous caster is used, the casting speed is 0.70 m / min, and the superheat is 15±3 °C; soft reduction technology is adopted for the strand passing through the straightener; the specific water consumption of the secondary cooling of continuous casting is 0.35 L / kg; during the pouring process, the liquid level of the mold and the stroke of the stopper rod are controlled stably, and the liquid level fluctuation is controlled within ±5 mm; the parameters of the electromagnetic stirring in the mold are 250 A and 2.5 Hz, and the parameters of the electromagnetic stirring at the end of solidification are 250 A and 8.0 Hz.

[0072] S2. The continuously cast large billet after stacking cooling is subjected to primary rolling and blooming treatment to obtain small billets;

[0073] The steps of the primary rolling and blooming treatment are as follows:

[0074] S2.1.1. The large billet is descaled, heated, rolled and heat-insulated to obtain small billets;

[0075] During heating, the heating temperature of the preheating section is controlled at 700 °C; the furnace temperature of the first heating section is 1000 °C; the furnace temperature of the second heating section is 1200 °C; the temperature of the soaking section is 1200 °C, and the total heating time is 420 min;

[0076] During rolling, the starting rolling temperature is 1180 °C, the finishing rolling temperature is 1000 °C, and the sawing temperature is controlled at 550 °C;

[0077] S3. After the small billets are ground, they are subjected to homogenizing treatment, descaling treatment, horizontal-vertical alternating continuous rolling, sizing and reducing, wire laying, cooling, coiling, and finished product pickling to obtain non-quenched and tempered steel wire rods;

[0078] Among them, in the grinding process, a grinding wheel type skin peeling machine is used to grind the steel billet. The grinding depth on the face of the steel billet is 1.0 mm, and the grinding width at the corner of the steel billet is 10.0 mm. After the steel billet is ground, flaw detection is carried out, and a magnetic particle flaw detector is used to check the surface quality of the ground steel billet.

[0079] In the homogenizing heat treatment, the temperature of the preheating section is 850 °C, the temperature of the soaking section is 1200 °C, the total heating time is 150 min, the rough and medium rolling and pre-finishing rolling mills adopt temperature-controlled rolling at 952 °C, the finishing rolling mill adopts two-phase zone controlled rolling at 825 °C, and low-temperature wire laying is carried out at 838 °C after rolling. After rolling, it is cooled through the Stelmor controlled cooling line, and the fan and the heat preservation cover are closed.

[0080] Example 2

[0081] Example 2 provides a production method of non-quenched and tempered steel wire rod. The target composition of the non-quenched and tempered steel wire rod is as follows:

[0082] C: 0.38%, Mn: 1.43%, Si: 0.26%, Cr: 0.20%, Al: 0.017%, V: 0.09%, Ti: 0.020%, N: 0.019%, P: 0.012%, S: 0.003%, and the balance is iron and inevitable impurities.

[0083] The steps are as follows:

[0084] S1. Continuously cast the molten steel to obtain a continuously cast bloom and stack-cool it for 30 h;

[0085] S1.1. The preparation steps of the molten steel are as follows:

[0086] S1.1.1. Obtain 121 t of hot metal and 29 t of scrap steel to make the hot metal for smelting. After the hot metal is smelted in a converter, refined by LF, and refined by VD, molten steel is obtained.

[0087] Among them, in the converter smelting, bottom blowing nitrogen stirring is carried out throughout the process, 500 kg of lime and 200 kg of synthetic slag material are added to make slag, and the tapping temperature is 1605 °C; slag blocking tapping is adopted; the tapping carbon content is 0.04%, the P content is 0.008%, and the S content is 0.012%; aluminum blocks, silicomanganese alloy, medium-carbon ferrochrome, and vanadium-nitrogen alloy are added during the tapping process to adjust the composition.

[0088] In LF refining, silicon carbide and a small amount of aluminum grains are used for diffusion deoxidation; the holding time of the refined white slag is 26 min, the total slag amount is controlled at 10 kg / ton of steel, nitrogen alloy wire is fed after the molten steel temperature reaches 1595 °C to increase nitrogen, the composition is slightly adjusted according to the target composition, and the alkalinity control target is 4.0.

[0089] In VD refining, the refining time is 34 min, the vacuum holding time is 15 min, nitrogen gas is blown in a circulating manner during the vacuum treatment process, and the soft blowing argon time is controlled at 23 min after breaking the vacuum.

[0090] S1.2. Continuous casting of molten steel: A 350×430 rectangular billet continuous caster is used, with a casting speed of 0.70 m / min and a superheat of 16±3°C; soft reduction technology is adopted for the straightening machine; the specific water consumption for secondary cooling in continuous casting is 0.35 L / kg; during the casting process, the liquid level in the mold and the travel of the stopper rod are stably controlled, and the liquid level fluctuation is controlled within ±5 mm; the parameters of electromagnetic stirring in the mold are 250 A and 2.5 Hz, and the parameters of electromagnetic stirring at the end of solidification are 250 A and 8.0 Hz.

[0091] S2. The continuously cast large billet after stacking cooling is subjected to primary rolling and blooming to obtain small billets;

[0092] S2.1. The steps of primary rolling and blooming are as follows:

[0093] S2.1.1. The large billet is descaled, rolled, and then heat-insulated to obtain small billets;

[0094] In step S2.1.1, the rolling consists of heating and rolling;

[0095] During heating, the heating temperature in the preheating section is controlled at 700°C; the furnace temperature in the first heating section is 1050°C; the furnace temperature in the second heating section is 1230°C; the soaking temperature is 1210°C, and the total heating time is 420 min;

[0096] During rolling, the starting rolling temperature is 1200°C, the finishing rolling temperature is 1080°C, and the sawing temperature is controlled at 580°C;

[0097] S3. After the small billets are ground, subjected to homogenizing treatment, descaling treatment, horizontal-vertical alternating continuous rolling, sizing, spinning, cooling, coiling, and finished product pickling, non-quenched and tempered steel wire rods are obtained;

[0098] Among them, in the grinding process, a grinding-wheel type skin peeling machine is used to grind the steel billets. The grinding depth on the face of the steel billet is 1.0 mm, and the grinding width at the corner of the steel billet is 10.0 mm; after the steel billets are ground, flaw detection is carried out, and a magnetic particle flaw detector is used to check the surface quality of the ground steel billets;

[0099] During homogenizing treatment, the temperature in the preheating section is 830°C, the soaking temperature is 1220°C, the total heating time is 150 min, the rough and medium rolling and pre-finishing rolling mills adopt temperature-controlled rolling at 950°C, the finishing rolling mill adopts two-phase zone controlled rolling at 827°C, and low-temperature spinning is carried out at 837°C after rolling. After rolling, it is cooled through a Stelmor controlled cooling line, and the fan and heat preservation cover are turned off.

[0100] Comparative Example 1

[0101] A production method of non-quenched and tempered steel wire rods in Comparative Example 1 is as follows:

[0102] SD1. Molten steel is continuously cast to obtain continuously cast large billets, which are stacked and cooled for 30 h;

[0103] SD2. After subjecting the continuously cast bloom after bank cooling to homogenizing heat treatment, descaling treatment, horizontal-vertical alternating continuous rolling, sizing, wire laying, cooling, coiling, and finished product pickling, a non-quenched and tempered steel wire rod is obtained;

[0104] The conditions for the preparation of the molten steel, continuous casting, homogenizing heat treatment, descaling treatment, horizontal-vertical alternating continuous rolling, sizing, wire laying, cooling, coiling, and finished product pickling are the same as those in Example 1.

[0105] To verify the progressiveness of the production method of the non-quenched and tempered steel wire rod in the embodiments of the present invention, mechanical property tests such as yield strength, tensile strength, elongation after fracture, and reduction of area were carried out on the non-quenched and tempered steel wire rods produced by the production methods of the examples and comparative examples. Tests on non-metallic inclusions, tissue types, grain size, complete decarburization, and total decarburization were also carried out, as shown in Tables 1 to 3 below. Taking Example 1 as an example, metallographic tests and detection of the decarburized tissue control effect were carried out on the non-quenched and tempered steel wire rod, and the results are as shown in the attached Figures 1-2 as shown.

[0106] Table 1

[0107] -- Example 1 Example 2 Comparative Example 1 Yield strength (MPa) 550 554 500 Tensile strength (MPa) 862 873 720 Elongation after fracture (%) 22 21 12 Reduction of area (%) 54 53 46

[0108] Table 2

[0109]

[0110] Table 3

[0111] Example 1 Example 2 Comparative Example 1 Microstructure type Ferrite + pearlite Ferrite + pearlite Ferrite + pearlite Grain size / grade 10 11 6 Total decarburization / mm 0 0 0 Total decarburization / mm 0.03 0.05 0.16

[0112] From the above Tables 1 to 3 and the attached Figures 1-2 at least the following conclusions can be drawn:

[0113] (1) For the production method of the non-quenched and tempered steel wire rod provided in the embodiments of the present invention, after the continuously cast bloom is initially rolled and bloomed (secondary blooming) and then ground, and then subsequent treatments are carried out, the surface defects of the product can be significantly reduced; grinding can remove defects such as scabs, cracks, pinholes, pitting, sand holes, and non-metallic inclusions on the surface of the small bloom, as well as indentations with a depth greater than 1.5 mm and cracks with a depth greater than 0.2 mm, making the surface of the small bloom smooth and providing a billet with good surface quality for subsequent treatments. The yield strength of the non-quenched and tempered steel wire rod produced by the production method is above 520 MPa, the tensile strength is 800 MPa - 950 MPa, and the elongation after fracture is above 17%.

[0114] (2) The grain size of the non-quenched and tempered steel wire rod provided by the embodiment of the present invention is ≥ grade 10, without complete decarburization, and the total decarburization depth is detected within 0.05 mm; the dimensional tolerance is -0.15 mm to 0.15 mm; the yield strength is above 520 MPa, the tensile strength is 800 MPa to 950 MPa, the elongation after fracture is above 17%, and the reduction of area is above 50%.

[0115] It should be noted that the present invention is not limited to the above embodiments. The above embodiments are only examples, and the embodiments with the same composition and the same effect as the technical idea within the technical solution scope of the present invention are all included in the technical scope of the present invention. In addition, within the scope of not departing from the gist of the present invention, various deformations that can be thought of by those skilled in the art are applied to the embodiments, and other ways constructed by combining some constituent elements in the embodiments are also included in the scope of the present invention.

Claims

1. A method for producing a non-quenched and tempered steel wire rod, characterized in that: The steps include: The continuous casting bloom is subjected to a primary rolling process to obtain a small billet, and the small billet is used to prepare a non-quenched and tempered steel wire rod; The initial rolling process includes heating and rolling; During the heating, the preheating temperature is controlled at 690°C to 710°C; the first heating furnace temperature is controlled at 950°C to 1050°C; the second heating furnace temperature is controlled at 1180°C to 1230°C; the soaking temperature is controlled at 1190°C to 1220°C, and the total heating time is controlled at 420min to 450min; During the rolling, the starting rolling temperature is 1180°C to 1210°C, the final rolling temperature is 1000°C to 1080°C, and the sawing temperature is controlled to be no less than 550°C.

2. The method for producing non-quenched and tempered steel wire rod according to claim 1, characterized in that: The preparation of the continuous casting bloom comprises the following steps: After the molten iron is smelted in a converter, refined by LF and refined by VD, molten steel is obtained; The molten steel is continuously cast to obtain the continuously cast large square bloom.

3. The method for producing non-quenched and tempered steel wire rod according to claim 2, characterized in that: During the converter smelting, 1.25kg / t to 1.43kg / t of synthetic slag is added to make slag, and the tapping temperature is ≥1580°C.

4. The method for producing a non-quenched and tempered steel wire rod according to claim 2 or 3, characterized in that: In the LF refining, the refining time is more than 40 minutes, the white slag holding time is more than 30 minutes, and the total slag amount of slag making is controlled at 10kg / t to 12kg / t.

5. The method for producing a non-quenched and tempered steel wire rod according to any one of claims 2 to 4, characterized in that: In the VD refining, the refining time is more than 30 minutes, the vacuum holding time is more than 15 minutes, nitrogen is blown in a circulation during the vacuum treatment, and the soft blowing time of argon is controlled to be 20 minutes to 30 minutes after breaking the air.

6. The method for producing a non-quenched and tempered steel wire rod according to any one of claims 2 to 5, characterized in that: In the continuous casting, the pulling speed is below 0.70 m / min; and the superheat is below 20°C.

7. The method for producing a non-quenched and tempered steel wire rod according to any one of claims 2 to 6, characterized in that: The initial blanking process specifically comprises the following steps: The large square billet is descaled, heated, rolled and kept warm to obtain a small square billet.

8. The method for producing a non-quenched and tempered steel wire rod according to any one of claims 1 to 7, characterized in that: The non-quenched and tempered steel wire rod consists of the following mass fractions composition: C: 0.32% ~ 0.40%, Mn: 1.30% ~ 1.55%, Si: 0.20% ~ 0.30%, Cr: 0.10% ~ 0.30%, Al: 0.010% ~ 0.030%, V: 0.05% ~ 0.12%, Ti: 0.010% ~ 0.030%, N: 0.012% ~ 0.022%, P ≤ 0.020%, S ≤ 0.004%, the balance is iron and unavoidable impurities.

9. A non-quenched and tempered steel wire rod produced by the production method of non-quenched and tempered steel wire rod according to any one of claims 1 to 8, having a diameter of 16 mm to 22 mm.

10. Use of the non-quenched and tempered steel wire rod according to any one of claims 1 to 8 in the field of automobile manufacturing technology.

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