High-strength and high-toughness hot-rolled wire rod for mattress spring and preparation method of high-strength and high-toughness hot-rolled wire rod

Abstract

The invention provides a high-strength and high-toughness hot-rolled wire rod for a mattress spring and a preparation method of the high-strength and high-toughness hot-rolled wire rod. The preparation method comprises the following steps of (1) KR pretreatment of molten iron, (2) converter smelting, (3) deoxidation alloying, (4) LF furnace refining, (5) VD vacuum refining, (6) molten steel casting, (7) casting blank slow cooling and (8) steel blank rolling, and the hot-rolled wire rod with the following chemical components and performance: 0.82-0.86 wt% of C, 0.18-0.30 wt% of Si, 0.76-0.90 wt% of Mn, 0.19-0.25 wt% of Cr, less than or equal to 0.010 wt% of S, less than or equal to 0.010 wt% of P, less than or equal to 0.0015 wt% of O, less than The tensile strength of the hot-rolled wire rod is larger than or equal to 1250 MPa, the percentage reduction of area is larger than or equal to 38%, the sorbite quantity of a microscopic structure is larger than or equal to 95%, the central network cementite is smaller than or equal to 1.5 level, the central martensite is smaller than or equal to 1.0 level, the wire breaking rate per hundred tons does not exceed 2 times, the hot-rolled wire rod can be drawn to phi 1.8-1.9 mm, and the cost is reduced by 200-400 yuan / ton.

Description

Technical Field

[0001] This invention relates to a hot-rolled wire rod and its preparation method, particularly a high-strength, high-toughness hot-rolled wire rod for mattress springs and its preparation method, belonging to the field of metal material processing technology. Background Technology

[0002] Mattress springs are primarily made of high-carbon steel, stainless steel, and alloy steel. High-carbon steel springs offer excellent elasticity, resisting long-term pressure and deformation. They also boast high strength, durability, resistance to breakage or deformation, ease of processing, and low cost. Currently, the most widely used high-carbon steel springs on the market are made from 60, 65, and 70 grade hardened wire rods. While stainless steel and alloy steel springs offer even better performance, their higher price limits their suitability for high-end mattresses, making them unsuitable for ordinary mattresses.

[0003] With increasingly fierce competition in the mattress market and growing demand for lightweight mattresses, mattress manufacturers are considering using lightweight springs in mattresses and are looking for a suitable material with better strength and resilience to process and manufacture mattress springs. For example, one mattress spring processing plant uses 65 or 70 steel wire rods with a diameter of 6.5mm, drawn to a diameter of 2.0-2.2mm for spring processing.

[0004] For example, the Chinese patent application CN202010096557.5, entitled "A Deep-Drawn Cold-Drawn Spring Steel Wire Rod and Its Preparation Method," utilizes a series of measures including electric furnaces, LF furnaces, VD furnaces, and continuous casting control. Through the organic combination of optimized chemical composition design, smelting process control, and controlled rolling and cooling processes, the purity of the deep-drawn wire rod is significantly improved. The nitrogen content is controlled below 70 ppm, central carbon segregation is controlled to ≤1.09%, the sorbite ratio is ≥85%, and the fluctuation of the mechanical properties (within the same ring) is within 50 MPa. This overcomes the influence of residual elements and nitrogen content from electric furnace smelting on drawing performance, achieving a synergy between tensile strength and sorbite ratio. Through optimized process experiments, some deep-drawn products can be produced without a VD furnace under certain conditions, reducing production costs. The composition of the deep-drawn cold-drawn spring steel wire rod includes: C 0.60-0.67%, Si 0.2-0.3%, Mn 0.8-1.2%, P≤0.02%, S≤0.02%, Cu 0-0.2%, As 0-0.020%, Sn 0-0.010%, Cr 0-0.1%, O≤0.0020%, N≤0.0070%, with the balance being Fe.

[0005] For example, Chinese patent application CN202311768900.6, entitled "A 2200MPa Grade High Strength and Toughness Spring Steel Wire and Its Preparation Method," solves the problem that existing spring steel wires cannot simultaneously achieve high strength and high ductility and toughness. The chemical composition of its 2200MPa grade high strength and toughness spring steel wire, by mass percentage, includes: C 0.45~0.70%, Si 1.00~2.50%, Mn 0.40~3.00%, Cr 0.10~3.00%, Mo 0.02~0.30%, Nb 0.02~0.30%, V 0.02~0.30%, N 0.008~0.012%, P≤0.015%, S≤0.002%, with the remainder being Fe and unavoidable impurities. The single-element composition of the spring steel wire has a wide design range and a large number of alloying elements added, which is detrimental to the production cost and quality control of the wire rod.

[0006] For example, Chinese patent application CN202410160025.1, entitled "Cold-drawn spring steel wire, hot-rolled wire rod for cold-drawn spring steel wire and its preparation method," specifies that the chemical composition of the hot-rolled wire rod for cold-drawn spring steel wire, by mass percentage, includes: C 0.80–0.84%, Si 0.40–0.55%, Mn 0.65–0.85%, V… The alloy composition is 0.08-0.10%, S≤0.004%, P≤0.010%, O≤0.002%, N≤0.004%, and Si+10V=1.30-1.40%, with the remainder being Fe and unavoidable impurities. The tensile strength of this wire rod is increased from 1000MPa of commonly used 65Mn wire rod to over 1250MPa, and the yield strength ratio is increased from below 0.65 to over 0.70. The intermediate wire heat treatment can be omitted, and the steel wire for automotive springs that meets the requirements of GB / T4357-2009 can be produced directly by drawing. However, the addition of the precious alloy V still results in a higher production cost.

[0007] In summary, existing technologies lack specific production techniques for hot-rolled wire rods used in mattress springs, only covering some deep-drawn and cold-drawn spring steel wire rods. Some of these rods contain the expensive alloy V, while others contain excessive amounts of alloying elements, which is extremely detrimental to the production cost and quality control of the wire rods. Therefore, it is necessary to improve existing technologies. Summary of the Invention

[0008] To address the problems of high production costs and difficulty in quality control caused by the addition of precious alloy V or excessive alloying elements in the existing spring steel wire rod production process, and the lack of specialized hot-rolled wire rods and production methods for mattress springs, this invention provides a high-strength, high-toughness hot-rolled wire rod for mattress springs and its production method.

[0009] This invention provides a high-strength, high-toughness hot-rolled wire rod for mattress springs, characterized by comprising the following chemical components by weight percentage:

[0010] C: 0.82–0.86 wt%, Si: 0.18–0.30 wt%, Mn: 0.76–0.90 wt%, Cr: 0.19–0.25 wt%, S ≤ 0.010 wt%, P ≤ 0.010 wt%, O ≤ 0.0015 wt%, N ≤ 0.0035 wt%, V: 0.030–0.046 wt%, with the remainder being Fe and unavoidable impurities; and the hot-rolled wire rod has a tensile strength ≥ 1250 MPa, a reduction of area ≥ 38%, a sorbite content ≥ 95%, a central network cementite grade ≤ 1.5, and a central martensite grade ≤ 1.0.

[0011] The high-strength, high-toughness hot-rolled wire rod for mattress springs of the present invention is obtained through the following steps:

[0012] (1) Pretreatment of molten iron KR: After the molten iron is transported to the desulfurization station, it is first treated by slag removal and then by desulfurization. During the desulfurization treatment, 90% CaO and 10% CaF2 are added as desulfurizing agents at a rate of 5-12 kg / ton of iron. The mixture is stirred for 10-18 minutes with an immersion depth of 1100-1500 mm, a starting speed of 25-35 r / min, and a normal speed of 90-120 r / min. After stirring, the desulfurization slag is removed to obtain the pretreated molten iron.

[0013] (2) Converter smelting: The pretreated molten iron obtained in step (1) is added to the converter along with scrap steel for top and bottom composite blowing. The amount of molten iron added is 880-920 kg / t steel, and the amount of scrap steel added is 180-140 kg / t steel. At the same time, lime and lightly calcined dolomite are added for slag formation and smelting. The amount of lime added is 23-25 ​​kg / t steel, and the amount of lightly calcined dolomite added is 18-20 kg / t steel, until molten steel with a carbon content of 0.10-0.20 wt% and a temperature of 1590-1620℃ is obtained. Argon blowing is carried out at the bottom of the converter throughout the entire process before smelting and during tapping.

[0014] (3) Deoxidation and alloying: The molten steel obtained in step (2) is poured into a ladle. When the amount of molten steel in the ladle is greater than 1 / 4, the following alloys are added in sequence: low-aluminum silicon-calcium-barium → high-carbon ferromanganese → ferrosilicon → high-carbon ferrochrome → carbon raiser. All the alloys are added when the amount of molten steel in the ladle reaches 3 / 4, so as to carry out deoxidation and alloying treatment, wherein:

[0015] The mass percentage of low-aluminum silicon-calcium-barium is as follows: Si: 50-55 wt%, Ca: 9-13 wt%, Ba: 11-14 wt%, Al≤0.50 wt%, P≤0.100 wt%, S≤0.100 wt%, O≤1.5 wt%, with the remainder being Fe and unavoidable impurities. The addition amount of low-aluminum silicon-calcium-barium is 1.14 kg / t steel.

[0016] The mass percentage of high-carbon ferromanganese is: Mn: 75~82wt%, C≤8.0wt%, Si≤2.5wt%, with the remainder being unavoidable impurities. The amount of high-carbon ferromanganese added is 9.8~10.6kg / t steel.

[0017] The mass percentage of ferrosilicon is: Si: 72-75wt%, with the remainder being unavoidable impurities. The amount of ferrosilicon added is 2.3-2.7 kg / t steel.

[0018] The mass percentage of high-carbon ferrochrome is: Cr≥60wt%, C≤6.0wt%, Si≤3.0wt%, with the remainder being Fe and unavoidable impurities. The amount of high-carbon ferrochrome added is 3.20~3.50kg / t steel.

[0019] Argon blowing is carried out at the bottom of the converter throughout the entire steel tapping process until the steel is tapped.

[0020] (4) LF furnace refining: The ladle filled with molten steel in step (3) is hoisted to the LF refining furnace station. Argon gas is blown into the ladle to make the surface of the molten steel creep. After 8 to 10 minutes, the temperature of the molten steel is measured and a steel sample is taken. According to the analysis results of the steel sample, the following alloying elements of the molten steel composition are adjusted: When the C, Si, Mn, S and P elements in the molten steel are qualified, ferrovanadium is added at a rate of 0.30 to 0.36 kg / t of steel. The mass percentage of V in the ferrovanadium is 48 to 55 wt%, and the rest is Fe and unavoidable impurities. The molten steel is heated to 1610 to 1620℃ and then argon is blown for ≥3 minutes.

[0021] (5) VD vacuum refining: The molten steel from step (4) is hoisted into the vacuum tank of the VD furnace, the vacuum tank cover is closed, and the vacuum is evacuated to 67 Pa. At the same time, argon gas is blown in from the bottom at a flow rate of 150-250 L / min, and degassing is performed under this vacuum for 15-18 min. Then, the temperature is measured by a molten steel thermometer, the oxygen is determined by a molten steel thermometer, and the hydrogen is determined by a molten steel thermometer.

[0022] (6) Steel casting: The molten steel from step (5) is cast in an tundish at a temperature of 1487–1497°C, a casting speed of 1.9–2.0 m / min, and a cooling water flow rate of 120 m³ / min. 3Under the conditions of 0.7 L / kg for secondary cooling water and 300 A and 4 Hz for electromagnetic stirring in the crystallizer, the steel billet is cast into 165 mm × 165 mm steel billet by a seven-strand continuous casting machine with seven runners on an R9m scale.

[0023] (7) Slow cooling of billet: In the slow cooling zone, first lay two layers of hot billets of other steel grades with a temperature ≥350℃, and then stack the steel billets obtained in step (6) in order of pouring sequence in up to 6 layers on the bottom layer. Then, cover the steel billet with two layers of hot billets of other steel grades with a temperature ≥350℃, and keep it warm and slow cooling for more than 72 hours.

[0024] (8) Billet rolling: The billet that has been kept warm and slowly cooled in step (7) is fed into a walking beam furnace. The temperature of the soaking zone is controlled at 1080-1130℃ and the time in the furnace is 120-150 min. Then, it is rough rolled for 6 passes on a roughing mill at a speed of 0.25 m / s, then rolled for 5 passes on an intermediate mill at a speed of 12.0 m / s, then rolled for 5 passes on a pre-finishing mill at a speed of 48.0 m / s, then rolled for 5 passes on a finishing mill at a speed of 65 m / s, and then rolled for 5 passes on a finishing mill at a speed of 65 m / s. The wire rod is rolled in two passes on a 70 m / s reducing mill. Then, it is spun into coils at a temperature of 880–910°C and a speed of 80–88 m / s. The coils are fed into a Steyrmo air-cooling line with a roller speed of 1.10–1.30 m / s and five fans for air cooling. The first four fans have an air volume of 100%, and the fifth fan has an air volume of 50% of the air volume of the first four fans. After exiting the Steyrmo air-cooling line, the coils are naturally air-cooled to room temperature to obtain hot-rolled wire rods for mattress springs.

[0025] Furthermore, the chemical composition of the molten iron in step (1) is: C: 4.10-4.6 wt%, Si: 0.20-0.40 wt%, Mn: 0.10-0.20 wt%, P: 0.090-0.120 wt%, S≤0.030 wt%, with the remainder being Fe and unavoidable impurities, and the temperature of the molten iron is 1350-1400℃.

[0026] Furthermore, the amount of desulfurizing agent added in step (1) is determined according to the S content and temperature of the molten iron, as follows: For molten iron with S content of 0.020wt% ≤ S ≤ 0.030wt%, add more desulfurizing agent; for molten iron with S content of S < 0.020wt%, add less desulfurizing agent; for molten iron with temperature of 1375℃ ≤ molten iron temperature ≤ 1400℃, add more desulfurizing agent; for molten iron with low temperature of 1350℃ ≤ molten iron temperature < 1375℃, add less desulfurizing agent while ensuring the desulfurization rate.

[0027] Furthermore, in step (3), to ensure the quality of molten steel, lime is added to the ladle at a rate of 1-2 kg / t of steel before tapping, and refining slag is added to the ladle at a rate of 0.5-1 kg / t of steel for slag washing.

[0028] Furthermore, the chemical composition of the scrap steel in step (2) is: C≤2.0wt%, Si≤1.5wt%, Mn≤3.0wt%, P≤0.045wt%, S≤0.045wt%, with the remainder being Fe and unavoidable impurities.

[0029] Furthermore, the continuous casting machine in step (6) adopts full-process protective casting to ensure the quality of the continuous casting billet. Specifically, the continuous casting billet to the tundish is protected by the long nozzle of the ladle, the liquid surface of the tundish is protected by a micro-carbon covering agent, the liquid surface of the tundish to the crystallizer is protected by an immersion nozzle, and the liquid surface of the crystallizer is protected by a high-carbon steel protective slag.

[0030] Furthermore, the number of steel billet stacking layers in step (7) is determined specifically based on the current production batch.

[0031] Furthermore, after the wire rod is air-cooled in step (8), it is naturally air-cooled in an environment with an insulation cover to further control the amount of martensite in the wire rod structure.

[0032] The present invention has the following advantages and effects: the hot-rolled wire rods for mattress springs produced using the above-described method have low gas and harmful impurity content, high steel cleanliness, and possess high strength and excellent ductility to meet user requirements. Simultaneously, the wire rods exhibit good processing performance, with a breakage rate of no more than 2 times per 100 tons, and can be drawn to Φ1.8-1.9mm. With the same number of mattress springs, the weight can be reduced by 10-35%, and the processing cost per ton of springs can be reduced by 200-400 yuan, resulting in considerable economic and social benefits. Detailed Implementation

[0033] The technical solution of the present invention will be clearly and completely described below with reference to this embodiment. Obviously, the described embodiment is only a part of the embodiment of the present invention, and not all of the embodiment. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] A method for producing high-strength, high-toughness hot-rolled wire rod for mattress springs includes the following steps:

[0036] (1) KR pretreatment of molten iron: Molten iron with the following chemical composition: C 4.10wt%, Si 0.20wt%, Mn 0.10wt%, P 0.090wt%, S 0.015wt%, the remainder being Fe and unavoidable impurities, and the temperature of the molten iron is 1350℃. It is transported to the desulfurization station for slag removal. After slag removal, the molten iron is sent to the desulfurization station for desulfurization treatment. During desulfurization treatment, 90% CaO and 10% CaF2 are added as desulfurizing agents at a rate of 5kg / ton of iron. The mixture is stirred for 10min with an immersion depth of 1100mm, a starting speed of 25r / min, and a normal speed of 90r / min. After stirring, the desulfurization slag is removed to obtain pretreated molten iron.

[0037] (2) Converter smelting: The pretreated molten iron obtained in step (1) is added to the converter along with scrap steel for top and bottom composite blowing. The amount of molten iron added is 880 kg / t steel, and the amount of scrap steel added is 180 kg / t steel. The chemical composition of the scrap steel is: C≤2.0wt%, Si≤1.5wt%, Mn≤3.0wt%, P≤0.045wt%, S≤0.045wt%, with the remainder being Fe and unavoidable impurities. At the same time, lime and lightly calcined dolomite are added for slag formation and smelting. The amount of lime added is 23 kg / t steel, and the amount of lightly calcined dolomite added is 18 kg / t steel, until molten steel with a carbon content of 0.10wt% and a tapping temperature of 1590℃ is obtained. Argon blowing is carried out at the bottom of the converter throughout the entire process before smelting and during tapping.

[0038] (3) Deoxidation and alloying: Before the molten steel obtained in step (2) flows into the ladle, lime is added to the ladle at a rate of 1-2 kg / t of steel, and refining slag is added to the ladle at a rate of 0.5-1 kg / t of steel for slag washing. Then the molten steel is flowed into the ladle. When the amount of molten steel in the ladle is greater than 1 / 4, low-alumina silicon-calcium-barium → high-carbon ferromanganese → ferrosilicon → high-carbon ferrochrome → carbon raiser are added in sequence. All the alloys are added when the amount of molten steel in the ladle reaches 3 / 4 for deoxidation and alloying treatment, wherein:

[0039] The mass percentage of low-aluminum silicon-calcium-barium is Si: 50wt%, Ca: 9wt%, Ba: 11wt%, Al: 0.50wt%, P: 0.100wt%, S: 0.100wt%, O: 1.5wt%, with the remainder being Fe and unavoidable impurities. The addition amount of low-aluminum silicon-calcium-barium is 1.14kg / t steel.

[0040] The mass percentage of high-carbon ferromanganese is Mn: 75wt%, C: 8.0wt%, Si: 2.5wt%, with the remainder being unavoidable impurities. The amount of high-carbon ferromanganese added is 9.8kg / t steel.

[0041] The mass percentage of ferrosilicon is Si: 72wt%, with the remainder being unavoidable impurities. The amount of ferrosilicon added is 2.3kg / t steel.

[0042] The mass percentage of high-carbon ferrochrome is Cr: 60wt%, C: 6.0wt%, Si: 3.0wt%, with the remainder being Fe and unavoidable impurities. The amount of high-carbon ferrochrome added is 3.20 kg / t steel.

[0043] Argon blowing is carried out at the bottom of the converter throughout the entire steel tapping process until the steel is tapped.

[0044] (4) Steel refining in LF furnace: The ladle filled with molten steel in step (3) is hoisted to the LF refining furnace station. Argon gas is blown into the ladle to make the surface of the molten steel creep. After 8 to 10 minutes, the temperature of the molten steel is measured and a steel sample is taken. Based on the analysis results of the steel sample, the following alloying elements of the molten steel are adjusted: When the C, Si, Mn, S, P and other elements in the molten steel are controlled to be qualified, ferrovanadium is added at a rate of 0.30 kg / t steel. The mass percentage of V in the ferrovanadium is 48 wt%, and the rest is Fe and unavoidable impurities. The molten steel is heated to 1610℃ and then argon is blown for 3 minutes.

[0045] (5) VD vacuum refining: The molten steel from step (4) is hoisted into the vacuum tank of the VD furnace, the vacuum tank cover is closed, the vacuum is evacuated to 67 Pa, and argon gas is blown in from the bottom at a flow rate of 150 L / min. The gas is then degassed for 15 min under this vacuum. After that, the temperature is measured and the oxygen and hydrogen are determined.

[0046] (6) Steel casting: The molten steel from step (5) is cast in a tundish at a temperature of 1487℃, a casting speed of 1.9 m / min, and a cooling water flow rate of 120 m³ / min. 3 Under the conditions of a flow rate of 0.7 L / kg for secondary cooling water, and a process parameter of 300A and 4Hz for electromagnetic stirring in the crystallizer, molten steel is sent to a 9m seven-strand small billet continuous casting machine to cast molten steel into 165mm×165mm billets. The continuous casting machine adopts full-process protective casting to ensure the quality of the continuously cast billets. Specifically, from the ladle to the tundish, the ladle long nozzle is used for protection, the tundish liquid surface is covered with a micro-carbon covering agent for protection, the tundish to the crystallizer uses an immersion nozzle for protection, and the crystallizer liquid surface is protected with high-carbon steel protective slag.

[0047] (7) Slow cooling of billet: In the slow cooling zone, first lay two layers of hot billet of other steel grades at a temperature of 350℃, and then stack 6 layers of steel billet obtained in step (6) on the bottom layer according to the order of pouring. Then, cover the billet with two layers of hot billet of other steel grades at a temperature of 350℃ and keep it warm for 72 hours.

[0048] (8) Billet rolling: The billet that has been kept warm and slowly cooled in step (7) is fed into a walking beam furnace. The temperature of the soaking zone is controlled at 1080℃ and the time in the furnace is 120min. Then, it is rough rolled for 6 passes on a roughing mill at a speed of 0.25m / s, then rolled for 5 passes on an intermediate mill at a speed of 12.0m / s, then rolled for 5 passes on a pre-finishing mill at a speed of 48.0m / s, then rolled for 5 passes on a finishing mill at a speed of 65m / s, then rolled for 2 passes on a reducing and sizing mill at a speed of 70m / s, and then spun into a coil at a temperature of 880℃ and a speed of 80m / s. The coil is fed into a Stellmore air-cooling line with a roller speed of 1.10m / s and five fans for air cooling. The first four fans are used for air cooling. The air volume is 100%, and the air volume of the fifth fan is 50% of that of the first four fans. After the wire rod comes out of the Stellmore air-cooling line, it is naturally air-cooled to room temperature in an environment with an insulation cover, resulting in hot-rolled wire rod for mattress springs with the following composition and properties: C: 0.82wt%, Si: 0.18wt%, Mn: 0.76wt%, Cr: 0.19wt%, S: 0.010wt%, P: 0.010wt%, O: 0.0015wt%, N: 0.0035wt%, V: 0.030wt%, with the remainder being Fe and unavoidable impurities; the hot-rolled wire rod has a tensile strength of 1250MPa, a reduction of area of ​​48%, a sorbite content of 96% in its microstructure, a central network cementite grade of 0, and a central martensite grade of 0.5.

[0049] The mechanical properties and metallographic structure of the hot-rolled wire rod for mattress spring steel wire obtained in Example 1 are shown in Table 1 below:

[0050] Table 1 Mechanical properties and metallographic structure of hot-rolled wire rods for mattress springs

[0051]

[0052] In this embodiment 1, the hot-rolled wire rod is drawn to Φ1.8mm. According to user feedback, with the same number of mattress springs, replacing the original 2.2mm spring steel wire can reduce the weight by 35% and reduce the processing cost per ton of springs by 400 yuan, which has considerable economic and social benefits.

[0053] Example 2

[0054] A method for producing high-strength, high-toughness hot-rolled wire rod for mattress springs includes the following steps:

[0055] (1) KR pretreatment of molten iron: Molten iron with the following chemical composition: C 4.60wt%, Si 0.40wt%, Mn 0.20wt%, P 0.120wt%, S 0.030wt%, the remainder being Fe and unavoidable impurities, and the temperature of the molten iron is 1400℃. It is transported to the desulfurization station for slag removal. After slag removal, the molten iron is sent to the desulfurization station for desulfurization treatment. During the desulfurization treatment, 90% CaO and 10% CaF2 are added as desulfurizing agents at a rate of 12kg / ton of iron. The mixture is stirred for 18min with an immersion depth of 1500mm, a starting speed of 35r / min, and a normal speed of 90r / min. After stirring, the desulfurization slag is removed to obtain pretreated molten iron.

[0056] (2) Converter smelting: The pretreated molten iron obtained in step (1) is added to the converter along with scrap steel for top and bottom composite blowing. The amount of molten iron added is 920 kg / t steel, and the amount of scrap steel added is 140 kg / t steel. The chemical composition of the scrap steel is: C≤2.0wt%, Si≤1.5wt%, Mn≤3.0wt%, P≤0.045wt%, S≤0.045wt%, with the remainder being Fe and unavoidable impurities. At the same time, lime and lightly calcined dolomite are added for slag formation and smelting. The amount of lime added is 25 kg / t steel, and the amount of lightly calcined dolomite added is 20 kg / t steel, until molten steel with a carbon content of 0.20wt% and a tapping temperature of 1620℃ is obtained. Argon blowing is carried out at the bottom of the converter throughout the entire process before smelting and during tapping.

[0057] (3) Deoxidation and alloying: Before the molten steel obtained in step (2) flows into the ladle, lime is added to the ladle at a rate of 2 kg / t of steel, and refining slag is added to the ladle at a rate of 1 kg / t of steel for slag washing. Then the molten steel is flowed into the ladle. When the amount of molten steel in the ladle is greater than 1 / 4, low-alumina silicon-calcium-barium → high-carbon ferromanganese → ferrosilicon → high-carbon ferrochrome → carbon raiser are added in sequence. All the alloys are added when the amount of molten steel in the ladle reaches 3 / 4 for deoxidation and alloying treatment, wherein:

[0058] The mass percentage of low-aluminum silicon-calcium-barium is Si: 55wt%, Ca: 13wt%, Ba: 14wt%, Al: 0.50wt%, P: 0.100wt%, S: 0.100wt%, O: 1.5wt%, with the remainder being Fe and unavoidable impurities. The addition amount of low-aluminum silicon-calcium-barium is 1.14kg / t steel.

[0059] The mass percentage of high-carbon ferromanganese is Mn: 82wt%, C: 7.5wt%, Si: 2.1wt%, with the remainder being unavoidable impurities. The amount of high-carbon ferromanganese added is 10.4 kg / t steel.

[0060] The mass percentage of ferrosilicon is Si: 75wt%, with the remainder being unavoidable impurities. The amount of ferrosilicon added is 2.7kg / t steel.

[0061] The mass percentage of high-carbon ferrochrome is Cr: 62wt%, C: 6.0wt%, Si: 3.0wt%, with the remainder being Fe and unavoidable impurities. The amount of high-carbon ferrochrome added is 3.50 kg / t steel.

[0062] Argon blowing is carried out at the bottom of the converter throughout the entire steel tapping process until the steel is tapped.

[0063] (4) Steel refining in LF furnace: The ladle filled with molten steel in step (3) is hoisted to the LF refining furnace station. Argon gas is blown into the ladle to make the surface of the molten steel creep. After 10 minutes, the temperature of the molten steel is measured and a steel sample is taken. Based on the analysis results of the steel sample, the following alloying elements of the molten steel are adjusted: When the C, Si, Mn, S, P and other elements in the molten steel are controlled to be qualified, ferrovanadium is added at a rate of 0.35 kg / t steel. The mass percentage of V in the ferrovanadium is 52 wt%, and the rest is Fe and unavoidable impurities. The molten steel is heated to 1620℃ and then argon is blown for 3 minutes.

[0064] (5) VD vacuum refining: The molten steel from step (4) is hoisted into the vacuum tank of the VD furnace, the vacuum tank cover is closed, the vacuum is evacuated to 67 Pa, and argon gas is blown in from the bottom at a flow rate of 250 L / min. The gas is then degassed for 18 min under this vacuum. After that, the temperature is measured and the oxygen and hydrogen are determined.

[0065] (6) Steel casting: The molten steel from step (5) is cast in a tundish at a temperature of 1497℃, a casting speed of 2.0 m / min, and a cooling water flow rate of 120 m³ / min. 3 Under the conditions of a flow rate of 0.7 L / kg for secondary cooling water, and a process parameter of 300A and 4Hz for electromagnetic stirring in the crystallizer, molten steel is sent to a 9m seven-strand small billet continuous casting machine to cast molten steel into 165mm×165mm billets. The continuous casting machine adopts full-process protective casting to ensure the quality of the continuously cast billets. Specifically, from the ladle to the tundish, the ladle long nozzle is used for protection, the tundish liquid surface is covered with a micro-carbon covering agent for protection, the tundish to the crystallizer uses an immersion nozzle for protection, and the crystallizer liquid surface is protected with high-carbon steel protective slag.

[0066] (7) Slow cooling of billet: In the slow cooling zone, first lay two layers of hot billet of other steel grades at a temperature of 350℃, and then stack three layers of steel billet obtained in step (6) on the bottom layer according to the order of pouring. Then, cover the billet with two layers of hot billet of other steel grades at a temperature of 350℃ and keep it warm and slow cooling for 72 hours.

[0067] (8) Billet rolling: The billet that has been kept warm and slowly cooled in step (7) is fed into a walking beam furnace. The temperature of the soaking zone is controlled at 1130℃ and the time in the furnace is 150min. Then, it is rough rolled for 6 passes on a roughing mill at a speed of 0.25m / s, then rolled for 5 passes on an intermediate mill at a speed of 12.0m / s, then rolled for 5 passes on a pre-finishing mill at a speed of 48.0m / s, then rolled for 5 passes on a finishing mill at a speed of 65m / s, and finally rolled for 5 passes on a reduction mill at a speed of 70m / s. The sizing mill rolls the wire rod in two passes, then spins it into coils at 900℃ and 88m / s. The coils are fed into a Stellmore air-cooling line with a roller conveyor speed of 1.30m / s and five fans. The first four fans provide 100% airflow, and the fifth fan provides 50% of the airflow from the first four fans. After exiting the Stellmore air-cooling line, the coils are naturally air-cooled to room temperature under an insulation cover, yielding hot-rolled wire rods for mattress springs with the following composition and properties: C The composition is as follows: 0.86 wt%, Si 0.30 wt%, Mn 0.90 wt%, Cr 0.25 wt%, S 0.010 wt%, P 0.006 wt%, O 0.0011 wt%, N 0.0035 wt%, V 0.046 wt%, with the remainder being Fe and unavoidable impurities; the hot-rolled wire rod has a tensile strength of 1310 MPa, a reduction of area of ​​40%, a microstructure of 95.5% sorbite, a central network cementite grade of 1.5, and a central martensite grade of 1.0.

[0068] The mechanical properties and metallographic structure of the hot-rolled wire rod for mattress spring steel wire obtained in Example 2 are shown in Table 2 below:

[0069] Table 2 Mechanical Properties and Metallographic Structure of Hot-Rolled Wire Rods for Mattress Spring Steel Wires

[0070]

[0071] The hot-rolled wire rod of this embodiment 2 can be drawn to Φ1.9mm. According to user feedback, with the same number of mattress springs, replacing the original 2.0mm spring steel wire can reduce the weight by 23% and reduce the processing cost per ton of springs by 200 yuan, which has considerable economic and social benefits.

[0072] Example 3

[0073] A high-strength, high-toughness hot-rolled wire rod for mattress springs comprises the following chemical composition by weight percentage:

[0074] A method for producing high-strength, high-toughness hot-rolled wire rod for mattress springs includes the following steps:

[0075] (1) KR pretreatment of molten iron: Molten iron with the following chemical composition: C 4.35wt%, Si 0.30wt%, Mn 0.15wt%, P 0.105wt%, S 0.020wt%, the remainder being Fe and unavoidable impurities, and the temperature of the molten iron is 1375℃. It is transported to the desulfurization station for slag removal. After slag removal, the molten iron is sent to the desulfurization station for desulfurization treatment. During desulfurization treatment, 90% CaO and 10% CaF2 are added as desulfurizing agents at a rate of 8.5kg / ton of iron. The mixture is stirred for 14min with an immersion depth of 1300mm, a starting speed of 30r / min, and a normal speed of 105r / min. After stirring, the desulfurization slag is removed to obtain pretreated molten iron.

[0076] (2) Converter smelting: The pretreated molten iron obtained in step (1) is added to the converter along with scrap steel for top and bottom composite blowing. The amount of molten iron added is 900 kg / t steel, and the amount of scrap steel added is 160 kg / t steel. The chemical composition of the scrap steel is: C≤2.0wt%, Si≤1.5wt%, Mn≤3.0wt%, P≤0.045wt%, S≤0.045wt%, with the remainder being Fe and unavoidable impurities. At the same time, lime and lightly calcined dolomite are added for slag formation and smelting. The amount of lime added is 24 kg / t steel, and the amount of lightly calcined dolomite added is 19 kg / t steel, until molten steel with a carbon content of 0.15wt% and a tapping temperature of 1600℃ is obtained. Argon blowing is carried out at the bottom of the converter throughout the entire process before smelting and during tapping.

[0077] (3) Deoxidation and alloying: Before the molten steel obtained in step (2) flows into the ladle, lime is added to the ladle at a rate of 2 kg / t of steel, and refining slag is added to the ladle at a rate of 1 kg / t of steel for slag washing. Then the molten steel is flowed into the ladle. When the amount of molten steel in the ladle is greater than 1 / 4, low-alumina silicon-calcium-barium → high-carbon ferromanganese → ferrosilicon → high-carbon ferrochrome → carbon raiser are added in sequence. All the alloys are added when the amount of molten steel in the ladle reaches 3 / 4 for deoxidation and alloying treatment, wherein:

[0078] The mass percentage of low-aluminum silicon-calcium-barium is Si: 53wt%, Ca: 11wt%, Ba: 12wt%, Al: 0.45wt%, P: 0.100wt%, S: 0.100wt%, O: 1.3wt%, with the remainder being Fe and unavoidable impurities. The addition amount of low-aluminum silicon-calcium-barium is 1.12kg / t steel.

[0079] The mass percentage of high-carbon ferromanganese is Mn: 78wt%, C: 7.5wt%, Si: 2.3wt%, with the remainder being unavoidable impurities. The amount of high-carbon ferromanganese added is 10.4 kg / t steel.

[0080] The mass percentage of ferrosilicon is Si: 73wt%, with the remainder being unavoidable impurities. The amount of ferrosilicon added is 2.7kg / t steel.

[0081] The mass percentage of high-carbon ferrochrome is Cr: 62wt%, C: 6.0wt%, Si: 3.0wt%, with the remainder being Fe and unavoidable impurities. The amount of high-carbon ferrochrome added is 3.30 kg / t steel.

[0082] Argon blowing is carried out at the bottom of the converter throughout the entire steel tapping process until the steel is tapped.

[0083] (4) Steel refining in LF furnace: The ladle filled with molten steel in step (3) is hoisted to the LF refining furnace station. Argon gas is blown into the ladle to make the surface of the molten steel creep. After 9 minutes, the temperature of the molten steel is measured and a steel sample is taken. Based on the analysis results of the steel sample, the following alloying elements of the molten steel are adjusted: When the C, Si, Mn, S, P and other elements in the molten steel are controlled to be qualified, ferrovanadium is added at a rate of 0.32 kg / t steel. The mass percentage of V in the ferrovanadium is 50 wt%, and the rest is Fe and unavoidable impurities. The molten steel is heated to 1620℃ and then argon is blown for 4 minutes.

[0084] (5) VD vacuum refining: The molten steel from step (4) is hoisted into the vacuum tank of the VD furnace, the vacuum tank cover is closed, the vacuum is evacuated to 67 Pa, and argon gas is blown in from the bottom at a flow rate of 200 L / min. The gas is then degassed for 18 min under this vacuum. After that, the temperature is measured and the oxygen and hydrogen are determined.

[0085] (6) Steel casting: The molten steel from step (5) is cast in a tundish at a temperature of 1490℃, a casting speed of 2.0 m / min, and a cooling water flow rate of 120 m³ / min. 3 Under the conditions of a flow rate of 0.7 L / kg for secondary cooling water, and a process parameter of 300A and 4Hz for electromagnetic stirring in the crystallizer, molten steel is sent to a 9m seven-strand small billet continuous casting machine to cast molten steel into 165mm×165mm billets. The continuous casting machine adopts full-process protective casting to ensure the quality of the continuously cast billets. Specifically, from the ladle to the tundish, the ladle long nozzle is used for protection, the tundish liquid surface is covered with a micro-carbon covering agent for protection, the tundish to the crystallizer uses an immersion nozzle for protection, and the crystallizer liquid surface is protected with high-carbon steel protective slag.

[0086] (7) Slow cooling of billet: In the slow cooling zone, first lay two layers of hot billets of other steel grades at a temperature of 350℃, and then stack four layers of steel billets obtained in step (6) on the bottom layer in the order of pouring. Then, cover the billet with two layers of hot billets of other steel grades at a temperature of 350℃ and keep it warm for 72 hours.

[0087] (8) Billet rolling: The billet that has been kept warm and slowly cooled in step (7) is fed into a walking beam furnace. The temperature of the soaking zone is controlled at 1100℃ and the time in the furnace is 130min. Then, it is rough rolled for 6 passes on a roughing mill at a speed of 0.25m / s, then rolled for 5 passes on an intermediate mill at a speed of 12.0m / s, then rolled for 5 passes on a pre-finishing mill at a speed of 48.0m / s, then rolled for 5 passes on a finishing mill at a speed of 65m / s, and finally rolled for 5 passes on a reduction mill at a speed of 70m / s. The sizing mill rolls the wire rod in two passes, then spins it into coils at a temperature of 890℃ and a speed of 86m / s. The coils are then fed into a Stellmore air-cooling line with a roller conveyor speed of 1.20m / s and five fans. The first four fans provide 100% airflow, and the fifth fan provides 50% of the airflow from the first four fans. After exiting the Stellmore air-cooling line, the coils are naturally air-cooled to room temperature under an insulation cover, yielding hot-rolled wire rods for mattress springs with the following composition and properties: C The composition is 0.84 wt%, Si 0.24 wt%, Mn 0.83 wt%, Cr 0.22 wt%, S 0.005 wt%, P 0.008 wt%, O 0.0012 wt%, N 0.0030 wt%, V 0.038 wt%, with the remainder being Fe and unavoidable impurities; the hot-rolled wire rod has a tensile strength of 1280 MPa, a reduction of area of ​​44%, a microstructure of 95% sorbite, a central network cementite grade of 1.0, and a central martensite grade of 0.

[0088] The mechanical properties and metallographic structure of the hot-rolled wire rod for mattress spring steel wire obtained in Example 3 are shown in Table 3 below:

[0089] Table 3 Mechanical properties and metallographic structure of hot-rolled wire rods for mattress springs

[0090]

[0091] The hot-rolled wire rod of this embodiment 3 can be drawn to Φ1.8mm. According to user feedback, with the same number of mattress springs, replacing the original 2.0mm spring steel wire can reduce the weight by 10% and reduce the processing cost per ton of springs by 300 yuan, which has considerable economic and social benefits.

[0092] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0093] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A high-strength, high-toughness hot-rolled wire rod for mattress springs, characterized in that... Includes the following chemical components by mass percentage: C: 0.82~0.86wt%, Si: 0.18~0.30wt%, Mn: 0.76~0.90wt%, Cr: 0.19~0.25wt%, S≤0.010wt%, P≤0.010wt%, O≤0.0015wt%, N≤0.0035wt%, V: 0.030~0.046wt%, with the remainder being Fe and unavoidable impurities; and the hot-rolled wire rod has a tensile strength ≥1250MPa, a reduction of area ≥38%, a sorbite content ≥95%, a central network cementite ≤1.5 grade, and a central martensite ≤1.0 grade.

2. A method for preparing high-strength, high-toughness hot-rolled wire rod for mattress springs as described in claim 1, characterized in that... Includes the following steps: (1) Pretreatment of molten iron KR: After the molten iron is transported to the desulfurization station, it is first treated by slag removal and then by desulfurization. During the desulfurization treatment, 90% CaO and 10% CaF2 are added as desulfurizing agents at a rate of 5-12 kg / ton of iron. The mixture is stirred for 10-18 minutes with a stirring depth of 1100-1500 mm, a starting speed of 25-35 r / min, and a normal speed of 90-120 r / min. After stirring, the desulfurization slag is removed to obtain pretreated molten iron. (2) Converter smelting: The pretreated molten iron obtained in step (1) is added to the converter along with scrap steel for top and bottom composite blowing. The amount of molten iron added is 880-920 kg / t steel, and the amount of scrap steel added is 180-140 kg / t steel. At the same time, lime and lightly calcined dolomite are added for slag formation and smelting. The amount of lime added is 23-25 ​​kg / t steel, and the amount of lightly calcined dolomite added is 18-20 kg / t steel, until molten steel with a carbon content of 0.10-0.20 wt% and a temperature of 1590-1620℃ is obtained. Argon blowing is carried out at the bottom of the converter throughout the entire process before smelting and during tapping. (3) Deoxidation and alloying: The molten steel obtained in step (2) is poured into the ladle. When the amount of molten steel in the ladle is greater than 1 / 4, the following alloys are added in sequence: low-aluminum silicon-calcium-barium → high-carbon ferromanganese → ferrosilicon → high-carbon ferrochrome → carbon raiser. All the alloys are added when the amount of molten steel in the ladle reaches 3 / 4, so as to carry out deoxidation and alloying treatment, wherein: The mass percentage of low-aluminum silicon-calcium-barium is: Si: 50-55 wt%, Ca: 9-13 wt%, Ba: 11-14 wt%, Al≤0.50 wt%, P≤0.100 wt%, S≤0.100 wt%, O≤1.5 wt%, with the remainder being Fe and unavoidable impurities. The addition amount of low-aluminum silicon-calcium-barium is 1.14 kg / t steel. The mass percentage of high-carbon ferromanganese is: Mn: 75~82wt%, C≤8.0wt%, Si≤2.5wt%, with the remainder being unavoidable impurities. The amount of high-carbon ferromanganese added is 9.8~10.6kg / t steel. The mass percentage of ferrosilicon is: Si: 72-75wt%, with the remainder being unavoidable impurities. The amount of ferrosilicon added is 2.3-2.7 kg / t steel. The mass percentage of high-carbon ferrochrome is: Cr≥60wt%, C≤6.0wt%, Si≤3.0wt%, with the remainder being Fe and unavoidable impurities. The amount of high-carbon ferrochrome added is 3.20~3.50kg / t steel. Argon blowing is carried out at the bottom of the converter throughout the entire steel tapping process until the steel is tapped. (4) LF furnace refining: The ladle filled with molten steel in step (3) is hoisted to the LF refining furnace station. Argon gas is blown into the ladle to make the surface of the molten steel creep. After 8 to 10 minutes, the temperature of the molten steel is measured and a steel sample is taken. According to the analysis results of the steel sample, the following alloy element adjustments are made to the composition of the molten steel: When the C, Si, Mn, S and P elements in the molten steel are qualified, ferrovanadium is added at a rate of 0.30 to 0.36 kg / t of steel. The mass percentage of V in the ferrovanadium is 48 to 55 wt%, and the rest is Fe and unavoidable impurities. The molten steel is heated to 1610 to 1620℃ and then argon is blown for ≥3 minutes. (5) VD vacuum refining: The molten steel from step (4) is hoisted into the vacuum vessel of the VD furnace, the vacuum vessel lid is covered, and the vacuum is evacuated to 67 Pa. At the same time, argon gas is blown in from the bottom at a flow rate of 150-250 L / min, and degassing is performed under this vacuum for 15-18 min. Then, the temperature is measured by a molten steel thermometer, the oxygen is determined by a molten steel thermometer, and the hydrogen is determined by a molten steel thermometer. (6) Steel casting: The molten steel from step (5) is cast in a tundish at a temperature of 1487–1497°C, a casting speed of 1.9–2.0 m / min, and a cooling water flow rate of 120 m³ / min in the crystallizer. 3 Under the conditions of 0.7 L / kg for secondary cooling water and 300 A and 4 Hz for electromagnetic stirring in the crystallizer, the steel billet is cast into 165 mm × 165 mm steel billet by a seven-strand continuous casting machine with seven runners on an R9m scale. (7) Slow cooling of billet: In the slow cooling zone, first lay two layers of hot billets of other steel grades with a temperature ≥350℃, and then stack the steel billets obtained in step (6) in order of pouring sequence in up to 6 layers on the bottom layer. Then, cover the billet with two layers of hot billets of other steel grades with a temperature ≥350℃ and keep it warm for more than 72 hours. (8) Billet rolling: The billet that has been kept warm and slowly cooled in step (7) is fed into a walking beam furnace. The temperature of the soaking zone is controlled at 1080-1130℃ and the time in the furnace is 120-150 min. Then, it is rough rolled for 6 passes on a roughing mill at a speed of 0.25 m / s, then rolled for 5 passes on an intermediate mill at a speed of 12.0 m / s, then rolled for 5 passes on a pre-finishing mill at a speed of 48.0 m / s, then rolled for 5 passes on a finishing mill at a speed of 65 m / s, and then rolled for 5 passes on a finishing mill at a speed of 65 m / s. The wire rod is rolled in two passes on a 70 m / s reducing mill. Then, it is spun into coils at a temperature of 880–910°C and a speed of 80–88 m / s. The coils are fed into a Steyrmo air-cooling line with a roller speed of 1.10–1.30 m / s and five fans for air cooling. The first four fans have an air volume of 100%, and the fifth fan has an air volume of 50% of the air volume of the first four fans. After exiting the Steyrmo air-cooling line, the coils are naturally air-cooled to room temperature to obtain hot-rolled wire rods for mattress springs.

3. The preparation method according to claim 2, characterized in that... The chemical composition of the molten iron in step (1) is: C: 4.10-4.6wt%, Si: 0.20-0.40wt%, Mn: 0.10-0.20wt%, P: 0.090-0.120wt%, S≤0.030wt%, with the remainder being Fe and unavoidable impurities. The temperature of the molten iron is 1350-1400℃.

4. The preparation method according to claim 2, characterized in that... The amount of desulfurizing agent added in step (1) depends on the S content and temperature of the molten iron, as follows: S content in molten iron: 0.020wt%≤S≤0.030wt%, add more desulfurizing agent as appropriate; S content in molten iron: S<0.020wt%, add less desulfurizing agent as appropriate; molten iron temperature: 1375℃≤molten iron temperature≤1400℃, add more desulfurizing agent as appropriate; low molten iron temperature: 1350℃≤molten iron temperature<1375℃, add less desulfurizing agent as appropriate on the premise of ensuring the desulfurization rate.

5. The preparation method according to claim 2, characterized in that... In step (3), to ensure the quality of molten steel, lime is added to the ladle at a rate of 1-2 kg / t of steel before tapping, and refining slag is added to the ladle at a rate of 0.5-1 kg / t of steel for slag washing.

6. The preparation method according to claim 2, characterized in that... The chemical composition of the scrap steel in step (2) is: C≤2.0wt%, Si≤1.5wt%, Mn≤3.0wt%, P≤0.045wt%, S≤0.045wt%, with the remainder being Fe and unavoidable impurities.

7. The preparation method according to claim 2, characterized in that... The continuous casting process in step (6) adopts full-process protective casting to ensure the quality of the continuous casting billet. Specifically, the continuous casting tundish to the ladle is protected by the ladle long nozzle, the tundish liquid surface is protected by micro-carbon covering agent, the tundish to the crystallizer is protected by the immersion nozzle, and the crystallizer liquid surface is protected by high-carbon steel protective slag.

8. The preparation method according to claim 2, characterized in that... The number of steel billet stacking layers in step (7) is determined based on the specific production batch of the current period.

9. The preparation method according to claim 2, characterized in that... After the wire rod is air-cooled in step (8), it is naturally air-cooled in an environment with an insulation cover to further control the amount of martensite in the wire rod structure.

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