High-temperature-resistant high-carbon alloy spring steel and manufacturing method of hot-rolled coiled plate thereof

Abstract

The invention discloses high-temperature-resistant high-carbon alloy spring steel and a manufacturing method of a hot-rolled coil plate of the high-temperature-resistant high-carbon alloy spring steel. The high-temperature-resistant high-carbon alloy spring steel comprises, by weight, 0.58%-0.66% of C, 1.60%-2.00% of Si, 0.60%-0.90% of Mn, 0.015%-0.060% of Al, smaller than or equal to 0.015% of P, smaller than or equal to 0.010% of S, 0.30%-0.50% of Cr, 0.15%-0.25% of Ni, 0.02%-0.05% of Nb, smaller than or equal to 0.080% of Cu and the balance Fe and inevitable impurities. The manufacturing method of the high-temperature-resistant high-carbon alloy spring steel hot-rolled coil plate comprises the steps of molten iron pretreatment, converter smelting, LF refining, RH refining, slab continuous casting, slab hot rolling, heat treatment and the like. A high-temperature-resistant spring made of the high-temperature-resistant high-carbon alloy spring steel hot-rolled coil plate has the characteristics of high purity, high precision, high-temperature resistance, high yield point, high elastic limit, excellent toughness, fatigue resistance, corrosion resistance and hardenability, meets the use requirements of users on high-temperature-resistant spring steel, can completely replace imported springs, and has wide application prospects. And the technical blank in the field in China is filled.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and in particular relates to a method for manufacturing a high-temperature resistant high-carbon alloy spring steel and a hot-rolled coil thereof. Background Art

[0002] High temperature resistant springs include high temperature resistant compression springs, high temperature resistant tension springs, high temperature resistant torsion springs, high temperature resistant mold springs, high temperature resistant disc springs, etc., which can adapt to high temperature environments of 300-950℃. With its latest production process and material technology and long service life, high temperature resistant springs are widely used in industries such as automobiles, engineering machinery, printing machinery, and textile equipment. The choice of high temperature resistant spring material is determined according to actual needs. Commonly used high temperature resistant spring materials include silicon chrome steel, heat-treated stainless steel, chrome-molybdenum steel, and nickel-titanium shape memory alloy.

[0004] Therefore, developing a high-temperature resistant high-carbon alloy spring steel and its products to replace imports is of great significance for meeting the market demand of my country's products and improving the relevant technical level. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method for manufacturing high temperature resistant high carbon alloy spring steel and hot rolled coil thereof.

[0006] The high-temperature resistant high-carbon alloy spring steel provided by the present invention comprises, by weight percentage, C: 0.58%-0.66%, Si: 1.60%-2.00%, Mn: 0.60%-0.90%, Al: 0.015%-0.060%, P≤0.015%, S≤0.010%, Cr: 0.30%-0.50%, Ni: 0.15%-0.25%, Nb: 0.02%-0.05%, Cu≤0.080%, and the balance is Fe and unavoidable impurity elements.

[0007] Furthermore, the above-mentioned high temperature resistant high carbon alloy spring steel includes, by weight percentage: C: 0.59% to 0.65%, Si: 1.62% to 1.98%, Mn: 0.62% to 0.88%, Al: 0.018% to 0.038%, P≤0.010%, S≤0.006%, Cr: 0.31% to 0.49%, Ni: 0.16% to 0.24%, Nb: 0.022% to 0.049%, Cu≤0.020%, and the balance is Fe and unavoidable impurity elements.

[0008] The method for manufacturing a high temperature resistant high carbon alloy spring steel hot rolled coil provided by the present invention comprises the following steps:

[0009] (1) Pretreatment of molten iron to reduce the S content in the molten iron to ≤ 0.003%;

[0010] (2) converter smelting, adding molten iron and scrap steel into a converter for smelting and alloying, followed by argon blowing treatment, and outputting molten steel, wherein the sulfur content in the scrap steel is controlled to be S≤0.03%, and the weight percentage of the molten iron and scrap steel added to the converter is controlled to be (80% to 95%): (5% to 20%);

[0011] (3) LF refining, sending the molten steel into the LF furnace for desulfurization treatment until the S content in the molten steel is ≤0.002%, and then fine-tuning the alloy element composition and stirring until uniform to obtain refined molten steel;

[0012] (4) RH refining, the refined molten steel is sent to the RH furnace for circulation under vacuum, and after breaking the vacuum, the molten steel is subjected to inclusion denaturation treatment under weak stirring conditions;

[0013] (5) Slab continuous casting, wherein the continuous casting slab is produced by continuous casting, wherein the pouring temperature is controlled at 1460-1560°C, the target pulling speed is controlled at 0.80-1.60 m / min, the superheat of the molten steel is controlled at 15-50°C, the slab is lightly pressed down by 0-5 mm, the electromagnetic stirring frequency is controlled at 2.5-5.0 Hz, and the protective slag parameters used in the continuous casting process are: melting point 1050±30°C, viscosity 0.5±0.05 poise at 1300°C, basicity 1.0±0.05, and melting speed 25±10 seconds;

[0014] (6) slab hot rolling, wherein the continuous casting slab is sequentially subjected to slab heating, high-pressure water descaling, rough rolling, high-pressure water descaling, finishing rolling, cooling after rolling, coiling, and cooling after coiling to obtain a hot rolled coil, wherein the slab heating temperature is controlled at 1200 to 1320° C., the rough rolling and finishing rolling temperature is controlled at 970 to 1170° C., the intermediate slab thickness is controlled at 25 to 60 mm, the finishing rolling and finishing rolling temperature is controlled at 780 to 940° C., and the coiling temperature is controlled at 550 to 830° C.;

[0015] (7) Heat treatment: heat treatment is performed on the hot-rolled coil to finally obtain a high-temperature resistant high-carbon alloy spring steel hot-rolled coil, wherein the heat treatment temperature of the hot-rolled coil is controlled to be 550-870°C.

[0016] As an optional embodiment, before the slab hot rolling step of the above-mentioned method for manufacturing high-temperature resistant high-carbon alloy spring steel hot-rolled coil, it also includes a step of hot transporting and hot loading the continuous casting slab, and the slab hot transport and hot loading temperature is controlled to be ≥150°C.

[0017] As another optional embodiment, before the slab hot rolling step of the above-mentioned method for manufacturing high-temperature resistant high-carbon alloy spring steel hot-rolled coil, it also includes slab heat treatment + slab grinding + slab coating treatment, wherein the slab heat treatment temperature is controlled to be 550-870°C.

[0018] Furthermore, in the converter smelting step of the above-mentioned method for manufacturing the hot-rolled coil of high-temperature resistant high-carbon alloy spring steel, alloying is performed by adding carbon powder, aluminum iron, high-carbon ferromanganese, silicon-manganese alloy and ferrochrome into the converter before the converter taps the steel.

[0019] Furthermore, in the LF refining step of the above-mentioned method for manufacturing the hot-rolled coil of high-temperature resistant high-carbon alloy spring steel, desulfurization is carried out by adding lime into the LF furnace, and stirring is carried out by bottom blowing argon, wherein the bottom blowing argon flow rate is 25 to 220 NL / min, and the stirring time is not less than 10 minutes.

[0020] Furthermore, in the RH refining step of the above-mentioned method for manufacturing the hot-rolled coil of high-temperature resistant high-carbon alloy spring steel, circulation under vacuum is performed by circulating for more than 12 minutes at a vacuum pressure value not greater than 8 mbar, wherein weak stirring is performed by bottom blowing argon, and the bottom blowing argon weak stirring time is not less than 10 minutes.

[0021] Furthermore, in the above-mentioned manufacturing method of the hot-rolled coil of high-temperature resistant high-carbon alloy spring steel, the yield strength of the hot-rolled coil of high-temperature resistant high-carbon alloy spring steel is 550-1350MPa, the tensile strength is 735-1650MPa, the elongation is ≥10.5%, the Brinell hardness is 220-460, and the depth of the single-sided decarburization layer is <0.01mm; the yield strength of the hot-rolled coil of high-temperature resistant high-carbon alloy spring steel in the heat treatment annealing state is 335-835MPa, the tensile strength is 450-1050MPa, the elongation is ≥20%, the Brinell hardness is 130-320, and the depth of the single-sided decarburization layer is ≤0.01mm; the total amount of inclusions of the hot-rolled coil of high-temperature resistant high-carbon alloy spring steel is ≤0.5.

[0022] As an optional implementation, the manufacturing method of the high temperature resistant high carbon alloy spring steel hot rolled coil may further include inspection and packaging steps after the heat treatment step, that is, after the hot rolled coil is heat treated, quality and performance inspection → packaging marking → warehousing are carried out in sequence.

[0023] The technical solution of the present invention has the following beneficial effects: the present invention develops a high-temperature resistant high-carbon alloy spring steel and a hot-rolled coil product thereof, and the manufactured high-temperature resistant spring has the characteristics of high purity, high precision, high temperature resistance, high yield point, high elastic limit, and excellent toughness, fatigue resistance, corrosion resistance and hardenability, which meets the user's requirements for the use of high-temperature resistant spring steel, can completely replace imports, and fills the technical gap in this field in my country. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0025] Figure 1 This is a microstructure image of the annealed state of a high temperature resistant high carbon alloy spring steel hot rolled coil prepared by the method for manufacturing the high temperature resistant high carbon alloy spring steel hot rolled coil according to an embodiment of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] The present invention aims to provide a high-temperature resistant high-carbon alloy spring steel and a method for manufacturing a hot-rolled coil thereof, which has the characteristics of high purity, high precision, high temperature resistance, high yield point, high elastic limit, and excellent toughness, fatigue resistance, corrosion resistance and hardenability, so as to meet the user's requirements for the use of high-temperature resistant spring steel and fill the technical gap in this field.

[0028] In a first aspect of the present invention, a high-temperature resistant high-carbon alloy spring steel is provided. The high-temperature resistant high-carbon alloy spring steel uses C, Si, Mn, and Al as main elements, and uses Cr, Ni, and Nb as alloying elements. Specifically, the high-temperature resistant high-carbon alloy spring steel includes, by weight percentage, C: 0.58% to 0.66%, Si: 1.60% to 2.00%, Mn: 0.60% to 0.90%, Al: 0.015% to 0.060%, P≤0.015%, S≤0.010%, Cr: 0.30% to 0.50%, Ni: 0.15% to 0.25%, Nb: 0.02% to 0.05%, Cu≤0.080%, and the remainder is Fe and unavoidable impurity elements.

[0029] Preferably, the high temperature resistant high carbon alloy spring steel of the present invention comprises, by weight percentage: C: 0.59% to 0.65%, Si: 1.62% to 1.98%, Mn: 0.62% to 0.88%, Al: 0.018% to 0.038%, P≤0.010%, S≤0.006%, Cr: 0.31% to 0.49%, Ni: 0.16% to 0.24%, Nb: 0.022% to 0.049%, Cu≤0.020%, and the balance is Fe and unavoidable impurity elements.

[0030] The present invention optimizes the material elements and their contents to achieve a synergistic effect between the elements. The effects of the elements in the high temperature resistant high carbon alloy spring steel of the present invention are described as follows:

[0031] Carbon: Carbon is the most economical and basic strengthening element in steel. In the present invention, the C content is controlled within a range of 0.58% to 0.66%, preferably within a range of 0.59% to 0.65%.

[0032] Silicon: Silicon can significantly improve the elastic limit, yield point and tensile strength of steel, and combined with Cr, it can improve corrosion resistance and oxidation resistance. In the present invention, the Si content is controlled at 1.60% to 2.00%, preferably 1.62% to 1.98%.

[0033] Manganese: Manganese can strengthen steel, improve its strength, hardness and wear resistance, and can also reduce the critical cooling rate of steel, improve its hardenability, refine pearlite and improve the strength of pearlite steel. In the present invention, the Mn content is controlled at 0.60% to 0.90%, preferably 0.62% to 0.88%.

[0034] Aluminum: Aluminum is the main deoxidizing element and nitrogen-fixing element in steel. Adding a small amount of aluminum to steel can refine the grains, improve impact toughness, and especially reduce the brittle transition temperature of steel. However, if too much aluminum is used during deoxidation, the graphitization tendency of steel will be promoted. When the aluminum content is high, its high-temperature strength and toughness are low. Aluminum also has antioxidant and corrosion resistance. The present invention controls the Al content to 0.015% to 0.060%, preferably 0.018% to 0.038%, which can not only improve the toughness of steel at low temperatures, reduce the brittle transition temperature of steel, but also avoid the graphitization tendency of steel.

[0035] Phosphorus: Phosphorus is a harmful element in steel. Its biggest harm is serious segregation, increased temper brittleness, significantly reduced toughness and brittleness of steel, and increased cold brittleness of steel. In the present invention, the P content is controlled to ≤0.015%, preferably ≤0.010%.

[0036] Sulfur: Sulfur is also a harmful element, which makes steel hot brittle, reduces the ductility and toughness of steel, and reduces corrosion resistance. In the present invention, the S content is controlled to ≤ 0.010%, preferably ≤ 0.006%.

[0037] Chromium: Chromium can improve the strength, hardness, high temperature mechanical properties, hardenability, and wear resistance of steel, and make the steel have good corrosion resistance and oxidation resistance, tempering stability and toughness, and also has the function of preventing graphitization. The present invention controls the Cr content to 0.30% to 0.50%, preferably 0.31% to 0.49%, which can effectively improve various properties of steel.

[0038] Nickel: Nickel is a solid solution strengthener in steel and a good hardenability additive. It can improve the hardenability by reducing the critical transition temperature and the diffusion rate of each element in the steel. It can improve the fatigue performance of steel and reduce the sensitivity of steel to notches. Nickel can increase the pearlite content in the normalized state and refine the grains. Nickel-chromium or nickel-chromium-molybdenum steel used in mechanical manufacturing can obtain comprehensive mechanical properties with good strength and toughness after heat treatment. The present invention controls the Ni content to 0.15% to 0.25%, preferably 0.16% to 0.24%.

[0039] Niobium: Niobium is mainly used in the steel industry to manufacture various alloy steels, heat-resistant alloys, niobium-based alloys and niobium carbide. Niobium is one of the main alloying elements of steel, and has excellent properties such as improving the mechanical and welding properties of steel, increasing the heat resistance and corrosion resistance of steel, and reducing the brittleness of steel. In the present invention, the Nb content is controlled to 0.02% to 0.05%, preferably 0.022% to 0.049%.

[0040] Copper: In order to solve the influence of residual Cu on intergranular cracks of continuous casting billets, it is generally required that the Cu content of medium-high carbon steel is less than 0.3%, and low secondary cooling intensity and high continuous casting speed are required. In the present invention, the Cu content is controlled to ≤ 0.080%, preferably ≤ 0.020%.

[0041] In a second aspect of the present invention, a method for manufacturing a high temperature resistant high carbon alloy spring steel hot rolled coil is provided, comprising the following steps:

[0042] (1) Pretreatment of molten iron to reduce the S content in the molten iron to ≤0.003%. The molten iron is blast furnace molten iron and the slag must be removed cleanly during pretreatment of the molten iron;

[0043] (2) converter smelting, adding molten iron and scrap steel into a converter for smelting and alloying, followed by argon blowing to output molten steel, wherein the weight percentage of molten iron and scrap steel added into the converter is controlled to be (80% to 95%): (5% to 20%), the sulfur content in the scrap steel is controlled to be S≤0.03%, and alloying is performed by adding carbon powder, aluminum iron, high carbon ferromanganese, silicon manganese alloy and ferrochrome into the converter before steel is tapped from the converter;

[0044] (3) LF refining, wherein the molten steel is sent to the LF furnace for desulfurization treatment until the S content in the molten steel is ≤0.002%, and then the alloy element composition is finely adjusted and stirred until uniform to obtain refined molten steel. Preferably, lime is added to the LF furnace in proportion to carry out desulfurization treatment, and stirring is carried out by bottom blowing argon, wherein the bottom blowing argon flow rate is 25 to 220 NL / min, and the stirring time is not less than 10 minutes;

[0045] (4) RH refining, wherein the molten steel is fed into an RH furnace for circulation under vacuum, and after breaking the vacuum, the molten steel is subjected to inclusion denaturation treatment under weak stirring conditions. Preferably, the molten steel is subjected to vacuum circulation for more than 12 minutes under a vacuum pressure value of not more than 8 mbar, thereby achieving control of hydrogen and nitrogen as well as uniform control of the contents of other components and the temperature of the molten steel, wherein weak stirring is performed by bottom blowing argon, and the bottom blowing argon weak stirring time is not less than 10 minutes;

[0046] (5) Slab continuous casting: Continuously cast slabs are produced by continuous casting, wherein the pouring temperature is controlled at 1460-1560°C, the target pulling speed is controlled at 0.80-1.60 m / min, the superheat of the molten steel is controlled at 15-50°C, the ingot is lightly pressed down by 0-5 mm, and the electromagnetic stirring frequency is controlled at 2.5-5.0 Hz, thereby effectively preventing the occurrence of slab cracks. Special protective slag is used in the continuous casting process, and its parameters are: melting point 1050±30°C, viscosity 0.5±0.05 poise at 1300°C, basicity 1.0±0.05, melting speed 25±10 seconds, thereby effectively avoiding slag inclusions and pore defects on the slab surface.

[0047] (6) hot rolling of slabs, wherein the continuous casting slabs are sequentially subjected to slab heating, high-pressure water descaling, rough rolling, high-pressure water descaling, finishing rolling, cooling after rolling, coiling, and cooling after coiling to obtain hot rolled coils. Preferably, the continuous casting slabs are heated to 1200-1320° C. in a walking beam heating furnace, the rough rolling and finishing rolling temperatures are controlled to be 970-1170° C., the intermediate slab thickness is controlled to be 25-60 mm, the finishing rolling temperature is controlled to be 780-940° C., and the coiling temperature is controlled to be 550-830° C., thereby achieving control over oxidation, burning, temperature and uniformity of the slabs, and effectively controlling slab crack defects that may occur in the hot rolling connection process;

[0048] (7) Heat treatment: The hot-rolled coil is heat treated to obtain a high-temperature resistant high-carbon alloy spring steel hot-rolled coil, which is then inspected and packaged. That is, after the hot-rolled coil is heat treated, it is inspected for quality and performance → packaged and marked → put into storage. The heat treatment temperature of the hot-rolled coil is controlled at 550-870°C, thereby improving the performance and structure of the hot-rolled coil and preparing for subsequent processing.

[0049] As an optional embodiment, the step of hot-transferring and hot-loading the continuous casting slab may be included before the slab hot rolling step, wherein the slab hot-transferring and hot-loading temperature is controlled to be ≥150°C, thereby achieving control over the generation of cracks in the continuous casting slab.

[0050] As another set of optional implementations, the slab hot rolling step may also include slab heat treatment + slab grinding + slab coating treatment, wherein the slab heat treatment temperature is controlled to be 550-870°C, thereby achieving control over the generation of cracks in the continuous casting slab.

[0051] As an embodiment, the high temperature resistant high carbon alloy spring steel hot rolled coil of the present invention can be produced by an 80 ton or 180 ton top and bottom combined blowing converter and a 1549mm or 2250mm hot rolling mill. The prepared high temperature resistant high carbon alloy spring steel hot rolled coil has a thickness of 1.5 to 25.4 mm and a width of 1000 to 2130 mm.

[0052] After performance testing, the high temperature resistant high carbon alloy spring steel hot rolled coil prepared by the above-mentioned manufacturing method of high temperature resistant high carbon alloy spring steel hot rolled coil has the following properties:

[0053] (1) Mechanical properties in hot-rolled state: yield strength is 550-1350MPa, tensile strength is 735-1650MPa, elongation is ≥10.5%, Brinell hardness is 220-460, single-side decarburization layer depth is <0.01mm;

[0054] (2) Mechanical properties of heat-treated annealed state: yield strength 335-835 MPa, tensile strength 450-1050 MPa, elongation ≥ 20%, Brinell hardness 130-320, single-side decarburization layer depth ≤ 0.01 mm;

[0055] (3) The total amount of inclusions is ≤0.5.

[0056] The following is a detailed description of the method for manufacturing the high temperature resistant high carbon alloy spring steel and the hot rolled coil thereof of the present invention in conjunction with the embodiments. The implementation methods without specific conditions in the following embodiments are carried out according to conventional methods and conditions, and the present invention does not make specific limitations on this.

[0057] The standards and methods for measuring the performance parameters in the following embodiments are as follows:

[0058] Yield strength: GB / T 228 Metal material room temperature tensile test method

[0059] Tensile strength: GB / T 228 Metal material room temperature tensile test method

[0060] Elongation: GB / T 228 Metal material room temperature tensile test method

[0061] Brinell hardness: GB / T 231.1 Metal Brinell hardness test method

[0062] Decarburization layer thickness: GB / T 224 steel decarburization layer depth determination method

[0063] Inclusions: GB / T 10561 Microscopic evaluation method for non-metallic inclusions

[0064] Example 1

[0065] The components and weight percentages of the high temperature resistant high carbon alloy spring steel of Example 1 of the present invention are: C: 0.62%, Si: 1.85%, Mn: 0.78%, Al: 0.025%, P≤0.008%, S≤0.002%, Cr: 0.40%, Ni: 0.20%, Nb: 0.03%, Cu≤0.06%, and the remainder is Fe and unavoidable impurity elements.

[0066] The manufacturing method of the high temperature resistant high carbon alloy spring steel hot rolled coil of Example 1 of the present invention is carried out on an 80 ton top and bottom combined blowing converter and a 1549 mm hot rolling mill, and specifically comprises the following steps:

[0067] (1) Pretreatment of molten iron: blast furnace molten iron is used for pretreatment, slag is removed during pretreatment, and the molten iron is desulfurized to a sulfur content of 0.003% by molten iron pretreatment;

[0068] (2) converter smelting, adding 70 tons of pre-treated molten iron that meets the requirements of converter smelting and 15 tons of scrap steel with [S] ≤ 0.03% into the converter for smelting, and adding carbon powder, ferroaluminum, high carbon ferromanganese, silicon manganese alloy and ferrochrome into the converter before steel is tapped from the converter for alloying;

[0069] (3) LF refining, in which the molten steel is desulfurized to a sulfur content of 0.0013% by adding lime to the LF furnace, followed by microalloying, fine-tuning of the composition, and weak stirring with bottom blowing of argon at a flow rate of 120 NL / min for 16 minutes;

[0070] (4) RH refining, circulating for 20 minutes at a vacuum pressure of 5 mbar, after breaking the vacuum, feeding 150 mCa-Si wire for inclusion denaturation treatment, and then blowing argon at a flow rate of 125 NL / min for 15 minutes with weak stirring;

[0071] (5) Slab continuous casting: adding molten steel from the ladle into the tundish, passing through a crystallizer, and continuously casting into a slab with a thickness of 220 mm, a width of 1250 mm, and a length of 8000 m. The continuous casting slab pulling speed is 1.50 m / min, the continuous casting pouring temperature is 1530°C, the slab is gently pressed down by 2.6 mm, the electromagnetic stirring frequency is 3.0 Hz, and the parameters of the special protective slag are: melting point 1050±30°C, viscosity 0.5±0.05 poise at 1300°C, basicity 1.0±0.05, and melting speed 25±10 seconds;

[0072] (6) Hot delivery and hot loading of slabs, the temperature of hot delivery and hot loading of slabs is 300°C;

[0073] (7) Slab hot rolling: the slab is rolled into hot rolled coils through the following processes:

[0074] a. Heating the slab: heating the slab in a walking beam heating furnace at a heating temperature of 1250°C;

[0075] b. Rough rolling high-pressure water descaling: the heated slab is subjected to rough rolling high-pressure water descaling to remove the iron oxide scale formed on the surface of the slab;

[0076] c. Rough rolling unit rolling: the slab is reciprocated and rolled for 7 times in a four-roll reversible rough rolling unit to form an intermediate slab with a thickness of 30 mm, a width of 1250 mm and a length of 58667 mm. The rough rolling final rolling temperature is 1100°C;

[0077] d. Finish rolling high-pressure water descaling, which removes the secondary iron oxide scale on the surface of the intermediate billet;

[0078] e. Rolling by the finishing mill, the intermediate billet is made into a steel strip with a thickness of 4.0 mm, a width of 1250 mm and a length of 440 m in the 7-stand finishing mill, and the finishing rolling temperature is 860°C;

[0079] e. Coiling: Use a 3-roller fully hydraulic mobile coiler to coil the steel strip into hot-rolled coils at a coiling temperature of 630°C;

[0080] (8) Heat treatment: heat treatment is performed on the hot-rolled coil to finally obtain a high-temperature resistant high-carbon alloy spring steel hot-rolled coil, wherein the heat treatment temperature of the hot-rolled coil is 670°C.

[0081] The annealed microstructure of the high temperature resistant high carbon alloy spring steel hot rolled coil prepared by the manufacturing method of the high temperature resistant high carbon alloy spring steel hot rolled coil of Example 1 of the present invention is shown in FIG. Figure 1 After quality and performance inspection, the inspection results of the high temperature resistant high carbon alloy spring steel hot rolled coil prepared by the manufacturing method of the high temperature resistant high carbon alloy spring steel hot rolled coil of Example 1 of the present invention are as follows:

[0082] (1) Mechanical properties in hot-rolled state: yield strength is 810 MPa, tensile strength is 1210 MPa, elongation is 13%, Brinell hardness is 330, and single-side decarburization layer depth is 0.00 mm;

[0083] (2) Mechanical properties of heat-treated annealed state: yield strength is 550 MPa, tensile strength is 860 MPa, elongation is 25%, Brinell hardness is 188, and single-side decarburization layer depth is 0.01 mm;

[0084] (3) The total amount of inclusions is 0.

[0085] Embodiment 2 to Embodiment 5

[0086] The components and weight percentages of the high temperature resistant high carbon alloy spring steels of Examples 2 to 5 of the present invention are shown in Table 1 below:

[0087] Table 1 Composition of high temperature resistant high carbon alloy spring steel of Examples 2 to 5 (wt%, the rest is Fe and unavoidable impurities)

[0088] C Si Mn P S Al Cr Ni Nb Cu Example 2 0.58 1.70 0.65 0.010 0.002 0.025 0.32 0.20 0.045 0.02 Example 3 0.60 1.80 0.68 0.009 0.005 0.030 0.45 0.22 0.035 0.01 Example 4 0.63 1.91 0.80 0.006 0.003 0.055 0.35 0.15 0.038 0.06 Example 5 0.65 1.78 0.82 0.007 0.006 0.018 0.42 0.18 0.026 0.04

[0089] The manufacturing methods of the high temperature resistant high carbon alloy spring steel hot rolled coils of Examples 2 to 5 of the present invention are the same as those of Example 1 except for the process parameters listed in Table 2 below.

[0090] Table 2 Process parameters of the manufacturing method of high temperature resistant high carbon alloy spring steel hot rolled coils of Examples 2 to 5

[0091]

[0092] The properties of the high temperature resistant high carbon alloy spring steel hot rolled coils prepared by the manufacturing methods of high temperature resistant high carbon alloy spring steel hot rolled coils of Examples 2 to 5 of the present invention are shown in Table 3 below:

[0093] Table 3 Hot-rolled mechanical properties of high-temperature resistant high-carbon alloy spring steel hot-rolled coils of Examples 2 to 5

[0094]

[0095] In summary, the present invention has developed a high-temperature resistant high-carbon alloy spring steel and its hot-rolled coil product. The manufactured high-temperature resistant spring has the characteristics of high purity, high precision, high temperature resistance, high yield point, high elastic limit, and excellent toughness, fatigue resistance, corrosion resistance, and hardenability. It meets the user's requirements for the use of high-temperature resistant spring steel, can completely replace imports, and fills the technical gap in this field in my country. Compared with the prior art, the manufacturing method of the high-temperature resistant high-carbon alloy spring steel and its hot-rolled coil of the present invention has the following advantages and beneficial effects:

[0096] (1) Through chemical composition optimization and production process design, the molten iron is pretreated to make the S in the molten iron ≤ 0.003%, and high-quality scrap steel with S ≤ 0.03% is selected. After entering the converter for smelting, LF deep desulfurization is used to reduce the S to ≤ 0.002%, which can effectively ensure that the springs made of high-temperature resistant high-carbon alloy spring steel hot-rolled coils have good performance;

[0097] (2) Pure steel can be obtained by adopting the off-furnace refining technology of LF deep desulfurization + RH vacuum degassing and Ca treatment spheroidizing inclusion technology; the occurrence of corner cracks can be effectively prevented by the reasonable application of temperature control at each node of the smelting process, oxygen and nitrogen control in the whole process, light pressure reduction and electromagnetic stirring technology;

[0098] (3) By optimizing the continuous casting process parameters and developing special mold slag, the uneven melting of the mold slag caused by low pouring temperature and low pouring speed is avoided, which causes slag inclusion and porosity defects on the slab surface;

[0099] (4) Through specific hot delivery and hot loading processes, heat treatment processes, slab grinding and coating processes, the slab crack defects that may occur in the connection process between steelmaking and hot rolling are effectively controlled, and high-temperature resistant high-carbon alloy spring steel hot-rolled coils with pure steel quality and excellent quality are obtained;

[0100] (5) The hot-rolled high-carbon alloy spring steel coil of the present invention has a yield strength of 550-1350 MPa, a tensile strength of 735-1650 MPa, an elongation of ≥10.5%, a Brinell hardness of 220-460, and a single-sided decarburization layer depth of <0.01 mm in the hot-rolled state; the yield strength of the heat-treated annealed state is 335-835 MPa, the tensile strength is 450-1050 MPa, the elongation is ≥20%, the Brinell hardness is 130-320, and the single-sided decarburization layer depth is ≤0.01 mm; the total amount of inclusions in the hot-rolled coil is ≤0.5, which is fully suitable for the production of high-temperature resistant springs, and the performance meets the use requirements, and the applicable temperature meets 300-950°C.

[0101] It should be noted that, in addition to the explicit description herein, the process method of the present invention can be implemented by conventional methods or devices in the art, and the noun terms in this article, unless otherwise specified, have the meanings generally understood by those skilled in the art. Moreover, when a numerical range is disclosed herein, the above range is deemed to be continuous and includes the minimum and maximum values ​​of the range, and each value between such minimum and maximum values. Further, when the range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple range description features are provided, the range can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges included therein.

[0102] It should also be noted that, in this article, the term "comprise" or any other variation thereof is intended to cover non-exclusive inclusion, so that an article or device that includes a series of elements includes not only those elements, but also includes other elements that are not explicitly listed, or also includes elements that are inherent to such article or device.

[0103] In addition, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the present invention.

Claims

1. A high temperature resistant high carbon alloy spring steel, characterized in that: The high temperature resistant high carbon alloy spring steel comprises, by weight percentage, C: 0.58% to 0.66%, Si: 1.60% to 2.00%, Mn: 0.60% to 0.90%, Al: 0.015% to 0.060%, P≤0.015%, S≤0.010%, Cr: 0.30% to 0.50%, Ni: 0.15% to 0.25%, Nb: 0.02% to 0.05%, Cu≤0.080%, and the remainder is Fe and unavoidable impurity elements.

2. The high temperature resistant high carbon alloy spring steel according to claim 1, characterized in that: The high temperature resistant high carbon alloy spring steel comprises, by weight percentage, C: 0.59% to 0.65%, Si: 1.62% to 1.98%, Mn: 0.62% to 0.88%, Al: 0.018% to 0.038%, P≤0.010%, S≤0.006%, Cr: 0.31% to 0.49%, Ni: 0.16% to 0.24%, Nb: 0.022% to 0.049%, Cu≤0.020%, and the remainder is Fe and unavoidable impurity elements.

3. A method for manufacturing a high temperature resistant high carbon alloy spring steel hot rolled coil, characterized in that: The steps include: (1) Pretreatment of molten iron to reduce the S content in the molten iron to ≤ 0.003%; (2) converter smelting, adding molten iron and scrap steel into a converter for smelting and alloying, followed by argon blowing treatment, and outputting molten steel, wherein the sulfur content in the scrap steel is controlled to be S≤0.03%, and the weight percentage of the molten iron and scrap steel added to the converter is controlled to be (80% to 95%): (5% to 20%); (3) LF refining, sending the molten steel into the LF furnace for desulfurization treatment until the S content in the molten steel is ≤0.002%, and then fine-tuning the alloy element composition and stirring until uniform to obtain refined molten steel; (4) RH refining, the refined molten steel is sent to the RH furnace for circulation under vacuum, and after breaking the vacuum, the molten steel is subjected to inclusion denaturation treatment under weak stirring conditions; (5) Slab continuous casting, wherein the continuous casting slab is produced by continuous casting, wherein the pouring temperature is controlled at 1460-1560°C, the target pulling speed is controlled at 0.80-1.60 m / min, the superheat of the molten steel is controlled at 15-50°C, the slab is lightly pressed down by 0-5 mm, the electromagnetic stirring frequency is controlled at 2.5-5.0 Hz, and the protective slag parameters used in the continuous casting process are: melting point 1050±30°C, viscosity 0.5±0.05 poise at 1300°C, basicity 1.0±0.05, and melting speed 25±10 seconds; (6) slab hot rolling, wherein the continuous casting slab is sequentially subjected to slab heating, high-pressure water descaling, rough rolling, high-pressure water descaling, finishing rolling, cooling after rolling, coiling, and cooling after coiling to obtain a hot rolled coil, wherein the slab heating temperature is controlled at 1200 to 1320° C., the rough rolling and finishing rolling temperature is controlled at 970 to 1170° C., the intermediate slab thickness is controlled at 25 to 60 mm, the finishing rolling and finishing rolling temperature is controlled at 780 to 940° C., and the coiling temperature is controlled at 550 to 830° C.; (7) Heat treatment: heat treatment is performed on the hot-rolled coil to finally obtain a high-temperature resistant high-carbon alloy spring steel hot-rolled coil, wherein the heat treatment temperature of the hot-rolled coil is controlled to be 550-870°C.

4. The method for manufacturing a high temperature resistant high carbon alloy spring steel hot rolled coil according to claim 3, characterized in that: Before the slab hot rolling step, the method also includes a step of hot transporting and hot charging the continuous casting slab, wherein the slab hot transporting and hot charging temperature is controlled to be ≥150°C.

5. The method for manufacturing a high temperature resistant high carbon alloy spring steel hot rolled coil according to claim 3, characterized in that: Before the slab hot rolling step, it also includes slab heat treatment + slab grinding + slab coating treatment, wherein the slab heat treatment temperature is controlled at 550-870°C.

6. The method for manufacturing a high temperature resistant high carbon alloy spring steel hot rolled coil according to claim 3, characterized in that: In the converter smelting step, alloying is performed by adding carbon powder, ferroaluminum, high carbon ferromanganese, silicon manganese alloy and ferrochrome into the converter before the steel is tapped.

7. The method for manufacturing a high temperature resistant high carbon alloy spring steel hot rolled coil according to claim 3, characterized in that: In the LF refining step, desulfurization is carried out by adding lime into the LF furnace, and stirring is carried out by bottom blowing argon, wherein the bottom blowing argon flow rate is 25 to 220 NL / min, and the stirring time is not less than 10 minutes.

8. The method for manufacturing a high temperature resistant high carbon alloy spring steel hot rolled coil according to claim 3, characterized in that: In the RH refining step, circulation under vacuum is performed by circulating for more than 12 minutes at a vacuum pressure value of not more than 8 mbar, wherein weak stirring is performed by bottom blowing argon, and the bottom blowing argon weak stirring time is not less than 10 minutes.

9. The method for manufacturing a hot-rolled coil of high-temperature resistant high-carbon alloy spring steel according to any one of claims 3 to 8, characterized in that: The yield strength of the hot-rolled coil of the high-temperature resistant high-carbon alloy spring steel is 550-1350MPa, the tensile strength is 735-1650MPa, the elongation is ≥10.5%, the Brinell hardness is 220-460, and the depth of the single-sided decarburization layer is <0.01mm; the yield strength of the hot-rolled coil of the high-temperature resistant high-carbon alloy spring steel in the heat treatment annealing state is 335-835MPa, the tensile strength is 450-1050MPa, the elongation is ≥20%, the Brinell hardness is 130-320, and the depth of the single-sided decarburization layer is ≤0.01mm; the total amount of inclusions of the hot-rolled coil of the high-temperature resistant high-carbon alloy spring steel is ≤0.5.

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