Alloy steel hot-rolled coil plate for bearing as well as preparation method and application thereof

Abstract

The invention relates to an alloy steel hot-rolled coil plate for a bearing as well as a preparation method and application of the alloy steel hot-rolled coil plate. The coil plate comprises the following components in percentage by weight: 0.95-1.15% of C; 0.15% to 1.30% of Si; 0.20% to 1.20% of Mn; 0.015% to 0.080% of Al; p < = 0.012%; s < = 0.009%; 1.25% to 5.0% of Cr; 0 to 1.00% of Mo; 0 to 0.50 percent of V; 0 to 0.50 percent of Ni; 0 to 0.060 percent of Nb; cu: less than or equal to 0.080%; ti: less than or equal to 0.005%; h: < = 0.0002%; n < = 0.008%; o: < = 0.0012%; as: less than or equal to 0.010%; less than or equal to 0.002% of Pb; ca is less than or equal to 0.003%, and the balance is Fe and impurity elements. The steel has the advantages of good comprehensive performance and capability of meeting the use requirements of the bearing steel.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a hot-rolled alloy steel coil for bearings and a preparation method and application thereof. Background Art

[0002] Bearings are parts that support the rotating parts on the shaft neck or shaft. They are widely used and demanding supporting basic parts in the mechanical industry and civil equipment, and are called mechanical joints.

[0003] The service life and reliability of bearings determine the performance of bearings to a certain extent. With the development of science and technology, many fields have put forward many newer, higher and more stringent requirements for bearings, such as requiring bearings to have higher rotation speeds, higher operating temperatures, higher wear resistance and fatigue life, and higher reliability; secondly, the working conditions of bearings are becoming more and more complex. Correspondingly, the requirements for bearing steel are also getting higher and higher. Bearing steel is divided into high carbon chromium bearing steel, carburized bearing steel, stainless bearing steel and high temperature bearing steel. The output of bearing steel in my country has increased year by year. With the development of technology, it has expanded from rod and wire profiles to plates and strips, especially in the field of wide strip steel. The demand for bearing steel has also continued to increase, which is a good time for vigorous development. Therefore, the development of a hot-rolled coil of alloy steel for bearings is of great significance to the development of the national economy. Summary of the invention

[0004] In order to solve all or part of the above problems, the present invention aims to provide a hot-rolled alloy steel coil for bearings and a preparation method and application thereof.

[0005] According to one aspect of the present invention, there is provided a hot-rolled alloy steel coil for bearings, wherein the hot-rolled alloy steel coil for bearings comprises the following components by weight percentage:

[0006] C: 0.95%-1.15%; Si: 0.15%-1.30%; Mn: 0.20%-1.20%; Al: 0.015%-0.080%; P≤0.012%; S≤0.009%; Cr: 1.25%-5.0%; Mo: 0-1.00%; V: 0-0.50%; Ni: 0-0.50%; Nb: 0-0.060%; Cu: ≤0.080%; Ti: ≤0.005%; H: ≤0.0002%; N≤0.008%; O: ≤0.0012%; As: ≤0.010%; Pb: ≤0.002%; Ca: ≤0.003%, the balance is Fe and unavoidable impurity elements.

[0007] Furthermore, the bearing alloy steel hot-rolled coil comprises the following components by weight percentage:

[0008] C: 1.00%-1.15%; Si: 0.20%-1.20%; Mn: 0.30%-1.10%; Al: 0.016%-0.075%; P: ≤0.009%; S: ≤0.004%; Cr: 1.25%-4.85%; Mo: 0.15%~0.95%; V: 0.08%-0.50%; Ni: 0.15%-0.45%; Nb: 0.02%-0.055%; Cu: ≤0.020%; Ti: ≤0.005%; H: ≤0.0002%; N ≤0.008%; O: ≤0.0012%; As: ≤0.010%; Pb: ≤0.002%; Ca: ≤0.003%, the balance is Fe and unavoidable impurity elements.

[0009] The present invention also provides a method for preparing any one of the hot-rolled alloy steel coils for bearings, comprising:

[0010] Performing desulfurization pretreatment on the molten iron to reduce the S content in the molten iron to less than or equal to 0.003%;

[0011] Adding molten iron into a converter for converter smelting, and alloying the molten iron before tapping the converter to obtain molten steel;

[0012] The molten steel is sent to an LF furnace for desulfurization treatment, and the composition of each element in the molten steel is adjusted to obtain refined molten steel;

[0013] The refined molten steel is sent to an RH furnace for vacuum treatment, and after breaking the vacuum, the molten steel is subjected to inclusion modification treatment;

[0014] Continuously casting the molten steel to obtain a continuously cast slab;

[0015] The continuous casting slab is sequentially heated, rolled, coiled, cooled after coiling, and subjected to heat treatment of the hot-rolled coil to obtain the bearing alloy steel hot-rolled coil.

[0016] Furthermore, the step of adding molten iron into a converter for converter smelting, and alloying the molten iron before tapping the converter to obtain molten steel further comprises:

[0017] Adding molten iron and scrap steel into a converter for converter smelting, wherein the scrap steel refers to scrap steel with a sulfur content of ≤0.03%, and the weight percentage of the molten iron to the scrap steel is (80%-95%):(5%-20%);

[0018] The molten iron is alloyed and argon blown before being tapped from the converter to obtain molten steel.

[0019] Furthermore, the step of sending the molten steel into an LF furnace for desulfurization and adjusting the composition of each element in the molten steel to obtain the refined molten steel further comprises:

[0020] The molten steel is fed into an LF furnace, lime is added to the LF furnace, and the molten steel is stirred by bottom blowing argon to desulfurize the molten steel until the S content in the molten steel does not exceed 0.002%; wherein the argon flow rate is controlled to be 25NL / min-220NL / min during the bottom blowing process, and the bottom blowing time is greater than or equal to 15 minutes;

[0021] The components of each element in the molten steel are adjusted to obtain refined molten steel.

[0022] Furthermore, the step of sending the refined molten steel into the RH furnace for vacuum treatment, and performing inclusion modification treatment on the molten steel after breaking the vacuum further comprises:

[0023] The refined molten steel is sent to the RH furnace for vacuum treatment, wherein the vacuum pressure value of the vacuum treatment is less than or equal to 8 mbar, and the vacuum treatment time is controlled to be more than 15 minutes;

[0024] After breaking the vacuum, the molten steel is subjected to inclusion modification treatment, and the molten steel is stirred by bottom blowing argon, and the bottom blowing time is greater than or equal to 10 minutes.

[0025] Furthermore, the continuous casting of molten steel to obtain a continuous casting slab is specifically as follows:

[0026] The molten steel is continuously cast to obtain a continuous casting slab, and the pouring temperature is controlled to be 1450°C-1550°C; the target pulling speed is 0.80m / min-1.60m / min; the superheat of the molten steel is 15°C-50°C; the billet reduction is 0-5mm; and the frequency of electromagnetic stirring is 2.5Hz-5.0Hz.

[0027] Furthermore, the step of sequentially heating, rolling, coiling, cooling after coiling, and heat treating the hot-rolled coil to obtain the hot-rolled alloy steel coil for bearings further comprises:

[0028] The continuous casting slab is heated in a walking beam heating furnace, and the slab heating temperature is controlled at: 1180° C.-1300° C.;

[0029] The heated slab is subjected to rough rolling high-pressure water descaling treatment to remove the iron oxide scale generated on the surface of the slab; the treated slab is rough rolled using a four-roll reversible rough rolling unit to obtain an intermediate slab, wherein the end temperature of the rough rolling is controlled to be 980°C-1180°C, and the thickness of the intermediate slab is 20mm-60mm;

[0030] The slab is subjected to a high-pressure water descaling treatment for finishing rolling to remove the iron oxide scale on the surface of the intermediate slab; the intermediate slab after the treatment is subjected to finishing rolling, the termination temperature of the finishing rolling is controlled to be 790°C-950°C, and the slab obtained by the finishing rolling is subjected to cooling treatment;

[0031] The slab after cooling treatment is coiled, cooled after coiling and heat treated on the hot-rolled coil in sequence to obtain the alloy steel hot-rolled coil for bearings, wherein the coiling temperature is controlled at 560°C-840°C, and the hot-rolled coil heat treatment temperature is controlled at 570°C-890°C.

[0032] Furthermore, after the continuous casting of the molten steel to obtain the continuously cast slab, the preparation method also includes: hot transporting and hot loading the continuously cast slab, and controlling the temperature of the hot transport and hot loading to be ≥150°C; or, performing slab heat treatment, slab grinding and slab coating treatment on the continuously cast slab, and controlling the temperature of the slab heat treatment to be 570°C-890°C.

[0033] The present invention further provides application of the above alloy steel hot-rolled coil for bearings in producing bearings.

[0034] It can be seen from the above technical scheme that the hot-rolled alloy steel coil for bearings and the preparation method and application thereof provided by the present invention have the following beneficial effects:

[0035] The hot-rolled mechanical properties of the bearing alloy steel hot-rolled coil of the present invention are as follows: its yield strength is 850MPa-1350MPa, its tensile strength is 1200MPa-1830MPa, its elongation is ≥2.0%, its Rockwell hardness is HRC42-51.5, and its single-side decarburization layer depth is ≤0.01mm; its mechanical properties in the heat-treated annealed state are as follows: its yield strength is 315MPa-650MPa, its tensile strength is 500MPa-980MPa, its elongation is ≥10%, its Rockwell hardness is HRB 75-97, its single-side decarburization layer depth is ≤0.01mm; the total amount of inclusions is ≤0.5; it has the advantages of good comprehensive performance, high and uniform hardness after quenching and tempering, high wear resistance and contact fatigue resistance, good hot workability, and good machinability after spheroidizing annealing.

[0036] The preparation method of the present invention obtains pure steel by adopting converter smelting, LF deep desulfurization + RH vacuum degassing, and inclusion modification treatment; temperature control at each node in the smelting process and oxygen and nitrogen control in the whole process, reasonable application of light pressure and electromagnetic stirring, and the settings of cooling after finishing rolling and cooling after coiling can effectively prevent the occurrence of corner cracks and longitudinal cracks.

[0037] The preparation method of the present invention avoids the problem of uneven melting of the protective slag due to low pouring temperature and low pouring speed, thereby causing slag inclusion and pore defects on the surface of the slab, by setting the protective slag.

[0038] The preparation method of the present invention effectively reduces the slab crack defects that may be generated in the connection process between steelmaking and hot rolling through specific hot delivery and hot loading processes, heat treatment processes, slab grinding and coating processes, and obtains hot-rolled alloy steel coils for bearings with pure steel and excellent quality.

[0039] The hot-rolled alloy steel coil for bearings of the present invention meets the use requirements of bearing steel and can be suitable for use in producing bearings. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a microstructure diagram of a hot-rolled coil annealed state of a bearing alloy steel according to an embodiment of the present invention. DETAILED DESCRIPTION

[0041] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific embodiments. Except for the following contents, the process method of the present invention adopts conventional methods or devices in the art. Unless otherwise specified, the following terms have the meanings commonly understood by those skilled in the art.

[0042] When a numerical range is disclosed herein, the above range is considered to be continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0043] The bearing alloy steel hot-rolled coil of the embodiment of the present invention has C, Si, Mn, and Al as the main elements, and the balance is Fe and inevitable impurity elements. On this basis, one or more of the following elements can be added for alloying: Cr, Mo, V, Ni, and Nb; and the content of Cu, Ti, H, N, O, As, Pb, and Ca is controlled. On the other hand, the hot-rolled coil with excellent performance is obtained by controlling the molten steel refining, continuous casting control, slab crack control, heating method, rolling method, cooling method, heating temperature, rough rolling temperature, final rolling temperature, coiling temperature, and temperature drop after coiling.

[0044] Specifically, a hot-rolled alloy steel coil for bearings according to an embodiment of the present invention comprises the following components by weight: C: 0.95%-1.15%; Si: 0.15%-1.30%; Mn: 0.20%-1.20%; Al: 0.015%-0.080%; P≤0.012%; S≤0.009%; Cr: 1.25%-5.0%; Mo :0-1.00%;V:0-0.50%;Ni:0-0.50%;Nb:0-0.060%;Cu:≤0.080%;Ti:≤0.005%;H:≤0.0002%;N≤0.008%;O:≤0.0012%;As:≤0.010%;Pb:≤0.002%;Ca:≤0.003%, the balance is Fe and unavoidable impurity elements.

[0045] More preferably, the hot-rolled alloy steel coil for bearings comprises the following components by weight percentage: C: 1.00%-1.15%; Si: 0.20%-1.20%; Mn: 0.30%-1.10%; Al: 0.016%-0.075%; P: ≤0.009%; S: ≤0.004%; Cr: 1.25%-4.85%; Mo: 0.15%~0.95%; V: 0 .08%-0.50%; Ni: 0.15%-0.45%; Nb: 0.02%-0.055%; Cu: ≤0.020%; Ti: ≤0.005%; H: ≤0.0002%; N ≤0.008%; O: ≤0.0012%; As: ≤0.010%; Pb: ≤0.002%; Ca: ≤0.003%, the balance is Fe and unavoidable impurity elements.

[0046] The embodiments of the present invention optimize the elements and their contents so that the elements have a synergistic effect. The effects of the elements and the preferred ranges of their contents are specifically described as follows:

[0047] Carbon: It is the most economical and basic strengthening element in steel and has a decisive influence on the hardness of the structure. Considering the requirement of ultra-high hardness of bearing steel, in the embodiment of the present invention, the C content is controlled in the range of 0.95%-1.15%, preferably 1.00%-1.15%.

[0048] Silicon: Silicon can significantly improve the elastic limit, yield point and tensile strength of steel; Silicon combined with chromium can improve corrosion resistance and oxidation resistance. In the embodiment of the present invention, the Si content is controlled to Si: 0.15%-1.30%; preferably 0.20%-1.20%.

[0049] Manganese: Manganese can strengthen steel, improve its strength, hardness and wear resistance, and reduce its critical cooling rate, improve its hardenability and refine pearlite. In the embodiment of the present invention, the Mn content is controlled at 0.20%-1.20%, preferably 0.30%-1.10%.

[0050] 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. Aluminum also has antioxidant and corrosion resistance. However, if too much aluminum is used during deoxidation, the graphitization tendency of the steel will be promoted. When the aluminum content is high, its high-temperature strength and toughness are lower. The embodiment of the present invention controls the Al content to 0.015%-0.080%, 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; preferably, the aluminum content is 0.016%-0.075%.

[0051] Phosphorus: Generally speaking, 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 embodiment of the present invention, the P content is controlled to ≤0.012%, preferably ≤0.009%.

[0052] Sulfur: Generally, sulfur is a harmful element that makes steel hot brittle, reduces the ductility and toughness of steel, and reduces corrosion resistance. In the embodiment of the present invention, the sulfur content is controlled to ≤ 0.009%, preferably ≤ 0.004%.

[0053] Chromium: Chromium can improve the strength, hardness, high temperature mechanical properties, hardenability, and wear resistance of steel, making the steel have good corrosion resistance and oxidation resistance, tempering stability and toughness, and at the same time has the effect of preventing graphitization. The special carbides of chromium are mainly used in bearing steel to contribute to wear resistance and the advantages of high surface finish after grinding. The embodiment of the present invention controls the Cr content to 1.25%-5.0%, which can effectively improve the various properties of steel, preferably 1.25%-4.85%.

[0054] Molybdenum: Molybdenum is a good element for forming carbides. As an alloying element of steel, molybdenum can improve the strength of steel, especially high temperature strength and toughness; improve the wear resistance of steel and improve hardenability, weldability and heat resistance. In the embodiment of the present invention, the molybdenum content is controlled at 0-1.00%, preferably 0.15% to 0.95%.

[0055] Vanadium: It is a strong carbide-forming element. It can obtain dense steel with good deoxidation and dehydrogenation. It can also refine grains, reduce overheat sensitivity, and improve the strength, toughness and fatigue performance of steel. Vanadium carbide is almost the hardest and most wear-resistant of all metal carbides. Dispersed V4C3 will improve the hardness and wear resistance of steel. In the embodiment of the present invention, the vanadium content is controlled at 0-0.50%, preferably 0.08%-0.50%.

[0056] Nickel: Nickel is a solid solution strengthener in steel, which can improve strength while maintaining good plasticity and toughness, improve hardenability, and improve fatigue performance of steel. Nickel has high corrosion resistance to acids and alkalis, and is rust-proof and heat-resistant at high temperatures. Nickel-chromium or nickel-chromium-molybdenum steel used in mechanical manufacturing can obtain comprehensive mechanical properties with good strength and toughness after heat treatment. In the embodiment of the present invention, the Ni content is controlled to 0-0.50%, preferably 0.15%-0.45%.

[0057] Niobium: Niobium is one of the main alloying elements of steel, which can refine grains and reduce overheat sensitivity and temper brittleness of steel, increase strength, improve mechanical and welding properties of steel, and improve corrosion resistance of steel in the atmosphere and at high temperatures. In the embodiment of the present invention, the Nb content is controlled at 0-0.060%, preferably 0.02%-0.055%.

[0058] 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 0.25%, and low secondary cooling intensity and high continuous casting speed are required. In the embodiment of the present invention, the Cu content is controlled at ≤ 0.080%, preferably ≤ 0.020%.

[0059] Titanium: Titanium is a strong deoxidizer in steel. Titanium can make the internal structure of steel dense, refine the grains, reduce aging sensitivity and cold brittleness, improve welding performance, and avoid intergranular corrosion. To avoid the formation of nitrides, in the embodiment of the present invention, the Ti content is controlled to ≤0.005%.

[0060] Through the synergistic effect of various elements, the embodiment of the present invention makes the high carbon chromium alloy steel hot-rolled coil for bearings have the advantages of good comprehensive performance, high and uniform hardness after quenching and tempering, high wear resistance and contact fatigue resistance, good hot workability, and good machinability after spheroidizing annealing, thereby meeting the user's requirements.

[0061] After testing, the hot-rolled mechanical properties of the hot-rolled coil of the bearing alloy steel in the embodiment of the present invention are as follows: the yield strength is 850MPa-1350MPa, the tensile strength is 1200MPa-1830MPa, the elongation is ≥2%, the Rockwell hardness is HRC42-51.5, and the single-sided decarburization layer depth is ≤0.01mm; the heat treatment annealing mechanical properties are as follows: the yield strength is 315MPa-650MPa, the tensile strength is 500MPa-980MPa, the elongation is ≥10%, the Rockwell hardness is HRB 75-97, the single-sided decarburization layer depth is ≤0.01mm; the total amount of inclusions is ≤0.5, wherein the microstructure morphology of the hot-rolled coil annealed state of the bearing alloy steel in the embodiment of the present invention is as follows Figure 1 shown.

[0062] Among them, the measurement methods of various mechanical properties are as follows: yield strength: GB / T 228, room temperature tensile test method for metal materials; tensile strength: GB / T 228, room temperature tensile test method for metal materials; elongation: GB / T 228, room temperature tensile test method for metal materials; Rockwell hardness: GB / T 230.1, metal Rockwell hardness test method; decarburization layer thickness: GB / T 224, decarburization layer depth measurement method for steel; inclusions: GB / T10561, microscopic evaluation method for non-metallic inclusions.

[0063] Therefore, the bearing alloy steel hot-rolled coil of the present invention has good performance and meets the use requirements of bearing steel. Through practice, the bearings made of the bearing alloy steel hot-rolled coil of the present invention have good comprehensive performance; high and uniform hardness after quenching and tempering; high wear resistance and contact fatigue resistance; good hot workability; good machinability after spheroidizing annealing, and meet the use requirements of users.

[0064] On the other hand, an embodiment of the present invention further provides a method for preparing the aforementioned hot-rolled alloy steel coil for bearings, comprising the following steps: molten iron pretreatment → converter smelting → refining outside the furnace LF+RH → slab continuous casting → hot delivery and hot charging → slab heating → rough rolling high-pressure water descaling → rough rolling unit rolling → finishing rolling high-pressure water descaling → finishing rolling unit rolling → cooling after rolling → coiling → cooling after coiling → heat treatment of hot-rolled coil; or,

[0065] Hot metal pretreatment → converter smelting → LF+RH refining outside the furnace → slab continuous casting → slab heat treatment → slab grinding → slab coating → slab heating → rough rolling high-pressure water descaling → rough rolling unit rolling → finishing rolling high-pressure water descaling → finishing rolling unit rolling → cooling after rolling → coiling → cooling after coiling → heat treatment of hot rolled coil.

[0066] Furthermore, after the hot-rolled coil is heat treated, the preparation method of the embodiment of the present invention may further include subsequent testing and packaging steps, that is, quality and performance inspection → packaging marking → warehousing are sequentially performed after the hot-rolled coil is heat treated.

[0067] Specifically, the method for preparing the hot-rolled alloy steel coil for bearings according to the embodiment of the present invention comprises:

[0068] Step S001: performing desulfurization pretreatment on molten iron to reduce the S content in the molten iron to less than or equal to 0.003%; wherein the molten iron is blast furnace molten iron, and when performing desulfurization pretreatment on the molten iron, the slag needs to be cleaned.

[0069] Step S002: adding molten iron into a converter for converter smelting, and alloying the molten iron before tapping the converter to obtain molten steel.

[0070] Step S003: Send the molten steel into the LF furnace for desulfurization treatment, and adjust the composition of each element in the molten steel to obtain refined molten steel.

[0071] Step S004: sending the refined molten steel into the RH furnace for vacuum treatment, and performing inclusion modification treatment on the molten steel after breaking the vacuum;

[0072] Step S005: continuously casting the molten steel to obtain a continuously cast slab;

[0073] Step S006: sequentially heating, rolling, coiling, cooling after coiling, and heat treating the hot-rolled coil to obtain a hot-rolled alloy steel coil for bearings.

[0074] Among them, step S002 adds molten iron into the converter for converter smelting, and alloys the molten iron before tapping the converter to obtain molten steel, further comprising:

[0075] Adding molten iron and scrap steel into a converter for converter smelting, wherein the scrap steel refers to scrap steel with a sulfur content of ≤0.03%, and the weight percentage of the molten iron to the scrap steel is (80%-95%):(5%-20%);

[0076] Before tapping the converter, the molten iron is alloyed and argon blown to obtain molten steel.

[0077] Alloying treatment of molten iron before steel is tapped from the converter refers to adding carbon powder, ferroaluminum, high carbon ferromanganese, silicon-manganese alloy and ferrochrome to the converter when steel is tapped from the converter to alloy the molten iron into molten steel.

[0078] The converter smelting in the embodiment of the present invention can be carried out in an 80-ton or 180-ton top and bottom combined blowing converter.

[0079] Step S003: sending the molten steel into the LF furnace for desulfurization treatment and adjusting the composition of each element in the molten steel to obtain the refined molten steel further comprises:

[0080] The molten steel is fed into the LF furnace, lime is added into the LF furnace, and the molten steel is stirred by bottom blowing argon to desulfurize the molten steel until the S content in the molten steel does not exceed 0.002%; wherein the argon flow rate is controlled to be 25NL / min-220NL / min during the bottom blowing process, and the bottom blowing time is greater than or equal to 15 minutes;

[0081] Adjust the composition of each element in the molten steel to obtain refined molten steel.

[0082] In order to ensure the purity of steel, the embodiment of the present invention has strict requirements on the control of S content. Specifically, the molten iron is pretreated to make the S content in the molten iron ≤0.003%, and high-quality scrap steel with a sulfur content of ≤0.03% is selected. After entering the converter for smelting, the LF furnace is used for deep desulfurization (to S≤0.002%). The desulfurization of the embodiment of the present invention can effectively ensure that the bearings made of the hot-rolled alloy steel coil for bearings have good performance.

[0083] Among them, step S004 sends the refined molten steel into the RH furnace for vacuum treatment, and performs inclusion modification treatment on the molten steel after breaking the vacuum further includes:

[0084] The refined molten steel is sent to the RH furnace for vacuum treatment, wherein the vacuum pressure value of the vacuum treatment is less than or equal to 8 mbar, and the vacuum treatment time is controlled to be more than 15 minutes;

[0085] After breaking the vacuum, the molten steel is subjected to inclusion modification treatment and is stirred by bottom blowing argon, the bottom blowing time of which is greater than or equal to 10 minutes.

[0086] In this embodiment, the refined molten steel is sent to the RH furnace for vacuum treatment, that is, the refined molten steel is sent to the RH furnace for circulation under vacuum. The circulation under vacuum is preferably carried out for more than 15 minutes at a vacuum pressure value not greater than 8 mbar, thereby achieving control of hydrogen and nitrogen; as well as uniform control of the content of other components and the temperature of the molten steel.

[0087] Among them, step S005 continuously casts the molten steel to obtain a continuously cast slab, specifically:

[0088] The molten steel is continuously cast to obtain a continuous casting slab, and the pouring temperature is controlled to be 1450°C-1550°C; the target pulling speed is 0.80m / min-1.60m / min; the superheat of the molten steel is 15°C-50°C; the billet reduction is 0-5mm; and the frequency of electromagnetic stirring is 2.5Hz-5.0Hz.

[0089] By controlling the pouring process, the occurrence of slab cracks can be effectively prevented.

[0090] Among them, after continuously casting the molten steel to obtain the continuously cast slab in step S005, the preparation method also includes: hot transporting and hot loading the continuously cast slab, and controlling the temperature of hot transport and hot loading to be ≥150°C; or, performing slab heat treatment, slab grinding and slab coating treatment on the continuously cast slab, and controlling the temperature of the slab heat treatment to be 570°C-890°C.

[0091] The heat treatment temperature of the hot-rolled coil in the embodiment of the present invention is 570° C.-890° C., thereby achieving the purpose of improving the performance and structure of the hot-rolled coil and preparing for subsequent processing.

[0092] Among them, in step S005, in the process of continuously casting molten steel to obtain continuous casting slabs, a protective slag with a melting point of 1050℃±30℃, a viscosity of 0.5 poise±0.05 poise at 1300℃, a basicity of 1.0±0.05, and a melting speed of 25 seconds±10 seconds is used.

[0093] Step S006 sequentially heats, rolls, coils, cools after coiling, and heat treats the hot-rolled coil to obtain a hot-rolled alloy steel coil for bearings, further comprising:

[0094] The continuous casting slab is heated in a walking beam heating furnace, and the heating temperature of the slab is controlled at: 1180℃-1300℃; thereby, the oxidation, burning, temperature and uniformity of the slab can be controlled.

[0095] The heated slab is subjected to rough rolling high-pressure water descaling treatment to remove the iron oxide scale generated on the surface of the slab; the treated slab is subjected to reciprocating rough rolling by a four-roll reversible rough rolling mill to obtain an intermediate slab, wherein the termination temperature of the rough rolling is controlled to be 980°C-1180°C, and the thickness of the intermediate slab is 20mm-60mm;

[0096] The slab is subjected to a high-pressure water descaling treatment for finishing rolling to remove the iron oxide scale on the surface of the intermediate slab; the intermediate slab after the treatment is subjected to finishing rolling, the termination temperature of the finishing rolling is controlled to be 790°C-950°C, and the slab obtained by the finishing rolling is subjected to cooling treatment;

[0097] The slab after cooling treatment is coiled, cooled after coiling and heat treated on the hot-rolled coil in sequence to obtain a hot-rolled alloy steel coil for bearings, wherein the coiling temperature is controlled at 560°C-840°C, and the hot-rolled coil heat treatment temperature is controlled at 570°C-890°C.

[0098] In the embodiment of the present invention, the termination temperature of rough rolling is controlled at 980℃-1180℃, and the thickness of the intermediate billet is 20mm-60mm; the termination temperature of finishing rolling is controlled at 790℃-950℃, and the coiling temperature is controlled at 560℃-840℃, thereby effectively controlling the slab crack defects that may occur in the connection process between hot rolling, and obtaining high-quality alloy steel hot-rolled coils for bearings.

[0099] The finishing rolling of the embodiment of the present invention can be carried out on a 1549mm or 2250mm hot rolling mill.

[0100] The hot-rolled alloy steel coil for bearings obtained in this embodiment has a thickness of 1.5 mm to 25.4 mm and a width of 1000 mm to 2130 mm.

[0101] The hot-rolled mechanical properties of the alloy steel hot-rolled coil for bearings prepared by the preparation method of the embodiment of the present invention are as follows: its yield strength is 850MPa-1350MPa, the tensile strength is 1200MPa-1830MPa, the elongation is ≥2.0%, the Rockwell hardness is HRC42-51.5, and the depth of the single-sided decarburization layer is ≤0.01mm; the mechanical properties of the heat-treated annealed state are as follows: its yield strength is 315MPa-650MPa, the tensile strength is 500MPa-980MPa, the elongation is ≥10%, the Rockwell hardness is HRB 75-97, the depth of the single-sided decarburization layer is ≤0.01mm; the total amount of inclusions is ≤0.5.

[0102] The preparation method of the embodiment of the present invention obtains pure steel by adopting converter smelting, LF deep desulfurization + RH vacuum degassing, and inclusion modification treatment; temperature control at each node of the smelting process and oxygen and nitrogen control in the whole process, reasonable application of light pressure and electromagnetic stirring, and the setting of cooling after finishing rolling and cooling after coiling can effectively prevent the occurrence of corner cracks and longitudinal cracks.

[0103] The preparation method of the embodiment of the present invention avoids the problem of uneven melting of the protective slag due to low pouring temperature and low pouring speed, thereby causing slag inclusions and pore defects on the surface of the slab, by setting the protective slag.

[0104] The preparation method of the embodiment of the present invention effectively reduces the slab crack defects that may be generated in the connection process between steelmaking and hot rolling through specific hot delivery and hot loading processes, heat treatment processes, slab grinding and coating processes, and obtains hot-rolled alloy steel coils for bearings with pure steel and excellent quality.

[0105] The alloy steel hot-rolled coil for bearings prepared by the preparation method of the embodiment of the present invention has the advantages of good comprehensive performance, high and uniform hardness after quenching and tempering, high wear resistance and contact fatigue resistance, good hot workability, and good machinability after spheroidizing annealing.

[0106] Again, the present application also provides the use of any of the above hot-rolled alloy steel coils for bearings or the hot-rolled alloy steel coils for bearings prepared by any of the above preparation methods in the production of bearings.

[0107] The hot-rolled alloy steel coil for bearings of the embodiment of the present invention meets the use requirements of bearing steel and can be suitable for use in producing bearings. The hot-rolled alloy steel coil for bearings prepared by the preparation method of the embodiment of the present invention meets the use requirements of bearing steel and can be suitable for use in producing bearings.

[0108] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods without specific conditions in the following examples are based on conventional methods and conditions.

[0109] Embodiment 1:

[0110] The bearing alloy steel hot-rolled coil of this embodiment includes the following components by weight percentage:

[0111] C: 1.05%; Si: 0.25%; Mn: 0.38%; Al: 0.020%; P: 0.007%; S: 0.0018%; Cr: 1.60%; Mo: 0.20%; V: 0.25%; Ni: 0.30%; Nb: 0.025%; Cu: 0.02%; Ti: 0.003%. H: 0.00015%; N: 0.0032%; O: 0.00018%; As: 0.0034%; Pb: 0.0016%; Ca: 0.001%, the balance is Fe and unavoidable impurity elements.

[0112] This embodiment is carried out on an 80-ton top and bottom combined blowing converter and a 1549 mm hot rolling mill. The preparation process includes the following steps in sequence:

[0113] Ⅰ. Hot metal pretreatment:

[0114] Perform desulfurization pretreatment on blast furnace molten iron, remove slag cleanly during pretreatment, and reduce the S content in molten iron to less than or equal to 0.003% after pretreatment;

[0115] Ⅱ. Converter smelting:

[0116] 70 tons of molten iron and 15 tons of scrap steel that meet the requirements of converter smelting are added to the converter for converter smelting, wherein the sulfur content in the scrap steel is ≤0.03%. The molten iron is alloyed and argon-blown before tapping the converter;

[0117] III. LF refining:

[0118] The molten iron after molten iron pretreatment, converter smelting and argon blowing treatment is sent to the LF furnace for treatment. In the LF furnace, sulfur is removed to 0.0013%. After desulfurization, micro-alloying treatment is performed to fine-tune the composition of alloy elements, and weak stirring is performed by bottom blowing argon.

[0119] IV. RH refining:

[0120] The vacuum pressure was 5 mbar and the mixture was circulated for 20 minutes. After breaking the vacuum, 150 m of Ca-Si wire was fed to denature the inclusions, followed by weak stirring for 15 minutes by bottom blowing of argon at an argon flow rate of 125 NL / min.

[0121] Ⅴ. Slab continuous casting:

[0122] The molten steel in the ladle is added to the tundish, and is continuously cast into slabs through a crystallizer. The continuous casting slab pulling speed is 1.30 m / min, the continuous casting pouring temperature is 1500°C, the slab light reduction is 2.7 mm, and the electromagnetic stirring frequency is 3.5 Hz. The protective slag used has a melting point of 1050°C±30°C, a viscosity of 0.5 poise±0.05 poise at 1300°C, a basicity of 1.0±0.05, and a melting speed of 25 seconds±10 seconds.

[0123] The specifications of the slab obtained by slab continuous casting are: thickness 220mm, width 1260mm, length 8000m.

[0124] VI. Hot delivery and hot loading of slabs or heat treatment of slabs, slab grinding and slab coating treatment:

[0125] When the slab is hot transported and hot loaded, the slab hot transport and hot loading temperature is 320℃; when the slab is heat treated, the slab is ground and the slab is coated, the slab heat treatment temperature is 680℃.

[0126] Ⅶ. Slab heating:

[0127] The slab is heated in a walking beam heating furnace at a heating temperature of 1250°C.

[0128] Ⅷ. Rough rolling high pressure water descaling:

[0129] The heated slab is descaled by rough rolling with high-pressure water to remove the iron oxide scale formed on the surface of the slab.

[0130] Ⅸ. Rough rolling mill:

[0131] The slab is reciprocated and rolled 7 times in a four-roll reversible rough rolling mill to form an intermediate strip with a thickness of 30 mm, a width of 1260 mm, and a length of 58667 mm. The final rough rolling temperature is 1100°C.

[0132] Ⅹ. Finishing rolling high pressure water descaling:

[0133] Before finishing rolling, the secondary iron oxide scale on the surface of the intermediate billet is removed by finishing high-pressure water descaling.

[0134] Ⅺ. Rolling of finishing mill:

[0135] The slab is finish-rolled on a 7-stand finishing mill to be rolled into a steel strip with a thickness of 3.0 mm, a width of 1260 mm and a length of 440 m. The final rolling temperature of the finishing mill is 880°C.

[0136] Ⅻ. Coiling:

[0137] The steel strip is rolled into a steel coil at 650°C using a fully hydraulic mobile coiler with 3 sets of rolls.

[0138] ⅩⅢ、Heat treatment of hot rolled coil:

[0139] Hot rolled coil heat treatment temperature: 680℃.

[0140] The properties of the hot-rolled alloy steel coil for bearings obtained by the above steps are as follows: the yield strength of the hot-rolled state is 920MPa, the tensile strength is 1350MPa, the elongation is 5.0%, the Rockwell hardness HRC: 42.5, and the depth of the single-sided decarburization layer is 0.00mm; the yield strength of the hot-rolled coil in the heat-treated annealed state is 350MPa, the tensile strength is 630MPa, the elongation is 35%, the Rockwell hardness HRB: 85, and the depth of the single-sided decarburization layer is 0.01mm; the total amount of inclusions is 0.

[0141] The above properties of the hot-rolled alloy steel coil for bearings obtained through the above steps meet the performance requirements of the high-carbon chromium alloy steel hot-rolled coil for bearings.

[0142] Embodiment 2 to embodiment 6:

[0143] The chemical compositions of the hot-rolled alloy steel coils for bearings of Examples 2 to 6 are shown in Tables 1 and 2.

[0144] Table 1: Summary of chemical compositions of hot-rolled alloy steel coils for bearings of Examples 2 to 6 except iron (wt%)

[0145] C Si Mn P S Al Cr Mo V Ti Example 2 0.95 1.10 0.31 0.009 0.002 0.055 4.5 0.85 0.44 0.0031 Example 3 1.01 0.52 0.57 0.007 0.0019 0.042 3.2 0.52 0.35 0.0033 Example 4 1.08 0.35 0.85 0.010 0.003 0.073 2.26 0.38 0.26 0.0032 Example 5 1.13 0.75 0.42 0.008 0.004 0.025 1.66 0.65 0.28 0.0035 Example 6 0.96 0.20 1.00 0.007 0.002 0.022 1.90 0.40 0.30 0.0032

[0146] Table 2: Summary of chemical compositions of hot-rolled alloy steel coils for bearings of Examples 2 to 6 except iron (wt%)

[0147] Ni Nb Cu H N O As Pb Ca Example 2 0.45 0.045 0.01 0.00014 0.0032 0.0002 0.0036 0.0015 0.0026 Example 3 0.38 0.022 0.02 0.00013 0.003 0.00019 0.0032 0.0018 0.0022 Example 4 0.31 0.031 0.01 0.00011 0.0035 0.000196 0.0033 0.0016 0.0015 Example 5 0.25 0.020 0.02 0.00012 0.0033 0.00021 0.0030 0.0017 0.0020 Example 6 0.20 0.021 0.01 0.00014 0.0031 0.0002 0.0034 0.0018 0.0023

[0148] Some process parameters in the preparation process of hot-rolled alloy steel coils for bearings in Examples 2 to 6 are shown in Table 3, and the process parameters not listed in Table 3 are the same as those in Example 1.

[0149] Table 3: Partial process parameters in the preparation process of hot-rolled alloy steel coils for bearings in Examples 2 to 6

[0150] Slab heating temperature℃ Rough rolling and final rolling temperature ℃ Finish rolling temperature℃ Coiling temperature℃ Example 2 1300 1170 950 780 Example 3 1260 1150 940 680 Example 4 1230 1130 920 650 Example 5 1190 1020 810 590 Example 6 1210 1080 860 670

[0151] Table 4: Summary of the properties of the hot-rolled alloy steel coils for bearings prepared in Examples 2 to 6

[0152]

[0153]

[0154] The present invention has been disclosed above with preferred embodiments, but those skilled in the art should understand that these embodiments are only used to describe the present invention and should not be understood as limiting the scope of the present invention. It should be noted that all changes and substitutions equivalent to these embodiments should be deemed to be included in the scope of the claims of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined in the claims.

Claims

1. A hot-rolled alloy steel coil for bearings, characterized in that: The bearing alloy steel hot-rolled coil comprises the following components by weight percentage: C: 0.95%-1.15%; Si: 0.15%-1.30%; Mn: 0.20%-1.20%; Al: 0.015%-0.080%; P≤0.012%; S≤0.009%; Cr: 1.25%-5.0%; Mo: 0-1.00%; V: 0-0.50%; Ni: 0-0.50%; Nb: 0-0.060%; Cu: ≤0.080%; Ti: ≤0.005%; H: ≤0.0002%; N≤0.008%; O: ≤0.0012%; As: ≤0.010%; Pb: ≤0.002%; Ca: ≤0.003%, the balance being Fe and unavoidable impurity elements.

2. The hot-rolled alloy steel coil for bearings according to claim 1, characterized in that: The bearing alloy steel hot-rolled coil comprises the following components by weight percentage: C: 1.00%-1.15%; Si: 0.20%-1.20%; Mn: 0.30%-1.10%; Al: 0.016%-0.075%; P: ≤0.009%; S: ≤0.004%; Cr: 1.25%-4.85%; Mo: 0.15%~0.95%; V: 0.08%-0.50%; Ni: 0.15%-0.45%; Nb: 0.02%-0.055%; Cu: ≤0.020%; Ti: ≤0.005%; H: ≤0.0002%; N≤0.008%; O: ≤0.0012%; As: ≤0.010%; Pb: ≤0.002%; Ca: ≤0.003%, the balance being Fe and unavoidable impurity elements.

3. The method for preparing the hot-rolled alloy steel coil for bearings according to any one of claims 1 to 2, characterized in that: include: Performing desulfurization pretreatment on the molten iron to reduce the S content in the molten iron to less than or equal to 0.003%; Adding molten iron into a converter for converter smelting, and alloying the molten iron before tapping the converter to obtain molten steel; The molten steel is sent to an LF furnace for desulfurization treatment, and the composition of each element in the molten steel is adjusted to obtain refined molten steel; The refined molten steel is sent to an RH furnace for vacuum treatment, and after breaking the vacuum, the molten steel is subjected to inclusion modification treatment; Continuously casting the molten steel to obtain a continuously cast slab; The continuous casting slab is sequentially heated, rolled, coiled, cooled after coiling, and subjected to heat treatment of the hot-rolled coil to obtain the bearing alloy steel hot-rolled coil.

4. The preparation method according to claim 3, characterized in that: The step of adding molten iron into a converter for converter smelting and alloying the molten iron before tapping the converter to obtain molten steel further comprises: Adding molten iron and scrap steel into a converter for converter smelting, wherein the scrap steel refers to scrap steel with a sulfur content of ≤0.03%, and the weight percentage of the molten iron to the scrap steel is (80%-95%):(5%-20%); The molten iron is alloyed and argon blown before being tapped from the converter to obtain molten steel.

5. The preparation method according to claim 3, characterized in that: The step of sending the molten steel into the LF furnace for desulfurization and adjusting the composition of each element in the molten steel to obtain the refined molten steel further comprises: The molten steel is fed into an LF furnace, lime is added to the LF furnace, and the molten steel is stirred by bottom blowing argon to desulfurize the molten steel until the S content in the molten steel does not exceed 0.002%; wherein the argon flow rate is controlled to be 25NL / min-220NL / min during the bottom blowing process, and the bottom blowing time is greater than or equal to 15 minutes; The components of each element in the molten steel are adjusted to obtain refined molten steel.

6. The preparation method according to claim 3, characterized in that: The step of sending the refined molten steel into the RH furnace for vacuum treatment and performing inclusion modification treatment on the molten steel after breaking the vacuum further comprises: The refined molten steel is sent to the RH furnace for vacuum treatment, wherein the vacuum pressure value of the vacuum treatment is less than or equal to 8 mbar, and the vacuum treatment time is controlled to be more than 15 minutes; After breaking the vacuum, the molten steel is subjected to inclusion modification treatment, and the molten steel is stirred by bottom blowing argon, and the bottom blowing time is greater than or equal to 10 minutes.

7. The preparation method according to claim 3, characterized in that: The continuous casting of molten steel to obtain a continuous casting slab specifically comprises: The molten steel is continuously cast to obtain a continuous casting slab, and the pouring temperature is controlled to be 1450°C-1550°C; the target pulling speed is 0.80m / min-1.60m / min; the superheat of the molten steel is 15°C-50°C; the billet reduction is 0-5mm; and the frequency of electromagnetic stirring is 2.5Hz-5.0Hz.

8. The preparation method according to claim 3, characterized in that: The step of sequentially heating, rolling, coiling, cooling after coiling and heat treating the hot rolled coil to obtain the bearing alloy steel hot rolled coil further comprises: The continuous casting slab is heated in a walking beam heating furnace, and the slab heating temperature is controlled at: 1180° C.-1300° C.; The heated slab is subjected to rough rolling high-pressure water descaling treatment to remove the iron oxide scale generated on the surface of the slab; the treated slab is rough rolled using a four-roll reversible rough rolling unit to obtain an intermediate slab, wherein the end temperature of the rough rolling is controlled to be 980°C-1180°C, and the thickness of the intermediate slab is 20mm-60mm; The slab is subjected to a high-pressure water descaling treatment for finishing rolling to remove the iron oxide scale on the surface of the intermediate slab; the intermediate slab after the treatment is subjected to finishing rolling, the termination temperature of the finishing rolling is controlled to be 790°C-950°C, and the slab obtained by the finishing rolling is subjected to cooling treatment; The slab after cooling treatment is coiled, cooled after coiling and heat treated on the hot-rolled coil in sequence to obtain the alloy steel hot-rolled coil for bearings, wherein the coiling temperature is controlled at 560°C-840°C, and the hot-rolled coil heat treatment temperature is controlled at 570°C-890°C.

9. The preparation method according to claim 3, characterized in that: After the molten steel is continuously cast to obtain the continuously cast slab, the preparation method further comprises: hot transporting and hot loading the continuously cast slab, and controlling the temperature of the hot transport and hot loading to be ≥150°C; or, heat treating, grinding and coating the continuously cast slab, and controlling the temperature of the heat treatment to be 570°C-890°C.

10. Use of the hot-rolled alloy steel coil for bearings according to any one of claims 1 to 2 or the hot-rolled alloy steel coil for bearings prepared by the preparation method according to any one of claims 3 to 9 in the production of bearings.

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