CN111363976B - Microalloyed steel with long service life, high strength and toughness for high-speed rail plate spring and production process thereof - Google Patents
Microalloyed steel with long service life, high strength and toughness for high-speed rail plate spring and production process thereof Download PDFInfo
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Abstract
The invention discloses microalloyed steel with long service life, high strength and toughness for a high-speed rail plate spring, which consists of the following chemical elements in percentage by mass: c: 0.45% -0.47%, Si: 0.20% -0.30%, Mn: 0.95% -1.10%, Cr: 1.00% -1.20%, V: 0.10-0.20%, Cu is less than or equal to 0.20%, Ni: 0.10% -0.20%, Nb: 0.02-0.03%, P is less than or equal to 0.010%, S is less than or equal to 0.003%, Sn is less than or equal to 0.005%, H is less than or equal to 0.00015%, O is less than or equal to 0.0015%, N is less than or equal to 0.0050%, and the balance is Fe. The invention also discloses a production process of the steel for the high-speed rail leaf spring, which has reasonable component design and advanced process, and has higher purity, higher obdurability, finer grain size and longer fatigue life compared with the steel for the high-speed rail leaf spring supplied in the current market. The inclusions of A class, B class, D class and Ds class are stably controlled to be less than or equal to 1.0 level, and the inclusions of C class are not detected.
Description
Technical Field
The invention belongs to the technical field of alloy steel, relates to spring flat steel in the steel industry, and particularly relates to a steel grade design for a high-iron leaf spring with long service life and high strength and toughness of microalloying and a production process thereof.
Background
In recent years, Chinese high-speed rail is coming out of the air and is striking. On the basis of introducing foreign technology digestion and absorption, innovation is carried out according to the national conditions and the road conditions of China, a technical standard system with independent intellectual property rights and leading world is established, and in the short time of less than ten years, the eight longitudinal and eight transverse high-speed rail nets are laid out in China at present in the south, the east and the west and the north. At present, the total mileage of high-speed railways in China exceeds 3.5 kilometers, the high-speed railways live in the first world, and China is also the only country in which high-speed railways run in a net mode in the world, and the high-speed railways accelerate the process of urbanization and industrialization in China.
The high-speed rail is the embodiment of the achievement of the manufacturing industry in China and is a business card for the high-end manufacturing industry in China to move to the world. However, the core components of high-speed rails in China, such as bearings, axles, wheels, damping springs and the like still depend on import, the localization still faces a lot of difficulties, and the related matching components of the high-speed rails in China are far behind the development speed of the high-speed rails, especially basic materials, high-precision processing equipment and the like.
The high-speed rail motor train unit is a passenger electric locomotive, the running speed is 250 km/h-360 km/h, the requirements on safety and comfort are very high, a high-speed rail plate spring is generally manufactured by using 51CrV4 abroad, the high-speed rail plate spring is equivalent to a 51CrMnV spring material in the spring steel (GB/T1222-2016) standard in China, the plate spring is used for a motor train bogie motor suspension system, the plate spring is subjected to a vertical load of 40KN and a transverse displacement of 12mm in work, and the running safety of the high-speed rail is seriously influenced by the quality of the plate spring. The existing steel grade 51CrV4(51CrMnV) has the defects that the weight of the manufactured plate spring is large due to the limitation of obdurability, the weight of high-speed rails is influenced, and a large amount of energy is consumed; and due to the limitation of the existing rolling process, the fatigue life of the existing plate spring can only reach 500 ten thousand times, and the existing plate spring cannot replace imported products. Therefore, it is necessary to develop a new steel for a high-speed rail plate spring with long service life and high strength and toughness, which has proprietary intellectual property rights. The toughness of the material mainly depends on alloy elements and the structure form thereof, and the fatigue life relates to purity, decarburized layer, structure uniformity and the like.
The material of the 51CrMnV spring is regulated in the national Standard of spring Steel (GB/T1222-2016) as follows: 0.47 to 0.55 percent of C, 0.17 to 0.37 percent of Si, 0.70 to 1.10 percent of Mn, 0.90 to 1.20 percent of Cr, less than or equal to 0.025 percent of P, less than or equal to 0.020 percent of S, 0.10 to 0.25 percent of V, less than or equal to 0.35 percent of Ni, less than or equal to 0.25 percent of Cu, and less than or equal to 0.0025 percent of O. The comprehensive mechanical properties of the steel after oil quenching at 850 +/-20 ℃ and tempering heat treatment at 450 +/-50 ℃ are as follows: rm is more than or equal to 1350MPa, Rel is more than or equal to 1200MPa, A is more than or equal to 6 percent, and Z is more than or equal to 30 percent; the decarburized layer is less than or equal to 1.2% of the thickness; terminal hardenability: j1.5: 57 HRC-65 HRC, J3: 56 HRC-65 HRC, J5: 55 HRC-64 HRC, J7: 54 HRC-64 HRC, J9: 53 HRC-63 HRC, J11: 51 HRC-63 HRC, J13: 50 HRC-63 HRC, J15: 48 HRC-62 HRC, J20: 44 HRC-62 HRC, J25: 41 HRC-62 HRC, J30: 37 HRC-61 HRC, J35: 35 HRC-60 HRC, J40: 34 HRC-60 HRC, J45: 33 HRC-59 HRC, J50: 32 HRC-58 HRC; the non-metallic inclusion A is less than or equal to 1.5 grade in thickness, the A is less than or equal to 2.0 grade in thickness, the B is less than or equal to 1.5 grade in thickness, the B is less than or equal to 2.0 grade in thickness, the C is less than or equal to 1.0 grade in thickness, the C is less than or equal to 1.5 grade in thickness, the D is less than or equal to 1.0 grade in thickness, the D is less than or equal to 1.5 grade in thickness and the Ds is less than or equal to 2.0 grade. The steel for the high-speed rail plate spring imported at present can reach Rm: 1350-1500 MPa, Rel: 1200-1300 MPa, A: 6% -10%, Z: 30% -40%; the decarburized layer is less than or equal to 1.2% of the thickness; terminal hardenability: j1.5: 57 HRC-65 HRC, J3: 56 HRC-65 HRC, J5: 55 HRC-64 HRC, J7: 54 HRC-64 HRC, J9: 53 HRC-63 HRC, J11: 51 HRC-63 HRC, J13: 50 HRC-63 HRC, J15: 48 HRC-62 HRC, J20: 44 HRC-62 HRC, J25: 41 HRC-62 HRC, J30: 37 HRC-61 HRC, J35: 35 HRC-60 HRC, J40: 34 HRC-60 HRC, J45: 33 HRC-59 HRC, J50: 32 HRC-58 HRC; the non-metallic inclusion A is less than or equal to 1.5 grade in thickness, the A is less than or equal to 2.0 grade in thickness, the B is less than or equal to 1.5 grade in thickness, the B is less than or equal to 2.0 grade in thickness, the C is less than or equal to 1.0 grade in thickness, the C is less than or equal to 1.5 grade in thickness, the D is less than or equal to 1.0 grade in thickness, the D is less than or equal to 1.5 grade in thickness and the Ds is less than or equal to 2.0 grade. However, the plate spring produced by the steel ensures the safety, so that the plate spring is large in thickness and low in carrying efficiency; because crystal grains cannot be fully refined, the plate spring has poor obdurability, short service life and high comprehensive use cost.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide the steel for the high-iron plate spring with long service life and high strength and toughness, and the product of the invention has higher strength and toughness, purity and fatigue life than a 51CrMnV spring material in the national spring Steel (GB/T1222-2016) standard; the invention also aims to provide a production process of the steel for the high-speed rail plate spring.
The invention is realized by the following technical scheme:
the steel for the microalloyed high-iron plate spring with long service life and high strength and toughness comprises the following chemical elements in percentage by mass: c: 0.45% -0.47%, Si: 0.20% -0.30%, Mn: 0.95% -1.10%, Cr: 1.00% -1.20%, V: 0.10-0.20%, Cu is less than or equal to 0.20%, Ni: 0.10% -0.20%, Nb: 0.02 to 0.03 percent of the total weight of the alloy, less than or equal to 0.010 percent of P, less than or equal to 0.003 percent of S, less than or equal to 0.005 percent of Sn, less than or equal to 0.00015 percent of H, less than or equal to 0.0015 percent of O, less than or equal to 0.0050 percent of N, and the balance of Fe.
The invention further improves the scheme as follows:
a production process of microalloyed steel for a high-speed rail plate spring with long service life and high strength and toughness comprises the following steps:
(1) KR desulfurization: stirring molten iron in a ladle by adopting a KR desulfurization method to form a vortex, adding a self-made desulfurizer into the vortex to enable the desulfurizer to fully react with sulfur in the molten iron, thoroughly slagging off to remove desulfurization products, reducing the content of S in the molten iron, and ensuring that the S content of the desulfurized molten iron is less than or equal to 0.003%;
(2) smelting in a converter: smelting in a top-bottom combined blowing converter of more than 100 tons, carrying out primary smelting by taking pure molten iron as a raw material to realize pre-deoxidation, adding lime, synthetic refining slag and various high-purity alloys into the steel to carry out pre-deoxidation and primary component adjustment;
(3) refining: carrying out deep deoxidation and alloying on the molten steel in an LF (ladle furnace) with the weight of more than 100 tons, stirring in the whole refining process, stirring greatly in the early stage of refining, and carrying out enhanced S removal and impurity removal through steel slag reaction; weak stirring is adopted in the later stage of refining, so that secondary oxidation of molten steel is prevented;
(4) vacuum degassing: performing vacuum degassing and inclusion removal treatment by adopting RH (relative humidity) circulating degassing equipment after LF (ladle furnace) refining;
(5) modifying inclusions and soft blowing: feeding 60-80 m of calcium-silicon silk thread to denature the impurities after vacuum treatment, and performing soft blowing at the first time for more than 35 minutes to ensure that the impurities are fully floated and removed;
(6) continuous casting: a large round billet continuous casting machine is adopted, a low-silicon tundish covering agent and special crystallizer covering slag for spring steel are used, automatic baking and automatic adding devices are adopted to ensure uniform and timely addition of the covering slag, and full-protection casting in the whole process is carried out to produce continuous casting round billets;
(7) cogging: heating by adopting a heat accumulating type stepping heating furnace;
(8) and (3) billet finishing: peeling the surface of the steel billet, and removing a decarburized layer;
(9) heating: a heat accumulating type stepping heating furnace is adopted for heating, and a full-automatic intelligent combustion system is adopted for heating steel billets;
(10) rolling: and producing the flat steel by using a continuous rolling and water penetrating production line.
(11) And (3) finishing: and manual inspection and grinding are adopted to inspect and eliminate the defects one by one, so that the surface quality of the steel is ensured.
Further, when the converter in the step (2) is smelted, the slag blocking cone and the sliding plate are adopted for carrying out composite slag blocking, and the automatic alarm interlocking device for slag tapping detection ensures that no slag tapping is carried out, and zero return P is realized.
Further, in the refining in the step (3), the alkalinity forming ratio R: 5-8 of refining slag; the ratio of lime to refining slag is controlled to be 2: 1.
Further, in the vacuum degassing in the step (4), the vacuum is kept for 25-30 minutes under high vacuum of <67Pa, and the content of [ H ] is less than or equal to 0.000015%, the content of [ O ] is less than or equal to 0.0008%, the content of [ N ] is less than or equal to 0.0030%, and all the components enter the required internal control range.
Furthermore, when the continuous casting is carried out in the step (6), an M-EMS + S-EMS + F-EMS three-section electromagnetic stirring device is adopted, the structure is fully and uniformly formed, and the internal quality is improved.
Further, when cogging in the step (7), a cogging and continuous rolling production line is used for producing square steel with the thickness of 150mm multiplied by 150 mm.
Further, when the steel billet is finished, the steel billet is subjected to 100% flaw detection by adopting magnetic powder flaw detection and ultrasonic flaw detection equipment.
Further, when heating in the step (9), the deviation of the heating temperature is not more than +/-10 ℃, the temperature of a soaking section is 1050-1080 ℃, and the heating time is controlled within 100-120 min.
Further, during rolling in the step (10), low-temperature controlled rolling is adopted, the rolling start temperature is controlled to be 950-980 ℃, 15 tandem mills are adopted for controlled rolling, three sections of water tanks are adopted for controlled cooling after a finish mill, the temperature of a water inlet tank is controlled to be 920-940 ℃, the water pressure is 10Kg, the flow rate of a 1# water tank is 120m3/m, the flow rate of a 2# water tank is 150m3/m, the flow rate of a 3# water tank is 100m3/m, and the temperature of a water outlet tank is ensured to be 600-650 ℃.
The chemical composition comparison of the currently domestic 51CrMnV spring steel and the steel for the microalloyed high-iron plate spring with long service life, high strength and toughness is shown in the following table 1.
TABLE 1 chemical composition comparison (wt%)
The invention has the following reasons for limiting the chemical components of steel for the microalloyed high-iron plate spring with long service life and high strength and toughness:
c is one of the most effective elements for improving strength and hardenability, but in order to prevent quenching deformation and cracking, the content of C is controlled between 0.45 percent and 0.47 percent in consideration of the requirement of matching of the strength and toughness of the plate spring;
si can be dissolved in ferrite and austenite to improve the strength and hardness of steel, particularly the yield strength of the steel; silicon has the deoxidation effect, but the corrosion resistance is not good when the content exceeds 0.30 percent, so the content of Si is controlled between 0.20 percent and 0.30 percent;
mn can improve the hardness and wear resistance of steel, enhance the hardenability of steel, and improve the hot workability of steel. Mn also has the effect of solid solution strengthening, can enlarge an austenite region, reduce the transformation temperature from austenite to ferrite, further refine ferrite grains, improve the strength and toughness of steel, and compensate the strength loss caused by low carbon, but the Mn content is too high to generate segregation, so the Mn content is controlled to be between 0.95 and 1.10 percent;
cr can significantly improve the strength, hardness, wear resistance and hardenability of steel, but at the same time reduces the plasticity and toughness. A layer of passive film can be formed on the surface of the steel, the steel has the capabilities of oxidation resistance and corrosion resistance, and meanwhile, the carbon dioxide corrosion resistance can be improved by Cr, so that the Cr element of the steel is controlled to be between 1.00 and 1.20 percent;
the addition of V element can refine crystal grains and improve the toughness and wear resistance of steel, thereby improving the comprehensive mechanical property and fatigue life of steel, but the V element is very expensive and is not suitable for being added in large quantity. The V content of the steel grade is controlled to be 0.10-0.20%.
Cu is generally used as a harmful element in steel, and when the Cu content exceeds 0.20% and the steel temperature exceeds 1100 ℃, oxidation and decarburization are generated on the surface of the steel, the Cu is easily enriched in a decarburized layer grain boundary, copper brittleness and surface cracking are formed, and the quality of the steel is seriously influenced. Therefore, the present invention limits the Cu content to 0.20% or less.
Ni can stabilize austenite in steel, improve strength, and simultaneously, does not reduce plasticity and toughness, especially can reduce brittle transition temperature, and improve low-temperature impact toughness. Ni also has certain corrosion resistance, but because Ni is a precious alloy and affects the production cost of steel, 0.10-0.20% of Ni is added into the steel.
Nb can increase the recrystallization temperature of austenite in steel, enlarge the temperature range of a non-recrystallization region, promote the deformation of austenite grains and the accumulation of defects, refine ferrite grains, and play a role in obviously refining grains by only adding 0.020% of Nb, thereby improving the toughness of the steel. As Nb is a precious alloy, 0.020-0.030% of Nb is added into the steel grade.
P causes cold brittleness of steel, lowers impact toughness of steel, deteriorates weldability of steel, lowers plasticity, and deteriorates cold bending property. Therefore, the content of P is controlled to be below 0.010 percent;
s is an easily segregated element, reduces ductility and toughness of steel, and also has adverse effects on welding performance and corrosion resistance. Therefore, the S content is strictly controlled and must be less than or equal to 0.003 percent;
sn is positioned in the fourth and fifth main groups of the periodic table of elements, has lower oxidability than iron and cannot be removed in a smelting link; the alloy has large atomic radius, is easy to enrich in crystal boundary and surface, is extremely uneven in distribution, increases the hot brittleness tendency of steel, causes low-temperature brittleness, reduces the thermoplasticity of the steel, leads to surface cracking of a casting blank, and reduces the fatigue property of steel. Sn is controlled to be less than or equal to 0.005 percent in the steel grade.
H: hydrogen reduces the plasticity of the steel. Hydrogen can generate 'hair lines' or form stress areas in steel, and the hair lines are expanded to form cracks when the steel is subjected to rolling processing, so that the mechanical property, particularly the plasticity of the steel is deteriorated, even the steel is broken, and 'white spots' appear on steel fracture. Meanwhile, the hydrogen can cause point segregation and hydrogen embrittlement, and the fatigue life of the plate spring is seriously influenced. Therefore, the invention and the process control the H to be less than 0.00015%.
O: the strength of the steel is not greatly influenced at room temperature, but the elongation and the surface shrinkage of the steel are obviously reduced, and the strength and the plasticity of the material are both sharply reduced along with the increase of the O content at a lower temperature and when the O content is extremely low. In the impact property, the maximum value of the impact is gradually decreased with an increase in the O content, the brittle transition temperature is rapidly increased, and the range of the brittle transition temperature is widened. Meanwhile, with the increase of the content of O, the occurrence probability of oxide inclusions of the material is greatly increased, so that the fatigue life of the material is reduced. The invention and the production process can stably control the O content within 0.0015 percent.
N: nitrogen can strengthen steel, but obviously reduce the plasticity and toughness of the steel, and increase the aging tendency and cold brittleness. Generally, the content is required to be less than 0.0070%. The invention and the production process control the N content within 0.0050%.
The invention has the beneficial effects that:
(1) the invention uses conventional alloy elements such as C, Si, Mn, Cr and the like to carry out alloying, adds a small amount of V, Ni and Nb to carry out micro-alloying, designs the C content to be 0.45-0.47%, and leads the performance to have higher obdurability than 51CrMnV in the national spring steel (GB/T1222-2016) standard.
(2) And aiming at the characteristics of steel grades, KR pre-desulfurization is carried out by adopting a self-made desulfurizer, so that the desulfurized molten iron S is less than or equal to 0.003 percent, and favorable conditions are created for refining desulfurization.
(3) The slag blocking cone and the sliding plate are adopted for carrying out composite slag blocking, and the automatic alarm interlocking device for slag tapping detection ensures that no slag tapping is carried out, and zero return P is realized;
(4) the ratio of lime to refining slag is controlled to be 2:1, the whole refining process is stirred, the refining process is stirred greatly in the early stage, the steel slag reaction is used for strengthening S removal and removing impurities, and the refining later stage is stirred weakly to prevent secondary oxidation of molten steel; effectively reduces the content of the end point S and improves the purity of the steel.
(5) The steel grade adopts a BOF + LF + RH + CCM process, vacuum degassing is kept for 25-30 minutes under a high vacuum of <67Pa, and lower gas and harmful residual element contents are ensured, so that the material has excellent comprehensive mechanical properties.
(6) Feeding 60-80 m of calcium-silicon silk thread to denature the impurities after vacuum treatment, and performing soft blowing at the first time for more than 35 minutes to ensure that the impurities are fully floated and removed;
(7) the continuous casting adopts an M-EMS + S-EMS + F-EMS three-section electromagnetic stirring device, so that the structure is sufficiently and uniformly formed, and the internal quality is improved.
(8) The rolling billet is peeled by a mechanical peeling machine to remove the oxidation decarburized layer, so that the decarburized layer of the flat steel is reduced, and the flat steel is ensured not to be decarburized completely.
(9) The billet heating adopts a full-automatic intelligent combustion system, the heating temperature deviation does not exceed +/-10 ℃, the temperature of a soaking section is 1050-1080 ℃, and the heating time is controlled within 100-120 min.
(10) The method comprises the steps of rolling under low temperature control, controlling the initial rolling temperature to be 950-980 ℃, controlling rolling by using a 15-frame tandem mill, cooling under control by using three sections of water tanks after a finishing mill, controlling the temperature of a water inlet tank to be 920-940 ℃, the water pressure to be 10Kg, the flow of a No. 1 water tank to be 120m3/m, the flow of a No. 2 water tank to be 150m3/m and the flow of a No. 3 water tank to be 100m3/m, and ensuring the temperature of the water outlet tank to be 600-650 ℃.
The steel has reasonable component design and advanced process, and has higher purity, higher obdurability, finer grain size and longer fatigue life compared with the steel for the high-iron leaf spring supplied in the current market. The inclusions of A class, B class, D class and Ds class are stably controlled to be less than or equal to 1.0 level, and the inclusions of C class are not detected. The B-type, D-type and Ds-type inclusions have the greatest influence on the fatigue life of the material, and the process control level of the invention reaches the international advanced level. The tensile strength Rm is stably controlled to be 1500-1650 MPa, the yield strength Rel is stably controlled to be 1350-1400 MPa, the elongation A after fracture is more than or equal to 10 percent, and the reduction of area Z is more than or equal to 45 percent; the decarburized layer is less than or equal to 1.0 percent of the thickness of the decarburized layer, and no full decarburization is performed; terminal hardenability: j1.5: 60 HRC-65 HRC, J3: 60 HRC-65 HRC, J5: 60 HRC-64 HRC, J7: 59 HRC-64 HRC, J9: 59 HRC-63 HRC, J11: 58 HRC-63 HRC, J13: 58 HRC-63 HRC, J15: 57 HRC-63 HRC, J20: 56 HRC-62 HRC, J25: 55 HRC-62 HRC, J30: 52 HRC-61 HRC, J35: 50 HRC-60 HRC, J40: 47 HRC-60 HRC, J45: 43 HRC-59 HRC, J50: 40 HRC-58 HRC. Austenite grain size is greater than or equal to 7.5 grade, and fatigue life is greater than or equal to 1000 ten thousand times. The thickness of the high-speed rail plate spring can be effectively reduced, the energy consumption is reduced, and the transportation efficiency is improved; the invention can obviously improve the product quality, prolong the service life of the plate spring and improve the safety and the comfort.
Drawings
FIG. 1 is a schematic view of a continuous rolling and water passing production line for the rolling in step (10);
FIG. 2 is a schematic view of a water tank;
Detailed Description
Examples 1 to 4
The preparation method comprises the following steps:
(1) KR desulfurization: stirring molten iron in a ladle by adopting a KR desulfurization method to form a vortex, adding a self-made desulfurizer into the vortex to enable the desulfurizer to fully react with sulfur in the molten iron, thoroughly slagging off to remove desulfurization products, reducing the content of S in the molten iron, and ensuring that the S content of the desulfurized molten iron is less than or equal to 0.003%;
(2) smelting in a converter: smelting in a top-bottom combined blowing converter of more than 100 tons, carrying out primary smelting by taking pure molten iron as a raw material to realize pre-removing P, adding lime, synthetic refining slag and various high-purity alloys into the steel, carrying out pre-deoxidation and primary component adjustment, and carrying out composite slag blocking by adopting a slag blocking cone and a sliding plate to ensure slag-free steel tapping and prevent P return;
(3) refining: deep deoxidation and alloying of molten steel are carried out in an LF furnace with the weight of more than 100 tons, and the alkalinity R: 5-8 of refining slag; the ratio of lime to refining slag is controlled to be 2:1, the whole refining process is stirred, the refining process is stirred greatly in the early stage, and the steel slag reaction is used for strengthening S removal and removing impurities; weak stirring is adopted in the later stage of refining, so that secondary oxidation of molten steel is prevented;
(4) vacuum degassing: after LF refining, RH circulation degassing equipment is adopted for vacuum degassing and inclusion removal treatment, the vacuum is kept for 25-30 minutes under high vacuum of <67Pa, the conditions that [ H ] is less than or equal to 0.000015%, [ O ] is less than or equal to 0.0008%, and [ N ] is less than or equal to 0.0030% are ensured, and all components enter the required internal control range;
(5) modifying inclusions and soft blowing: feeding 60-80 m of calcium-silicon silk thread to denature the impurities after vacuum treatment, and performing soft blowing at the first time for more than 35 minutes to ensure that the impurities are fully floated and removed;
(6) continuous casting: a large round billet continuous casting machine is adopted, a low-silicon tundish covering agent and special crystallizer covering slag for spring steel are used, automatic baking and automatic adding devices are adopted to ensure uniform and timely addition of the covering slag, and full-protection casting in the whole process is carried out to produce continuous casting round billets; the M-EMS + S-EMS + F-EMS three-section electromagnetic stirring device is adopted, the tissue is fully and uniformly organized, and the internal quality is improved.
(7) Cogging: a regenerative stepping heating furnace is adopted for heating, and a cogging and continuous rolling production line is utilized to produce square steel with the thickness of 150mm multiplied by 150 mm.
(8) And (3) billet finishing: peeling the surface of the steel billet, and removing a decarburized layer; and (3) carrying out 100% flaw detection on the steel billet by adopting magnetic powder flaw detection and ultrasonic flaw detection equipment.
(9) Heating: the heat accumulating type stepping heating furnace is adopted for heating, a full-automatic intelligent combustion system is adopted for heating the steel billet, the heating temperature deviation does not exceed +/-10 ℃, the temperature of a soaking section is 1050-1080 ℃, and the heating time is controlled within 100-120 min.
(10) Rolling: and producing the flat steel by using a continuous rolling and water penetrating production line. The method comprises the steps of rolling under low temperature control, controlling the initial rolling temperature to be 950-980 ℃, rolling under control by using a 15-frame tandem mill, cooling under control by using three sections of water tanks after a finish mill, controlling the temperature of a water inlet tank to be 920-940 ℃, controlling the water pressure to be 10Kg and controlling the flow of a No. 1 water tank to be 120m3Flow rate of the 2# water tank is 150m3Flow rate of/m, 3# water tank 100m3And m, ensuring the temperature of the water outlet tank to be 600-650 ℃.
(11) And (3) finishing: and manual inspection and grinding are adopted to inspect and eliminate the defects one by one, so that the surface quality of the steel is ensured.
In the embodiment, the schematic view of a continuous rolling and water passing production line for rolling in the step (10) is shown in fig. 1, and the schematic view of a water tank is shown in fig. 2.
The process conditions not limited in the above preparation method can be referred to the conventional techniques in the art.
The chemical composition of the steel for a high-speed rail leaf spring obtained is shown in table 2,
TABLE 2 Steel composition (wt%) for high-speed rail leaf spring
The gas content, mechanical properties, grain size, decarburized layer and nonmetallic inclusions, and end hardenability are shown in tables 3, 4, 5, and 6 in comparison with the prior art.
Table 3 comparison of gas content, grain size, decarburized layer of the invention with the prior art
TABLE 4 comparison of mechanical Properties of the invention with the prior art
TABLE 5 comparison of non-metallic inclusions of the invention with the prior art
The class A, class B, class D and class Ds inclusions are stably controlled to be less than or equal to 1.0 level, and class C inclusions are not detected. The B-type, D-type and Ds-type inclusions have the greatest influence on the fatigue life of the material, and the process control level of the invention reaches the international advanced level.
TABLE 6 terminal hardenability
As shown in tables 3, 4, 5 and 6, the steel for the high-speed rail plate spring provided by the invention has the advantages that the tensile strength Rm is stably controlled to be 1500-1650 MPa, the yield strength Rel is stably controlled to be 1350-1400 MPa, the elongation A after fracture is more than or equal to 10 percent, and the reduction of area Z is more than or equal to 45 percent; the decarburized layer is less than or equal to 1.0 percent of the thickness of the decarburized layer, and no full decarburization is performed; terminal hardenability: j1.5: 60 HRC-65 HRC, J3: 60 HRC-65 HRC, J5: 60 HRC-64 HRC, J7: 59 HRC-64 HRC, J9: 59 HRC-63 HRC, J11: 58 HRC-63 HRC, J13: 58 HRC-63 HRC, J15: 57 HRC-63 HRC, J20: 56 HRC-62 HRC, J25: 55 HRC-62 HRC, J30: 52 HRC-61 HRC, J35: 50 HRC-60 HRC, J40: 47 HRC-60 HRC, J45: 43 HRC-59 HRC, J50: 40 HRC-58 HRC. Austenite grain size is greater than or equal to 7.5 grade, and fatigue life is greater than or equal to 1000 ten thousand times. The thickness of the high-speed rail plate spring can be effectively reduced, the energy consumption is reduced, and the transportation efficiency is improved; the invention can obviously improve the product quality, prolong the service life of the plate spring and improve the safety and the comfort.
Claims (7)
1. A production process of microalloyed steel for a high-strength high-toughness high-strength steel leaf spring with long service life is characterized by comprising the following steps:
(1) KR desulfurization: stirring molten iron in a ladle by adopting a KR desulfurization method to form a vortex, adding a self-made desulfurizer into the vortex to enable the desulfurizer to fully react with sulfur in the molten iron, thoroughly slagging off to remove desulfurization products, reducing the content of S in the molten iron, and ensuring that the S content of the desulfurized molten iron is less than or equal to 0.003%;
(2) smelting in a converter: smelting in a top-bottom combined blowing converter of more than 100 tons, carrying out primary smelting by taking pure molten iron as a raw material to realize pre-deoxidation, adding lime, synthetic refining slag and various high-purity alloys into the steel to carry out pre-deoxidation and primary component adjustment;
(3) refining: carrying out deep deoxidation and alloying on the molten steel in an LF (ladle furnace) with the weight of more than 100 tons, stirring in the whole refining process, stirring greatly in the early stage of refining, and carrying out enhanced S removal and impurity removal through steel slag reaction; weak stirring is adopted in the later stage of refining, so that secondary oxidation of molten steel is prevented; in refining, the alkalinity forming value R: 5-8 of refining slag; controlling the ratio of lime to refining slag to be 2: 1;
vacuum degassing: performing vacuum degassing and inclusion removal treatment by adopting RH (relative humidity) circulating degassing equipment after LF (ladle furnace) refining; during vacuum degassing, the vacuum is kept for 25-30 minutes under the high vacuum of <67Pa, the content of [ H ] is less than or equal to 0.000015%, the content of [ O ] is less than or equal to 0.0008%, the content of [ N ] is less than or equal to 0.0030%, and all the components enter the required internal control range;
(5) modifying inclusions and soft blowing: feeding 60-80 m of calcium-silicon silk threads to denature the impurities after vacuum treatment, and performing soft blowing at the first time, wherein the soft blowing time is over 35 minutes, so as to ensure that the impurities are fully floated and removed;
(6) continuous casting: a large round billet continuous casting machine is adopted, a low-silicon tundish covering agent and special crystallizer covering slag for spring steel are used, automatic baking and automatic adding devices are adopted to ensure uniform and timely addition of the covering slag, and full-protection casting in the whole process is carried out to produce continuous casting round billets;
(7) cogging: heating by adopting a heat accumulating type stepping heating furnace;
(8) and (3) billet finishing: peeling the surface of the steel billet, and removing a decarburized layer;
(9) heating: a heat accumulating type stepping heating furnace is adopted for heating, and a full-automatic intelligent combustion system is adopted for heating steel billets;
(10) rolling: producing flat steel by using a continuous rolling and water passing production line;
(11) and (3) finishing: manual inspection and grinding are adopted to inspect and eliminate the defects one by one, so that the surface quality of the steel is ensured;
the prepared steel for the high-speed rail plate spring consists of the following chemical elements in percentage by mass: c: 0.45% -0.47%, Si: 0.20% -0.30%, Mn: 0.95% -1.10%, Cr: 1.10% -1.20%, V: 0.10-0.20%, Cu is less than or equal to 0.20%, Ni: 0.10% -0.20%, Nb: 0.02-0.03%, P is less than or equal to 0.010%, S is less than or equal to 0.003%, Sn is less than or equal to 0.005%, H is less than or equal to 0.00015%, O is less than or equal to 0.0015%, N is less than or equal to 0.0050%, and the balance is Fe;
the fatigue life of the prepared steel for the high-speed rail plate spring is not less than 1000 ten thousand times.
2. The production process of the microalloyed steel for the high-iron leaf spring with long service life and high strength and toughness as claimed in claim 1, is characterized in that: and (3) when the converter in the step (2) is smelted, carrying out composite slag blocking by adopting a slag blocking cone and a sliding plate, and automatically alarming and interlocking the slag tapping detection to ensure that no slag tapping is carried out and realize zero return P.
3. The production process of the microalloyed steel for the high-iron leaf spring with long service life and high strength and toughness as claimed in claim 1, is characterized in that: and (5) during continuous casting in the step (6), an M-EMS + S-EMS + F-EMS three-section electromagnetic stirring device is adopted, so that the structure is sufficiently and uniformly formed, and the internal quality is improved.
4. The production process of the microalloyed steel for the high-iron leaf spring with long service life and high strength and toughness as claimed in claim 1, is characterized in that: and (7) when cogging is performed in the step (7), producing square steel with the thickness of 150mm multiplied by 150mm by using a cogging and continuous rolling production line.
5. The production process of the microalloyed steel for the high-iron leaf spring with long service life and high strength and toughness as claimed in claim 1, is characterized in that: and (8) when the steel billet is finished, carrying out 100% flaw detection on the steel billet by adopting magnetic powder flaw detection and ultrasonic flaw detection equipment.
6. The production process of the microalloyed steel for the high-iron leaf spring with long service life and high strength and toughness as claimed in claim 1, is characterized in that: and (3) when heating in the step (9), the deviation of the heating temperature is not more than +/-10 ℃, the temperature of a soaking section is 1050-1080 ℃, and the heating time is controlled within 100-120 min.
7. The production process of the microalloyed steel for the high-iron leaf spring with long service life and high strength and toughness as claimed in claim 1, is characterized in that: during rolling in the step (10), low-temperature controlled rolling is adopted, the initial rolling temperature is controlled to be 950-980 ℃, 15 tandem mills are adopted for controlled rolling, three sections of water tanks are adopted for controlled cooling after a final rolling mill, the temperature of a water inlet tank is controlled to be 920-940 ℃, the water pressure is 10Kg, and the flow of a No. 1 water tank is 120m3Flow rate of the 2# water tank is 150m3Flow rate of/m, 3# water tank 100m3And m, ensuring the temperature of the water outlet box to be 600-650 ℃.
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