CN113930680B - Low-temperature-resistant high-strength spring flat steel and production method thereof - Google Patents

Low-temperature-resistant high-strength spring flat steel and production method thereof Download PDF

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CN113930680B
CN113930680B CN202111151331.1A CN202111151331A CN113930680B CN 113930680 B CN113930680 B CN 113930680B CN 202111151331 A CN202111151331 A CN 202111151331A CN 113930680 B CN113930680 B CN 113930680B
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丁礼权
张贤忠
夏艳花
朱志鹏
叶途明
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Wuhan Iron and Steel Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0081—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for slabs; for billets
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C33/04—Making ferrous alloys by melting
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract

The invention discloses low-temperature-resistant high-strength spring flat steel which comprises the following chemical components in percentage by weight: c:0.48 to 0.60wt%, si:0.40 to 0.90wt%, mn:0.80 to 1.50 weight percent, more than or equal to 1.5 (Mn/C) and less than or equal to 2.8, less than or equal to 0.025 weight percent of P, less than or equal to 0.025 weight percent of S, and the weight percent of Cr:0.40 to 1.00wt%, ni:0.10 to 0.40wt%, nb:0.01 to 0.05wt%, B:0.001 to 0.004wt%, zr: 0.002-0.009 wt%, ce:0.02 to 0.06 weight percent, less than or equal to 0.0045 weight percent of N, less than or equal to 0.00012 weight percent of H, less than or equal to 0.0011 weight percent of O, and the balance of Fe and inevitable impurities. Through the innovation of components and process, the invention develops the product with the following performances: reL is more than or equal to 1750MPa, rm is more than or equal to 1950MPa, A is more than or equal to 10 percent, Z is more than or equal to 36 percent, KV2 at minus 60 ℃ is more than or equal to 35J, and the grain size is not coarser than 8.5 grade.

Description

Low-temperature-resistant high-strength spring flat steel and production method thereof
Technical Field
The invention relates to a long steel product and a production method thereof, belongs to the field of ferrous metallurgy production and manufacturing, and particularly relates to low-temperature-resistant high-strength spring flat steel and a production method thereof.
Background
The spring flat steel is the most important elastic element in various truck, passenger car and engineering machinery vehicle damping systems, is mainly used for manufacturing steel plate springs, and is widely applied to the fields of automobiles, railways, aviation, national defense and the like.
The automobile lightweight technology is an important means for automobile fuel saving, and researches show that: when the mass of the automobile is reduced by 10 percent, the oil consumption is reduced by about 3 to 5 percent, and the heavy automobile adopts the high-strength flat spring steel, so that the mass of the steel plate spring assembly can be reduced by 20 to 45 percent. Along with the development requirements of the logistics transportation industry and resource exploitation engineering, many projects in China have been developed into various extremely cold fields. In the wide northern areas of China, such as northeast and Xinjiang, the temperature in winter can reach below-40 ℃, and the temperature in some areas is lower than-50 ℃. Under the condition of low temperature, the performance of the metal material can be greatly changed, and the mechanical properties, especially the impact toughness and the fracture toughness, shown under different environmental temperatures are greatly changed.
Generally, the higher the strength of a steel material, the lower the toughness, and the lower the toughness index in a low-temperature environment. The spring flat steel is used as a raw material of the important parts of the vehicle, and the service performance of the whole vehicle, even the safety and the reliability, can be influenced by the strength and the toughness in a low-temperature environment.
In the prior art, a plurality of similar technical products relate to the field of manufacturing of low-temperature-resistant high-strength automobile steel, and particularly the number of the technical products is less in the aspect of low-temperature-resistant high-strength spring flat steel.
After retrieval: CN 104213051A discloses a low temperature resistant and wear resistant spring body, which comprises the following chemical elements in parts by mass: 300-600 parts of iron, 30-70 parts of carbon, 10-30 parts of copper, 5-15 parts of aluminum, 2-8 parts of silicon, 0.15-0.25 part of ruthenium, 0.08-0.15 part of nickel, 0.25-0.45 part of sulfur, 0.008-0.015 part of chromium and 0.044-0.068 part of selenium, wherein the surface of the spring body is sprayed with an antifreezing antirust paint. The mechanical property and the low-temperature property of the spring body are not described, and only from the existing components, the high S content has great adverse effect on the low-temperature impact property.
CN 104630650A discloses a low temperature resistant high strength spring steel and a preparation method thereof, wherein the spring steel contains (by weight percent): the chemical components and the weight percentage thereof are as follows: 0.45 to 0.55 percent of C, 1.0 to 1.3 percent of Si, 1.2 to 1.4 percent of Mn, 3.5 to 5.5 percent of Ni, 0.8 to 1.0 percent of Cr, 0.3 to 0.5 percent of Cu, 0.006 to 0.008 percent of Ti, 0.03 to 0.06 percent of Zn, 0.004 to 0.005 percent of Sn, less than or equal to 0.025 percent of P, less than or equal to 0.025 percent of S, and the balance of Fe. The preparation method comprises mixing the raw materials, heating to molten state, pouring into purified water, chilling, and pulverizing into 100-200 mesh powder; adding silane coupling agent KH-550 and nano carbon powder 2-4 wt% into the obtained powder, mixing, pressing at 8-15Mpa to obtain blank, calcining at 1000-1100 deg.C for 3-4 hr, cooling, and pulverizing into 150-250 mesh powder. The spring steel is prepared by a powder metallurgy method, has low efficiency and high cost, and is difficult to produce and popularize on a large scale.
CN111118398A discloses a high-hardenability high-strength low-temperature-toughness spring steel, which comprises the following chemical elements in percentage by mass: c:0.54 to 0.64%, si:1.40 to 2.00%, mn: 0.40-0.80%, cr:1.00 to 1.50%, ni:0.10 to 0.40%, mo:0.10 to 0.40%, al: 0.015-0.080 percent of Fe, less than or equal to 0.025 percent of P, less than or equal to 0.020 percent of S, less than or equal to 0.25 percent of Cu, and the balance of Fe and inevitable impurity elements; the hardenability J1.5mm of the tail end of the spring steel is more than or equal to 60HRC, and the hardenability J30mm of the spring steel is more than or equal to 55HRC; after oil quenching at 850 +/-20 ℃ and tempering at 450 +/-30 ℃, the tensile strength is more than or equal to 1700MPa, the yield strength is more than or equal to 1500MPa, and the impact energy KU2 at minus 40 ℃ is more than or equal to 16J. The spring steel has higher hardenability and strength, but the low-temperature impact energy is lower, so that the low-temperature toughness of the material in a cold region cannot be ensured at the same time.
Disclosure of Invention
In order to meet the requirement that spring flat steels for various trucks, buses and engineering machinery vehicles are suitable for severe environments, particularly cold environments, the technical problem to be solved by the invention is to provide a spring flat steel which has good low-temperature toughness, high strength and high toughness and is used for a variable cross-section steel plate spring. Through the innovation of components and process, the invention develops the product with the following performances: reL is more than or equal to 1750MPa, rm is more than or equal to 1950MPa, A is more than or equal to 10 percent, Z is more than or equal to 36 percent, KV2 is more than or equal to 35J at minus 60 ℃, and the grain size is not thicker than 8.5 grade low-temperature resistant high-strength spring flat steel.
The technical scheme adopted by the invention for solving the problems is as follows:
the low-temperature-resistant high-strength spring flat steel comprises the following chemical components in percentage by weight: c:0.48 to 0.60wt%, si:0.40 to 0.90wt%, mn:0.80 to 1.50 weight percent, more than or equal to 1.5 (Mn/C) and less than or equal to 2.8, less than or equal to 0.025 weight percent of P, less than or equal to 0.025 weight percent of S, and the weight percent of Cr:0.40 to 1.00wt%, ni:0.10 to 0.40wt%, nb:0.01 to 0.05wt%, B:0.001 to 0.004wt%, zr: 0.002-0.009 wt%, ce:0.02 to 0.06 weight percent, less than or equal to 0.0045 weight percent of N, less than or equal to 0.00012 weight percent of H, less than or equal to 0.0011 weight percent of O, and the balance of Fe and inevitable impurities. The production process comprises the following steps:
(1) And (3) carrying out composite KR deep desulfurization: the molten iron pretreatment, based on active lime, stirring the molten iron in a ladle by a desulfurizer in a KR stirring mode to form a vortex, adding the active lime and magnesium powder of the desulfurizer twice in sequence to reduce the S content of the molten iron, deeply slagging after the desulfurization is finished, avoiding resulfurization, and controlling the sulfur content [ S ] of the molten iron out of a station to be less than or equal to 0.01 percent; wherein, 5-10kg/t of active lime and 2-6kg/t of magnesium powder are added for the first time, 3-6kg/t of active lime and 1-5kg/t of magnesium powder are added for the second time, and sampling is carried out after the first addition to detect the sulfur content so as to carry out the second addition;
(2) Heating a ladle: covering the ladle and heating by adopting electromagnetic induction to ensure that the temperature is more than or equal to 1490 ℃ in the process of conveying molten iron from an iron works to a steel works;
(3) Smelting in a converter, and controlling the end point C to be more than or equal to 0.06-0.40%; the tapping temperature is more than or equal to 1630 ℃;
(4) And (3) refining in an LF (ladle furnace), wherein in the refining process of the LF, 2-5kg/t of calcium carbide and special silicon: 1-4kg/t of deoxidizing materials, strengthening the white slag making process, and reducing the oxidability of the molten slag: feO is less than or equal to 0.5 percent;
(5) RH vacuum treatment is carried out, the vacuum degree is less than or equal to 100Pa, the vacuum time is not less than 20min, the soft argon blowing flow is 20-68 NL/min, and the soft argon blowing time is 12-28 min;
(6) The section size of the continuous casting billet is 280mm multiplied by 380mm, the throwing speed is stably controlled at 0.70m/min, the throwing speed of the section size of the billet is controlled, and the throwing speed is adjusted not to exceed 2 times per furnace; adopting a solidification end electric stirring process, wherein the stirring current is 350-450A, and the frequency is 8Hz; carrying out soft reduction on the casting blank, wherein the reduction rate is 3% -10%; the temperature fluctuation of the tundish does not exceed 15 ℃;
(7) After slowly cooling for 72h, heating the casting blank, soaking at 1210-1250 ℃ for 560-340 min, and rolling into a small square blank with the section of 160 x 160 mm;
(8) After local grinding, heating the small square billet at the soaking temperature of 1110-1148 ℃ for 110-145 min;
(9) Rough rolling, controlling the initial rolling temperature: 1050 to 1100 ℃;
(10) Finish rolling, wherein the initial rolling temperature is controlled to be 980-1060 ℃, and the accumulated deformation is 10-60%;
(11) Rolling into spring flat steel with the thickness of 31-40 mm and the width of 90-110 mm for standby;
(12) After the spring flat steel is slowly cooled, the primary sub-temperature quenching temperature is 810 +/-20 ℃, the tempering temperature is 420 +/-20 ℃, the secondary sub-temperature quenching temperature is 810 +/-20 ℃, and the tempering temperature is 400 +/-20 ℃ for heat treatment, so that uniform and stable tempered troostite and residual austenite, namely the low-temperature-resistant high-strength spring flat steel, are obtained.
The following analysis shows the effects of the important elements in the steel of the present invention and the production method thereof:
Mn/C: the low-temperature toughness of the spring flat steel can be obviously improved by improving the Mn/C ratio in the steel, and in addition, the cost can be reduced and the economical efficiency can be improved by replacing part of Ni with a proper amount of Mn. The excessive Mn/C increases the overheating sensitivity of steel, so that crystal grains are easy to grow up during the quenching heat treatment of the spring flat steel, and the toughness is reduced. The Mn/C ratio of the invention is 1.5-2.8.
Ni: ni is a main alloy element of the low-temperature steel, can reduce the brittle transition temperature and improve the low-temperature impact toughness while improving the strength, but the yield strength of the material can be reduced due to the excessively high content of Ni, so that the elastic deformation of the spring flat steel under a higher load is not facilitated, and the fatigue life of the spring flat steel in the operation of an automobile is shortened. The Ni content of the invention is 0.10-0.40%.
B: when the B element is less than 0.005 percent, the material can obtain excellent low-temperature toughness; when the content of B is higher than the range, B is easy to form FeB with Fe, the possibility of brittle fracture tendency along the crystal is greatly increased by the presence of FeB, so that the low-temperature toughness of the material is damaged, and the yield strength, the tensile strength, the fatigue strength, the hydrogen-induced intergranular fracture resistance and the like of steel are improved or enhanced to different degrees by a trace amount of B, wherein the content of B is 0.001-0.004%.
Zr: zr can make the steel obtain very good low-temperature toughness, but the content of Zr also needs to be strictly controlled. Zirconium can play a role in degassing and grain refinement, and the impact energy AKV of the steel at minus 50 ℃ is kept between 100 and 120J; however, when the content is increased to 0.06%, the local segregation is caused, the steel performance is deteriorated, the impact energy AKV at-50 ℃ is obviously reduced, and the Zr content is 0.002-0.009%.
Ce: ce, trace O and N form a compound ceramic reinforcing phase which can be dispersedly distributed in the steel, so that nucleation particles are provided for the solidification of the alloy, the minimum nucleation work is reduced, the grain refinement of the flat spring steel is facilitated, and the obdurability is improved.
N: the important constituent elements of microalloying can strengthen the steel, but obviously reduce the toughness of the steel, and increase the aging tendency and cold brittleness, so that the N content of the invention is controlled below 0.0045 percent.
H: in steel, "hairlines" or stress zones are generated, and the hairlines are expanded during rolling or heat treatment to form cracks, which deteriorate the strength and toughness of the steel, and even cause cracking, and point-like segregation and hydrogen embrittlement, which seriously affect the fatigue life of the spring flat steel. In the invention, H is controlled below 0.00012%.
O: at a lower temperature, the strength and the toughness of the spring flat steel are both sharply reduced along with the increase of the O content, the brittle transition temperature is greatly increased, the low-temperature impact toughness is not favorable, and meanwhile, the occurrence probability of oxide inclusions is greatly increased along with the increase of the O content, so that the fatigue life of the spring flat steel is reduced. The invention controls the O content within 0.0011%.
Induction heating of the ladle: the invention adopts induction heating and covering heat preservation in the transportation process, can reduce the refractory consumption, improve the package age and improve the molten iron yield, and simultaneously, the temperature rise of the molten iron can use less or no covering agent, clean the molten iron, reduce harmful elements such as S, P and the like, and lead the converter to add more steel scraps and use less molten iron, thereby being beneficial to energy conservation and emission reduction of steel plants.
And (3) carrying out composite KR deep desulfurization: sulfide inclusions have obvious adverse effects on the fatigue performance of the spring flat steel, and for the reason, a deep desulfurization technology of the spring flat steel is innovated, and a full-process desulfurization and sulfur control technology is adopted, wherein the full-process control technology comprises deep desulfurization of molten iron pretreatment, converter control sulfur increase, secondary deep desulfurization of a ladle furnace and vacuum furnace control sulfur increase. The molten iron pretreatment, with active lime as the basis, the desulfurizer adopts the mode of KR stirring to carry out the deep desulfurization to the molten iron, carries out the degree of depth after the desulfurization and takes off the sediment, avoids resulfurizing. The converter smelting strictly adopts low-sulfur slagging material and selects low-sulfur scrap steel. And (2) refining and desulfurizing in the LF furnace, firstly, reducing the oxidizing ladle slag by forming a reducing environment, then absorbing oxygen in molten steel and slag in a FeO form by slag particles, reducing in white slag, and balancing.
The ultra-low oxygen control technology comprises the following steps: the temperature fluctuation of the tundish is controlled, the times of continuous casting pulling speed adjustment are reduced, the stability of the liquid level of the molten steel of the crystallizer is kept, and the slag alkalinity is improved. In the LF furnace refining process, deoxidizing materials such as calcium carbide and special silicon are added to the slag surface, the white slag making process is strengthened, and the oxidability of slag is reduced, so that the molten oxygen in steel is reduced, the slag adsorption and inclusion capacity is improved, and the content of O in the flat spring steel is effectively reduced.
Secondary sub-temperature quenching and tempering: the secondary quenching can refine the austenite grain size, shorten the length of lath martensite obtained after quenching, and temper the steel to obtain better strength and elongation. The too high quenching temperature can cause the growth of austenite grains, a coarse grain martensite structure is obtained after quenching, the toughness is poor, the too low quenching temperature can easily cause undissolved ferrite to exist in the austenite, and the ferrite is a soft phase structure, so that the strength of the steel is reduced. The hypoeutectoid steel of the invention is quenched at the temperature between Ac1 and Ac3 which is 40 ℃ lower than the normal subtemperature, which is beneficial to the low-temperature obdurability and the fatigue life of the invention.
A secondary firing forming process: the invention adopts the two-fire forming process, the residence time of the molten steel tundish in the bloom casting process is long, the removal of impurities is facilitated, meanwhile, the casting blank compression ratio can be increased through cogging, the structure uniformity is improved, crystal grains are refined, the compactness and toughness of the spring flat steel are facilitated to be improved, and the method is an important means for ensuring the low-temperature performance of the high-strength spring flat steel.
Compared with the prior art, the invention has the beneficial effects that:
firstly, trace alloy elements Nb, ni, B, ce and the like are added on the basis of carbon and manganese series low alloy steel, a ladle induction heating, composite KR deep desulfurization, an ultra-low oxygen control technology, secondary sub-temperature quenching and tempering and a secondary heating forming process are innovatively coupled to form a pearlite structure with fine grain size, and the spring flat steel with good low-temperature performance at the temperature of 60 ℃ below zero and above is obtained, so that the following performances can be realized: reL is more than or equal to 1750MPa, rm is more than or equal to 1950MPa, A is more than or equal to 10 percent, Z is more than or equal to 36 percent, KV2 is more than or equal to 35J at minus 60 ℃, and the grain size is not coarser than 8.5 grade.
Secondly, the production method is simple and low in production cost, and the process production can be carried out without greatly changing production equipment and process flow under the existing production conditions. .
Detailed Description
In order to better understand the present invention, the following examples are further provided to illustrate the content of the present invention, but the present invention is not limited to the following examples.
Examples 1 to 10
The production process of the low-temperature-resistant high-strength flat spring steel in the embodiment 1 to 10 comprises the following steps:
(1) And (3) carrying out composite KR deep desulfurization: the molten iron pretreatment, on the basis of active lime, the desulfurizer adopts KR stirring mode to stir the molten iron in the ladle to form vortex, the desulfurizer active lime and magnesium powder are added twice in sequence to reduce the S content of the molten iron, deep slag skimming is carried out after desulfurization is finished, resulfurization is avoided, and the sulfur content [ S ] of the molten iron discharged from the station is controlled to be less than or equal to 0.01%; wherein, 5-10kg/t active lime and 2-6kg/t magnesium powder are added for the first time, 3-6kg/t active lime and 1-5kg/t magnesium powder are added for the second time, and sampling is carried out after the first addition to detect the sulfur content so as to carry out the second addition;
(2) Heating a ladle: covering the ladle and heating by adopting electromagnetic induction to ensure that the temperature is more than or equal to 1490 ℃ in the process of conveying molten iron from an iron works to a steel works;
(3) Smelting in a converter, and controlling the end point C to be more than or equal to 0.06-0.40%; the tapping temperature is more than or equal to 1630 ℃;
(4) And (3) refining in an LF (ladle furnace), adding calcium carbide to the slag surface: 2-5kg/t, special silicon: 1-4kg/t of deoxidizing materials, strengthening the white slag making process, and reducing the oxidability of the molten slag: feO is less than or equal to 0.5 percent;
(5) RH vacuum treatment, the vacuum degree is less than or equal to 100Pa, the vacuum time is not less than 20min, the soft argon blowing flow is 20-68 NL/min, and the soft argon blowing time is 12-28 min;
(6) The section size of the continuous casting billet is 280mm multiplied by 380mm, the blank drawing speed is stably controlled at 0.70m/min, the blank drawing speed of the section size of the billet is controlled, and the drawing speed is adjusted to be not more than 2 times per furnace; adopting a solidification end electric stirring process, wherein the stirring current is 350-450A, and the frequency is 8Hz; carrying out soft reduction on the casting blank, wherein the reduction rate is 3-10%; the temperature fluctuation of the tundish does not exceed 15 ℃.
(7) After slowly cooling for 72h, heating the casting blank, soaking at 1210-1250 ℃ for 560-340 min, and rolling into a small square blank with the section of 160 x 160 mm;
(8) After local grinding, heating the small square billet at a soaking temperature of 1110-1148 ℃ for 110-145 min;
(9) Rough rolling, controlling the initial rolling temperature: 1050 to 1100 ℃;
(10) Finish rolling, wherein the initial rolling temperature is controlled to be 980-1060 ℃, and the accumulated deformation is 10-60%;
(11) Rolling into spring flat steel with the thickness of 31-40 mm and the width of 90-110 mm for standby;
(12) After the spring flat steel is slowly cooled, the primary sub-temperature quenching temperature is 810 +/-20 ℃, the tempering temperature is 420 +/-20 ℃, the secondary sub-temperature quenching temperature is 810 +/-20 ℃, and the tempering temperature is 400 +/-20 ℃ for heat treatment, so that uniform and stable tempered troostite and residual austenite, namely the low-temperature-resistant high-strength spring flat steel, are obtained.
Comparative examples 1 to 3
The production process of the flat spring steel described in comparative examples 1 to 3 is substantially the same as that of the example of the present invention.
The chemical compositions of the spring flat steels obtained in examples 1 to 10 and comparative examples 1 to 3 are shown in Table 1, the smelting process parameters are shown in Table 2, and the rolling and heat treatment processes are shown in Table 3; the main performance test results are shown in Table 4.
Table 1 examples chemical composition wt%
Figure SMS_1
Table 1 examples chemical composition wt% (continue)
Figure SMS_2
Figure SMS_3
TABLE 2 smelting Process parameters
Figure SMS_4
TABLE 3 Rolling and Heat treatment Process parameters
Figure SMS_5
Figure SMS_6
TABLE 4 Main Performance test results of examples of the present invention and comparative examples
Figure SMS_7
The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, many modifications and changes can be made without departing from the inventive concept of the present invention, and these modifications and changes are within the protection scope of the present invention.

Claims (8)

1. The low-temperature-resistant high-strength spring flat steel is characterized by comprising the following chemical components in percentage by weight: c:0.56 to 0.60wt%, si:0.40 to 0.90wt%, mn:1.02 to 1.50 weight percent, more than or equal to 1.89 (Mn/C) and less than or equal to 2.8, less than or equal to 0.025 weight percent of P, less than or equal to 0.025 weight percent of S, and the weight percent of Cr:0.6 to 0.75wt%, ni:0.18 to 0.40wt%, nb:0.01 to 0.05wt%, B:0.001 to 0.004wt%, zr: 0.002-0.009 wt%, ce: 0.02-0.06 wt%, N is less than or equal to 0.0045wt%, H is less than or equal to 0.00012wt%, O is less than or equal to 0.0011wt%, and the balance is Fe and inevitable impurities;
the spring flat steel has the following properties: reL is more than or equal to 1750MPa, rm is more than or equal to 1950MPa, A is more than or equal to 10 percent, Z is more than or equal to 36 percent, KV2 is more than or equal to 35J at minus 60 ℃, and the grain size is not coarser than 8.5 grade.
2. The production process of the low temperature resistant high strength spring flat steel as claimed in claim 1, characterized by comprising the steps of:
(1) And (3) composite KR deep desulfurization: the molten iron pretreatment, based on active lime, stirring the molten iron in a ladle by a desulfurizer in a KR stirring mode to form a vortex, adding the active lime and magnesium powder of the desulfurizer twice in sequence to reduce the S content of the molten iron, deeply slagging after the desulfurization is finished, avoiding resulfurization, and controlling the sulfur content [ S ] of the molten iron out of a station to be less than or equal to 0.01 percent; wherein, 5-10kg/t of active lime and 2-6kg/t of magnesium powder are added for the first time, 3-6kg/t of active lime and 1-5kg/t of magnesium powder are added for the second time, and after the first addition is finished, a sample is taken to detect the sulfur content for the second addition;
(2) Heating a ladle: covering the ladle and heating by adopting electromagnetic induction to ensure that the temperature is more than or equal to 1490 ℃ in the process of conveying the molten iron from the iron works to the steel works;
(3) Smelting in a converter;
(4) Refining in an LF (ladle furnace), namely adding 2-5kg/t calcium carbide and 1-4kg/t special silicon into the slag surface in the refining process of the LF to strengthen the white slag making process, and reducing the oxidizing FeO of the slag by less than or equal to 0.5 percent;
(5) RH vacuum treatment;
(6) Continuous casting, wherein the blank drawing speed of the section size of the blank is controlled, and the drawing speed is adjusted to be not more than 2 times per furnace; adopting a solidification end electric stirring process and carrying out soft reduction on the casting blank; the temperature fluctuation of the tundish does not exceed 15 ℃;
(7) Heating the casting blank after slow cooling, and rolling into a small square blank;
(8) After local grinding, heating the small square billet;
(9) Rough rolling; wherein, the initial rolling temperature is controlled: 1050 to 1100 ℃;
(10) Fine rolling; wherein, the initial rolling temperature is controlled to be 980-1060 ℃, and the accumulated deformation is 10-60%;
(11) Rolling into spring flat steel;
(12) After slow cooling, the spring flat steel is subjected to heat treatment at the first sub-temperature quenching temperature of 810 +/-20 ℃, the tempering temperature of 420 +/-20 ℃, the second sub-temperature quenching temperature of 810 +/-20 ℃ and the tempering temperature of 400 +/-20 ℃ to obtain the low-temperature-resistant high-strength spring flat steel.
3. The production process of the low temperature resistant high strength spring flat steel according to claim 2, characterized in that in the step (3), smelting is carried out in a converter, and the control of the terminal point C is more than or equal to 0.06-0.40%; the tapping temperature is more than or equal to 1630 ℃.
4. The production process of the low temperature resistant high strength spring flat steel according to claim 2, characterized in that in the step (4), RH vacuum treatment is carried out, the vacuum degree is less than or equal to 100Pa, the vacuum maintaining time is not less than 20min, the soft argon blowing flow is 20-68 NL/min, and the soft blowing time is 12-28 min.
5. The production process of the low temperature resistant high strength spring flat steel according to claim 2, characterized in that the size of the continuous casting billet section in the step (5) is 280mm x 380mm, the drawing speed is stably controlled at 0.70m/min, a solidification end electric stirring process is adopted, the stirring current is 350-450A, and the frequency is 8Hz; and carrying out soft reduction on the casting blank, wherein the reduction rate is 3-10%.
6. The production process of the low temperature resistant high strength spring flat steel according to claim 2, characterized in that after slowly cooling for 72 hours in the step (6), the casting blank is heated, the soaking temperature is 1210-1250 ℃, the furnace time is 560-340 min, and the casting blank is rolled into a small square billet with the section of 160 x 160 mm.
7. The production process of the low temperature resistant high strength flat spring steel according to claim 2, characterized in that the billet is heated in the step (7) at a soaking temperature of 1110-1148 ℃ for 110-145 min.
8. The production process of the low temperature resistant high strength spring flat steel according to claim 2, characterized in that the spring flat steel with the thickness of 31-40 mm and the width of 90-110 mm is rolled in the step (10).
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