CN113930681B - High-hardenability high-fatigue-life low-temperature-resistant spring flat steel and production method thereof - Google Patents
High-hardenability high-fatigue-life low-temperature-resistant spring flat steel and production method thereof Download PDFInfo
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- C21D6/008—Heat treatment of ferrous alloys containing Si
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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- C22C33/06—Making ferrous alloys by melting using master alloys
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- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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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
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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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
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- 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
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- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
Abstract
The invention discloses a high-hardenability high-fatigue-life low-temperature-resistant spring flat steel which comprises the following chemical components in percentage by weight: c:0.50 to 0.65wt%, si:0.40 to 0.90wt%, mn: 0.80-1.50 wt%, P is less than or equal to 0.025wt%, S is less than or equal to 0.025wt%, cr:0.50 to 1.25wt%, ni:0.10 to 0.40%, ti:0.05 to 0.08wt%, B:0.002 to 0.006wt%, zr: 0.002-0.009 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%, mo:0.10 to 0.65wt%, and the balance of Fe and inevitable impurities. The invention develops the following performance requirements through the innovation of components and process: 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, and hardenability J25 is more than or equal to 58HRC; the fatigue life of the steel plate spring reaches more than 15 ten thousand times under the highest design stress of 1050 MPa; KV2 is more than or equal to 35J at minus 60 ℃.
Description
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 a high-hardenability, high-fatigue-life and low-temperature-resistant spring flat steel and a production method thereof.
Background
The weight reduction of automobiles inevitably requires the weight reduction of automobile parts. The heavy-duty car adopts high-strength spring flat steel which can reduce 30% -50% of the self-weight of the plate spring assembly, and the total weight of the plate spring is reduced by improving the thickness of each flat steel and reducing the total number of assembled sheets, so that the aim of lightening the car parts is fulfilled. The current technical path is as follows: multiple leaf springs → few leaf springs → single leaf spring.
On one hand, the spring flat steel is used after being subjected to quenching and tempering heat treatment, the requirement on the hardenability of the steel is higher and higher along with the increase of the thickness of the steel, otherwise, once the steel cannot be quenched, the metallurgical structure is not appropriate and the strength is reduced, and the damping purpose of the steel plate spring cannot be met.
On the other hand, with social progress and industrial development, the safety requirement of automobiles is higher and higher, and although the national standard requirement of the fatigue life of the steel plate spring is not less than 8 ten thousand times at present, most domestic famous host factories require not less than 10 ten thousand times, even not less than 12 ten thousand times. The high fatigue life spring flat steel can ensure that the plate spring component cannot be damaged due to premature fatigue under the action of long-term vibration and alternating stress.
Meanwhile, with the development requirements of the logistics transportation industry and resource exploitation engineering, many projects in China have been expanded to 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 spring flat steel can be greatly changed, and the mechanical properties, especially the impact toughness and the fracture toughness, shown at different environmental temperatures are greatly changed. The toughness of the automobile at low temperature will affect the service performance of the whole automobile, even the safety and reliability.
Before the invention is put forward, the similar technical products related to the field of manufacturing of the high-hardenability high-fatigue-life low-temperature-resistant steel are few, and particularly, the invention aims at the aspects of the high-hardenability high-fatigue-life low-temperature-resistant spring flat steel.
Chinese patent application No. CN 200610081227.9 discloses a high strength spring steel with excellent fatigue resistance, which is mainly suitable for high strength spring steel with tensile strength of more than 1800MPa and excellent fatigue failure resistance. The steel comprises the following specific chemical components in percentage by weight: 0.35 to 0.55 percent of C, 1.70 to 2.50 percent of Si, 0.40 to 0.70 percent of Mn, 0.70 to 1.10 percent of Cr0.05 to 0.20 percent of V, 0.005 to 0.10 percent of RE, 0.0005 to 0.020 percent of Ca, less than or equal to 0.020 percent of P, less than or equal to 0.015 percent of S, less than or equal to 0.0015 percent of O, and the balance of Fe and other inevitable impurities. The steel further contains 0.0005 to 0.0030% of B, 0.01 to 0.10% of Ti, or 0.01 to 1.50% of Ni. The steel of the invention contains a high Si component, has a very large tendency to oxidation and decarburization, and is not favorable for fatigue resistance.
Chinese patent application No. CN 200510018800.7 discloses a high-strength-toughness high-hardenability spring flat steel, which is characterized in that: the chemical components (weight percentage) are as follows: 0.48 to 0.55 percent of C, 0.17 to 0.37 percent of Si, 0.70 to 1.00 percent of Mn, 0.80 to 1.10 percent of Cr, 0.001 to 0.004 percent of B, less than or equal to 0.35 percent of Ni, less than or equal to 0.25 percent of Cu, less than or equal to 0.03 percent of P, less than or equal to 0.03 percent of S and the balance of Fe. The invention aims to provide a spring steel material with high strength, toughness and hardenability, wherein the spring steel material has the strength and toughness equivalent to 50CrVA and the hardenability equivalent to 60CrMnBA, and is economical in price. The steel has poor tempering resistance, mainly contains low silicon content; meanwhile, the strength grade is low, and the automobile is not suitable for lightweight development of automobiles.
Chinese patent application No. CN 201510064475.1 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 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.
Disclosure of Invention
In order to meet the requirements of various spring flat steels for trucks, buses and engineering machinery vehicles on adapting to working conditions of high thickness, variable cross section, long fatigue life and low temperature resistance, the development of a spring flat steel with good quenching performance, high fatigue performance and low temperature toughness is urgently needed. 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, and hardenability J25 is more than or equal to 58HRC; the fatigue life of the steel plate spring reaches more than 15 ten thousand times under the highest design stress of 1050 MPa; the-60 ℃ KV2 is more than or equal to 35J spring flat steel.
The technical scheme adopted by the invention for solving the problems is as follows:
a high-hardenability high-fatigue-life low-temperature-resistant spring flat steel comprises the following chemical components in percentage by weight: c:0.50 to 0.65wt%, si:0.40 to 0.90wt%, mn: 0.80-1.50 wt%, P is less than or equal to 0.025wt%, S is less than or equal to 0.025wt%, cr:0.50 to 1.25wt%, ni:0.10 to 0.40%, ti:0.05 to 0.08wt%, B:0.002 to 0.006wt%, zr: 0.002-0.009 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%, mo:0.10 to 0.65wt%, and the balance of Fe and inevitable impurities. The production process comprises the following steps:
(1) KR desulfurization: stirring molten iron in a ladle by adopting a composite KR desulfurization method to form a vortex, adding active lime and magnesium powder serving as desulfurizing agents twice in sequence to reduce the S content of the molten iron, and controlling the sulfur content [ S ] of the molten iron at the outlet to be less than or equal to 0.01 percent;
(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) 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;
(5) The section size of the continuous casting billet is 280mm multiplied by 380mm, the billet drawing speed is stably controlled at 0.70m/min, the solidification end electric stirring process is adopted, 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%;
(6) 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;
(7) After local grinding, heating the small square billet at a soaking temperature of 1110-1148 ℃ for 110-145 min;
(8) Rough rolling, controlling the initial rolling temperature: 1050-1100 ℃.
(9) Finish rolling, wherein the initial rolling temperature is controlled to be 980-1060 ℃, and the accumulated deformation is 10-60%.
(10) Rolling into spring flat steel with the thickness of 35-56 mm and the width of 90-110 mm for standby.
(11) After the spring flat steel is slowly cooled, the first sub-temperature quenching temperature is 800 +/-20 ℃, the tempering temperature is 420 +/-20 ℃, the second sub-temperature quenching temperature is 800 +/-20 ℃, and the tempering temperature is 400 +/-20 ℃ for heat treatment, uniform and stable tempered sorbite is obtained, and the high-hardenability high-fatigue-life low-temperature-resistant spring flat steel is obtained.
The following analysis explains the effects of the elements in the steel of the present invention and the production method thereof:
c: c is an extremely important element in steel, has a remarkable effect on the hardenability of the spring flat steel, has excellent hardenability when the content is higher, and has an adverse effect on low-temperature toughness when the content is too high. The content of C in the invention is 0.50-0.65%.
Si: si is the most main contributing element for ensuring the elasticity of the spring flat steel, has obvious solid solution strengthening effect, does not form carbide, exists in the steel in a solid solution state, can improve the strength of the steel, is one of main deoxidizing elements, but has high content, and increases the decarburization and graphitization tendency of the steel. The Si content of the invention is 0.40-0.90%.
Mn: mn is dissolved in ferrite to improve the strength of the steel; is also a good deoxidizer, and reduces the O content in steel; can combine with S to form MnS, reduce the adverse effect of S on the low-temperature performance of the material, and excessively high Mn can cause the steel to become brittle and hard and reduce the toughness. The Mn content of the invention is 0.80-1.50%.
Cr: cr can effectively prevent the growth of prior austenite grains, and is favorable for hardenability and toughness of the spring flat steel when being added in a proper amount. The Cr content of the invention is 0.50-1.25%.
Ni: ni is a main alloy element of the low-temperature steel, the brittle transition temperature can be reduced while the strength is improved, the low-temperature impact toughness is improved, but the yield strength of the material can be reduced due to the excessively high content of Ni, 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 running process of an automobile is shortened. The Mn content of the invention is 0.48-0.60%.
Ti: ti can refine crystal grains, improve strength and toughness and also improve hardenability. Meanwhile, in the heat treatment process of the spring flat steel, the coarseness of austenite grains can be avoided, and the precipitation of carbonitride of the austenite grains can play a role in precipitation strengthening, so that the quenching performance and the fatigue performance of the steel can be improved. The invention relates to a Ti:0.05 to 0.08 weight percent.
B: b is an element for improving the hardenability of the material, trace B in medium-high carbon steel can effectively reduce the segregation of P and S in a crystal boundary and improve the form of oxide inclusions, and the addition of B in the steel is beneficial to combining the high strength of the steel with good weldability and cold brittleness resistance, so that the yield strength, tensile strength, fatigue strength, wear resistance, hydrogen-induced intergranular fracture resistance and the like of the material are improved or improved to different degrees, but the content is too high, and the functions are weakened or even deteriorated. In the range of less than 0.005%, which is a major benefit for the low temperature toughness of the steel, and in the case where the content of B is in this range, B tends to form FeB with Fe, which greatly increases the possibility of brittle fracture along the grain, thereby impairing the low temperature toughness of the material, the content of B of the present invention is 0.002 to 0.006%.
Zr can make the steel obtain very good low-temperature toughness, but the content of Zr also needs to be strictly controlled. The Zr can play the role of degassing and grain refinement, and the Zr content of the invention is 0.002-0.009%.
P, S: p and S are harmful elements in the steel, the lower the content of P and S is, the better the content of P and S is, the lower the content of P and S is, the P is less than or equal to 0.025 percent and the S is less than or equal to 0.025 percent in consideration of the actual control condition of steelmaking.
Mo: the hardenability of the steel is improved, the temper brittleness of the steel is reduced, the ductile-brittle transition temperature is reduced, and the fatigue performance is improved, wherein the content of Mo is 0.10-0.65%.
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 molten iron temperature rise 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, thus being beneficial to energy conservation and emission reduction of steel plants and promoting carbon neutralization.
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 austenite grains grow due to the over-high quenching temperature, a coarse-grain martensite structure is obtained after quenching, the toughness is poor, and the undissolved ferrite exists in the austenite due to the over-low quenching temperature, and the ferrite is a soft phase structure, so that the strength of the steel is reduced. The hypoeutectoid steel is quenched at the temperature between Ac1 and Ac3, which is 40 ℃ lower than the normal subtemperature, and is favorable for the low-temperature strength and toughness and the fatigue life of the hypoeutectoid steel.
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.
The large-compression-ratio forming process comprises the following steps: the invention adopts a rolling and material forming process with a large compression ratio, the residence time of the molten steel tundish in the process of pouring the bloom is long, the removal of impurities is facilitated, meanwhile, the casting blank compression ratio can be increased through rolling with a large deformation amount, the improvement of the tiny and uniform microscopic grains of the spring flat steel is facilitated, and the quality of high-quality metallurgical material objects and excellent manufacturing process performance are ensured.
Compared with the prior art, the invention has the beneficial effects that:
1. the invention couples a plurality of trace alloy elements on the basis of carbon and manganese series low alloy steel, and innovatively adopts ladle induction heating, secondary sub-temperature quenching and tempering, secondary hot-forming process and large-compression ratio forming process to form finer grain and uniform sorbite structure, thereby obtaining the spring flat steel with good low-temperature performance at and above-60 ℃.2. The spring flat steel produced by the invention comprises the following components: reL is more than or equal to 1600MPa, rm is more than or equal to 1830MPa, A is more than or equal to 10 percent, Z is more than or equal to 36 percent, and hardenability J25 is more than or equal to 58HRC; the fatigue life of the steel plate spring reaches more than 15 ten thousand times under the highest design stress of 1050 MPa; KV2 is more than or equal to 35J at the temperature of minus 60 ℃.3. The method has the advantages of simple production process and low production cost, and can carry out process production 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 high-hardenability, high-fatigue-life and low-temperature-resistant spring flat steel in the embodiments 1 to 10 comprises the following steps:
(1) KR desulfurization: stirring molten iron in a ladle by adopting a composite KR desulfurization method to form a vortex, adding active lime and magnesium powder serving as desulfurizing agents twice in sequence to reduce the S content of the molten iron, and controlling the sulfur content [ S ] of the molten iron at the outlet to be less than or equal to 0.01 percent;
(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, 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) 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;
(5) The section size of the continuous casting billet is 280mm multiplied by 380mm, the billet drawing speed is stably controlled at 0.70m/min, the solidification end electric stirring process is adopted, 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%;
(6) 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;
(7) After local grinding, heating the small square billet at the soaking temperature of 1110-1148 ℃ for 110-145 min;
(8) Rough rolling, controlling the initial rolling temperature: 1050-1100 ℃.
(9) Finish rolling, wherein the initial rolling temperature is controlled to be 980-1060 ℃, and the accumulated deformation is 10-60%.
(10) Rolling into spring flat steel with the thickness of 35-56 mm and the width of 90-110 mm for standby.
(11) After the spring flat steel is slowly cooled, the spring flat steel is subjected to heat treatment at the first sub-temperature quenching temperature of 800 +/-20 ℃, the tempering temperature of 420 +/-20 ℃, the second sub-temperature quenching temperature of 800 +/-20 ℃ and the tempering temperature of 400 +/-20 ℃ to obtain uniform and stable tempered sorbite, namely the spring flat steel with high hardenability, high fatigue life and low temperature resistance
Table 1 examples chemical composition wt%
| Examples | C | Si | Mn | P | S | Cr | Ni | Ti | B | Zr |
| 1 | 0.50 | 0.40 | 0.80 | 0.004 | 0.006 | 0.50 | 0.10 | 0.05 | 0.002 | 0.002 |
| 2 | 0.51 | 0.45 | 0.82 | 0.008 | 0.009 | 0.52 | 0.16 | 0.05 | 0.003 | 0.003 |
| 3 | 0.52 | 0.60 | 0.95 | 0.007 | 0.015 | 0.55 | 0.20 | 0.06 | 0.002 | 0.004 |
| 4 | 0.54 | 0.62 | 1.02 | 0.009 | 0.006 | 0.60 | 0.25 | 0.07 | 0.004 | 0.005 |
| 5 | 0.58 | 0.70 | 1.15 | 0.012 | 0.006 | 0.75 | 0.30 | 0.08 | 0.005 | 0.006 |
| 6 | 0.58 | 0.76 | 1.20 | 0.020 | 0.008 | 0.82 | 0.35 | 0.08 | 0.006 | 0.007 |
| 7 | 0.60 | 0.80 | 1.30 | 0.025 | 0.007 | 0.91 | 0.40 | 0.06 | 0.005 | 0.008 |
| 8 | 0.65 | 0.82 | 1.35 | 0.009 | 0.015 | 1.10 | 0.35 | 0.07 | 0.002 | 0.009 |
| 9 | 0.58 | 0.88 | 1.41 | 0.015 | 0.020 | 1.25 | 0.29 | 0.08 | 0.005 | 0.006 |
| 10 | 0.65 | 0.90 | 1.50 | 0.011 | 0.025 | 1.25 | 0.18 | 0.05 | 0.004 | 0.004 |
| Comparative example 1 | 0.49 | 0.39 | 0.79 | 0.026 | 0.007 | 0.49 | 0.09 | 0.09 | 0.001 | 0.001 |
| Comparative example 2 | 0.50 | 0.81 | 1.51 | 0.028 | 0.010 | 1.05 | 0.42 | 0.04 | 0.007 | 0.010 |
| Comparative example 3 | 0.65 | 0.91 | 1.36 | 0.030 | 0.020 | 1.26 | 0.41 | 0.08 | 0.008 | 0.008 |
TABLE 1 examples chemical composition in wt.% (continuous)
TABLE 2 smelting Process parameters
TABLE 3 Rolling and Heat treatment Process parameters
TABLE 4 Main Performance test results of examples of the invention and comparative examples
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 (6)
1. A high-hardenability high-fatigue-life low-temperature-resistant spring flat steel is characterized by comprising the following chemical components in percentage by weight: c:0.58 to 0.65wt%, si:0.70 to 0.90wt%, mn: 1.30-1.50 wt%, P is less than or equal to 0.025wt%, S is less than or equal to 0.025wt%, cr:0.50 to 1.25wt%, ni:0.10 to 0.40%, ti:0.05 to 0.08wt%, B:0.002 to 0.006wt%, zr:0.007 to 0.009wt%, 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%, mo: 0.37-0.65 wt%, and the balance of Fe and inevitable impurities;
the spring flat steel has the following properties: reL is more than or equal to 1600MPa, rm is more than or equal to 1830MPa, A is more than or equal to 10 percent, Z is more than or equal to 36 percent, and hardenability J25 is more than or equal to 58HRC; the fatigue life reaches more than 15 ten thousand times under the highest design stress of 1050 MPa; KV2 is more than or equal to 35J at minus 60 ℃.
2. The production process of the low temperature resistant spring flat steel with high hardenability and fatigue life as claimed in claim 1, characterized by comprising the following steps:
(1) KR desulfurization: stirring molten iron in a ladle by adopting a composite KR desulfurization method to form a vortex, adding active lime and magnesium powder serving as desulfurizing agents twice in sequence to reduce the S content of the molten iron, and controlling the sulfur content [ S ] of the molten iron at the outlet to be less than or equal to 0.01 percent;
(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) RH vacuum treatment;
(5) Continuous casting, wherein the blank drawing speed of the section size of a blank is controlled, a solidification end electric stirring process is adopted, and the casting blank is lightly reduced; wherein 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 solidification end electric stirring process is adopted, 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%;
(6) Heating the casting blank after slow cooling, and rolling into a small square blank; wherein, after slowly cooling for 72h, 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 blank with the section of 160 x 160 mm;
(7) After local grinding, heating the small square billet;
(8) Rough rolling, controlling the initial rolling temperature: 1050-1100 deg.C
(9) Finish rolling, wherein the initial rolling temperature is controlled to be 980-1060 ℃, and the accumulated deformation is 10-60%;
(10) Rolling into spring flat steel;
(11) After the spring flat steel is slowly cooled, the first sub-temperature quenching temperature is 800 +/-20 ℃, the tempering temperature is 420 +/-20 ℃, the second sub-temperature quenching temperature is 800 +/-20 ℃, and the tempering temperature is 400 +/-20 ℃ for heat treatment, uniform and stable tempered sorbite is obtained, and the high-hardenability high-fatigue-life low-temperature-resistant spring flat steel is obtained.
3. The production process of the high-hardenability high-fatigue-life low-temperature-resistant spring flat steel according to claim 2, characterized in that in the step (3), smelting is carried out in a converter, and the end point C is controlled to be 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 spring flat steel with high hardenability, high fatigue life and the like 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 flat spring steel with high hardenability, high fatigue life and high temperature resistance according to claim 2, characterized in that the billet is heated in the step (7), the soaking temperature is 1110-1148 ℃, and the soaking time is 110-145 min.
6. The process for producing a low temperature resistant flat spring steel with high hardenability and fatigue life as claimed in claim 2, wherein the step (10) is to roll the flat spring steel with a thickness of 35-56 mm and a width of 90-110 mm.
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