CN118256699A - 40Cr hot rolled steel coil, production method thereof and heat treatment method - Google Patents
40Cr hot rolled steel coil, production method thereof and heat treatment method Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 74
- 239000010959 steel Substances 0.000 title claims abstract description 74
- 238000010438 heat treatment Methods 0.000 title claims abstract description 53
- 238000000034 method Methods 0.000 title claims abstract description 29
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 21
- 238000005096 rolling process Methods 0.000 claims abstract description 60
- 238000001816 cooling Methods 0.000 claims abstract description 24
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 15
- 238000007670 refining Methods 0.000 claims abstract description 12
- 238000009749 continuous casting Methods 0.000 claims abstract description 8
- 229910001562 pearlite Inorganic materials 0.000 claims abstract description 7
- 238000003723 Smelting Methods 0.000 claims abstract description 6
- 229910052742 iron Inorganic materials 0.000 claims abstract description 6
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 6
- 238000005266 casting Methods 0.000 claims description 19
- 229910000677 High-carbon steel Inorganic materials 0.000 claims description 14
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 13
- 238000002844 melting Methods 0.000 claims description 8
- 230000008018 melting Effects 0.000 claims description 8
- 239000002893 slag Substances 0.000 claims description 8
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 6
- 229910052757 nitrogen Inorganic materials 0.000 claims description 6
- 238000002791 soaking Methods 0.000 claims description 6
- 239000000126 substance Substances 0.000 claims description 5
- 238000010791 quenching Methods 0.000 claims description 4
- 230000000171 quenching effect Effects 0.000 claims description 4
- 238000005496 tempering Methods 0.000 claims description 4
- 229910052799 carbon Inorganic materials 0.000 claims description 3
- 238000007599 discharging Methods 0.000 claims description 3
- 239000012535 impurity Substances 0.000 claims description 3
- 229910052698 phosphorus Inorganic materials 0.000 claims description 3
- 229910052717 sulfur Inorganic materials 0.000 claims description 3
- 230000004907 flux Effects 0.000 claims 2
- 230000001186 cumulative effect Effects 0.000 claims 1
- 238000005261 decarburization Methods 0.000 abstract description 5
- 230000000052 comparative effect Effects 0.000 description 16
- 239000000843 powder Substances 0.000 description 4
- 229910004742 Na2 O Inorganic materials 0.000 description 3
- 229910004298 SiO 2 Inorganic materials 0.000 description 3
- 229910000746 Structural steel Inorganic materials 0.000 description 3
- 229910045601 alloy Inorganic materials 0.000 description 3
- 239000000956 alloy Substances 0.000 description 3
- 238000005097 cold rolling Methods 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 238000000137 annealing Methods 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 238000005098 hot rolling Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 229910000851 Alloy steel Inorganic materials 0.000 description 1
- 229910000975 Carbon steel Inorganic materials 0.000 description 1
- 229910001294 Reinforcing steel Inorganic materials 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 229910001566 austenite Inorganic materials 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000010962 carbon steel Substances 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000000295 emission spectrum Methods 0.000 description 1
- 238000005461 lubrication Methods 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 239000002436 steel type Substances 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
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Abstract
The invention discloses a 40Cr hot rolled steel coil, a production method and a heat treatment method thereof, wherein the production method comprises the following steps: molten iron pretreatment, converter smelting, LF furnace refining, RH furnace refining, continuous casting, heating, rolling, laminar cooling and coiling; the 40Cr hot rolled steel coil with the microstructure of pearlite and ferrite, the band structure of 1.5 grade, no decarburization on the upper surface and the lower surface and good comprehensive performance is produced by reasonably controlling the parameters of each process.
Description
Technical Field
The invention belongs to the technical field of steel, and particularly relates to a 40Cr hot rolled steel coil, a production method thereof and a heat treatment method.
Background
The 40Cr alloy structural steel is one of the most widely used steel types in the mechanical manufacturing industry, with the rapid development of the mechanical manufacturing industry, the demand of the 40Cr alloy structural steel is increased increasingly, and products can obtain good strength, plasticity and hardness after proper cold rolling, annealing or heat treatment, can meet the complex machining requirements of mechanical parts, are used for manufacturing parts bearing high load, impact and wear resistance, and are widely applied to the fields of high-end chains, chain wheels, automobile parts, mechanical structural parts and the like. Therefore, the steel has special quality requirements, and the requirements are uniform and stable in components, low in harmful elements, high in steel purity, and good in internal and surface quality and processing technological properties.
The current common 40Cr alloy structural steel products are round steel products, and the round steel products are commonly used for manufacturing reinforcing steel bars, bolts and various mechanical parts, for example, chinese patent CN 108193136A discloses a 40Cr hot-rolled round steel and a production method thereof. In order to widen the application direction, the product types, such as coiled material products, are widened, but the prior art discloses less production methods of 40Cr hot rolled steel coils, and the 40Cr hot rolled steel coils have a plurality of difficulties compared with hot rolled round steel, such as decarburization problems of hot coils with high C content, cracking problems of hot curled edges with high C content, thickness precision of hot coils, hot coil strip pressure oxygen caused by high Cr content, and the like. It is a very challenging task to produce a 40Cr hot rolled steel coil with good overall properties.
Disclosure of Invention
In order to solve the technical problems, the invention provides a 40Cr hot rolled steel coil, a production method and a heat treatment method thereof, and the method can produce the 40Cr hot rolled steel coil with a microstructure of pearlite and ferrite, a band structure of 1.5 grade, no decarburization on the upper surface and the lower surface and good comprehensive performance.
The technical scheme adopted by the invention is as follows:
A method for producing a 40Cr hot rolled steel coil, comprising the steps of:
1) Pretreating molten iron;
2) Smelting in a converter;
3) Refining: nitrogen increment is reduced in LF refining and RH refining processes, N is controlled to be less than or equal to 50ppm, and if the N content is higher, a high-carbon steel casting blank is easy to crack;
4) Continuous casting: the temperature of the tundish is controlled to 1520-1530 ℃, and high carbon steel covering slag is adopted;
5) Heating: the temperature of the casting blank entering a heating furnace is controlled to be more than 600 ℃, the first heating temperature in the furnace is controlled to be 1180-1220 ℃, the second heating temperature is controlled to be 1210-1250 ℃, the third heating temperature is controlled to be 1200-1240 ℃, the temperature of a soaking section is controlled to be 1180-1220 ℃, the total time of the second heating, the third heating and the soaking sections is controlled to be 60-80 min, the total furnace time is 130-150 min, and the casting blank discharging temperature is controlled to be 1180-1200 ℃; through the heating process, the surface of the 40Cr hot rolled steel coil is controlled to have no decarburized layer, and if the decarburized layer exists on the surface of the steel coil or the depth of the decarburized layer is deeper, the surface hardness of a subsequent product is affected;
6) Rolling: the rough rolling inlet and outlet descaling water is fully opened, and coarse iron scales of the slab are removed through high-pressure descaling water, so that the surface quality of the product in the rolling of the subsequent working procedure is ensured; the initial rolling temperature of the finish rolling is controlled at 1000-1050 ℃, the final rolling temperature of the finish rolling is controlled at 860-890 ℃, the excessive load of a rolling mill caused by rolling in a low-temperature double-phase region is avoided, mixed crystals are avoided, and the coarsening of austenite grains caused by the excessive final rolling temperature is also avoided;
7) Laminar cooling;
8) And (3) coiling: the coiling temperature is 700-740 ℃, the coiling temperature is too high, excessive pearlite tissues are generated, and the coiling temperature is too low, so that the subsequent cold rolling is not facilitated; and after coiling, the steel coil is slowly cooled for at least 72 hours, so that the outer ring temperature of the steel coil is prevented from falling faster, and the rolling performance fluctuation of the steel coil is ensured to be smaller.
In the step 4), the melting point of the high-carbon steel covering slag is 1134+/-60 ℃, the melting speed of 1350 ℃ is 25+/-10S, the viscosity of 1300 ℃ is 0.18+/-0.06 Pa.S, and the weight percentages of all components in the high-carbon steel covering slag are 29.0+/-4.0% of CaO, 6.8+/-1.5% of SiO 2 32.2±4.0％,MgO 3.5±1.5％,Na2 O and 10.3+/-2.0%. The 40Cr hot rolled steel provided by the invention not only requires good lubrication of casting blanks in a crystallizer, but also avoids rapid cooling of the lower blank shell in the crystallizer, so that the high-lubricity and better crystallinity casting powder is adopted, and the lubricity and crystallinity of the high-carbon steel casting powder used by the invention are better.
In the step 4), the casting blank is subjected to hot-charging rolling, namely, when the temperature of the casting blank is more than or equal to 600 ℃, the casting blank is sent into a heating furnace.
In the step 6), the rough rolling descaling water pressure is 18-22 MPa, the descaling is carried out in the 1 st, 3 rd, 5 th and 6 th passes of rough rolling, and the descaling water pressure of each pass is 20MPa, 22MPa, 20MPa and 20MPa respectively.
In step 6), the rough rolling adopts a 3+3-pass rolling mode instead of a 3+5 rolling mode, so that each pass can be greatly reduced to ensure refined grains.
In the step 6), the accumulated rolling reduction of the finish rolling is more than or equal to 74 percent, and the grain size is refined through accumulated large deformation; the finish rolling speed is controlled to be 10-15 m/s, and the finish rolling speed is too small or too large, which is not beneficial to the accurate control of the subsequent temperature.
In the step 7), the laminar cooling is the front-stage laminar cooling, the cooling speed is controlled to be 25-30 ℃/s, and the cooling speed is too high or too low, which is unfavorable for the formation of fine ferrite and pearlite structures.
In the steps 6) to 7), the total time t from the finish rolling to the coiling is as follows: and T is more than or equal to 7.3s and less than or equal to 10.2s, t=34/V 1+(T1-T2)/V2, wherein V 1 is finish rolling speed, T 1 is finish rolling temperature, T 2 is coiling temperature, V 2 is cooling speed of laminar cooling, and the numerical value of each parameter is taken into calculation when calculated according to a formula.
The 40Cr hot rolled steel coil comprises the following chemical components in percentage by weight: 0.38 to 0.42 percent of C, 0.17 to 0.30 percent of Si, 0.50 to 0.80 percent of Mn, less than or equal to 0.012 percent of P, less than or equal to 0.002 percent of S, 0.015 to 0.035 percent of Alt, 0.90 to 1.00 percent of Cr, less than or equal to 0.005 percent of N, and the balance of Fe and unavoidable impurities.
The metallographic structure of the 40Cr hot rolled steel coil is pearlite and ferrite, the band structure is 1.5 grade, and the upper surface and the lower surface of the 40Cr hot rolled steel coil are not decarburized.
Yield strength 359-402 MPa, tensile strength 666-724 MPa, elongation 19.5% -24.5%, brinell hardness 186-199 HBW and through-coil tensile strength performance fluctuation 68-85 MPa of the 40Cr hot rolled steel coil; after the heat treatment of the 40Cr hot rolled steel coil, the yield strength is 960-1010 MPa, the tensile strength is 1084-1140 MPa, and the elongation is 13.7-17.9%.
The invention also provides a heat treatment method of the 40Cr hot rolled steel coil, which comprises the following steps: firstly heating to 845-855 ℃ and preserving heat for 20-30 min for quenching, and then heating to 515-525 ℃ again and preserving heat for 55-65 min for tempering. The steel coil after the heat treatment process has excellent strength performance and elongation.
Compared with the prior art, the invention has the following beneficial effects:
according to the production method of the 40Cr hot rolled steel coil, provided by the invention, the hot rolled steel coil with excellent performance is produced by reasonably controlling parameters of smelting, continuous casting, hot rolling, cooling and coiling processes, and the steel plate with excellent heat treatment performance is obtained after heat treatment. The metallographic structure of the 40Cr hot rolled steel coil provided by the invention is pearlite and ferrite, the band structure is 1.5 grade, and the upper surface and the lower surface of the band structure are not decarburized. The yield strength is 359-402 MPa, the tensile strength is 666-724 MPa, the elongation is 19.5-24.5%, the Brinell hardness is 186-199 HBW, and the through-roll tensile strength performance fluctuates by 68-85 MPa; after heat treatment, the yield strength of the steel coil is 960-1010 MPa, the tensile strength is 1084-1140 MPa, and the elongation is 13.7-17.9%.
The thickness range of the 40Cr hot rolled steel coil provided by the invention is 3.0-12.0 mm, and the 40Cr hot rolled steel coil is mainly used for cold rolling annealing base materials or heat treatment and is widely applied to the fields of high-end chains, chain wheels, automobile parts, mechanical structural parts and the like.
Drawings
FIG. 1 is a metallographic structure diagram of a 40Cr hot rolled steel coil in example 1;
FIG. 2 is a schematic view of the decarburized layer on the surface of the 40Cr hot rolled steel coil in example 1, from which it is seen that there is no decarburization on the surface;
FIG. 3 is a surface quality diagram of a 40Cr hot rolled steel coil in example 1;
FIG. 4 is a surface quality diagram of a 40Cr hot rolled steel coil in comparative example 1.
Detailed Description
The invention provides a production method of a 40Cr hot rolled steel coil, which comprises the following steps:
1) Pretreating molten iron;
2) Smelting in a converter;
3) Refining: nitrogen increment is reduced in the LF+RH refining process, and N is controlled to be less than or equal to 50ppm;
4) Continuous casting: the temperature of the tundish is controlled to 1520-1530 ℃, and high carbon steel covering slag is adopted;
5) Heating: the temperature of the casting blank entering a heating furnace is controlled to be more than 600 ℃, the first heating temperature in the furnace is controlled to be 1180-1220 ℃, the second heating temperature is controlled to be 1210-1250 ℃, the third heating temperature is controlled to be 1200-1240 ℃, the temperature of a soaking section is controlled to be 1180-1220 ℃, the total time of the second heating, the third heating and the soaking sections is controlled to be 60-80 min, the total furnace time is 130-150 min, and the casting blank discharging temperature is controlled to be 1180-1200 ℃;
6) Rolling: the rough rolling inlet and outlet descaling water is fully opened, the finish rolling starting temperature is controlled at 1000-1050 ℃, and the finish rolling finishing temperature T 1 is controlled at 860-890 ℃;
7) Laminar cooling;
8) And (3) coiling: the coiling temperature T 2 is 700-740 ℃, and the coiled steel coil is slowly cooled for at least 72 hours.
In the step 4), the casting blank is subjected to hot-charging rolling, namely, when the temperature of the casting blank is more than or equal to 600 ℃, the casting blank is sent into a heating furnace.
In the step 4), the melting point of the high-carbon steel covering slag is 1134+/-60 ℃, the melting speed of 1350 ℃ is 25+/-10S, the viscosity of 1300 ℃ is 0.18+/-0.06 Pa.S, and the weight percentages of all components in the high-carbon steel covering slag are 29.0+/-4.0% of CaO, 6.8+/-1.5% of SiO 2 32.2±4.0％,MgO 3.5±1.5％,Na2 O and 10.3+/-2.0%.
In the step 6), the rough rolling descaling water pressure is 18-22 MPa, the descaling is carried out in the 1 st, 3 rd, 5 th and 6 th passes of rough rolling, and the descaling water pressure of each pass is 20MPa, 22MPa, 20MPa and 20MPa respectively.
In step 6), the rough rolling adopts a 3+3 pass rolling mode.
In the step 6), the accumulated rolling reduction of the finish rolling is more than or equal to 74 percent; the finish rolling speed is controlled to be 10-15 m/s.
In the step 7), the laminar cooling is the front-stage laminar cooling, and the cooling speed is controlled at 25-30 ℃/s.
In the steps 6) to 7), the total time t from the finish rolling to the coiling is as follows: and T is more than or equal to 7.3s and less than or equal to 10.2s, t=34/V 1+(T1-T2)/V2, wherein V 1 is finish rolling speed, T 1 is finish rolling temperature, T 2 is coiling temperature, V 2 is cooling speed of laminar cooling, and the numerical value of each parameter is taken into calculation when calculated according to a formula.
The 40Cr hot rolled steel coil comprises the following chemical components in percentage by weight: 0.38 to 0.42 percent of C, 0.17 to 0.30 percent of Si, 0.50 to 0.80 percent of Mn, less than or equal to 0.012 percent of P, less than or equal to 0.002 percent of S, 0.015 to 0.035 percent of Alt, 0.90 to 1.00 percent of Cr, less than or equal to 0.005 percent of N, and the balance of Fe and unavoidable impurities.
The present invention will be described in detail with reference to examples.
The chemical compositions of the 40Cr hot rolled steel coils in each example and comparative example are shown in table 1. The component detection is carried out according to GB/T4336 method for analyzing atomic emission spectra of spark sources of carbon steel and medium-low alloy steel (conventional method).
TABLE 1
The 40Cr hot rolled steel coil in each example and comparative example was produced by the following method: 1) Pretreating molten iron; converter smelting, LF refining, RH refining, continuous casting, heating, rolling, laminar cooling and coiling.
Wherein in the continuous casting step, the ladle temperatures in examples 1 to 5 and comparative examples 1 to 4 were controlled at 1520 ℃, 1521 ℃, 1523 ℃, 1525 ℃, 1527 ℃, 1530 ℃, 1525 ℃ and 1524 ℃ respectively.
The same high-carbon steel casting powder is adopted for protection casting in the continuous casting process, and the physicochemical properties of the high-carbon steel casting powder meet the following conditions: the melting point is 1134+/-60 ℃, the melting speed is 25+/-10S at 1350 ℃, the viscosity is 0.18+/-0.06 Pa.S at 1300 ℃, and the weight percentages of all components in the high-carbon steel covering slag are 29.0+/-4.0% of CaO, 6.8+/-1.5% of SiO 232.2±4.0％,MgO 3.5±1.5％,Na2 O and 10.3+/-2.0%.
The main rolling process parameters of the 40Cr hot rolled steel coil of each of the examples and comparative examples are shown in table 3.
TABLE 3 heating process parameters
The descaling water pressure process parameters of the 40Cr hot rolled steel coils of each example and comparative example are shown in Table 4. The descaling is carried out in the 1 st, 3 rd, 5 th and 6 th passes, and the descaling water pressure is respectively 20MPa, 22MPa, 20MPa and 20MPa.
Table 4 descaling water pressure process parameters
| Sample numbering | Thickness/mm | Rough rolling pass 1 | Rough rolling for 3 rd pass, | Rough rolling pass 5 | Rough rolling 6 th pass |
| Example 1 | 3.0 | 20 | 22 | 20 | 20 |
| Example 2 | 5.0 | 20 | 22 | 20 | 20 |
| Example 3 | 8.0 | 20 | 22 | 20 | 20 |
| Example 4 | 10.0 | 20 | 22 | 20 | 20 |
| Example 5 | 12.0 | 20 | 22 | 20 | 20 |
| Comparative example 1 | 5.0 | 10 | 12 | 10 | 10 |
| Comparative example 2 | 8.0 | 20 | 22 | 20 | 20 |
| Comparative example 3 | 10.0 | 20 | 22 | 20 | 20 |
| Comparative example 4 | 3.0 | 20 | 22 | 20 | 20 |
The main rolling process parameters of the 40Cr hot rolled steel coil in each of the examples and comparative examples are shown in table 5.
TABLE 5 Main Process parameters of Rolling Process
The mechanical properties of the 40Cr hot rolled steel coils in each of the examples and comparative examples are shown in Table 5.
TABLE 5 mechanical Properties
The inclusion results of the 40Cr hot rolled steel coils in each of the examples and comparative examples are shown in table 6.
TABLE 6 nonmetallic inclusion of various embodiments of the invention
The decarburized layer results of the 40Cr hot rolled steel coils in the examples and comparative examples are shown in Table 7.
TABLE 7 decarburized layer of each example of the present invention
The mechanical properties of the 40Cr hot rolled steel coils in each example and comparative example after being subjected to the heat treatment process in table 8 are shown in table 8, and it is seen that the 40Cr hot rolled steel coils in examples have good comprehensive mechanical properties after being subjected to the heat treatment. The compositions and production processes of the hot rolled steel coils in comparative examples 5 to 8 in Table 8 are the same as those in example 1 except that the heat treatment process different from example 1 is adopted, and it is seen that too low or too high a quenching temperature, too long a quenching time and too long a tempering time result in lower strength performance and too short a tempering time result in lower elongation.
TABLE 8 heat treatment Property of test steels according to the invention
In conclusion, the 40Cr hot rolled steel coil produced according to the chemical composition, steelmaking and hot rolling process design provided by the invention has the yield strength of 359-402 MPa, the tensile strength of 666-724 MPa, the elongation of 19.5-24.5%, the Brinell hardness of 186-199 HBW, the through-coil tensile strength performance fluctuation of 68-85 MPa, no decarburization on the upper surface and the lower surface, and has good comprehensive mechanical properties after heat treatment, the yield strength of 960-1010 MPa, the tensile strength of 1084-1140 MPa and the elongation of 13.7-17.9%.
The above detailed description of a 40Cr hot rolled steel coil, a method for producing the same and a heat treatment method thereof, with reference to the examples, is illustrative and not restrictive, and several examples can be enumerated according to the limited scope, so that variations and modifications are possible within the scope of the present invention without departing from the general inventive concept.
Claims (10)
1. The production method of the 40Cr hot rolled steel coil is characterized by comprising the following steps of:
1) Pretreating molten iron;
2) Smelting in a converter;
3) Refining: nitrogen increment is reduced in LF refining and RH refining processes, and N is controlled to be less than or equal to 50ppm;
4) Continuous casting: the temperature of the tundish is controlled to 1520-1530 ℃, and high carbon steel covering slag is adopted;
5) Heating: the temperature of the casting blank entering a heating furnace is controlled to be more than 600 ℃, the first heating temperature in the furnace is controlled to be 1180-1220 ℃, the second heating temperature is controlled to be 1210-1250 ℃, the third heating temperature is controlled to be 1200-1240 ℃, the temperature of a soaking section is controlled to be 1180-1220 ℃, the total time of the second heating, the third heating and the soaking sections is controlled to be 60-80 min, the total furnace time is 130-150 min, and the casting blank discharging temperature is controlled to be 1180-1200 ℃;
6) Rolling: the rough rolling inlet and outlet descaling water is fully opened, the finish rolling starting temperature is controlled at 1000-1050 ℃, and the finish rolling finishing temperature T 1 is controlled at 860-890 ℃;
7) Laminar cooling;
8) And (3) coiling: the coiling temperature T 2 is 700-740 ℃, and the coiled steel coil is slowly cooled for at least 72 hours.
2. The method of producing 40Cr hot rolled steel coil according to claim 1, wherein in step 4), the high carbon steel mold flux has a melting point of 1134±60 ℃, a melting rate of 1350 ℃ of 25±10S, a viscosity of 1300 ℃ of 0.18±0.06pa·s, and the weight percentages of the components in the high carbon steel mold flux are cao29.0±4.0%, siO 2 32.2±4.0％,MgO 3.5±1.5％,Na2 O6.8±1.5%, and F10.3±2.0%.
3. The method of producing 40Cr hot rolled steel coil according to claim 1, wherein in step 6), the rough rolling descaling water pressure is 18 to 22MPa, the descaling is performed in 1 st, 3 rd, 5 th and 6 th passes of rough rolling, and the descaling water pressures of the respective passes are 20MPa, 22MPa, 20MPa and 20MPa, respectively.
4. The method for producing 40Cr hot rolled steel coil according to claim 1, wherein in the step 6), the cumulative rolling reduction of the finish rolling is not less than 74%; the finish rolling speed V 1 is less than or equal to 10m/s and less than or equal to 15m/s.
5. The method of producing 40Cr hot rolled steel coil according to claim 1, wherein in step 7), the laminar cooling is a front stage laminar cooling, and the cooling rate V 2 of the laminar cooling is controlled to be 25-30 ℃/s.
6. The method of producing 40Cr hot rolled steel coil according to claim 1, wherein the total time T from finish rolling to coiling is 7.3 s.ltoreq.t.ltoreq.10.2 s, t=34/V 1+(T1-T2)/V2, wherein V 1 is finish rolling speed, T 1 is finish rolling temperature, T 2 is coiling temperature, V 2 is cooling speed of laminar cooling, and the values of the parameters are taken in the calculation of the formula.
7. The method for producing 40Cr hot rolled steel coil according to claim 1, wherein the chemical components and weight percentages of the 40Cr hot rolled steel coil are: 0.38 to 0.42 percent of C, 0.17 to 0.30 percent of Si, 0.50 to 0.80 percent of Mn, less than or equal to 0.012 percent of P, less than or equal to 0.002 percent of S, 0.015 to 0.035 percent of Alt, 0.90 to 1.00 percent of Cr, less than or equal to 0.005 percent of N, and the balance of Fe and unavoidable impurities.
8. The 40Cr hot rolled steel coil produced by the production method as claimed in any one of claims 1 to 7, wherein the metallographic structure of the 40Cr hot rolled steel coil is pearlite and ferrite, the band structure is 1.5 grade, and the upper and lower surfaces are not decarburized.
9. The 40Cr hot rolled steel coil according to claim 8, wherein the 40Cr hot rolled steel coil has a yield strength of 359-402 MPa, a tensile strength of 666-724 MPa, an elongation of 19.5-24.5%, a brinell hardness of 186-199 HBW, and a through-coil tensile strength performance fluctuation of 68-85 MPa; after the heat treatment of the 40Cr hot rolled steel coil, the yield strength is 960-1010 MPa, the tensile strength is 1084-1140 MPa, and the elongation is 13.7-17.9%.
10. The heat treatment method of 40Cr hot rolled steel coil as claimed in claim 8 or 9, wherein the heat treatment method comprises: firstly heating to 845-855 ℃ and preserving heat for 20-30 min for quenching, and then heating to 515-525 ℃ again and preserving heat for 55-65 min for tempering.
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