A flexible production method for thin gauge 65Mn steel

Abstract

The present application provides a flexible production method for thin-gauge 65Mn steel, which includes: step one, smelting and continuous casting: smelting molten steel and continuously casting it into slabs; step two, heating: uniformly heating the continuously cast slabs to 1150-1170°C and then taking them out of the furnace, and keeping the continuously cast slabs warm for 25-35 minutes; step three, descaling and finishing rolling: high-pressure water descaling the continuously cast slabs after taking them out of the furnace, and then seven-stand finishing rolling, and the final rolling temperature is 880-920°C; step four, selection of laminar flow and coiling: when the user has low requirements for material strength and uniformity, a control process based on coiling in the austenite single-phase region is selected, and the coiling temperature CT≥Ar3+ΔT; when the user has high requirements for material strength and uniformity, a medium-temperature coiling control process based on intermediate temperature control is selected; step five, slow cooling of the steel coil: the coiled steel coil is placed in a slow cooling box for slow cooling. This method can meet the user's personalized needs for 65Mn steel performance and achieve flat coil control.

Description

Technical Field

[0001] The present application relates to the field of hot-rolled strip steel, and in particular to a flexible production method for thin-gauge 65Mn steel. Background Art

[0002] 65Mn steel is widely used in the production of knives, saw blades and other hardware tools. Its production process at the steel manufacturing end is generally smelting and continuous casting → heating → hot rolling → cooling → coiling. Its post-processing process at the steel user end varies from user to user, mainly pickling, multiple cold rolling and annealing, forming stamping, final heat treatment, etc. The main demand of the steel user end for 65Mn steel is mainly on thin specifications, which is conducive to the thinning of the final specifications of cold rolling, which helps users reduce the rolling process and thus reduce costs. In addition, some users have high requirements for the uniformity of the performance of 65Mn steel to prevent large fluctuations in rolling force during cold rolling and cause belt breakage accidents.

[0003] The process characteristics of the thin slab continuous casting and rolling process help to inhibit chemical composition segregation, refine non-metallic inclusions, reduce surface decarburization, and reduce the spacing between pearlite lamellae. These characteristics make the thin slab continuous casting and rolling process very suitable for producing high-quality medium and high carbon steel plates and strips. In addition, the thin slab continuous casting and rolling process also has significant advantages in thin material production. Thin-size 65Mn has become a key development variety for short-process production lines. However, in the production process, the flat coil problem of 65Mn steel is more prominent, especially for thin specifications. Flat coil refers to the horizontal storage and transportation of steel coils that gradually collapse and become elliptical after being pulled out of the reel of the coiler. Measures need to be taken to flatten the steel coils that have flat coils, such as manual flame cutting of the inner ring, which increases additional production costs and affects production efficiency and product yield; in addition, steel coils with large ellipticity are prone to scratches on the surface of the steel coils due to inconsistent circumferential speeds and violent tension fluctuations during the flattening process, resulting in product degradation or scrapping.

[0004] How to control the flat coil problem of thin-gauge 65Mn steel while meeting the performance requirements of the user for the strip has become a challenge for the short-process production line. In response to the flat coil problem of hot-rolled strip steel, the invention patent with publication number CN1506174A discloses a control method, which controls the coiling temperature of steel strips with a carbon content of more than 0.25% within the range of Ar1+ (-10 to +60°C), so that the phase transformation of the steel coil gradually eliminates the flat coil from the outer layer and the core in contact with the reel to the middle layer. The patent with publication number CN108754104A discloses a method for eliminating the defects of dual-phase steel flat coils, in which the hot rolling final rolling temperature is controlled according to the starting temperature of the phase transformation of austenite ferritization to promote the transformation of austenite to ferrite; the hot rolling cooling section is divided into a fast cooling section and a slow cooling section, in which the hot-rolled plate is cooled to the intermediate temperature of the layer cooling to promote the transformation of austenite to ferrite, and in the slow cooling section, the austenite is promoted to pearlite, and the proportion of residual austenite is reduced. The patent with publication number CN107904376A provides a method and device for preventing flat coils of dual-phase steel. By controlling the finishing rolling outlet temperature to 860-900°C and the cooling rate to 70-100°C / s, energy is accumulated for the phase change of the strip steel so that the phase change of the strip steel occurs in advance, preventing the strip steel from undergoing phase change and forming flat coils after being coiled. The patent with publication number CN102335681A discloses a coiling method for preventing flat coils of hot-rolled strip steel. The coiling temperature is 500-600°C, and then the coiled steel coil is left on the coiler drum for 20s-60s. The patent with publication number CN107812789A discloses a method for preventing flat coils, in which the hot-rolled strip is laminar-cooled and rapidly cooled to 650-700°C or 500-550°C for coiling, and the hot-rolled steel coil after coiling stays on the coiler for 5-20 seconds; the patent with patent number ZL202010183210.4 discloses a method for controlling flat coils of hot-rolled advanced high-strength steel, which controls the flat coils through the strip finishing surface roughness control stage, the laminar cooling austenite phase transformation control stage, the coiling tension control stage, and the rotation control stage after coiling. Summary of the invention

[0005] One of the purposes of the present application is to provide a flexible production method for thin-gauge 65Mn steel to solve the problem that the existing 65Mn steel is prone to flattening.

[0006] The technical solution of this application is:

[0007] A flexible production method for thin-gauge 65Mn steel comprises the following steps:

[0008] Step 1, smelting and continuous casting: smelting molten steel and continuously casting into slabs, the composition of the continuous casting slabs is C: 0.63-0.69%, Si: 0.20-0.30%, Mn: 0.95-1.05%, P: ≤0.02%, S≤0.01%, Al: 0.020-0.040%, N: ≤0.006, and the balance is iron;

[0009] Step 2, heating: uniformly heating the continuous casting slab to 1150-1170° C. and then taking it out of the furnace, and keeping the continuous casting slab warm for 25-35 minutes;

[0010] Step 3, descaling and finish rolling: the continuous casting slab after being discharged from the furnace is descaled by high-pressure water, and then subjected to seven-stand finish rolling, and the final rolling temperature is 880-920° C.;

[0011] Step 4, selection of laminar flow and coiling: When the user has low requirements for material strength and uniformity, a control process based on coiling in the austenite single phase region is selected, and the coiling temperature CT ≥ Ar3 + ΔT, where Ar3 is the starting temperature of the transformation from austenite to ferrite when the steel is cooled, and ΔT is the temperature drop of the strip from the coiling thermometer to the coiling drum of the coiler; when the user has high requirements for material strength, material adaptability and material uniformity, a medium-temperature coiling control process based on intermediate temperature control is selected;

[0012] Step 5: Slow cooling of the steel coil: The coiled steel coil is quickly placed in a slow cooling box for slow cooling.

[0013] As a technical solution of the present application, in step four, the control process based on coiling in the austenite single-phase region is to adjust the final rolling temperature and final rolling speed of the strip so that the coiling temperature CT satisfies CT≥Ar3+ΔT, wherein Ar3 is the starting temperature of the transformation of austenite to ferrite when the steel is cooled, ΔT is the temperature drop of the strip from the coiling thermometer to the coiling drum stage of the coiler, and the cooling method is front-stage slow cooling or air cooling. When the cooling method is adopted, the water spray on the front side of the pinch roller, the pinch roller cooling water and the coiling drum cooling water are turned off.

[0014] As a technical solution of the present application, in step 4, the medium-temperature coiling control process based on intermediate temperature control takes the intermediate temperature as the control target and rapidly cools the strip to the intermediate temperature through the front-stage rapid cooling method. The value range of the intermediate temperature is set to the pearlite transformation nose point T of the C curve. nose ~T nose +20℃, where C curve is the isothermal transformation kinetic curve of supercooled austenite of steel, T nose The temperature is the shortest temperature for austenite transformation incubation period; air cooling is then performed, and the phase transformation rate of austenite on the laminar roller is increased by reducing the final rolling speed of the strip.

[0015] As a technical solution of the present application, the Ar3 temperature and C curve rules can be calculated by empirical formulas, phase change simulation software or thermal simulation test measurements, wherein Ar3 is the starting temperature of the transformation of austenite to ferrite when the steel is cooled, and the C curve is the isothermal transformation kinetic curve of supercooled austenite of steel.

[0016] As a technical solution of the present application, in step five, the interval time from the lower coiler to the slow cooling box of the steel coil is ≤30s.

[0017] As a technical solution of the present application, the thickness of the strip steel is 1.0 to 2.5 mm.

[0018] Furthermore, the reasons why the present application adopts the above technical solution are analyzed below.

[0019] First, there are three locations where the phase change of strip steel is completed during the hot rolling production process, such as Figure 1 :

[0020] (1) The strip is on the laminar roller table: stage ①;

[0021] (2) The strip is between the pinch roller and the coiler drum, and for a period of time after entering the coiler (such as 1-3 turns of strip), which is stage ②;

[0022] (3) The strip is in the transport chain behind the lower coiler and stored in the coil warehouse, which is stage ③;

[0023] When the strip is in the phase change stage at stage ②, it is very likely to produce flat coils (phase change while coiling). Flat coils will not occur when the phase change is completed at stage ① or when the phase change begins at stage ③. The mechanism of flat coils produced by the phase change of the strip at stage ② is as follows: (1) The phase change expansion of the strip toward the tail end of the coil interferes with the tension of the pinch roller, resulting in coiling tension loss; (2) The strip is in the phase change stage between the pinch roller and the reel, and for a period of time after entering the coiler (the range of 1-3 coils of strip), the strip undergoes phase change expansion and phase change plastic elongation. This elongation process occurs simultaneously with the coiling process, making it difficult to coil the steel coil tightly, thereby reducing the radial compressive stress between layers and the friction between layers, making it easy for the strip to slip between layers and reduce stiffness. After unloading, the strip will flatten under the weight of the steel coil. Due to the high C and Mn contents in 65Mn steel, the phase transformation C curve shifts to the right, increasing the stability of supercooled austenite and prolonging the gestation period of pearlite and bainite phase transformation. If the cooling phase transformation path of 65Mn steel is not intervened, it will be in the phase transformation stage in stage ②, and thus it is easy to flatten.

[0024] Therefore, according to the mechanism of hot-rolled flat coil, by controlling the cooling path of the strip, that is, by intervening in phase change, the phase change of the strip is avoided as much as possible in stage ②, which is the control direction of the flat coil, two control ideas are generated:

[0025] (1) Phase change is completed at the laminar roller table (i.e. stage ①);

[0026] (2) Phase transition starts completely at stage ③.

[0027] Among them, control idea (1) adopts the medium-temperature coiling control process based on intermediate temperature control: its theoretical basis is that there is a temperature range with a faster transformation speed during the isothermal transformation of steel austenite, that is, the nose point T of the phase transformation C curve. nose If the structural properties of the steel grade allow MT = T nose , the cooling path of the strip can be controlled by this process, and the strip can be quickly cooled to the pearlite or bainite transformation nose point T by rapid cooling in the front section. nose , and then air-cooled for a period of time to allow the strip to complete most of the austenite transformation on the laminar roller. For the same steel grade, the final rolling temperature and speed, laminar flow and coiling line length characteristics, and product specifications will affect the austenite transformation rate of the strip reaching the reel Lower alloy composition, lower final rolling speed, longer laminar roller, and thicker strip thickness (affecting rolling speed) are all beneficial to the austenite transformation rate. Increase. With this cooling method, the strip basically completes the phase change on the laminar roller, so its uniformity in the length and width directions is good, but due to its low phase change temperature, the pearlite interlamellar spacing is small and the strength is high. When the user has good adaptability to high strength but high requirements for performance uniformity, the medium-temperature coiling control process based on intermediate temperature control is selected.

[0028] In addition, control idea (2) adopts a control process based on austenite single phase coiling. The reason for setting the strip coiling temperature CT ≥ Ar3 + ΔT is that the strip reaches the coiling temperature T 卷筒 It is a more reasonable and critical flat coil control parameter than the coiling temperature CT. However, at present, the CT thermometer of the hot rolling production line is still some distance away from the coiler, that is, there is still a cooling process ΔT between the CT thermometer and the coiler. Therefore, CT≥Ar3+ΔT is set to make T 卷筒 ≥Ar3 can prevent flat coiling. T can be improved by increasing the final rolling temperature, increasing the speed of the strip head through the plate and the rolling speed, and air cooling the entire length of the laminar roller. 卷筒 ≥Ar3. With this control process, the strip completes phase transformation after coiling. Since the cooling speed of each part of the steel coil is different after coiling (the inner ring, outer ring and end are cooled faster than the center), the phase transformation process is different, resulting in differences in organizational properties. However, the overall pearlite lamellar spacing is larger than that of the medium-temperature coiling control process, so the strength is lower, which is more friendly to users with limited cold rolling mill capacity. When the user requires lower material strength but not high material uniformity, the control process based on austenite single-phase coiling is selected.

[0029] In the slow cooling stage of the steel coil after coiling, the coiled steel coil is quickly placed in the slow cooling box for slow cooling. The purpose is to reduce the cooling rate difference between the inner and outer rings and the ends of the steel coil compared with the center, while reducing the average cooling rate of the steel coil and homogenizing the performance of the steel coil.

[0030] The reason for limiting the strip thickness to 1.0-2.5mm is that when the strip thickness is relatively thick (h>2.5mm), the inner ring stiffness formed by coiling the steel coil is large enough to support the weight of the steel coil. At this time, even if the strip undergoes phase change and coiling loss, serious flattening will not occur.

[0031] Beneficial effects of this application:

[0032] In the flexible production method of thin-gauge 65Mn steel of the present application, it can realize the flat coil control of the strip steel and meet the flexible performance requirements of users by selecting the medium-temperature coiling control process based on intermediate temperature control or the control process based on austenite single-phase zone coiling for different deep processing processes and performance requirements of downstream enterprises. This method can meet the personalized needs of users for the performance of 65Mn steel, and flexibly select the cooling and coiling process according to the user's requirements for the performance of 65Mn hot-rolled materials: when the user requires lower material strength but not high material uniformity, the control process based on austenite single-phase zone coiling can be selected; when the user has good adaptability to high-strength steel but high uniformity requirements, the medium-temperature coiling control process based on intermediate temperature control is selected; in this method, the control process based on austenite single-phase zone coiling takes the temperature of the strip steel reaching the coil as the key control parameter, and realizes the control of the flat coil by phase transformation after coiling. In the method, the medium-temperature coiling control process based on intermediate temperature control takes the cooling intermediate temperature as the key control parameter instead of the coiling temperature, and realizes the control of flat coil and the control of performance uniformity by completing phase change in the laminar roller. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the implementation methods of the present application, the drawings required for use in the implementation methods will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0034] Figure 1 A flow chart of a flexible production method for thin-gauge 65Mn steel provided in an embodiment of the present application;

[0035] Figure 2 A schematic diagram of a strip steel production line provided in an embodiment of the present application;

[0036] Figure 3A schematic diagram of the length characteristics of the laminar roller in the strip steel production line provided in the embodiment of the present application;

[0037] Figure 4 A schematic diagram of the CCT curve of 65Mn steel calculated by the phase change simulation software provided in the embodiment of the present application;

[0038] Figure 5 A schematic diagram of a TTT curve of 65Mn steel measured by a thermal simulation experiment provided in an embodiment of the present application;

[0039] Figure 6 A schematic diagram of the anatomical tensile strength performance of a representative steel coil head 150m using a control process based on austenite single phase coiling provided in an embodiment of the present application;

[0040] Figure 7 A schematic diagram of the anatomical tensile strength performance of a representative steel coil head 150m using a medium-temperature coiling control process based on intermediate temperature control provided in an embodiment of the present application;

[0041] Figure 8 A schematic diagram of a pearlite slice scanning of a representative steel coil head at 150 m using a control process based on austenite single phase coiling provided in an embodiment of the present application;

[0042] Fig. 9 A schematic diagram of a pearlite slice scan of the metallographic structure at 150 m from the head of a representative steel coil using a medium-temperature coiling control process based on intermediate temperature control provided in an embodiment of the present application.

[0043] Icons: 1-continuous casting machine; 2-slab heating machine; 3-descaling machine; 4-rolling mill; 5-laminar cooler; 6-coiler; 7-slow cooling box; 8-hot rolled strip; 9-steel coil. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0045] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for which protection is sought, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0046] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0047] In the description of the present application, it should be noted that the terms "upper", "lower", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or the orientations or positional relationships in which the inventive product is usually placed when in use. These are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0048] Example:

[0049] Please refer to Figure 1 , with reference Figures 2 to 9 , which provides a flexible production method for thin-gauge 65Mn steel, and the method is applied to the production of thin-gauge 65Mn steel, which includes the following methods:

[0050] Production steel grade: 65Mn;

[0051] The production line is a CSP production line, and the characteristics of the production line are as follows Figure 2 And attached Figure 3 The laminar roller length characteristics are shown in Table 1. It should be noted that Figure 3 In the figure, P1, P2, and P3 are the final rolling thermometer, the intermediate thermometer, and the coiling thermometer, respectively; L is the distance from the final rolling thermometer P1 to the coiling thermometer P3; ΔL1 and ΔL2 are the distances from the coiling thermometer to the 1# coiler and the 2# coiler, respectively;

[0052] Table 1: Laminar roller length characteristics of hot rolling production line

[0053] Production line category L ΔL1 ΔL2 CSP production line 90m 12m 21m

[0054] 65Mn steel production includes the following steps:

[0055] (1) Smelting and continuous casting: Molten steel is smelted and continuously cast into slabs through a continuous casting machine 1. The composition of the slabs is shown in Table 2 by weight percentage, and the remainder is Fe and unavoidable impurities.

[0056] Table 2: Chemical composition of 65Mn steel (wt.%)

[0057] C Si Mn P S N Alt 0.66 0.25 1.00 ≤0.012 ≤0.005 0.005 0.03

[0058] (2) Heating: The continuous casting slab is heated to 1150-1170°C by the slab heating machine 2 and the holding time is 25-35 minutes;

[0059] (3) Descaling and finishing rolling: After the slab is discharged from the furnace, it is descaled by high-pressure water in the descaling machine 3, and then it is finished by the rolling mill 4 with seven stands. The thickness of the finished steel strip is 1.0 mm to 2.5 mm, and the final rolling temperature is 880-920°C.

[0060] (4) Laminar flow and coiling:

[0061] The cooling and coiling process is selected according to the user's requirements for material properties, and the hot-rolled strip 8 is subjected to laminar flow and coiling respectively by the laminar flow cooler 5 and the coiler 6;

[0062] a. When the user requires lower material strength but not high uniformity, the control process based on austenite single-phase coiling is selected, CT≥Ar3+ΔT, where Ar3 is the starting temperature of the transformation from austenite to ferrite when the steel is cooled, and ΔT is the temperature drop of the strip from the coiling thermometer to the coiler drum;

[0063] Firstly, the CCT curve of 65Mn steel is calculated using phase transformation simulation software, such as Figure 4 As shown, the Ar3 temperature is 715°C. The control process based on austenite single-phase coiling adjusts the final rolling temperature and final rolling speed of the hot-rolled strip 8 so that the coiling temperature CT satisfies CT≥Ar3+ΔT. The cooling method is front-end slow cooling or air cooling, where ΔT is the temperature drop of the hot-rolled strip 8 from the coiling thermometer to the coiler drum, which is related to the distance from the coiling thermometer to the coiler drum, the rolling speed, the cooling water of the pinch rolls, and other cooling. When this cooling method is used, the front side water spraying of the pinch rolls, the pinch roll cooling water, and the coil cooling water are turned off. The control process based on austenite single-phase coiling and the coil shape control performance of 65Mn are shown in Table 3.

[0064] Table 3: 65Mn adopts the control process and coil shape control performance based on austenite single phase coiling

[0065]

[0066] It can be seen that the ratio of the inner diameter major axis a to the minor axis b of the steel coil 9 is ≤1.05, indicating that the coil shape of the steel coil 9 is good and the hot-rolled strip 8 has not undergone phase transformation in stage ②. The performance of the representative steel coils (No. 1-6) was analyzed. The tensile strength of the hot-rolled strip from the head to 150 meters inward is shown in the following figure. Figure 6 As shown, Figure 6 The performance anatomy of representative steel coils 1-6 using a control process based on austenite single phase coiling shows that the tensile strength in the middle is low, 750MPa, but the strength fluctuation in the length direction is large, reaching 250MPa. Metallographic scanning of representative samples shows that the pearlite sheet spacing is 500-550nm, as shown in the attached Figure 8 As shown, Figure 8Schematic diagram of pearlite lamellar scanning of representative steel coils 1-6 using a control process based on austenite single phase region coiling.

[0067] b. When the user has good adaptability to the high strength of the hot-rolled steel strip 8 but has high requirements for the uniformity of the performance of the hot-rolled steel strip 8, a medium-temperature coiling control process based on intermediate temperature control is selected;

[0068] The isothermal transformation TTT law of 65Mn austenite was obtained through thermal simulation test, and the nose point temperature T of pearlite transformation was obtained. nose = 570℃, at this temperature, the pearlite transformation incubation period is the shortest and the phase transformation speed is the fastest. Figure 5 As shown. Since the pearlite phase transformation temperature is lower, the strength is higher. Therefore, the strip is cooled in stages, and the high cooling rate strategy is used to quickly cool the strip to the intermediate temperature MT = 570 ~ 590 ° C above the nose of the C curve. MT is above the nose of the C curve. Then air cooling is performed without controlling CT. The phase transformation rate of 65Mn strip steel when it reaches the coiler drum is increased by adjusting the process parameters such as the final rolling temperature and speed. When the phase change rate of the laminar roller is large, the latent heat of phase change is released to increase the strip temperature, and the coiling temperature CT will be higher than the intermediate temperature MT after natural evolution. The medium-temperature coiling control process based on intermediate temperature control and the coil shape control performance of 65Mn are shown in Table 4.

[0069] It can be seen that the hot-rolled steel strip 8 undergoes a large phase transformation in stage ①, and the ratio of the inner diameter major axis a to the minor axis b of the steel coil 9 is ≤1.05, indicating that the coil shape of the steel coil 9 is good. The performance of the representative steel coils 9 (No. 2-6) is analyzed, and the tensile strength of the hot-rolled steel strip 8 from the head to 150 meters inward is analyzed as follows Figure 7 As shown, Figure 7 The performance anatomy diagram of representative steel coils 2-6 using the medium-temperature coiling control process based on intermediate temperature control shows that the tensile strength in the middle is relatively high, at 900-950MPa, but the strength in the length direction is relatively uniform, with a strength difference of only about 70MPa. Metallographic scanning of representative samples shows that the pearlite sheet spacing is 160-180nm, such as Fig. 9 As shown, Fig. 9 Schematic diagram of pearlite lamellar scanning of representative steel coils 2-6 using a medium-temperature coiling control process based on intermediate temperature control.

[0070] Table 4: 65Mn adopts medium temperature coiling control process based on intermediate temperature control and coil shape control performance

[0071]

[0072] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A flexible production method for thin-gauge 65Mn steel, characterized in that: The following steps are involved: Step 1, smelting and continuous casting: smelting molten steel and continuously casting into slabs, the composition of the continuous casting slabs is C: 0.63-0.69%, Si: 0.20-0.30%, Mn: 0.95-1.05%, P: ≤0.02%, S≤0.01%, Al: 0.020-0.040%, N: ≤0.006, and the balance is iron; Step 2, heating: uniformly heating the continuous casting slab to 1150-1170° C. and then taking it out of the furnace, and keeping the continuous casting slab warm for 25-35 minutes; Step 3, descaling and finish rolling: the continuous casting slab after being discharged from the furnace is descaled by high-pressure water, and then subjected to seven-stand finish rolling, and the final rolling temperature is 880-920°C; Step 4, selection of laminar flow and coiling: When the user has low requirements for material strength and material uniformity, a control process based on austenite single-phase coiling is selected, and the coiling temperature CT ≥ Ar3 + ΔT, where Ar3 is the starting temperature of the transformation from austenite to ferrite when the steel is cooled, and ΔT is the temperature drop of the strip from the coiling thermometer to the coiler drum; When the user has high requirements for material strength, material adaptability and material uniformity, a medium-temperature coiling control process based on intermediate temperature control is selected; In step 4, The control process based on austenite single phase coiling is to adjust the final rolling temperature and final rolling speed of the strip so that the coiling temperature CT satisfies CT≥Ar3+ΔT, and the cooling method is front-end slow cooling or air cooling. When the cooling method is adopted, the water spray on the front side of the pinch roll, the pinch roll cooling water and the coil cooling water are turned off; the medium-temperature coiling control process based on intermediate temperature control takes the intermediate temperature as the control target and uses the front-end fast cooling method to quickly cool the strip to the intermediate temperature. The value range of the intermediate temperature is set to the pearlite transformation nose point T of the C curve. nose ~T nose +20℃, where C curve is the isothermal transformation kinetic curve of supercooled austenite of steel, T nose The temperature is the shortest temperature for the austenite transformation incubation period; air cooling is then performed, and the phase transformation rate of the austenite on the laminar roller is increased by reducing the final rolling speed of the strip; Step 5: Slow cooling of the steel coil: The coiled steel coil is quickly placed in a slow cooling box for slow cooling.

2. The flexible production method of thin gauge 65Mn steel according to claim 1, characterized in that: The Ar3 temperature and C curve are calculated by empirical formula, phase change simulation software or thermal simulation test measurement, where Ar3 is the starting temperature of the transformation of austenite to ferrite when the steel is cooled, and the C curve is the isothermal transformation kinetic curve of supercooled austenite of the steel.

3. The flexible production method of thin gauge 65Mn steel according to claim 1, characterized in that: In step 5, the interval time from the lower coiler to the slow cooling box of the steel coil is ≤30s.

4. The flexible production method of thin gauge 65Mn steel according to claim 1, characterized in that: The thickness of the strip steel is 1.0~2.5mm.

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