CN115647075A - Flexible production method of thin 65Mn steel - Google Patents

Abstract

The application provides a flexible production method of thin 65Mn steel, which comprises the following steps: step one, smelting and continuous casting: smelting molten steel and continuously casting into a plate blank; step two, heating: uniformly heating the continuous casting plate blank to 1150-1170 ℃, discharging, and preserving heat of the continuous casting plate blank for 25-35 min; step three, descaling and finish rolling: performing high-pressure water descaling on the continuously cast plate blank discharged from the furnace, and then performing seven-frame finish rolling at the finishing temperature of 880-920 ℃; step four, selecting laminar flow and coiling: when the requirement of a user on the strength and the uniformity of the material is low, selecting a control process based on austenite single-phase region coiling, wherein the coiling temperature CT is more than or equal to Ar3+ delta T; when the requirement of a user on the strength and the uniformity of the material is high, selecting a medium-temperature coiling control process based on medium-temperature control; step five, slowly cooling the steel coil: and placing the coiled steel coil into a slow cooling box for slow cooling. The method can meet the individual requirements of users on the performance of the 65Mn steel and realize the control of flat coils.

Description

Flexible production method of thin 65Mn steel

Technical Field

The application relates to the field of hot-rolled strip steel, in particular to a flexible production method of thin 65Mn steel.

Background

The 65Mn steel is widely used for manufacturing hardware tools such as cutters, saw blades and the like, and the manufacturing process of the steel manufacturing end is generally smelting and continuous casting → heating → hot rolling → cooling → coiling. The post-treatment process of the steel user side is different from user to user, and mainly comprises pickling, multi-pass cold rolling and annealing, forming and stamping, final heat treatment and the like. The key requirement of the steel user end on 65Mn steel mainly lies in the thin specification, which is beneficial to the reduction of the final specification of cold rolling and the reduction of the rolling process by the user, thereby reducing the cost. In addition, some users have higher requirements on the performance uniformity of the 65Mn steel, and the strip breakage accident caused by larger fluctuation of the rolling force during cold rolling is prevented.

The technological characteristics of the thin slab continuous casting and rolling process are beneficial to inhibiting chemical composition segregation, refining nonmetallic inclusions, reducing surface decarburization and reducing pearlite lamella spacing, and the characteristics enable the thin slab continuous casting and rolling process to be very suitable for producing high-quality medium-high carbon steel strips. In addition, the thin slab continuous casting and rolling process has remarkable advantages in the aspect of thin material production, and the thin 65Mn standard becomes a key development variety of a short-process production line. However, in the production process, the problem of flat rolling of 65Mn steel is more prominent, especially in the thin specification. The flat coil means that the horizontally stored steel coil gradually collapses to be oval after being drawn out from a winding drum of a coiler. The steel coil which is subjected to flat rolling needs to be opened flatly by taking measures, for example, the inner ring is cut by manual flame, so that the additional production cost is increased, and the production efficiency and the product yield are influenced; in addition, the steel coil with large ovality is easy to cause surface scratch of the steel coil due to inconsistent peripheral speed and violent tension fluctuation in the uncoiling process, so that the product is degraded or judged to be waste.

The problem of how to control the flat rolling of thin 65Mn steel and meet the performance requirements of users on the strip steel becomes the challenge of a short-process production line. In order to solve the problem of flat winding of hot rolled steel strip, the invention with the publication number of CN1506174A discloses a control method, the winding temperature of the steel strip with the carbon content of more than 0.25% is controlled in the range of Ar1+ (-10 to +60 ℃), so that the phase change of the steel strip is gradually eliminated from the core part contacted with the outer layer and the winding drum to the middle layer. The patent with publication number CN108754104A discloses a method for dual-phase steel flat coil defects, the hot rolling finishing temperature is controlled according to the phase transition starting temperature of ferrite of austenite, and the transformation from austenite to ferrite is promoted; the hot rolling cooling section is divided into a fast cooling section and a slow cooling section, the hot rolled plate is cooled to the intermediate temperature of laminar cooling in the fast cooling section, the transformation of austenite to ferrite is promoted, the transformation of austenite to pearlite is promoted in the slow cooling section, and the occupation ratio of retained austenite is reduced. The patent with publication number CN107904376A provides a method and a device for preventing flat coiling of dual-phase steel, which can accumulate energy for the phase change of strip steel to lead the phase change of the strip steel to be generated in advance and prevent the strip steel from being transformed into flat coils after being coiled into coils by controlling the temperature of a finish rolling outlet to be 860-900 ℃ and the cooling speed to be 70-100 ℃/s. The patent publication No. CN102335681A discloses a coiling method for preventing the flat coil of hot rolled strip steel, the coiling temperature is 500-600 ℃, and then the coiled steel coil stays on a coiling drum of a coiler for 20-60 s. The patent with publication number CN107812789A discloses a method for preventing flat coiling, which comprises the steps of cooling hot-rolled strip steel by laminar flow, rapidly cooling the strip steel to 650-700 ℃ or 500-550 ℃ for coiling, and keeping the coiled hot-rolled steel coil on a coiling machine for 5-20 s; patent No. ZL202010183210.4 discloses a method for controlling the edgewise coiling of hot-rolled advanced high-strength steel, which controls the edgewise coiling through a control stage of the finish rolling surface roughness of strip steel, a control stage of the phase change of laminar cooling austenite, a control stage of coiling tension, and a control stage of rotation after coiling.

Disclosure of Invention

One of the purposes of the present application is to provide a flexible production method for thin 65Mn steel, so as to solve the problem that the conventional 65Mn steel is easy to be flatly rolled.

The technical scheme of the application is as follows:

a flexible production method of thin 65Mn steel comprises the following steps:

step one, smelting and continuous casting: smelting molten steel and continuously casting the molten steel into a plate blank, wherein the continuously cast plate blank comprises the following components in percentage by weight: 0.63 to 0.69%, si:0.20 to 0.30%, mn:0.95 to 1.05%, P: not more than 0.02%, S not more than 0.01%, al:0.020 to 0.040%, N: less than or equal to 0.006 and the balance of iron;

step two, heating: uniformly heating the continuous casting plate blank to 1150-1170 ℃, discharging, and carrying out heat preservation on the continuous casting plate blank for 25-35 min;

step three, descaling and finish rolling: carrying out high-pressure water descaling on the continuously cast slab discharged from the furnace, and then carrying out seven-rack finish rolling at the finishing temperature of 880-920 ℃;

step four, selecting laminar flow and coiling: when the requirement of a user on the strength and the uniformity of the material is low, selecting a control process based on austenite single-phase zone coiling, wherein the coiling temperature CT is more than or equal to Ar3+ delta T, ar3 is the starting temperature of austenite-ferrite transformation when the steel is cooled, and delta T is the temperature drop generated in the stage from a coiling temperature meter to a coiler mandrel of the strip steel; when the requirements of a user on the strength, adaptability and uniformity of the material are high, selecting a medium-temperature coiling control process based on medium-temperature control;

step five, slowly cooling the steel coil: and quickly placing the coiled steel coil into a slow cooling box for slow cooling.

In the fourth step, the finishing temperature and the finishing speed of the strip steel are adjusted so that the coiling temperature CT is equal to or more than Ar3+ delta T, wherein Ar3 is the starting temperature of austenite to ferrite transformation when the steel is cooled, delta T is the temperature drop generated in the stage from a coiling temperature detector to a coiling drum of a coiler, the cooling mode is front-section slow cooling or air cooling, and water spray on the front side of a pinch roll, pinch roll cooling water and coiling drum cooling water are closed when the cooling mode is adopted.

As a technical scheme of the application, in the fourth step, the intermediate temperature control-based intermediate temperature coiling control process takes the intermediate temperature as a control target and rapidly cools the strip steel to the intermediate temperature through a front section rapid cooling mode, and the value range of the intermediate temperature is set as the pearlite transformation nose tip point T of the C curve _nose ～T _nose +20 ℃, wherein the C curve is the steel undercooled austenite isothermal transformation kinetic curve, T _nose The temperature with the shortest austenite transformation incubation period; and then air-cooling, and increasing the phase transformation rate of austenite on a laminar flow roller way by reducing the finish rolling speed of the strip steel.

As a technical scheme of the application, the Ar3 temperature and the C curve rule can be calculated by an empirical formula, calculated by phase change simulation software or measured by a thermal simulation test, wherein Ar3 is the starting temperature of the transformation from austenite to ferrite when steel is cooled, and the C curve is a steel undercooling austenite isothermal transformation kinetic curve.

As a technical scheme of the application, in the fifth step, the clearance time of the steel coil from the lower coiling machine to the slow cooling box is less than or equal to 30s.

As a technical scheme of the application, the thickness of the strip steel is 1.0-2.5 mm.

Further, the following explains the reason why the present application adopts the above technical solution.

Firstly, the positions of the strip steel after phase change in the hot rolling production process are divided into three positions, as shown in figure 1:

(1) The strip steel is positioned on a laminar flow roller way: is stage (1);

(2) The band steel is positioned between the pinch roll and a coiling block of the coiling machine and enters the coiling machine for a period of time (such as the range of 1-3 circles of band steel), and the stage (2) is shown;

(3) The transportation chain of the strip steel after the strip steel is placed in the lower coiling machine is stored in a steel coil warehouse, and the step (3) is carried out;

and when the strip steel is in the phase change stage in the stage (2), flat rolling (the situation of phase change while coiling) can be generated at a high probability, and the flat rolling can not be generated when the phase change is completed in the stage (1) or the phase change starts to occur in the stage (3). The mechanism that the strip steel generates phase change in the stage (2) to generate flat coils is as follows: (1) The phase change expansion of the strip steel towards the tail end of the steel coil interferes with the tension of the pinch roll, and the strip steel loses tension during coiling; (2) The strip steel is in a phase change stage between the pinch roll and the winding drum and after the strip steel enters the coiler for a period of time (the range of coiling 1-3 circles of strip steel), the strip steel generates phase change expansion and phase change plastic elongation, the elongation process and the coiling process are carried out simultaneously, so that the steel coil is difficult to coil tightly, the radial compressive stress between layers is reduced, the interlayer friction is reduced, the strip steel is easy to slide between layers, the rigidity is reduced, and the strip steel is flatly coiled under the self-weight action of the steel coil after being uncoiled. Because the 65Mn steel has higher C and Mn contents, the phase transformation C curve is shifted to the right, the stability of the super-cooled austenite is increased, the incubation period of the phase transformation of pearlite and bainite is prolonged, and if the 65Mn steel does not interfere with the cooling phase transformation path, the 65Mn steel is in the phase transformation stage in the stage (2), so the 65Mn steel is easy to be flatly rolled.

Therefore, according to the mechanism of hot rolling flat coils, two control ideas are generated by controlling the cooling path of the strip steel, namely, the phase (2) of avoiding the phase change of the strip steel as much as possible through phase change intervention is the flat coil control direction:

(1) Completing phase change at a laminar flow roller way (namely, stage (1));

(2) The phase transition is completely initiated in phase (3).

Wherein, control thinking (1) adopts the medium temperature based on intermediate temperature control to batch control process: the theoretical basis thereofThe temperature range with higher transformation speed exists in the austenite isothermal transformation of the steel, namely the nose point T of the transformation C curve _nose Nearby, if the structural property requirement of the steel grade allows MT = T _nose The cooling path of the strip steel can be controlled by the process, and the strip steel is rapidly cooled to the pearlite or bainite transformation nose point T by the front-section rapid cooling _nose And then the strip steel is cooled in air for a period of time to complete the transformation of the austenite of the maximum part of the strip steel on a laminar flow roller way. For the same steel type, the austenite phase-change rate of the strip steel reaching a winding drum can be influenced by the finish rolling temperature and speed, the laminar flow, the length characteristics of a coiling line and the product specification

The austenite phase-change rate is facilitated by lower alloy composition, lower finishing rolling speed, longer laminar flow roller way and thicker strip steel thickness (influencing the rolling speed)

And (4) increasing. By adopting the cooling mode, the strip steel basically finishes phase change on the laminar flow roller way, so the strip steel has better uniformity in the length and width directions, but has lower phase change temperature, smaller pearlite lamellar spacing and higher strength. When the user has better adaptability to high strength but higher requirement on performance uniformity, the medium-temperature coiling control process based on the medium-temperature control is selected.

In addition, the control idea (2) adopts a control process based on austenite single-phase zone coiling. The reason why the coiling temperature CT of the strip steel is more than or equal to Ar3+ delta T is that the strip steel reaches the temperature T of a winding drum _{Winding drum} Is a more reasonable and key flat coil control parameter than the coiling temperature CT, but the CT thermometer of the current hot rolling production line is away from the coiling machine at a certain distance, namely the strip steel has a temperature-reducing delta T process between the CT thermometer and the coiling machine, therefore, the CT is set to be more than or equal to Ar3+ delta T so as to ensure that the T is ensured to be equal to or more than the Ar3+ delta T _{Winding drum} The occurrence of flat rolling can be prevented only by more than or equal to Ar3. T can be achieved by measures of increasing the finish rolling temperature, increasing the speed of the strip steel head through plate and the rolling speed, and the full-length air cooling of a laminar flow roller way _{Winding drum} And more than or equal to Ar3. By adopting the control process, the phase change of the strip steel is finished after the strip steel is coiled, and the strip steel is coiled into a steel coilAfter rolling, the cooling speed of each part is different (the inner ring, the outer ring and the end part are cooled faster than the center), so that the phase change process is different, and the structure performance is different. But the integral pearlite sheet interlayer spacing is larger than that of a medium-temperature coiling control process, so that the strength is lower, and the method is friendly to users with limited capability of a cold rolling mill. When the user requires that the material strength is low but the requirement on the uniformity of the material is not high, a control process based on austenite single-phase zone coiling is selected.

In the steel coil slow cooling stage after the steel coil is coiled, the coiled steel coil is quickly placed into a slow cooling box for slow cooling, and the purpose is that the average cooling speed of the steel coil is reduced while the steel coil reduces the cooling speed difference of the inner ring, the outer ring and the end part compared with the center, and the performance of the steel coil is homogenized.

The reason for limiting the thickness of the strip steel to the specification of 1.0-2.5 mm is that when the thickness h of the strip steel is thicker than 2.5mm, the rigidity of an inner ring formed by coiling the steel coil is large enough to support the self weight of the steel coil, and at the moment, even if the strip steel is subjected to phase change, coiling tension losing cannot cause serious flat coiling.

The beneficial effect of this application:

according to the flexible production method of the thin 65Mn steel, aiming at different deep processing flows and performance requirements of downstream enterprises, the medium-temperature coiling control process based on intermediate temperature control or the control process based on austenite single-phase zone coiling is selected, so that the flat coiling control of the strip steel can be realized, and the flexible performance requirements of users can be met. The method can meet the individual requirements of users on the performance of the 65Mn steel, flexibly selects the cooling and coiling process according to the requirements of the users on the performance of the 65Mn hot rolled material: when a user requires that the strength of the material is low but the requirement on the uniformity of the material is not high, a control process based on austenite single-phase zone coiling can be selected; when a user has good adaptability to high strength of steel but has high requirement on uniformity, selecting a medium-temperature coiling control process based on medium-temperature control; in the method, the control process based on austenite single-phase zone coiling takes the temperature of the strip steel reaching a coiling drum as a key control parameter, and the flat coiling is controlled by carrying out phase change after coiling. In the method, the medium-temperature coiling control process based on medium temperature control takes the cooling medium temperature as a key control parameter, does not take the coiling temperature as a control parameter, and realizes the control of flat coils and the control of performance uniformity by finishing phase change on a laminar flow roller way.

Drawings

In order to more clearly explain the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and that for those skilled in the art, other related drawings can be obtained from these drawings without inventive effort.

FIG. 1 is a flow chart of a flexible production method of thin gauge 65Mn steel according to an embodiment of the present application;

FIG. 2 is a schematic view of a production line of strip steel provided in an embodiment of the present application;

FIG. 3 is a schematic diagram illustrating a length characteristic of a laminar flow table in a strip steel production line according to an embodiment of the present disclosure;

FIG. 4 is a schematic diagram of CCT curve of 65Mn steel calculated by phase change simulation software provided in the embodiments of the present application;

FIG. 5 is a schematic diagram of TTT curve of 65Mn steel measured by a thermal simulation experiment provided by an embodiment of the application;

FIG. 6 is an anatomical diagram representing the 150m tensile strength performance of the head of a steel coil by adopting a control process based on austenite single-phase region coiling, which is provided by the embodiment of the application;

fig. 7 is an anatomical diagram representing the 150m tensile strength performance of the head of a steel coil by using a medium-temperature coiling control process based on medium-temperature control according to an embodiment of the present application;

FIG. 8 is a pearlite lamellar scanning schematic diagram representing a metallographic structure at 150m of the head of a steel coil by adopting a control process based on austenite single-phase zone coiling provided by an embodiment of the application;

fig. 9 is a pearlite lamellar scanning schematic diagram representing a metallographic structure at 150m of the head of a steel coil by using a medium-temperature coiling control process based on medium temperature control according to an embodiment of the present application.

Icon: 1-a continuous casting machine; 2-a slab heater; 3-a descaler; 4-rolling mill; 5-a laminar flow cooler; 6-a coiler; 7-slow cooling box; 8-hot rolling the strip steel; 9-steel coil.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. The components of the embodiments of the present application, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations.

Thus, the following detailed description of the embodiments of the present application, as presented in the figures, is not intended to limit the scope of the claimed application, but is merely representative of selected embodiments of the application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.

In the description of the present application, it should be noted that the terms "upper", "lower", and the like refer to orientations or positional relationships based on the orientations or positional relationships shown in the drawings or orientations or positional relationships that the products of the present invention are conventionally placed in use, and are used for convenience in describing the present application and simplifying the description, but do not indicate or imply that the devices or elements referred to must have a specific orientation, be constructed in a specific orientation, and be operated, and thus should not be construed as limiting the present application.

The embodiment is as follows:

referring to fig. 1 in combination with fig. 2 to 9, a flexible production method of a thin gauge 65Mn steel is provided, which is applied to the production of a thin gauge 65Mn steel, and includes the following steps:

producing steel grade: 65Mn;

the production line is CSP production line, and the characteristics of the production line are shown in attached figures 2 and 3. The laminar roller table length characteristics are shown in table 1. In fig. 3, P1, P2, and P3 are respectively a finish rolling thermometer, an intermediate thermometer, and a coiling thermometer, L is a distance from the finish rolling thermometer P1 to the coiling thermometer P3, and Δ L1 and Δ L2 are respectively distances from the coiling thermometer to the 1# coiler and the 2# coiler;

table 1: length characteristic of laminar flow roller way of hot rolling production line

Class of production line	L	ΔL1	ΔL2
				CSP production line	90m	12m	21m

The production of the 65Mn steel comprises the following steps:

(1) Smelting and continuous casting: the molten steel is smelted and continuously cast into a slab by a continuous casting machine 1, the components of which are shown in table 2 by weight percentage, and the balance being Fe and inevitable impurities.

Table 2: chemical composition (wt.%) of 65Mn steel

C

Si

Mn

P

S

N

Alt

0.66

0.25

1.00

≤0.012

≤0.005

0.005

0.03

(2) Heating: soaking the continuous casting slab to 1150-1170 ℃ by a slab heater 2, and discharging the slab out of the furnace, wherein the heat preservation time is 25-35 min;

(3) Descaling and finish rolling: after the plate blank is taken out of the furnace, the plate blank is subjected to high-pressure water descaling by a descaling machine 3, then is subjected to seven-frame finish rolling by a rolling mill 4, the thickness specification of the finish rolling strip steel is 1.0mm to 2.5mm, and the finish rolling temperature is 880-920 ℃;

(4) Laminar flow and coiling:

selecting a cooling and coiling process according to the requirement of a user on the material performance, and respectively carrying out laminar flow and coiling on the hot-rolled strip steel 8 through a laminar flow cooler 5 and a coiler 6;

a. when a user requires low material strength but does not have high requirement on the uniformity of the material, selecting a control process based on austenite single-phase region coiling, wherein CT is more than or equal to Ar3+ delta T, wherein Ar3 is the starting temperature of austenite-ferrite transformation when steel is cooled, and delta T is the temperature drop generated in the stage of the strip steel from a coiling temperature detector to a coiling drum of a coiler;

firstly, CCT curve of 65Mn steel is calculated by adopting phase change simulation software, and as shown in figure 4, the obtained Ar3 temperature is 715 ℃. The control process based on austenite single-phase zone coiling enables the coiling temperature CT to meet the condition that CT is more than or equal to Ar3+ delta T by adjusting the finish rolling temperature and the finish rolling speed of the hot rolled strip steel 8, the cooling mode is front-section slow cooling or air cooling, wherein delta T is the temperature drop generated by the hot rolled strip steel 8 from a coiling temperature detector to a coiler mandrel and is related to the cooling of the distance from the coiling temperature detector to the coiler mandrel, the rolling speed, pinch roll cooling water and the like. When the cooling mode is adopted, the water spray from the front side of the pinch roll, the cooling water of the pinch roll and the cooling water of the winding drum are closed. The actual results of 65Mn using the austenite single phase zone coiling-based control process and the coil shape control are shown in table 3.

Table 3:65Mn adopts a control process based on austenite single-phase zone coiling and a coil shape control achievement

It can be seen that the ratio of the major axis a to the minor axis b of the inner diameter of the steel coil 9 is less than or equal to 1.05, which indicates that the coil shape of the steel coil 9 is good and the hot-rolled strip 8 does not undergo phase transition in stage (2). The representative steel coils (numbers 1-6) are subjected to performance anatomy, the inward tensile strength anatomy of the head of the hot rolled strip steel of 150 meters is shown in figure 6, figure 6 is a performance anatomy figure of the representative steel coils 1-6 by adopting a control process based on austenite single-phase zone coiling, and it can be seen that the tensile strength of the middle part is lower and is 750MPa, but the strength fluctuation in the length direction is larger and reaches 250MPa. And performing metallographic scanning detection on the representative sample, wherein the pearlite inter-lamellar spacing is 500-550nm, as shown in the attached drawing 8, and FIG. 8 is a pearlite lamellar scanning schematic diagram representing steel coils 1-6 by adopting a control process based on austenite single-phase region coiling.

b. When the user has good adaptability to the high strength of the hot rolled strip steel 8 but has high requirement on the performance uniformity of the hot rolled strip steel 8, selecting a medium temperature coiling control process based on medium temperature control;

obtained by thermal simulation testObtaining the pearlite transformation nose point temperature T by the isothermal transformation TTT rule of 65Mn austenite _nose =570 ℃, at which temperature the pearlite transformation induction period is shortest and the transformation speed is fastest, as shown in fig. 5. Because the pearlite phase transformation temperature is lower and the strength is higher, the strip steel is quickly cooled to the intermediate temperature MT = 570-590 ℃ at the upper part of the nose tip of the C curve by a high cooling speed strategy in a sectional cooling mode, and the MT is above the nose tip of the C curve; then air cooling is carried out, and CT is not controlled. The phase transformation rate of the 65Mn strip steel when reaching a coiler mandrel is increased by adjusting process parameters such as finishing temperature, speed and the like

When the laminar flow roller bed phase change rate is large, the phase change latent heat is released to increase the temperature of the strip steel, and the coiling temperature CT is higher than the intermediate temperature MT after being naturally evolved. The actual results of the intermediate temperature coiling control process and the coil shape control based on the intermediate temperature control for 65Mn are shown in table 4.

It can be seen that the hot rolled strip 8 has a great part of phase change in the stage (1), and the ratio of the major axis a to the minor axis b of the inner diameter of the steel coil 9 is less than or equal to 1.05, which indicates that the coil shape of the steel coil 9 is good. The representative steel coil 9 (number 2-6) is subjected to performance anatomy, the tensile strength anatomy of the hot rolled strip steel 8 with the head part facing inwards for 150 meters is shown in fig. 7, fig. 7 is a performance anatomy diagram of the representative steel coil 2-6 adopting the medium temperature coiling control process based on medium temperature control, and it can be seen that the tensile strength of the middle part is high and is 900-950 MPa, but the strength in the length direction is uniform, and the strength difference is only about 70 MPa. And performing metallographic scanning detection on the representative sample, wherein the pearlite inter-lamellar spacing is 160-180nm, as shown in fig. 9, and fig. 9 is a pearlite lamellar scanning schematic diagram representing the steel coils 2-6 by adopting a medium-temperature coiling control process based on medium temperature control.

Table 4:65Mn adopts intermediate temperature control-based intermediate temperature coiling control process and coil shape control achievement

The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims (6)

1. The flexible production method of the thin 65Mn steel is characterized by comprising the following steps:

step one, smelting and continuous casting: smelting molten steel and continuously casting into a plate blank, wherein the continuously cast plate blank comprises the following components in percentage by weight: 0.63 to 0.69%, si:0.20 to 0.30%, mn:0.95 to 1.05%, P: less than or equal to 0.02 percent, less than or equal to 0.01 percent of S, al:0.020 to 0.040%, N: less than or equal to 0.006 and the balance of iron;

step two, heating: uniformly heating the continuous casting slab to 1150-1170 ℃, discharging, and preserving heat of the continuous casting slab for 25-35 min;

step three, descaling and finish rolling: carrying out high-pressure water descaling on the continuously cast slab discharged from the furnace, and then carrying out seven-rack finish rolling at the finishing temperature of 880-920 ℃;

step four, selecting laminar flow and coiling: when the requirement of a user on the strength and the uniformity of the material is low, selecting a control process based on austenite single-phase region coiling, wherein the coiling temperature CT is more than or equal to Ar3+ delta T, wherein Ar3 is the starting temperature of austenite-ferrite transformation when the steel is cooled, and delta T is the temperature drop generated in the stage from a coiling temperature detector to a coiling drum of a coiling machine of the strip steel; when the requirements of a user on the strength, adaptability and uniformity of the material are high, selecting a medium-temperature coiling control process based on medium-temperature control;

step five, slowly cooling the steel coil: and quickly placing the coiled steel coil into a slow cooling box for slow cooling.

2. The flexible production method of the thin gauge 65Mn steel according to claim 1, characterized in that in the fourth step, the control process based on austenite single-phase zone coiling is to adjust the finishing temperature and the finishing speed of the strip steel so that the coiling temperature CT satisfies the condition that CT is not less than Ar3+ Δ T, wherein Ar3 is the starting temperature of austenite to ferrite transformation when the steel is cooled, Δ T is the temperature drop generated in the stage from the coiling temperature detector to the coiler mandrel of the strip steel, the cooling mode is front-stage slow cooling or air cooling, and the water spray, the pinch roll cooling water and the mandrel cooling water on the front side of the pinch roll are closed when the cooling mode is adopted.

3. The flexible production method of thin-gauge 65Mn steel according to claim 2, characterized in that in step four, the intermediate temperature control-based intermediate temperature coiling control process rapidly cools the strip steel to the intermediate temperature by the front-stage rapid cooling mode with the intermediate temperature as a control target, and the value range of the intermediate temperature is set as the pearlite transformation nose point T of the C curve _nose ～T _nose +20 ℃, wherein the C curve is the steel undercooled austenite isothermal transformation kinetic curve, T _nose The temperature at which the austenite transformation incubation period is the shortest; and then performing air cooling, and increasing the phase transformation rate of austenite on a laminar flow roller way by reducing the finishing rolling speed of the strip steel.

4. The flexible production method of the thin gauge 65Mn steel according to claim 3, characterized in that the Ar3 temperature and the C curve law are calculated by an empirical formula, calculated by phase change simulation software, or measured by a thermal simulation test, wherein Ar3 is the starting temperature of austenite to ferrite transformation when the steel is cooled, and the C curve is the isothermal transformation kinetic curve of the supercooled austenite of the steel.

5. The method for flexibly producing the thin gauge 65Mn steel according to claim 1, wherein in step five, the clearance time of the steel coil from the lower coiling machine to the annealing box is less than or equal to 30s.

6. The method for flexibly producing the thin gauge 65Mn steel according to claim 2, wherein the strip steel has a thickness of 1.0 to 2.5mm gauge.

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