A rolling process for stainless steel composite plate

Abstract

The present invention discloses a rolling process for a stainless steel composite plate. The present invention belongs to the field of rolling process; the specific steps are: 1. Heating process; 2. Descaling process; 3. Rolling and controlled cooling process; 4. Plate shape correction. Through the implementation of the scheme, the present invention does not need to modify the rolling mill, and can use the existing equipment of the medium and thick plate rolling mill to achieve the normal rolling of the single-layer stainless steel composite billet in the medium and thick plate rolling mill, ensuring that the rolling mill equipment accidents will not be caused by the billet buckling during the rolling process, and can be used to produce thick stainless steel composite plates with excellent performance and good plate shape.

Description

Technical Field

[0001] The invention relates to the field of rolling technology, in particular to a rolling technology for a stainless steel composite steel plate. Background Art

[0002] Stainless steel composite plate is the most widely used composite plate among layered metal composite plates. As a manufacturing method for stainless steel composite steel plates, hot rolling composite method is increasingly used in the production of stainless steel composite steel plates due to its advantages such as low cost, low pollution, short delivery cycle, and the ability to achieve mass industrial production. Hot rolled composite plates are usually made by symmetrical assembly. Symmetrical assembly can keep the upper and lower billets symmetrical, thereby ensuring a smooth rolling process. However, symmetrical assembly also has many problems, especially when producing composite plates with a thickness of ≥50mm, the billet thickness will exceed 500mm and the rolling thickness will be ≥100mm, which brings great difficulties to the control of the organizational properties of high-end composite plates.

[0003] Asymmetric composite billets can be obtained by vacuum assembling a single stainless steel sheet and a single carbon steel sheet. This assembling method can reduce the thickness and rolling thickness of the composite billet, which is beneficial to reduce the difficulty of production and performance control of composite plates. However, due to the huge differences in physical properties such as deformation resistance of the coating and base layer, surface friction and linear expansion coefficient between stainless steel and carbon steel during the hot rolling process, the low-alloy strong steel side has large deformation during the rolling process, while the austenitic stainless steel has small deformation. Therefore, during rolling, the composite billet will bend toward the stainless steel side. If it is not well controlled, not only will it not be able to roll normally, but in serious cases, accidents may occur, causing equipment damage. Especially for medium and thick plate mills, since there is no tension constraint between the hot rolling mill frames, rolling is more difficult, and special process settings must be used to solve the problem of rolling single-layer stainless steel composite plates. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide an asymmetric rolling process for stainless steel composite plates suitable for medium and thick plate rolling mills. Through the implementation of this scheme, the existing equipment of the medium and thick plate rolling mill can be used to realize the normal rolling of single-layer stainless steel composite billets in the medium and thick plate rolling mill without the need to modify the rolling mill, ensuring that the rolling mill equipment accidents will not be caused by the buckling of the billet during the rolling process, and it can be used to produce thick stainless steel composite plates with excellent performance and good plate shape.

[0005] Technical solution: The rolling process of a stainless steel composite plate described in the present invention has the following specific operating steps:

[0006] Step (1), heating process, heating the single-layer composite billet by a heating process of long-term high temperature + upper and lower surface temperature difference heating, reducing the strength difference between stainless steel and carbon steel and reducing the difficulty of rolling;

[0007] Step (2), descaling process, by reducing the number of descaling passes in the initial stage of rough rolling to ensure the plate shape in the initial stage of rolling; by increasing the number of descaling passes in the finishing rolling to ensure the surface quality of the steel plate;

[0008] Step (3), rolling and controlled cooling process; by controlling the rough rolling reduction, setting the SKI parameters for suppressing buckles, and performing water penetration with different flow rates between the upper and lower tables between rolling passes, the stability of the rolling process is ensured;

[0009] Step (4), plate shape correction, by controlling the temperature of the straightening process, controls the rebound of the unevenness of the steel plate after correction.

[0010] Furthermore, in step (1), the specific operation process of the heating process is as follows:

[0011] (1.1) Use a continuous heating furnace to heat the stainless steel layer;

[0012] (1.2) Heating system: long-term high-temperature heating system is adopted; the lower limit of heating time is set to 12 hours, the total time in the furnace is ≤18 hours, and the heating temperature is set at 1200℃~1280℃;

[0013] (1.3) After the billet enters the soaking section, the heating intensity of the lower burner is increased and the heating intensity of the upper burner is decreased to form a temperature difference between the upper and lower surfaces of the composite billet, wherein the lower surface temperature - the upper surface temperature ≥ 30℃-50℃.

[0014] Furthermore, in step (2), the descaling process is as follows: descaling is performed in a descaling box, and fine descaling is not performed in the forming pass, the widening pass, and the first two passes after the widening is completed. After the plate shape of the subsequent rough rolling pass is stable, descaling is performed manually once, and fine descaling is performed in the first finishing rolling pass. Depending on the plate shape and surface conditions, other descaling passes are added in the finishing rolling stage.

[0015] Furthermore, in step (3), the specific operation process of the rolling and controlled cooling process is as follows:

[0016] (3.1) The rolling method is to first roll the product longitudinally, then roll it to width, and finally roll it longitudinally to the finished product size;

[0017] (3.2) The forming and widening passes adopt a multi-pass small reduction rolling strategy, and the single-pass reduction is controlled to ≤15mm;

[0018] (3.3) After the widening is completed, the steel plate is driven to the intermediate billet cooling device in front of the machine, the upper nozzle of the device is opened, all the lower nozzles are closed, the upper nozzle is opened to the maximum flow rate, and water is passed through before reciprocating rolling; then the steel plate is driven to the rolling mill for rolling;

[0019] (3.4) The rough rolling and finishing rolling pass procedures are set according to the large pressure reduction. After the steel is turned, the speed difference between the upper and lower rolls is formed by adjusting the SKI parameters to suppress the buckle;

[0020] Among them, the roller speed ratio: lower roller speed / upper roller speed is 1.04-1.10;

[0021] (3.5) The pre-straightening machine is put into use to determine the plate shape and cooling conditions before entering the water;

[0022] (3.6) During cooling, control the water volume in the upper part of the cooling equipment to be greater than the water volume in the lower part to suppress the tendency of the plate to bend toward the stainless steel side.

[0023] Furthermore, in step (4), the plate shape correction is specifically as follows: after controlling the temperature of the steel plate to drop below 400°C, an online hot straightening machine or a warm straightening machine is used for straightening, and the straightening passes are ≥3 passes; during straightening, the temperature of the steel plate needs to be ≤400°C.

[0024] Beneficial effect: Compared with the prior art, the present invention does not need to modify the rolling mill through the implementation of this scheme. The existing equipment of the medium and thick plate rolling mill can be used to achieve the normal rolling of the single-layer stainless steel composite billet in the medium and thick plate rolling mill, ensuring that the rolling process will not cause rolling mill equipment accidents due to the billet buckling. The present invention can be used to produce thick-specification stainless steel composite plates with excellent performance and good plate shape. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with the embodiments.

[0026] The present invention provides a rolling process for a stainless steel composite plate, wherein: 1. The applicable billet requirements for the process are:

[0027] This process is suitable for stainless steel composite plates with austenitic stainless steel as the cladding material and carbon steel as the base material.

[0028] The stainless steel is austenitic stainless steel, and the steel grades are 304, 316, 304L, 316L, 317L, etc.

[0029] The base materials are container steel, structural steel, shipbuilding steel, bridge steel, etc.

[0030] Base-to-cover ratio = low alloy high strength steel thickness / stainless steel thickness ≥ 12, finished product size ≥ 40 mm.

[0031] The billet needs to be rolled on a single-stand or double-stand medium and thick plate mill.

[0032] Stainless steel and carbon steel are welded and vacuum treated using mature technology to prepare a vacuum composite billet of stainless steel + carbon steel.

[0033] The specific preparation steps are as follows:

[0034] 2. Heating process:

[0035] 2.1. Use a continuous heating furnace for heating. When loading the furnace, the stainless steel layer is placed on the lower side in contact with the roller and then heated in the furnace;

[0036] The stainless steel is placed on the lower side. During rolling, the bending of the billet toward the stainless steel side can be suppressed by the rollers in front and behind the rolling mill, thereby reducing the amount of buckle and facilitating rolling.

[0037] 2.2. Heating system:

[0038] The steel plate adopts a long-term high-temperature heating system, and the process is as shown in the following table. The thermal conductivity of austenitic stainless steel is lower than that of carbon steel, so the heating time must be extended to ensure the heating quality. Therefore, the lower limit of the heating time is set to 12 hours. At the same time, in order to prevent the heating time from being too long, considering the organizational performance characteristics of low-alloy high-strength steel, the total time in the furnace cannot exceed 18 hours; in addition, the heating temperature is set at 1200℃~1280℃. The difference in deformation resistance between austenitic stainless steel and carbon steel becomes smaller at high temperatures. Therefore, high-temperature heating is used under the premise of ensuring the performance of carbon steel, which can reduce the tendency of the steel plate to buckle;

[0039]

[0040] H is the blank thickness in mm.

[0041] 2.3. After the billet enters the soaking section, the heating intensity of the lower burner is increased and the heating intensity of the upper burner is decreased to form a temperature difference between the upper and lower surfaces of the composite billet, where the lower surface temperature - the upper surface temperature ≥ 30℃-50℃.

[0042] The reason for this setting: Since the stainless steel side is difficult to deform, by increasing the temperature of the stainless steel side, the deformation resistance of the stainless steel is reduced, the difference in deformation resistance between stainless steel and low-alloy high-strength steel is narrowed, and the difficulty of rolling is reduced.

[0043] 3. Descaling process:

[0044] The descaling box performs descaling normally. No fine descaling is performed in the forming pass, widening pass and the first two passes after widening. After the plate shape of the subsequent rough rolling pass is stable, descaling is performed manually one pass at a time. Fine descaling is performed in the first pass of finishing rolling. Other descaling passes are added in the finishing stage depending on the plate shape and surface conditions.

[0045] 4. Rolling and controlled cooling process

[0046] 4.1. The rolling method is to first roll the steel longitudinally to form the steel, then roll the steel wide, and finally roll the steel longitudinally to the finished product size:

[0047] The first longitudinal rolling is because the expansion coefficients of stainless steel and carbon steel are different during the heating process, and the billet will bend toward the carbon steel side. In addition, the thickness changes unevenly during the heating process. The first longitudinal rolling is used to level the thickness of the billet, which is beneficial to the subsequent widening accuracy control.

[0048] 4.2. The forming and widening passes adopt a multi-pass small reduction rolling strategy, and the single-pass reduction is controlled at ≤15mm; the widening pass is set as an odd pass to ensure that the steel plate is located in front of the machine after the widening is completed; the forming and widening passes adopt the method of adjusting the SKI parameters to form a speed difference between the upper and lower rolls within 500mm of the steel plate biting into the head, so that the lower roll speed is greater than the upper roll speed, thereby suppressing the buckle, and the lower roll speed / upper roll speed is 1.06~1.12;

[0049] 4.3. After widening, the steel plate is driven to the intermediate billet cooling device in front of the machine, the upper nozzle of the device is opened, all the lower nozzles are closed, the upper nozzle is opened to the maximum flow rate, and water is passed through before reciprocating rolling; then the steel plate is quickly driven to the rolling mill for rolling;

[0050] 4.4. The rough rolling and finishing rolling pass procedures are set according to the large pressure reduction. After the steel is transferred, the speed difference between the upper and lower rolls is formed by adjusting the SKI parameters to suppress the buckle. The roll speed ratio: the lower roll speed / upper roll speed is 1.04-1.10;

[0051] 4.5. The pre-straightening machine is put into use to ensure the plate shape before entering the water and to ensure uniform cooling;

[0052] 4.6. Since the shrinkage of stainless steel during cooling is greater than that of low alloy steel, the water volume at the upper part of the cooling equipment should be controlled to be greater than that at the lower part during cooling to suppress the tendency of the plate to bend toward the stainless steel side;

[0053] During controlled cooling, the height of the ultra-fast cooling upper frame is raised by 50mm compared to the conventional setting height to prevent equipment accidents caused by steel plate shape.

[0054] 5. Plate shape correction

[0055] After the temperature of the steel plate is controlled to drop below 400℃, an online hot straightener or warm straightener is used for straightening, with ≥3 straightening passes. During straightening, the temperature of the steel plate must be ≤400℃. Otherwise, if the temperature is higher than 400℃, the steel plate will deteriorate during the cooling process after high-temperature straightening due to the inconsistent shrinkage degree of stainless steel and carbon steel, thereby affecting the qualified rate of the rolled plate shape.

[0056] Embodiment 1:

[0057] Taking 4+60mm S31603+Q345B composite board as an example, the specific implementation method is explained.

[0058] The cladding material is made of austenitic stainless steel S31603, and the base material is low alloy high strength steel Q345B.

[0059] Base-to-cover ratio = low alloy high strength steel thickness / stainless steel thickness = 15

[0060] Stainless steel and carbon steel are welded and vacuum treated by vacuum electron beam welding to prepare a vacuum composite billet of S31603 stainless steel + Q345B low alloy high strength steel. The total thickness of the billet after combination is 320mm.

[0061] The billet is rolled on a 5m single-stand medium and thick plate mill.

[0062] 1. Heating process:

[0063] 1.1. Use a continuous heating furnace for segmented heating. When loading the furnace, the S31603 stainless steel layer is placed at the bottom for heating;

[0064] 1.2. Heating system:

[0065] The steel plate adopts a long-term high-temperature heating system, and the billet thickness is 320mm;

[0066]

[0067] H is the blank thickness, in mm;

[0068] 1.3. After the billet enters the soaking section, the heating intensity of the lower burner is increased and the heating intensity of the upper burner is decreased to form a temperature difference between the upper and lower surfaces of the composite billet, where the lower surface temperature is 35°C higher than the upper surface temperature.

[0069] 2. Descaling process:

[0070] The descaling box performs descaling normally. No fine descaling is performed in the forming pass, widening pass and the first two passes after widening. After the plate shape of the rough rolling pass is stable, descaling is performed manually one by one, and fine descaling is performed in the first pass of finishing rolling.

[0071] 3. Rolling and controlled cooling process:

[0072] 3.1. The rolling method is to first roll the steel longitudinally to form the steel, then roll the steel wide, and finally roll the steel longitudinally to the finished product size:

[0073] The first longitudinal rolling is performed because the thickness of the composite plate changes greatly during the heating process. The thickness of the blank is leveled by the first longitudinal rolling, which is beneficial to the control of the subsequent widening accuracy.

[0074] 3.2. The forming and widening passes adopt a multi-pass small reduction rolling strategy, and the single-pass reduction is controlled at ≤15mm; the widening pass is set as an odd pass to ensure that the steel plate is located in front of the machine after the widening is completed; the forming and widening passes adopt the method of adjusting the SKI parameters to form a speed difference between the upper and lower rolls within 500mm of the steel plate biting into the head, thereby suppressing the buckle, and the lower roll speed / upper roll speed is 1.06;

[0075] 3.3. After widening, the steel plate is driven to the intermediate billet cooling device in front of the machine, the upper nozzle of the device is opened, all the lower nozzles are closed, the upper nozzle is opened to the maximum flow rate, and water is pierced before reciprocating rolling; then it is quickly driven to the rolling mill for rolling; the rough rolling and finishing rolling pass procedures are set according to the large pressure reduction; after steel transfer, the SKI parameters are adjusted to form the upper and lower roll speed difference, thereby suppressing the buckle, and the lower roll speed / upper roll speed is 1.04;

[0076] 3.4. The pre-straightening machine is put into use to ensure the plate shape before entering the water;

[0077] 3.5. Since the shrinkage of stainless steel during cooling is greater than that of low alloy steel, the water volume at the upper part of the cooling equipment should be controlled to be greater than that at the lower part during cooling to suppress the tendency of the plate to bend toward the stainless steel side;

[0078] During controlled cooling, the height of the ultra-fast cooling upper frame is 50mm higher than the conventional setting height to prevent equipment accidents caused by steel plate shape;

[0079] 3.6. Plate shape correction

[0080] When the temperature of the steel plate is controlled to drop to 350℃, a warm straightening machine is used for straightening, and the straightening is performed for 5 times;

[0081] Through the implementation of the above-mentioned process measures, this embodiment realizes the normal rolling of 4+60mm S31603+Q345B on the medium and thick plate rolling mill. The rolling process is smooth, and there is no abnormal buckle head that causes rolling to be stopped. The interface of the composite plate is well bonded, the mechanical properties are excellent, and the rolled plate shape is flat.

[0082] Embodiment 2:

[0083] Taking 3+37mm S30403+Q345D composite board as an example, the specific implementation method is explained.

[0084] The cladding material is made of austenitic stainless steel S31603, and the base material is low alloy high strength steel Q345D.

[0085] Base-to-cover ratio = low alloy high strength steel thickness / stainless steel thickness = 12.3

[0086] Stainless steel and carbon steel are welded and vacuum treated by vacuum electron beam welding to prepare a vacuum composite billet of S30403 stainless steel + Q345D low alloy high strength steel. The total thickness of the billet after combination is 200mm.

[0087] The billet is rolled on a 3.8m double-stand medium and thick plate mill.

[0088] 1. Heating process:

[0089] 1.1. Use a continuous heating furnace for segmented heating. When loading the furnace, the S30403 stainless steel layer is placed at the bottom for heating;

[0090] 1.2 Heating system

[0091] The steel plate adopts a long-term high-temperature heating system, and the billet thickness is 200mm;

[0092]

[0093] H is the blank thickness, in mm;

[0094] After the billet enters the soaking section, the heating intensity of the lower burner is increased and the heating intensity of the upper burner is decreased, so that a temperature difference is formed between the upper and lower surfaces of the composite billet, wherein the lower surface temperature is 50°C higher than the upper surface temperature.

[0095] 2. Descaling process

[0096] The descaling box performs descaling normally. No fine descaling is performed in the forming pass, widening pass and the first two passes after widening. After the rough rolling pass is stable, the plate shape is manually descaled once, and fine descaling is performed in the first pass of finishing rolling.

[0097] 3. Rolling and controlled cooling process

[0098] 3.1. The rolling method is to first roll the steel longitudinally to form the steel, then roll the steel wide, and finally roll the steel longitudinally to the finished product size.

[0099] 3.2. The forming and widening passes adopt a multi-pass small reduction rolling strategy, and the single-pass reduction is controlled at ≤15mm; the widening pass is set as an odd pass to ensure that the steel plate is located in front of the machine after the widening is completed; the forming and widening passes adopt the method of adjusting the SKI parameters to form a speed difference between the upper and lower rollers within 500mm of the steel plate biting into the head, thereby suppressing the buckle, and the lower roller speed / upper roller speed is 1.10;

[0100] 3.3. After widening, the steel plate is driven to the intermediate billet cooling device in front of the machine, the upper nozzle of the device is opened, all the lower nozzles are closed, the upper nozzle is opened to the maximum flow rate, and water is pierced before reciprocating rolling; then it is quickly driven to the rolling mill for rolling; the rough rolling and finishing rolling pass procedures are set according to the large pressure reduction; after steel transfer, the SKI parameters are adjusted to form the upper and lower roll speed difference, thereby suppressing the buckle, and the lower roll speed / upper roll speed is 1.08;

[0101] 3.4. The pre-straightening machine is put into use to ensure the plate shape before entering the water;

[0102] 3.5. Since the shrinkage of stainless steel during cooling is greater than that of low alloy steel, the water volume at the upper part of the cooling equipment should be controlled to be greater than that at the lower part during cooling to suppress the tendency of the plate to bend toward the stainless steel side;

[0103] During controlled cooling, the height of the ultra-fast cooling upper frame is 50mm higher than the conventional setting height to prevent equipment accidents caused by steel plate shape;

[0104] 3.6. Plate shape correction

[0105] When the temperature of the steel plate is controlled to drop to 300℃, a warm straightening machine is used for straightening, with 5 straightening passes.

[0106] Through the implementation of the above-mentioned process measures, this embodiment realizes the normal rolling of 3+37mm S30403+Q345D on the medium and thick plate rolling mill. The rolling process is smooth, and there is no abnormal buckle that causes rolling to be stopped. The interface of the composite plate is well bonded, the mechanical properties are excellent, and the rolled plate shape is flat.

[0107] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A rolling process for a stainless steel composite plate, characterized in that: The cladding material is austenitic stainless steel S31603, and the base material is low alloy high strength steel Q345B; Base-to-cover ratio = low alloy high strength steel thickness / stainless steel thickness = 15; Stainless steel and low alloy high strength steel are welded and vacuum treated by vacuum electron beam welding to prepare a vacuum composite billet of S31603 stainless steel + Q345B low alloy high strength steel. The total thickness of the billet after assembly is 320mm. The billets are rolled on a 5m single-stand medium and heavy plate mill; The specific steps are as follows: (1) Heating process: (1.1) Use a continuous heating furnace for segmented heating. When loading the furnace, the S31603 stainless steel layer is placed at the bottom for heating; (1.2) Heating system: long-term high-temperature heating system; (1.3) After the billet enters the soaking section, the heating intensity of the lower burner is increased and the heating intensity of the upper burner is decreased to form a temperature difference between the upper and lower surfaces of the billet, where the lower surface temperature is 35°C higher than the upper surface temperature; (2) Descaling process: Descaling is done by descaling box. No fine descaling is done in the forming pass, widening pass and the first two passes after widening. After the rough rolling pass is stable, descaling is done manually. Fine descaling is done in the first pass of finishing rolling. (3) Rolling and controlled cooling process: (3.1) The first longitudinal rolling is used to form the product, followed by widening rolling, and finally longitudinal rolling to the finished product size: (3.2) The single pass reduction of the forming pass and the widening pass is controlled to ≤15mm; the widening pass is set to odd pass; The forming and widening passes use the SKI parameter adjustment method to form a speed difference between the upper and lower rollers within 500mm of the blank biting head, thereby suppressing buckling. The speed of the lower roller / the speed of the upper roller is 1.06; (3.3) After the widening is completed, the billet is moved to the intermediate billet cooling device in front of the machine, the upper nozzle of the device is opened, all the lower nozzles are closed, the upper nozzle is opened to the maximum flow rate, and water is passed before reciprocating rolling; Then it is quickly driven to the rolling mill for rolling; After steel transfer, the speed difference between the upper and lower rolls is formed by adjusting the SKI parameters to suppress buckling. The speed of the lower roll / the speed of the upper roll is 1.

04. (3.4) The pre-straightening machine is put into use to ensure the plate shape before entering the water; (3.5) During cooling, the water volume in the upper part of the cooling equipment should be greater than that in the lower part to prevent the plate from bending toward the stainless steel side; (3.6) Plate shape correction: When the temperature of the steel plate is controlled to drop to 350℃, a warm straightening machine is used for straightening for 5 times.

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