A method for producing thick homogeneous target plates by rolling

Abstract

The present invention relates to a method for producing a thick homogeneous target plate by rolling, comprising the following steps: smelting; die casting: casting molten steel to obtain a flat steel ingot or a plum blossom ingot with a unit weight of more than 20 tons; heating and blanking: heating the steel ingot, blanking and rolling it to an intermediate billet with a thickness of 350-600 mm; rolling: adopting single-stand rolling and full longitudinal rolling, the rolling process is divided into two stages: rough rolling and finishing rolling, the single-pass reduction rate of rough rolling is increased, the core microstructure and properties of the steel plate are improved, and the grains are fully refined; the starting rolling temperature of the finishing rolling is 830-950° C., the last pass is a leveling pass, and the reduction is ≤1 mm to control the plate shape; step five, quenching and tempering: obtaining a uniform tempered bainite structure through quenching and tempering; and step six, cutting: cutting the steel plate into the required size of the target plate. The target plate obtained according to the method has a low inclusion level and uniform performance. The finished product meets the requirements of high-level flaw detection standards such as GB / T2970-2016 Level I through ultrasonic testing, and is suitable for testing and accepting the penetration capability of armor-piercing projectiles.

Description

Technical Field

[0001] The invention relates to a rolling production method for thick steel plates, in particular to a production method for thick target plates. Background Art

[0002] With the rapid development of my country's cutting-edge military weaponry and defense industry, the research and development of anti-tank weapons, particularly armor-piercing projectiles, has achieved remarkable success. As the power of anti-tank weapons increases, the thickness of the target plates used to test their power must also increase accordingly. Thick target plates place stringent demands on material properties such as strength, elongation, impact toughness, reduction of area, and fracture grade. Furthermore, the target plates must exhibit uniform properties and minimize anisotropy.

[0003] In recent years, China has relied primarily on imports for homogeneous target plates used in acceptance testing of thick armored projectiles. These imported plates have high alloy content and are generally more expensive. Currently, only a few domestic companies have the capacity to produce these thick target plates, using a process that involves casting steel ingots and then forging them in a press.

[0004] Patent document CN108411074A discloses a process for preparing a quenched and homogeneous target plate. The process flow includes sequentially subjecting a steel ingot to press forging, annealing, machining, and quenching and tempering. The resulting quenched and homogeneous target plate has a uniform planar structure, uniform hardness, and low anisotropy in performance. However, the annealing process in the production method is relatively cumbersome, resulting in a long production cycle and complex heat treatment process. In addition, the use of ingot forging technology to produce target plates has the disadvantages of low production efficiency and high production costs compared to the current continuous casting and rolling steel plate production process. Summary of the Invention

[0005] In order to overcome the shortcomings of the existing production process, the present invention provides a method for producing a thick homogeneous target plate by rolling, which is used to produce a homogeneous target plate with a thickness of 200-450 mm.

[0006] The technical solution adopted by the present invention to solve the above problems is: a method for producing a thick homogeneous target plate by rolling, comprising:

[0007] Step 1, smelting process: molten iron and scrap steel raw materials are selected for primary refining, a dephosphorization agent is added to the primary refining slag for dephosphorization, alloying is carried out during the tapping process, and then the molten steel is sent to the LF furnace for refining. The alkaline reducing slag is used for desulfurization during the refining process. After LF refining, the molten steel is vacuum degassed, and the vacuum degree during the treatment is ≤133Pa, and the holding time is not less than 20 minutes. The light elements in the molten steel are reduced by vacuum. After the vacuum treatment, argon is blown and stirred for 10-15 minutes to promote the floating of inclusions in the molten steel. The final finished target plate has P≤0.015%, S≤0.005%, O≤15ppm, H≤2.0ppm, and N≤60ppm. The inclusions are evaluated according to GB / T10561-1989 standard, and the sum of the grades of A, B, C, and D inclusions is below grade 2.0;

[0008] Step 2: Die casting: Molten steel is cast into flat steel ingots or plum blossom ingots weighing more than 20t. After the ingots are uncapped, they are slowly cooled in the mold for 48 hours or more. After the slow cooling, the surface is cleaned to remove surface defects.

[0009] Step 3, heating and blanking: heating the steel ingot to a soaking temperature of 1220-1260°C for 4-6 hours, descaling the steel ingot with high-pressure water after it is taken out of the furnace, preferably using a descaling pressure of >20MPa, and rolling the first 4 passes of blanking with a reduction of ≥40mm per pass, rolling the intermediate blank to a thickness of 350-600mm, and slowly cooling the intermediate blank for more than 48 hours;

[0010] Step 4, rolling: single-stand rolling and full longitudinal rolling are adopted. The rolling process is divided into two stages: rough rolling and finishing rolling. The rough rolling adopts a low-speed and large-reduction process. The starting rolling temperature is 1050-1100°C, the rolling speed is controlled at 1.0-1.5m / s, and the reduction of each of the first three passes is ≥30mm. During the rolling process, the steel billet is descaled 3-5 times to remove the oxide layer on the surface of the steel plate; the starting rolling temperature of the finishing rolling is 830-950°C, at least the last pass is a leveling pass, and the reduction is ≤1mm to control the plate shape;

[0011] Step 5, quenching and tempering: quenching, quenching heating temperature 870-930℃, holding time 1.8-3.0min / mm, water quenching in a quenching water tank, quenching to water temperature; after quenching, tempering, tempering heating temperature 580℃-680℃, holding time 3.0-5.0min / mm, and then air cooling to room temperature to obtain a uniform tempered sorbite structure;

[0012] Step 6: Cutting: Cut the steel plate into the required size of the target plate.

[0013] Preferably, the above method is suitable for producing homogeneous target plates with a thickness of 200 to 450 mm.

[0014] Preferably, the superheat degree during the die casting in step 2 is 25-45° C., the thickness of the flat steel ingot is ≥950 mm, and the size of the plum blossom ingot is selected according to the thickness of the finished target plate, which should satisfy the rolling compression ratio of the target plate ≥3.0.

[0015] Preferably, in step three, the steel ingot is heated using a soaking furnace, with the heating rate in the low-temperature and medium-temperature sections being less than 80°C / h, and the high-temperature section being rapidly heated to the soaking temperature at a rate of more than 100°C / h, so that the alloy elements are fully dissolved, the uniformity of the performance of the finished target plate is improved, and the austenite grains are not excessively coarse.

[0016] Preferably, in step 1, the composition of the molten steel comprises, by mass percentage, C 0.20-0.40%, Si 0.10-0.70%, Mn 0.20-1.80%, Cr 0.50-2.50%, Ni 0-3.50%, Mo 0-1.0%, Nb 0-0.20%, V 0-0.20%, P≤0.020%, S≤0.010%, and the balance is iron and unavoidable impurity elements.

[0017] Compared with the prior art, the advantages of the present invention are:

[0018] The present invention controls the P and S impurity element contents, inclusion levels and gas content in molten steel through smelting processes such as electric arc furnace primary refining, LF refining and vacuum degassing, thereby obtaining molten steel with low residual elements and high molten steel cleanliness, thereby improving the material uniformity of the finished target plate.

[0019] The invention discloses a preparation process for producing homogeneous target plates of large thickness by a rolling method. The process adopts a steel ingot blanking and rolling process. A set of blooming mills can be used to produce steel blanks of various shapes and specifications. The process has the characteristics of flexible selection and change of blank specifications, and meets the blank requirements of finished target plates of various specifications.

[0020] The present invention is a preparation process for producing a thick homogeneous target plate by rolling, which adopts die casting, slab opening and rolling , quenching and tempering process. Through the cleaning and rolling process of steel ingots and intermediate billets, the flatness of the plate is ensured and the thickness of the finished product is within the tolerance range. No mechanical processing operations such as surface milling are required. reason Compared with the "preparation" process of quenching and tempering treatment, it does not require mechanical processing, has a simple production process and low production cost. At the same time, since the blanking process adopts low-speed and large-reduction rolling technology, the pass deformation permeability is improved, which is conducive to eliminating defects such as looseness and shrinkage holes in the core of the steel plate. The metallographic structure and density of the finished target plate are comparable to those of the thick target plate forged by a press, achieving the effect of "rolling instead of forging".

[0021] The finished target plate of the present invention meets the requirements of high-level flaw detection standards such as GB / T2970-2016 standard Level I through ultrasonic testing, and meets the fracture level requirements of fibrous level 2, slate level 1, and layered level 1 according to the GJB 31A-2000 standard. It can meet the use requirements of armor-piercing projectile test acceptance and is conducive to the domestic substitution of large-thickness homogeneous target plates. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below with reference to the examples. The examples are illustrative and intended to explain the present invention, but are not to be construed as limiting the present invention.

[0023] Example 1:

[0024] The chemical composition and weight percentage of the homogeneous target plate of Example 1 are: C: 0.30%, Si: 0.35%, Mn: 1.30%, Cr: 1.00%, Mo: 0.71%, Al: 0.025%, Re: 0.08%, P: 0.010%, S: 0.003%, O: 0.0013%, N: 0.0053%, H: 0.00015%, the balance is Fe and unavoidable impurity elements, and the total grade of A, B, C, and D inclusions is 2.0.

[0025] The target plate size is 320mm*1200mm*1500mm, and its preparation process is as follows:

[0026] (1) Smelting process: High-quality molten iron and scrap steel are selected for smelting in an electric arc furnace. A dephosphorization agent is added to the slag for dephosphorization. The steel is alloyed during the tapping process and then refined in an LF furnace. The LF process removes sulfur through alkaline reducing slag. After LF refining, the molten steel undergoes VD vacuum degassing treatment. The vacuum degree during the treatment is ≤133Pa and maintained for 20 minutes. The vacuum method reduces the solubility of gas in the molten steel, thereby reducing the gas content in the molten steel. After the vacuum treatment, soft argon blowing is carried out for 15 minutes to promote the floating of inclusions in the molten steel. The final target plate has P 0.010%, S 0.003%, O 13ppm, H 1.5ppm, and N 53ppm. The inclusion rating is carried out in accordance with GB / T10561-1989 standard. The total level of inclusions A, B, C, and D is 2.0.

[0027] (2) Mold casting process: The oxidation of molten steel is reduced by argon protection pouring technology, and the superheat is controlled at 25-38 ° C to obtain a 25t single weight plum blossom ingot with the upper and lower opening dimensions ≥1350mm. The plum blossom ingot is slowly cooled with the mold for 52 hours, and the surface of the steel ingot is cleaned after slow cooling.

[0028] (3) Heating and blanking process: The steel ingot is heated in a soaking furnace. The heating rate in the low and medium temperature sections is less than 80°C / h. The high temperature section is rapidly heated to 1235°C at a rate of 100°C / h and kept at this temperature for 6 hours. This allows the alloying elements to be fully dissolved, improving the uniformity of the finished target plate performance while also ensuring that the austenite grains are not excessively coarse. After the steel ingot is heated and removed from the furnace, it is descaled with high-pressure water at a descaling pressure of 21 MPa and then rolled into a 500mm thick intermediate billet.

[0029] (4) Rolling process: Single-stand rolling and full longitudinal rolling are adopted. The rolling process is divided into two stages: rough rolling and finishing rolling. Rough rolling adopts a low-speed large reduction process, with a starting rolling temperature of 1060℃ and a rolling speed controlled at 1.0-1.3m / s. The reduction in the first three passes is ≥40mm, which improves the core structure and properties of the steel plate and fully refines the grains. High-pressure water descaling is used in the first three passes and the last pass of rolling to remove the iron oxide scale on the surface of the steel plate. The starting rolling temperature of finishing rolling is 930℃, and the last pass is a flattening pass with a reduction of ≤1mm to ensure the shape of the steel plate.

[0030] (5) Quenching and Tempering Process: Quenching heating temperature 910°C, holding time 3.0 min / mm. The steel plate is quenched in a quenching water tank with water as the quenching medium, and quenched to water temperature. The steel plate is tempered in a trolley furnace with tempering heating temperature 615°C, holding time 4 min / mm, and then air-cooled to room temperature. Through quenching and tempering heat treatment, a uniform tempered bainite structure is obtained.

[0031] (6) Cutting process: Use sawing to cut the steel plate into the required size of the target plate.

[0032] The properties of the homogeneous target plate produced using the above method are as follows:

[0033] The Brinell hardness is 265HBW, the Charpy impact energy at -40℃ is 43J, and the fracture grade is tested according to GJB 31A-2000 standard. The test results are fibrous grade 2, slate grade 1, and stratified grade 1. The flaw detection meets the requirements of Grade I in GB / T 2970-2016 and meets the requirements for target plate acceptance and use.

[0034] Example 2

[0035] The chemical composition and weight percentage of the homogeneous target plate of Example 2 are: C: 0.29%, Si: 0.32%, Mn: 1.35%, Cr: 1.06%, Mo: 0.768%, Al: 0.020%, Re: 0.07%, P: 0.012%, S: 0.003%, O: 0.0012%, N: 0.0050%, H: 0.00013%, the balance is Fe and unavoidable impurity elements, and the total grade of A, B, C, and D inclusions is 2.0.

[0036] The target plate size is 280mm*1200mm*1500mm, and its preparation process is as follows:

[0037] (1) Smelting process: High-quality molten iron and scrap steel are selected for smelting in an electric arc furnace. A dephosphorization agent is added to the slag for dephosphorization. During the tapping process, part of the alloy is added to the molten steel, and then the molten steel is refined in an LF furnace. In the LF process, desulfurization is carried out by making alkaline reducing slag. After the LF process, the molten steel undergoes VD vacuum degassing treatment. The vacuum degree during the treatment is ≤133Pa and maintained for 20 minutes. The vacuum method reduces the solubility of the gas in the molten steel, thereby reducing the gas content in the molten steel. After the vacuum treatment, soft argon is blown for 15 minutes to promote the floating of inclusions in the molten steel. The final target plate has P 0.012%, S 0.003%, O 12ppm, H 1.3ppm, and N 50ppm. The inclusion rating is carried out in accordance with GB / T10561-1989 standard, and the total level of inclusions of types A, B, C, and D is 2.0.

[0038] (2) Mold casting process: The oxidation of molten steel is reduced by argon protection pouring technology, and the superheat is controlled at 25-38 ° C to obtain a flat steel ingot with an upper thickness of 990 mm. The steel ingot is slowly cooled with the mold for 52 hours, and the surface of the steel ingot is cleaned after slow cooling.

[0039] (3) Heating and blanking process: The steel ingot is heated in a soaking furnace. The heating rate in the low and medium temperature sections is less than 80℃ / h. The high temperature section is rapidly heated to 1240℃ at a rate of 100℃ / h and kept at this temperature for 5.5 hours. This allows the alloy elements to be fully dissolved, improving the uniformity of the finished target plate performance while also ensuring that the austenite grains are not excessively coarse. After the steel ingot is heated and removed from the furnace, it is descaled with high-pressure water at a descaling pressure of 21 MPa and then rolled into a 450mm thick intermediate billet.

[0040] (4) Rolling process: Single-stand rolling and full longitudinal rolling are adopted. Rolling is divided into two stages: rough rolling and finishing rolling. Rough rolling adopts low-speed and large reduction process, with the starting rolling temperature of 1060℃ and the rolling speed controlled at 1.0-1.3m / s. The reduction of each of the first three passes is ≥40mm, which improves the core structure and properties of the steel plate and fully refines the grains. High-pressure water descaling is used in the first three passes of the rolling stage to remove the iron oxide scale on the surface of the steel plate. The starting rolling temperature of finishing rolling is 920℃, and the last pass is a flattening pass with a reduction of ≤1mm to ensure the shape of the steel plate.

[0041] (5) Quenching and Tempering Process: Quenching heating temperature 910°C, holding time 2.5 min / mm. The steel plate is quenched in a quenching water tank with water as the quenching medium, and quenched to water temperature. The steel plate is tempered in a trolley furnace with tempering heating temperature 620°C, holding time 4.0 min / mm, and then air-cooled to room temperature. Through quenching and tempering heat treatment, a uniform tempered bainite structure is obtained.

[0042] (6) Cutting process: Use sawing to cut the steel plate into the required size of the target plate.

[0043] The properties of the homogeneous target plate produced using the above method are as follows:

[0044] The Brinell hardness is 273HBW, the Charpy impact energy at -40℃ is 49J, and the fracture grade is tested according to GJB 31A-2000 standard. The test results are fibrous grade 1, slate grade 2, and stratified grade 1. The flaw detection meets the requirements of Grade I in GB / T 2970-2016 and meets the requirements for target plate acceptance and use.

[0045] Example 3

[0046] The chemical composition and weight percentage of the homogeneous target plate of Example 3 are: C: 0.30%, Si: 0.36%, Mn: 1.28%, Cr: 1.02%, Mo: 0.71%, Al: 0.023%, Re: 0.06%, P: 0.011%, S: 0.004%, O: 0.0012%, N: 0.0048%, H: 0.00016%, the balance is Fe and unavoidable impurity elements, and the total grade of A, B, C, and D inclusions is 2.0.

[0047] The target plate size is 220mm*1200mm*1500mm, and its preparation process is as follows:

[0048] (1) Smelting process: High-quality molten iron and scrap steel are selected for smelting in an electric arc furnace. A dephosphorization agent is added to the slag for dephosphorization. During the tapping process, part of the alloy is added to the molten steel, and then the molten steel is refined in an LF furnace. In the LF process, desulfurization is carried out by making alkaline reducing slag. After the LF process, the molten steel undergoes VD vacuum degassing treatment. The vacuum degree during the treatment is ≤133Pa and maintained for 22 minutes. The vacuum method reduces the solubility of the gas in the molten steel, thereby reducing the gas content in the molten steel. After the vacuum treatment, soft argon is blown for 14 minutes to promote the floating of inclusions in the molten steel. The final target plate has P 0.011%, S 0.004%, O 12ppm, H 1.6ppm, and N 48ppm. The inclusion rating is carried out in accordance with GB / T10561-1989 standard, and the total level of inclusions of types A, B, C, and D is 2.0.

[0049] (2) Mold casting process: The oxidation of molten steel is reduced by argon protection pouring technology, and the superheat is controlled at 25-38 ° C to obtain a flat steel ingot with a thickness of 990 mm. The steel ingot is slowly cooled in the mold for 50 hours, and the surface of the steel ingot is cleaned after slow cooling.

[0050] (3) Heating and blanking: The steel ingot is heated in a soaking furnace. The heating rate in the low and medium temperature sections is less than 80°C / h. The high temperature section is rapidly heated to 1230°C at a rate of 100°C / h and kept at this temperature for 5 hours. This allows the alloying elements to be fully dissolved, improving the uniformity of the finished target plate performance while also ensuring that the austenite grains are not excessively coarse. After the steel ingot is heated and removed from the furnace, it is descaled using high-pressure water at a descaling pressure of 20 MPa and then rolled into a 450mm thick intermediate billet.

[0051] (4) Rolling: Single-stand rolling and full longitudinal rolling are adopted. The rolling process is divided into two stages: rough rolling and finishing rolling. Rough rolling adopts a low-speed large reduction process, with a starting rolling temperature of 1070℃ and a rolling speed controlled at 1.0-1.4m / s. The reduction of each of the first three passes is ≥30mm to improve the core structure and properties of the steel plate and fully refine the grains. High-pressure water descaling is used in the first three passes of rolling to remove the iron oxide scale on the surface of the steel plate. The starting rolling temperature of finishing rolling is 910℃, and the last pass is a flattening pass with a reduction of ≤1mm to ensure the shape of the steel plate.

[0052] (5) Quenching and Tempering: Quenching temperature: 910°C, holding time: 2.3 min / mm. The steel plate is quenched in a quenching water tank with water as the quenching medium, and quenched to water temperature. Tempering temperature: 630°C, holding time: 3.5 min / mm, followed by air cooling to room temperature. The steel plate is tempered in a trolley furnace.

[0053] (6) Cutting process: Use sawing to cut the steel plate into the required size of the target plate.

[0054] The properties of the homogeneous target plate produced using the above method are as follows:

[0055] The Brinell hardness is 285HBW, the Charpy impact energy at -40℃ is 63J, and the fracture grade is tested according to GJB 31A-2000 standard. The test results are fibrous grade 1, slate grade 2, and stratified grade 1. The flaw detection meets the requirements of Grade I in GB / T 2970-2016, and meets the requirements for target plate acceptance and use.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for producing a thick homogeneous target plate by rolling, characterized in that: include, Step 1, smelting process: The composition of molten steel includes C 0.20-0.40%, Si 0.10-0.70%, Mn 0.20-1.80%, Cr 0.50-2.50%, Ni 0-3.50%, Mo 0-1.0%, Nb 0-0.20%, V 0-0.20%, P≤0.020%, S≤0.010%, the balance is iron and inevitable impurity elements, molten iron and scrap steel are used for primary refining, and a dephosphorizing agent is added to the slag of the primary refining for dephosphorization. The steel is alloyed during the tapping process, and then the molten steel is sent to the LF furnace for refining. The alkaline reducing slag is used for desulfurization during the refining process. After LF refining, the molten steel is vacuum degassed with a vacuum degree of ≤133Pa during the treatment, and the holding time is not less than 20min. The light elements in the molten steel are reduced by vacuum. After the vacuum treatment, argon is blown and stirred for 10-15min to promote the floating of inclusions in the molten steel. The final target plate contains P≤0.015%, S≤0.005%, O≤15ppm, H≤2.0ppm, and N≤60ppm. The inclusions are evaluated according to GB / T10561-1989 standard, and the sum of the grades of A, B, C, and D inclusions is below grade 2.

0. Step 2: Die casting: Molten steel is cast into flat steel ingots or plum blossom ingots weighing more than 20t. After the ingot is removed from the cap, it is slowly cooled in the mold for a cooling time of ≥48 hours. After the cooling, the surface is cleaned to remove surface defects. Step 3, heating and blanking: heating the steel ingot to a soaking temperature of 1220-1260°C for 4-6 hours, descaling the steel ingot with high-pressure water after it is taken out of the furnace, and rolling the first 4 passes of blanking with a reduction of ≥40mm per pass to an intermediate billet of 350-600mm in thickness, and slow cooling the intermediate billet for more than 48 hours; Step 4, rolling: single-stand rolling and full longitudinal rolling are adopted. The rolling process is divided into two stages: rough rolling and finishing rolling. The rough rolling adopts a low-speed and large-reduction process. The starting rolling temperature is 1050-1100°C, the rolling speed is controlled at 1.0-1.5m / s, and the reduction of each of the first three passes is ≥30mm. During the rolling process, the steel billet is descaled 3-5 times to remove the surface oxide layer; the starting rolling temperature of the finishing rolling is 830-950°C, at least the last pass is a leveling pass, and the reduction is ≤1mm to control the plate shape; Step 5, quenching and tempering: quenching, quenching heating temperature 870-930℃, holding time 1.8-3.0min / mm, water quenching in a quenching water tank, quenching to water temperature; tempering after quenching, tempering heating temperature 580℃-680℃, holding time 3.0-5.0min / mm, and then air cooling to room temperature to obtain a uniform tempered bainite structure. The finished target plate meets the requirements of high-level flaw detection standards such as GB / T2970-2016 Level I by ultrasonic testing, and meets the fracture level requirements of fibrous level 2, slate level 1, and layered level 1 according to GJB 31A-2000 standard. Step 6: Cutting: Cut the steel plate into the required size of the target plate.

2. The method according to claim 1, wherein: Suitable for producing homogeneous target plates with a thickness of 200-450mm.

3. The method according to claim 1, wherein: Step 2: The superheat during die casting is 25-45°C, the thickness of the flat steel ingot is ≥950mm, and the size of the plum blossom ingot is selected according to the thickness of the finished target plate, which should meet the rolling compression ratio of the target plate ≥3.

0.

4. The method according to claim 1, wherein: Step 3: Use a soaking furnace to heat the steel ingot. The heating rate in the low-temperature and medium-temperature sections is less than 80°C / h, and the high-temperature section is heated to the soaking temperature at a rate of more than 100°C / h to allow the alloy elements to be fully dissolved and the austenite grains to be not too coarse.