A high-performance quenched and tempered homogenized target plate and its manufacturing method

Abstract

The present invention relates to a high-performance quenched and tempered homogeneous target plate and a manufacturing method thereof. The chemical composition, by mass percentage, is C: 0.25-0.35%, Si: 0.18-0.38%, Mn: 0.25-0.55%, Cr: 1.60-2.40%, Ni: 1.60-2.40%, Mo: 0.25-0.45%, Al: 0.015-0.045%, Nb+V+Ti≤0.12%, P: ≤0.013%, S: ≤0.005%, O: ≤0.002%, H: ≤0.0002%, and the balance is Fe and unavoidable impurity elements. The manufacturing process is EAF electric furnace smelting, LF refining, VD vacuum degassing, die casting, cogging, rolling, quenching and tempering, and shearing. The homogeneous target plate manufactured by the present invention has a thickness of 150-180 mm and has the characteristics of high strength, good toughness, uniform composition and performance, low segregation, and small thickness tolerance. It can be used to test the armor-piercing power of different types of armor-piercing projectiles.

Description

Technical Field

[0001] The invention belongs to the technical field of special steel smelting, and particularly relates to a high-performance quenched and tempered homogenized target plate and a manufacturing method thereof. Background Art

[0002] In range testing of anti-tank ammunition, target plates serve as targets for evaluating the performance of armor-piercing, high-explosive, and fragmentation rounds and warheads. Target plates are categorized by material into metallic and non-metallic types. They are also categorized by armor structure into single-layer, spaced, composite, spaced-composite, and reactive armor types. Single-layer targets are divided into homogeneous and heterogeneous types, depending on whether their mechanical properties or chemical composition are consistent across their thickness.

[0003] The quality of homogeneous target plate is one of the important factors affecting the results of armor-piercing power test. It places certain requirements on the mechanical properties, size and shape of the material, and requires uniform performance and small anisotropy.

[0004] The invention patent, "A Process for Preparing a Quenched and Tempered Homogeneous Target Plate," with publication number CN108411074B, describes a process that involves sequentially subjecting a steel ingot to press forging, annealing, machining, and quenching and tempering. The resulting quenched and tempered homogeneous target plate exhibits uniform planar structure, uniform hardness, and minimal anisotropy in performance. This patent describes a process for producing a quenched and tempered homogeneous target plate, but does not describe the chemical composition and performance indicators of the homogeneous target plate, nor does it specify requirements for target plate flatness. Furthermore, the production process described in this patent is characterized by a long cycle and complex procedures. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a high-performance tempered homogenized target plate and a manufacturing method thereof in view of the above-mentioned prior art, which has the characteristics of high strength, excellent toughness, uniform performance, low production cost and short processing cycle.

[0006] The technical solution adopted by the present invention to solve the above problems is: a high-performance tempered homogenized target plate, characterized in that the chemical composition of the target plate is as follows by mass percentage: C: 0.25-0.35%, Si: 0.18-0.38%, Mn: 0.25-0.55%, Cr: 1.60-2.40%, Ni: 1.60-2.40%, Mo: 0.25-0.45%, Al: 0.015-0.045%, Cu: ≤0.20%, Nb+V+Ti≤0.12%, P: ≤0.013%, S: ≤0.005%, O: ≤0.002%, H: ≤0.0002%, and the balance is Fe and unavoidable impurity elements.

[0007] The target plate of the present invention has a thickness of 150-180 mm and an unevenness of ≤4 mm / m.

[0008] The metallographic structure of the target plate at 1 / 4 and 1 / 2 thickness and near the surface is uniform tempered troostite.

[0009] According to tests, the target plate of the present invention has a hardness of 241-302 HBW, a yield strength of 680-800 MPa, an elongation of ≥10%, a cross-sectional shrinkage of ≥50%, and a 20° C. Charpy U-shaped impact energy of ≥90 J.

[0010] The reasons why the present invention adopts the above-mentioned components and their weight percentages are described in detail below:

[0011] C: As a solid solution element, C can improve the strength and hardness of steel and increase its hardenability. However, too high a C content can reduce the plasticity and impact toughness of the steel. Therefore, the C content of the present invention is preferably controlled at 0.25-0.35%.

[0012] Si: Si acts as a reducing agent and deoxidizer during the steelmaking process, and also improves the strength of steel through solid solution strengthening. However, excessive Si content increases cold crack sensitivity and reduces the surface quality of the steel plate. In the present invention, the Si content is controlled within a range of 0.18-0.38%.

[0013] Mn: Mn is a weak deoxidizer in the steelmaking process and can also improve steel strength through solid solution strengthening. However, excessive Mn content can easily lead to segregation in the core of the steel plate. This segregation can worsen toughness and affect the uniformity of the steel plate as a whole. Therefore, the Mn content in this invention is controlled to 0.25-0.55%.

[0014] Cr: Cr is an element that improves the hardenability of steel, enhancing its strength, hardness, wear resistance, and corrosion resistance. Its primary function in quenched and tempered steel is to enhance hardenability, resulting in better overall mechanical properties after quenching and tempering. The Cr content in this invention is controlled within a range of 1.60 to 2.40%.

[0015] Ni: Ni is a solid solution strengthener in steel and a good hardenability additive, which can increase the strength of steel. Ni also has a beneficial effect on impact toughness and the ductile-brittle transition temperature. Therefore, the Ni content of the present invention is controlled to be 1.60-2.40%.

[0016] Mo: Mo significantly improves the strength and hardenability of steel, particularly its tempering stability. Adding a certain amount of Mo to low-alloy steel increases its strength without degrading its low-temperature impact properties. This helps produce fine-grained tempered bainite after quenching and tempering, improving the toughness of the steel plate. In the present invention, the Mo content is controlled between 0.25% and 0.45%.

[0017] Nb, V, and Ti: Nb, V, and Ti are microalloying elements, primarily responsible for refining austenite grain size. Nb refines grains through solid solution strengthening and strain-induced precipitation strengthening, thereby improving the strength and toughness of steel, making it the preferred element for controlled rolling. V, an element that causes V (C, N) precipitation, can significantly enhance steel strength through dispersed precipitation. Ti, an effective element for fixing N and C, refines the original austenite grains and can also dissolve in austenite to form a solid solution, strengthening the steel. The present invention prioritizes grain refinement, and considering all factors, the total Nb, V, and Ti content is controlled to ≤0.12%.

[0018] P: P is an impurity element in steel that easily forms intergranular segregation and makes the steel prone to brittle cracks, which has an adverse effect on the toughness of high-strength steel plates. Its content should be reduced as much as possible. In the present invention, P is controlled to be ≤0.013%.

[0019] S: S is generally a harmful element in steel. It easily exists in the form of sulfide inclusions in steel, reducing the ductility and toughness of the steel. In the present invention, the S content is controlled to be no more than 0.005%.

[0020] H and O: H and O are harmful gas elements in the steel of the present invention. High content of H and O will cause many inclusions and processing cracks. The lower the content, the better. In the present invention, the O content is controlled to be no higher than 0.0020%; the H content is ≤ 0.0002%.

[0021] The manufacturing method of the high-performance tempered homogeneous target plate mainly comprises the following steps:

[0022] (1) Smelting and pouring: Scrap steel and part of molten iron are used as raw materials for electric furnace steelmaking. The smelted raw materials are sequentially smelted in an EAF electric furnace, refined in LF, and vacuum degassed in VD, and then cast into steel ingots with chemical composition that meets the requirements. The superheat of the molten steel casting process is controlled at 15-45°C, and argon protection is used throughout the process. Flat steel ingots with a thickness of ≥900mm and a single ingot weight of ≥35 tons are cast. The ingots are slowly cooled in the mold for ≥24 hours and then the cap is removed. After the cap is removed, the ingots are cleaned while still warm, with the cleaning temperature ≥100°C.

[0023] (2) Billeting: The steel ingot is heated in stages in a soaking furnace to 1220-1260°C and then held at this temperature for 2-4 hours. After being removed from the furnace, it is descaled with high-pressure water and then rolled into intermediate billets with a thickness of 370-450mm in the blooming mill. The first 2-3 passes of billet rolling are widening passes, and after widening, the steel is transferred to the rolling mill.

[0024] (3) Rolling: The intermediate billet is heated in a step-beam heating furnace to 1220-1260°C for 12-15 min / cm2 to fully dissolve the alloying elements in the steel and ensure the uniformity of the composition and performance of the finished product. After the intermediate billet leaves the heating furnace, it is descaled with high-pressure water and then rolled. The starting rolling temperature is controlled at 1030-1100°C. The reduction of each pass in the first three passes is 30mm-50mm, and the final rolling temperature is 800-900°C. The last 1-2 passes of rolling are leveling passes to ensure the flatness of the steel plate. After rolling, the steel plate is removed from the production line at a surface temperature of ≥500°C. After removal from the production line, it is placed in a slow cooling pit or covered with a hood for slow cooling, and the slow cooling time is ≥48 hours.

[0025] (4) Heat treatment: The steel plate after slow cooling is subjected to normalizing, quenching and tempering heat treatment in sequence. Normalizing is to achieve uniform structure and reduce the degree of segregation of the steel plate. Quenching obtains martensite structure, which improves the strength and hardness of the steel plate. After tempering, tempered bainite structure is obtained, and quenching residual stress is eliminated. Normalizing temperature is 880-900℃, holding time coefficient is 2.2-2.5min / mm, and air cooling is performed. Quenching heating for quenching and tempering treatment is carried out in a continuous furnace, quenching temperature is 880-900℃, holding time coefficient is 2.5-3.0min / mm, and water quenching is performed in a quenching machine until the surface temperature of the steel plate out of water is ≤100℃, and then air cooling is performed to room temperature. Tempering treatment is also carried out in a continuous furnace, tempering temperature is 600-660℃, holding time coefficient is 3.0-4.0min / mm, and air cooling is performed to room temperature after leaving the furnace.

[0026] (5) Shearing: According to the size requirements of the finished target plate, the steel plate is cut into the required size by sawing or flame cutting.

[0027] Compared with the prior art, the advantages of the present invention are:

[0028] The composition design of the present invention adopts medium carbon and Cr+Ni+Mo alloy composition design to improve the strength, hardness, toughness and wear resistance of the steel, while matching the Nb+V+Ti microalloying composition design to give full play to the precipitation strengthening and fine grain strengthening effects, thereby obtaining a high-performance target plate.

[0029] The present invention sets the first 3-5 rolling passes as widening passes in the slab opening stage, and performs steel transfer rolling after widening to improve the flatness of the intermediate slab. The last 1-2 rolling passes are set as leveling passes to improve the flatness of the steel plate and ensure that the unevenness of the finished target plate is ≤4mm / m.

[0030] The present invention arranges a normalizing process before the quenching process in the heat treatment stage, reduces the segregation of alloy elements, improves the composition and performance uniformity of the target plate after quenching and tempering, and thus significantly improves the performance of the product. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be described in more detail with reference to the preferred embodiments of the present invention. However, these embodiments are merely descriptions of preferred implementations of the present invention and do not limit the scope of the present invention in any way.

[0032] Example 1-3:

[0033] According to the chemical composition range and manufacturing method of the present invention, high-performance, quenched and tempered homogeneous target plates with a thickness of 150-180 mm are manufactured through the steps of EAF electric furnace smelting, LF refining, VD vacuum degassing, die casting, cogging, rolling, heat treatment, and shearing. The specific compositions of the target plates in each example are shown in Table 1.

[0034] The specific process of the above-mentioned manufacturing method is:

[0035] (1) Smelting and pouring: Scrap steel and part of molten iron are used as raw materials for electric furnace steelmaking. The smelted raw materials are sequentially smelted in an EAF electric furnace, refined in LF, and vacuum degassed in VD, and then cast into steel ingots with chemical composition that meets the requirements. The superheat of the molten steel casting process is controlled at 20-45°C, and argon protection is used throughout the process. Flat steel ingots with a thickness of ≥900 mm and a single ingot weight of ≥35 tons are cast. The ingots are slowly cooled in the mold for ≥48 hours and then decapped. After decapping, the ingots are cleaned while still warm, with the cleaning temperature being ≥100°C. The smelting and pouring process parameters of each embodiment are shown in Table 2.

[0036] (2) Blooming: The steel ingot is heated in stages in a soaking furnace to 1220-1260°C and then held at that temperature for 3 hours. After being removed from the furnace, it is descaled with high-pressure water and then slabbed into intermediate billets with a thickness of 450-550 mm in the blooming mill. The first 3-5 passes of blooming are widening passes, and after widening, transfer rolling is performed.

[0037] (3) Rolling: The intermediate billet is heated in a step-beam heating furnace to 1220-1260°C for 12-15 min / cm2 to fully dissolve the alloying elements in the steel and ensure the uniformity of the composition and performance of the finished product. After leaving the heating furnace, the intermediate billet is descaled with high-pressure water and then rolled to avoid the impact of iron oxide scale on the surface quality of the steel plate during rolling. The starting rolling temperature is controlled at 1030-1100°C. The reduction of each pass in the first three passes is 30mm-50mm, and the final rolling temperature is 800-900°C. After rolling, the steel plate is removed from the production line when the surface temperature is ≥500°C. After removal from the production line, it is placed in a slow cooling pit or covered with a hood for slow cooling, and the slow cooling time is ≥48 hours. The rolling process parameters of each embodiment are shown in Table 3.

[0038] (5) Heat treatment: The steel plate after slow cooling is subjected to normalizing, quenching and tempering heat treatment in sequence. Normalizing is to achieve uniform structure and eliminate segregation. Quenching obtains martensite structure, and tempering obtains tempered bainite structure. Normalizing heating temperature is 880-900℃, holding time coefficient is 2.2-2.5min / mm, and air cooling is performed. Quenching heating for quenching and tempering treatment is performed in a continuous furnace, quenching temperature is 880-900℃, holding time coefficient is 2.5-3.0min / mm, water quenching is performed in a quenching machine to a surface temperature of 70-80℃ at the outlet of the water, and then air cooling is performed to room temperature. Tempering treatment is also performed in a continuous furnace, tempering temperature is 620-640℃, holding time coefficient is 3-4min / mm, and air cooling is performed to room temperature after leaving the furnace. The heat treatment process parameters of each embodiment are shown in Table 4.

[0039] (6) Shearing: Cut the steel plate into the required size according to the size requirements of the finished target plate.

[0040] Table 1 Chemical composition of homogeneous target plates of Examples 1-3 (wt%)

[0041] C To Mn P S Cr In Al Know In Nb+V+Ti H O 0.28 0.25 0.36 0.008 0.003 1.95 1.90 0.028 0.36 2.9 0.12 0.00015 0.0012 0.29 0.27 0.35 0.007 0.003 1.90 2.02 0.030 0.35 2.88 0.13 0.00016 0.0010 0.30 0.26 0.34 0.008 0.002 1.98 1.96 0.026 0.35 2.89 0.11 0.00014 0.0013

[0042] Table 2 Process parameters of homogeneous target plate smelting and casting process of Examples 1-3

[0043]

[0044] Table 3 Process parameters of the homogeneous target plate rolling process of Example 1-3

[0045]

[0046] Table 4 Process parameters of heat treatment process of homogeneous target plate of Example 1-3

[0047]

[0048]

[0049] Table 5: Roughness, tensile and impact properties of homogenized target plates in implementation 1-3

[0050]

[0051] Although the preferred embodiments of the present invention have been described in detail above, it should be clearly understood that various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A method for manufacturing a high-performance quenched and tempered homogeneous target plate, characterized in that The target plate has a chemical composition of C: 0.25-0.35%, Si: 0.18-0.38%, Mn: 0.25-0.45%, Cr: 1.60-2.40%, Ni: 1.60-2.40%, Mo: 0.25-0.45%, Al: 0.015-0.045%, Nb+V+Ti≤0.12%, P:≤0.013%, S:≤0.005%, O:≤0.002%, H:≤0.0002%, and the balance is Fe and unavoidable impurity elements; the target plate has a thickness of 150-180 mm and an unevenness of ≤4 mm / m. The method comprises the following steps: 1) Smelting and pouring: Scrap steel and part of molten iron are used as raw materials for electric furnace steelmaking. The raw materials are sequentially smelted in an EAF furnace, refined in LF, and vacuum degassed in VD, and then cast into steel ingots with chemical composition that meets the requirements; 2) Billeting: The steel ingot is heated in stages in a soaking furnace to 1220-1260°C and then kept at this temperature for 2-4 hours. After being removed from the furnace, it is descaled with high-pressure water. After descaling, the steel ingot is split into intermediate billets with a thickness of 370-450mm in the blooming mill. 3) Rolling: The intermediate billet is heated in a walking beam heating furnace to 1220-1260°C for 12-15 min / cm2 to fully dissolve the alloying elements in the steel and ensure the uniformity of the composition and performance of the finished product. After leaving the heating furnace, the intermediate billet is descaled with high-pressure water and then rolled. 4) Heat treatment: The steel plate after slow cooling is subjected to normalizing, quenching and tempering heat treatment in sequence. Normalizing is to achieve uniform structure and reduce the degree of segregation of the steel plate; quenching obtains martensite structure to improve the strength and hardness of the steel plate; tempering obtains tempered bainite structure and eliminates quenching residual stress at the same time; 5) Shearing: According to the size requirements of the finished target plate, the steel plate is cut into the required size by sawing or flame cutting.

2. The method for manufacturing a high-performance quenched and tempered homogeneous target plate according to claim 1, characterized in that The target plate has a hardness of 241-302 HBW, a yield strength of 680-800 MPa, an elongation of ≥10%, a cross-sectional shrinkage of ≥50%, and a 20°C Charpy U-shaped impact energy of ≥90 J.

3. The method for manufacturing a high-performance quenched and tempered homogeneous target plate according to claim 1, characterized in that The metallographic structure of the target plate at 1 / 4 and 1 / 2 thickness and near the surface is uniform tempered troostite.

4. The method for manufacturing a high-performance quenched and tempered homogenized target plate according to claim 1, characterized in that: In step 1), the superheat of the molten steel during the casting process is controlled at 15-45°C, and argon protection is used throughout the process. The molten steel is cast into a flat steel ingot with a thickness of ≥900 mm and a single weight of ≥35 tons. The ingot is slowly cooled in the mold for ≥24 hours and then the cap is removed. After the ingot is removed from the mold, it is cleaned while still warm, and the cleaning temperature is ≥100°C.

5. The method for manufacturing a high-performance quenched and tempered homogenized target plate according to claim 1, characterized in that: In step 2), the first 2-3 passes of the slab rolling are widening passes, and the steel rolling is carried out after widening.

6. The method for manufacturing a high-performance quenched and tempered homogenized target plate according to claim 1, characterized in that: In step 3), the rolling temperature is controlled at 1030-1100°C, the reduction of each of the first three passes is 30mm-50mm, the final rolling temperature is 800-900°C, and the last 1-2 passes of rolling are leveling passes to ensure the flatness of the steel plate. After rolling, the steel plate is removed from the production line when the surface temperature is ≥500°C. After removal from the production line, it is placed in a slow cooling pit or covered with a hood for slow cooling, and the slow cooling time is ≥48 hours.

7. The method for manufacturing a high-performance quenched and tempered homogenized target plate according to claim 1, characterized in that: In step 4), the normalizing temperature is 880-900° C., the holding time coefficient is 2.2-2.5 min / mm, and air cooling is performed. The quenching heating for the quenching and tempering treatment is performed in a continuous furnace at a quenching temperature of 880-900° C., the holding time coefficient is 2.5-3.0 min / mm, and the steel plate is water quenched in a quenching machine until the surface temperature of the steel plate out of water is ≤100° C., and then air cooling is performed to room temperature. The tempering treatment is also performed in a continuous furnace at a tempering temperature of 600-660° C., the holding time coefficient is 3.0-4.0 min / mm, and the steel plate is air cooled to room temperature after being discharged from the furnace.

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