Method for improving hardness uniformity of 600HBW-grade bulletproof steel

Abstract

The invention discloses a method for improving hardness uniformity of 600HBW-grade bulletproof steel. The method comprises the following steps: (1) carrying out desulfurization pretreatment on molten iron for smelting; (2) heating and rolling; (3) heat treatment: primary quenching; carrying out secondary quenching; tempering is conducted; the bulletproof steel comprises the following chemical components in percentage by mass: 0.40 to 0.42 percent of C, 0.40 to 0.42 percent of Si, 0.35 to 0.45 percent of Mn, more than or equal to 0.015 percent of Al, 0.0015 to 0.0025 percent of B, less than or equal to 0.012 percent of P, less than or equal to 0.005 percent of S, 0.015 to 0.025 percent of Nb, 0.022 to 0.030 percent of Ti, 2.50 to 3.00 percent of Cr + Ni + Mo and the balance of Fe and inevitable impurities. The 600HBW-grade bulletproof steel disclosed by the invention has excellent obdurability matching, and the hardness distribution is uniform after heat treatment.

Description

Technical Field

[0001] The present invention relates to a method for improving the hardness uniformity of 600HBW grade bulletproof steel. Background Art

[0002] In the forefront of current protection technologies, 600HBW grade bulletproof steel occupies an indispensable position in the manufacture of various high-end protection equipment due to its specific combination of strength and toughness. However, in the actual industrial production and trial production processes, this strength grade of bulletproof steel has always faced a thorny problem - uneven hardness distribution. In some areas, the hardness value is too high, which makes the material prone to brittle fracture when subjected to external impacts and unable to effectively absorb and disperse the impact energy; while in other areas, the hardness is low, making it difficult to withstand the impact of bullets or other projectiles and simply unable to meet the basic ballistic performance requirements. This uneven hardness condition, like a "fatal weakness" hidden in the protective armor, severely restricts the performance of the bulletproof steel and also greatly shortens its service life, hindering its wide application in fields with extremely high requirements for protective performance.

[0003] Therefore, while ensuring the excellent strength and toughness matching of the bulletproof steel, how to improve its hardness uniformity is a technical problem that needs to be solved for 600HBW grade bulletproof steel at present. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for improving the hardness uniformity of 600HBW grade bulletproof steel to solve the problems raised in the background art. The invented 600HBW grade bulletproof steel has excellent strength and toughness matching and uniform hardness distribution after heat treatment.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A method for improving the hardness uniformity of 600HBW grade bulletproof steel according to the present invention includes:

[0007] (1) The molten iron for smelting is pretreated by desulfurization, and self-produced high-quality scrap steel is added. After LF refining heating, composition fine-tuning, and alloying, ensure that the composition and temperature of the molten steel meet the requirements of subsequent processes; during RH vacuum treatment, the vacuum treatment time is 15 - 25 min. After the vacuum treatment, soft blowing is carried out, and the slag surface of the ladle remains calm during soft blowing, and there shall be no molten steel surface exposed to the air.

[0008] The whole continuous casting process adopts protective casting, and at the same time, electromagnetic stirring and soft reduction are carried out. The low magnification inspection requirements for the slab are that the central segregation is not greater than grade C3 and the central porosity is not greater than grade 2.

[0009] (2) Heating and rolling

[0010] The slab tapping temperature is 1220 ± 20 °C. Two-stage rolling is adopted, with the rough rolling starting temperature being 1100 ± 50 °C; the finish rolling temperature of the finish rolling is 850 - 950 °C, and it is cooled to 500 - 550 °C after rolling;

[0011] (3) Heat treatment

[0012] Primary quenching: The heating temperature is 890 - 910 °C to fully austenitize the internal structure of the steel billet, laying a good foundation for subsequent microstructure transformation; the holding time is 2 - 2.5 h to ensure a uniform and thorough austenitization process; after the holding is completed, it is rapidly cooled to room temperature to obtain martensite structure in the steel, providing a microstructure guarantee for the high strength of the steel;

[0013] Secondary quenching: The heating temperature is 820 - 840 °C, and the holding time is 1.5 - 2 h to make the ratio of austenite and ferrite in the steel reach an ideal balance state. It is rapidly cooled to room temperature;

[0014] Tempering: The heating temperature is 200 - 220 °C, the holding time is 3.5 - 4 h, and it is air-cooled to room temperature;

[0015] The mass percentage content of the chemical components of the bulletproof steel is as follows: C: 0.40 - 0.42%, Si: 0.40 - 0.42%, Mn: 0.35 - 0.45%, Al: ≥0.015%, B: 0.0015 - 0.0025%, P ≤ 0.012%, S ≤ 0.005%, Nb: 0.015 - 0.025%, Ti: 0.022 - 0.030%, Cr + Ni + Mo: 2.50 - 3.00%, and the rest are Fe and unavoidable impurities.

[0016] Furthermore, the vacuum treatment time is 20 min.

[0017] Furthermore, the slab tapping temperature of the heating furnace is 1223 °C; two-stage rolling is adopted, with the rough rolling starting temperature being 1105 °C; the finish rolling temperature of the finish rolling is 906 °C, and the final cooling temperature is 508 °C; the heating temperature of the primary quenching is 901 °C, the heating temperature of the secondary quenching is 832 °C, and the tempering temperature is 218 °C.

[0018] Furthermore, the slab tapping temperature of the heating furnace is 1221 °C; two-stage rolling is adopted, with the rough rolling starting temperature being 1103 °C; the finish rolling temperature of the finish rolling is 905 °C, and the final cooling temperature is 506 °C; the heating temperature of the primary quenching is 905 °C, the heating temperature of the secondary quenching is 830 °C, and the tempering temperature is 215 °C.

[0019] Furthermore, the slab tapping temperature of the heating furnace is 1223 °C; two-stage rolling is adopted, with the rough rolling starting temperature being 1102 °C; the finish rolling temperature of the finish rolling is 903 °C, and the final cooling temperature is 502 °C; the heating temperature of the primary quenching is 902 °C, the heating temperature of the secondary quenching is 833 °C, and the tempering temperature is 220 °C.

[0020] Furthermore, the mass percentage of the chemical components of the bulletproof steel is as follows: C: 0.41%, Si: 0.41%, Mn: 0.42%, Alt: 0.035%, B: 0.0018%, P: 0.012%, S: 0.005%, Nb: 0.022%, Ti: 0.026%, Cr + Ni + Mo: 2.74%, and the rest is Fe and inevitable impurities.

[0021] Furthermore, the mass percentage of the chemical components of the bulletproof steel is as follows: C: 0.41%, Si: 0.40%, Mn: 0.43%, Alt: 0.035%, B: 0.0020%, P: 0.012%, S: 0.004%, Nb: 0.023%, Ti: 0.028%, Cr + Ni + Mo: 2.72%, and the rest is Fe and inevitable impurities.

[0022] Furthermore, the mass percentage of the chemical components of the bulletproof steel is as follows: C: 0.42%, Si: 0.42%, Mn: 0.40%, Alt: 0.035%, B: 0.0021%, P: 0.010%, S: 0.005%, Nb: 0.020%, Ti: 0.025%, Cr + Ni + Mo: 2.68%, and the rest is Fe and inevitable impurities.

[0023] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0024] The 600HBW-level bulletproof steel produced by the method provided by the present invention has excellent strength and toughness matching, and the hardness distribution is uniform after heat treatment, meeting relevant standards and customer requirements. At the same time, the alloy cost of the present invention is low, the preparation method is simple, and it is suitable for industrial production. Detailed implementation manners

[0025] The present invention will be described in more detail below through specific embodiments. The embodiments are only descriptions of the best implementation manners of the present invention and do not limit the scope of the present invention in any way.

[0026] Embodiment 1

[0027] The weight percentages of the chemical components of the steel plate are shown in Table 1 below. The tapping temperature of the slab heating furnace is 1223°C. Two-stage rolling is adopted, and the rough rolling starting temperature is 1105°C. The finish rolling temperature of the finish rolling is 906°C, and the finish cooling temperature is 508°C. The primary quenching heating temperature is 901°C, the secondary quenching heating temperature is 832°C, and the tempering temperature is 218°C. Then the steel plate can be obtained.

[0028] Embodiment 2

[0029] The weight percentages of the chemical components of the steel plate are shown in Table 1 below. The tapping temperature of the slab heating furnace is 1221 °C. Two-stage rolling is adopted, and the rough rolling starting temperature is 1103 °C. The finish rolling final temperature is 905 °C, and the finish cooling temperature is 506 °C. The primary quenching heating temperature is 905 °C, the secondary quenching heating temperature is 830 °C, and the tempering temperature is 215 °C. Thus, the steel plate can be obtained.

[0030] Example 3

[0031] The weight percentages of the chemical components of the steel plate are shown in Table 1 below. The tapping temperature of the slab heating furnace is 1223 °C. Two-stage rolling is adopted, and the rough rolling starting temperature is 1102 °C. The finish rolling final temperature is 903 °C, and the finish cooling temperature is 502 °C. The primary quenching heating temperature is 902 °C, the secondary quenching heating temperature is 833 °C, and the tempering temperature is 220 °C. Thus, the steel plate can be obtained.

[0032] Table 1 Chemical composition (wt%) of the steel plates in Examples 1-3 of the present invention

[0033]

[0034]

[0035] The tensile properties of the steel plates in Examples 1-3 of the present invention were inspected, and the inspection results are shown in Table 2.

[0036] Table 2 Tensile properties of the steel plates in Examples 1-3 of the present invention

[0037]

[0038] The impact tests were carried out on the steel plates in Examples 1-3 of the present invention, and the test results are shown in Table 3.

[0039] Table 3 Impact properties of the steel plates in Examples 1-3 of the present invention

[0040]

[0041] Samples were taken from the steel plates in Examples 1-3 of the present invention for hardness inspection, and the inspection results are shown in Table 4.

[0042] Table 4 Hardness values of the steel plates in Examples 1-3 of the present invention

[0043]

[0044] It can be seen from Tables 2-4 that the 600 HBW grade bulletproof steel produced by the method provided by the present invention has excellent strength and toughness performance matching, and the hardness distribution is uniform at different positions, meeting the use requirements.

[0045] The embodiments described above are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for improving the hardness uniformity of 600HBW grade bulletproof steel, characterized in that: include: (1) The molten iron for smelting is pre-treated with desulfurization, high-quality scrap steel is added, and LF refining, heating, component fine-tuning, and alloying are performed to ensure that the composition and temperature of the molten steel meet the requirements of subsequent processes; during RH vacuum treatment, the vacuum treatment time is 15-25 minutes, and soft blowing is performed after the vacuum treatment. During the soft blowing, the slag surface of the ladle is kept calm, and the molten steel liquid surface must not be exposed to the air; The whole continuous casting process adopts protective pouring, and electromagnetic stirring and light pressure are used at the same time. The low-magnification detection of slabs requires that the center segregation is not greater than Class C 3 and the center looseness is not greater than Class 2; (2) Heating and rolling The slab temperature out of the furnace is 1220±20℃. Two-stage rolling is adopted, with the starting temperature of rough rolling at 1100±50℃; the final rolling temperature of fine rolling is 850~950℃, and the temperature after rolling is cooled to 500-550℃; (3) Heat treatment Primary quenching: The heating temperature is 890-910℃, so that the internal structure of the steel billet is fully austenitized, laying a good foundation for the subsequent organizational transformation; the holding time is 2-2.5h to ensure that the austenitization process is uniform and thorough; after the holding is completed, it is quickly cooled to room temperature so that the steel obtains martensitic structure, providing organizational guarantee for the high strength of the steel; Secondary quenching: heating temperature is 820-840℃, holding time is 1.5-2h, so that the ratio of austenite and ferrite in the steel reaches an ideal balance. Rapidly cool to room temperature; Tempering: heating temperature is 200-220℃, holding time is 3.5-4h, air cooling to room temperature; The mass percentage of the chemical components of the bulletproof steel is: C: 0.40-0.42%, Si: 0.40-0.42%, Mn: 0.35-0.45%, Al: ≥0.015%, B: 0.0015-0.0025%, P≤0.012%, S≤0.005%, Nb: 0.015-0.025%, Ti: 0.022-0.030%, Cr+Ni+Mo: 2.50-3.00%, and the rest is Fe and unavoidable impurities.

2. The method for improving the hardness uniformity of 600HBW grade bulletproof steel according to claim 1, characterized in that: The vacuum treatment time is 20 minutes.

3. The method for improving the hardness uniformity of 600HBW grade bulletproof steel according to claim 1, characterized in that: The heating furnace exit temperature of the slab is 1223℃; two-stage rolling is adopted, the starting temperature of rough rolling is 1105℃; the final rolling temperature of fine rolling is 906℃, and the final cooling temperature is 508℃; the primary quenching heating temperature is 901℃, the secondary quenching heating temperature is 832℃, and the tempering temperature is 218℃.

4. The method for improving the hardness uniformity of 600HBW grade bulletproof steel according to claim 1, characterized in that: The slab's heating furnace exit temperature is 1221°C; two-stage rolling is adopted, with the rough rolling start temperature being 1103°C; the finishing rolling temperature being 905°C, and the final cooling temperature being 506°C; the primary quenching heating temperature being 905°C, the secondary quenching heating temperature being 830°C, and the tempering temperature being 215°C.

5. The method for improving the hardness uniformity of 600HBW grade bulletproof steel according to claim 1, characterized in that: The heating furnace exit temperature of the slab is 1223°C; two-stage rolling is adopted, the starting temperature of rough rolling is 1102°C; the final rolling temperature of fine rolling is 903°C, and the final cooling temperature is 502°C; the primary quenching heating temperature is 902°C, the secondary quenching heating temperature is 833°C, and the tempering temperature is 220°C.

6. The method for improving the hardness uniformity of 600HBW grade bulletproof steel according to claim 3, characterized in that: The mass percentage of the chemical composition of the bulletproof steel is: C: 0.41%, Si: 0.41%, Mn: 0.42%, Alt: 0.035%, B: 0.0018%, P: 0.012%, S: 0.005%, Nb: 0.022%, Ti: 0.026%, Cr+Ni+Mo: 2.74%, and the rest is Fe and unavoidable impurities.

7. The method for improving the hardness uniformity of 600HBW grade bulletproof steel according to claim 4, characterized in that: The mass percentage of the chemical composition of the bulletproof steel is: C: 0.41%, Si: 0.40%, Mn: 0.43%, Alt: 0.035%, B: 0.0020%, P: 0.012%, S: 0.004%, Nb: 0.023%, Ti: 0.028%, Cr+Ni+Mo: 2.72%, and the rest is Fe and unavoidable impurities.

8. The method for improving the hardness uniformity of 600HBW grade bulletproof steel according to claim 5, characterized in that: The mass percentage of the chemical composition of the bulletproof steel is: C: 0.42%, Si: 0.42%, Mn: 0.40%, Alt: 0.035%, B: 0.0021%, P: 0.010%, S: 0.005%, Nb: 0.020%, Ti: 0.025%, Cr+Ni+Mo: 2.68%, and the rest is Fe and unavoidable impurities.

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