Microstructure Control And Application Of High Strength Armor Protective Steel Plate AP500

Low alloy and high strength martensite protective steel has attracted much attention because of the advantages of low alloy content,good bulletproof and anti-penetration performance,flexible and convenient production process,etc.It is widely used in the national security fields such as tanks,escort vehicles,explosion-proof vehicles of armed police and warships.In general,the bulletproof performance of high strength armor plate is closely related to its hardness and toughness,but the improvement of hardness will affect its toughness to some extent.Due to the strict control of relevant technologies in Europe and the United States and other countries,the development and application of high-strength armor protection steel in China is relatively slow.Therefore it has significant meanings to research on the high strength armor plate.This paper through the composition and microstructure design of the high level high intensity of armor plate AP500,combined with rolling,cooling after rolling and off-line heat treatment process,to control the phase change process and the final group of materials,and then get an excellent low alloy and high strength armor protection steel plate with comprehensive performance on hardness,strength,toughness and bulletproof performance.The high-strength armored protective steel plate was industrially trial-produced in a steel mill in China,and the AP500 armor plate produced by the industrialized trial was tested for ballistic resistance.The main research contents and conclusions of this paper are as follows:(1)The microstructure evolution of experimental steel during continuous cooling was researched and the rolling experiment was carried out.The results showed that at the cooling rate of 0.5℃/s,the experimental steel was a single bainite structure,and martensite structure began to appear as the cooling rate increased.When the cooling rate ≥5℃/s,all the structures were transformed into martensite.The hardness of experimental steel increases sharply first,then slowly,and finally tends to be stable.After controlled rolling and cooling of the experimental steel,we got the bainite structure,and the hardness of the experimental steel plate after hot rolling is relatively uniform,about 320 HV.(2)The variation rules of microstructure and mechanical properties of experimental steel at different quenching temperatures was researched.The results show that the microstructure of the experimental steel is slab martensite during quenching in the temperature range of 830～890℃.As the temperature increases,the microstructure become thickens.With the increase of quenching temperature,the hardness and strength of test steel decreases slightly,while the elongation remain unchanged.The experimental steel is ductile fracture under low temperature impact,and the energy absorbed is mainly in the crack initiation stage,while the energy absorbed in the crack growth stage of experimental steel is relatively low.The mechanical properties of experimental steel are the optimal when quenched at 830℃.(3)The variation rules of the microstructure and mechanical properties of 830℃quenched steel at different low tempering temperatures was research.The results show that the structure of tempered steel is tempered martensite.After the tempering treatment,the hardness of the experimental steel was slightly lowered,and the yield strength and low temperature impact toughness were improved.With the increase of tempering temperature,the strength of the experimental steel decreases slightly,but the hardness,elongation and impact toughness at low temperature all show a trend of first increasing and then decreasing.The optimum heat treatment process of experimental steel is 830℃ quenching +200℃tempering.(4)The microstructure and mechanical properties of experimental steel under the optimal heat treatment process was research.The results show that the microstructure of the experimental steel is mainly composed of several martensite slats with different orientations.The mechanical properties of the experimental steel under the optimal heat treatment process all meet the technical objectives of armor steel.Its yield strength reached 1306 MPa,the tensile strength was 1611 MPa and the percentage of elongation(A25)was 12.3%.The impact energy of the experimental steel decreases slightly with the decrease of temperature.Even if the temperature is drop to-60 ℃,the experimental steel still has excellent low temperature impact performance,and the low temperature impact performance can maintain at more than 1.5 times of the same grade steel Armox 500T produced by SSAB in Sweden.(5)The microstructure,mechanical properties and bullet-proof properties of different thickness AP500 armor steel of the industrial reagents was research.The results show that the AP500 armor steel with different thickness is lath martensite,and its original austenite grain size is between 4 and 5 μm.The mechanical properties of different thickness AP500 armor steel are better than the same level at domestic and overseas.AP500 armor plate has good bullet-proof and anti-penetration capability,and its bullet-proof performance meets the requirements of STANG 4569 standard.Compared with the AP500 armor steel with a thickness of 6 mm,the bullet depth of the impact surface and the bullet height of the reverse side of the armor steel with a thickness of 8 mm and 10 mm were significantly reduced.The bulletproof capability of AP500 armor steel increases with the thickness of the steel plate.