Research Of Anti-bullet Property And Welding Performance Of New High-Strength Armor Steel Plates

In order to meet the operational performance requirements of modern and future AFV(armored fighting vehicle)in new and complex serving environment,armored steel needs to have good mechanical properties and connection process performance to meet the structure intensity and manufacturing process.In addition,good low-temperature toughness is needed for armored steel to adapt to the cold war,fine bulletproof-antiknock-tearing resistance performance to meet long-distance & high-speed transfer fight and comprehensive anti-bullet property also to meet the requirements of passive protection.The study was carried out through scientific experiments to the new-high-strength armor plate including but not limited to: correlated mechanical property,low-temperature toughness,molten brazing connection between dissimilar metals,the drop weight tear test(DWTT)and shooting simulated test(SST).The thesis researched the mechanism of ductile-brittle transition,the connection characteristics between dissimilar metals,the bulletproof-antiknock-tearing resistance performance and accompanying influencing factors.The systematic research shows the following results :(1)The new-high-strength armor steel plate has good impact toughness at room temperature but the toughness reduced significantly when the temperature dropped below-20℃,and the reduction is the most significant of impact toughness between-20 ~-30℃.The experimental armor steel appears the first kind of temper brittleness when tempering at 250℃.Along with the increase of tempering temperature,the hardness reduces and the impact absorption energy increases gradually.The experimental armor steel has the best comprehensive performances of hardness and impact toughness when tempering in the range of 350~400℃.(2)The connection strength of the joint between armor steel and AZ31 B magnesium alloy connected by TIG arc melting brazing reaches the maximum when the welding current is 60 A.The steel substrate close to the brazed joint will have a softening phenomenon under the action of the welding heat cycle.The transition zone of oxide accumulation,which is formed in the interface,is a mixed group composed of compound Fe-mg-O,phase of intermetallic compound Al Fe3,matrix Fe,as well as Mg elements having diffused from molten metal.And its width generally increases with the increase of welding current.(3)The fracture mode of the melt-brazing joint formed under small welding current is a mixture fracture including ductile and quasi-cleavage fracture.Meanwhile,higher welding current will lead to more brittle compounds in the interfacial transition zone due to excessive oxidation and the cleavage plane will increase under tensile-shear stress.In addition,the fracture mode of the joint is subject to the brittle fracture dominated by cleavage fracture and the bond strength decreases.(4)Bending elastic deformation,yield plastic deformation,crack formation,stable extension(tear)of the experimental armor steel plate occurs in sequence with DWTT impact load,and at last tearing shear lip is formed.The fracture is mixed with transgranular cleavage and intergranular fracture and the fracture initiation area increases as the thickness increases.In addition,the experimental armor steel has the same crack performance due to the same unit extended energy density.(5)The fracture characteristics of SST are similar to those of shooting test.The impact failure process is the contact between simulate bullet and target;the elastic deformation of target;yield plastic deformation;failure with small plug;failure with circular pieces accompanied by cylindrical deformation;circular shear lip formation.(6)The results of SST show that the impact failure mechanism of new-high-strength armor steel plate is ductile bearizing damage mode of plugging and punching shear fracture.The mathematical strength model,damage model and the ballistic limit velocity of SST are put forward and verified.