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The Experiment – Ballistic testing Austempering of the material Material and Microstructure Austempered Ductile Iron Perforated Plate with an Increased Mass Effectiveness Sebastian Balos 1 , Igor Radisavljevic 2 , Petar Janjatovic 1 , Dragan Rajnovic 1 , Leposava Sidjanin 1 , Miroslav Dramicanin 1 , Olivera Eric Cekic 3 1 Faculty of Technical Sciences, University of Novi Sad, Trg Dositeja Obradovica 6, 21000 Novi Sad, Serbia 2 Military Technical Institute, Ratka Resanovica 1, 11132 Belgrade, Serbia 3 Faculty of Mechanical Engineering, Innovation Centre, University of Belgrade, Kraljice Marije 16, 11120 Belgrade, Serbia Ballistic protection of vehicle can be increased by add-on armor, such as perforated plates. The most common material used for perforated plates is armor steel, which contains considerable amounts of critical raw materials (CRMs), such as chromium (up to 2%) and molybdenum (up to 1%). By replacing the steel with unalloyed heat treated ductile iron (austempered ductile iron – ADI material), significant savings could be achieved. ADI material has a similar tensile and yield strengths to some types of steels, but the manufacturing and machining costs are lower. Also, the density is around 10 % lower in comparison to steel. The aim of the experiment is to achieve smallest mass of the add-on armor, which is expected to protect against five armor piercing incendiary 12.7x99 mm projectiles. Aim of the study Base material used in the experiment is ductile iron alloyed with copper. The nodulation of ductile iron was 87%. Metal matrix consisted of ferrite and perlite. The ADI materials were produced by austenitization at 900°C/2h, followed by 1 hour austempering at 275°C (ADI–275) and 400°C (ADI–400). This resulted in a fully ausferritic microstructure consisting of a mixture of ausferritic ferrite and retained austenite (9.8 and 26%, respectively). 7 mm perforated plate is selected as mass equivalent to steel perforated plate thickness 6 mm due to a lower density of ADI compared to steel. Perforated plates was mounted at 400 mm from the basic 13mm RHA plate. Results Summary Perforated plates made of ADI material with a higher hardness and a lower ductility (ADI–275) were proved to be superior to the softer and more ductile ones (ADI–400). In the ADI–400 is found that during the impact of the projectile, in the volume of material is present SITRAM effect, causing partial brittle fracture resulting in lowering of ballistic protection. Compared to previous results with steel perforated plates, the perforated plates made of ADI material have a similar mass effectiveness, a larger damaged area and a lower cost of fabrication. No. of interconnected holes Damaged area [mm 2 ] Description of basic plate damage ADI–275 7 mm 7 2124 Cracked bulge with one crack 4 630 Smooth bulge 14 4856 Smooth bulge 6 2004 Smooth bulge 5 768 Smooth bulge Average 7.2 2076 ADI–400 7 mm 2 375 Smooth bulge 5 702 Hole normal 6 1296 Cracked bulge with one crack 6 902 Hole normal 5 722 Cracked bulge with two cracks Average 4.8 799 It is concluded that ADI 275 is more effective in inducing bending stress inside the core of piercing projectile in comparison to ADI 400. Microstructure and hardness after impact ADI–275 have less pronounced plastic deformation, no phase changes have occurred. Faze transformations due to intense plastic deformation are present in ADI–400, this leads to the creation of martensite (martensite is indicated by white arrow) by SITRAM (Strain Induced Transformation of Austenite into Martensite) mechanism. Mass effectiveness Hardox 450 1.4%Cr; 0.6%Mn ADI-275 0.04%Cr; 0.38%Mn Hardness VHN 445 498 Elongation (%) 11 1 Thickness (mm) 6 7 Damaged area (mm 2 ) 551 2076 Em of the armor system compared to 460 BHN RHA 1.76 1.75 ADI-275 compared to Hardox 450 steel ballistic testing results reveal that a similar mass effectiveness is obtained, but ADI-275 damaged area is larger. 1472 Ultimate tensile strength Rm [MPa] 914 - Proof strength R p0,2% [MPa] 679 1 Elongation A [%] 8 23 Impact energy K0 [J] 44 498 Hardness HV 10 300 ADI–275 ADI–400 C Si Mn Cu Ni Cr Mg P S mass. % 3.51 2.21 0.38 0.189 0.022 0.04 0.031 0.035 0.014 Ultimate tensile strength R m [MPa] 627 Proof strength R p0,2% [MPa] 455 Elongation A [%] 6 Impact energy K0 [J] 34 Hardness HV 10 220 The authors gratefully acknowledge research funding from the Ministry of Education, Science and Technological Development of the Republic of Serbia under grant number TR34015. Acknowledgment
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