The Experiment – Ballistic testing

Austempering of the materialMaterial and Microstructure

Austempered Ductile Iron Perforated Plate with an Increased Mass Effectiveness

Sebastian Balos1, Igor Radisavljevic2, Petar Janjatovic1, Dragan Rajnovic1,Leposava Sidjanin1, Miroslav Dramicanin1, Olivera Eric Cekic3

1Faculty of Technical Sciences, University of Novi Sad, Trg Dositeja Obradovica 6, 21000 Novi Sad, Serbia 2Military Technical Institute, Ratka Resanovica 1, 11132 Belgrade, Serbia

3Faculty 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 platesis 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. ADImaterial has a similar tensile and yield strengths to some types of steels, but the manufacturing and machining costs are lower. Also, the density isaround 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 protectagainst five armor piercing incendiary 12.7x99 mm projectiles.

Aim of the study

Base material used in the experiment is ductile iron alloyed withcopper. The nodulation of ductile iron was 87%. Metal matrixconsisted of ferrite and perlite.

The ADI materials were produced by austenitization at 900°C/2h, followed by1 hour austempering at 275°C (ADI–275) and 400°C (ADI–400). Thisresulted in a fully ausferritic microstructure consisting of a mixture ofausferritic ferrite and retained austenite (9.8 and 26%, respectively).

7 mm perforated plate is selected as mass equivalent to steelperforated plate thickness 6 mm due to a lower density of ADIcompared to steel. Perforated plates was mounted at 400 mmfrom the basic 13mm RHA plate.

Results

SummaryPerforated plates made of ADI material with a higher hardness and a lowerductility (ADI–275) were proved to be superior to the softer and more ductileones (ADI–400). In the ADI–400 is found that during the impact of theprojectile, in the volume of material is present SITRAM effect, causing partialbrittle fracture resulting in lowering of ballistic protection. Compared toprevious results with steel perforated plates, the perforated plates made ofADI material have a similar mass effectiveness, a larger damaged area anda lower cost of fabrication.

No. of interconnected

holes

Damaged area[mm2]

Description of basic plate damage

ADI–275 7 mm

7 2124Cracked 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–4007 mm

2 375 Smooth bulge

5 702 Hole normal

6 1296Cracked bulge with

one crack

6 902 Hole normal

5 722Cracked bulge with

two cracks

Average 4.8 799

It is concluded that ADI 275 is more effective in inducing bending stressinside the core of piercing projectile in comparison to ADI 400.

Microstructure and hardness after impactADI–275 have less pronounced plastic deformation, no phasechanges have occurred. Faze transformations due to intenseplastic deformation are present in ADI–400, this leads to thecreation of martensite (martensite is indicated by white arrow) bySITRAM (Strain Induced Transformation of Austenite intoMartensite) mechanism.

Mass effectiveness

Hardox 4501.4%Cr; 0.6%Mn

ADI-2750.04%Cr; 0.38%Mn

Hardness VHN 445 498Elongation (%) 11 1Thickness (mm) 6 7

Damaged area (mm2) 551 2076Em of the armor system

compared to 460 BHN RHA1.76 1.75

ADI-275 compared to Hardox 450 steel ballistic testing results reveal that asimilar mass effectiveness is obtained, but ADI-275 damaged area is larger.

1472Ultimate tensile strength Rm

[MPa]914

- Proof strength Rp0,2% [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 Smass. % 3.51 2.21 0.38 0.189 0.022 0.04 0.031 0.035 0.014

Ultimate tensile strength Rm [MPa]

627

Proof strength Rp0,2%

[MPa]455

Elongation A [%] 6

Impact energy K0 [J] 34

Hardness HV 10 220

The authors gratefully acknowledge research fundingfrom the Ministry of Education, Science andTechnological Development of the Republic of Serbiaunder grant number TR34015.

Acknowledgment