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Case hardened steel plates for ballistic armour: A study of ballistic and mechanical properties of case hardened ARMOX® steel
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
2017 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesisAlternative title
Sätthärdad plåt för ballistiskt skydd : En studie av ballistiska och mekaniska egenskaper hos sätthärdat ARMOX® stål (Swedish)
Abstract [en]

Protective materials are a necessity to ensure the safety of personnel or property subjected to impacts by bullets, fragments and/or explosions. To shatter an inbound projectile, the surface of the target needs to exhibit a very high hardness but also the ability to prevent crack growth and plastically deform to avoid brittle fracture. The need for a combination of hardness and toughness led to the invention of dual hard steel which can be achieved within a homogeneous plate by modification of the surface through single-sided case hardening. In this work ARMOX® 440T and ARMOX® 500T was case hardened with a case depth of 2 and 2.3 mm and shoot upon with armour piercing rounds P80 to determine the ballistic limit of the material and to compare with the reference ARMOX®. Metallographic investigation was performed together with grain size measurement and mechanical properties were tested including hardness, impact toughness, dimensional deviation and tensile strength.

A considerable increase of the ballistic performance with 40-70 % was reached by single-sided case hardening even though an irregular failure of the diffusion barrier had led to double-sided cases in various areas. Mass efficiency also increased considerably. Especially ARMOX® 440T was suitable for the treatment since it increased by the largest relative amount despite the fact that it had a thinner case then ARMOX® 500T plates.

The complete penetrations were caused by formation of adiabatic shear bands and lead to punching of the plates except for hits at areas with double-sided case where back spall also occurred. The backside-case also resulted in a sharp reduction in impact toughness. Crack formation in close proximity to the impact site was found in all case hardened plates perpendicular to the front surface originating from inter-granular oxides near the surface.

All the conventionally case hardened plates deviated from the reference plate flatness. Most likely because of placement in the furnace.

Collectively the material is not recommended to be implemented in structural components until further investigations have been made concerning multi-hit threat, heat treat optimisation to minimize dimensional changes and bending because of the formation of perpendicular cracks under tensile load.

Place, publisher, year, edition, pages
2017. , p. 93
Keyword [en]
ARMOX, armour steel, case hardening, carburizing, ballistic
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kau:diva-62597OAI: oai:DiVA.org:kau-62597DiVA, id: diva2:1130359
External cooperation
BAE Systems Hägglunds AB
Subject / course
Mechanical Engineering
Educational program
Engineering: Mechanical Engineering, spec. in Materials Engineering (300 ECTS credits)
Supervisors
Examiners
Available from: 2017-08-25 Created: 2017-08-09 Last updated: 2017-08-25Bibliographically approved

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  • apa
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