An Analysis of Coil Dimensions on Induction Heating Machine Against Microstructure and Hardness Distribution as New Candidate of Projectile-resistant Steel Plates Materials

The field of defense and security requires ballistic resistant materials for self-protection. Ballistic resistant materials must be able to withstand projectile spin rate and absorb impact energy. A combination of hardness on the surface and ductility on the other side is required to make the projectile resistance plate. Hardness is required to withstand the projectile rate, while ductility is required to reduce cracking, brittle fracture and absorption of impact energy. The objective of this study is to find the effect of the coil shape on microstructure and hardness distribution on the steel plate that is carried out by surface hardening using an induction machine. Medium carbon steel plate with the thickness 8 mm is austenitized using the induction heating machine with coil dimension and shape variations. Austenizing on the surface and rapid quenching in oil media are up to 900 °C. A micro-observation was conducted on quench plates and hardness distribution on their cross-section. The result of microstructure observation and micro Vickers hardness test of coil variation at a diameter 5 mm and with the number of turns of 2 and 3 is microstructures on all sides formed with martensite structure and equal hardness on the entire cross-section, so that no surface hardening formed. Micro-observations showed martensite structure on the surface side and the ferrite and perlite structures are still visible on the middle and lower sides using 8 mm diameter coils and 2 turns. The maximum hardness is 497 HVN on the upper side surface and 257 HVN on the lower side surface using an 8 mm diameter coil and 2 turns. An increased hardness on one of the plate surfaces while maintaining the ductile on the opposite side can be proposed as a candidate for a ballistic-resistant plate through further researc