Increased Hardness RHA Steel,â AMMRC Let- ter Report to the U. S. Army Tank-Automotive. Command, Warren, MI. 6. Crouch, I. G., 1988, âMetallic Armour-from ...
Journal of the Chinese Institute of Engineers, Vol. 25, No. 1, pp. 99-107 (2002)
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BALLISTIC PERFORMANCE AND MICROSTRUCTURE OF MODIFIED ROLLED HOMOGENEOUS ARMOR STEEL
Chia-Jung Hu and Pee-Yew Lee* Institute of Materials Engineering National Taiwan Ocean University Keelung, Taiwan 202, R.O.C.
Jium-Shyong Chen Materials & Electro-Optics Research Division Chung-Shan Institute of Science &Technology Tao-Yuan, Taiwan 325, R.O.C.
Key Words: armor, ballistic, adiabatic shear band, penetration mode.
ABSTRACT The purpose of this research was to evaluate the performance of a modified rolled homogeneous armor (MRHA) steel during ballistic impact tests. AerMet 100, AISI 1045 and 4130 steels were also tested for comparison with the MRHA results. The “white”-etched portion of adiabatic shear bands was found on the front surface around penetration cavities in all the impacted armor plates. Scanning electron microscopic observation indicates that the adiabatic shear bands found in 4130, MRHA and AerMet 100 belong to transformed bands while those of 1045 steel are deformed bands. Ballistic test results show that the ballistic limit velocities of the 2.5-mm thick MRHA steels are higher than those of AISI 1045 and 4130, and possibly compatible with AerMet 100 steel. For 2.5-mm thick armor plates, the penetration modes were found to be dominated by ductile hole growth and plugging modes.
I. INTRODUCTION Armor plate of hardened steel has been used for many years to provide protection of objects against impact damage (Doig, 1998a). Applications such as tanks, military sites, vaults, and safes, etc. have used steel armor plates to provide such protection. Two basic types of armor plate are conventionally utilized at the present time. One type is high-hardness armor that is extremely hard and thus capable of preventing penetration by projectiles (Raghaven et al., 1969). The other type is rolled homogeneous armor (RHA) that is somewhat softer than high-hardness armor, and is more ductile to prevent brittle fracture (U. S.
*Correspondence addressee
Department of Defense, 1984). Due to cost-saving fabrication requirements and more complex vehicle configurations, RHA has become the principal material employed for heavy combat and recovery vehicles since World War II. In the years 1950 to 1975, many metallurgical advances have improved the ballistic performance of RHA (Manganello and Abbott 1972; Wingrove and Wulf, 1973; Woodward, 1976). However, none have been considered successful, and thus RHA material has not been upgraded ballistically since 1950. In order to increase the ballistic performance of RHA, projects on improved rolled homogeneous armor (IRHA) were undertaken by the U.S. Army
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Journal of the Chinese Institute of Engineers, Vol. 25, No. 1 (2002)
Table 1 Heat treatment processes for impacted armor steels Steel
Austenitizing temperature/time
MRHA MRHA 1045 1045 1045 4130 4130 4130 AerMet 100
885°C/30 885°C/30 850°C/90 850°C/30 850°C/30 850°C/50 850°C/30 850°C/30 913°C/50
min. min. min. min. min. min. min. min. min.
AerMet 100
913°C/50 min.
AerMet 100
913°C/50 min.
Tempering temperature/time 200°C/90 min. 530°C/90 min. 200°C/90 min. 350°C/90 min. 510°C/90 min. 180°C/90 min. 290°C/90 min. 500°C/90 min. 470°C/180 min. plus 460°C/90 min. 470°C/180 min. plus 510°C/90 min. 470°C/180 min. plus 530°C/90 min.
Research Laboratory in 1970. The goal was to improve ballistic performance and maintain weldability of RHA, by increasing armor hardness but not brittleness. The important facts learned from 15 years of investigations include: (1) processed steel armor plates with Rockwell C hardness (Rc) higher than 52 can not retain structural integrity when impacted by full-scale-caliber kinetic energy (KE) rounds; (2) the hardened steel must demonstrate a V-notch Charpy (CHV) impact value greater than 20 ft-lb measured at -40°F (Avyazian and Papetti, 1973; Campbell and Avyazian, 1985; Papetti, 1978). Based on the aforementioned information and a consensus of the U.S. Army’s armor experts, a suitable composition of IRHA was 0.25%C-2.05%Ni-1.00%Cr-0.46%Mo0.34%Mn-0.03%Si, P
