Effect of weld metal composition on ballistic performance of shielded metal arc welded ultra high hard armour steel joints

Abstract

Rolled homogenous armour (RHA) steels having hardness of 350 HV are widely used in the fabrication of armour fighting vehicles (AFVs). Recently, these steels are being replaced by ultra high hard armour (UHA) steels having hardness of 600HV to improve mobility. Usually, UHA steels are welded using shielded metal arc welding (SMAW) process with austenitic stainless steel (ASS) consumables to eliminate hydrogen induced cracking (HIC). But the mechanical and ballistic properties are degraded by the use of under matching ASS consumables. Hence, in this investigation, an attempt was made to study the effect of weld metal composition (especially Ferrite Number) on ballistic resistance of the UHA steel joints. Five different ASS electrodes with different Creq/Nieq ratio were used to fabricate the joints using SMAW process. The welded joints were tested against the Ball Ammunition (7.62 x 51 mm) using self-loading Refile and all the joints completely stopped the projectile. To analyse the ballistic immunity of the weld metal region, the depth of penetration and width of penetration were measured at the location of project attack. It is found that the UHA steel joints composed of weld metal having ferrite number of 3 to 9 exhibited superior ballistic resistance (lowest depth of penetration) due to high energy absorption capability of austenitic phase with vermicular secondary phase delta ferrite morphology. It is also found that the solidification mode, morphology and delta ferrite percentage (Ferrite Number) in the weld metal are altered by the Creq/Nieq ratio, which directly affects the mechanical, metallurgical properties and ballistic resistance. The ballistic resistance of the weld metal region showed inversely proportional relationship with the ferrite number (and Creq/Nieq ratio) of the weld metal.