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Materials with high hardness are usually preferred in armour applications and are difficult to weld due to high Carbon Equivalent (C.E). In this investigation, an attempt was made to weld Ultra-high Hard Armour (UHA) steel (having C.E of 0.91) by Shielded Metal Arc Welding (SMAW) process using three electrodes (i) austenitic stainless steel (ASS- E307-16), (ii) super duplex stainless steel (SDSS-E2594-16) (iii) low hydrogen ferritic (LHF-E12018M-low-alloy steel electrode). The mechanical properties (tensile, impact toughness, and microhardness) were evaluated and correlated with microstructural features along with Creq/Nieq ratio of weld metal. The joints fabricated using LHF electrodes showed superior strength of 962 MPa and hardness of 341 HV. The joints made using ASS electrode showed superior impact toughness of 72 J and Notch Strength Ratio (NSR) of 1.32 due to the higher energy absorption capability of the austenitic phase. At the weld interface, joints fabricated using ASS and SDSS electrodes show the unmixed zone (UMZ) and martensitic band (MB) due to sudden change of crystal structure (Face Centred Cubic (FCC) / Body Centred Tetragonal (BCT)). It is also found that the strength property increases (651 MPa to 856 MPa) with an increase in Creq/Nieq ratio (1.87 to 3.2) of weld metal and with a decrease in ductility.

This work is aimed to investigate the arc rotation effect on mechanical properties and metallurgical characteristics of 18 mm thickness armour grade quenched and tempered (Q & T) steel joints. Mechanical properties like tensile, impact toughness and microhardness were evaluated from welded joints. Metallurgical characteristics of welded joints like macrostructure, microstructure, and weld metal chemical composition were analyzed. From the results, it is observed that the rotating arc gas metal welded (RTA-GMW) joint contain minimum heat affected zone width (1.8 mm) and exhibits better tensile properties (784 MPa) due to the decrease in heat density caused by arc rotation of the joining process. The impact toughness properties of weld joint showed 36 % improvement than the unwelded base metal. Microstructural studies also revealed higher volume percentage of fine delta ferrite (δ-Fe) with vermicular type δ-Fe morphological future in the weld joint. The rotation arc caused reduction in heat input, enhanced strength, impact toughness properties and creation of vermicular type δ-Fe morphology in armour grade Q&T steel welded joints. [ABSTRACT FROM AUTHOR]

This paper investigates the effectiveness of honeycomb sandwich structure in an MBT hull through a Finite Element Analysis based study. Two hulls, one with steel floor plate and the other with a honeycomb-sandwich floor plate made of aluminium alloy were modelled. Both these hull models were subjected to the same loads and boundary conditions and the resulting stress and deformation results are discussed and compared. It was observed that although the honeycomb sandwich floor plate did undergo higher stress and deformation compared to the steel floor plate, the values were within safe design limits. In addition to this, using these honeycomb structure would result in a substantial mass saving as found from the study. Finally, this paper also covers the practical difficulties associated with incorporating honeycomb structures in MBT hull construction and recommends future courses of investigation. [ABSTRACT FROM AUTHOR]