The paper presents results of bead-on-plate test for comparison of microhardness and microstructure of the heat-affected zone of quenched and tempered protection steels «Miilux Protection 500», «Swebor Armor 500», «ATI 500+» and alloy armor steel. GMAW with heat-input values varying from 0.50 kJ·mm-1 to 0.90 kJ·mm-1. The micro-hardness profiles in the heat-affected zones of the investigated materials have shown that the most significant loss of strength was detected in the «ATI 500+» steel. Even when bead was deposited with the lowest welding heat-input (0.5 kJ·mm-1) the length of softened heat-affected zone region of the «ATI 500+» steel is 1.6...2.0 times bigger than that of other materials. Alloy armor steel was found to be the less sensitive to welding heating and the most resistant to heat-affected zone softening in comparison to other protection steels. The results obtained are explained by studies of microstructure of softened heat-affected zone regions and by comparison of the chemical composition of steels. Significantly higher content of Si, Cr, Ni, Mo as well as additional alloying with V in the steel has lead to suppression of the processes of softening of heat-affected zone regions which are heated to the temperature values of high tempering and partial austenization. The results obtained show the need of improving of GMAW technologies used in production of hulls and towers of armored fighting vehicles.

Statistical methods of analysis are currently widely used to develop control and monitoring systems for different welding processes. These methods allow to obtain information about the process including effect of all factors on its results, which is often difficult to evaluate due to the complexity of the process. The authors made efforts to apply these methods to develop the system for monitoring the parameters of flash-butt welding in real-time mode. The paper gives brief information about the features of flash-butt welding of reinforcement bars and some basic limitation of this process application. The main reasons of formation of defects in welded joints are given as well as analysis of possibility of application of monitoring systems for their determination. The on-line monitoring system based on neural networks was developed for evaluation of process deviations. This system is believed to be adequate for determination of process violations resulting in disturbances of welding parameter and can be used for prediction of possible defects in the welded joints.