Abstract
<jats:p>Technological development of laser and hybrid (laser–arc) welding (HLAW) processes has become a decisive factor in ensuring the structural integrity of high-hardness steels with hardness above 500 HB, which are widely used in protective and armor applications. The relevance of the reviewed topic is determined by the need to maintain a balance between high hardness, sufficient toughness, and ballistic resistance in welded joints subjected to dynamic and impact loading. The purpose of the chapter is to systematize and critically analyze contemporary scientific research devoted to the technological parameters of laser and hybrid welding of ultra-high-hardness steels and to determine how these parameters influence microstructural evolution, heat-affected zone (HAZ) characteristics, mechanical behavior, and ballistic performance of welded joints. The subject of research is the interrelation between key welding parameters (laser power, welding speed, linear heat input, arc current and voltage in hybrid processes, distance between energy sources, shielding gas conditions, and groove geometry) and the structural, mechanical, and operational properties of welded joints in steels with hardness exceeding 500 HB. Special attention is given to steels of the ARMOX and ARMSTAL type, which represent typical examples of quenched and tempered armor materials used in modern engineering practice. The methodology of the study is based on a systematic review and comparative analysis of experimental data presented in contemporary international scientific publications. General research methods of analysis and synthesis, induction and deduction, abstraction and systematization are employed to identify regularities in the formation of fusion zones and HAZ microstructures under different thermal cycles. The chapter integrates results of metallographic observations, microhardness measurements, residual stress evaluation, and ballistic testing reported in the literature. Comparative assessment of laser welding, HLAW, and conventional arc welding processes is carried out to determine their technological advantages and limitations. Particular emphasis is placed on evaluating strategies for controlling heat input and minimizing softening phenomena in the HAZ. The results of the analysis demonstrate that precise control of heat input and welding speed is the dominant factor in preserving the hardened martensitic structure characteristic of steels above 500 HB. Laser welding, due to its high energy density and rapid cooling rates, ensures a narrow HAZ and high hardness levels in the fusion zone, often exceeding 520 HV, while minimizing distortion. Hybrid welding, combining laser and arc energy sources, provides improved gap tolerance and technological flexibility, though it may lead to a slightly wider HAZ and moderate reduction of hardness due to tempering effects. Optimization of groove geometry, particularly double-Y configurations, significantly reduces the width of the softened zone and enhances structural stability under dynamic loading. Practical implications. The generalized findings may be applied in the design and technological preparation of welded armor structures, enabling engineers to select optimal parameter combinations that ensure minimal softening in the HAZ and stable ballistic performance of high-hardness steel joints. The conclusion is that both laser and hybrid welding technologies are capable of producing structurally sound joints in steels with hardness above 500 HB, provided that process parameters are carefully optimized. Technological parameter control directly determines microstructural stability, hardness distribution, and ballistic resistance of welded armor structures. Value/originality. The chapter offers a structured synthesis of dispersed experimental studies and provides an integrated analytical framework for understanding the technological and structural determinants of high-performance welded joints in ultra-high-hardness steels, thereby contributing to the consolidation of research findings in this field.</jats:p>