Mechanical properties and microstructure analysis of laser welded hybrid parts made of additively and conventionally manufactured 1.4313 soft martensitic steel

• Microstructure-strength relationship of hybrid parts was investigated. • Heat treatment caused grain refinement, especially in the laser weld. • Heat treatment lowered the strength due to finely dispersed austenite. • Laser welding lowered the ductility of the specimens. • Weakest point was the heat affected zone after heat treatment. This study investigates laser welding of additively (AM) and conventionally manufactured (CM) parts, aiming to enhance cost and energy efficiency for a diverse product range. In this context, hybrid specimens combining AM/CM subparts were produced, where AM subparts were created using DED, CM parts by hot forming, and the two were joined using laser welding. The material analysed is soft martensitic stainless steel. Mechanical characterisation was performed through tensile testing and hardness measurements and microstructure characterisation through EBSD, SEM, EDS, and light microscopy. The study reveals the presence of ultra-fine grains in the heat treated laser weld segments which suggests grain subdivision due to martensite deformation. As built hybrid specimens exhibited lower toughness due to the laser welds and lower strength due to the CM segments. The weakest point after the heat treatment was the HAZ of the CM segment. The best mechanical performance was observed in homogeneously heat-treated AM specimens. Moreover, the variability in grain size were examined but did not conform grain boundary strengthening, particularly after the heat treatment. This study highlights the critical influence of microstructural variations on the mechanical properties of hybrid welds, emphasizing the need for further investigation into strengthening mechanisms and individual heat treatments.