Refining the hierarchical structure of lath martensitic steel by in situ alloying with nickel: morphology, crystallography, and mechanical properties

Recent advances in mitigating fusion zone softening during laser welding of Al-Si coated 22MnB5 press-hardened steels

“…However, despite the production of defect-free joints, the FZ softening issue due to the dilution of the Al-Si coating into the molten weld pool still poses significant concerns. The remainder of this paper considers recently proposed solutions to the issue of FZ softening, particularly looking at the effect of welding Al-Si coated 22MnB5 through a pure colloidal graphite coating [44], modifying the Al-Si coating prior to welding using electro-spark deposition (ESD) [45], and welding the sample through pure Ni without prior removal of the Al-Si coating [46,47].…”

“…A comprehensive investigation was conducted to analyze the influence of introducing approximately 8 wt% Ni into 22MnB5 steel. The study aimed to assess the impact of this alloying element on various aspects, including the martensitic morphology, crystallography, internal transformational strain, and mechanical properties of the lath martensite within the bulk matrix [47]. The results of the study offered valuable information on how the martensitic morphology of hot-stamped 22MnB5 can be controlled through the in situ alloying with Ni.…”

“…Additionally, it led to a notable refinement in the packet size, block width, and lath size within the microstructure, as shown in figure 20. The ideal martensitic transformation was triggered by the addition of Ni, leading to the majority of the austenite grains transforming into four packets [47]. In the sample alloyed with Ni, each packet, representing a parallel plane according to the K-S model, exhibited a composition comprising three distinct block structures.…”

“…As a result, the transformational strain observed in the Ni-alloyed base metal (NABM) was predominantly dilatational, with minimal strain measured in the bulk microstructure, as shown in figure 20. Khan et al [47] argued that the refinement of the average lath width and average block width in the bulk microstructure would likely lead to an improvement in the yield strength of the NABM.…”

“…These methods involve welding the sample directly through the Al-Si coating using secondary or modified coatings made of austenite stabilizing elements, which decreases the ferrite content and increases the strength of the weld [44,45]. In addition to the above-mentioned solutions, recent research has also explored the effect of alloying Ni with 22MnB5 on the properties of the steel [46,47]. This study provides insights into the potential advancement regarding the development of new press-hardened steels or new coating types used for advanced applications, which can be used to address the issue of ferrite formation and FZ softening during laser welding of Al-Si coated presshardened steels.…”