**2. Experimental Section**

The purpose of the performed experiments was to compare the structure and properties of Fe-Cr-Nb-B nanocrystalline surface layers deposited by manual metal arc (MMA) welding with a covered electrode 3.2 mm in diameter to previously used abrasion-resistant materials. HARDOX 400 steel was used as a reference material in the assessment of resistance to metal-mineral abrasion. The following materials were tested in the experiments:


Metallographic examinations of the deposited coatings were carried out on a Zeiss SteREO Discovery, and LEICA MEF4A optical microscope (Leica Microsystems, Cambridge, UK) in addition to a Zeiss Supra 35 (SEM) scanning electron microscope (Carl Zeiss GmbH, Jena, Germany). Metallographic images were taken of transverse sections with respect to weld deposition direction. The specimens were prepared by standard metallographic techniques and etched in Nital solution. Phase compositions of the investigated materials in addition to the size of the crystallographic grains of nanocrystalline microstructure were determined using an Xpert PRO X-ray diffractometer with step data logging, employing the filtered K@ X-rays. The chemical composition of precipitates was determined by energy-dispersive X-ray spectroscopy (EDS) with an EDAX detector. Hardness tests were conducted on a Zwick Roell ZHR hardness tester based on the Rockwell method, while cross-sectional hardness was measured using the Vickers method with a Future-Tech FM-700 tester (Future-Tech Corp., Kawasaki, Kanagawa Prefecture, Japan).
