This paper discusses changes in the microstructure and abrasive wear resistance of G17CrMo5-5 cast steel modified with rare earth metals (REM). The changes were assessed using scanning microscopy. The wear response was determined in the Miller test to ASTM G75. Abrasion tests were supplemented with the surface profile measurements of non-modified and modified cast steel using a Talysurf CCI optical profilometer. It was demonstrated that the modification substantially affected the microstructure of the alloy, leading to grain size reduction and changed morphology of non-metallic inclusions. The observed changes in the microstructure resulted in a three times higher impact strength (from 33 to 99 kJ/cm2) and more than two times higher resistance to cracking (from 116 to 250 MPa). The following surface parameters were computed: Sa: Arithmetic mean deviation of the surface, Sq: Root-mean-square deviation of the surface, Sp: Maximum height of the peak Sv: Maximum depth of the valley, Sz: Ten Point Average, Ssk: Asymmetry of the surface, Sku: Kurtosis of the surface. The findings also indicated that the addition of rare earth metals had a positive effect on the abrasion behaviour of G17CrMo5-5 cast steel.
 Sakwa, W., Jura, S., Sakwa, J. (1980). Abrasion resistant iron Alloy (in Polish). Krakow: Wyd. STOP.
 Bolanowski, K. (2013). Effect of hardness of the layer surface on the abrasion resistance of hadfield steel (in Polish). Problemy eksploatacji. 1, 127-139.
 Przybyłowicz, K. (2003). Metallography. Warszawa: WNT. (in Polish).
 Blicharski, M. (2004). Materials Engineering, Steel. Warszawa: WNT. (in Polish).
 Stradomski, Z. (2005). Evaluation of the explosive strength and temperature stability of the Hadfield cast steel structure. Przegląd Odlewnictwa. 10, 644-651. (in Polish).
 Kalandyk, B. & Zapała, R. (2009). The abrasive wear behaviour of alloy cast steel in SiC-water slurry. Archives of Foundry Engineering. 9(4), 91-94.
 Bayraktar, E. & Khalid, F. & Levaillant, Ch. (2004). Deformation and fracture behavior of high manganese austenitic steel. Journal of Mat. Processing. 147, 145-154. DOI:10.1016/j.jmatprotec.2003.10.007
 Chałko, L. & Żurowski, W. (2006). Study and use of Cr-Mo-V-Cu alloy steels for armament items. Problemy Technik Uzbrojenia. 35 (98), 115-124. (in Polish).
 Dobrzański, L.A. (2004). Metal Engineering Materials. Warszawa: Publisher WNT.
 Studnicki, A., Kondracki, M., Suchoń, J., Szajnar, J., Bartocha, D. & Wróbel, T. (2015). Abrasive Wear of Alloyed Cast Steels Applied for Heavy Machinery. Archives of Foundry Engineering. 15(1), 99-104.
 Sude Ma, Jianjun Zhang, (2016). Wear resistant high boron cast alloy - a review. Rev. Adv. Mater. Sci. 44, 54-62.
 Dąbrowski, R. Rożniata, E. Musiał, A. (2010). Abrasion resistance testing of structural and tool Mn-Cr-Mo-V steels Hutnik, Wiadomości Hutnicze. 77(11), 640-646. (in Polish).
 Mikulska, A. (2010), Effect of chemical composition on impact strength of Cr-Mo-V-Cu-Ni cast steel at low temperatures. XXVI Szkoła Tribologiczna, 99-105. (in Polish).
 Gajewski, M. & Kasińska, J. (2009). Rare earth metals influence on mechanical properties and crack resistance of GP240GH and G17CrMo5-5 cast steels. Archives of Foundry Engineering. 9(4), 37-44.
 Kasińska, J. (2015), Wide–ranging influence of mischmetal on properties of G17CrMo5-5 cast steel. Metalurgija. 54(1), 135-138.