Comparison of microstructure and properties of two wear resistance structural steels

Cilj ovoga diplomskoga rada bio je odrediti i usporediti mikrostrukturu, tvrdoću i otpornost na abrazijsko trošenje dvaju konstrukcijskih čelika poboljšane otpornosti na abrazijski mehanizam trošenja – čelika Hardox 450 i čelika XAR 450. Ispitivanje otpornosti na abraziju provedeno je standardnom metodom „suhi pijesak – gumeni kotač“ te na uređaju Taber abrader. Oba čelika imaju sličnu homogenu sitnozrnatu martenzitnu mikrostrukturu. Kod obaju čelika dobivene su podjednake vrijednosti tvrdoće HV2 u svim karakterističnim presjecima ploče. Vrijednosti tvrdoća HV0,2 i HV1 nešto su više od vrijednosti tvrdoće HV2, no puno veća su i rasipanja rezultata. Ispitivanje otpornosti na abraziju metodom „suhi pijesak – gumeni kotač“ pokazuje da čelik Hardox 450, u odnosu na čelik XAR 450, ima manji gubitak volumena za oko 8 %, ali rasipanja rezultata kod ovog čelika su puno veća nego kod čelika XAR 450. Pri ispitivanju otpornosti na abraziju na uređaju Taber abrader, oba čelika pokazala su vrlo sličnu otpornost. Također, kod obaju čelika može se uočiti fenomen „kritične veličine abrazivnog zrna“. Kritična veličina abrazivnog zrna slična je kod oba čelika i nalazi se između 21,8 μm i 30,2 μm.The aim of this master's thesis was to determine and compare microstructure, hardness and resistance to abrasion wear of two structural steels of improved resistance to the abrasion wear mechanism – the Hardox 450 steel and the XAR 450 steel. The abrasion resistance test was carried out using the standard "dry sand – rubber wheel" method and on the Taber abrader. Both steels have a similar homogeneous fine-grained martensitic microstructure. In both steels, equal values of HV2 hardness were obtained in all characteristic sections of the plate. The hardness values of HV0.2 and HV1 were slightly higher than the value of HV2 hardness, but the scattering of results was much higher. Abrasion resistance testing using the "dry sand - rubber wheel" method shows that the Hardox 450 steel, compared to the XAR 450 steel, has a lower volume loss of about 8 %, but the scattering of results in this steel was much higher than in steel XAR 450. When testing abrasive wear resistance on the Taber abrader, both steels showed very similar resistance. Also, in both steels, the phenomenon of "critical size of abrasive grain" can be observed. The critical size of the abrasive grain is similar in both steels and is located between 21.8 μm and 30.2 μm