Usporedba mikrostrukture i tvrdoće čelika Hardox 450 i čelika XAR 450

master's thesis

• Title (english): Comparison of the microstructure and hardness of Hardox 450 and XAR 450 steels
• Author: Mario Stojaković
• Mentor: Vera Rede (mentor)
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2022-12-15, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mechanical Engineering

Abstract

Cilj ovoga diplomskog rada bio je analizirati i usporediti kemijski sastav, mikrostrukturu te
mikrotvrdoću i makrotvrdoću dvaju konstrukcijskih čelika otpornih na trošenje: čelika Hardox 450
i čelika XAR 450.
Utvrđeno je da su oba čelika niskougljična. Čelik Hardox 450 sadrži više ugljika, oko 0,14 %C. U
čeliku XAR 450 ima oko 0,08 %C, ali sadrži tri puta viši udio karbidotvornih legirnih elemenata
(Cr i Mo). Mikrostruktura obaju čelika je slična i sastoji se od niskougljičnog martenzita. Zbog
visoke tvrdoće moguće je da u strukturi postoji i određena količina precipitiranih karbida, ali njih
je teško uočiti na svjetlosnom mikroskopu. Tvrdoće HV1, HV0,5 i HV0,2 podjednake su za oba
čelika i iznose oko 500 HV. Tvrdoće obaju čelika podjednake su i kod nižih opterećenja, a iznose
547 HV0,05 odnosno oko 620 HV0,02. Porastom opterećenja pri mjerenju smanjuju se vrijednosti
tvrdoće do opterećenja od 4,91 N (HV0,5) nakon čega tvrdoća ostaje konstantna. Smanjenjem
opterećenja pri mjerenju tvrdoće povećavaju se rasipanja vrijednosti, što je posljedica
nehomogenosti u mikrostrukturi i mogućih nepreciznijih očitanja sitnijih otisaka kod najnižih
opterećenja. Veća rasipanja prisutna su kod čelika XAR 450 pa su i vrijednosti standardne
devijacije te koeficijenata varijacije više.

Abstract (english)

The aim of this thesis was to analyze and compare the chemical composition, microstructure,
microhardness, and macro hardness of two wear-resistant structural steels: Hardox 450 steel and
XAR 450 steel.
Both steels were found to be low in carbon. Hardox 450 steel contains more carbon, about 0.14
%C. In XAR 450 steel, there is about 0.08% C, but it contains three times the proportion of carbideforming alloying elements (Cr and Mo). The microstructure of both steels is similar and consists
of low-carbon martensite. Due to the high hardness, it is possible that there is a certain amount of
precipitated carbides in the structure, but they are difficult to see under a light microscope. The
hardness HV1, HV0.5, and HV0.2 are equal for both steels and around 500 HV. The hardness of
both steels is equal even at lower loads, exactly 547 HV0.05 and around 620 HV0.02. As the
measurement load increases, the hardness values decrease up to a load of 4.91 N (HV0.5), after
which the hardness remains constant. By reducing the load when measuring the hardness, the
dispersion of values increases, which is a consequence of inhomogeneity in the microstructure and
possible less precise measurement of smaller prints at the lowest loads. Larger dispersions of
values are present in XAR 450 steel, so the values of standard deviation and coefficient of variation
are also higher.

• Keywords: konstrukcijski čelici otporni trošenju; sastav; mikrostruktura; tvrdoća
• Keywords (english): wear-resistant structural steels; composition; microstructure; hardness
• Language: croatian
• URN:NBN: urn:nbn:hr:235:483273
• Study programme: Title: Mechanical Engineering; specializations in: Design, Process and Energy Engineering, Production Engineering, Engineering Modelling and Computer Simulation, Marine Engineering, Industrial Engineering and Management, Materials Engineering, Mechatronics and Robotics, Autonomous Systems; Course: Materials Engineering; Study programme type: university; Study level: graduate; Academic / professional title: magistar/magistra inženjer/inženjerka strojarstva (magistar/magistra inženjer/inženjerka strojarstva)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2022-11-30 13:02:12