Ispitivanje otpornosti alatnih čelika prema lokalnoj koroziji u mediju 3,5 % NaCl

master's thesis

• Title (english): Testing of tool steel on resistance to local corrosion in 3,5% NaCl medium
• Author: Marija Rajković
• Mentor: Anita Begić Hadžipašić (mentor)
• Mentor: Sandra Brajčinović (pomoć pri izradi, neposredni voditelj)
• Committee member: Ljerka Slokar Benić (predsjednik povjerenstva)
• Committee member: Anita Begić Hadžipašić (član povjerenstva)
• Committee member: Stjepan Kožuh (član povjerenstva)
• Granter: University of Zagreb; Faculty of Metallurgy; Sisak
• Defense date and country: 2022-09-29, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Metallurgy

Abstract

U ovom radu provedena su elektrokemijska i metalografska ispitivanja na alatnom čeliku za hladni i topli rad te na čeliku za cementiranje, a sve u svrhu dobivanja korozijskih parametara i zaključka koji od ispitanih uzoraka je otporniji na lokalnu pitting koroziju. Elektrokemijska ispitivanja su izvedena u mediju 3,5 % NaCl, a zasnivala su se na provođenju cikličke anodne polarizacije u području potencijala od -2000 mV do 200 mV vs SCE i povratno. Rezultati istraživanja su pokazali da su sva tri uzorka podložna pitting koroziji, ali se najlošijim pokazao uzorak alatnog čelika za cementiranje X19NiCrMo4 kod kojeg je registriran najniži pitting potencijal. Najboljim se pokazao uzorak alatnog čelika za topli rad oznake W600, kod kojeg je registriran najviši pitting potencijal.
Rezultati elektrokemijskih ispitivanja se podudaraju s metalografskim ispitivanjima jer su na površini uzorka W600 nakon korozije u kloridnom mediju vidljivi tek početci pitting korozije u obliku djelomičnih nakupina korozijskih produkata, dok je uzorak čelika za cementiranje oznake X19NiCrMo4 bio u potpunosti prekriven korozijskim produktima, što znači da je od tri ispitana alatna čelika najpodložniji pitting koroziji čelik za cementiranje te se isti ne preporučuje za korištenje u uvjetima gdje dolazi u kontakt s kloridnim ionima. Za vrlo nizak pitting potencijal i posljedično tome izrazitu pitting koroziju odgovorna je martenzitna mikrostruktura alatnog čelika za cementiranje. S druge strane alatni čelik oznake W600 je pokazao bolju korozijsku otpornost zbog sitnijeg zrna i ujednačene raspodjele karbida.

Abstract (english)

In this paper, electrochemical and metallographic tests were performed on tool steel for cold and hot work and on steel for cementation, all with the purpose of obtaining corrosion parameters and concluding which of the tested samples is more resistant to local pitting corrosion. Electrochemical tests were performed in a medium of 3.5% NaCl, and were based on conducting cyclic anodic polarization in the potential range from -2000 mV to 200 mV vs SCE and vice versa. The results of the research showed that all three samples are subject to pitting corrosion, but the worst was the cementing tool steel sample X19NiCrMo4, which registered the lowest pitting potential. The W600 tool steel sample for hot work proved to be the best, with the highest pitting potential.
The results of the electrochemical tests coincide with the metallographic tests, because after corrosion in the chloride medium only the beginnings of pitting corrosion are visible on the surface of the W600 sample in the form of partial accumulations of corrosion products, while the X19NiCrMo4 cementing steel sample was completely covered with corrosion products, which means that of the three tested tool steels, cementing steel is the most susceptible to pitting corrosion and is not recommended for use in conditions where it comes into contact with chloride ions. The martensitic microstructure of cementing tool steel is responsible for the very low pitting potential and, consequently, pronounced pitting corrosion. On the other hand, the W600 tool steel showed better corrosion resistance due to its finer grain and uniform carbide distribution.

• Keywords: pitting korozija; alatni čelici; ciklička anodna polarizacija; 3; 5 % NaCl; mikrostruktura
• Keywords (english): pitting corrosion; tool steels; cyclic anodic polarization; 3.5% NaCl; microstructure
• Language: croatian
• URN:NBN: urn:nbn:hr:115:707905
• Study programme: Title: Graduate study program Metallurgy; Study programme type: university; Study level: graduate; Academic / professional title: magistar/magistra inženjer/inženjerka metalurgije (magistar/magistra inženjer/inženjerka metalurgije)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access; Embargo expiration date: 2022-09-29
• Created on: 2022-09-21 19:11:36