Razvoj mikrostrukture med kontinuirnim ohlajanjem jekla Protac 600

Pašić, Armin (avtor), Nagode, Aleš (mentor)

V okviru diplomskega dela smo analizirali razvoj mikrostrukture med kontinuirnim ohlajanjem jekla PROTAC 600 z namenom določiti optimalno temperaturo avstenitizacije in potrebne ohlajevalne hitrosti. Poznavanje teh dveh parametrov je ključno za doseganje najosnovnejših zahtev jekla PROTAC 600. V okviru eksperimentalnega dela smo izvajali dilatometrske preizkuse na vzorcih v obliki valjčka dolžine 10 mm in premera 3 mm, s pomočjo katerih smo določili temperaturo avstenitizacije in temperature faznih premen ter nato na njih še izmerili trdote in naredili metalografsko analizo. Na podlagi dobljenih rezultatov smo izrisali kontinuirani premenski diagram (CCT), iz katerega smo določili parametre za toplotno obdelavo oklepne pločevine iz jekla PROTAC 600. Z dilatometrijo določene premenske temperature so: Ac1 = 720 °C, Ac3 = 780 °C, Ms = 260 °C in Mf = 154 °C. Te vrednosti smo primerjali s premenskimi temperaturami, ki smo jih izračunali z empiričnimi enačbami. Razvoj mikrostrukture smo spremljali pri ohlajanju iz temperature avstenitizacije (870 °C) s hitrostmi ohlajanja med 0,05 °C/s in 100 °C/s. Pri ohlajevalni hitrosti do 0,1 °C/s je mikrostruktura sestavljena iz ferita, perlita, bainita in martenzita. Pri ohlajevalnih hitrostih med 0,3 °C/s in 1 °C/s imamo v mikrostrukturi bainit in martenzit. Od zgornje kritične ohlajevalne hitrosti 3 °C/s je v mikrostrukturi prisoten samo še martenzit. Skladno z mikrostrukturo se spreminjajo tudi trdote, ki naraščajo s povečevanjem ohlajevalne hitrosti. Najvišje izmerjena trdota znaša 656 HV0,5 pri hitrosti 20 °C/s, najmanjša pa 449 HV0,5 pri 0,1 °C/s. Zahtevano minimalno trdoto 570 HB, kar je preračunano po Vickersu 600 HV, dosežemo pri hitrosti ohlajanja 0,3 °C/s.

• Jezik: Slovenski jezik
• Ključne besede: PROTAC 600, dilatometrska analiza, kontinuirni premenski diagram (CCT), trdote, mikrostrukturna analiza
• Vrsta gradiva: Diplomsko delo/naloga
• Organizacija: NTF - Naravoslovnotehniška fakulteta
• Leto izida: 2019
• PID: 20.500.12556/RUL-113286
• COBISS.SI-ID: 1851487
• Datum objave v RUL: 19.12.2019

Sekundarni jezik

• Jezik: Angleški jezik
• Naslov: Microstructure development of Protac 600 steel during continious cooling

Izvleček

In this diploma thesis the microstructure development during the continuous cooling of PROTAC 600 steel was analyzed in order to determine the optimum austenitization temperature and cooling rates. The two parameters are crucial for meeting the required hardness of PROTAC 600 steel. Experimental part consisted of dilatometer tests, hardness measurements and metallographic analysis. Dilatometer tests were performed, using specimens in the form of a cylinder with a length of 10 mm and a diameter of 3 mm, to determine the austenitization and phase transformation temperatures. Based on the obtained results, a continuous cooling diagram (CCT) was drawn from which the heat treatment parameters of the armor plate made of PROTAC 600 steel were determined. The temperatures determined with dilatometric analysis are: Ac1 = 720 °C, Ac3 = 780 °C, Ms = 260 °C and Mf = 154 °C. These values were compared with the transformation temperatures calculated with the empirical equations. The evolution of the microstructure was monitored during the cooling from austenitization temperature (870 °C) with cooling rates between 0.05 °C/s and 100 °C/s. At a cooling rate of up to 0.1 °C/s, the microstructure consists of ferrite, perlite, bainite and martensite. At cooling rates between 0.3 °C/s and 1 °C/s, bainite and martensite are present in the microstructure. When upper critical cooling rate of 3 °C/s is applied, only martensite is present in the microstructure. Increased cooling rate while affecting the microstructure also causes the hardness increment. The maximum hardness measured is 656 HV0.5 at a cooling rate of 20 °C/s and the lowest is 449 HV0.5 at a cooling rate of 0.1 °C/s. The minimum required Brinell hardness of 570 HB (converted to Vickers 600 HV) is achieved at a cooling rate of 0.3 °C/s.

• Ključne besede: PROTAC 600, dilatometric analysis, continuous cooling transformation diagram (CCT), hardness measurement, microstructure analysis