Dvodimenzionalni model razogljičevanja jekla 51CrV4

Operčkal, Neja (avtor), Karpe, Blaž (mentor), Kovačič, Miha (komentor)

V diplomskem delu smo na brušenih vzorcih raziskovali razogljičenje podevtektoidnega jekla 51CrV4 v odvisnosti od temperature in časa žarjenja. Vzorce smo žarili 2 in 4 ure v zračni atmosferi na temperaturah 760°C (Ac1 < Tž < Ac3), 860°C (Ac3 < Tž < TG) in 1092°C (Tž > TG), ki smo jih izbrali na podlagi faznega diagrama tega jekla. Na metalografski način smo izmerili debelino oksidne plasti in globino razogljičenja ter raziskali vpliv temperature na mehanizem razogljičenja. Z upoštevanjem pridobljenih rezultatov smo najprej izdelali enostavni enodimenzionalni matematični model, s katerim smo določili okvirne vrednosti difuzijskih koeficientov ogljika pri posameznih temperaturah ter nato še dvodimenzionalni matematični model razogljičenja (MKD), ki upošteva sprotno oksidacijo jekla in s katerim lahko napovemo stopnjo razogljičenja pri teh temperaturah in časih žarjenja tudi na robovih in utorih vzorca. Z višjo temperaturo in daljšim časom žarjenja globina razogljičenja narašča, zaradi kemične nehomogenosti v jeklu pa ne bo konstantna niti pod ravno brušeno površino. Izračunane vrednosti difuzijskih koeficientov ogljika v jeklu 51CrV4 zato predstavljajo mejne vrednosti. Z dvodimenzionalnim modelom, ki upošteva sprotno oksidacijo jekla, dobimo nižje vrednosti difuzijskih koeficientov, nekoliko večje razlike pa so samo pri najvišji temperaturi žarjenja. Izračunane vrednosti difuzijskih koeficientov so znotraj velikostnega razreda vrednosti podanih v literaturnih virih.

• Jezik: Slovenski jezik
• Ključne besede: razogljičenje, oksidacija, jeklo 51CrV4, toplotna obdelava, dvodimenzionalni model razogljičenja
• Vrsta gradiva: Diplomsko delo/naloga
• Organizacija: NTF - Naravoslovnotehniška fakulteta
• Leto izida: 2019
• PID: 20.500.12556/RUL-111125
• COBISS.SI-ID: 1837407
• Datum objave v RUL: 25.09.2019

OPERČKAL, Neja, 2019, Dvodimenzionalni model razogljičevanja jekla 51CrV4 [na spletu]. Diplomsko delo. [Dostopano 6 maj 2025]. Pridobljeno s: https://repozitorij.uni-lj.si/IzpisGradiva.php?lang=slv&id=111125

Sekundarni jezik

• Jezik: Angleški jezik
• Naslov: Two-dimensional model of decarburization of 51CrV4 steel

Izvleček

In this diploma work, we have been studied decarburization of 51 CrV4 plain steel with respect to the temperature and time of annealing. Experiments were done on ground samples, which were heat treated for 2 and 4 hours in an air atmosphere at temperatures: 760°C (Ac1<Tž<Ac3), 860°C (Ac3<Tž<TG) and 1092°C (Tž>TG). The distinctive temperatures have been chosen on the basis of the steel phase diagram. Using metallographic methods, we measured the thickness of the oxide layer and decarburization depth and analysed the influence of temperature on decarburization mechanisms. Considering the obtained results, we first programmed a simple one-dimensional mathematical model to determine the approximate values of the carbon diffusion coefficients at individual temperatures, and then a two-dimensional numerical model of decarburization (FDM), which takes into account the simultaneous oxidation of steel during decarburization and can predict the degree of decarburization at these temperatures and the annealing times also at the edges and grooves of the sample. With higher temperature and longer annealing time the depth of the decarburization increases, but because of the chemical inhomogeneity in the steel, it will not be constant even under a smooth ground surface. The calculated values of the carbon diffusion coefficients in the steel 51CrV4, therefore, represent the limit values. With a two-dimensional model that considers the simultaneous oxidation of steel, we get lower values of diffusion coefficients, and slightly larger differences are only at the highest temperature of the annealing. The calculated values of the diffusion coefficients are within the size class of the values given in the literature sources.

• Ključne besede: decarburization, oxidation, 51CrV4 steel, annealing, FDM two-dimensional decarburization model