An investigation of boride layers growth kinetics on carbon steels

U ovom radu analizirana je kinetika nastanka boridnih slojeva na nelegiranim C15 i C70W2 čelicima. Boriranje u krutom sredstvu provedeno je u temperaturnom intervalu 870 ÷ 970 °C u trajanju 4 ÷ 8 h. Prosječna debljina boridnih slojeva na čeliku C15 kreće se u intervalu 69,9 ÷ 239,2 µm, a na čeliku C70W2 u intervalu 60,6 ÷ 181,2 µm. Mikrotvrdoća boridnog sloja određena je Vickersovom metodom HV 0,1. Utvrđeno je da je tvrdoća željeznog borida Fe2B približno jednaka za oba čelika i da ne ovisi o temperaturi i trajanju boriranja. Na osnovu prosječnih debljina boridnih slojeva i uz pomoć klasične metode za boriranje oba čelika određene su vrijednosti aktivacijske energije i faktora frekvencije. Na osnovu ovih vrijednosti za oba čelika dobiveni su praktični empirijski izrazi koji pokazuju ovisnost debljine boridnog sloja o temperaturi i trajanju boriranja.Kinetics of boride layers formation on C15 and C70W2 carbon steels has been investigated in this paper. Pack boronizing was carried out in temperature range 870 ÷ 970 °C with durations 4 ÷ 8 h. Average thickness of boride layers obtained on C15 steel ranges was from 69,9 to 239,2 µm, and on C70W2 steel from 60,6 to 181,2 µm. Microhardness of boride layers was estimated by means of Vickers HV 0,1 method. It was determined that hardness values of Fe2B iron boride obtained on both steels were almost equal, and did not depend on temperature and duration of boronizing. Based on the average thickness of boride layers and through usage of classical kinetics method, values of activation energy and frequency factor were determined. Based on these values, practical empirical expressions for boronizing of C15 and C70W2, indicating the dependence of boride layer thickness on boronizing temperature and time, were derived