Normalization and Spheroidization Treatment of Fe-1.55C-1.14Cr-1.15Al Ultra-High Carbon Steel

In view of the shortage of the isothermal annealing process during the preparation of Fe-1.55C-1.14Cr-1.15Al ultra-high carbon steel with high strength and toughness, the treatment process composed of first with normalizing instead of isothermal annealing and then spheroidizing was presented. The effects of normalizing temperatures and spheroidizing temperatures on the microstructures of tested steels were studied, and then a relatively optimum normalizing and spheroidizing process was determined. The results show that with the increase of normalizing temperature, the lamellar spacing of pearlite in the microstructure of the tested steel increased and the amounts of net-like carbide decreased. The fined microstructure can be obtained after the substitution treatment of normalizing at 1 050 ℃ for 20 min for isothermal annealing. The eutectoid transformation temperature of the tested steel was 790 ℃. At or beyond the temperature, a lot of spheroidized carbides were observed and the spheroidizing completed better and better with the increase of the temperature. The triphase microstructure (F-A-Fe3C) appeared at the temperature between 750 ℃ and 810 ℃ during the spheroidizing process. The appropriate spheroidization process was heating at 850 ℃ for 1 h. The austenite transformed completely and the spheroidized carbides distributed dispersively in austenite substrate after treated with the new process.