Effects of austenitizing temperature and cooling rate on microstructure and properties of Nb-containing high carbon steel

doi:10.13251/j.issn.0254-6051.2020.06.001

Abstract

Abstract: Heat treatment of a Nb-containing high carbon steel at different austenitizing temperatures and cooling rates was carried out by Gleeble 1500 thermal simulation test machine. The microstructure, hardness and pearlite lamellar spacing of the tested steel were observed and measured by means of metallographic microscope, scanning electron microscope and hardness tester. The results show that when the austenitizing temperature is 950 ℃, the grain size of the tested steel after quenching is 34 μm, the hardness is 813 HV5, and the microstructure cooled to room temperature with cooling rate of 0.1-5 ℃/s is pearlite+ferrite. When the austenitizing temperature is 1200 ℃, the grain size after quenching is 134 μm, the hardness is 827 HV5, and the microstructure cooled to room temperature with cooling rate of 0.1-1 ℃/s is pearlite + ferrite, while that with 5 ℃/s cooling rate is acicular martensite+a small amount of ferrite. Above 1220 ℃, all Nb is completely dissolved in austenite, and too high austenitizing temperature will result in too much grain growth. The pearlite lamellar spacing becomes smaller as the austenitizing temperature increases and the cooling rate increases, and the decrease in the lamellar spacing can increase the hardness value.

Key words: Nb-containing high carbon steel, austenitizing temperature, cooling rate, hardness, pearlite lamellar spacing

CLC Number:

TG142

Da Guangjie, Yang Zhongmin, Wang Kai, Chen Ying, Wang Huimin, Li Shaohua. Effects of austenitizing temperature and cooling rate on microstructure and properties of Nb-containing high carbon steel[J]. Heat Treatment of Metals, 2020, 45(6): 1-6.

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