关键词: 非调质钢, 原位观察, 固态相变, 先共析铁素体, 冷却速率

Abstract: Type and distribution of ferrite precipitated in a non-equilibrium austenite phase at different cooling rates were observed by high temperature laser scanning confocal microscope, and the effect of cooling rate on the solid-state phase transformation behavior of non-quenched and tempered steel was investigated. The results show that at the low cooling rate of 0.1 ℃/s, the ferrite shows the characteristics of zigzag, strip and needle diversity. When the cooling rate increases to 5 ℃/s, the ferrite morphology is mainly acicular and cellular. When the cooling rate is between 0.1 ℃/s and 5 ℃/s, the phase transformation process of γ→α is delayed with the increase of the cooling rate, which decreases from 723-665 ℃ at 0.1 ℃/s to 602-550 ℃ at 5 ℃/s. Moreover, with the increase of cooling rate, the incubation time difference between the grain boundary and intragranular acicular ferrite decreases from 77 s at 0.1 ℃/s to 5 s at 5.0 ℃/s. The Al₂O₃ inclusion enriched with carbon nitride can be used as nucleating particle to induce cellular ferrite growth. The growth direction diffuses around the particle, and the diffusion rate is affected by the cooling rate. Multiple cells of cellular ferrite connect to form lamellar ferrite films.

Key words: non-quenched and tempered steel, in-situ observation, solid-state phase transformation, proeutectoid ferrite, cooling rate