In situ observation of continuous cooling transformation of Mn-Cr-Mo bainite rail steel

doi:10.13251/j.issn.0254-6051.2022.08.005

Abstract

Abstract: Effects of austenitizing temperature of 1250 ℃, 950 ℃ and cooling rate of 0.8 ℃/s, 1.5 ℃/s on continuous cooling transformation of Mn-Cr-Mo bainite rail steel were studied by in-situ observation. The results show that the bainite plates nucleate and grow up orderly on grain boundaries simultaneously or non-simultaneously, but disorderly non-simultaneously in grain. The nucleated bainite plates on grain boundaries and in the grains grow at approximately the same constant rate, and the plates with different orientation stop growing when colliding grain boundaries or the preformed bainite plates and form a "cross-like" bainite structure. The growth rate of the plates is mainly controlled by the driving force of phase transformation, and the size and strength of austenite are the main factors affecting the length of the final bainite plates. It is concluded that lowering the austenitizing temperature and accelerating the cooling rate of bainite transformation can speed up the growth of the plates, shorten the transformation time and reduce the amount of transformed bainite. As a result, a fine, uniform and stable bainite plate structure can be obtained. Further, the average growth rate of bainite plates in Mn-Cr-Mo bainite rail steel is calculated to be 4.053 μm/s, which supports the diffusion-controlled phase transformation mechanism.

Key words: in situ observation, austenitizing temperature, cooling rate, growth rate

CLC Number:

TG111.5

Zhang Di, Bao Xirong, Chen Lin, Wang Xiaodong, Zhao Wenqian, Song Ran. In situ observation of continuous cooling transformation of Mn-Cr-Mo bainite rail steel[J]. Heat Treatment of Metals, 2022, 47(8): 34-39.

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