Continuous cooling transformation behavior of austenite in 0.6Ni alloyed medium carbon steel

doi:10.13251/j.issn.0254-6051.2020.04.003

Abstract

Abstract: The dynamic and static continuous cooling transformation and effects of deformation and nickel in 0.6Ni medium carbon steel were carefully investigated by means of hot simulation tests, optical microscope and SEM observations and Vickers hardness test. Experimental results show that the ferrite and pearlite transformations are effectively suppressed while the bainite and martensite transformations are greatly promoted by the deformation in austenite region of the tested steel. Then, the critical cooling rate of full martensite is also lowered from 5 ℃/s to 3 ℃/s. The hardness of full martensite is 810 HV0.1 at the cooling rate of 3 ℃/s under the dynamic continuous cooling condition. However, the hardness of full martensite is 689 HV0.1 at the cooling rate of 5 ℃/s under the static continuous cooling condition. The improvement of martensite hardness can be attributed to the refinement of martensite due to the deformation recrystallization of austenite. The ferrite and pearlite transformations are suppressed and the bainite and martensite transformations are promoted by the addition of 0.6Ni because of the improvement of austenite stability. Then, the Ms temperature is lowered from 329 ℃ to 304 ℃ and also the critical cooling rate of martensite transformation is reduced from 0.5 ℃/s to 0.3 ℃/s. Compared with that of the addition of 0.4Mn, the ferrite and pearlite transformation is largely hindered and the Ms temperature is lowered from 320 ℃ to 304 ℃ by the addition of 0.6Ni. At the same time, the microstructure after cooling is also effectively refined.

Key words: medium carbon alloying steel, CCT curves, alloying element, microstructure, hardness

CLC Number:

TG142.1

Jiang Bo, Hu Xuewen, Zhou Leyu, Wang Zhilin, Zhao Haidong, Liu Yazheng. Continuous cooling transformation behavior of austenite in 0.6Ni alloyed medium carbon steel[J]. Heat Treatment of Metals, 2020, 45(4): 10-15.

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