Effect of cooling rate on undercooling austenite transformation of 700 MPa automotive beam steel

doi:10.13251/j.issn.0254-6051.2021.02.032

Abstract

Abstract: The continuous cooling transformation (CCT) curves of 700 MPa automotive beam steel 700L were determined by using DIL805L quenching dilatometer. Combined with metallography-hardness method, the phase transformation rules and microstructure as well as the influence factors were analyzed. The results show that the critical point of 700L steel is Ac₃=898 ℃, Ac₁=772 ℃. The transformation product of undercooling austenite is ferrite, pearlite and bainite when the cooling rate is less than 0.5 ℃/s, then pearlite disappears when the cooling rate is more than 0.5 ℃/s, ferrite disappears and the transformation product is all bainite when the cooling rate is 5 ℃/s. A few martensite appears in the transformation products when the cooling rate is 10 ℃/s, and with the increase of cooling rate, martensite increases and bainite decreases gradually until totally disappears. The hardness of the steel gradually increases with the increase of cooling rate, and increases significantly at 10 ℃/s.

Key words: automotive beam steel, continuous cooling transformation (CCT) curve, critical point, microstructure, hardness

CLC Number:

TG151.2

Zhao Nan, Xue Feng, Pan Jin, Guo Weichao, Li Jianchao. Effect of cooling rate on undercooling austenite transformation of 700 MPa automotive beam steel[J]. Heat Treatment of Metals, 2021, 46(2): 178-181.

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