Effect of Nb micro-alloying on granular bainite transformation and SH-CCT curves in simulated heat-affected zone of high strength low alloy steel

doi:10.13251/j.issn.0254-6051.2023.09.026

Abstract

Abstract: Four kinds of high strength low alloy steels with niobium content were designed, and the effect of niobium microalloying on the granular bainite transformation in the simulated weld heat affected zone was studied by using the Gleeble-3500 thermal simulator, which was characterized by SH-CCT (Simulated heat affected zone continuous cooling transformation). The result shows that the transformation temperature of continuous cooling transformation decreases with the addition of Nb. The continuous cooling phase transformation temperature is about 700 ℃ to 500 ℃ at the range of medium welding heat input, where the granular bainite transformation takes place. The t_8/5 range of the granular bainite transformation increases with the increase of Nb content. When the Nb content in the tested steel is increased to 0.180wt%, the range of cooling rate t_8/5 for transformation of granular bainite is around 3-150 s. The increase of Nb content promotes the continuous cooling granular bainite transformation and expands the t_8/5 range. The microhardness increases with the increase of Nb content. The higher the Nb content, the higher the microhardness at the same t_8/5condition. When the content of Nb is 0.085wt%, the change of microhardness value is the smallest in the large heat input range (t_8/5=15-80 s). The microhardness value varies from 183 HV to 192 HV. The SH-CCT curves provides a theoretical design of niobium microalloyed steel based on the weldability.

Key words: high strength low alloy steel, Nb micro-alloying, SH-CCT curves, granular bainite

CLC Number:

TG113.26⁺3

Yan Wenze, Yan Wenqing, Lin Xuanyi, Wang Honghong. Effect of Nb micro-alloying on granular bainite transformation and SH-CCT curves in simulated heat-affected zone of high strength low alloy steel[J]. Heat Treatment of Metals, 2023, 48(9): 150-156.

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