Abstract
The present paper is aimed at the study of the kinetics of Mn, Si, Cr partitioning in 0.2wt%C-Si2Mn2CrMoVNb TRIP-assisted steel under the annealing at 770 oC and 830 oC to be within the intercritical temperature range. The work was fulfilled using SEM, EDX, dilatometry, and hardness measurements. It was found that under heating a redistribution of the alloying elements between ferrite and austenite took place. Specifically, silicon partitioned to ferrite while chromium diffused to austenite with distribution coefficient values of 1.12-1.21 (KSi) and 0.75-0.86 (KCr). Manganese was found to partition to a much greater extent resulting in a distribution coefficient of KMn=0.38-0.50 and 2.6 times higher concentration in austenite as compared to ferrite. As annealing temperature raised from 770 oC to 830 oC the elemental partitioning was accelerated, followed by the decrease in manganese content in austenite (by 1.44 time) and ferrite (by 1.34 time) caused by an increase in austenite volume fraction. Silicon featured uneven distribution within ferrite to be accumulated at the “martensite/ferrite” interface and near ferrite grain boundaries, while manganese was concentrated in MC carbides. The recommendation for annealing holding was formulated based on elemental partitioning kinetics.
Highlights
Low carbon Mn-Si(Al) steels with TRIP effect (TRIP-assisted steels) remain attractive for researchers due to improved mechanical properties achieved under the low content of alloying elements [1,2,3]
TRIP-assisted steels are subjected to bainitizing heat treatment with preliminary annealing at intercritical temperature range (ITR), where carbon partitioning between ferrite and austenite takes place [1, 7, 8]
Increasing the temperature between Ac1 and Ac3 leads to alteration of the “ferrite/martensite” ratio in favour of martensite causing the increase in hardness
Summary
Low carbon Mn-Si(Al) steels with TRIP effect (TRIP-assisted steels) remain attractive for researchers due to improved mechanical properties achieved under the low content of alloying elements [1,2,3] They belong to the group of Advanced High Strength Steels (AHSSs) [4]. Other (substitutional) elements (Si, Mn, Cr, etc.) could be involved in partitioning under ITR, affecting the stability of austenite to phase transformations upon bainitizing treatment or cooling [21]. This phenomenon was studied repeatedly to highlight its importance for steel transformation behaviour [22,23,24,25,26]. The same results for manganese were reported in [23] for 6 wt% Mn - 1.4 wt% Si TRIP-assisted steel, no partitioning of Si and Al
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