A Coupled Carbide Precipitation Kinetics Model for Tempering of Hot Stamped Ultra-High Strength Boron Steel

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University of Guelph

Abstract

This thesis details the modelling of two coupled phenomena: the competing precipitation of the two extant carbide phases present during short-cycle tempering (0.5 – 15 s) of a martensitic microstructure between 100 ⁰C and 700 ⁰C; and the impact of tempering on the steel’s hardness. Precipitated carbides are quantified using SEM images and adjusted stereologically to account for errors in 2D quantification of 3D objects. A single-class precipitation model is applied, predicting the mean values of competing particle growth between a metastable and stable phase. The particle number density and mean radius are then applied to a microstructure-based hardness model. This model is compared with the typical Hollomon-Jaffe kinetic hardness model. Additionally, the extraction of a meaningful particle size distribution from the mean value precipitation model is examined.

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Keywords

Steel hardness, Hot stamped, Boron steels

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