Control of precipitation morphology in the novel HSLA steel
Journal
Materials Science and Engineering A
Journal Volume
634
Pages
123-133
Date Issued
2015
Author(s)
Abstract
Examination of 20 thin foils of the specimens with or without deformed austenite with transmission electron microscopy revealed both interphase precipitation and random precipitation in the ferrite for each experimental condition. In the hot deformed condition, random precipitation is more likely to occur within most ferrite grains. Without hot deformation, interphase precipitation is likely to occur in the ferrite matrix. Based on the austenite decomposition kinetics, the occurrence of random precipitation within the most deformed ferrite grains can be ascribed to the acceleration of the austenite/ferrite interface movement velocity resulting from the heavy hot deformation, which causes many microalloying elements to remain mostly in the ferrite matrix and then precipitate homogeneously after further isothermal holding.Vickers hardness data revealed that, in specimens isothermally held at 650. °C without hot deformation, the range of hardness distribution was 180-320. HV 0.1 after 5. min of isothermal holding, and 170-250. HV 0.1 after 60. min. For specimens isothermally held at 650. °C with 20% hot deformation at 900. °C, the range of the hardness distribution was 200-260 for 5. min of isothermal holding, and 210-240 for 60. min. Therefore, the average microhardness decreased with the isothermal holding temperature and time, and a narrower range of hardness distribution occurred in specimens that underwent hot deformation. The narrower Vickers hardness distribution reflects more uniform precipitation in each ferrite grain.
Type
journal article