Precipitate evolution in grain oriented electrical steel and high strength low alloy steel

Abstract

Grain oriented (GO) electrical steels are used in transformers and high strength low alloy (HSLA) steels are used in automotive industry. Precipitates play an important role in both steels. The evolution of precipitate composition and size in GO electrical steel during simulate high temperature coil annealing was investigated in detail using state-of-the-art scanning transmission electron microscopy (STEM) based techniques. The role of precipitates with different compositions and sizes play during the secondary recrystallization process was illuminated. Precipitation and recrystallization behaviors were investigated in a cold-rolled Ti-V HSLA steel both during isothermal annealing and continuous annealing. A unique combination of techniques including state-of-the-art TEM and STEM, a matrix dissolution based method and SANS was used to quantify precipitates. In this way precipitate size, composition and volume fraction was always quantitatively obtained by two techniques allowing their close comparison. Recrystallization kinetics, geometrically necessary dislocation (GND) density and texture evolution were investigated in detail based on EBSD data. The effects of different soaking temperatures and times on the microstructure and mechanical properties were revealed after precipitation and recrystallization behavior investigation at the early stage of continuous annealing. All microstructural experimental inputs (and their change during annealing) allowed quantitative modeling of the strengthening mechanisms, which together are in good agreement with the obtained yield strengths during annealing of the steel.