Block Boundary Analyses to Identify Martensite and Bainite

Revealing the Unexpected Two Variant Pairing Shifts Due to Temperature Change in a Single Bainitic Medium Carbon Steel

“…Changes in variant pairing of bainite with temperature have previously been reported [34,35,46,48] but the observation of three different dominating variant pairing in the same alloy at different temperatures, as here observed, has not been reported previously. Kaneshita et al, [34] investigated a low alloyed steel with 0.75 wt pct carbon partly transformed to bainite at 400°C and 500°C and observed variant pairs with small misorientation such as V1-V4 and V1-V8 dominating at high temperature as also observed in this work.…”

“…The large difference in carbon content makes the comparison difficult, but they did report the same trend for variant pairing at intermediate and high temperatures as in the present study. Morito et al [48] determined the variant pairing of bainite at temperatures between 300 and 400°C. For the bainite formed at the lower temperature the most frequent variant pairing was V1-V6 in accordance with the results in this work.…”

“…In the work previously mentioned by Morito et al [48] they used variant pairing as a tool for structural determination of martensite, lower bainite and upper bainite. The bainite formed at the lower temperature was characterized as lower bainite where the most frequent variant pairing was V1-V6 and with increased temperature they characterized the bainitic structure as upper bainite when the most frequent variant pairing had shifted to V1-V2.…”

“…For bainite formed at intermediate austempering temperature, and medium carbon martensite, 0.6-1.05 wt pct, V1-V2 is the preferred variant pairing. [33,48] For bainite formed at high austempering temperatures and for low carbon martensite, 0-0.35 wt pct, [33,46] both have variant pairs with low angle boundaries, V1-V4. For bainite formed at the lowest austempering temperatures V1-V6 is the most frequent variant pairing while for high carbon martensite, >1.05 wt pct, the most frequent variant pairing is V1-V16.…”

Effect of Carbon Content on Variant Pairing in Bainitic Low Alloy Steel

“…They suggested that this effect was attributed to the increased strength of the austenite as a result of the increased amount of carbon, where slip deformation becomes more difficult resulting in multiplication of the variants. [27] Morito et al observed V1-V6 variant pairing for bainite formed at lower temperatures [43] in accordance with the present work. However, in their study only two temperatures were investigated, and thus the two types of dominant variant pairing which were found were coupled with lower bainite for the V1-V6, and upper for the V1-V2.…”