BAINITE TRANSFORMATION IN A SILICON STEEL

The processes of upper bainite formation, the crystallographic aspects and the internal structure in a 1.83% silicon steel have been investi gated. The T-T-T diagram is separated into two C-curves as in the case of steels containing strong carbide forming elements. in the early st age of upper bainitic transformation, very fine needlelike ferrite sub units with the parallelogram cross sections elongated in a (110)(gamma )//(111)(alpha) direction form on a {111}(gamma) sheet in a side-by-si de fashion. in the later stage of transformation, these subunits are c oalesced on a {111}(gamma) plane and produces upper bainite laths. Thi s bainite is always related to the parent austenite with the Kurdjumov -Sachs relationship and accompanies the surface reliefs. epsilon carbi de particles precipitate mainly after the ferrite subunits formation o r after the coalescence of them. Therefore, the carbide precipitation is not a fundamental characteristic of bainite transformation but is a secondary effect. epsilon carbide needles precipitating within a bain ite lath by long time holding are aligned almost parallel to the (112) (alpha) with almost constant intervals and are related to the ferrite by the Jack relationship. These aspects are exactly similar to those i n tempered martensite. Such an epsilon carbide configuration is though t to arise from the precipitation on the dislocations introduced durin g transformation.