Welding Inspection & Metallurgy API ICP Self Study Notes

Bainite
If the steel is cooled such that the formation of pearlite by the short range
diffusion of iron atoms is not possible, bainite can be produced. The bainite
that forms at temperatures just below those at which pearlite forms is termed
upper bainite. At lower temperatures, lower bainite forms. Both lower and
upper bainite consist of aggregates of platelets or laths of ferrite, separated
by regions of residual phases consisting of untransformed austenite or of
phases such as martensite or cementite