TRANSFORMATION OF UPPER BAINITE IN 55SiMnMo STEEL DURING TEMPERING

The transformation of upper bainite of normalized 55SiMnMo steel during tempering hasbeen studied by optical microscopy,X-ray diffraction,transmission electron microscopy anddifferential scanning calorimetry.Ferrite plate surface is parallel to ferrite{110}and is thecoherent interface for α and γ,the crystallographic relationship is(111)_γ,∥(011)_α.The smallplate surface of Fe_3C precipitated during tempering is parallel to(100).The strengtheningmechanism for carbon-rich austenite in normalized condition is primarily uniform solid so-lution hardening,however,in the tempered state,it is strengthened chiefly by non-uniformone.