Characterization of Precipitated Phases in the Weld of G520 Steel during Short-Time High-Temperature Tempering and its Influence on Properties.

The formation mechanism of the reversed austenite and the interaction between austenite inversion and plastic deformation in the G520 martensitic stainless steel welds was studied by adjusting the tempering holding time during post-weld heat treatment. The results show that the weld microstructure has consisted mainly of tempered lath martensite, reversed austenite, and grain boundary precipitation carbides. The volume fraction of the reversed austenite has a great influence on the mechanical properties of the weld. The nucleation position and size of reversed austenite formed at the tempered martensite laths sub-block boundaries or austenite grain boundary are strictly restricted by the orientation of crystal attributing to the parallel orientation relationship between {110} _M and {111}_A. The reversed austenite with low dislocation density is mostly flakiness particle morphology, which greatly refines the tempered martensite laths. The transformation of martensite into reversed austenite is a diffused phase transformation, and the increase in reversed austenite is consistent with the increase in Mn content and Mo content reduction in the weld. For weld with Mn 0.87 wt.% and Mo 1.16 wt.%, the volume fraction of reversed austenite is 14.53%, and the welds exhibit excellent mechanical performance. [ABSTRACT FROM AUTHOR]