Contribution of interphase precipitation on yield strength in thermomechanically simulated Ti–Nb and Ti–Nb–Mo microalloyed steels

The contribution of interphase precipitation on yield strength was studied in Ti–Nb and Ti–Nb–Mo microalloyed steels. The high yield strength is partially attributed to strengthening induced by high degree of interphase precipitation of nanoscale carbides, which are nucleated during continuous cooling. The nanoscale carbides in Ti–Nb–Mo steel were identified as (Ti,Nb,Mo)C crystal structure similar to (Ti,Nb)C in Ti–Nb steel. The interphase precipitation of these carbides with planar or curved boundary, different row spacing and different orientation of the rows in the ferrite grain is related to the mobility of grain boundaries during γ/α transformation based on ledge mechanism. The contribution of interphase precipitation to yield strength was estimated to be ~320 MPa and ~170 MPa for Ti–Nb–Mo and Ti–Nb steels. The low yield ratio that is important from the perspective of structure application is attributed to the dual phase microstructural consisting of ferrite and bainite.