The accurate prediction of soluble Nb content during reheating is helpful for the design of chemical composition and reheating parameters for Nb-containing steels.The dissolution behavior of Nb in high Nb microalloyed steels was investigated.The results show that Nb does not entirely dissolve for high Nb microalloyed steels containing Ti after holding at 1 300℃ for 3h.The soluble Nb content increases with the decrease of C content and/or the increase of Nb content in steels.Moreover,an expression has been established to describe the amount evolution of soluble Nb in high Nb microalloyed steels during reheating and the validity of this expression has also been verified by experiment.
Nb is often considered to be a powerful alloying element for controlling the recrystallization process in microalloyed high strength steels.However,Nb can be presented either as solute in solution,where it is thought to exhibit a strong solute drag effect,or as NbC precipitates,which are thought to be effective at pinning grain boundaries.Therefore,it is very important to quantitatively measure Nb in solution or in NbC precipitates.A quantitative analysis method of Nb in solution and in precipitates was proposed.The test procedure involved chemical dissolution,filtration and inductively coupled plasma atomic emission spectroscopic(ICP-AES) analysis.The amount of Nb in solution in Nb-microallyed steels under different treatment conditions was evaluated.The results show that the niobium and carbon contents in steels have a great effect on niobium dissolution kinetics.The solute Nb is more effective to retard dynamic recrystallization,while the NbC precipitates are more effective to inhibit static recrystallization.The results may help to comprehend effect of Nb in steels,and provide some guides in the design of new high strength Nb-bearing steels.
XIAO Fu-renCAO Ya-binQIAO Gui-yingZHANG Xiao-bingLIAO Bo
The behavior of the flow deformation and the effects of contents of Nb and C on deformation behaviors of high Nb X80 pipeline steels during hot compression deformation were studied by thermal simulation test. The content of solid solution Nb was quantificationally studied during the reheating and hot deformation process, and the effects of change of solid solution Nb in steels on hot deformation behaviors were discussed. The results show that the contents of Nb and C have great effects on the flow stress behaviors of high Nb X80 pipeline steels. When the C content in steels is constant, the recrystallization activation energy increases from 387 to 481 kJ/mol with increasing the Nb from 0.082% to 0.13% (mass fraction). However, the effect of Nb is correlative to the C content, i.e. w(Nb)/w(C). When w(Nb)/w(C) decreases from 3.61 to 2.18, the recrystallization activation energy decreases from 481 to 434 kJ/mol.
