| With the improvement of national industrialization,the demand for steel with excellent comprehensive performance is becoming more and more urgent.Ti micro-alloyed steel has attracted more attention because of its excellent performance and low price.But Ti is relatively active,and easy to combine with O,S and impurity element to form inclusion,therefore the function of Ti reduces in the steel.In addition,the precipitate of TiC has a high temperature sensibility,which may lead to fluctuation in steel plate property.According to these problems,the researches are focused on the compound of the micro-alloyed elements,such as Ti,Nb,V,Mo.However,Zr is also a kind of micro-alloyed elements,but the research reports on the influence of Ti micro-alloyed elements are still few.Therefore,the paper researches on how Zr affects Ti micro-alloyed steel austenitizing and carbonitride solution treatment of Ti,and the influence rule of precipitate and recrystallization in Zr deformation austenite on the basis of two micro-alloyed steel,like Ti and Zr-Ti.The research takes advantage of the metallographic microscope(OM),scanning electron microscope(SEM)and transmission electron microscope(TEM)by theoretical calculation,heat treatment and thermal simulation.Calculated by the thermodynamic model,the interaction coefficients of the elements in Zr-Ti steel are as follows,?ZrTi=-0.976+166.15/T??ZrZr=-1.07+190.06/T??CZr=-0.387-2.08/T??NZR=18.9-184.41/T.Therefore,it can be concluded that Zr can reduce the activity of Ti and C in iron matrix and increase the solid solubility in austenite;increase the activity of N in iron matrix and reduce the solid solubility in austenite.The effects experiment of Zr on austenization of Ti micro-alloyed steel and solid solution of Ti carbonitride under different soaking temperatures shows the following results.At 1150?,TiC in Ti micro-alloyed steel may still in a dissolved state.Between 1200 to 1250?,the TiC in these two testing steels is totally dissolved in the austenite in which Zr improves the homogenization of austenite in the testing steels and refines the austenite grain as well.Ti4C2S2 exists in Ti micro-alloyed steel and(Mn,Zr)S and other sulfides exist in Zr-Ti steel.Large-sized and small-sized nitrides exist in both of the testing steels.The large-sized can deteriorate steel's plasticity,toughness and formability,so it should be avoided.Small-sized nitride plays an important role in refining austenite grains.Stress relaxation experiment shows the following results.The PTT curve of micro-alloyed carbonitride in the austenite in these two testing steels shows a"C"-shape curve,the fastest precipitation temperature is about 925?.Zr will postpone precipitation time of carbides with Ti at a low temperature.According to the result of double compression test,the static recrystallization kinetics models of Ti and Zr-Ti are Xs=1-exp[-0.693(t/t0.5)0.715]for Ti steel and for Zr-Ti steel.Furthermore,the static recrystallization activation energy is also calculated,and the results are:142.292kJ/mol for Ti stell and 115.052kJ/mol for Zr-Ti.The deformation austenite structure well anastomotic with soften fraction-time curve.In addition,Zr can improve the deformation resistance of Ti micro-alloyed steel,effectively inhibit the deformation of austenite.According to the analysis result of strain induced precipitated phases,it can be confirmed that the strain induced precipitation in Ti steel is TiC,and the strain induced precipitates in Zr-Ti steel are(Zr,Ti)C.The strain induced precipitated phase is mostly boundary nucleation,and some parts will grow up around the undissolved particles.The strain induced precipitated phase impedes formation of recrystallization.With the addition of Zr,it delays carbide precipitation in the low temperature,and the strain induced precipitation become large(Zr,Ti)C,which may lead static recrystallization more easier to carry out. |
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