| Titanium resources are very abundant in China and its price is relatively cheap.The precipitation of titanium can make precipitation strengthening and grain refinement in steels,so it is an effective way to develop high strength steel used Ti microalloying technology.In this paper,the casting blank(main component is 0.051% C-0.96%Mn-0.104%Ti)comes from the production site.By means of physical thermal simulation method in laboratory,the static recrystallization behavior and the microstructure evolution under different process parameters were all studied,on this basis,the effect of TMCP progress to the organization and performance was researched.The experimental results showed that:(1)In the same pass interval time,the recrystallization softening rate under different experimental parameters show that: the high temperature and large deformation are beneficial to the occurrence of static recrystallization,the effect of strain rate and original austenite grain size on the static recrystallization is relatively small.Both the deformation temperature above 980? and deformation more than 30%,the static recovery is dominant when the pass interval time was less than 1s,within 1s to 10 s,the static recrystallization softening rate increase rapidly,After more than 30 s,the recrystallization softening rate rise slowly.(2)When the pass interval time is 1s,the number of TiC particles is less,when the pass interval time is 100 s,the strain-induced precipitation of TiC particles increases significantly and will pin the dislocation at 950?,which will inhibit the static recrystallization process.(3)With the increase of cooling rate,the starting and ending temperature of phase transition show a trend of decline,grain size becomes more and more refined.When the cooling rate is 20?/s,the temperature range of dynamic phase transition is 513.4~717.8?.The deformation can make the CCT curve move upwards and will improve the phase transition staring temperature.Meanwhile,the deformation will accelerate the transformation speed of the phase transition and enlarge the region of proeutectoid ferrite,it aslo will refine the bainite grain.(4)Due to the low carbon content of the test steel,there is no pearlite transition on the static CCT curve.When the cooling rate is greater than 5?/s,the proeutectoid ferrite phase transition will be restrained and the main structure is granular bainite.when the cooling rate is less than 1?/s,there has pearlite transition on the dynamic CCT curve.when the cooling rate is more than 10?/s,the proeutectoid ferrite phase transition will be restrained and the main structure is granular bainite.With the further improvement of the cooling rate,the organization of the phase transition changes from granular bainite to lath bainite.(5)Comparison of strength under different deformation and cooling processes,DW and DA steel has 30% of the deformation at 1050? and 900?,the strength value of DW steel which heated preservation at 600? for 60 min is 696 MPa,the strength value of DA steel which has air cooling direct is 614 MPa,their organization were first eutectoid ferrite and granular bainite.SW and SA steel has 50% of the deformation at 1050 ?,the strength value of SW and SA were 625 MPa and 570 MPa,their organization were first eutectoid ferrite and granular bainite,accompanied by a small amount of acicular ferrite.The strength value of the steel DW is highest and its strengthening methods were fine grain strengthening and precipitation strengthening.The cooling process has the greatest influence on the yield strength of the experimental steel.(6)TiC particles will precipitate at 600? and its particle size is nanometer.These precipitated particles can pin the dislocation and play a important role in precipitation strengthening.Air cooling will inhibit the precipitation of TiC because of the high speed of cooling rate. |
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