EFFECT OF HEATING PROCESS ON AUSTENITE GRAIN AND PRECIPITATES IN 780 MPa GRADE DUAL PHASE HIGH STRENGTH STEEL
The composition of dual-phase high-strength steel contains many alloying elements such as Nb,V and Ti.The heating temperature and heating time have an effect on the austenite grain size,the dissolution,precipitation and recrystallization of alloying elements in the steel,which also have a great impact on the final structure and properties of the product.In this paper,metal material simulation software Jmatpro was used to calculate the precipitated phase in 780 MPa grade dual-phase high-strength steel.According to the calculation results,there are mainly three equilibrium precipitated phases of MN,M(C,N)and MB2 in the test steel in the range of 950～1 600 ℃,and MN begins to precipitate at 1 460 ℃.M(C,N)begins to precipitate at 1 108 ℃.MB2 begins to precipitate at 1 147℃.The annealing test shows that the heating temperature has a significant effect on the austenite grain size of 780 MPa dual-phase high-strength steel.When the heating time is 30 min,1 200～1 300 ℃ is the safe temperature range,the grain size is appropriate and uniform within the temperature range,below the range of mixed crystal phenomenon is serious,above the range of grain coarsening;When the heating temperature is 1 250 ℃,the austenite grain size of 780 MPa dual-phase high-strength steel increases with the increase of heating time,but the effect of heating time on the austenite grain size is weak.
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