By comparing the phosphorated steel sheets containing different P content with Al-killed steel sheet, P distribution and AlN precipitation as well as their interaction and their effect on dynamic phase transformation, dynamic recrystallization and mechanical properties during hot deformation process have been studied. The results show that P segregates in sub-grain boundary and grain boundary. The segregation coefficient increases with the increase of P content, but decreases with the increase of deformation temperature. P moves with the movement of dislocation during hot deformation process and segregates in grain boundary after recrystallization. Hot deformation promotes AlN precipitation. The size of AlN is 130 ～ 360 A when deformation is below 900 ℃ and their shapes display as square、needle and particle, the pinning effect of particle on dislocation is obvious. When the deformation temperature is above 900 ℃, the size of AlN is below 100A and the pinning effect of particle isn't obvious. The value and size of AlN decrease with the increase of deformation temperature. There is affinity effect between P and [N], the effect increases with the increase of P content. P doesn't promote AlN precipitation. On the contrary, it diminishes AlN precipitation. The static phase transformation point of phosphorated steel sheets is higher than that of Al-killed steel sheet, P increases the Ar_3 point while AlN precipitation decreases the point, both of the effects are obvious. The Ar_3 point of phosphorated steel sheets and Al-killed steel sheet are higher than their corresponding Ar_3 point. the reason is mainly due to hot deformation. Both of steel sheets have characteristic dynamic recrystallization curves. P and AlN has different effect on promoting recrystallization. AlN precipitation promotes the dynamic recrystallization, and diminishing effect of P on growing of recrystallization grain is not obvious. Hot deformation stress is mainly effected by AlN precipitation. The solid solutioned strengthening effect of P isn't obvious during hot deformation process. Comparing with Al-killed steel sheet, phosphorated steel sheets have good hot plasticity. AlN precipitation decrease hot plasticity, the property increases with the increase of P content because P diminishes AlN precipitation. P is very beneficial to the hot deformation process.
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