Void-closing Behavior and Estimation Using Finite Element Analysis via Hydrostatic Integration in Hot Rolling of S10C Steel Plates

Abstract

The closure of large voids, whose thickness-to-void-height ratio exceeds 0.2, in S10C steel plates during hot rolling was investigated to determine whether hydrostatic integration (Q-value) can be used to predict the closing behavior of large voids. The steel plates with an open void along the rolling (RD), transverse (TD), and normal (ND) directions were hot rolled at 1 000 and 1 300°C with a target rolling reduction of 10% at each pass until 40% total target reduction. It was found that the effect of temperature on the closing behavior was negligibly small. RD and TD voids were almost entirely closed at a reduction of 40%, whereas ND voids could not be closed. The width of RD void was almost linearly decreased with reduction increase. TD void were closed at a lower reduction ratio than RD void. The thickness above and below the void was compressed after rolling in RD void but less reduced in TD void, which is presumable reason of the earlier closure of TD void. The FE analysis clarified that the void volume over initial volume (V/V 0 ) of the voids could be expressed as a function of the Q-value in the case of RD and TD voids. However, the closure behavior of the ND void cannot be expressed by the Q-value. These results indicate that the Q-value can be used to predict the closure of large voids in the RD and TD during rolling, although it cannot be used if the void shape is elongated in the compression direction.