A Novel Way Refining the Partially Reverted Globular Austenite in Reversion from Martensite

Abstract

Refining of the partially reverted globular austenite grain is of great importance to obtain high mechanical property of advanced high strength steels and a new approach for such refining, pretempering of initial martensite, is proposed in this study. The pre-tempering results in precipitation of the coarse and alloying-elements partitioned cementite particles in an Fe-2.5Mn-1.5Si-0.35C alloy. The cementite particles with Mn and Si partitioning enhanced the nucleation of globular austenite grains but suppressed its growth during continuous heating. The enhancement in nucleation and restriction in growth of globular austenite resulted in the refinement of partially reverted globular austenite grains and fully transformed austenite grains after reversion. This provides a new strategy to control the growth of partially reverted globular austenite by tailoring coarse and partitioned cementite particles.

Assessment of Reactivity between Submerged Entry Nozzle (SEN) and Ultra‐low C Liquid Steel: Comparison between Oxide‐Based SEN and Oxide‐Less SEN

“…(2) the aspiration of air into the nozzle, [2,6] (3) chemical reactions between the nozzle refractory and the steel, [7][8][9][10] and (4) the solidification of steel within the nozzle. [2,11] Various countermeasures have been reported, [2,[12][13][14][15][16] but the cause of SEN clogging is not simple. This implies there should be different countermeasures that are suitable for each circumstance.…”

“…However, it has been a long‐standing problem that the SEN is often clogged during the casting process for several reasons: (1) the transport of oxide inclusions present in the steel [ 2–5 ] , (2) the aspiration of air into the nozzle, [ 2,6 ] (3) chemical reactions between the nozzle refractory and the steel, [ 7–10 ] and (4) the solidification of steel within the nozzle. [ 2,11 ] Various countermeasures have been reported, [ 2,12–16 ] but the cause of SEN clogging is not simple. This implies there should be different countermeasures that are suitable for each circumstance.…”