Ferrite Grain Refinement during Hot Rolling of Seamless Tubes
Hot rolling of seamless tubes is performed in two stages: one at high temperature, ie, above 1000oC and a second part at low temperature range, namely below 900oC. Above 1000oC, dynamic, metadynamic and static recrystallization may happen leading to full softening and grain refinement. Below 900oC, however, some pancaking may occur and ferrite is thus refined during transformation. Nonetheless, in order to refine ferrite grains further, cooling to room temperature and re-austenitization at an intermediate reheating furnace can be a viable alternative to be explored. The present paper examines the implications of re-austenitization followed by phase transformation plus low temperature deformation on ferrite grain refinement. Phase transformation on re-heating and cooling as well as recrystallization play important roles in the process of ferrite grain refinement. These mechanisms are analyzed and discussed. Results indicate that ferrite grain refinement is most effective in the case of processing using a re-austenitization cycle in the intermediate furnace followed by rapid cooling after deformation in the stretch reducing mill.
S.-J.L. Kang, M.Y. Huh, N.M. Hwang, H. Homma, K. Ushioda and Y. Ikuhara
R. Barbosa et al., "Ferrite Grain Refinement during Hot Rolling of Seamless Tubes", Materials Science Forum, Vols. 558-559, pp. 689-694, 2007