Effects of hot deformation on austenite transformation in 10w carbon Mo-Nb and C-Mn steels

Abstract

The 0.15C-1.5Mn and 0.07C-0.3Mo-0.055Nb steels were subjected to hot rolling to determine the effects on transformation to ferrite and to hot torsion to measure strength. After 25 or 50% reduction at 830°C, the acceleration during isothermal transformation in the range 700–600°C is much greater for C-Mn than for Mo-Nb; delays of 5–10 s before cooling reduce the acceleration markedly. In continuous cooling, three passes of 20% reduction raise the temperature of austenite decomposition, most noticeably at the higher rate 9 K S^-l. At this rate, for the C-Mn the pearlite is refined and for Mo-Nb the promoted ferrite is refined more and enhanced over bainite than at lower rates. Intercritical rolling below Ar₃ enhanced ferrite formation more in C-Mn in the range 780–720°C than in Mo-Nb over 750–690°C. The stronger Mo-Nb in torsion (900–1100°C, 0.1-5 S^-l) exhibits an activation energy of 353 kJ mol^-l compared with 316 kJ mol^-l for C-Mn.