The Effect of Hot Rolling Condition and Chemical Composition on the Onset Temperature of γ-α Transformation after Hot Rolling

Abstract

The effect of hot rolling condition and chemistry of steels on the onset temperature of r-a transformation after hot rolling was investigated using a thermal analyzer developed for the measurement of Ar3 temperature after hot rolling. The changes of Ar3 temperature and austenitic microstructure in connection with reheating temperature, rolling temperature and reduction rate were investigated in a Si-Mn and a Nb-bearing steels. The results were analyzed based on the changes of the effective interfacial area per unit volume (Sv) that included both of the recrystallized and unrecrystallized grain boundaries and deformation band as nucleation sites for ferrite. Although the Sv value increased with the refinement of recrystallized r grain or the increase of rolling reduction below recrystallization temperature of austenite, the latter resulted in a much greater change of Ar3 temperature in the Nb steel. This was considered to be due to a reduced amount of dissolved Nb atoms around the grain boundary or deformation band through the strain induced precipitation of Nb(CN). The effect of chemistry and plate thickness on the Ar3 temperature after controlled rolling was studied in a large number of steels with different chemistry, and the relation between the Ar3 and chemistry was quantitatively established based on the multiple regression analysis.

Evaluation of the Hot Ductility of a C–Mn Steel Produced from Scrap Recycling

“…Ae 3 temperatures (austenite to ferrite transformation temperature under equilibrium conditions) were calculated using Andrew's formula 8) and have a value of 802°C and 811°C for the as-cast and the as-rolled steels respectively. Ar 3 temperature (austenite to ferrite transformation temperature in continuous cooling conditions) was calculated using the formula of Ouchi 9) and has a value of 733°C for the as-cast steel and 713°C for the as-rolled one.…”

“…Under these circumstances, the embrittlement caused by the existence of a ferrite layer would be extended to higher temperatures than the ones initially calculated. According to the equations used to calculate Ae 3 and Ar 3 , 8,9) most alloying additions decrease these transformation temperatures and only Si and Mo would increase them. Therefore, and increase of Ae 3 related to segregation is not likely to be taking place since neither Si nor Mo have tendency to segregate.…”

The Effect of Thermal History on the Hot Ductility of Microalloyed Steels.

“…7, all the microstructures were fully martensitic. A simllar examination of the evolution of a more brittle specimen which was fractured at I 020'C (sim-1 (15)), Ieading to a ductility 140/0, also revealed fully martensltic structures at all stages investigated, except in the specimen quenched at T~i~(780'C for this simulation). Here, films of ferrite at the prior austenite grain boundaries were revealed (Fig.…”

“…(a) Fracture surface of NbTi steel tested at I 020'C subjected to sim-1 (15) (RA= 140/0). surface of Ti-B steel tested at I OOO'C subjected to sim-6 (15) …”

Thermomechanical Processing of Structural Steels with Dilute Niobium Additions

“…The increment of the total interfacial area Sv contributed by the intragranular planar defects has been expressed by Ouchi et al [54] in the following equation:…”