Warm deformation of low carbon steels

Finish rolling of low carbon strip below Ars has been found to offer a number of advantages during subsequent processing. This has been associated with the substantial ferrite grain coarsening which occurs after rolling below Ars. In the present work three steels ranging in carbon content from 0.005 to 0.1 %C were deformed at a series of temperatures below Ars using hot compression. It was found that coarse ferrite grain size occurred in all three steels provided that certain processing conditions were met. In 0.05 and 0.005%C steels coarse ferrite grain size was exhibited at finish deformation temperatures (FDT's) ranging from 640°C to 790°C, provided that the finishing strain was above a critical level (Scrit)- This was due to the fact that reasonably high ferrite volume fraction was present at these temperatures in these steels. In 0.1 %C steel, on the other hand, high austenite volume fraction occurred at the highest FDT (ie 790°C). This led to the production of considerably finer grain size than that at lower FDT. This indicates that coarse ferrite grain size is associated with presence of ferrite during deformation whereas fine grain size is associated with austenite.