What temperatures does hot rolling occur at?
~0.5-0.7Tm
What’s the purpose of hot rolling?
to achieve large reductions, eliminate structure variations, remove porosity, attain compositional homogeneity
What are the challenges of hot rolling?
surface reactions (oxidation), melting/softening of secondary phases
What temperatures does cold working occur at?
T < 0.3Tm
What’s the purpose of cold rolling?
to achieve final geometry, generate fine grain size, produce high hardness, textured, oriented grains
Effect of hot rolling on microstructures
- breaks down coarse columnar microstructure
- homogenizes the dendritic segregation of solutes
- nonmetallic inclusions break up and form stringers
- fine grain size is obatined if final temp > recrystallization temp
- porosity is healed
Why are properties spatially uniform?
thermal diffusion allows everything to homogenize
Why does hot rolled steel have higher ultimate tensile strength?
porosity decreases
Why does hot rolled steel have higher ductility?
porosity decreases
