Hot and Cold rolling

Question 1

What temperatures does hot rolling occur at?

Answer 1

~0.5-0.7Tm

Question 2

What’s the purpose of hot rolling?

Answer 2

to achieve large reductions, eliminate structure variations, remove porosity, attain compositional homogeneity

Question 3

What are the challenges of hot rolling?

Answer 3

surface reactions (oxidation), melting/softening of secondary phases

Question 4

What temperatures does cold working occur at?

Answer 4

T < 0.3Tm

Question 5

What’s the purpose of cold rolling?

Answer 5

to achieve final geometry, generate fine grain size, produce high hardness, textured, oriented grains

Question 6

Effect of hot rolling on microstructures

Answer 6

1. breaks down coarse columnar microstructure
2. homogenizes the dendritic segregation of solutes
3. nonmetallic inclusions break up and form stringers
4. fine grain size is obatined if final temp > recrystallization temp
5. porosity is healed

Question 7

Why are properties spatially uniform?

Answer 7

thermal diffusion allows everything to homogenize

Question 8

Why does hot rolled steel have higher ultimate tensile strength?

Answer 8

porosity decreases

Question 9

Why does hot rolled steel have higher ductility?

Answer 9

porosity decreases