Flow stress is defined as the instantaneous value of stress required to continue deforming the material - to keep the metal flowing. It is the Yield Strength of the metal as a function of strain, which can be expressed: [1]

Yf = Ke^n

Yf = Flow stress, MPa K = Strength Coefficient, MPa n = Strain hardening exponent

Hence, Flow stress can also be defined as the stress required to sustain plastic deformation at a particular strain.

The flow stress is a function of plastic strain.

Metal Properties that have an effect on flow stress .

a) Chemical composition

b) Purity

c) Crystal structure

d) Phase constitution

e) Exit microstructure

f) Grain size

g) Heat treatment state

References

[1] Mikell P. Groover, 2007, "Fundamentals of Modern Manufacturing; Materials, Processes, and Systems," Third Edition, John Wiley & Sons Inc.