1987 Volume 27 Issue 6 Pages 419-424
Flow stress of a Si-Mn steel in ferrite plus metastable austenite region and austenite plus ferrite two phase region has been examined by single-stage and multi-stage tension tests. Flow stress of “ferrite” (92% ferrite plus 8 metastable austenite) has been found to be expressed by an equation similar to that applicable to austenite. Strain hardening exponent is smaller in “ferrite” than in austenite region, while strain rate exponent is larger in “ferrite” region. The hot deformation resistance in austenite ferrite two phase region can be approximated by the law of mixture for the hot deformation resistance of austenite and “ferrite”. By adding a term expressing release of strain concurrent with phase transformation to the conventional formula describing static restoration process in austenite, the kinetic of static restoration in austenite-ferrite two phase region can be formulated as a simple mathematical equation. On the basis of experimental results a mathematical model of hot deformation resistance in austenite ferrite two phase region has been developed and successfully applied to roll force prediction in a production plate mill.
