Theoretical Study of the Deformation of Quenched Steel Bar

Abstract

The deformation of quenched steel bar was theoretically studied by the finite element method. The findings are as follows:
1) In the austenite steel, a convex type plastic deformation proceeds owing to shrinking of the case in the initial stage of the cooling where the temperature difference between the case and the core of the bar increases. As the cooling proceeds and the temperature difference decreases, a concave type plastic deformation proceeds, cancelling the convex, owing to the shrinking of the core. As the latter concave does not fully cancell the convex, some convex type deformation remains at room temperature.
2) Transformation to martensite and/or bainite enhance the concave type deformation of the latter stage because of their higher rigidity. Therefore, the concave type deformation results when the bar was water-quenched and the steel transformed into the low temperature products.
3) When the bar was quenched in oil the martensite transformation has less effect on the concave type deformation than in the case of water-quenching, because of smaller temperature defference at low temperature range.
The deformations obtained by theoretical and experimental study were in reasonable agreement.