抄録
The effect of grain size on the relation between non-ductile transition behaviour and bending speed of a low carbon steel has been examined with Charpy type specimens (V-notch).
The principal results obtained are summarized as follows:
(1) Under a constant bending speed, the relation between non-ductile transition temperature TB and grain size D is represented by the following form
1/TB=A'-B'logD (a)
where A' and B' are constants. However, this relation does not hold when the bending speed becomes higher and the grain size is larger.
(2) In the regions of higher bending speed and of larger grain size, the non-ductile transition temperature is lower than that estimated from eq. (a) and the difference between them increases with increasing speed and grain size. It may be considered that difference arises because the plastic constraint force is affected by grain size.
