Prediction of KIc in a high strength bainitic steel

• Specimens to fracture mechanics tests were machined according to ASTM E 399 standard.
• The expression given by Lescovsek acceptably predicts the value of KIc.
• The value of CVN has more of an influence on KIc than HRc.
• Reducing the bainitic packet size the KIc is increased.

In this work the stress intensity factor (KIc) has been determined for a high strength bainitic steel, making reference to ASTM E 399 standard, which involves the use of complex geometry specimens. An experimental value of 1627 N mm−3/2 has been obtained for KIc, which is equivalent to 51.4 MPa m1/2. It has been verified that Lescovsek’s expression, which predicts KIc as a function of hardness (HRc) and the CVN Charpy impact test value, can be applied to steels with a bainitic microstructure, as the CVN value is more influential than HRc. The acceptable prediction of Lescovsek’s expression shows the way to improve the KIc value in bainitic steels.