Mechanical Properties of High Strength Low Alloy Steel Controlled Rolled at Austenite and Ferrite Two Phase Regions

Abstract

Changes in strength and toughness in conjunction with controlled rolling in austenite and ferrite two phase region were investigated.
The results are summarized as follows.
(1) Strength increased with the lowering of rolling temperature and the raising of rolling reduction in two phase region. This strengthening will be attributed to dislocation hardening and minimizing the subgrain and cell size in warm worked ferrite grains.
(2) Toughness is dependent on the rolling temperature at two phase region. Good toughness can be obtained by the rolling at temperatures where recovery and recrystallization of warm worked ferrite are recognized. But Charpy transition temperature is raised by rolling bellow these temperatures.
(3) The prior hot rolling just above Ar₃ temperature is effective to supress the rise of Charpy transition temperature, even though the final rolling is carried out at temperature where no recovery occurs in deformed ferrite grains.
Because it promotes the separations which appear on fractured Charpy specimens. So in this case high strength and good toughness can be obtained.