Effect of Intercritical Rolling by Hot Strip Mill on the Strength and Notch Toughness of Plain Carbon Steel

Abstract

The application of the intercritical rolling on plain carbon steel, of which beneficial effect on strength and notch toughness was proved by laboratory mill experiment, has been made to hot strip mill.
The following results are obtained:
(1) Both spiral-welded and electric-resistance-welded pipes manufactured of intercritically-rolled coils show strength of X 52 grade and good notch toughness at low temperature.
(2) Improvement of strength and notch toughness in intercritically-rolled coils are due to grain refinement of ferrite and pearlite which are transformed from worked austenite, and formation of substructure in ferrite worked in intercritical range.
(3) No disadvantageous influence of intercritical rolling is observed such as lowering of strength or deterioration of notch toughness in welds in comparison to conventionally-rolled steel.
(4) Though the intercritically-rolled coils have the texture in midthickness similar with that of cold rolled plate with strong fiber structure having<110>-axis parallel to rolling direction as main component, the mechanical properties as pipes are good as the change of properties due to pipe manufacturing is small and anisotropy of yield strength even decreases.
It is concluded that the intercritically-rolled strip is suitable for structural steel required high yield strength and good notch toughness such as high-test line pipe.