An Analysis of the Reasons for Unqualified Impact Property of X80M Steel Hot Rolled Coil

The reasons for unqualified impact property of X80M steel hot rolled coil were analyzed by mechanical property test, chemical composition analysis, metallographic examination, energy dispersive spectroscopy and impact fracture morphology observation. The results show that the impact property of the coil was unqualified because there was severe banded microstructure, a sort of brittle microstructure mainly composed of lath martensite, in the coil. The obvious segregation of manganese and silicon was founded in the banded microstructure which was the crack source of impact coil. There were many carbonitride inclusions of niobium and titanium in the banded microstructure. The inclusions were square with a maximum size of 13 μm, which reduced the impact toughness further. The most effective method to get rid of or reduce the banded microstructure is reducing or eliminating dendritic segregation in ingot during rolling process.