Properties of a nanostructured bainitic steel

In some recent work, we produced a nanostructured steel was produced using a clean steel-making technique. Hoping that applying VIM-VAR processing would achieve better mechanical properties by reducing tramp elements, like sulphur and phosphorous. Resulting in less problems of embrittlement by these elements and by manganese sulphide inclusions, etc.

No doubt these steels have impressive combinations of properties. We had the chance to measure many different mechanical properties of the same batch of steel. Only complicated by the fact that we were trying to develop heat treatments to improve the properties at the same time.

These results have been published in Materials Science and Technology, here: http://dx.doi.org/10.1080/02670836.2016.1271522

The maximum strength of the material recorded was 2.2 GPa at yield, with an ultimate tensile strength of 2.5 GPa, accompanied by a Charpy impact energy of 5 J, achieved by heat treatment to refine the prior austenite grain size from 145 to 20 µm. This increased the strength by 40% and the Charpy V-notch energy more than doubled. In terms of resistance of the hardness to tempering, the behaviour observed was similar to previous alloys. Despite reducing the hardness and strength, tempering was observed to reduce the plane-strain fracture toughness.

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