Difficulties he was greatly embarrassed by the brittleness or " redshortness " of his steel, which he did not know how to cure.
Brittleness and ready inflammability.
But the invaluable and rather delicate art of tempering the hardened steel by a very careful and gentle reheating, which removes its extreme brittleness though leaving most of ifs precious hardness, needs such skilful handling that it can hardly have become known until very long after the art of hot-forging.
The casting of the molten cast iron into shapes which were useful in spite of its brittleness, naturally followed.
The presence of a small quantity of the hard cementite ought naturally to strengthen the mass, by opposing the tendency of the soft ferrite to flow under any stress applied to it; but more cementite by its brittleness naturally weakens the mass, causing it to crack open under the distortion which stress inevitably causes.