Thermit steel being much stronger than gray iron, its shrinking sometimes strains and cracks the iron casting.
The pistons as provided in the A-7 engines are cast from a mixture of steel and gray iron.
The first reason is that gray iron is cheaper than steel, and a new casting often can be turned out by the mills quickly.
One of the things thermit is not extensively used for is the repairing of gray iron castings.
Face set in a fighting mask and eyes hard as gray iron, deeper and deeper he drove his now irresistible forces.
At one point, not far from Cle-ellum River, a bed of gray iron ore crosses the magnetic ore at right angles.
An average of over 400 tons of iron is poured daily, and 426 tons of gray iron have been poured in a single day.