There are several ways of producing cast steel, some of which will now be mentioned.
The ingots produced by any of these processes generally contain cavities. In order to get rid of these, they are reheated at a low temperature and hammered into bars, being increased in length and reduced in section, by which they are made compact, solid, and homogeneous.
"The appearance of the fractured surface of ingots of cast steel varies with their hardness or relative proportion of carbon. The softer kinds are bright and finely granular. The harder qualities often show crystalline plates of a certain size, arranged in parallel stripes or columns at right angles to the surface of the mould, so that in a square ingot the columns intersect, forming a cross."2
Crucible Cast Steel may be made by melting fragments of blister steel in covered fireclay crucibles, and running the metal into iron moulds. This process was originally introduced by Huntsman of Sheffield.
Most crucible steel, however, is now made direct from bars of the best wrought iron (often Swedish iron produced from pure magnetic ores). The bars are broken into lengths and placed in the crucibles together with a small quantity of charcoal, the amount varying according to the temper of the steel to be produced, Spiegeleisen (see below), or oxide of manganese, is subsequently added.
1 Bauermann's Metallurgy.
Cast steel made in this way should never be raised beyond a red heat, or it will become brittle, so that it cannot easily be forged. It is unweldable, for it will fly to pieces when struck by the hammer.
In making tools, after forging, the cutting edge should be well hammered down, so as to close the pores or grain of the metal.
The fracture of cast steel should have a slaty-grey tint almost without lustre, the crystals being so fine that they are hardly distinguishable.
It is used for the finest cutlery, for cutting tools composed of steel only, especially those in which great hardness is required.
Heath's Process is an improvement on the method just described, and consists in adding to the molten metal a small quantity of carburet of manganese.
"After this addition the cast steel possesses much more tenacity at a high temperature, and can be welded either to itself or to wrought iron, so that it may be employed for the fabrication of many implements which were formerly obliged to be made of shear steel. Thus the blades of table knives can be made of cast steel, welded on to an iron tang, as that part of the knife is called which is fixed into the handle."1
Heaton's Process consists in adding nitrate of soda to molten pig-iron, thus removing most of the carbon and silicon.
In this malleable iron is melted in crucibles with oxide of manganese and charcoal.