Pipe and Blowholes in an Ingot of Steel
Then, too, the metalloids of the steel do not always stay where they belong. Even if the steel has been of a uniform chemical composition when poured, the interior portions of the ingot after cooling will be found to have a greater amount of sulphur, phosphorus and carbon than parts which are nearer the surface. Such gathering together of constituents of the steel is known as “segregation.”
With the development of the steel industry and the demand for greater and greater tonnages, ingots have been made larger and larger. Piping, segregation, etc., are very naturally accentuated in the large masses of steel.
Much “gray matter” has been expended in attempting to overcome these and other defects to which large steel ingots are liable. Covering the molten ingot top with charcoal; filling in before complete solidification with additional molten metal; and keeping the ingot top molten by application of powerful gas flames have been, perhaps, the most useful methods.
But, even so, piping and segregation have not been completely prevented, though great improvement has resulted.
The usual way around the difficulty is to make certain that only the bottom (or best half) of each ingot is used for the most important products, such as locomotive and car axles, firebox and boiler plates, rails, etc. The next or third quarter or a little more is utilized for products which go into less exacting service. These may be plates for ordinary water tanks, for flooring, for ship plates, etc. The top part which contains the pipe is cut off and goes back to the furnace to be remelted. It is termed “discard.”
The big steel makers themselves shape most of their steel into such finished products as rails, plates, rods, and wire. Some of it is by them reduced from the ingot into intermediate “blooms,” “billets,” “bars,” etc., and sold in this form for the manufacture of axles, drop forgings and the hundreds of products which we each day see.
It is a very fortunate circumstance that at a cherry-red or white heat the carbonless irons and most of the steels can be quite easily fashioned into products. As is well known to us the most usual methods of mechanically shaping these metals while hot are by hammering, by rolling and by forging in a press.
With sufficient power and proper appliances, soft and medium steel to a considerable extent can be fashioned cold, but, of course, in this condition its resistance to reshaping is immensely greater. The cold treatment of these metals is usually some form of tube or wire drawing.
Certain other methods such as extrusion, spinning, etc., are also in use, and, through them, some otherwise difficultly formed products are made.