The Working of Steel | Page 4

The steel to be made was a high-carbon chrome steel used
for balls for ball bearings:
6-TON HEROULT FURNACE
11:50 A.M.--Material charged: Boiler plate 5,980 lb. Stampings 5,991
lb. ----------- 11,971 lb. Limestone 700 lb. 12:29 P.M.--Completed
charging (current switched on). 3:20 P.M.--Charge melted down.
Preliminary analysis under black slag. Analysis: Carbon Silicon
Sulphur Phosphorus Manganese 0.06 0.014 0.032 0.009 0.08 Note the
practical elimination of phosphorus. 3:40 P.M.--The oxidizing (black)
slag is now poured and skimmed off as clean as possible to prevent
rephosphorizing and to permit of adding carburizing materials. For this
purpose carbon is added in the form of powdered coke, ground
electrodes or other forms of pure carbon.
The deoxidizing slag is now formed by additions of lime, coke and
fluorspar (and for some analyses ferrosilicon). The slag changes from
black to white as the metallic oxides are reduced by these deoxidizing
additions and the reduced metals return to the bath. A good finishing
slag is creamy white, porous and viscous. After the slag becomes white,
some time is necessary for the absorption of the sulphur in the bath by
the slag.
The white slag disintegrates to a powder when exposed to the
atmosphere and has a pronounced odor of acetylene when wet.
Further additions of recarburizing material are added as needed to meet
the analysis. The further reactions are shown by the following:
3:40 P.M.--Recarburizing material added: 130 lb. ground electrodes. 25
lb. ferromanganese. Analysis: Carbon Silicon Sulphur Phosphorus
Manganese 0.76 0.011 0.030 0.008 0.26

To form white slag there was added:
225 lb. lime. 75 lb. powdered coke. 55 lb. fluorspar. 4:50 P.M.--
Analysis: Carbon Silicon Sulphur Phosphorus Manganese 0.75 0.014
0.012 0.008 0.28 Note reduction of the sulphur content.
During the white-slag period the following alloying additions were
made:
500 lb. pig iron. 80 lb. ferrosilicon. 9 lb. ferromanganese. 146 lb. 6 per
cent carbon ferrochrome.
The furnace was rotated forward to an inclined position and the charge
poured into the ladle, from which in turn it was poured into molds.
5:40 P.M.--Heat poured. Analysis: Carbon Silicon Sulphur Phosphorus
Manganese Chromium 0.97 0.25 0.014 0.013 0.33 0.70
Ingot weight poured 94.0 per cent Scull 2.7 per cent Loss 3.3 per cent
Total current consumption for the heat, 4,700 kW.-hr. or 710 kw.-hr.
per ton.
Electric steel, in fact, all fine steel, should be cast in big-end-up molds
with refractory hot tops to prevent any possibility of pipage in the body
of the ingot. In the further processing of the ingot, whether in the
rolling mill or forge, special precautions should be taken in the heating,
in the reduction of the metal and in the cooling.
No attempt is made to compare the relative merits of open hearth and
electric steel; results in service, day in and day out, have, however,
thoroughly established the desirability of electric steel. Ten years of
experience indicate that electric steel is equal to crucible steel and
superior to open hearth.
The rare purity of the heat derived from the electric are, combined with
definite control of the slag in a neutral atmosphere, explains in part the
superiority of electric steel. Commenting on this recently Dr. H. M.

Howe stated that "in the open hearth process you have such atmosphere
and slag conditions as you can get, and in the electric you have such
atmosphere and slag conditions as you desire."
Another type of electric furnace is shown in Figs. 7 and 8. This is the
Ludlum furnace, the illustrations showing a 10-ton size. Figure 7 shows
it in normal, or melting position, while in Fig. 8 it is tilted for pouring.
In melting, the electrodes first rest on the charge of material in the
furnace. After the current is turned on they eat their way through,
nearly to the bottom. By this time there is a pool of molten metal
beneath the electrode and the charge is melted from the bottom up so
that the roof is not exposed to the high temperature radiating from the
open arc. The electrodes in this furnace are of graphite, 9 in. in
diameter and the current consumed is about 500 kw.-hr. per ton.
[Illustration: FIG. 7.--Ludlum electric furnace.]
[Illustration: FIG. S.--The furnace tilted for pouring.]
One of the things which sometimes confuse regarding the contents of
steel is the fact that the percentage of carbon and the other alloys are
usually designated in different ways. Carbon is usually designated by
"points" and the other alloys by percentages. The point is one
ten-thousandth while 1 per cent is one one-hundredth of the whole. In
other words, "one hundred point carbon" is steel containing 1 per cent
carbon. Twenty point carbon, such as is used for carbonizing purposes
is 0.20 per cent. Tool steel varies from one hundred to one hundred and
fifty points carbon,