: The Working Of Steel

A combination of the characteristics of nickel and the characteristics

of chromium, as described, should obviously give a very excellent

steel as the nickel particularly affects the ferrite of the steel

and the chromium the carbon. From this combination, we are able to

get a very strong ferrite matrix and a very hard tough cementite.

The strength of a strictly pearlitic steel over a pure iron is due

to the pearlitic be
ng a layer arrangement of cementite running

parallel to that of a pure iron layer in each individual grain. The

ferrite i.e., the iron is increased in strength by the resistance

offered by the cementite which is the simple iron-carbon combination

known to metallurgists as Fe3C. The cementite, although adding

to the tensile strength, is very brittle and the strength of the

pearlite is the combination of the ferrite and cementite. In the

event of the cementite being strengthened, as in the case of strictly

chromium steels, an increased tensile strength is readily obtained

without loss of ductility and if the ferrite is strengthened then

the tensile strength and ductility of the metal is still further


Nickel-chromium alloy represents one of the best combinations available

at the present time. The nickel intensifies the physical characteristics

of the chromium and the chromium has a similar effect on the nickel.

For case-hardening, nickel-chromium steels seem to give very excellent

results. The carbon is very rapidly taken up in this combination,

and for that reason is rather preferable to the straight nickel steel.

With the mutually intensifying action of chromium and nickel there

is a most suitable ratio for these two alloys, and it has been found

that roughly 2-1/2 parts of nickel to about 1 part of chromium

gives the best results. Therefore, we have the standard types of

3.5 per cent nickel with 1.5 per cent chromium to 1.5 per cent

nickel with 0.6 per cent chromium and the various intermediate

types. This ratio, however, does not give the whole story of

nickel-chromium combinations, and many surprising results have

been obtained with these alloys when other percentage combinations

have been employed.