Introduction Of Carbon

: CASE-HARDENING OR SURFACE-CARBURIZING
: The Working Of Steel

The matter to which these notes are primarily directed is the

introduction of carbon into the case of the article to be hardened.

In the first place the chances of success are increased by selecting

as few brands of steel as practicable to cover the requirements of

each component of the mechanism. The hardener is then able to become

accustomed to the characteristics of that particular material, and

after determining th most suitable treatment for it no further

experimenting beyond the usual check-test pieces is necessary.



Although a certain make of material may vary in composition from

time to time the products of a manufacturer of good steel can be

generally relied upon, and it is better to deal directly with him

than with others.



In most cases the case-hardening steels can be chosen from the

following: (1) Case-hardening mild steel of 0.20 per cent carbon;

(2) case-hardening 3-1/2 per cent nickel steel; (3) case-hardening

nickel-chromium steel; (4) case-hardening chromium vanadium. After

having chosen a suitable steel it is best to have the sample analyzed

by reliable chemists and also to have test pieces machined and pulled.



To prepare samples for analysis place a sheet of paper on the table

of a drilling machine, and with a 3/8-in. diameter drill, machine

a few holes about 3/8 in. deep in various parts of the sample bar,

collecting about 3 oz. of fine drillings free from dust. This can be

placed in a bottle and dispatched to the laboratory with instructions

to search for carbon, silicon, manganese, sulphur, phosphorus and

alloys. The results of the different tests should be carefully

tabulated, and as there would most probably be some variation an

average should be made as a fair basis of each element present,

and the following tables may be used with confidence when deciding

if the material is reliable enough to be used.



TABLE 16.--CASE-HARDENING MILD STEEL OF 0.20 PER CENT CARBON



Carbon 0.15 to 0.25 per cent

Silicon Not over 0.20 per cent

Manganese 0.30 to 0.60 per cent

Sulphur Not over 0.04 per cent

Phosphorus Not over 0.04 per cent



A tension test should register at least 60,000 lb. per square inch.



TABLE 17.--CASE-HARDENING 3-1/2 PER CENT NICKEL STEEL



Carbon 0.12 to 0.20 per cent

Manganese 0.65 per cent

Sulphur Not over 0.045 per cent

Phosphorus Not over 0.04 per cent

Nickel 3.25 to 3.75 per cent



TABLE 18.--CASE-HARDENING NICKEL CHROMIUM STEEL



Carbon 0.15 to 0.25 per cent

Manganese 0.50 to 0.80 per cent

Sulphur Not over 0.045 per cent

Phosphorus Not over 0.04 per cent

Nickel 1 to 1.5 per cent

Chromium 0.45 to 0.75 per cent



TABLE 19.--CASE-HARDENING CHROMIUM VANADIUM STEEL



Carbon Not over 0.25 per cent

Manganese 0.50 to 0.85 per cent

Sulphur Not over 0.04 per cent

Phosphorus Not over 0.04 per cent

Chromium 0.80 to 1.10 per cent

Vanadium Not less than 0.15 per cent



Having determined what is required we now proceed to inquire into

the question of carburizing, which is of vital importance.