Man's physical universe

xanabras

METALLURGY 637

have been investigated. Corrosion-resistant steels are now produced

by adding silicon to produce such products as "duriron," while the

addition of chromium and nickel produce "stainless steel."

Tungsten,

titanium, nickel, vanadium, cobalt, and molybdenum are added to

produce other desired properties, and a variation of 0.1 per cent in

some of these metals will produce a marked change in properties, A

steel containing 11 to 14 per cent manganese is too hard to be machined

and is therefore used in constructing burglar-proof safes and armor

plate.

The addition of a little zirconium (0.3 per cent) to nickel steel

makes it very resistant to perforation by bullets. The addition of

tungsten and other elements produces high-speed cutting-steels that

do not lose their cutting-power even at white heat. These new cuttingsteels

revolutionized shop practice by enabling cutting-tools to plow

through steel ten times as fast as formerly. "Invar" is a nickel steel

which contracts or expands very little with changes of temperature

and is therefore used in watches and measuring instruments.

Space will not permit an account of many other valuable alloys.

It is important to note that the properties of steels depend quite as

much on heat treatment as on chemical composition. When red-hot

steel is slowly cooled, it is said to be annealed. If it is cooled very

suddenly, as by quenching in water or oil, it is hardened. Hardened

steel may be tempered by reheating to a temperature much below

redness. These and other methods of treating steels produce in the

finished product different types and sizes of crystals that play a very

important part in determining its properties. Modern metallographic

methods, in which the crystalline structure of the steel is studied,

enable the steel industry to carry out the various methods of treatment

under scientific control. The use of X rays has also been of

great value in detecting and locating flaws in

study of the structure of steels.

metals, as well as in a

The Prevention of Corrosion Is Being Accomplished in Many Ways.

The usefulness of iron and steel is limited by their tendency to

rust. In spite of all the efforts made to combat corrosion, the losses

due to this one item amount to millions of dollars a year. Corrosion

is essentially a process in which metals form compounds {i.e., lose

electrons). When two metals are in contact with an electrolyte, corrosion

will take place, inasmuch as one metal will always have a

greater tendency to lose electrons than the other.

Corrosion will also take place when there is some substance present,

other than another metal, which is capable of accepting electrons.

Acid solutions contain hydronium ions, (HsO)"*", which will accept

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