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Optical System And Electrical Circuit Of The Leeds & Northrup Optical Pyrometer
For extremely high temperature, the optical pyrometer is lar...

Phosphorus
Phosphorus is one of the impurities in steel, and it has been...

Lathe And Planer Tools
TO FORGE.--Gently warm the steel to remove any chill is parti...

Surface Carburizing
Carburizing, commonly called case-hardening, is the art of pr...

Properties Of Alloy Steels
The following table shows the percentages of carbon, manganes...

Temperature Recording And Regulation
Each furnace is equipped with pyrometers, but the reading an...

Carbon Steels For Different Tools
All users of tool steels should carefully study the different...

The Pyrometer And Its Use
In the heat treatment of steel, it has become absolutely nece...

High-carbon Machinery Steel
The carbon content of this steel is above 30 points and is ha...

Lathe And Planer Tools
FORGING.--Gently warm the steel to remove any chill, is parti...

The Influence Of Size
The size of the piece influences the physical properties obta...

Preventing Cracks In Hardening
The blacksmith in the small shop, where equipment is usually ...

Liberty Motor Connecting Rods
The requirements for materials for the Liberty motor connecti...

Cutting-off Steel From Bar
To cut a piece from an annealed bar, cut off with a hack saw,...

For Milling Cutters And Formed Tools
FORGING.--Forge as before.--ANNEALING.--Place the steel in a ...

Introduction Of Carbon
The matter to which these notes are primarily directed is the...

The Theory Of Tempering
Steel that has been hardened is generally harder and more br...

Short Method Of Treatment
In the new method, the packed pots are run into the case-har...

Calibration Of Pyrometer With Common Salt
An easy and convenient method for standardization and one whi...

Suggestions For Handling High-speed Steels
The following suggestions for handling high-speed steels are ...



Refining The Grain






Category: CASE-HARDENING OR SURFACE-CARBURIZING

This is remedied by reheating the piece to a temperature slightly
above the critical temperature of the case, this temperature
corresponding ordinarily to that of steel having a carbon content
of 85 points, When this is again quenched, the temperature, which
has not been high enough to disturb the refined core, will have
closed the grain of the case and toughened it. So, instead of but
one heat and one quenching for this class of work, we have three
of each, although it is quite possible and often profitable to
omit the quenching after carburizing and allow the piece or pieces
and the case-carburizing box to cool together, as in annealing.
Sometimes another heat treatment is added to the foregoing, for
the purpose of letting down the hardness of the case and giving
it additional toughness by heating to a temperature between 300 deg.
and 500 deg.. Usually this is done in an oil bath. After this the piece
is allowed to cool.

It is possible to harden the surface of tool steel extremely hard
and yet leave its inner core soft and tough for strength, by a
process similar to case-hardening and known as pack-hardening.
It consists in using tool steel of carbon contents ranging from
60 to 80 points, packing this in a box with charred leather mixed
with wood charcoal and heating at a low-red heat for 2 or 3 hr.,
thus raising the carbon content of the exterior of the piece. The
article when quenched in an oil bath will have an extremely hard
exterior and tough core. It is a good scheme for tools that must
be hard and yet strong enough to stand abuse. Raw bone is never
used as a packing for this class of work, as it makes the cutting
edges brittle.





Next: Case-hardening Treatments For Various Steels

Previous: The Quenching Tank



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