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Placing The Thermo-couples
The following illustrations from the Taylor Instrument Compan...

Ebbw Vale And The Bessemer Process
After his British Association address in August 1856, Besseme...

Standard Analysis
The selection of a standard analysis by the manufacturer is t...

Carburizing Material
The simplest carburizing substance is charcoal. It is also th...

Chromium
Chromium when alloyed with steel, has the characteristic func...

Temperatures To Use
As soon as the temperature of the steel reaches 100 deg.C. (...

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

An Automatic Temperature Control Pyrometer
Automatic temperature control instruments are similar to the ...

Tungsten
Tungsten, as an alloy in steel, has been known and used for a...

William Kelly's Air-boiling Process
An account of Bessemer's address to the British Association w...

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

Heat Treatment Of Steel
Heat treatment consists in heating and cooling metal at defin...

The Packing Department
In Fig. 56 is shown the packing pots where the work is packe...

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

Effect Of A Small Amount Of Copper In Medium-carbon Steel
This shows the result of tests by C. R. Hayward and A. B. Joh...

Alloying Elements
Commercial steels of even the simplest types are therefore p...

The Leeds And Northrup Potentiometer System
The potentiometer pyrometer system is both flexible and subst...

S A E Heat Treatments
The Society of Automotive Engineers have adopted certain heat...

Corrosion
This steel like any other steel when distorted by cold worki...

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



Knowing What Takes Place






Category: HARDENING CARBON STEEL FOR TOOLS

How are we to know if we have given a
piece of steel the very best possible treatment?

The best method is by microscopic examination of polished and etched
sections, but this requires a certain expense for laboratory equipment
and upkeep, which may prevent an ordinary commercial plant from
attempting such a refinement. It is highly recommended that any
firm that has any large amount of heat treatment to do, install
such an equipment, which can be purchased for from $250 to $500.
Its intelligent use will save its cost in a very short time.

The other method is by examination of fractures of small test bars.
Steel heated to its correct temperatures will show the finest possible
grain, whereas underheated steel has not had its grain structure
refined sufficiently, and so will not be at its best. On the other
hand, overheated steel will have a coarser structure, depending
on the extent of overheating.

To determine the proper quenching temperature of any particular
grade of steel it is only necessary to heat pieces to various
temperatures not more than 20 deg.C. (36 deg.F.) apart, quench in water,
break them, and examine the fractures. The temperature producing
the finest grain should be used for annealing and hardening.

Similarly, to determine tempering temperatures, several pieces
should be hardened, then tempered to various degrees, and cooled
in air. Samples, say six, reheated to temperatures varying by 100 deg.
from 300 to 800 deg.C. will show a considerable range of properties,
and the drawing temperature of the piece giving the desired results
can be used.

For drawing tempers up to 500 deg.F. oil baths of fresh cotton seed
oil can be safely and satisfactorily used. For higher temperature
a bath of some kind of fused salt is recommended.





Next: Hints For Tool Steel Users

Previous: Temperatures To Use



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