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Flange Shields For Furnaces
Such portable flame shields as the one illustrated in Fig. 1...

Fatigue Tests
It has been known for fifty years that a beam or rod would fa...

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

Forging High-speed Steel
Heat very slowly and carefully to from 1,800 to 2,000 deg.F....

Crucible Steel
Crucible steel is still made by melting material in a clay or...

Heating Of Manganese Steel
Another form of heat-treating furnace is that which is used ...

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

Hardening High-speed Steel
In forging use coke for fuel in the forge. Heat steel slowly ...

A combination of the characteristics of nickel and the charac...

Classifications Of Steel
Among makers and sellers, carbon tool-steels are classed by g...

Leeds And Northrup Optical Pyrometer
The principles of this very popular method of measuring tempe...

The Effect
The heating at 1,600 deg.F. gives the first heat treatment w...

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

Composition Of Transmission-gear Steel
If the nickel content of this steel is eliminated, and the pe...

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

Blending The Compound
Essentially, this consists of the sturdy, power-driven separa...

The material used for all gears on the Liberty engine was sel...

Quenching The Work
In some operations case-hardened work is quenched from the bo...

Refining The Grain
This is remedied by reheating the piece to a temperature slig...

Separating The Work From The Compound
During the pulling of the heat, the pots are dumped upon a ca...

Tempering Colors On Carbon Steels


Opinions differ as to the temperature which is indicated by the
various colors, or oxides, which appear on steel in tempering.

The figures shown are from five different sources and while the
variations are not great, it is safer to take the average temperature
shown in the last column.

A B C D E Average
Faint yellow 430 430 430 430 430 430
Light straw 475 460 450 ... 450 458
Dark straw 500 500 470 450 470 478
Purple (reddish) 525 530 520 530 510 523
Purple (bluish) ... 555 550 550 550 551
Blue 575 585 560 580 560 572
Gray blue ... 600 ... 600 610 603
Greenish blue ... 625 ... ... 630 627

Fahrenheit High temperatures judged by color
430 Very pale yellow
460 Straw-yellow
480 Dark yellow
500 Brown-yellow > Visible in full daylight
520 Brown-purple
540 Full purple
560 Full blue
600 Very dark blue /
752 Red heat, visible in the dark
885 Red heat, visible in the twilight
975 Red heat, visible in the daylight
1,292 Dark red
1,652 Cherry-red
1,832 Bright cherry-red
2,012 Orange-red
2,192 Orange-yellow
2,372 Yellow-white
2,552 White welding heat
2,732 Brilliant white
2,912 Dazzling white (bluish-white)

These differences might easily be due to the difference in the light
at the time the colors were observed. It must also be remembered
that even a thin coating of oil will make quite a difference and
cause confusion. It is these possible sources of error, coupled
with the ever present chance of human error, that makes it advisable
to draw the temper of tools in an oil bath heated to the proper
temperature as shown by an accurate high-temperature thermometer.

Another table, by Gilbert and Barker, runs to much higher temperatures.
Beyond 2,200 deg., however, the eye is very uncertain.

color and Kind of tool
Yellow Thread chasers, hollow mills (solid type) twist drills
430 to 450 deg.F. centering tools, forming tools, cut-off tools, profile
cutters, milling cutters, reamers, dies, etc.
Straw-yellow Thread rolling dies, counterbores, countersinks. Shear
460 deg.F. blades, boring tools, engraving tools, etc.
Brown-yellow Taps, Thread dies, cutters, reamers, etc.
500 deg.F.
Light purple Taps, dies, rock drills, knives, punches, gages, etc.
530 deg.F.
Dark purple Circular saws for metal, augers, dental and surgical
550 deg.F. instruments, cold chisels, axes.
Pale blue Bone saws, chisels, needles, cutters, etc.
580 deg.F.
Blue Hack saws, wood saws, springs, etc.
600 deg.F.

Next: High Speed Steel

Previous: The Effect Of Tempering On Water-quenched Gages

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