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Steel Making

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

SILICON is a very widespread element (symbol Si), being an es...

Carbon In Tool Steel
Carbon tool steel, or tool steel as it is commonly called, us...

Carbon-steel Forgings
Low-stressed, carbon-steel forgings include such parts as car...

MANGANESE is a metal much like iron. Its chemical symbol is M...

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

Correction By Zero Adjustment
Many pyrometers are supplied with a zero adjuster, by means ...

Quality And Structure
The quality of high-speed steel is dependent to a very great ...

Shrinking And Enlarging Work
Steel can be shrunk or enlarged by proper heating and cooling...

Chrome-nickel Steel
Forging heat of chrome-nickel steel depends very largely on ...

Affinity Of Nickel Steel For Carbon
The carbon- and nickel-steel gears are carburized separately...

Effects Of Proper Annealing
Proper annealing of low-carbon steels causes a complete solu...

Placing Of Pyrometers
When installing a pyrometer, care should be taken that it re...

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

Testing And Inspection Of Heat Treatment
The hard parts of the gear must be so hard that a new mill f...

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

Open Hearth Process
The open hearth furnace consists of a big brick room with a l...

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

Typical Oil-fired Furnaces
Several types of standard oil-fired furnaces are shown herew...

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

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.

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Previous: The Effect Of Tempering On Water-quenched Gages

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