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Non-shrinking Oil-hardening Steels
Certain steels have a very low rate of expansion and contract...

Composition And Properties Of Steel
It is a remarkable fact that one can look through a dozen tex...

Preventing Carburizing By Copper-plating
Copper-plating has been found effective and must have a thick...

Cyanide Bath For Tool Steels
All high-carbon tool steels are heated in a cyanide bath. Wi...

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

Steel For Chisels And Punches
The highest grades of carbon or tempering steels are to be re...

Application Of Liberty Engine Materials To The Automotive Industry
The success of the Liberty engine program was an engineer...

Protective Screens For Furnaces
Workmen needlessly exposed to the flames, heat and glare from...

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

ANNEALING can be done by heating to temperatures ranging from...

Heavy Forging Practice
In heavy forging practice where the metal is being worked at...

Heat Treatment Of Gear Blanks
This section is based on a paper read before the American Gea...

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

Care In Annealing
Not only will benefits in machining be found by careful anne...

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

Molybdenum steels have been made commercially for twenty-five...

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

Tempering Round Dies
A number of circular dies of carbon tool steel for use in too...

Application To The Automotive Industry
The information given on the various parts of the Liberty eng...

Annealing In Bone
Steel and cast iron may both be annealed in granulated bone. ...

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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