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Reheating for machine ability was done at 100 deg. less than ...

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

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

Bessemer Process
The bessemer process consists of charging molten pig iron int...

There is no mystery or secret about the proper annealing of d...

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

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

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

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

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

The Electric Process
The fourth method of manufacturing steel is by the electric f...

Furnace Data
In order to give definite information concerning furnaces, fu...

Case-hardening Treatments For Various Steels
Plain water, salt water and linseed oil are the three most co...

Robert Mushet
Robert (Forester) Mushet (1811-1891), born in the Forest of D...

Annealing Alloy Steel
The term alloy steel, from the steel maker's point of view, r...

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

Critical Points
One of the most important means of investigating the properti...

Mushet And Bessemer
That Mushet was "used" by Ebbw Vale against Bessemer is, perh...

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

Knowing What Takes Place
How are we to know if we have given a piece of steel the ver...

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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