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Annealing Work
With the exception of several of the higher types of alloy s...

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

Restoring Overheated Steel
The effect of heat treatment on overheated steel is shown gra...

Hardening
Steel is hardened by quenching from above the upper critical....

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

Heat-treating Equipment And Methods For Mass Production
The heat-treating department of the Brown-Lipe-Chapin Company...

Complete Calibration Of Pyrometers
For the complete calibration of a thermo-couple of unknown e...

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

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

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

Hardening High-speed Steels
We will now take up the matter of hardening high-speed steels...

Phosphorus
PHOSPHORUS is an element (symbol P) which enters the metal fr...

Rate Of Cooling
At the option of the manufacturer, the above treatment of gea...

Heat Treatment Of Lathe Planer And Similar Tools
FIRE.--For these tools a good fire is one made of hard foundr...

Making Steel Balls
Steel balls are made from rods or coils according to size, st...

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

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

Carburizing Low-carbon Sleeves
Low-carbon sleeves are carburized and pushed on malleable-ir...

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

Annealing Of High-speed Steel
For annealing high-speed steel, some makers recommend using g...



Tempering Colors On Carbon Steels






Category: HIGH-SPEED STEEL

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.

TABLE 25.--COLORS, TEMPERATURES, DEGREES FAHRENHEIT
----------------------------------------------------------
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
----------------------------------------------------------

TABLE 26.--ANOTHER COLOR TABLE
----------------------------------------------------------
Degrees
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.

TABLE 26.--COLORS FOR TEMPERING TOOLS
-----------------------------------------------------------------------
Approximate
color and Kind of tool
temperature
----------------------------------------------------------------------
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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