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Steel Making

The Influence Of Size
The size of the piece influences the physical properties obta...

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

Hardening Carbon Steel For Tools
For years the toolmaker had full sway in regard to make of st...

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

Hardness Testing
The word hardness is used to express various properties of me...

Sulphur is another impurity and high sulphur is even a greate...

Plant For Forging Rifle Barrels
The forging of rifle barrels in large quantities and heat-tre...

Heat Treatment Of Punches And Dies Shears Taps Etc
HEATING.--The degree to which tools of the above classes shou...

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

An Automatic Temperature Control Pyrometer
Automatic temperature control instruments are similar to the ...

Chromium when alloyed with steel, has the characteristic func...

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

Annealing Of Rifle Components At Springfield Armory
In general, all forgings of the components of the arms manufa...

Tensile Properties
Strength of a metal is usually expressed in the number of pou...

Steel Can Be Worked Cold
As noted above, steel can be worked cold, as in the case of ...

Brown Automatic Signaling Pyrometer
In large heat-treating plants it has been customary to mainta...

It is considered good practice to quench alloy steels from th...

Placing The Thermo-couples
The following illustrations from the Taylor Instrument Compan...

Detrimental Elements
Sulphur and phosphorus are two elements known to be detrimen...

Carburizing By Gas
The process of carburizing by gas, briefly mentioned on page ...

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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