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Steel Making

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

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

Blending The Compound
Essentially, this consists of the sturdy, power-driven separa...

Armor plate makers sometimes use the copper ball or Siemens' ...

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

Suggestions For Handling High-speed Steels
The following suggestions for handling high-speed steels are ...

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

Rate Of Absorption
According to Guillet, the absorption of carbon is favored by ...

Martien was probably never a serious contender for the honor ...

Pyrometers For Molten Metal
Pyrometers for molten metal are connected to portable thermoc...

S A E Heat Treatments
The Society of Automotive Engineers have adopted certain heat...

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

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

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

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

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

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

Preventing Decarbonization Of Tool Steel
It is especially important to prevent decarbonization in such...

Compensating Leads
By the use of compensating leads, formed of the same materia...

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

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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