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Steel Making

The Pyrometer And Its Use
In the heat treatment of steel, it has become absolutely nece...

Annealing To Relieve Internal Stresses
Work quenched from a high temperature and not afterward tempe...

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

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

Crucible Steel
Crucible steel is still made by melting material in a clay or...

Instructions For Working High-speed Steel
Owing to the wide variations in the composition of high-speed...

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

Lathe And Planer Tools
FORGING.--Gently warm the steel to remove any chill, is parti...

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

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

Gas Consumption For Carburizing
Although the advantages offered by the gas-fired furnace for ...

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

Take Time For Hardening
Uneven heating and poor quenching has caused loss of many ve...

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

Correction By Zero Adjustment
Many pyrometers are supplied with a zero adjuster, by means ...

Temperature Recording And Regulation
Each furnace is equipped with pyrometers, but the reading an...

Nickel-chromium
A combination of the characteristics of nickel and the charac...

Using Illuminating Gas
The choice of a carburizing furnace depends greatly on the fa...

Oil-hardening Steel
Heat slowly and uniformly to 1,450 deg.F. and forge thorough...

Uses Of The Various Tempers Of Carbon Tool Steel
DIE TEMPER.--No. 3: All kinds of dies for deep stamping, pres...



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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