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.



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.

-----------------------------------------------------------------------





Temperatures To Use Tempering Round Dies facebooktwittergoogle_plusredditpinterestlinkedinmail

Feedback