The Temper Colors on Steel

P A U L G O R D O N

It is common and long-time knowledge that steel heated in contact with air at temperatures in the tempering range takes on various temper colors due to the forma- tion of a thin oxide film. There is, however, little detailed informat ion on this phenomenon in the readily available literature. As an example, the 1948 ASM Metals H a n d b o o k gives the following table:

Heating Tempera ture , ~ Color

400 Faint straw 440 Straw 475 Deep straw 520 Bronze 540 Peacock 590 Full blue 640 Light blue

The later volumes of the ASM Handbook (8th Ed.) ignore temper colors.

In the course of a research program we have been engaged in, it became desirable to have some more de- tailed informat ion on temper colors for plain carbon steel, especially on the effect o f time as well as tempera- ture. This was obtained using 5/8 in. diam hot-rolled bars of a s tandard SAE 1035 steel. Two in. long samples cut from the bars were carefully machined and cleaned

PAUL GORDON Professor, Dept. of Metallurgical and Materials Engineering, Illinois Institute of Technology, Chicago, I11.

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TEMPER COLORS AFTER HEATING 1035 STEEL IN CIRCULATING AIR (ATMOSPHERIC PRESSURE)

to give smooth, bright surfaces. They were then heated for various times at several temperatures in air-circulat- ing furnaces controlled to within +_ 3~ (___ 5~ of the desired temperatures. Since it seemed worthwhile to have the resulting informat ion generally available, it is given herewith in the accompanying figure.

Maintaining Adjusting Combustion Systems for

Fuel Economy

R I C H A R D J. R E E D

To save fuel, reduce excess fuel and reduce excess air. In other words try to have close to perfect or stoichio- metric combust ion with just the right proport ion of air to fuel. This " r igh t p r o p o r t i o n " can best be determined by calling the fuel supplier, but it is about:

10 volumes o f air for each volume of natural gas,

RICHARD J. REED, North American Mfg. Co., Cleveland, OH 44104

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0 500 1000 1500 2000 2500 3000 F u r n a c e g a s e x i t t e r n p , F

I I I I I I I I I I 0 200 400 600 800 1000 1200 1400 16(}0 1800

F u r n a c e g a s ex i t t e m p , C

Fig. l . - - F o r an 1800 F furnace, use of 30 pct excess air requires 115W2 pct as much fuel as using only 10 pct excess air. The fuel saved is therefore (115 .5 -100) /115 .5= i3 .4 pct.

ISSN0190-9177/79/0806-0093500.75/0 J. H E A T T R E A T I N G �9 1979 A M E R I C A N SOCIETY FOR METALS V O L U M E 1, NUMBER 1--93