Fahrenheit Color Use

430 Very pale yellow Dies, punches, etc.

440 Light yellow Chamber reamers

450 Pale straw yellow Action pins, etc.

460 Straw yellow Triggers, sears

470 Deep straw yellow Milling cutters 480 Dark yellow 490 Yellow brown

500

Brown yellow

510

Spotted red brown

520

Brown purple

530

Light purple

540

Full purple

550

Dark purple

560

Full blue

570

Dark blue

640

Light blue

Drills, firing pin bodies Taps, threading dies

Hammers, extractors Flat springs Screwdrivers Firing pin noses Action parts, breech block

As mentioned, thin parts and those of uneven thickness should be heated in a bath so that they temper evenly. Otherwise, these parts will likely have hard and soft spots. Molten salt baths, nitrate baths, and oil baths are all suitable for this purpose. Different materials and alloys have specific melting points. Often it is possible to pick one of these materials with a melting point equivalent to the temperature needed for tempering purposes. The material is melted and the temperature held constant at its melting point. The part to be tempered is immersed in this bath until heated thoroughly, then quenched immediately.

Melting points of some bath materials are given below:

Bismuth 475 to 510 F.

Lead 618 F

Tin 466 F

Zinc 680 to 780 F

Potassium nitrate 600 F Sulphur 225 F

The lead bath is also used to heat steel for tempering, as well as for hardening it. Heat the lead bath to the part's tempering temperature, and place the preheated part in the bath until it reaches this temperature; remove and quench.

Since the melting temperature of pure lead is approximately 620 degrees F, tin is usually added to the lead to lower its melting point. The temperature of this alloy is reduceable by varying the proportions of lead and tin, as shown in the table below:

Temperatures of Lead Alloy Baths Parts Lead Parts Tin Melting Point Degrees F

200

8

560

100

8

550

75

8

540

60

8

530

48

8

520

39

8

510

33

8

500

28

8

490

24

8

480

21

8

460 450 440 430 420

If no precautions are taken, the hot lead will stick to the parts heated in it. To prevent this, paint the parts to be lead-heated with a mixture of powdered chalk and alcohol. Water may be used instead of alcohol, but the water-based paint must be allowed to dry thoroughly; otherwise, its moisture will cause the lead to spatter.

Another method requires heating the part to a blue color—about 600 degrees F—and then dipping it in a strong solution of salt water. The part is then heated in the lead bath. Remove any lead clinging to the parts with a stiff brush just before immersion in the cooling bath. This will prevent the formation of soft spots in the part.

A sand bath can prove useful for tempering certain types of parts. To make one, first fill a shallow box with sand and place it over a burner. With this method of tempering, parts such as hammers can be variably tempered by placing them edgewise in the sand. Since the temperature of the sand bath is higher toward the bottom of the box, a part can be positioned so that the color of the part's lower edge will be a deep dark blue, while its middle portion is a dark straw, and its upper side is a light straw color. Thus the part's hardness gradually increases from its bottom to its top.

Molten salt baths are also useful for tempering or drawing operations. Nitrate baths are particularly adapted to the usual tempering/drawing temperature range of 300 to 1100 degrees F. Tempering in an oil bath is generally limited to a temperature of 500 to 600 degrees.

Uneven heating is the principal cause of most hardening defects. Cracks running from the corners or edges of the part are indicators of such uneven heating. Vertical cracks and dark-colored fissures indicate that the steel has been overheated and burned. Pieces having hard and soft places have either been unevenly heated, unevenly cooled, or soaked— a term which means overheated. Parts not moved around in the hardening liquid will show hard and soft spots, and may have a tendency to crack. Similarly, those which are hardened simply by dropping them to the bottom of the tank will likely have soft places, due to contact with the bottom or sides of the tank. Also, thoroughly quench parts before dropping them to cool completely.

Too much heat or soaking too long usually decarbonizes the surface of the metal, in which case it will not harden properly until the surface is removed.

Overheated steel that is not actually burned is partially restoreable. Begin by heating it to the right temperature, and allow it to cool slowly in hot sand or ashes. After cooling, the steel is again hardened. If the over-heating originally resulted during a forging operation, the chances of the part cracking during the next hardening will be reduced by using this process.

Except where noted, the small parts described here must be heat treated. If left in a softened or annealed state, they will be brittle and break. If you take my suggestion, and use drill rod and annealed automobile spring to make these parts, the heat treatment will present few problems. Obtaining and recognizing the proper hardening and tempering temperatures present the biggest problem in this situation. And the use of the hardening and tempering baths will simplify this step appreciably.

In the event that tempering baths are unavailable, and the acetylene torch or forge is used to heat the parts, pay close attention to the following procedure, which I described briefly at the beginning of this chapter.

Begin by placing small irregularly-shaped parts on top of a large iron or steel plate. Heat the plate to a cherry red heat. When the parts also reach a cherry red heat, quench them in water.

The next step is to "draw" the temper. The part is polished bright, and again placed on the heated plate until the proper tempering color appears. Remove again and quench in water.

By referring to the chart shown earlier in this chapter, it may be seen that the hammer should be drawn at a dark purple, the sear at a deep straw yellow, the breech block at a light blue, and so on.

Test these parts after hardening with a file. If they remain soft, heat again to a slightly higher temperature, quench, then try the file test again.

If aircraft tubing is used for the receiver and slide, they will not require heat treatment. Nor will the frame require heat treatment if suitable steel is used. Likewise, making the barrel from a military or commercial barrel will save you the trouble of heat treating it.

After finishing the heat treatment of the pistol's components, assemble them again. Test fire the pistol once more before bluing it; if it works satisfactorily, disassemble, and proceed to the next chapter.

There are many tools and parts that are useable as sources of steel if you know what they are made of, and how to heat treat them. The following table gives an indication of the types of carbon steels used in common tools. It is included here to show the many alternate sources for steel, which might prove quite useful in an emergency situation.

Application

Carbon

Auger, wood

0.60-0.70

Ace

1.20

Ball bearing

1.20

Barrel, gun

1.60-0.70

Bits, mining

0.80

Blade, pocket knife

0.90

Blade, reamer

1.20-1.22

Bushing, spring

0.80

Centers, lathe

0.80-0.90

Chisels, cold

0.85

Chisels, chipping

0.80-0.90

Chisels, woodworking

0.60-0.70

Dies, envelope

1.15

Dies, drop forging

0.85-0.90

Drills, twist

1.20-1.22

Driver, screw

0.60-0.70

Edge, straight

1.05-1.12

Facing, anvil

0.85-0.90

Files

1.25-1.30

Hammer, blacksmith

0.67-0.78

Hammer, machinists

0.90-1.00

Hatchet

1.15-1.22

Hoe

0.85-0.90

Jaw, vise

0.85-0.90

Knife, belt

0.80-0.85

Knife, paper

1.05-1.10

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