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Heat treating and tempering- temperatures and hardness values included

in Gun Discussion Sat Jan 01, 2011 7:55 am
by Nitris | 94 Posts

Here are some general temperatures based on carbon content
for .65 to .80 percent carbon content 1450F to 1550F
for .80 to .95 percent carbon content 1410F to 1460F
for .95 to 1.10 percent carbon content 1390F to 1430F
for 1.10 and over carbon content 1380F to 1420F

Some alloys commonly used for AK flats are 1050, 1080, and 4130. The last two digits of the alloy designation indicate the carbon content in one-hundredths of a percent, so 1050 has 5 hundredths of a percent or .5 carbon content. The particular alloy should be specified by either the maker or the supplier of the flat. Note-there is a color to approximate temperature chart, but I cannot find it within my reference material at this time.

For 1050, a temperature of 1475F-1550F is appropriate.
For 1080, a temperature of 1450F-1500F is appropriate.
For 4130, a temperature of 1600F-1650F is appropriate.

Quenching is required for proper hardening immediately after the steel reaches temperature. Do not waste time getting the part into the quenching medium! Oil(5 weight motor oil will suffice) is the preferred quench on 1050, 1080, and 4130. Water will work, but may cause cracks. When using water as a quenching medium, the addition of common dish soap will provide a better quench. The soap basically keeps the water from boiling away from the hot steel. Completely submerge the part, then agitate the part while quenching(provide some form of movement) to keep liquid flowing over the surface.

For tempering, these are approximate color to temperature indicators for plain carbon steel. Be certain to polish away all of the dirty black scale left from the heat treating process or it will impede your ability to correctly identify the color. It also helps somewhat to be in a medium lighting environment-not too bright and not too dark. Note-the color will appear almost like oxidation it should not glow the specified color

Steel Color vs Temperature

2000°F Bright yellow 1093°C
1900°F Dark yellow 1038°C
1800°F Orange yellow 982°C
1700°F Orange 927°C
1600°F Orange red 871°C
1500°F Bright red 816°C
1400°F Red 760°C
1300°F Medium red 704°C
1200°F Dull red 649°C
1100°F Slight red 593°C
1000°F Very slight red, mostly grey 538°C
0800°F Dark grey 427°C
0575°F Blue 302°C
0540°F Dark Purple 282°C
0520°F Purple 271°C
0500°F Brown/Purple 260°C
0480°F Brown 249°C
0465°F Dark Straw 241°C
0445°F Light Straw 229°C
0390°F Faint Straw 199°C

Here are the various temperatures for the individual alloys and the hardness after tempering.
Alloy 1050
600F-650F will give a hardness of around 40 Rockwell C scale, which is ideal for the purpose

Alloy 1080
400F will give a hardness of around 41 Rockwell C scale

Alloy 4130
800F will give a hardness of around 41 Rockwell C scale

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