[skip]

Please excuse if this has been covered, but my searches haven't yielded any results. I need to re-do the main spring (flat leaf) on a CVA double-barrel shotgun, and I cannot find the proper temperature to temper with. I've heard stories about tempering in melted lead, but that could be quite a range of temperature. I would rather know a more precise (and obtainable) number.

[Third_Rail]

What do you need it tempered to? What metal is it exactly?

If you answer those, looking up the temperatures is easy enough, and I'll help to the best of my ability.

[4v50 Gary]

The temperature isn't a precise science. You need good eyes to judge the proper color for tempering. Darn if I recall though and I've done it before. Let me see if I can either find my notes or my Kit Ravenshare booklets.

[4v50 Gary]

Haven't found my books by Kit Ravenshear. Here's what I have for notes (from my class with Jack Brooks):

1) heat until red hot (we used a propane torch). Quench in oil.
2) Temper 750-800 degrees (I think it was straw yellow) and then allow to air cool.

The steel we worked with was 1065 investment casted steel.
If you use automobile springs, they're 1095 steel.
Old Model T springs are 5160 steel.

[skip]

In the meantime I've found my reference on tempering temperatures. Nothing is listed above 600degF (medium blue), and straw-yellow is 470degF. The temp listed for springs is 560degF (full blue), but it does not distinguish between flat springs and coil springs.

The spring I need to "re-train" is a flat spring from a CVA shotgun lock. I have a nifty little oven just the right size for objects up to the size of hunting knives ('twas a toaster-oven in a former life - I liberated it from the Salvation Army for $3.68).

Before I throw the switch, I want to be real sure I'm using the proper temperature.

[redneck]

Since your working with an unknown carbon steel, the best method is to heat until non magnetic and quench in a light oil (10W30 works Ok when heated to about 100-110 degrees), should be a pretty good red, but not glowing too much. Color is subjective, a magnet will tell you for sure that you've reached critical temp.
Now, clean the oil off or its going to stink when you put it in the oven. Throw it in there at 350F for about an hour and come back and check. More than likely you'll be getting a straw color. If this is a high carbon steel it will be in the low 60's on the RC scale at this point, too hard. Raise the temp 15deg F and let it go another half hour or so, check the color again. Continue raising and checking until you get the color you want.
The reason to start low and work your way up is that 1000 degrees will get it too soft and turn it the same color blue that 700 deg will. You want to hit your color from the low end of the temperature range that causes it.

[redneck]

Thought I should add that most tempering cylces max out on their effectiveness at 2 hours, so after reaching the color you want, you should let the peice cool a few hours and then give it another round in the oven for an hour or two at that same temperature.

You can temper by color with a torch as Gary mentioned but this takes careful judgement of the color, and generally you don't get as even or as good of results as you do with the longer cylce. I've read in some machinists books where they flash temper using a salt bath, but your talking about heating to an exact temperature for a given steel and then you have to hold it there for like 8 and a half minutes and quench, they also recommend using an oven instead if you have the time.

[skip]

All this is bringing up other questions I've been carrying around. I've been checking Machinery's Handbook, and various welding books, and some say to quench at the end of a temper, and others say to let the piece air cool.

I've done it both ways with knives and chisels and such, and cannot tell any difference. I personally prefer to let it air cool at its own rate - it feels more natural.

[4v50 Gary]

BTW, when we tempered it we did it with indirect heat and placed the object on a piece of brass and applied the torch to the brass. The spring absorbed the heat from the brass.

[Shanghai McCoy]

Using a block of iron or steel as an indirect heat source is a good way to temper knives.The brass block trick sounds good for a small item such as a spring.Good luck and let us know how it turns out.

[redneck]

Generally, I've only heard of quenching after temper for the method Gary is talking about using a brass or steel block. I forgot to mention the block trick, good thinking Gary. Gives much more even heat and you can see the color change much easier.

Using the oven, I haven't heard anyone recommend quenching afterward. I guess that since your using a more controlled heat source you don't have to worry about it overheating if you started at the right temp. With the block or torch it is continually getting hotter, when you see the color you want, its still is on there a little longer since you have to react and get the thing off of there.

Another reason for using the oven and starting at a much lower temp than you think is that oven thermostats are notoriously innacurate! I've heard stories of them being off by 100 deg :banghead:

[4v50 Gary]

No thinking on my part Redneck. Jack Brooks of Colorado deserves the credit. Several of his guns were displayed at the National Firearms Museum in Fairfax when I visited in August.