Heat Treating failure

[BulletFactory]

A couple weeks ago, I did a series of temperature tests for hardness, and found out that I could get 15.4 after heat treating for an hour at 425*. I tried again the other day, and wound up melting the bullet bases. Any suggestions on how to make a more stable environment for the bullets?

[Floydster]

You don't need the heat that high, turn it down to 375 max. for an hour, turn the heat off and keep in oven till cool.

[BulletFactory]

On my testing, I tried 25* F increments from 325 to 475, and got different BHN #s at each temperature. IIRC, 375 gave me a BHN around 13. I could be wrong here, but dont you have to water drop for the heat treating to take effect?

[BABore]

You don't need the heat that high, turn it down to 375 max. for an hour, turn the heat off and keep in oven till cool.

Doing that will do nothing more than anneal the boolits.

You should have no trouble heat treating at 425 F. I've done it as high as 450 F, but usually set my oven for 435 F with my alloy.

Number one question is what is your alloy? If it's WW's or a similar alloy, I would be looking at my oven. Have you checked and calibrated it with a good thermometer? Is the oven gas or electric. Gas has more temperture fluctuation than electric. Is it a toaster oven? They can also fluctuate and it happens fast due to their small size. Since you melted the bases, I would assume you had it low in the oven and had a rapid increase in heat as the oven tried to maintain temperature. A heat sink under the boolit pan would help with this. Bricks, pizza stone, double pans, something like that.

[BulletFactory]

mystery alloy. really isnt worth a ****.

Its a gas oven, the kitchen type. (no Its not used for food). I use the case for an old computer as a bullet holder. Its about 7 or 8 inches high off the bottom of the oven.

I'll have to check with a thermometer, I was going off the knob on the oven itself because it worked once.

I could throw a hundred pounds of iron lifting muscle weights in there.

[Iron Mike Golf]

Since you melted the bases, I would assume you had it low in the oven and had a rapid increase in heat as the oven tried to maintain temperature. A heat sink under the boolit pan would help with this. Bricks, pizza stone, double pans, something like that.

You don't want the surface the boolits are resting on to be dirctly heated by the heating element. You want only the air in the oven to be heating the boolits. So, like BABore said, make sure you have something between the boolit pan/tray and the heating elements.

[sqlbullet]

A really good oven will be accurate to the know ±25°. Most are ± 50°.

Get an oven thermometer.

However, I get the best heat treat by having a good casting cadence (count in your head) and dropping directly from the mold. No fuss after the fact.

[truckjohn]

It sounds like your real problem is that your oven isn't heating evenly..... try out putting a fireproof insulating cloth pot holder of some sort or another up under your tray of bullets....

The answer to the Alloy question is that hardening depends heavily on your alloy..... It's not really "Hardening" as much as it is "Accelerated aging".....

Arsenic/Antimony alloy OR a Calcium/Tin alloy can he heated to accelerate age hardening.... Straight Lead/Tin won't..... Lead/Tin/Antimony doesn't age harden nearly as well as when there's a teeny bit of Arsenic in it to help..... (Notice how Linotype doesn't get harder with heat treating....)

If it does harden in your oven - then you don't have to worry about the alloy bit....

Thanks

John

[AZ-Stew]

I discovered all these things a couple of years ago when I bought a yard-sale toaster oven to use for heat treating.

Oven knob markings are inaccurate. Use a thermometer. One that uses a thermocouple (TC) is very handy, as you can place the TC anywhere within the oven to find the localized temps. Do your temp settings with the TC in amongst some boolits to place it where the temp is normalized by the mass of metal around it.

Allow the oven to come up to temp BEFORE putting the tray of boolits inside. If the oven thermostat is outside the oven cavity, the oven can get VERY hot before the thermostat causes the temperature to stabilize.

Adding metal to the inside of the oven cavity will stabilize the temperature, causing smaller temperature swings between "on" and "off" of the heat source.

You must quench immediately after the one hour heat soak for hardening to occur. Your alloy must contain antimony for hardening to occur.

You'll figure out the rest for yourself.

Regards,

Stew

[Charlie Two Tracks]

http://www.lasc.us/HeatTreat.htm
Click on the above link........... very good info.

[BulletFactory]

I am positive that I have both arsenic, and antimony. I'll drill a hole inm the stove, so I can get the thermometer in there.

[BABore]

Based on your follow-up, I'd say your biggest problem is the stove being gas. Look at a typical rangetop in gas or electric. An electric coil heats up slowly due to the resistance. You can turn the burner on high and hold your hand on it for several seconds before heat builds up. With a gas burner you'd get crispy right quick. You have the same situation in a gas oven versus electric. Next to your gas pilot is a flamethrower under that thin, sheet steel box. It doesn't gently ramp up when the temperature drops below the set point. Your best bet to to heavily insulate your boolits so they don't get the wild temperature flucuations.

BTW as long as you use a decent HT container and don't leave your boolits rolling around in the oven, there is no contamination issue. I use my regular kitchen oven for heat treating.

[cbrick]

mystery alloy. really isnt worth a ****.

I am positive that I have both arsenic, and antimony.

Which is it?

First, you cannot test the hardness for at least a few days, two weeks is much better. Heat treated lead/antimony alloys "age Harden" once quenched. Soon after removing from the water they are quite soft and will give no indication of the potential hardness.

Second, tin will decrease the amount of increase in the final strength (hardness) of HT bullets, the higher the percentage of tin the less increase in strength and the longer it will take to reach final hardness. Tin will lower the melting point of the alloy, that's why solder melts at 362 degrees. So, the higher the tin percentage the lower the melting point and less hardening and more time.

Antimony (Sb) is the key heat treating. The lower the percentage of Sb the longer the hardening time curve. A 2% Sb alloy could take up to 2 weeks longer to acheive the same hardness as a 4-5% Sb alloy. Arsenic (As) will allow a higher level of hardening but Sb is the key to HT. You cannot HT without Sb, you can without As. All this is why Linotype will HT but not to the same percentage gains in strength as say wheel weight. Because lino has a high percentage of tin, a lower melting temp and no As.

Oven thermostats are notoriously inaccurate and inconsistent. Gas fired cook ovens have a wide swing in temps over an hour. Even if your thermostat is fairly close, if you have a high tin alloy the highest temp could well be above the slump temp of the alloy.

You said that you acheived 15 BHN, what are you shooting that you would need much harder than that? What was the starting BHN of your alloy (before heat teating)?

Hope this helps,

Rick

[243winxb]

Quote:
Q: Is there anything I can do to make the bullets harder?
A: Cast bullets can be heat treated to increase their hardness providing your alloy has some antimony present. To heat treat your bullets: Cast your bullets in the normal manner, saving several scrap bullets. Size your bullets but do not lubricate them. Place several scrap bullets on a pan in your oven at 450 degrees and increase the temperature until the bullets start to melt or slump. Be sure to use an accurate oven thermometer and a pan that will not be used again for food. Once the bullets start to melt or slump, back off the temperature about 5 to 10 degrees and slide in your first batch of good bullets. Leave these in the oven for a half hour. Remove the bullets from the oven and plunge them into cool water. Allow them to cool thoroughly. When you are ready to lubricate, install a sizing die .001" larger than the one used to initially size them. This will prevent the sides of the bullets from work-softening from contact with the sizing die. Next apply gas checks if required and lubricate. These are now ready for loading.

Many more casting tips at Lyman website.

[BulletFactory]

The starting BHN was 8.7

Im just going to toss this alloy, Im wasting my time until I can get some known alloy, and have the barrel repaired. He wants to open the throat up a thousandth, and even then, I dont know if it will still lead. Im not very confident.

[truckjohn]

If he's shooting it in a pistol - there are a million other factors besides just pure alloy/hardness.... 15.9 after a day probably translates to ~20 or so after 2-weeks... which should be sufficient.... Potentially too hard to "Bump up" when it shoots.....

Fit is king, and then powder makes a huge difference too..... I wouldn't overlook reloading practices either, as you can wreck a properly made and fitted boolit in 1 second by shoving it into a way undersize case with no bell at the mouth....

Thanks

[454PB]

Agree with cbrick, Linotype mixed 50/50 with pure lead and water dropped will reach 28 to 29 BHN within 2 weeks. In my opinion, that's a good way to achieve hardness, and it still produces an excellent alloy for crisp castings.

If you have a good supply of tin, adding 1% to wheelweights will produce an equally good casting, and nearly the same hardness. I have lots of linotype and pure lead but very little tin, so I use the 50/50 Pb/lino mix.

I seldom heat treat, but when I do, I water drop rather than use an oven......it's just too time consuming to use the oven method.

[RobS]

A heat shield is needed with many ovens and it as simple as layering 15 sheets or so of aluminum foil on a bottom rack that covers nearly the entire width and length of the rack/oven. This will help with keeping your tray of boolits (on the next rack up) at a more stable temp and will help eliminate the direct blast of heat from the bottom when the oven cycles on and off. Other advice given is also good as it relates to making sure the oven is preheated etc. and having a good thermometer.

[Von Gruff]

Here is a good guide that indicates heat levels for alloy types



Von Gruff.

[303Guy]

If the boolits were standing on a black tray they will melt the bases. Stand them on a shiny tray. Even put a second shiny try under it.