ANNEALING

Discussion in 'Reloading Forum (All Calibers)' started by Webster, Aug 6, 2019.

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  1. dgeesaman

    dgeesaman Gold $$ Contributor

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    Basically, this begs someone to perform flame annealing with proper hardness and microstructure measurements just as AMP did for induction and salt bath annealing. I don't think AMP owes a study of flame-annealing to anyone - they already tested salt bath annealing, which had a reputation for being a highly controllable at-home process.

    Has anyone in the flame annealing sphere done the metallography to back up their product/process? (I ask, openly because I'm not seeing any sources that go back to hardness in the cross-section)

    David
     
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  2. RegionRat

    RegionRat

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    There are temperature versus HV plots for cartridge brass in college level metallurgical text books. The main problem with a glance at those is that they always tend to show a 50% cold work starting point on a sample that is way too large and then soak times on the order of 30 minutes at the plotted temperature. We can't use those beautiful phase boundary plots or those annealing plots for our interests.

    One then has to account for the time factor and heat transfer relationship in terms of the difference between those plots for analysis pucks which are on the order of a quarter inch thick and a 12.5 mil case neck.

    There is also some contention as to the target HV. For example, is a HV of 110 good, or should the value be more like 95.

    Without a doubt, the cartridge manufacturers have had to tune their processes to achieve their goals. Those goals tend to show a similar target value in the micro-Vickers range of about 95 - 105 in the necks. Military rounds tend to have sealants in the case neck that eliminate the topic of how that science helps reloaders.

    So, we are typically on our own for precision reloading when it comes to the general science of what happens to multiple use brass and is there any such thing as "one right" answer for everybody. Short of laboratory access and a government sized budget, it is easy to see why there are not more folks publishing on the topic. I have to commend AMP for at least trying to set up the measurements that directly and indirectly show the relationship between brass processing and accuracy. It will take much more work to arrive at all those answers.
     
  3. RegionRat

    RegionRat

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    I agree. When I retired, I lost all access to the labs or it would have been a good study to run. I did manage to check my own Giraud work on (.30-06) Lapua and Remington brass when I first picked up the machine. I was able to see my necks were good, right about HV 95, and the body near the middle was unchanged. I don't know if that was luck or repeatable. I will admit, I agonize over the flame position and the timing, every time I set up the machine.

    I was also heartbroken to see the AMP report on salt bath annealing because I really liked the method. I have not run that salt since seeing the report.

    If I can go back and have the work run in the labs, it would be good to learn how sensitive or forgiving the flame method is compared to the Tempilaq and visual indicators we use,
     
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  4. riflewoman

    riflewoman Gold $$ Contributor

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    These charts are set up to show the function and these are easily repeatable by sophomore students. When you get low amounts of cold work and thin sections, the achievement of good results take a little more finesse. AMP found they had to get to higher temperatures to initiate recrystallization. That gave them the repeatable results they were looking for. I’ve always maintained that heating to the initiation of a very dull dark red heat on the neck in a very dark room will give good results. Strangely it’s the same advise Townsend Whelen and EH Harrison gave 40 years ago. But I digress.
     
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  5. Ned Ludd

    Ned Ludd Gold $$ Contributor

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    ^^^This. Although having the metallurgical data would be a bonus, it's not essential. Heating cases in my Giraud [torch] annealer until the neck turns dull red in a darkened room provides the results I want in the reloading room and on the target, firing after firing. Knowing the exact grain structure of the brass isn't going to change any of that. However, it IS very important for manufacturers of induction-based annealers to know that information, so they can provide users with appropriate guidelines for annealing their cases.
     
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  6. David101

    David101

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    The 750 degree temperature corresponds in the majority of cases to be the point where the actual colour of the case after the temperature has been applied has changed to that frosted slightly blueish. I am colour blind but you all know what I mean.

    I have a 1500W power supply in my unit so if the piece of metal to be heated has the right resistance about 31A is able to flow. With a 308 case in my coil the maximum current is about 14A

    @SGK how much needs to be heated like you said is a very good point for discussion. When you look at say new Lapua cases that case colour change is a long way down the case perhaps 1/2 inch. My thinking is that annealing is only needed where we are reshaping / sizing the brass. So in most cases that would be the neck only and even shoulder bumping is often only really the slope of the shoulder. Not really changing the point where the shoulder starts.

    However I have noticed that with even the round work coil the anneal is not perfectly the same distance from the base. There is a slight wave to it. Therefore I heat to about 1/4 inch down the case so the case shoulder point is consistent all the way around the case. I try to keep that distance to a minimum.
     
    Last edited: Aug 14, 2019
  7. jthor

    jthor

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    When cartridge manufacturers anneal their brass they calibrate their annealer, whether it is flame or induction, to anneal to a certain HV. When starting up a line they will anneal a cartridge and then go test the HV until it is right. I’ve had a discussion with Peterson Brass about this and their ideal HV on the neck is around 95-100.

    Also, everyone knows flame annealing will anneal and drop the HV, no one doubts that. AMP did a study on Salt Bathing, at least in my opinion, because it looked too good to be true and it was. For bottle-necked cases it looks to only start the recovery phase, barely dropping in HV which hints at stress relieving. With flame and induction you hit recovery, and can see recrystallization and grain growth under a x200 microscope.
     

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