What specs govern "gun quality steel"? 7

[Lyrl]

Today I had a customer contact me asking if "regular" 8620 steel would respond to heat treat any differently than "gun quality" 8620 steel. I speculated that "gun quality" steel might have tighter alloy and cleanliness tolerances but for their application (a small part with a shallow case depth) I didn't expect any significant difference.

I would like to follow up after having reviewed the actual (not my speculation) requirements for "gun quality" but wasn't able to find anything from my friend Google - maybe I'm searching for the wrong term?

Any tips on what criteria or specifications mills use when certifying a lot of steel as "gun quality" would be much appreciated. (I'm in the U.S. if that affects the answer.)

 

[EdStainless]

This is funny, some gun steels are 'H' so that they have tightly controlled hardenability. They also tend to be clean.
However I know of a number of gun applications that use free machining steels that have very dirty microstructures, and they do this on purpose to design in a failure mechanism.
I means whatever the buyer wants it to mean.

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P.E. Metallurgy, Plymouth Tube

 

[tbuelna]

Here is MIL-B-11595 which is a material spec for gun barrels under 2" dia. It's 4150 rather than 8620 though.

If you want a spec for vacuum melt 8620 bar try AMS 6277. It's "premium aircraft quality" as opposed to "gun quality".

 

[metengr]

You mean gun barrel quality steel. Specifications for these steels are based on agreement between the purchaser and supplier. They can range from carbon to low alloy steel to stainless steel.

 

[Jughandle]

Check the AMS Handbook. I think my Desk Edition says something about steel quality descriptors being qualitative and fairly loose industrial colloquialisms (e.g., aircraft quality, axle, ordnance, merchant, this or that quality). My suspicion is that these descriptors were more popular back in the day of open hearth furnaces. Today’s EAFs generally produce cleaner products, but I’d always recommend spec’ing out the chemistry with max level of undesired elements.

 

[tbuelna]

Lyrl-

I took a look at the material note on an old (1977) US Army M16 bolt carrier print. The note reads, "STEEL, AISI 8620, BASIC OPEN HEARTH, GUN QUALITY, COLD DRAWN, STRAIN RELIEVED BAR, MAX BRINELL HARDNESS 241, AIM FOR 217/229."

Here is a link to a public source US Army drawing for the M16 gas key. The material called out is, "STEEL, AISI 4130, GUN QUALITY, MAX BHN 229".

Apparently the description "gun quality" steel meant something to the US Army ordnance folks back in the 70's. But the specific definition of "gun quality" steel is probably part of some DoD procurement spec that was cancelled long ago.

 

[dgallup]

I've always assumed that weasel notes like that were there so they could reject a material lot if they found too many seams or stringers that caused problems during manufacturing. Agree it is much better (and more difficult) to explicitly state what is and is not acceptable. I know we have some old specs with phrases like "forging quality" and "fine blanking quality". The people who wrote those specs and knew what they meant are long gone.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[EdStainless]

In some cases these still have meaning, there are ASTM specs that have service conditions in the title (cold heading, or deep drawing). But in reality if people don't reference a raw material specification then they had might as well be asking for unicorns.

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P.E. Metallurgy, Plymouth Tube

 

[Compositepro]

In many cases material suppliers will know what a customer needs from experience as long as the end use application is known. This may simply be a way to tell the supplier what the material will be used for, so they know. That experience is gained through a history of complaints and rejections. Not everything can be quantified with great accuracy.

 

[EdStainless]

It it isn't quantified then they they don't care enough to measure it.
And if my customer doesn't care why should I?
I do try to deliver products that meet customers unstated needs, but at the same time there are people that I don't supply any longer because they were never satisfied and they couldn't explain why.


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P.E. Metallurgy, Plymouth Tube

 

[Lyrl]

I appreciate all the comments, the conversation is very insightful.

I passed on to our customer that there is no current industry standard for "gun quality" and that any certifications to that effect are referencing a specific agreement between that mill and that purchaser. It sounds like, as a few of you suggested, their company had some verbal agreement with their usual material supplier but all the people who knew what the agreement was have moved on.

They seemed happy with the information I gave them. Thank you to everyone for helping us both learn something

 

[EdStainless]

Goodwork Lyrl, dialog with customers is how progress is made. A little honest information and hand holding can go a long ways in building a relationship.

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P.E. Metallurgy, Plymouth Tube

 

[mfgenggear]

Seemed simple to to me. "gun quality" will be the final use so no major flaws that can cause an incident. just as for aircraft specification a more detail of the allowable defects. it was used before most of us was born. hahahahaha.

 

[KernOily]

"I do try to deliver products that meet customers unstated needs, but at the same time there are people that I don't supply any longer because they were never satisfied and they couldn't explain why."

Words to live by! Consulting engineering would be a great gig if it wasn't for the dang clients

 

[tbuelna]

In the US aerospace industry there is actually a class of metals for critical applications called "premium aircraft-quality". This description has a specific meaning in the aerospace industry, and there are specifications (AMS 2300, ASTM A646-95, etc) that list the requirements for premium aircraft-quality materials. On the engineering drawing or BOM callout for the raw material, a material spec such as AMS 6265 (double vacuum melt 9310) is listed along with a note stating something like "the raw material used shall conform to premium aircraft-quality requirements listed in the material specification". The AMS 6265 material specification references AMS 2300 for "premium aircraft-quality" requirements.

 

[EdStainless]

Some aerospace quality specs require re-melted material, and some are really just generic material. It is all in the details. And there are some specs for aircraft usage with ultra-high fatigue requirements where the title of the spec reveals nothing.

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P.E. Metallurgy, Plymouth Tube

 

[tbuelna]

There are AMS material specs that define single or double vacuum melt materials. And there are others that define air melt quality of similar alloys. But the premium aircraft-quality form of a material would never be generic air melt. For example, consider AMS 6444 which is a very high-quality CEVM 52100 steel used for aircraft bearings. When calculating L10 fatigue life of rolling element bearings, the material reliability factor used is based in part on the raw material quality. The raw material quality/cleanliness defined by AMS 6444 and AMS 2300 are a major consideration in the material reliability factor used for the fatigue life analysis.

As you note, the title of a particular material spec may not mean much on its own. But the detail information within the spec can be very important when it comes to establishing reliability, fatigue life or fracture properties of a critical component made from the material.

 

[mfgenggear]

good point Terry

 

[IRstuff]

as might be expected there is at least one military specification for gun barrel steel:

http://quicksearch.dla.mil/Transient/1A0B24BDA130470E90A26243BF6FBA09.pdf

MIL-S-21156 STEEL BARS, HEAT TREATED (FOR 20MM AND 30MM AIRCRAFT GUN BARRELS (NO S/S DOCUMENT)

It's no longer in force, and there is no superseding document, so it must not be that important now.

TTFN
I can do absolutely anything. I'm an expert!
faq731-376 forum1529

 

[mfgenggear]

http://www.lasc.us/RangingShotBarrelMakingFeature.htm

good info here