9310 Bolt Data

[lysander]

Yet many are sold as some new wonder improvement vs C158. That doesn’t make me trust the company with the other critical processes.

To the OP on Nitride. I’m very much against nitride on any critically heat treated part. The nitride is hot enough to alter the hardness.

That would depend on if the nitriding is done as an afterthought, or does as a integrated part of the overall heat treating process.

[JediGuy]

That would depend on if the nitriding is done as an afterthought, or does as a integrated part of the overall heat treating process.

Does anyone have a reason to believe/disbelieve which companies may nitride as part of the heat treating process?

Thanks to everyone contributing. Way outside my lane, but I am enjoying the read.

[sinister]

It cost about half a million dollars for the Army to change a drawing. The return on investment needs to positive in three or five years, let's say five as it makes the math easier.

A bolt cost the Govt about $40, and let's say they buy 100,000 a year, and let's assume that 10% of that is the raw material. So, in order for this to meet the return on investment requirement, the raw material would have to be 25% cheaper.

LMT spent a lot of their own money to offer the world a super-duper improved M16/M4 bolt and carrier. Per Karl Lewis, the improvements don't provide overwhelming superior performance or extended life over the legacy bolt and carrier group -- or, rather, enough for the .mil to replace all they have, and to start buying them as replacements vice what's tested, spec'ed, and in the system and drawings.

[Curlew]

That would depend on if the nitriding is done as an afterthought, or does as a integrated part of the overall heat treating process.

So is there actually a way to get the benefits of a hard nitride surface while still retaining the desired core hardness? On a bolt, specifically.

I had the impression that the nitriding is done in a high-temperature (~1000 F) salt bath after the primary heat-treat, and that’s hot enough to temper the core down to something softer than spec. How can this be avoided? Nitride first?

[prepare]

Apparently pre-2005 there were enough M16/M4 C158 bolt failures to conduct these tests.

Failure analysis of the M 16 rifle bolt
V. Yu, J. Kohl, +3 authors M. Veach
Published 2005
Recently, there have been several occurrences of failure in the bolt of the Ml6 rifle at a United States Army installation. Near the failure location, the bolt was subjected to repeated loading as the Ml6 was fired. In order to determine the stress distribution of the bolt due to the firing process, a geometric element analysis was performed using ProMechanica . The fracture surface was examined using both an optical stereomicroscope and a scanning electron microscope in order to determine failure initiation and failure mode. It was discovered that the fracture initiated at a localized corrosion pit and propagated by fatigue. A controlled experiment was conducted where 1800 and 3600 rounds were fired using new bolts. After 1800 rounds, a region of wear was observed near the site where fracture occurred in the failed bolt. After 3600 rounds, a notch was observed in this wear region. This suggests two possibilities: firstly, exposure of the base metal may have facilitated the formation of the observed corrosion pits; and secondly, the presence of a notch may facilitate the fracture of bolts in general. In addition, Vickers microhardness profiles were taken on cross-sectional areas near the fillet region and 10 mm away from the failed locking lug. Disparities between microhardness profiles near the fillet region and 10 mm away from this region revealed that the bolt may not have been uniformly case hardened. Published by Elsevier Ltd

More info and diagrams at link

https://www.semanticscholar.org/pape...20ed#extracted

[lysander]

Does anyone have a reason to believe/disbelieve which companies may nitride as part of the heat treating process?

Thanks to everyone contributing. Way outside my lane, but I am enjoying the read.

So is there actually a way to get the benefits of a hard nitride surface while still retaining the desired core hardness? On a bolt, specifically.

I had the impression that the nitriding is done in a high-temperature (~1000 F) salt bath after the primary heat-treat, and that’s hot enough to temper the core down to something softer than spec. How can this be avoided? Nitride first?

In order to achieve the required strength, you can't just plunk a piece of steel that has been tempered below the nitriding bath temperature, that goes for a nitrided Carpenter 155 or a nitrided 9310 bolt. As to "how", you will have to discuss that with a nitriding specialist.

[prepare]

Yes, as to how, you would have to discuss that with someone that handles nitriding.

I'll reach out to H&M Metal Processing tomorrow.

http://blacknitride.com/about-us/

Solving metal problems for over 70 years.
Through the H&M Blacknitride+™ process, or Ferritic Nitrocarburizing, we can improve the operational capabilities of your components, solving wear, lubricity and corrosion resistance problems. Whether one ounce or 4,000 lbs., orders are filled with the precision and quality for which we’re recognized. Our stringent quality testing process before, during and after treatment ensures the integrity of the product according to the requirements and specifications of its customers.
Our current facility is ISO 9001 certified. We’re equipped with comprehensive metallurgical laboratories, providing all related research and development for all operations.
Founded in 1946, by Ernie Hedler and Art Marble, our services included hardening, flame hardening and black oxide coating. In 1950, the Korean conflict brought considerable growth to H&M through the processing of tank tracks, breach blocks, brake discs and many other products used by the U.S. military and its allies. Over the years, the company continued to grow and, in the 1980’s, expanded its heat treating capabilities to include Black Nitriding. Our operations have expanded and moved with one goal in mind — to give our customers best-in-class service.

[lysander]

LMT spent a lot of their own money to offer the world a super-duper improved M16/M4 bolt and carrier. Per Karl Lewis, the improvements don't provide overwhelming superior performance or extended life over the legacy bolt and carrier group -- or, rather, enough for the .mil to replace all they have, and to start buying them as replacements vice what's tested, spec'ed, and in the system and drawings.

Low Plasticity Burnishing of the lug root fillet has the possibility of doubling the fatigue life, and allows the use of existing barrel extensions.

The big plus of the LMT bolt is the extractor spring(s) are a more sensible length to coil ratio.

[Todd.K]

That would depend on if the nitriding is done as an afterthought, or does as a integrated part of the overall heat treating process.

I think you may be overestimating the number of actual engineers in any but the biggest AR makers.

But yes, I’ll concede it’s a general rule based on my lack of trust and understanding of the AR market, rather than an absolute impossibility.

[prepare]

According to H&M Metal Processing They have developed a proprietary process using lower temperature and exposure time that achieves the benefits of SBN while maintaining core hardness.