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.
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?
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
Last edited by prepare; 04-11-21 at 11:06.
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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.
Last edited by lysander; 04-11-21 at 12:04.
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.
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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.
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