Modern Case Hardening

Finishes have advanced greatly since basic bluing. Ferritic nitrocarburizing is incredibly durable but was never aesthetically pleasing. Blacknitride+™ and ArmorTi changes that notion.

by American Gunsmith Staff

H&M BlackNitride+ video demo
Shade McMillen explaining the Blacknitride process from their Glendale, AZ facility

Ferritic nitrocarburizing (sometimes abbreviated FNC) is a case hardening processes that diffuses nitrogen and carbon into ferrous metals at sub-critical temperatures during a salt bath. Processing at a temperature of over 1,000°F where ferrous alloys and steel are in a ferritic phase provides advantages over other case hardening processes that occur in the hotter austenitic phase.

FNC improves surface integrity aspects by increasing corrosion and scuffing resistance as well as fatigue properties while inducing little shape distortion during the hardening process. By staying in the cooler ferritic phase and using a lower processing temperature, thermal shock is reduced and phase transitions in the steel are avoided.

The process dates back to experiments in the 1950s. Early attempts were difficult to clean and not very environmentally friendly. Degussa in Germany released their Tufftride/Tenifer process. This was commonly used for engine components in locomotives and known for its harsh wear and corrosive resistant properties.

FNC is known by a number of proprietary names, such as Tufftride, Tenifer, Melonite, Nu-Tride, and QPQ (Quench Polish Quench). These processes are commonly used on low-carbon, low-alloy steels, however they can also be used on medium and high-carbon steels. Common applications include spindles, cams, gears, dies, hydraulic piston rods, and powdered metal components.

This process is not new and always held potential for firearm parts. One problem is that ferritic nitrocarburizing has often been used for components that aren’t normally visible to the user. Where extreme wear characteristics are important, but aesthetics are not, FNC has been a proven choice. Thanks to further advances, it can now be done in a more aesthetic manner.

Blacknitride+™

H&M Metal Processing (Blacknitride.com, 330/745-3075) was originally founded in 1946 as a full-service heat treat factory. In 1948, the family grandfather bought an interest in the company and in the late 1980s, the factory expanded its capabilities to provide salt bath nitriding. Today, H&M is a fourth generation, family-owned company in Akron, Ohio and exclusively specializes in providing its proprietary metal surface treatment, Blacknitride+™.

Blacknitride+ is a QPQ steel hardening process tested for superior corrosion resistance, lower co-efficient of friction, and increase lubricity. With a 50,000 square foot facility staffed with 50 employees in Akron, Ohio and an additional 20,000 square foot Glendale, Arizona facility staffed with five employees, H&M maintains its own in-house metallurgical research and development testing laboratory and FFL license.

“Blacknitride+ uses our own propriety blend of chemistry to provide better uniformity and corrosion resistance,” said Ben McMillen, H&M’s Vice President. “FNC was never intended for aesthetics and the process makes it difficult to achieve uniformity. It often leaves a hard black finish meant to be in the middle of a motor and just perform. Our process results in a more uniform look. We took the known benefits of FNC and made it pretty. It replaces bluing and other less durable finishes.”

As H&M developed their process, the company introduced the technology to golf clubs and later expanded to firearms, finding it produces an excellent finish. The molten salt bath deposits nitrogen and carbon that actually penetrates into the surface of the steel and is not just a coating. Finishes such as PVD (Physical Vapor Deposition) or Cerakote are actually ceramic coatings applied on the surface’s outside rather like a hard candy shell. While this is durable and provides benefits, Blacknitride+ is impregnated into the metal and is measured by case depth as to how deep inside, like ice on a pond. This extends the life of barrels and other parts by hardening the interior and exterior surface by treating them outside and inside. This leaves a hard, lubricious surface that prevents galling. Blacknitride+ can be applied to parts after all components are fitted by a gunsmith.

H&M’s metal surface treatment attracts many recognizable and familiar OEM’s in the firearms industry in addition to providing services to consumers with requests to customize their firearms. “Roughly 90% of the industry uses us in one way or another, to include high-end custom guns,” McMillen says.

Blacknitride+ For Gunsmiths

While H&M works with big gun companies, they also run a custom shop that can work on individual customers and custom pieces. The first step is to contact them directly by phone or through their website and ask to speak with their custom shop. They will provide specific instructions and details to obtain optimum results for your project and then will create an account to log in your order in their computer system. Primary points are the gun must be completely detail stripped and disassembled down to the last screw. Not only because they can’t promise to be familiar with every possible firearm but because Blacknitride+ will surface harden everything inside and out. The process can’t be used on springs and will absolutely destroy any aluminum parts.

After making arrangements with their custom shop and completely detail stripping the gun, ship it to H&M. Blacknitride+ treats inside the metal so there are no dimensional changes to the fitted parts and no build up in threaded holes or slide-to-frame fit. This is not an outer finish but a surface treatment. This covers all internal areas, even inside screw holes and the like.

H&M charges a minimum fee based on the volume of each job. Each work order is a customized process for those components shipped to the factory. “Success for this process takes real effort to obtain our internal high standards,” McMillen explains. Because of this, the price per gun drops sharply when done in batches and volume work. H&M has customers that ship in 1-5,000 components per month which can dramatically reduce the price for a bulk savings. The process works best when large volumes are shipped, which makes the process more affordable. For reference, the company uses a vat for the drop-in dunk that is six-feet deep and 50 inches around. Once the arrangements are made through the custom shop and the guns shipped to H&M, the company has a two to three business day turn around for custom work. Just to send the point home, Blacknitride+ will degrade and eat aluminum. The customer is liable for all damage should they mistakenly included parts made of aluminum.

In addition to the hardening, increased slickening, durability, and other performance gains, Blacknitride+ is known for being an attractive finish. And you can have it in any color you want… as long as it’s black, satin or matte. As Henry Ford told his management team about the company’s Model T, there are no other color options, however, if color options are necessary, the surface offers exceptional adhesion for those products that have color variations.

ArmorTi

Blacknitride+ is for steel parts, however, this type of surface-hardening treatment and finish is also available for titanium. Titanium is a great material for gun building as it is light and strong but the friction is bad, galling is a big problem, and there are issues with impact damage. This creates problems in applications where titanium would otherwise work well. McMillen started Akron Research and Technology (AkronRT.com, 330/745-3075) to address these issues.

Galling is a form of wear caused by welding between two surfaces due to friction. When this welding occurs, the parts continue to slide against each other but a section breaks out, causing galls. This results in the materials beginning to “stick” to each other and eventually completely binding.

Thermal conductivity is the ability for a material to absorb and transfer heat. Steel has a thermal conductivity about four times higher than that of many titanium alloys. The lower thermal conductivity of titanium makes it more difficult for the heat to transfer into a titanium part, keeping it cooler longer and cooling faster once it becomes hot. Due to its thermal conductivity properties and light weight, it is common for titanium to be used in applications like firearm suppressors and muzzle devices, however sparking can be an issue.

Titanium has a reputation for deforming under impact. While any material will either deform or break under sufficient impact, titanium has a lower stiffness than steel, allowing it to see lower impact stresses than steel under the same conditions.

For these reasons, titanium hasn’t been used as extensively in firearms as its benefits would suggest. While light, strong, and having good thermal conductivity, the galling and impact deformation issues have limited it largely to peripheral, non-structural components such as muzzle devices, small controls, pins, and the like. The exception to this has been in suppressors as they don’t have to deal with friction.

Protective coatings designed for steel can’t accommodate titanium’s lower stiffness. The result is a failure of the coating (typically cracking or delamination) resulting in wear on the titanium, most often leading to galling.

The University of Akron is a public research university in Akron, Ohio. A STEM-focused institution, it focuses on polymers, advanced materials, and engineering. Having earned his Metallurgical Engineer degree there, McMillen and ART partnered with the school’s Research Foundation. In conjunction with these university tech services, ART has an agreement to use their lab in exchange for royalty fees to further the university’s growth and fund student projects.

ART develops metallurgical solutions for many industries, including aerospace, automotive, defense, energy, food, medical, mining, oil/gas, and steel. One of their developments is a wear-resistant coating for the defense industry, a thermochemical diffusion hardening process for titanium. Testing revealed the coating was an excellent treatment for Navy submarine fire suppression valves and has since become a prime choice for applications requiring wear resistance in submerged environments in salty water and corrosive environments. The coating took two years to develop and patent and is now used widely with the U.S. Navy and Coast Guard.

Of interest to gunsmiths, ART’s research led to creating their ArmorTi process. With their focus on titanium, ArmorTi creates a finish that overcomes the material’s weaknesses. It is a proprietary, patented process that produces a black, extremely hard, abrasion-resistant finish and allows titanium to be used for applications it was not previously suited for due to titanium’s tendency to gall. This surface treatment eliminates friction issues while improving impact resistance.

ArmorTi uses forced diffusion to harden titanium’s surface that results in a slick, durable, black finish with a Rockwell hardness of over 70 HRC. The finish only affects the surface layer of titanium and leaves its integrity and the most desirable properties of titanium intact at its core. Titanium parts are first machined to dimension and then run through the process. Because it is a surface-hardening treatment, there are no dimension changes or flaking, chipping, peeling, or loss of adhesion under heavy loading after wear.

Unlike other options, ArmorTi changes the metallurgy of the outer layer of the titanium by diffusing interstitial hardening elements into the surface instead of applying a new material to the outer surface of the titanium. Where traditional titanium anodizing results is an oxide finish intended to reduce galling, it fails to hold up under extreme friction and other heavy load-related conditions found in firearms and many aerospace and automotive applications.

This makes ArmorTi for titanium the equivalent of Blacknitride+ for steel. Like H&M, Akron Research and Technology offers a custom shop for gunsmiths. After making the same type of arrangements, gunsmith can have their titanium guns and parts finished with ArmorTi.

In addition to the custom work, ArmorTi is featured on pre-made titanium parts from Krytos Industries (KrytosIndustries.com, 234/303-2727). Krytos began by offering titanium AR-15 bolt carriers. This solves the problem that PVD coating failed to as PVD would instantly fall off due to the substrate not being strong enough to support the coating. After ArmorTi proved its worth there, Krytos started offering titanium pistol slides which had never been successfully accomplished before.

Using a ArmorTi-treated Krytos titanium slide, a Glock 19 weighs in at 16 ounces. The slide takes a lot of impact from rails and barrel but this treatment eliminates titanium’s galling issues and protects the core. Testing has demonstrated slides continue to hold up after tens of thousands of rounds fired.

Even though friction isn’t normally an issue, titanium use with suppressors leads to sparking issues. ArmorTi has been found to have 98% spark mitigation, making it an ideal treatment there.

Traditional finishing like bluing still looks great but performance and high-wear environments demand more durability. Blacknitride+ for steel and ArmorTi for titanium are great options to consider for your firearm projects.

Read more in the December 2018 issue.

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