I have a short piece of steel bar on my desk that has been surface hardened and coated with a beautiful matte black finish. It looks perfect for a rifle finish. A brief explanation of the process can be found at
http://www.macsteel.com/nitrosteel.htm

Can some of you hard core engineering types tell me if this is feasible for use as surface hardening and blueing on a gun. One problem I see is the high processing temp.

The finish is beautiful and is really tough. It doesn't scratch even with moderate effort with a file. Corrosion resistance is much better than uncoated stainless. The finish is so slick and tough I think you could use it on the interior of an action as well.

Any ideas?

Hello ForrestB,

Though I am a Mechanical (not Metallurgical) Engineer, I have worked with a variety of the "exotic" materials used on Helicopters. About the only place that we use "Nitriding" steels are as gears in gearboxes. These steels are designed differently than your more common alloy steels from the start, due to suitability for the Nitriding process.

Nitriding is similar to carburizing, where you get a very hard, brittle surface, with a softer, more ductile core. The surface provides superior wear resistance, and the core "carries the loads". The part must be machined to a near-net shape before nitriding/carburizing, because the effect is at the surface (you don't want to "machine it off"), and it is extremely hard to machine because of its' hardness. As the dimensions will change slightly during carburizing/nitriding/heat-treatment, you must allow for this and plan on doing a finish (usually) grinding operation to meet the final drawing requirements.

I believe most firearm's (blued) actions are machined from 4140/4340 alloy steel, and they are through-hardened after rough machining, probably to around Rockwell "C" scale hardness of 36 (160,000 pounds per square inch ultimate tensile strength). Stainless actions are through-hardened to similar strengths.

So, I'm sure it is possible to use this material for, say, a firearm's action, but you would, most likely, have to start with their (special) nitriding alloy bar stock, rough/final machine, and have them perform the nitriding/oxidation process after machining. Even then, they stated that the yield strength of the material is 100,000 psi minimum, so you may need more strength (depending on how much "above minimum" it is) to have the same strength as a through-hardened 4140 steel action. I don't think that you would be able to send them a 4140/4340 alloy steel action for "processing" and get the desired results, as these alloys are not generally suitable for nitriding.

But, you might give them a call anyway to see what they say....

Bill

Forrest,

Their 4045 alloy has about the desired properties for ordnance steels. Feel it would be a fair choice for the application of low-pressure receivers & barrels. Forget about bolts, tho. A bit lite on Ultimate Strength @ 115ksi. Their 4140 WOULD be fine ...... but largest size advertised is 1" dia.

The coating is somewhat similar to deposited coatings used on various modern metalworking tools (drill bits, milling cutters, carbide inserts, etc.) These coatings function to (among other things) promote lubricity & resist erosion. Heaven fer us gunnuts.

Not much impact on the manufacturing process either, as coating is a nominal .001 thick. Easily adjusted for. In fact, checking the title block of many formal machined part blueprints will reveal "Unless otherwise noted, finished dimensions are in inches and OVER PLATING".

Also, many thanks for the nice complement. Normally consider myself a flunky engineer.

He he nyuk nyuk snort

best,
joey

[This message has been edited by b0400879 (edited 05-09-2002).]

[This message has been edited by b0400879 (edited 05-09-2002).]

[This message has been edited by b0400879 (edited 05-09-2002).]