MIM 17-4 PH is a powder metal alloy containing iron, chromium, and nickel. It’s ideal for firearms manufacturers who demand final product integrity, part complexity, and lower cost per part.
1. Maintains Firearms Accuracy with Structural Integrity
In the case of firearms, heat is the enemy of accuracy. Gun models that require steady or repeated discharge, as is the case of many automatic weapons produced for the defense industry, produce heat in the barrel. And that heat leads to expansion of the bore, which, in turn, allows the ordnance to spread. Instead of a tight grouping, a shooter will begin to see looser target patterns.
This is where MIM 17-4 PH shines. The “PH” part of the alloy name refers to precipitation hardening, which uses heat to make a metal alloy stronger by hardening it and introducing precipitates into the alloy chemical structure that add stability and reduce dislocations (sometimes referred to as deformation, plasticity, or warping).
At 17 percent chromium, the 17-4 PH alloy adds the strength of precipitation hardening, and it provides tarnish resistance and the ability to add a high-polish finish. Nickel is a transitional metallic element that also contributes precipitation hardening characteristics as four percent of the 17-PH alloy.
The iron, chromium, and nickel elemental powders form the 17-4 PH alloy during sintering, a process that densifies the powders and produces component densification. After sintering these is no difference between the physical or mechanical properties of the powder metal part compared to traditional “solid” metallurgical sources.
By reducing material dislocations through precipitation within the crystalline structure of the alloy, the 17-4 PH can withstand extremely high temperatures without material dislocation. That means those barrels expand more slowly, allowing shooters to maintain accuracy over longer periods of time.
17-4 PH’s strength holds to approximately 572°F (300°C). In fact, with 17-4 PH hardened to 36-44RC, a shooter can fire double or triple the amount of rounds accurately compared to 416R stainless steel, which only hardens to about 28RC.
2. Longer Product Life Thanks to Corrosion Resistance
17-4 PH also resists corrosion, thanks to the chromium content and a low carbon level. In fact, the uniform corrosion rate for 17-4 PH drops to nearly zero at the 17 percent chromium. Alloy 17-4 PH withstands corrosive attacks better than any of the standard hardenable stainless steels.
The stainless steel creates a passive film to counteract the effects of atmospheric corrosion. It would take immersion in an acid bath or seawater to create a uniform corrosion pattern that would damage the protective layer and cause deterioration. Additionally, a very aggressive chlorinated environment could cause pitting, which is localized corrosion that creates small holes in the stainless steel.
For most land-based applications, 17-4 PH makes a good choice to resist environmental degradation of the stainless steel firearms components.
3. Finished Parts the First Time (But Good Machinability Options, Too)
Firearms manufacturers love the combination of MIM 17-4 PH’s durability and the reduction of cost per part through the additive manufacturing (AM) method, which reduces (or completely eliminates) the need for secondary processing. With 3DEO’s metal 3D printing process, fluting and other complex part design characteristics can be incorporated into the primary production step, thereby reducing lead time and production cost when compared to the additional tooling steps needed in CNC milling.
However, some firearms manufacturers might use additional finishing processes for 17-4 PH, like bead blasting to prepare handgun replacement slides with ejection ports for titanium nitride coating. 17-4 PH tolerates post-production machining and electroplating very well. The alloy used in 3DEO’s additive manufacturing process produces components with a matte surface finish that require no secondary deburring or polishing after sintering, but thanks to that chromium composition, the surface polishes up nicely with simple carbide tooling if you need a “shinier” finish.
MIM 17-4 PH Stainless Steel: A Viable Option for Firearms Production
The MIM 17-4 PH alloy is readily hardened and is ideal for use in firearms components that require heat and corrosion resistance, and structural strength, like barrels, bolts, receivers, and pistol safeties, and firearms accessories, like sling gun shafts, U-bracket and stops for high-volume magazine ammunition packs, flash suppressors, and silencers.
Combined with 3DEO’s revolutionary metal 3D printing process, MIM 17-4 PH stainless steel allows gun manufacturers to cost-effectively produce any volume of complex, durable parts for firearms.