Nitriding Options (Q vs QP vs QPQ)

Nitriding Options (Q vs QP vs QPQ)

At Nitrera, we understand the importance of tailoring the nitriding process to meet your unique application needs, ensuring the utmost value and performance. Our versatile range of nitriding processes includes Q, QP, QPQ, and AL>QP, allowing you to choose the ideal treatment for your components. Additionally, we offer the flexibility of customizing processes, such as 'no oil' options like QP>No Oil, to precisely match your specifications. Rest assured, unless specified otherwise, we provide a high-quality finish with post-nitriding oiling to enhance the performance, longevity and marketability of your components.

Pre-Process Prep

  1. Aluminum Oxide (AL): Remove heavy oxidization from prior heat treatments, blend tool marks and attain your desired surface finish or aesthetic with our aluminum oxide blasting option.
  2. Glass Bead (GB): Achieve impeccable surface finishes and aesthetics by opting for our glass bead process, which eliminates light oxidization, blends light tool marks.
  3. Acid Etch (AE): For parts previously plated, our acid etch process efficiently removes plating to prepare the surface for nitriding. 

Process Finish Type

  1. Nitride (Q): Experience the enduring benefits of nitriding with a sleek matte finish, enhancing both performance and aesthetics.
  2. Nitride + Polish (QP): Elevate your components with our nitride process, followed by ultra-fine glass bead polishing, reducing surface roughness and ensuring a refined appearance.
  3. Nitride + Polish + Re-Oxide (QPQ): Maximize corrosion resistance by combining nitriding, polishing, and a second black oxidization for a finish that excels in both functionality and appearance.

Post Process

  1. Oiling (Oil): By default, we treat your components with our standard oiling process, enhancing corrosion resistance and overall aesthetics. 
  2. No Oiling (No Oil): For parts requiring specific cleanliness standards or those slated for painting or food processing, we offer the flexibility to skip the oiling step, ensuring your components meet exacting requirements.

Using the process codes above, and the desired outcome was the smoothest surface finish + max corrosion resistance (QPQ), and we are starting with a part that was heat treated by quench & temper (or otherwise has mill scale or oxidization on the surface), and we want oil for the added corrosion resistance & aesthetics, the process code would be: AL QPQ Oil

Q vs QP vs QPQ Application Table

Nitride & Quench
(Standard process)
Nitride & Quench + Polish
Nitride & Quench +
Polish + Quench
Case Hardened Surface to 55HRC+1

Reduces Friction & Adhesion by up to 60%

Black Oxide (Quench) for Corrosion Resistance & Aesthetics.
Same as Q, plus a Polishing step which restores the original finish, and increases surface luster.
Same as QP, plus reimmersion into the oxidizing (Quench) salt bath to further enhance corrosion resistance.
Price & Delivery
Lowest cost & fastest delivery
Marginal increase in cost & delivery time
Highest cost & delivery time
Surface Roughness (RA)2
≤32µin (0.8µm)

Nitriding can increase RA up to ~32µin (0.8µm) total
≤16µin (0.4µm)

QP restores RA to ~8-16µin  (0.2-0.4µm)

RA can be restored to ~2µin (0.05µm) by hand polishing or other means.
Same as QP
Appearance / Aesthetics
Deep matte finish

Some material may be aesthetically affected by brown/red iron oxides (particularly stainless steels and cast iron)
Satin Luster

Very high quality & consistent appearance from part to part & batch to batch.

Polishing removes brown oxides and other surface contamination & visible defects.
Same as QP but with further handling and processing there is decreased part to part & batch to batch consistency of appearance.
Corrosion Resistance
(Compared to Raw / un-Nitrided Material)
Carbon, low-alloy & tool steels: Tremendous increase3

Martensitic stainless steels: Moderate increase

Nodular irons: Slight increase

Precipitation hardened stainless steels: Unchanged

Ferritic & Austenitic stainless steels: Decreased
Carbon, low-alloy & tool steels: Same as Q

Martensitic stainless steels: Same as Q

Nodular irons: Same as Q

Precipitation hardened stainless steels: Reduced compared to Q

Ferritic & Austenitic stainless steels: Further reduced compared to Q
Carbon, low-alloy & tool steels: Potentially better than Q & QP

Martensitic stainless steels: Likely better than Q

Nodular irons: Same as Q

Precipitation hardened stainless steels: Likely better than Q

Ferritic & Austenitic stainless steels: Significantly better than Q
Best Choice
Any material needing surface hardness, yet surface roughness does not need to be <32µin (0.8µm), and corrosion resistance & aesthetics are not critical.
Surface Roughness (RA) of <32µin (0.8µm) required. E.g.: seal surfaces, cylinder bores, etc. 

Components with high-spec aesthetic requirements. E.g.: Firearms, tools, etc.
Same as QP 

Stainless steels if corrosion resistance is critical  

Everything else if the additional cost is worth it.

1 55-60HRC for Carbon Steels, 60-70HRC for Low-alloy Steels, 70HRC+ for Stainless Steels
2 Nitriding is not expected to increase surface roughness (RA) where the starting roughness is >32µin (0.8µm)
3 Up to ~400hr ASTM B117 salt spray test