Nitride Service

Resolute Precision Manufacturing coordinates ion nitriding and gas nitriding for precision machined components requiring hard, wear-resistant surfaces with minimal dimensional distortion. Unlike quench hardening processes, nitriding occurs at relatively low temperatures and does not require quenching resulting in far less dimensional distortion than conventional heat treatment. We manage the complete process and deliver certified nitride parts from a single purchase order.

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What Nitriding Achieves

Nitriding is a thermochemical surface hardening process that diffuses nitrogen into the surface of steel parts, forming a hard compound layer and a diffusion zone below the surface. The compound layer (sometimes called the white layer) provides exceptional wear resistance and moderate corrosion resistance. The diffusion zone below provides a graduated transition between the hard surface and the core material, improving fatigue strength.

Because nitriding occurs below the lower critical temperature of steel typically between 480°C and 565°C the core properties established by prior heat treatment are not significantly altered, and there is no phase transformation requiring quenching. The result is a very hard surface with minimal distortion of the overall part geometry.

Ion Nitride vs. Gas Nitride

Two nitriding processes are available depending on part geometry, material, and surface requirement:

Ion nitride (plasma nitride) — nitrogen ions bombard the part surface in a vacuum chamber; precise control of compound layer thickness; suitable for blind holes and complex geometry; white layer can be minimized or eliminated per specification

Gas nitride — parts are exposed to ammonia gas atmosphere in a furnace; lower capital cost process; longer cycle times; white layer thickness less controllable than ion nitride; well-suited for large batches of simpler geometry

Specifications

Surface Hardness	Rc 60–72 compound layer; material dependent. 4140 and 4340 typically achieve Rc 62–65.
Case Depth	0.005″ to 0.030″ total case depth; effective case depth of 0.010″ to 0.020″ is typical, per specification.
Processes	Ion nitriding (plasma nitriding) and gas nitriding; process selected according to part requirements.
Distortion	Minimal; typically less than 0.001″ dimensional change on properly machined parts.
Materials	4140, 4340, H13, D2, 17-4 PH, Nitralloy 135M, and other nitriding-grade steels.
White Layer	Controllable thickness per specification; ion nitriding can eliminate the white layer upon request.
Specifications	AMS 2753 (plasma nitriding), AMS 2759/10, and customer-proprietary specifications.
Documentation	Hardness traverse, case depth reports, and white layer measurements provided with finished parts.
ISO	ISO 9001:2015; outside suppliers qualified under RPM’s approved vendor procedures.

Applications for Nitrided Precision Parts

Nitriding is the preferred surface hardening method for precision components where dimensional accuracy must be maintained after hardening:

Gears and gear shafts — hard tooth flanks with minimal distortion of gear geometry
Cams and cam followers — wear-resistant surfaces on complex contour profiles
Hydraulic and pneumatic spools and sleeves — hard bore surfaces for long service life
Extrusion screws and barrel liners — extreme wear resistance in abrasive processing applications
Tooling and fixtures — hard surfaces for repeated use without dimensional degradation
Aerospace actuator components — fatigue life improvement combined with surface hardness

Frequently Asked Questions

What steels are suitable for nitriding?

Not all steels respond equally to nitriding. Steels containing nitride-forming alloying elements chromium, molybdenum, aluminum, and vanadium achieve the best nitriding response. Common nitriding steels include 4140, 4340, H13, D2, and dedicated nitriding grades such as Nitralloy 135M. Plain carbon steels (1018, 1045) can be nitrided but achieve lower hardness than alloy grades.

What dimensional change should I expect after nitriding?

Properly machined and stress-relieved parts experience less than 0.001″ dimensional change through nitriding. Parts with significant machining-induced stress or thin wall sections may experience slightly more growth. We recommend stress relieving before nitriding for precision components to minimize distortion.

Can nitriding be applied selectively to some surfaces but not others?

Yes. Surfaces that should not be nitride can be protected by masking with copper plating or mechanical stop-off. Threads, precision bores, and functional surfaces that must remain at base material hardness are commonly masked during the nitriding process.

Is the white layer a problem for my application?

The white layer is a very hard, brittle compound layer on the surface. For most wear applications it is beneficial. For applications requiring a highly polished surface, fatigue loading, or subsequent grinding, the white layer may need to be removed or minimized. Ion nitriding can produce very thin or near-zero white layer thickness per specification.