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13 February 2020 | Stainless steel

The features and weldability of Nitronic alloys

Nitronic alloys, as their name suggests, consist of aseries of nitrogen-bearing austenitic stainless steels. Thefirst grade, Nitronic 40, was developed in 1961by Armco Steel. This registered trademark became the propertyof AK Steel in 2000.

The chemical composition of the main Nitronic alloys is shown in the tablebelow:

Key Characteristics of Nitronic Alloys

Nitronic alloys have unique properties that set them apart from traditional austenitic stainless steels like 304, 316L, CF3, and CF8M. Their distinctive features include:

✔️ High mechanical strength – Strength-to-density ratio up to 3 times that of mild steel.

✔️ Superior ductility – Up to 40%.
✔️ No sensitivity to ductile-to-brittle transition temperature (DBTT).

✔️ Excellent work hardening and forming ability – Nitronic 60 provides the best impact resistance.

✔️ Outstanding weldability – Good fusion and low susceptibility to cracking.

✔️ Resistance to oxidation and corrosion – Including localized corrosion such as pitting and crevice corrosion; Nitronic 50 offers the best protection.

✔️ High resistance to stress corrosion cracking (SCC) – Nitronic 33 excels in this area due to its low nickel content (~3%).

✔️ Superior intergranular corrosion resistance – Better than 304 stainless steel in chloride environments (ASTM G-48).

✔️ Good structural stability – Maintains integrity at temperatures up to 1800°F (900°C).

✔️ Exceptional cavitation and erosion resistance – Comparable to cobalt-based alloys and superior to austenitic and duplex stainless steels.

✔️ Superior metal-to-metal wear resistance – Reduces adhesive wear and seizing.

✔️ Better high-temperature wear resistance – Compared to hard chromium at 400°F (204°C).

✔️ Fretting resistance – Similar to Inconel 718 at 1110°F (600°C).

Work Hardening

The degree of work hardening in Nitronic alloys depends on:

Rate of deformation
Stability of the austenite phase
Working temperature

Unlike 304 stainless steel, which hardens through martensitic transformation (magnetic phase), Nitronic alloys retain their non-magnetic character due to the formation of an epsilon (Ɛ) phase.

A 60% cold reduction increases the yield strength by:

230% for Nitronic 33
220% for Nitronic 40
260% for Nitronic 50
225% for Nitronic 60
335% for AISI 304

Nitronic 50 is ideal for applications requiring a balance between strength, impact resistance, and corrosion protection.

Microstructure and Role of Alloying Elements

Manganese (Mn)

Partially replaces nickel, reducing costs.
Strengthens the microstructure through solid solution hardening.
Acts as a deoxidizer and desulfurizer, preventing hot cracking during welding.

Silicon (Si)

Reinforces the chromium oxide layer, improving oxidation resistance.
Increases strength through solid solution hardening.
Enhances friction and adhesion resistance in Nitronic 60.

Nitrogen (N2)

Stabilizes the austenite phase.
Increases mechanical strength at room and cryogenic temperatures.
Improves resistance to stress corrosion cracking (SCC).
Enhances resistance to localized corrosion (pitting and crevice).
Delays carbide precipitation, reducing the risk of intergranular corrosion.

Applications of Nitronic Alloys

Nitronic alloys are widely used in demanding industrial environments, including:

✅ Manufacturing of tanks and base frames
✅ Refrigerated trucks
✅ Container ships
✅ Armored vehicles
✅ Valve seats
✅ Centrifugal pumps
✅ Turbine blades (as a substitute for CA-6NM)
✅ Fasteners and bolts
✅ Hard surfacing of austenitic stainless steels

Wear and Friction Resistance

Nitronic alloys provide excellent resistance to various types of wear, including:

✔️ Abrasion
✔️ Impact
✔️ Metal-to-metal friction
✔️ Erosion and cavitation
✔️ Corrosive wear

Reducing Adhesive Wear (Seizing)

Adhesive wear occurs due to high contact pressure and friction between chemically compatible surfaces. Nitronic alloys reduce this effect through:

✅ Lubrication of contact surfaces
✅ Reducing pressure, temperature, and movement speed
✅ Increasing surface hardness through work hardening
✅ Choosing compatible mating surfaces
✅ Selecting roughness between 10 and 70 μinches for optimal friction control

Nitronic 60 provides the best wear resistance among the Nitronic series, outperforming hard chromium and martensitic stainless steel.

Weldability of Nitronic Alloys

Nitronic alloys are highly weldable and maintain excellent corrosion and mechanical properties post-weld.

Factors Affecting Welding

Matching vs. dissimilar filler metals
Mechanical strength of weld and base metal
Dilution rate
Work hardening potential
Resistance to hot cracking
Corrosion and wear resistance

Recommended Filler Metals

Nitronic Grade	Matching electrodes or filler metals (AWS A5.4/5.9)	Substitute electrodes or filler metals (AWS A5.4/5.9)	Special electrodes
30	ER218	E/ER307	SODEL 336*
32	E/ER240	E/ER219	SODEL 325*
33	E/ER240	E/ER219	SODEL 325*
40	E/ER219	E/ER240
50	E/ER209, E/ER309LMo	E/ER307	SODEL 336*
60	ER218		SODEL 336* SODEL 3500**

*Thick and hard weld deposit for surfaces undergoing impact wear rather than adhesion.

**Joining

Autogenous welding is possible for thin sections, maintaining similar wear and corrosion resistance to the base metal.

Wear-Resistant Overlays and Hard Surfacing

Nitronic alloys are ideal for build-up and hard surfacing applications on:

Carbon steel
Low-alloy steel
Austenitic stainless steel

Performance of Similar and Dissimilar Mating Surfaces

Nitronic 60/Nitronic 60 = 30% higher wear resistance than martensitic stainless steel 440C
Nitronic 60/SS440C = Superior to homogeneous Nitronic pairs
Nitronic 50/Nitronic 50 = 3x greater wear resistance than other Nitronic alloys

Why Choose Nitronic Alloys?

With their superior mechanical strength, corrosion resistance, and weldability, Nitronic alloys are ideal for demanding industrial applications. Their exceptional wear resistance and work hardening capabilities make them suitable for high-stress environments where traditional stainless steels fail.

Looking for the Right Solution?

Our team of experts can help you select the best Nitronic alloy for your specific needs. Whether you need a solution for high-temperature wear, stress corrosion, or metal-to-metal friction, we have the expertise to guide you.

➡️ Contact us today to discuss your project and discover how Nitronic alloys can enhance your operations!

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