Practical Nitriding – steel 11SMn30 – Hydraulics and Post-oxidation

Hydraulic cylinder head glands play a crucial role in sealing the system. They keep pressurized hydraulic fluid inside the cylinder, preventing leaks between the piston rod and the cylinder head.

In this study, we’ll explore how Ferritic Ion/Plasma Nitrocarburising + Post Oxidation can enhance head glands made from steel grade 11SMn30.

Part Requirements

These components must meet several requirements:

• Wear and galling resistance must be improved for longer service life.
• Threads must remain within tolerance for smooth, easy assembly.
• Corrosion resistance must be increased to protect against harsh operating environments.

Ferritic Ion/Plasma Nitrocarburising + Post-Oxidation

As explained in our other article on Ferritic Ion/Plasma Nitrocarburising: when a steel grade lacks strong nitride-forming alloy elements, we do a nitrocarburising process to create a slightly thicker white layer compared to standard ion nitriding.

Since 11SMn30 lacks these alloying elements, we are going to do just that.

The process is followed with post-oxidation in the same chamber.

Achieved Results

A surface hardness measurement after the process shows a hard, wear-resistant case with compressive stress: which gives significantly improved resistance to wear, scuffing, and galling resistance on both threads and spanner holes.

Because of the low ferritic process temperature, there are no distortions and the thread stays in tolerance.

The magnetite [Fe₃O₄] black layer formed on top as a result of the post-oxidation, boosts corrosion resistance and adds lubricity, further reducing galling and easing assembly.

And of course, as a bonus to the increased corrosion resistance, post-oxidation creates this nice-looking uniform technical black finish.

Comparison with other treatments

There are some other possibilities for treatment of these types of parts, but they each have their disadvantages compared to nitriding.

• Carburising which is a through hardening – gives a good wear resistance, but distortion ruins the thread fit.
• Zinc coating gives better corrosion but poor wear and galling properties on threads.
• And Hard Chrome coating has good wear and corrosion properties, but adds thickness, requires laborious finishing, and faces increasing regulatory restrictions.

Conclusion

Ferritic Ion/Plasma Nitrocarburising with post-oxidation is a very suitable heat treatment for hydraulic cylinder head glands, achieving excellent results as wear resistance, corrosion protection, dimensional stability, and technical appearance.