Author: Alexander

Hydrogen – whether applied in shipping, steel production, refineries or power-to-x application – it has become the energy source of the future, yet already used in many sectors. Due to its special properties, the hydrogen gas poses several technical challenges for the respective components with which it comes into contact, so that the use of corrosion-resistant stainless steel is essential. This in turn is susceptible to wear and galling and this is exactly where the technology of the Danish pioneer for surface hardening of stainless steel and titanium comes into play.

Hydrogen – the element that comes first in the periodic table and is therefore the smallest and lightest atom among all elements – has been traded for some time as the greatest hope for future energy supply. With a mass fraction of about 70%, hydrogen is the most common chemical element in the universe. On Earth, however, its mass fraction is only 0.87% and is largely bound in water.

Starting with production, over to transport ending with the actual usage, wherever hydrogen is involved, stainless steel components are also used, some of which are subject to extreme wear depending on the application and naturally subject to galling. In the past, this problem was countered with traditional wear protection methods and the respective components were protected with a coating (e.g. hard chrome plating, DLC or chrome carbide) or classic plasma nitriding or salt bath diffusion layers. However, these processes are generally known to affect the corrosion resistance of the stainless steel parts negatively.

The solution to this dilemma – a surface hardening that protects against wear and galling while at the same time maintains or even improves the corrosion resistance of the materials was developed by the founders of the Danish company Expanite and is increasingly being used in the hydrogen sector. For example, components of high pressure and control valves or clutch systems used in the hydrogen infrastructure up to components for fuel cells are hardened.

Sustainably prevent hydrogen embrittlement

“Our customers often ask whether the Expanite technology increases the risk of hydrogen embrittlement, which is not the case,” explains Dr. Holger Selg, application expert and Expanite Sales Director DACH, who going further into detail: “The cause of the hydrogen embrittlement can be traced back to the diffusion of the hydrogen into the material, and in theory the Expanite layer acts as a diffusion brake to a certain extent. Charged with nitrogen and carbon, the Expanite surface is harder for the hydrogen to penetrate than an untreated surface”

The gas-based diffusion process from Expanite is significantly more energy-efficient and environmentally friendly than comparable wear protection processes, and thanks to the treatment in a vacuum, no time-consuming cleaning of the parts, e.g. with aggressive chemicals, is necessary after hardening.

The Expanite technology, specially developed for corrosion-resistant materials, offers a solution for austenitic, martensitic, ferritic and duplex stainless steels as well as for expensive nickel-based alloys such as Inconel and Hastelloy. The new special process ExpaniteHard-Ti, which the Expanite team of experts in Denmark has developed to market maturity in recent years, is used for titanium materials.

About Expanite

Expanite offers state-of-the-art solutions for surface hardening treatment of stainless steels and titanium.
With Expanite’s processes, it is possible to increase the material’s surface hardness tenfold while at the
same time maintaining and even increasing its corrosion resistance. Expanite is a global organization with
a combined development and production facility near Copenhagen, Denmark, and hardening capacity in
both US, Germany, Korea and China. Expanite’s solutions are flexible and can be introduced directly into a
customer’s own production line as part of a licensing arrangement.

Engineer Zsolt Pataki wanted to create the ultimate fountain pen using innovative production methods with advanced materials. The result is a fountain pen made from a solid titanium bar for the ultimate weight, look and feel, hardened by ExpaniteHard-Ti to make it long-lasting and virtually unscratchable.

Hunting for the superior scratch resistance

Aerospace engineer Zsolt Pataki got a crazy idea; he wanted to create a unique fountain pen using his experience from aerospace in design, materials, and manufacturing. He chooses titanium grade 23 from the very beginning of the development process, but also knew that he wanted to go further. Mr. Pataki states: “In my search for increased wear resistance of the titanium, I was eager to avoid the hurdles of a coating; adding layers affecting the dimensions combined with the risk of layers chipping off – as I preferred a monolithic design with the original titanium surface instead of a coating”.

In the search for alternatives to coating, Mr. Pataki attended a webinar with Expanite presenting their unique hardening solution for titanium. “I soon realized that the ExpaniteHard-Ti process was the only matured and commercially available interstitial hardening technology for titanium. The webinar combined with the details of the technology on their web site helped me to develop realistic expectations and I reached out to them”, Mr. Pataki continues.

The solution

The ExpaniteHard-Ti process provides highly effective protection against wear and scratches. The method is not a coating process, hence all the drawbacks of coatings, including the risks of chipping/spalling off and inconsistencies in layers are completely avoided. In fact, it is the surface of the material itself, which is hardened. The ExpaniteHard-Ti process has a significantly greater level of protection against scratches than that afforded by the hardness of the base material and the hardened parts retains the design colour or as Mr. Pataki describe it: “I tried hard to scratch the pen after the process, but it is practically impossible – I made before and after comparison and the results are spectacular; the pen is now virtually unscratchable”

Professional knowledge sharing

Through the dialogue with the Expanite team, the optimal solution to increase scratch resistance of the fountain pen was found – Mr. Pataki states: “Throughout the whole process, the Expanite team has been very supportive and open to discuss questions and possible issues ensuring that I got exactly the solution that suited my requirements for the pens and the fact that the results were much better than advertised in terms of case depth of the hardened zone!” The ExpaniteHard-Ti process provides highly effective protection against wear and scratches.

About Capillaris

Capillaris was founded by aerospace engineer Zsolt Pataki. Working from his workshop in Budapest,
Hungary he created each sole piece of the fountain pen carved out of solid titanium himself. The
concept features a lightweight monolithic construction pen with continuous outer contour and
hexagonal sides reminiscent of a supersonic airfoil which enables the pen to lay stable on a desk. Visit
www.capillaris.eu for more.

About Expanite

Expanite offers state-of-the-art solutions for surface hardening treatment of stainless steels and titanium.
With Expanite’s processes, it is possible to increase the material’s surface hardness tenfold while at the
same time maintaining and even increasing its corrosion resistance. Expanite is a global organization with
a combined development and production facility near Copenhagen, Denmark, and hardening capacity in
both US, Germany, Korea and China. Expanite’s solutions are flexible and can be introduced directly into a
customer’s own production line as part of a licensing arrangement.

Corrosion-resistant stainless steel is widely used in industry and trade due to its outstanding properties. Despite its numerous advantages, particularly its resistance to corrosion in numerous media, stainless steel also has considerable weaknesses that sometimes severely limit its application. One of these weaknesses is its susceptibility to cold welding or galling, which can occur particularly with screw connections. Surface hardening offers a solution to this problem.

Galling on stainless steel

Galling can be favored by various aspects, such as insufficient surface hardness, excessive roughness or lack of lubricants. Nevertheless, fasteners are essential in many applications to ensure particularly frequent assembly and disassembly, or high tightening torques. It is therefore important to carefully adjust the properties of such elements.

Galling can be favored by various aspects, such as insufficient surface hardness, excessive roughness or lack of lubricants. Nevertheless, fasteners are essential in many applications to ensure particularly frequent assembly and disassembly, or high tightening torques. It is therefore important to carefully adjust the properties of such elements. When fasteners are jammed due to galling, their removal can be an enormous challenge without damaging the affected bolt or destroying the associated nut.

Surface hardening: the key to the solution

Surface hardening, a process in which only the surface layer of a workpiece is hardened, has the potential to significantly improve the seizure behavior of stainless steel screws. This diffusion-based process increases the hardness of the surface through solid solution hardening and reduces its susceptibility to plastic deformation. Depending on the material, the corrosion resistance is maintained or improved and neither the stiffness nor the ductility of the base material is impaired

The Process

Surface hardening is not an applied coating, but a diffusion-based thermo-chemical surface hardening process. Although classic processes for the surface hardening of corrosion-resistant stainless steels have been available to the industry for some time, their application has two main disadvantages: firstly, all classic processes such as On the other hand, the hardness values of stainless steels usually hardened with nitrogen or carbon drop very quickly, i.e. the hardening depth is only a few micrometres and the underlying base material is very soft, which can potentially lead to the egg-shell effect.

In contrast, Expanite has developed its process (SuperExpanite®), in which not only the outermost layer but also the underlying material is hardened to a greater depth which also contributes to an improvement in corrosion resistance in many cases.

In many cases, a two-stage process is used in the Expanite treatment for stainless steels, in which nitrogen is introduced deep into the edge zone in the first step (high-temperature process), whereby the material is hardened to approx. 300 HV (austenitic materials)-850 HV (martensitic materials) by up to 1 mm. In the second process step, the so-called low-temperature process, the workpiece is heated to a maximum of 470°C and the surface layer is hardened to 1100-1,300HV at a depth of 5-30µm by incorporating carbon and nitrogen (see Fig. 2).

By combining the two process steps, the so-called eggshell effect, which occurs in most surface hardening processes, can be avoided, which offers the decisive advantage for numerous applications

Wear resistance

To test wear resistance, Expanite tested some 316L samples hardened using its SuperExpanite® process to ASTM standard G 98. In this procedure (see Fig. 3), a ceramic test specimen is subjected to a contact pressure of 25N and moved back and forth on a test specimen. The wear volume is determined after a sliding distance of 100 meters. The results are shown in Fig. 2: The 316L sample with SuperExpanite is more resistant to abrasion by a factor of 125 than the untreated sample

Following ASTM G98, a cold wear test was carried out with test specimens made of 1.4404, the results of which are shown in Figure 4. In comparison to the un-hardened test specimens, which already exhibit galling at a contact pressure of 35 bar, the test specimens hardened by Expanite do not show any galling even at a contact pressure of 2,068 bar – although the first plastic deformations occur due to the yield strength being exceeded. The risk of galling is therefore completely eliminated in the case of both hardened friction partners.

Wear resistance

Although the basic intention of conventional surface hardening processes is to produce harder surfaces, this is usually at the expense of corrosion resistance.

This is where the Expanite process comes in. Tests have shown that 316L samples hardened with Expanite can spend up to 1,000 hours in a salt spray chamber without showing signs of corrosion.

In some cases, the corrosion resistance can even be significantly increased by the Expanite surface hardening process, even beyond the level of the unhardened base material. (Fig. 5). This effect is caused in particular by the nitrogen dissolved in the surface layer.

Environmentally friendly

Despite their widespread use, conventional surface layer hardening processes have various disadvantages. Harmful chemicals such as fluorides, chlorides, molten salts etc. are used. SuperExpanite® , on the other hand, which is produced using the two-stage process described above, is characterized by a resource-saving approach. No natural resources are consumed, and no polluted wastewater is produced. With a low energy consumption of just 1.9 kWh/kg of hardened stainless steel and without the use of harmful chemicals, it represents an environmentally friendly and sustainable alternative.

Summary and applications

To summarize, the nitrocarburizing process specially developed by Expanite delivers excellent results in terms of both hardness and corrosion resistance for all stainless steel materials, not just limited to individual alloys. The process is therefore recommended for all types of stainless steel screws and fittings to extend the service life of the corresponding components and thus ensure increased product safety and interchangeability.

About Expanite

Expanite offers state-of-the-art solutions for surface hardening treatment of stainless steels and titanium. With Expanite’s processes, it is possible to increase the material’s surface hardness tenfold while at the same time maintaining and even increasing its corrosion resistance. Expanite is a global organization with a combined development and production facility near Copenhagen, Denmark, and hardening capacity in both US, Germany, Korea and China. Expanite’s solutions are flexible and can be introduced directly into a customer’s own production line as part of a licensing arrangement. Learn more on www.expanite.com.

Expanite®, the Danish surface hardening specialist helped the Swiss watch brand Rado® by developing a hardening process to improve wear and scratch resistance on their titanium high-end watches which retains the designed color. This was once thought impossible.

New collections crafted from hardened titanium

Given its strength, titanium is remarkably light. When compared to steel in a strength-to-weight ratio, titanium is far superior, as it is as strong as steel but 45% lighter, and thus a material which is in high demand in mission critical designs for aerospace and high-tech medical applications, among others. Although it is also hypoallergenic and resistant to corrosion, titanium is relatively soft and scratches easily. But not anymore: Rado® unveiled the HyperChrome Ultra Light and Tradition Captain Cook MKIII collections crafted among others from hardened titanium. Where the Tradition Captain Cook MKIII watch has a hardened grade 5 titanium case, the HyperChrome Ultra Light combines high-tech ceramics and hardened titanium in a unique bronze color.

The solution: Expanite treatment offers surface hardness and increased wear and scratch resistance!

The solutions were developed by Expanite®; by using the superior hardening technology “ExpaniteHardTi”. By diffusing molecules into the surface of titanium in a gaseous process, the titanium becomes almost completely resistant to wear and scratches – while keeping the mechanical and corrosion properties, which defines the extraordinary qualities of titanium. ExpaniteHard-Ti is not a coating process, hence all the draws backs of coating including the risks of spalling and inconsistencies in layers are completely avoided. Furthermore, with the ability to harden both titanium grade 2 and grade 5, the process is suitable in a broad range of applications.

“While hardening of the watch case for the Captain Cook MKIII was relative straight forward, the requirements of the HyperChrome Ultra Light designers and development team from Rado® was quite unique; we basically had to redo and upscale a process which we originally thought was faulty. This had some years back yielded titanium grade 5 in a distinct bronze color, while still reaching scratch resistance beyond what had previously been possible with a diffusion-based hardening technique. Our team of experts solved the case and made this part of the HyperChrome Ultra Light watch reality.”, says CEO Thomas Abel Sandholdt from Expanite®.