Nitrocarburizing of SS Medical Devices by Expanite

Material optimization – The nitrocarburizing process developed by Expanite enhances both the hardness and corrosion resistance of stainless steel materials – and not just for individual alloys. Therefore, the process is also recommended for medical device applications. It extends the lifespan of the respective application, thereby increasing patient safety and reduces cost.

Because of its unique properties and versatility, Stainless steel is an essential material for medical devices and implants that frequently encounter liquids and tissue. The corrosion resistance of stainless steel guarantees an extended lifespan and prevents the development of rust or other forms of damage that could compromise the functionality and safety of the f medical products.

For decades, corrosion-resistant stainless steel has been extensively used in the field of medical technology and is offered in a diverse array of alloy variations in the market. Numerous companies opt for these materials due to their corrosion resistance, with particular emphasis on the austenitic and duplex variants. Nevertheless, , these options are challenged by their susceptibility to wear attributed to their relative low hardness, often resulting in issues such as galling.

Conventional techniques aimed to increase wear or galling resistance on stainless steel components come with a drawback – they often result in non-corroding steels becoming susceptible to corrosion post treatment. Coating methods designed to prevent this issue involve the application of material, but in numerous cases, they exhibit inconsistencies in terms of layer thickness. This inconsistency leads to the accumulation of material on flat surfaces, while corners and edges experience a reduction in the protective layer. Additionally, coatings can develop cracks during significant expansions or contractions of the underlying material due to the different thermal expansion coefficients of the base material and coating. Small openings present further challenges, as the coating process may not be effectively applied depending on the process used. Bypassing these hurdles has become the core objective of Expanite, the Danish provider of surface hardening technologies.

Enhancing Stainless Steel Performance

Addressing the aforementioned problems with stainless steels involves the application of surface layer hardening, a process distinct from coating that relies on diffusion-based surface hardening. While traditional methods of surface layer hardening for corrosion-resistant stainless steels have been available to the industry for some time, they inherently possess two primary drawbacks. Firstly, all conventional methods result I a reduction in corrosion resistance. Secondly, the hardness values of stainless steels typically treated with nitrogen or carbon experience rapid degradation, resulting in a shallow hardening depth in only a few micrometers. and the underlying structure is very soft, which could potentially lead to an eggshell effect. Consequently, the underlying structure remains quite soft, potentially leading to a fragile shell-like effect.

However, Expanite has pioneered its own FDA-compliant process that overcomes these limitations. In this process, not only the surface layer but also the underlying material is profoundly hardened. This specially developed nitrocarburizing method is a thermochemical process for steel, facilitating the diffusion of nitrogen and carbon into the workpiece’s surface. This achieves enhanced surface hardness, improved wear resistance, and heightened corrosion resistance Nitrocarburizing combines the benefits of both nitriding and carburizing with a single process.

Process Protects Workpiece from Wear and Corrosion

The Expanite treatment of stainless steels typically involves a two-step process. During the initial phase (high-temperature procedure), nitrogen is introduced deeply into the boundary zone. This results in the material being hardened up to around 1 mm, with hardness levels ranging from approximately 300 HV for austenitic materials to 850 HV for martensitic materials.

In the subsequent stage, referred to as the low-temperature procedure, the workpiece is gradually heated to a maximum of 470°C. This controlled heating enables the infusion of both carbon and nitrogen, effectively reinforcing the boundary layer to a depth ranging from 5 to 30 µ achieving hardness levels between 1100 and 1300 HV. Combining both process steps, the fragile eggshell effect is avoided.

To test wear resistance, Expanite conducted tests on several 316L samples that had undergone its proprietary hardening process, following the guidelines of ASTM standard G 98. In this test, a ceramic test body is moved back and forth on a test specimen under a constant pressing force of 25 N. After a sliding distance of 100 m, the resulting wear volume is qualified. Remarkably, the sample treated with Super-Expanite exhibited wear resistance levels 125 times superior to those of the untreated sample.

While conventional surface hardening methods aim to enhance surfaces hardness, they frequently come at the cost of compromising corrosion resistance. This is precisely where our procedure steps in: Extensive testing has demonstrated that samples subjected to Expanite´s hardening process can endure up to 1000 hours in a salt spray fog chamber without exhibiting subsequent corrosion indications. In fact, surface hardening can occasionally elevate corrosion resistance to levels surpassing those of the untreated base material.

About Expanite:

Expanite is a Danish company specializing in heat treatment and surface hardening of stainless steel and titanium. Expanite has established itself as a pioneer and trusted partner in the industry. The sustainable and patented surface hardening processes improves galling, wear and corrosion resistance on stainless steel and titanium parts in a wide range of applications and industries.

The company has its head office in Hillerød near Copenhagen and service centers and licensees in the USA, Germany, Korea, and China. Expanite’s DNA is based on sustainable solutions to extend the life of components made of stainless steel, titanium, and other high-value alloys – and the business model allows for license agreements whereby customers may implement the technology in their production lines.

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