In an interview with METALVERSE, Kirsten Baston, managing director at Eltropuls, explains why a coating thickness of just a few micrometers can determine a component’s survival, what fundamentally distinguishes plasma nitriding from other heat treatment processes—and why a family-owned business sometimes has more staying power than any other.

METALVERSE: Mrs. Baston, what personally fascinates you about surface technology?

Kirsten Baston: The realisation that you can make an enormous difference with comparatively simple means. The fact that, for example, a PVD coating just one micrometre thick determines whether a component survives or not – that is fascinating with every single project.

METALVERSE: Could you explain the basic technical principles of plasma nitriding?

Baston: Plasma nitriding is a vacuum process. The vacuum is needed to ignite a plasma at comparatively low temperatures. A voltage is applied between the furnace vessel and the charge – this creates ionised gas. The resulting nitrogen ions and excited nitrogen particles are automatically transported to the component surface by the applied voltage, where they diffuse in directly. This is a decisive advantage over conventional gas nitriding: gas nitriding uses ammonia, which is toxic and has to be incinerated at the end. With plasma nitriding, this is entirely eliminated – no harmful input materials, no harmful emissions, and gas consumption is minimal because the process takes place in a vacuum.

METALVERSE: What case depths are achievable?

Baston: That is ultimately a matter of material, cost, and time. With an unalloyed steel, we can achieve penetration depths of up to 0.8 millimetres – though that is already at the upper end. In practice, depending on the requirements and degree of alloying, case depths are usually lower.

METALVERSE: Eltropuls played a key role in developing the hot-wall plasma nitriding furnace. What was the decisive advance over its predecessor?

Baston: Before that, there were cold-wall systems with water-cooled furnace walls. The problem was that components close to the wall stayed very cold while those in the centre became hot. This led to significant variation in treatment results, charge density was low, and a great deal of effort was required with grids and other aids just to achieve uniform temperatures. With hot-wall technology, we were able to treat large charges with very consistent results for the first time – while at the same time drastically reducing energy consumption, because we no longer lose heat through the wall. We presented this at the Heat Treatment Congress in 1980 and filed the patent at the same time.

METALVERSE: The patent has expired. How do you maintain the technological edge without patent protection?

Baston: By simply staying better than everyone else. We develop the electronics, the controls, and all key components ourselves – everything is optimally tuned to the plasma nitriding process. That is not so easy to copy, because decades of experience stand behind it. And we constantly test our systems under real industrial conditions – in our own contract hardening shop. That knowledge feeds directly back into system development.

METALVERSE: What are the most common mistakes companies make when getting started?

Baston: Most of the time, the problem is not in the process itself, but in the specification. Many people tend to think along the lines of “more is more.” In surface finishing, however, the opposite is often true. A specification should be as tight as necessary for the component to function – but at the same time as wide as possible so that it can be realised cost-efficiently. And you have to factor in all upstream manufacturing steps and downstream assembly steps from the very beginning. Only then can the full potential of plasma nitriding be realised.

METALVERSE: How much effort is involved in introducing the process for a company without in-house expertise?

Baston: That is one of the most appealing aspects of the process: it is remarkably stable and forgiving of errors. The process is electrically controlled – meaning via well-measurable and manageable parameters – which makes it considerably more robust than processes that are controlled purely through chemistry. In our own contract hardening shop, we often treat mixed charges using a single programme in which only temperature and time are varied. That works for almost everything.

METALVERSE: Where do you see heat treatment heading in the coming years?

Baston: The strongest trend we are observing is the further electrification of processes and the replacement of natural gas. This affects us less directly, since plasma nitriding is inherently an electrical process – but it is a signal that we are on the right side. We are seeing a growing number of enquiries from regions where ammonia simply cannot be used. That benefits us directly.

METALVERSE: What is your most important advice for companies approaching this topic for the first time?

Baston: Bring heat treatment into the project as early as possible – while all design options are still open. And find an experienced partner. The goal should never be to optimise a single process step, but to think about the component and its entire process chain together.

Kirsten Baston, Managing Director of ELTRO GmbH (Source: Vulkan Verlag)

Kirsten Baston

Managing Partner

ELTRO GmbH

The full interview can be read in the 2nd issue of PROZESSWÄRME 2026.