In this week's newsletter, Aaron Moncur has a conversation with Scott Roberts, North American Application Specialist at Bodycote, where he leads the team responsible for educating and promoting the S3P Colsterizing process - an advanced low-temperature carbon diffusion technology that increases hardness and wear resistance of stainless steels and cobalt-chromium alloys without sacrificing corrosion resistance.
Every time I have to replace one of those fasteners for a galling issue, it's $1,000 in downtime
In this episode:
How colsterizing achieves ~70 Rockwell C hardness on austenitic stainless steel by diffusing carbon into interstitial spaces, without depleting chromium or causing corrosion
Why low-temperature diffusion outperforms coatings and nitriding on dimensional-critical components: no added material, no brittleness, no distortion
How a medical device team went from 4–5 clean suture cuts to 60 by switching alloys and applying the colsterizing process
Why a new large-format unit - 4-foot diameter by 6-foot long - is opening the process up to oil and gas valves, aerospace, and AI data center cooling systems
Bonus Content:
Five Mental Frameworks Engineering School Never Taught You
S7E5 Scott Roberts | The Stainless Steel Hardening Process Most Engineers Don’t Know Exists
Most engineers working with stainless steel have run into the wall at some point. The part needs to be harder, more wear-resistant, or resistant to galling — but every solution on the table either adds dimensions, creates embrittlement risk, introduces distortion from high heat, or strips out the corrosion resistance that made stainless the right call in the first place. Scott Roberts has spent over a decade meeting engineers in that exact moment, walking them through a process that solves nearly all of those problems simultaneously. His conversation with Aaron covers not just how colsterizing works physically — carbon diffused into the interstitial spaces of the alloy's grain structure, compressing it without adding surface buildup — but why the common objections engineers raise (Can you really harden stainless? Doesn't carbon kill corrosion resistance? Won't it crack at 70 Rockwell C?) all turn out to be wrong in this specific case. The episode includes real application stories from medical devices, food processing, poultry, cosmetics packaging, aerospace, and even the emerging AI data center cooling market — and a candid breakdown of where the process genuinely falls short.
>If YouTube isn’t your thing, check out this episode and all of our past episodes on Apple, Spotify, and all the rest.
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Misconceptions About Hardening Stainless Steel and Why Engineers Keep Getting Burned by the Alternatives
Engineers who've tried to harden austenitic stainless steel through traditional heat treatment methods have almost always destroyed the part in the process. That experience creates a very reasonable assumption: you cannot harden this material. Scott Roberts spends a significant portion of his work correcting that belief — not with a sales pitch, but with test data and free trial parts.
People don't believe you can harden stainless steel, because if they've tried to do it by traditional heat treatment methods, they've destroyed it. Especially austenitics or duplexes, so they don't believe it can happen.
The skepticism compounds from there. Engineers who do believe the hardening is possible often assume the carbon introduction must be destroying corrosion resistance — because that's what carbon does to most ferrous materials. The colsterizing process operates at low enough temperature that chromium carbides don't form, meaning the passive layer stays intact. But that requires proof, not just explanation.
They hear 'carbon' and their first instinct is, what's happening to corrosion? Are you ruining the corrosion resistance? Because if you add carbon to most things, it's going to turn into a rust-type situation. So we have to sometimes prove that or show that.
The third common objection is embrittlement. A surface hardness around 70 Rockwell C sounds like it should produce a part that fractures under stress. What actually happens is a gradual hardness gradient - the treated surface transitions back to base metal hardness through the diffusion zone, which is why treated parts retain bend and flex behavior rather than cracking.
People hear 70 Rockwell C and they think it's going to crack. It actually doesn't. It bends and moves because it's hard at its surface and gradually reduces within its own layer back to the base metal.
This is where the poultry blade example becomes instructive. A food processing company was using martensitic stainless for their blades and experiencing embrittlement-related chipping, essentially forcing a two-hour preventive maintenance schedule and product loss from metal contamination. Switching to 304 austenitic stainless and applying colsterizing eliminated the chipping and extended the PM interval from two hours to two weeks. The problem wasn't that the old material was the wrong hardness. It was that the hardening method created a failure mode the application couldn't tolerate.
Five Mental Frameworks Engineering School Never Taught You
Methodical engineers with average instincts consistently outperform brilliant ones -not occasionally, but as a pattern. The reason comes down to five mental frameworks nobody teaches in engineering school, each one operating upstream of the design itself, where most programs are actually won or lost. They're nameable, transferable, and rare in practice.
Explore what these principles are through the full article at The Wave.
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