The Problem with Stainless Steel

On the 9th of May 1985, a single event in Switzerland transformed how engineers think about stainless steel. In the small town of Ster, a lakeside community just outside Zurich. A quiet Sunday evening at the local swimming pool took a tragic turn. Around 40 swimmers were in the water when without warning, the suspended

concrete ceiling above them collapsed, crashing into the pool below. 12 people lost their lives and many more were injured. The collapse stunned Switzerland. The pool had only been open for 13 years, and nothing about the building's design seemed unusual. Investigators would quickly identify the culprit. The stainless steel rods that held up the ceiling panels had been

silently corroding away, setting off a sequence of events that would end in collapse. This was completely unexpected. Grade 304, the most commonly used stainless steel, was chosen for the rods precisely because of its excellent resistance to corrosion. The disaster forced engineers around the world to confront an uncomfortable truth. Even though we call them

stainless, these materials are by no means immune to corrosion. To understand what happened at Ster, we need to dive into the world of stainless steels. what they're made of, how they behave, and the unexpected failure mechanisms that can lead to disaster. Stainless steel is fundamentally an alloy of iron and carbon. That's what

makes it a steel. But it's the other elements in the mix that make stainless steels remarkable materials. The most important of these is chromium, a hard silver gray metal. In the atomic structure of stainless steel, the chromium atoms are substitutional. They take the place of some of the iron atoms. What makes chromium so useful in