Point of Interest: Metallurgy

Why is stainless steel so good against cavitation? If it were soft, wouldn't the imploding bubbles erode the material away in no time?

The reason for such excellent resistance of stainless steel to cavitation is its work-hardening property. You easily can make an indentation on a surface of an unworked stainless steel strip. However, after hitting the strip with a hammer for some time, it becomes very difficult to make such indentation because the surface work-hardens. (Ironically, this is why stainless steel, as soft as it is, is difficult to machine; it work-hardens as a cutting tool goes over it, resulting in a chunky, chisel-like chip instead of a smooth clean cut).

The same happens when cavitation bubbles bombard a stainless-steel surface. It work-hardens and begins to resist any further cavitation very quickly. 316ss (CF8M) resists cavitation about 10-15 times better than cast iron because of the work-hardening characteristics. Of course, further metallurgical modifications can make stainless steel even more resistant to cavitation. For example, CA6NM is roughly two to three times more resistant to cavitation as compared to 316ss.