`Duplex stainless steel centrifuge brittle failure`

Physical demonstration. Cast duplex stainless centrifuge (~1 ton, 3000 RPM, 4 ft diameter) for separating starch in corn-methanol production. Embrittled by iron-chrome intermetallic phases. Shows orange-peel surface where large casting grains stretched before fracture.

Duplex stainless steels: they increase the chromium and lower the nickel to get higher strength. You can double or triple the strength by going to a duplex. A duplex stainless is merely a mixture of about 50/50, or 30/70, or 70/30, of austenite and ferrite — ferrite being a body-centered cubic magnetic phase. [Tom holds up a piece of duplex stainless steel.] This came off a centrifuge that was used to separate starch from other things. They started selling a lot of these centrifuges when they started making methanol from corn, because they had to separate the starch from all the other liquid. The centrifuge weighs about a ton, spins around like 3,000 RPM, about four feet in diameter. Made out of cast duplex stainless steel because they needed high strength.