From: henry 01/04/2000 17:27:00 Subject: stainless steel post id: 52443 why doesn't stainless steel rust? how is it made? henry< From: Bruce(Boojum) 01/04/2000 19:15:00 Subject: re: stainless steel post id: 52459 Stainless steels have at least 11% by wt chromium as part of the alloy. Nickel and molybdenum can also help corrosion resistance. It is made in the same fashion as other steels and can be ferritic, austenitic or martenisitic. As I understand it, stainless steel was discovered when someone made a batch of steel with too much chromium in it, and threw it on the scrap heap. Some months later, someone else noticed it wasn't rusting... and the rest is history. Some stainless steels are very srong, but the main reason they're not universally used is that a corrosion resistant coating on normal steel is usually cheaper. You only find stailess steels where such a coating cannot be used. From: Bruce(Boojum) 01/04/2000 19:18:00 Subject: re: stainless steel post id: 52460 To answer the rest of your question... When the chromium is added to the alloy it increases the energy needed to oxidise (rust) the steel substantially, even at low temperatures or in corrosive environments. Stailess steels can also resist other forms of corrosion besides rust. From: MichaelT 01/04/2000 19:31:00 Subject: re: stainless steel post id: 52462 Stainless also has poor heat transfer ability and is bloody hard to work with. Anybody ever tried using holesaws on 316 grade stainless? :) Because is has strange heat characteristics, it cannot be oxy cut like normal steel, so all machining has to involve cold removal. (IE: sawing and filing) You cannot even grind the stuff easily so you have to make sure you get it right in the first place:) Bloody horrible stuff it is. From: Bruce(Boojum) 01/04/2000 19:34:00 Subject: re: stainless steel post id: 52463 Yeah, it's a bitch to work, but that depends on waht sort it is. How is 316 steel made? (annealed ,quencehd, tempered or cold worked etc) From: Alan™ 01/04/2000 19:43:00 Subject: re: stainless steel post id: 52464 why doesn't stainless steel rust? how is it made Actually stainless still corrodes (rusts) but it not in the form of general surface corrosion. It's susceptable to specific types of corrosion such as pitting (small pin hole style corrosion), stress corrosion cracking, and many other small scale forms of corrosion. It will also undergo general corrosion in specific environments such as one containing a sulfur / sulfuric acid. What protects stainless steel so well are the alloying elements in it. The most important alloying element with respect to corrosion resistance is chromium. Nickel the other major alloying element has more influence over the mechanical properties, but still assists in allowing the chromium to do its job. Chromium forms an oxide on the surface of the steel, which inhibits further oxidation, ie it forms an oxide layer of a certain thickness which is basically impossible for oxygen atoms to migrate through to the metal. This layer adheres extremely well to the metal substrate. If it didn't adhere, it would just corrode like steel does. Sulfur breaks down the integrity of the oxide layer. Stainless steel is manufactured usually by remelting steel of certain base compositions, adding chromium and usually nickel to it and then re-solidifying it. When the metal is cut, etc the chromium will migrate short distances through the metal grains, to the surface, where it will oxidise and thus protect the metal from further oxidation. From: MichaelT 01/04/2000 19:44:00 Subject: re: stainless steel post id: 52465 316 is the hardest commercially available - commonly referred to as "hospital" grade. It is quite common where "real" stainless is required. From: Alan™ 01/04/2000 19:53:00 Subject: re: stainless steel post id: 52466 Working with stainless need not be a problem, you just have to choose the correct alloy. If you go into the dual phase (ferretic and austenetic) stainless steel such as Sandvik 2304 you'll find them quite easy to work with. Please also remember there are dozens of comercial grades of stainless steel. 316 is one of the 5 or so most coomon, but there are others which are even harder to work with. From: Pedrothefish 01/04/2000 19:55:00 Subject: re: stainless steel post id: 52467 In my industry 316 stainless is known as marine grade steel From: Alan™ 01/04/2000 20:00:00 Subject: re: stainless steel post id: 52470 It's also known as mass produced crap.... but it has it's purpose. General good properties and excellent corrosion resistance, but nothing really special. From: MichaelT 01/04/2000 20:06:00 Subject: re: stainless steel post id: 52471 More difficult to work with than 316? Gee, I hope I never have to install an electrical cabinet made of that stuff. From: Nick 01/04/2000 22:02:00 Subject: re: stainless steel post id: 52504 Stainless can be plasma cut though, using high current and air pressure it melts the steel and then blows the molten material away. However there is a tendancy to rust at the cut edge as the alloy properties have been changed during the melting and chill stages. This forum is un-moderated. The views and opinions expressed are those of the individual poster and not the ABC. The ABC reserves the right to remove offensive or inappropriate messages.