Some History
Stainless metals originated five thousand years ago, when Qin dynasty Chinese included chromium in their weapons manufacturing processes. The weapons weren't steel--that came later--but, then as now, chromium oxidizes into a colorless film. People have understood metal quite well for quite a long time. Wootz steel (the word "Wootz" is an Anglican bastardization of various Dravidian words for steel), the variety from which the renowned Damascus steel is forged, features banding patterns caused by clustered ferrous particles. It looks like wood.
Pre-colonial stainless metal abounds. The 1600-year-old Iron Pillar of Delhi contains phosphorous instead of chromium; phosphorous oxides, like chromium oxides, fit well against the matrix of iron atoms.
Depending on your source, credit for the stainless steel we know/use today falls to either Henry Beardly or Leon Gillet. Beardley formulated martensitic stainless steel at Sheffield's Brown-Firth research laboratory in 1912, while pursuing a non-rusting alloy for use in gun barrels. It was Beardley who arrived at the figure, today's standard, of 10.5% chromium content by mass. Finding that chromium-infused steel also resists stains from things like vinegar and lemon juice, Beardley marketed his "rustless steel" as a cutlery material. His employers were not supportive, and the metal was not then suitable; the Beardley knife was known as "the knife that would not cut."
Gillet, who formulated stainless steel in 1904, never recognized the metal's corrosion resistance and made no attempts to market it. Individuals from five European countries and another American also discovered stainless steel. Two Englishmen named Stoddard and Faraday (as in Faraday cage) mixed iron and chromium and noted an acquired resistance to some acids. Because they were not metallurgists, they did not understand the impact of low carbon content as regards adding chromium, so their stainless metal contained little chromium. In 1912 Eduard Maurer and Benno Strauss won patents on two nickel-chromium stainless steels.
Alloys and patents accumulated with vigor in the next years. The Pioneer, the first stainless steel aircraft, appeared in Pennsylvania in 1931. Stainless steel sinks came four years later. Stainless features prominently in the Chrysler Building, the Petronas Towers, and the Burj Khalifa, whose empty halls hang three thousand feet above Dubai. Stainless steel is indeed expensive, partially for its own sake.
Grades & Applications
Each grade of stainless steel is denoted by several standardized numeric glyphs, which communicate a) percentages of included metals, b) names of other, non-stainless metals, and c) arbitrary shit. For example, 304 stainless--the most common stainless--might also be marked "18-8" or "X2CrNi18-9" or "1.4307," depending on where you bought it. The least obtuse and most common classifications are provided by SAE International. As of June 2014 the market bears 33 grades of stainless steel.
Broadly, stainless steel occupies three categories: austenitic, ferritic, and martensitic.
Most of the world's stainless steel is austenitic, including the aforementioned SAE Type 304, as well as the rest of the 200 and 300 series. Austenitic stainless steel is an alloy of iron, chromium, and nickel, with 16-26% chromium, 6-22% nickel, and low carbon content. "Austenitic" refers to the type of crystalline structure assumed by the metal; austenitic in particular has a face-centered cubic crystal. It is not magnetic and not reactive and very strong. Surgical tools and kitchen sinks and pipes that run salt water are all made of Type 304.
The very highest grade of austenitic--literally, "super austenitic"--will run you five figures for a 20' stick of 10" pipe.
Ferritic stainless steels, the 430s, are magnetic and more prone to corrosion than austenitics. They're also stronger and quite a bit cheaper, because they're easier to machine into shapes like plates and pipes and I-beams, and because they contain less (as little as 10.5%) chromium and no nickel. Ferritic stainless steel is used in engineering. Its crystalline structure is body-centered and is known as "ferrite." Note that iron is "Fe" on the periodic table.
Type 410, or martensitic stainless, stands apart from ferritic and austenitic because it can be tempered. It is almost all iron, with 12% chromium and 0.12% carbon. It is most commonly used to hold and transport crude oil and CO2.
Working
Stainless steel is hard. It's hard to cut and hard to drill and hard to grind and weld.
A good way to cut stainless steel is with a plasma cutter. Proceed slowly, holding your cutting tip at an angle. You'll want to keep your air pressure down so you don't blow melted metal all over the place. Also, wear lots of clothes. It is not advisable to try and cut anything thicker than 3/8" with a cheapo plasma cutter.
If cutting with a saw, you want a blade that is either slow-moving or goddamn strong, usually both. Stainless is frequently cut with bandsaws set to rotate and descend as slowly as they possibly can. Drilling is accomplished (again) slowly, with carbide tips and great effort. In all cases, a constant supply of lubrication prevents destruction of the cutting implement. Note that using an implement that is not corrosion-resistant will cause the stainless to rust at the site of the cut.
Be also aware that joining two incongruous grades (say 430 and 304) will require a weak, corrosion-prone weld, and may induce magnetism in previously non-magnetic steel. Also, do not weld iron to stainless.
Stainless steel shavings are nasty things. When grinding, protect your face and lungs. Use more than one layer of protection for your face, because steel shavings assume shapes that do curve in flight. I wear a face shield and eye shields and a respirator. Prepare to burn through a lot of grinding wheels.
Humble Advice On Purchasing
A pipe salesman I met with told me that during the 2008 fuck-up, steel mills were willing to hold their stainless prices until noon.
Metal markets are a little bit like the wild west. Stainless prices in particular are prone to far-flung logistical hiccups, political instability, changes in personal relationships, and whether or not somebody pissed in Al from sales' Cheerios this morning. Whenever sourcing stainless steel materials, big things to determine are a) whether the supplier actually specializes in the piece/material you seek, b) whether they keep/will keep a running stock, and c) whether there is actual incentive for this supplier to do business with you in the first place.
Suppliers often promise delivery on obscure items in order to secure a job, without mentioning details like the items' present state as iron and chromium deposits a mile underneath EU territory, requiring 6-8 weeks to be mined and machined and shipped (and $225 each for all the trouble, sucka). So, get pricing and availability and turnaround time, in writing, before committing.
Suppliers will also happily sell you items they don't specialize in for exhorbitant prices. Buy pipe from pipe suppliers, fittings from fittings suppliers, valves from valve suppliers. Companies that supply military and aerospace are almost categorically expensive as all hell.
Finally, buy ye in bulk, so the supplier (again) has sufficient reason to load up a truck and send it to you. You'd be amazed at how much of a price depends on simple energy conservation.
sources
Experience.
ThomasNet. "Stainless Steel Fabricating Processes."
http://www.thomasnet.com/articles/custom-manufacturing-fabricating/steel-fabricating-process
Brewing Techniques. "Working With Stainless Steel."
http://morebeer.com/brewingtechniques/library/backissues/issue5.5/mosher_sb.html
Wikipedia. "Stainless steel."
http://en.wikipedia.org/wiki/Stainless_steel
Anne Marie Helmenstine, Ph.D. "Why is Stainless Steel Stainless?"
http://chemistry.about.com/cs/metalsandalloys/a/aa071201a.htm
Fante's Kitchen Shop. "About Stainless Steel."
http://www.fantes.com/stainless-steel.html
Stainless Steel Information. "History of Stainless Steel."
http://www.estainlesssteel.com/historyofstainlesssteel.shtml
Stainless Steel Centennary. "100 Years of Stainless Steel."
http://www.stainlesssteelcentenary.info/stainlesshistory
British Stainless Steel Association. "The Discovery of Stainless Steel."
http://www.bssa.org.uk/about_stainless_steel.php?id=31