Types of Stainless

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I'm trying to do a little fun job with some stainless.  I don't have much experience with stainless so I've got some questions.  For 304 stainless I've been told to use 309 tig rod.  But I want to weld a stainless nut to some stainless rod.  The rod will differ from 1/8"- 1/4" diameter.  the nut will probably be a 5/8" nut or something.  Anyway, all the rod that is available to me is 304 stainless.  Some nuts are 18/8 stainless, and some aren't.  I think the 304 rod and 18/8 nut should go together fine?  Am I mistaken?  Also, I've seen some nuts with 316 stamped on them, so I'm assuming that they are a 316 stainless nut.  From what I've read, 316 and 304 might give me trouble welding them together?  How am I doing?  thanks, Nick.
Reply:18-8 refers to the Chromium-Nickel content of type 304 stainless steel.The common SS base metal you run across in the 300 series are 304 and 316.  Two common fillers are 308 and 309.  An "L" after the number means low carbon, and helps prevent chromium carbide formation in the heat affected zone during welding, which can reduce corrosion resistance.  Most all the 300 series SS are easily welded and not crack sensitive, because they have an austenitic microstructure and are not hardenable by heat treatment.  One exception is 303, which has very high sulfur for machinability, and will tend to centerline crack during welding (hot crack).  308 is the primary filler metal.  309 is kind of special, its more highly alloyed so it costs more, but it is recommended for dissimilar metal welding such as 300 SS to carbon steel, since the weld will have a chemistry that remains austenitic and non-hardenable.  There is no problem with welding 304 to 316, with either 308 or 309.But always face toward the west when welding type 347.
Reply:Many thanks.  Should have figured.  How about bending the rod I'm going to work with.  It is pretty thin so I should be able to bend it, but should I heat it while bending or bend cold.  I know stainless is really hard.
Reply:But always face toward the west when welding type 347.
Reply:Originally Posted by zapster   east...zap!
Reply:Originally Posted by RojodiabloNo, if you're left handed, face West!!
Reply:Originally Posted by Nick KentMany thanks.  Should have figured.  How about bending the rod I'm going to work with.  It is pretty thin so I should be able to bend it, but should I heat it while bending or bend cold.  I know stainless is really hard.
Reply:304 doesn't work harden significantly easily. This is why it is so nice for things like safety wire, where there will be significant bending during setup, often followed by significant vibration. That said, drilling and cutting most stainlesses (300 and 400 series) is different than carbon steels. When bending stainles, you generally don't want to use heat unless you know what you are doing. It is quite easy to adversely effect the properties of the material in several ways, both chemically and in terms of the microstructure.
Reply:Something else kinda funny about stainless.  I did a 180 degree 3/16 radius bend on 3/8 diameter 304 stainless rod.  It became magnetic in the bend area.  In other words a magnet would stick to the bend area.
Reply:riley, interesting observation on the magnetism.  I think I've heard that cold work of austenitic SS can cause some transformation to ferrite, hence making the steel magnetic.Generally the austenitic 300 series is considered non-magnetic, however some alloys such as 304 and 316 contain small amounts of ferrite by design.  The ferrite content of SS welds (base metal and filler metal) is often controlled within 3 to 12% to help prevent hot cracking.  In general terms, ferrite has a higher solubility than austenite for the impurities such as sulfur which contribute to hot cracking.  A couple of side notes, free machining, 303 SS contains mega doses of sulfur and is very crack sensitive.  310 SS is fully austenitic and therefore can be crack sensitive.The amount of ferrite can be measured on the steel or the weld.  One of the early devices for measuring ferrite, called a Magna Gage, measured the spring force required to lift a magnet from the surface.  Now, there are electronic units, still probably working on a magnetic principle?But, the science of calculating ferrite content based on the material chemistry has evolved through several iterations, and calculated ferrite values are accepted by the ASME code.  Basically Cr, Mo, Nb promote ferrite formation, while Ni, C, N, promote austenite formation, so there is a simple formula.Here is one link, for more than you ever wanted to know about hot cracking (solidification cracking) in SS.http://www.ias.ac.in/sadhana/Pdf2003JunAug/Pe1119.pdf
Reply:The materials book we had in our shop actually confirmed this property in stainless steel.  At first I thought I had bent cold rolled steel.  Cold rolled flat and round don't bend well at all.
Reply:Originally Posted by RojodiabloNo, if you're left handed, face West!!
Reply:Originally Posted by riley mcmillanSomething else kinda funny about stainless.  I did a 180 degree 3/16 radius bend on 3/8 diameter 304 stainless rod.  It became magnetic in the bend area.  In other words a magnet would stick to the bend area.