17-4 ph stainless rusting problem at welds

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this is most likly a Metallurgy question I am using 17-4 stainless steel to make a mechinical fishing gaff it has moving parts and used in saltwater. I am tig welding a 1/4 round bar to a 1/8 x 3/4 flat bar the flat bar is 3 inchs long, the entire flat bar and about 2 inches up the round bar is rusting very fast like 1 use in saltwater what can I do to stop this. I know it must have something to do with welding it I am using wire for 17-4 ph stainless so I know it is not the wire
Reply:You might look into electropolishing, is generally regarded a reducing corrosion, I believe that it is used for marine handrails, etc.RichardSculptures in copper and other metalshttp://www.fergusonsculpture.comSyncrowave 200 Millermatic 211Readywelder spoolgunHypertherm 600 plasma cutterThermal Arc GMS300 Victor OA torchHomemade Blacksmith propane forge
Reply:This can be evidence of iron contamination via sanding/grinding that has previouslyground steel, or contamination of the raw stock....I'll bet on the former.Any grinding/sanding/polishing tools you use must be new and not have touched steel.The work surface needs to be clean--and preferably, not steel.Any steel dust about, can contaminate as well.If the SS parts have to touch clean steel--then wet wipe them down after wards.Before one jumps to electropolishing, since you've got contamination problems,first thing is to passivate the ss after all work. That dissolves the iron particleson/in the SS. Electropolishing should follow the passivation.If you don't like the danger/hassle of dealing with passivation acids--then addressthe contamination problems. Repeatedly, multiple wet wiping, and being very carefulnot to contaminate, eliminates the need for passivation-normally.After a guy's been bit by SS contamination.....then he tends to get very fussy abouthow he handles the SS in the future! I sure as hell did.This is one of the reasons 'Why?' ss costs more to fab than steel does.Presumably you're wiping the tig rods down-prior and using argon?All of the above is very do-able. pic below is SS dental tool sterilizer pan, .024 thickness (24 Gauge)that was fixtured, had the side drain slots added, then deburred/chamfered, polished andpassivated in 10% Nitric acid. The passivation was done since the pan could have been contaminated, prior to my receiving it, any iron contamination was not acceptable, and thiswas not a $5 job. http://weldingweb.com/attachment.php...1&d=1276060046 Attached ImagesLast edited by dave powelson; 06-09-2010 at 01:15 AM.Reason: addition, added picBlackbird
Reply:I weld up SS spearshafts all the time. 17-4 is a magnetic SS, and it contains more iron than 304 or 316SS. It's heat treatable, and that is why you want it for a gaff. The slight drawback is it will get some surface rust. To minimize, use black rouge to polish the welds; problem 90% solved. That's all I do; no voodoo, no magic. Just a small polish wheel, and clean up the weld area, then send it tot he heat treat shop.And then, after so much work...... you have it in your hand, and you look over to your side...... and the runner has run off. Leaving you holding the prize, wondering when the runner will return.
Reply:I don't think it has anything to do with welding, I cut a lot of 17-4 in my machine shop and it will stain (rust) unlike 304 or 316 if in a wet enviromoment.LarryMiller XMT 304 CC/CVSyncrowave 180 SDLincoln PowerMig 255XTTermalDynamics 52Lincoln 305GComlpete machine shop to back it up
Reply:Originally Posted by dave powelsonThis can be evidence of iron contamination via sanding/grinding that has previouslyground steel, or contamination of the raw stock....I'll bet on the former.Any grinding/sanding/polishing tools you use must be new and not have touched steel.The work surface needs to be clean--and preferably, not steel.Any steel dust about, can contaminate as well.If the SS parts have to touch clean steel--then wet wipe them down after wards.Before one jumps to electropolishing, since you've got contamination problems,first thing is to passivate the ss after all work. That dissolves the iron particleson/in the SS. Electropolishing should follow the passivation.If you don't like the danger/hassle of dealing with passivation acids--then addressthe contamination problems. Repeatedly, multiple wet wiping, and being very carefulnot to contaminate, eliminates the need for passivation-normally.After a guy's been bit by SS contamination.....then he tends to get very fussy abouthow he handles the SS in the future! I sure as hell did.This is one of the reasons 'Why?' ss costs more to fab than steel does.Presumably you're wiping the tig rods down-prior and using argon?All of the above is very do-able. pic below is SS dental tool sterilizer pan, .024 thickness (24 Gauge)that was fixtured, had the side drain slots added, then deburred/chamfered, polished andpassivated in 10% Nitric acid. The passivation was done since the pan could have been contaminated, prior to my receiving it, any iron contamination was not acceptable, and thiswas not a $5 job. http://weldingweb.com/attachment.php...1&d=1276060046
Reply:Originally Posted by skippersprideI think you may be right I used a wire wheel to pollish and clean slag off the welds thus contaminating what all do I need to passivate the SS
Reply:Prep, contamination, or overheating the welding zone by piddling around with the arc instead of 'get in and then get out' could all be factors in the HAZ corrosion.As said, prep means keeping the work pieces clean of possible carbon steel contamination.  That could be from abrasives used on plain steel before you then work on the stainless, or cutting tools, or steel 'dust' in the area.Which leads into contamination.  Mentioned above.  Abrasives, cutting tools, steel dust.Then the HAZ, which without any pictures is just guessing, but that sounds the closest to what you described.  Bands outward of the weld bead rust/corrode first compared to the weld bead or the base materials themselves.  Cause by the steel spending too much time in the critical temperature range of around 1200F.  Also known as "sensitization", it is typically caused primarily by the chromium reacting with the carbon in the molten metal and forming chromium carbide.  Because that chromium is now unavailable as free chromium, the area corrodes faster then the rest of the metal either in the bead or away from the HAZ.  Solutions to sensitization corrosion include:- use minimal heat input when welding (get in and then get out, don't just sit there with the arc heating things up);- do NOT use preheat;- cool quickly (chill bars, quench, air stream, etc) ;- use extra-low carbon variants of filler, such as 308L (yes, 308 is a recommended filler for 17-4 as well as 304 aka 18-8 stainless);- use stabilized grades of stainless such as 347 (not so good because you want the slightly harder 17-4PH grade for your gaff point);- anneal the welded assembly at 1900F and then water quench;As mentioned, passivating (acid pickling) can work to remove trace iron from the surface, leaving a chromium-rich and thus more corrosion-resistant surface compared to a non-passivated stainless steel surface.And also as mention, polishing (physical or electro) also work to slow down or minimize some surface corrosion by reducing surface-nucleation sites.So clean it, weld it, anneal it, pickle/passivate it, and polish it.  So in good acronym speak, that would be CWAPP or CWAPPP.       I don't remember now if it supposed to be passivate and then polish, or vice versa.  I think it is passivate first to get rid of any possible surface iron, and then polish to smooth the 'cleaned' surface.side note to Rojo:17-4 does contain -slightly- more iron than 304, depending on exactly where the alloy range ends up in each batch.  But that is only about a 1-3% iron difference between the two alloys when you add up everything based on 'nominal'.17-4 is a nominal 17% Cr (15.5-17.5 range) and 4% Ni (3-5 range), as well as 1% Mn, 1% Si, and 3-5% Cu plus traces.  That gives ~ 26% alloying and thus 74% Fe (ranges from 70-78% Fe typical).304 aka 18-8 is nominally 18% Cr (18-20 range), 8% Ni (8.0 -10.5 range), 1% Si, 2% Mn, plus traces.  That works out to ~29% alloying and thus 71% Fe (ranges from 66-74% Fe typical).As you can see, the Fe % can overlap between the two alloys.  It's not the Fe % that makes the big difference between 17-4 and 304, it's all the other alloying elements in just the right amounts and proportions that make the steels different.  To the OP, also as you most likely know   , salt water is a tough environment for metal.    Clean and polished metal usually corrodes less or slower than rough metal, but no matter what, there is maintenance involved when metal is around salt water.yet another side note:Dave Powelson, I thought trap points such as an open or lap seam and the open rivets are a no-no in medical/food/clean work.  I thought everything had to be smooth and continuous with no rough surfaces, crevices, seams, trap points, or blind holes/pockets that could hold or trap contaminants, debris, or germs.  The sterilizer tray is somehow different?  The best laid schemes ... Gang oft agley ...
Reply:Originally Posted by MoonRiseyet another side note:Dave Powelson, I thought trap points such as an open or lap seam and the open rivets are a no-no in medical/food/clean work.  I thought everything had to be smooth and continuous with no rough surfaces, crevices, seams, trap points, or blind holes/pockets that could hold or trap contaminants, debris, or germs.  The sterilizer tray is somehow different?
Reply:Pretty much all been said until we see how bad the part is. Pickling and passivating are distinct processes some good articles on the subject...http://www.euro-inox.org/pdf/map/Passivating_Pickling_EN.pdf andcitric versus nitric acid passivation
Reply:After weld what should I quinch it in water , Oil ???
Reply:Originally Posted by skippersprideAfter weld what should I quinch it in water , Oil ???
Reply:A lot of good things about passivation, electro polishing, and contamination have been said. Not much more than I can add, besides to watch out for carbide precipitation which happens from too much carbon in the weld filler, or shielding gas (CO2)but your missing the most obvious one.  17-4PH is a precipitation hardening grade of stainless steel.  17-4 is incredibly prone to pitting and corrosion in sea water and is not recommended for wet contact. it's corrosion resistance is roughly equivalent to 304 which is also not a desirable marine grade.use a different type of stainless steel unless you absolutely need the higher strength associated with the PH grades, 17-4 is not really fit for saltwater contact.   The inclusion of copper is what reduces it's corrosion resistance. No  combination of passivation or electropolishing will protect 17-4 from prolonged exposure to seawater.  http://www.specialtysteelsupply.com/...less-steel.phpWelding EngineerCertified Scrap Producer
Reply:Originally Posted by MetarinkaA lot of good things about passivation, electro polishing, and contamination have been said. Not much more than I can add, besides to watch out for carbide precipitation which happens from too much carbon in the weld filler, or shielding gas (CO2)but your missing the most obvious one.  17-4PH is a precipitation hardening grade of stainless steel.  17-4 is incredibly prone to pitting and corrosion in sea water and is not recommended for wet contact. it's corrosion resistance is roughly equivalent to 304 which is also not a desirable marine grade.use a different type of stainless steel unless you absolutely need the higher strength associated with the PH grades, 17-4 is not really fit for saltwater contact.   The inclusion of copper is what reduces it's corrosion resistance. No  combination of passivation or electropolishing will protect 17-4 from prolonged exposure to seawater.  http://www.specialtysteelsupply.com/...less-steel.php
Reply:I'll agree with everything said about surface contamination being a likely cause of your corrosion problems.  You can passivate your components with Nitric acid, which is dangerous to work with, or warm Citric acid, which is much, much friendlier.  Search this forum for passivation, and you should find a post I made previously on proper procedures for passivating Stainless steel.  IF  you can't find it here, go to the website for Carpenter Steel.  They specialize in stainless, and have lots of good information on machining and passivating stainless.  One point I need to bring up.  What heat treatment grade of 17-4PH are you working with?  H1150?  If you anneal and quench this material after welding, to dissolve any chromium carbides that are formed during welding, you MUST temper this material.  Do not use 17-4PH in the quenched condition.  It is extremely brittle, and vunerable to sudden, catastrophic failure due to brittle fracture.  The material has almost Zero ductility in the quenched state.17-4PH will air quench, or it can be quenched in water.  If you're dealing with precision components, you need to beware of distortion after heat treatment.  You may need to do any final machining after you weld, anneal, quench, and then re-temper this steel.You'll need an inert gas or vacuum furnace to do the heat treatment properly.  I don't recommend trying this with a torch in open air.  If you do, you'll have severe scaling to clean up afterwards, and you'll probably wind up with huge inconsistencies in the material properties due to heat variations.  If this is critical work, I recommend that you find a local heat treatement shop who will work with you to get best performance possible from this alloy.  If this isn't practical, then you might want to consider re-designing this fabrication so you can use a friendlier austenitic grade like 316SS.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:Originally Posted by skippersprideI think you may be right I used a wire wheel to pollish and clean slag off the welds thus contaminating what all do I need to passivate the SS