I purchased a "470" stainless 2" exhaust from Allens A couple of months ago as recomemded by Jim at Allens. It was his recomendation for my judged 69. It is a magnetic stainless that he says will turn a light shade of brown in time but won't rust. He seemed to be VERY knowledgeable . Does any body have any input on this system?
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Re: 470 stainless exhaust
Jim at Allens called this material high carbon stainless. -
Re: 470 stainless exhaust
Brad-------
Yes, he gave you an accurate description; the folks at Allen's Exhaust usually do. If one is interested in a stainless exhaust that MIGHT fool a few judges into believing that it's carbon steel, this is the alloy you want. It is magnetic and it will darken as time and heat progress. Actually, considering it's magnetic properties, I don't know how anyone could say that it's not carbon steel unless they perform a spectrophotometric analysis of a sample of the material. I don't think that this is being done at the present time. Probably won't be done in the future, either.
The only "down-side" to this alloy is that it's not as overall resistant to corrosion as type 304. Type 304 is non-magnetic. If one wants an exhaust that will be as free from corrosion as possible for the longest possible time frame, 304 is what you want. 304 will also darken and yellow after exposure to heat, though. It's more expensive than 470.In Appreciation of John HinckleyComment
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Re: 470 stainless exhaust
Joe is correct about the 304 stainless. Currently costing about twice the price of the type 400 series of magnetic stainless steels because of the nickle content, and the mill surcharges placed on nickle. I have never heard of Type 470 stainless, must be a relatively new grade for a specific application. I do buy the T430 and the T304 at about 5 tons each per order. The T304 is a better grade by far and my choice for longevity, but it's corrosion resistance is substancial diminished with temperature ranges from 750-1500 degrees F. This is due to "carbide percipitation". Solution annealing is required to 1950 degrees F to restore full corrosion resistance. I have never measured the temperature at the motor pipe so I don't know if this is an issue. If temps do exceed these parameters than the upgrade may be a moot point! All one has to do to detect it is to carry a magnet which is what we do in the shop! I was always led to believe that exhaust systems were made from 409 stainless steel. Not a very good grade with a low corrosion resistance and nearly useless in a high saline or acidic atmosphere. T430 would be a better choice over the T409 as it has excellent resistance to heat and most atmospheric conditions.
DonComment
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Re: 470 stainless exhaust
I have never heard of Type 470 stainless, must be a relatively new grade for a specific application.
Roger that...It must have been an alloy searching for an application, or one mixed up just for NCRS Corvette exhaust pipes.
It seems mechanical technology, as well as electronic technology, is leaving me in the dust. I had just gotten where I can manage my PC pretty well, then they invent this new WiFi stuff. Then it was Ipods and MP3 player technology. Meantime, they have cell phones...cell phones that play music (You have to decide what type; MP3, XM), cell phones that show video; cell phone walkie-talkies. I've got a hundred-year back log of technology to try and understand...OR NOT.Comment
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Re: 470 stainless exhaust
Don-----
The more I think about it, I'm not sure that it is actually 470. It's a 400-series alloy and I was assuming that it was 470 (beccause that's what was mentioned in the original question), but I'm not sure that it is 470.In Appreciation of John HinckleyComment
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Re: 470 stainless exhaust
You guys are right it is 409 stainless. I was reading from my notes from my discussion with Jim at Allens which had alot of differant options. The invoice says 409 stainless. THanks to all for the help.Comment
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Re: 470 stainless exhaust
Brad
Type 409 is a 'straight chrome' stainless in the ferritic stainless family. It is the entry level stainless, containing a nominal 11% Cr. In order to achieve "stainless" properties, this is the minimum amount of Cr required. It is commonly called 'muffler steel', and is used in great tonnage by the auto and gas turbine (power plant) industries in exhaust products. It is a magnetic stainless, and is somewhat difficult to weld. Unlike the 3XX series of Cr-Ni steels, type 409 has an expansion/contraction coefficient similar to that of carbon steel, so it is a good choice for dis-similar metal joints that are thermal-cycled between ambient and exhaust gas temps. The weld heat affected zones can be problematic, however, and can present a rusty (oxidized) appearance due to volatizing Cr during the heat of welding and precipitation of Cr2C3 chromium-carbide during weld cooling. Expect the welded seams on your mufflers to need an occasional cleaning with a stainless steel bush (toothbrush size) to freshen the HAZ a couple times per year.Comment
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