Cryogenic rods?

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I'm building a dry ice machine where the welded parts are under alot of cycling stress and will be operating at -80C I'm worried about crack propagation.  Have been thinking about which rods to use I've thought of using a stainless rod because stainless exhibits good toughness at low temperatures.  I've also thought of using a GP rod as they are quite ductile I would think that they might be more ductile in the lower temperatures - I've also come across some rods called phillips 75 - which are made for that application - but they r pretty expensive and would like to get by without having to buy a packet if I can - plus I wasn't too impressed with their specs - toughness of only 70J at -60C. (304 stainless is 110J at -80C) I'm thinking of preheating the parts before welding to help reduce any cooling cracks, I'll also be destressing in a furnace afterwards at about 500C for an hour or so.  The steel is a medium carbon steel ranging in thickness from 10mm to 20mm.  I've got a force of 20 tonne over 5-600mm of weld - ie 0.4kN/mm, which is quite a high strain esp since it's repetitive.  I'd be very appreciative to hear from anyone who's got any experience in this area - Cheers
Reply:I wonder if you may be able to speak to someone knowlegable at one of the major suppliers like Air Liquide or BOC, possibly find out what base metal and filler metal combinations have been specified in the past for this type of equipment.  Sounds like it has be designed to hold some pressure?Air Liquide installed a 60 ton liquid CO2 tank, pumping system, and distribution piping in our plant, to spray quench parts with 300 psig CO2.I worked with one of the A-L process engineers on fine tuning the spray end of the system.By the way, I also consulted with a cryogenic expert, an old guy in the Boulder, Colorado area, on the intial concept for the system, don't have his name anymore, but found him through a seach under some cryogenic society.  As I recall, we chose to use liquid CO2 at 300 psig, because as this is sprayed it produces the highest percentage of dry ice.  It is the impact of dry ice particles and sublimation to gas, at the surface of the part, that produces the highly effective quenching action.Last edited by pulser; 01-30-2007 at 10:59 AM.
Reply:Interested site on CO2/dry ice.http://www.dryiceinfo.com/