It is well known that the best recommended practices for joining a martensitic SS (410) with a Austenitic SS (304) involve conducting a buttering in the lower alloy steel (410), a preheating at temperatures less than 315 ° C, an austenitic electrode (example: E309L) and a PWHT to 740 + - 20 ° C. But what happens when a buttering is not possible?. Is it advisable to use the same electrode, preheat both material and then to conduct a PWHT at 740 ° C?, What is the recommended cooling rate to avoid sensibilization of austenitic SS?, There is a way to avoid the PWHT in a single pass Gmaw joint?
Thanks for your comments!
E-Rod
Among other things, it probably depends on your thicknesses and service conditions. If you are welding sheet metal with just atmospheric exposure, you might be ok, but if you are welding thick walled piping subject to sour service, it would be a disaster waiting to happen.
Now you're talking about actual engineering. :)
You're looking at a 410 HAZ Rockwell C in the 40's w/o PWHT, depending on carbon content. Forget that.
Its not necessary to butter this dissimilar other than to avoid sensitization of course. So you need to take look at your service conditions. It might be that a sensitized austenitic will still have greater corrosion resistance than a martensitic. Especially if the BM and filler are L grades.
As an addenda, if you get 25% sensitization at the grain boundaries from your austenitic 304 you will still have more Cr in solution than the martensitic 410. And 410 is gonna form Cr carbides as well. And the 309 has even more Cr than the 304.
If you end up with 50% sensitization you will still (probably) have more Cr in solution than your 410 if your 410 lost 25% of its Cr to carbides.
A good place to start might be the ASTM A-262 interganular testing methods, though I do not know how they apply to martensitics since they are generally recommended for austenitics and these chemistries might be too severe to ligitimately judge martensitics. Though logic would dictate that if they are too severe for the martensitics then your sensitization problem is moot, maybe.
Again, we miss our friend Chuck.
Thanks Mr. Roberts, js. Now I know that I do not have to worry too much by the sensitizationf 304. In fact, in agreement with your comments, I understand that I may use a cooling rate of 50 ° C per minute with implementation of air and get a low level of sensitization that will not affect (large-scale) the properties of the weld.
Once again thanks.
Erik.
A dialogue with the engineer and some testing would still be a recommended idea.
The dissimilar metal weld joint should be subjected to PWHT to reduce residual stress and to temper the hardened weld deposit and base metal heat affected zone on the 410 side of the weld joint. What is the service condition of the 304 that you need to worry about sensitization? First off, you did not use an L Grade so from an exposure to degree of sensitization there is not much one can do in your case to really reduce sensitization (using an L Grade would have been better). You need to carefully evaluate your intended service conditions.
Thanks a lot. The serviced intended is in the very bottom of an oil well, so I can maybe deal with sour service conditions.
If that is the case, there is no way you want to put this into service without PWHT. You need to get the weld and HAZ to comply with NACE MR0175, and there is no way to do it without PWHT on 410 material.
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