using 253MA instead of 353MA for furnace muffles 3

Try going right to Avesta-Polarit, the developers of these grades. They have a good web site and respond to such enquiries. I would assume that as good as 253MA is, it would not come close to 353MA in performance.

My company sells both alloys. The 253MA grade is not suggested for carburizing conditions as it will embrittle from carburization. Carburization resistance is greatly related to nickel content in high temperature alloys. 353MA is 35% nickel vs. 253MA which is only 11% nickel. If 353MA is not available then I would suggest looking at RA330 as an option, which is also 35% nickel. The downside is RA330 is lower in strength since it does not have nitrogen added to it.

If strength is an issue you might look at alloy 602CA which is a higher nickel alloy with high strength at temperature. It is however more expensive.

Out of curiousity do you ever have issues with metal dusting in your equipment.

Jason Wilson
Rolled Alloys

As the furnaces I'm repairing work both in carburizing atmosphere and air, it's difficult to thay which prevails - dusting or sooting; normally, I'm using W 1.4841 if I'm expacting good mechanical strength, W 1.4828 if I don't want to have SIGMA status and, lately, SANICRO 31HT from SANDVIK, a steel that seams to have good stability in carburizing atmosphere (I'm making heating resistors from steel pipes - the construction is known under the name of PROLECTRIC and was first promoted by SURFACE (and the European STEIN - SURFACE)

We have seen metal dusting in this prolectric heating element application and have heard some reports of cracking in the pipe from thermal fatigue. RA330 has been used for such elements in the past, but like the Sanicro 31HT (800HT) it would be subject to metal dusting. RA330 is not as strong as the Sanicro 31HT, but its finer grain structure can be a benefit in resisting carburization/thermal fatigue cracking.

Disregard the 602CA suggestion it is not commercially available in a pipe product.

Normall, I wouldn't expect more then 4 years lifetime for the SANICRO 31HT pipes; once I could cover them with chromium oxide, in order to make them last longer, but my provider found out that he could use his high temperature furnaces for something more profitble, so ...