These are stabilized alloys, they have Al and Ti added to form carbides and suppress grain boundary Carbide formation. You would not normally stabilize HT these alloys, unless it was done after all welding, forming, and assembly. I have seen systems that operated at the lower end of the sensitization range (550-600C) and those were deliberately run at 900C prior to service so that they would not sensitize in service.
When you anneal at high temp you grow the grains and dissolve all of the C in the matrix. As these cool some Ti and Al carbide will form. If you then HT at a lower temperature it will not change the grain size but it will allow further growth of the carbides. If the stabilization temp is too low then you will get Cr carbides mostly in the grain boundaries (very bad). At higher temps (over 900C but less than 1050C) you will grow the Ti and Al carbides until there is a equilibrium of C. With later exposure this alloy will be fairly resistant to forming grain boundary Cr carbides.
BUT, I don't know what the strength and allowed stress would be for material in this condition. It has basically become 'used' material.
INCOLOY alloys 800H and 800HT are austenitic, solid-solution alloys. Titanium nitrides, titanium carbides, and chromium carbides normally appear in the alloys’ microstructure. The nitrides are stable at all temperatures below the melting point and are therefore unaffected by heat treatment.Chromium carbides precipitate in the alloys at temperatures between 1000 and 2000°F (540 and 1095°C). Consequently, alloys 800H and 800HT are similar to other austenitic alloys in that they can be rendered susceptible to intergranular corrosion (sensitized) in certain aggressive environments by exposure to temperatures of 1000 to1400°F (540-760°C).INCOLOY alloy 800H and 800HT products are produced so as to optimize their high temperature properties.The carbon content in alloys 800H and 800HT results in high temperature strength and resistance to creep and rupture. Alloy 800H and 800HT products are solution annealed as a final stage of production so that the carbon is in the condition to make its optimum contribution to high temperature properties. The solution anneal also results in a large grain size which further contributes to strength and resistance to creep and rupture at high temperatures
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P.E. Metallurgy, consulting work welcomed
