One Minute Mentor: Tempering Temperature and Corrosion Properties
The graph shows the corrosion resistance of martensitic stainless steels with high hardness. It compares nitrogen alloyed grade (M340 = AISI 440Mod) with the standard grade AISI 440C.
For the application of higher tempering temperatures, corrosion properties also have to be taken into consideration. Usually the minimum in corrosion resistance can be found slightly above the secondary hardening maximum. In 17%-Cr high-carbon grades such as AISI 440C, corrosion resistance already starts to deteriorate at tempering temperatures higher than 390°F, as shown in the graph; lower-carbon grades like AISI 420, and even more the nitrogen-alloyed grades, show a significant drop in corrosion resistance only at tempering temperatures higher than approximately 840°F.
Volume 4D, Heat Treating of Irons and Steels -> Tool Steels -> Heat Treating of Mold Steels and Corrosion-Resistant Tool Steels -> Recommended Heat Treating Practices
