Modifying metal or alloy substrates

An article comprising iron-based alloy substrate, the iron-based alloy substrate comprising:

• between about 24% and about 27% by weight of nickel, between about 13.5% and about 16% by weight of chromium, between about 1% and about 1.5% by weight of molybdenum, between about 1.9% and about 2.35% by weight of titanium, between about 0.1% and about 0.5% by weight of vanadium, between about 0.003% and about 0.01% by weight of boron, up to about 0.08% by weight of carbon, up to about 2% by weight of manganese, up to about 1% by weight of silicon, up to about 0.025% by weight of phosphorus, up to about 0.025% by weight of sulfur, up to about 0.35% by weight of aluminum, and a balance of iron;
• and
• a friction stir processed region, the friction stir processed region comprising a stir region and a second region outside of and adjacent to the stir region, wherein a first average grain size in the stir region and a second average grain size in the second region are modified compared to a pre-friction stir average grain size of the iron-based alloy substrate and a first microhardness in the stir region and a second microhardness in the second region are modified compared to a pre-friction stir microhardness of the iron-based alloy substrate.