Nickel-niobium stabilized stainless steel

AISI 321 and 347 are stainless steels that contain titanium and niobium iu order to stabilize the carbides (qv). These metals prevent iatergranular precipitation of carbides during service above 480°C, which can otherwise render the stainless steels susceptible to iatergranular corrosion. Grades such as AISI 316 and 317 contain 2—4% of molybdenum, which iacreases their creep—mpture strength appreciably. In the AISI 200 series, chromium—manganese austenitic stainless steels the nickel content is reduced iu comparison to the AISI 300 series. 

Stabilizing is done on certain corrosion resistant stainless steels and nickel alloys containing titanium, niobium or tantalum to enhance corrosion resistance. They are heated to specific temperatures so that these elements combine preferentially with carbon, preventing any detrimental loss of... 

Niobium, when added to AUoy 182, stabilizes the carbon content and prevents the precipitation of Cr carbides at the grain boundary [78]. C, P, Si, and S segregate or precipitate at the grain boundary and are critical to hot-cracking resistance of nickel-based weld metals [79]. When Si segregates at the grain boundaries of austenitic stainless steel. 

Nickel-based alloys can also be subjected to carbide precipitation and precipitation of intermetallic phases when exposed to temperatures lower than their annealing temperatures. As with austenitic stainless steels, low-carbon-content alloys are recommended to delay precipitation of carbides. In some alloys, such as alloy 625, niobium, tantalum, or titanium is added to stabilize the alloy against precipitation of chromium or molybdenum carbides. Those elements combine with carbon instead of the chromium or molybdenum. 

Typical stainless steels specified for aerospace use (many are covered by the BS 500 specifications) contain <0.15% carbon, 11—20% chromium, <2.0% manganese, 4—10% nickel, and 0—2% molybdenum. Other trace elements, including titanium and niobium, can also be present as stabilizers. 

---