Carbide stabilizers

Vanadium is used in producing rust resistant and high speed tools steels. It is an important carbide stabilizer in making steels. 

Antimony may be added to copper-base alloys such as naval brass. Admiralty Metal, and leaded Muntz metal in amounts of 0.02—0.10% to prevent dezincification. Additions of antimony to ductile iron in an amount of 50 ppm, preferably with some cerium, can make the graphite fliUy nodular to the center of thick castings and when added to gray cast iron in the amount of 0.05%, antimony acts as a powerflil carbide stabilizer with an improvement in both the wear resistance and thermal cycling properties (26) (see Carbides). 

The addition of carbide stabilizers to steel reduces the tendency toward internal Assuring. Elements such as chromium, molybdenum, tungsten, vanadium, titanium, and niobium reduce the number of nucleation sites by forming more stable alloy carbides which resist breakdown by hydrogen and, therefore, decrease the propensity to form methane.9 The solid-line curves in Figure 1 reflect the increased resistance to internal attack when molybdenum and chromium are present. 

Alloys other than those shown in Figure 1 are also suitable for resisting high temperature hydrogen attack. These include modifled carbon steels and low alloy steels to which carbide stabilizing elements (molybdenum, chromium, vanadium, titanium, or niobium) have been added. European alloys and heat-treating practices have been summarized by Class.11 Austenitic stainless steels are resistant to decarburization even at temperatures above 1000°F (538°C).12... 

The structure of Rhi2(CO)25(C2), reported in Fig. 10, is a further example of carbide stabilization (13). This is the most irregular cluster as yet characterized like Rh8(CO)i9C, it has no symmetry element. This cluster is also derived chemically from the oxidation of [Rh COVC]2-. The 2 central carbide atoms are definitely bonded together (1.47 A) and lead to... 

Most of these are carbon-manganese-molybdenum alloys with small additions of chromium and/or nickel plus vanadium or niobium. Vanadium or niobium acts as a carbide stabilizer and grain refiner, improving both elevated temperature strength and notch ductility. An exception is Fortiweld (MOBO 45 is the same steel), which is a boron-treated 1/2% molybdenum steel. This alloy is the cheapest of the group, but has hardly been used for reactors in the U.K., possible because its impact properties in thick sections are not so attractive as alternative steels. 

Austenitic stainless steels (AISI 304, 316L) - use ELI carbon content (<0.05 wt.% C), - add carbide stabilizers (e.g., Ti, Nb), - soln. anneal, after welding, - addition of Si for HN03 lOOSwt. service up to 90°C with cone, below 30 wt.% service at RT with cone, until 100 wt.%... 

Titanium Strong carbide-forming element Not used on its own, but added as a carbide stabilizer to some austenitic stainless steels... 

---