Stainless steels alloying effects

Stainless steel 316L material used for piping and equipment shows considerable corrosion resistance because of the beneficial effect of molybdenum on the surface properties. It is also observed that the surface treatment (pre-reduced, polished, passivated and chemically treated surfaces) of stainless steel equipment and piping reduces the corrosion process in seawater applications. The corrosion resistance of stainless steel in seawater applications can also be enhanced by bulk alloying the stainless steel with nitrogen, chromium, molybdenum and nickel by converting the stainless steel into super austenitic stainless steel. From leaching studies it is also observed that the release of iron, chromium and nickel from the super austenitic stainless steel to seawater is considerably... 

Precious, semi-precious, most Pd-base alloys, Ti-base alloys and stainless steel also produce excellent biological responses with a survival rate of 98% to 70% for the highest concentration. Two semi-precious alloys with high Ag-content reflect the cytotoxic effect of pure silver (Figure 5.1). Ni-Cr alloys (14% and 23%) induce a strong cytotoxic action, and dental amalgams produce total cell death at very low concentrations. 

Fig. 11.4 Cyclic oxidation resistance of nickel-base alloys and stainless steels in air at 900 °C [18]. Reprinted, with permission, from STP165 Symposium on Effect of Cyclic Heating and Stressing on Metals at Elevated Temperatures, copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA.

The thermal convection loop is also useful for studying dissimilar-metal mass transfer. The bimetallic loop design shown in Fig. 13 was used by DeVan and Jansen [86] to determine the transport rates of nitrogen and carbon between vanadium alloys and stainless steels in a sodium circuit. Mass transfer rates and carbon and nitrogen effects on mechanical properties were monitored by means of insert specimens in the hot and cold legs. The effects of surface area ratios of the two materials were determined by adding or subtracting insert specimens. 

The effect of sigma phase precipitation at 800 °C on the corrosion resistance in seawater of a high-alloyed duplex stainless steel... 

For similar reasons, the dissolution rate of Cr(III) oxide is extremely slow in the passive state. Additions of Cr therefore stabilize the passive behavior of Fe-Cr alloys and stainless steel. Fe-Cr alloys are more resistant to pitting in ehloride-containing electrolytes with more positive pitting potentials compared with pure Fe. The Cr concentration is increased within the passive layer relative to the composition of the bulk metal. Thus Fe-Cr alloys are more protected against the attack of aggressive anions and pitting by the beneficial effect of Cr. 

Effect of composition on the resistance to crevice and pitting corrosion of stainless alloys in chloride environments—the PREN index. (From Remanit 4565S-Nitrogen Alloyed Austenitic Stainless Steels with Maximum Corrosion Resistance and High Strength, Thyssen Stahl AG, Krefeld, Germany, 1995.)... 

Control of the core is affected by movable control rods which contain neutron absorbers soluble neutron absorbers ia the coolant, called chemical shim fixed burnable neutron absorbers and the intrinsic feature of negative reactivity coefficients. Gross changes ia fission reaction rates, as well as start-up and shutdown of the fission reactions, are effected by the control rods. In a typical PWR, ca 90 control rods are used. These, iaserted from the top of the core, contain strong neutron absorbers such as boron, cadmium, or hafnium, and are made up of a cadmium—iadium—silver alloy, clad ia stainless steel. The movement of the control rods is governed remotely by an operator ia the control room. Safety circuitry automatically iaserts the rods ia the event of an abnormal power or reactivity transient. 

Drums. Typical selection for the number of dmms used in the various appHcations is two to four for cobbers, one or two for roughers, and two or three for finishers. The inner dmm sheU, usually 3 mm thick, is specified Series 302 or 304 stainless steel. Dmm heads are usually of high tensile strength aluminum alloy or brass. Recessed head bolt constmction having an effective seal is specified. 

Nickel and Nickel Alloys A wide range of ferrous and nonfer-rous nickel and nickel-bearing alloys are available. They are usually selected because of their improved resistance to chemical attack or their superior resistance to the effects of high temperature. In general terms their cost and corrosion resistance are somewhat a func tion of their nickel content. The 300 Series stainless steels are the most generally used. Some other frequently used alloys are hsted in Table 10-35 together with their nominal compositions. For metallurgical and corrosion resistance data, see Sec. 28. 

Weld overlays of stainless steel or cobalt-based wear-resistant and hard-facing alloys such as Stellite may salvage damaged equipment. In addition, weld overlays incorporated into susceptible zones of new equipment may provide cost-effective resistance to cavitation damage. 

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