Heat-resistant iron-based alloys

Thus, in the future all great experience of processing iron-based alloys could be employed to produce the alloys on the basis of titanium. The preliminary data show that a level of properties, which could be realized with titanium "steels appears to be attractive enough. Some properties of the deformed alloys of system Ti-Si-Al-Zr are listed in the Table 1. It is obvious also some distinction in properties of titanium steels depending on deformation temperature. Namely, alloys deformed in a phase field, have higher plasticity conversely, alloys deformed in 3 phase field, possess higher heat resistance. 

The corrosion resistance of various metals and alloys in high-temperature liquid lithium is shown in Figure 11. Unfortunately, lithium is much more corrosive than sodium. Consequently, it will be impossible to take full advantage of its many attractive heat-transfer properties until a satisfactory container material is found. The most corrosion-resistant pure metals in a static isothermal system are molybdenum, niobium, tantalum, tungsten, and iron. Of the commercially available structural materials, no alloys tested to date have had satisfacto corrosion resistance at a temperature above 1400 F. for extended time periods in systems where temperature differentials exist. Even though iron has good resistance in static isothermal lithium, iron and iron-base alloys suffer from mass trans-... 

W. Schendler, W. Schwenk, Electrochemical studies of the corrosion of heat-resistant iron and nickel-base alloys in eutectic alkali sulfate melt at 700 °C, Werkst. Korros. 32 (1981) 428—434. 

Stainless Steel There are more than 70 standard types of stainless steel and many special alloys. These steels are produced in the wrought form (AISI types) and as cast alloys [Alloy Casting Institute (ACI) types]. Gener y, all are iron-based, with 12 to 30 percent chromium, 0 to 22 percent nickel, and minor amounts of carbon, niobium (columbium), copper, molybdenum, selenium, tantalum, and titanium. These alloys are veiy popular in the process industries. They are heat- and corrosion-resistant, noncontaminating, and easily fabricated into complex shapes. 

Thermal Expansion. Alloys differ in their thermal expansion, but the differences are modest. Coefficients for the ferritic grades of steel are perhaps 30 percent below those of the austenitic steels at best, while expansion of the nickel-base austenitic types may be no more than 12 to 15 percent less than tho.se of the less expensive, iron-base, austenitic, heat-resistant alloys. Unfortu-... 

Nickel-iron-chrome alloys include the iron base superalloys and the heat resistant castings (see previous section). Iron-base superalloys are an extension of the austenitic stainless steels and include alloys such as the Incoloy 800 series. They are used for piping and manifolds in refining, power generation and petrochemicals. 

Fe—Cr. The Fe—Cr phase diagram. Fig. 3.1-106, is the prototype of the case of an iron-based system with an a-phase stabilizing component. Chromium is the most important alloying element of corrosion resistant, ferritic stainless steels and ferritic heat-resistant steels. If a-Fe—Cr alloys are quenched from above 1105 K and subsequently annealed, they decompose according to a metastable miscibility gap shown in Fig. 3.1-107. This decomposition reaction can cause severe embrittlement which is called 475 C-embrittlement in ferritic chromium steels. Embrittlement can also occur upon formation of the a phase. 

The development of heat-resistant alloys was similarly lengthy and inefficient. In the 1970s the protective oxide layers on nickel-based alloys were much improved by alloying them with elements that resulted in a more stable and tenacious layers of alumina versus chromia. It is only now that the concept of alumina protective layers is being applied to more cost-effective and high-temperature iron-based heat-resistant alloys, effectively producing a new class of stainless steels based on the principles of selective oxidation and advanced microstructural control of precipitates for strengthening. ... 

---