Titanium creep strength

For resistance against fatigue, Nimonic 75 has been used with Nimonic 80 and Nimonic 90. Nimonic 75 is an 80-20 nickel-chromium alloy stiffened with a small amount of titanium carbide. Nimonic 75 has excellent oxidation and corrosion resistance at elevated temperatures, a reasonable creep strength, and good fatigue resistance. In addition, it is easy to press, draw, and mold. As firing temperatures have increased in the newer gas turbine models, HA-188, a Cr, Ni-based alloy, has recently been employed in the latter section of some combustion liners for improved creep rupture strength. 

Materials for catalyst tubes are selected in combination with the process conditions employed. Alloys with high chromium and nickel content are used for the reactor tubes in a steam-reforming furnace. The first centrifugally cast tubes such as HK 40 contained 25% Chromium and 25% Nickel. Today, tube material containing 25% Chromium and 35% nickel, niobium, and traces of zirconium and titanium are used (so called HP alloys) (50). The HP alloys are more expensive but allow a higher tube design temperature and have a better creep strength and oxidation as well as carburization resistance. 

PNC also developed a type of 316 stainless steel with significantly increased high temperature creep strength and low swelling properties by adding small amounts of phosphorus, boron, titanium and niobium to conventional SUS 316 stainless steel. The low-swelling PNC 316 steel used in Monju will be applicable to 90,000 MWd/t in the initial core and 130,000 MWd/t in a high bum-up core. It is a top performer compared with similar materials that have been developed around the world. A fuel pin behavior analysis code (CEDAR) was also developed by PNC to evaluate the behavior of the fuel pins in Monju. 

Figure 10.7 Effects of titanium and excess oxygen concentrations on nanostructure and creep strength of 9Cr-ODS steel.

Carbon content is usually about 0.15% but may be higher in bolting steels and hot-work die steels. Molybdenum content is usually between 0.5 and 1.5% it increases creep—mpture strength and prevents temper embrittlement at the higher chromium contents. In the modified steels, siUcon is added to improve oxidation resistance, titanium and vanadium to stabilize the carbides to higher temperatures, and nickel to reduce notch sensitivity. Most of the chromium—molybdenum steels are used in the aimealed or in the normalized and tempered condition some of the modified grades have better properties in the quench and tempered condition. 

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. 

Other alloys have been developed for use in particular corrosive environments at high temperatures. Several of these are age-hardenable alloys which contain additions of aluminum and titanium. Eor example, INCONEL alloys 718 and X-750 [11145-80-5] (UNS N07750) have higher strength and better creep and stress mpture properties than alloy 600 and maintain the same good corrosion and oxidation resistance. AHoy 718 exhibits excellent stress mpture properties up to 705°C as well as good oxidation resistance up to 980°C and is widely used in gas turbines and other aerospace appHcations, and for pumps, nuclear reactor parts, and tooling. 

Recently a new-generation tube material has emerged, called Micro Alloy [1490]-[1493]. This contains not only niobium but also titanium and zirconium (or lanthanum), and has improved creep rupture strength still further. Table 24 shows the chemical composition of the tube materials. 

The second method of surface modification permits the formation of a composite particle, the core of which is composed of polymer (UHMWPE or polyimide) and the surface of which is coated with titanium carbide which is hard and abrasion resistant. The composite particles can be incorporated into any suitable matrix resulting in improved abrasion resistance, lowered fiiction, higher compressive strength, improved creep resistance, etc. This new product is a unique form of raw material which has the potential to improve the properties of many products. 

Timetal 6-4 Ti-6A1-4V This titanium alloy is a versatile medium-strength titanium alloy that exhibits good tensile properties at room temperature, creep resistance up to 325°C, and an excellent fatigue strength. It is often used in less critical applications up to 400°C. It is the alloy most commonly used in wrought and cast forms. 

Strength at high temperature Inconels, Hastelloys Seawater corrosion resistance Copper, nickel, titanium alloys Creep resistance Steels and nickel alloys... 

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