Selecting and Developing Advanced Alloys for Creep-Resistance for Microturbine Recuperator Applications

ABSTRACT Recuperators are considered essential hardware to achieve the efficiencies desired for advanced microturbines. Compact recuperator technologies, including primary surface, plate and fin, and spiral, all require thin section materials that have hightemperature strength and corrosion resistance up to 750 o C or above, and yet remain as low-cost as possible. The effects of processing and microstructure on creep-rupture resistance at 750 o C and 100 MPa were determined for a range of austenitic stainless alloys made into 0.1 mm foils. Two groups of alloys were identified with regard to improved creep-resistance relative to type 347 stainless steel. Alloys with better creep-rupture resistance included alloys 120, 230, modified 803 and thermiealloy, while alloy 214 and 625 exhibited much better creep strength. Alloys 120 and modified 803 appeared to have the most cost-effective improvements in creep-strength relative to type 347 stainless steel, and should be attractive for advanced microturbine recuperator applications

New creep resistant cast alloys with improved oxidation resistance in water vapor at 650-800ºC

Cast stainless steel CF8C-Plus (19wt.%Cr/12%Ni) has excellent creep properties, but limited oxidation resistance above 700ºC in environments containing H2O. One strategy to improve the alloy oxidation performance is to increase the Cr and Ni concentration. Two new alloys, with respectively 21wt%Cr-15wt%Ni and 22wt%Cr-17.5wt%Ni were therefore developed and their long-term oxidation behavior in humid air were compared with the oxidation behavior of five other cast alloys. At 650 and 700ºC, all the alloys formed internal Cr-rich nodules, and outer nodules or layers rich in Fe and Ni, but they grew a protective Cr-rich inner layer over time. At 750ºC, the lower alloyed steels such as CF8C-Plus showed large metal losses, but the two new alloys still exhibited a protective oxidation behavior. The 21Cr-15Ni alloy was severely oxidized in locations at 800ºC, but that was not the case for the 22Cr-17.5Ni alloy. Therefore, the two new modified alloys represent a potential operating temperature gain of respectively 50 and 100ºC in aggressive environments compared with the CF8C-Plus alloy

Proceedings of CREEP8 Eighth International Conference on Creep and Fatigue at Elevated Temperatures PVP2007-26840 DEVELOPING NEW CAST AUSTENITIC STAINLESS STEELS WITH IMPROVED HIGH- TEMPERATURE CREEP RESISTANCE

ABSTRACT Oak Ridge National Laboratory (ORNL) and Caterpillar have recently developed a new cast austenitic stainless steel, CF8C-Plus, for a wide range of high-temperature applications, including diesel exhaust components and turbine casings. The creep-rupture life of the new CF8C-Plus is over ten times greater than that of the standard cast CF8C stainless steel, and the creep-strength is about double. Another variant, CF8C-Plus Cu/W has been developed with even more creep strength at 750-850 o C. The creep-strength of these new cast austenitic stainless steels is close to that of Ni-based superalloys like 617. CF8C-Plus steel was developed in about 1.5 years using an "engineered microstructure" alloy development approach, which produces creep resistance based on formation of stable nano-carbides (NbC) and prevention of deleterious intermetallics (sigma, Laves). CF8C-Plus steel won a 2003 R&D 100 Award, and to date, over 32,000 lb have been produced in various commercial component trials. The current commercialization status of the alloy is summarized. INTRODUCTION Austenitic stainless steel use world-wide is increasing significantly every year. For high-temperature applications, stainless steels and other alloys face the continued and conflicting demands of increasing performance, maximum temperature limits and lifetime, and all with similar or reduced cost. One example of such demanding applications is advanced heavy truck diesel engines, which must continue to have higher fuel efficiency as well as reduced exhaust emissions, without sacrificing durability and reliability. These more demanding normal duty cycles require exhaust manifolds and turbocharger housing materials to withstan

2001-GT-0540 MATERIALS SELECTION FOR HIGH TEMPERATURE METAL RECUPERATORS

ABSTRACT One method of increasing the efficiency of gas turbines i

Technology Review Overview of Creep Strength and Oxidation of Heat-Resistant Alloy Sheets and Foils for Compact Heat Exchangers

The Oak Ridge National Laboratory (ORNL