Oxidation Behaviors of Different Grades of Ferritic Heat Resistant Steels in High-Temperature Steam and Flue Gas Environments

Alumina-forming austenitic (AFA) heat-resistant steels have been reported as a promising new class of steels in recent years with potential applications in advanced ultra-supercritical power plants. It is well known that L12-ordered γ’ phase is the most important precipitate for high-temperature strengthening in Ni-based superalloys and it can be stabilized by increasing the Ni content in heat-resistant steels. In the current work, the evolution of L12-ordered precipitates were compared in the Cu-bearing AFA alloys with 20, 27 and 35 wt.% Ni. After slow tensile tests at 700°C (∼2 × 10−5 s−1), L12-ordered precipitates occurred in all the alloys. Alloy AFA27 displayed the most densely distributed L12-particles in the matrix, whose ultimate tensile strength was also the highest. However, the L12-ordered precipitates were only observed in alloy AFA27 after the slow tensile test at 750°C due to the thermodynamic and kinetic reasons. Flow curves of slow tensile tests indicated different precipitation behaviors at 700°C and 750°C. Chemical composition analysis and thermodynamic calculation revealed that the occurrence of L12-ordered Ni-Cu-Al phase depends on temperature, Ni content and the atomic ratio of Ni/Al. This opens up new opportunities to promote the formation of L12-ordered phase in Fe-based austenitic heat-resistant steels with low Ni content and benefits high-temperature strengthening.

Download Full-text

Studies on High Temperature Corrosion of Austenitic Heat-resistant Steels Super 304H/10Cr18Ni9Cu3NbN in Simulated and Real Combustion Gas Atmospheres

Energy Materials 2014 ◽

10.1007/978-3-319-48765-6_27 ◽

2014 ◽

pp. 243-250

Author(s):

Qinxin Zhao ◽

Zhiyuan Liang ◽

Weiwei Jiang

Keyword(s):

High Temperature ◽

High Temperature Corrosion ◽

Combustion Gas ◽

Heat Resistant ◽

Heat Resistant Steels

Download Full-text

Ferritic Stainless Steels for High-Temperature Applications: Stabilization of the Microstructure by Solid State Precipitation of MX Carbonitrides

High Temperature Materials and Processes ◽

10.1515/htmp-2013-0004 ◽

2013 ◽

Vol 32 (6) ◽

pp. 563-572 ◽

Cited By ~ 1

Author(s):

N. Nabiran ◽

S. Weber ◽

W. Theisen

Keyword(s):

High Temperature ◽

Solid State ◽

Stainless Steels ◽

High Temperature Strength ◽

Compression Tests ◽

Gas Temperature ◽

Solid Solution Strengthening ◽

Heat Resistant ◽

High Temperature Mechanical Properties ◽

Heat Resistant Steels

AbstractFerritic heat-resistant steels are commonly used for automotive exhaust systems and have replaced cast iron, the traditional material for this application. Efforts to improve the efficiency of engines, reduce weight, and minimize toxic ingredients by increasing the gas temperature have shifted the requirement for ferritic heat-resistant steels to a higher hot strength. Methods of improving the high-temperature strength are solid-solution strengthening, precipitation hardening, and grain refinement. In this work, the influence of MX precipitates on the high-temperature mechanical properties of three different ferritic Fe-Cr stainless steels was investigated and compared to a reference material. Investigations were performed with uniaxial compression tests of samples aged isothermally at 900 °C for up to 1440 h. The most effective method of increasing the high-temperature strength is to alloy the steel with 2 mass% tungsten. Grain growth during annealing at 900 °C was decelerated by solid-state formation of MX carbonitrides. Microstructural investigations also revealed a slow coarsening rate of the MX precipitates.

Download Full-text