Martensitic/Ferritic Super Heat-resistant 650°C Steels - Design and Testing of Model Alloys
V. Knezevic,Gerhard Sauthoff,J. Vilk,Gerhard Inden,André Schneider,R. Agamennone,Wolfgang Blum,Yan Wang,Alfred Scholz,Christina Berger,J. Ehlers,Lorenz Singheiser +11 more
TLDR
In this paper, the authors designed new super heat-resistant 12 % Cr martensitic/ferritic steels using basic principles and concepts of physical metallurgy, to test and optimize model alloys and to investigate and clarify their behavior under long-term creep conditions with emphasis on microstructural stability and corrosion resistance.Abstract:
In the recent two decades advanced martensitic/ferritic 9-12 % Cr steels are recognized to be the most potential materials for 650°C Ultra Super Critical (USC) Power Plants. The critical issues are the improvement of long-term creep strength and corrosion resistance. The aim of the present research is to design new super heat-resistant 12 % Cr martensitic/ferritic steels using basic principles and concepts of physical metallurgy, to test and optimize model alloys and to investigate and clarify their behavior under long-term creep conditions with emphasis on microstructural stability and corrosion resistance. Fine distributions of stable precipitates, which block the movement of subgrain boundaries (M 23 C 6 carbides, Laves phase) and dislocations (MX carbonitrides) and delay coarsening of microstructure, are the key to high creep strength of this type of steels. Therefore, different carbide, nitride and Laves phase forming elements (Cr, W, Nb, V, Ta, Ti) have been used to provide precipitation hardening. Furthermore, the aim is to produce a sequence of precipitates with different kinetics, i.e. with precipitation of a new phase during coarsening of the prior one. Co has been used for obtaining 100% martensite initially and for slowing down diffusion processes and particle coarsening. The partial replacement of Co by Cu is also investigated to reduce costs. The first results of mechanical tests of the studied model alloys have shown positive effects of the addition of W and Ta as Laves phase and MX forming elements, respectively, as well as of the addition of B. Alloying with Co has also shown beneficial effects on the creep strength.read more
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Journal ArticleDOI
Design of martensitic/ferritic heat-resistant steels for application at 650 °C with supporting thermodynamic modelling
TL;DR: In this paper, a series of martensitic/ferritic model steels with 12.5%Cr were studied to achieve an increased creep resistance through additional alloying with various elements for controlled precipitation of M23C6 carbides, MX carbonitrides and intermetallic Laves phase.
Journal ArticleDOI
Evolution of microstructure and deformation resistance in creep of tempered martensitic 9-12%Cr-2%W-5%Co steels
TL;DR: In this paper, the microstructural evolution during creep at 923 K of four tempered martensite 9-12%Cr-steels modified with 2%W and 5%Co was quantified by electron microscopy.
Journal ArticleDOI
Laves phases: a review of their functional and structural applications and an improved fundamental understanding of stability and properties
Frank Stein,Andreas Leineweber +1 more
TL;DR: There is a broad range of successful utilization of Laves phases in functional applications including hydrogen storage material (Hydraloy), as magneto-mechanical sensors and actuators (Terfenol), or for wear and corrosion-resistant coatings in corrosive atmospheres and at high temperatures (Tribaloy).
Journal ArticleDOI
Simulation of the kinetics of precipitation reactions in ferritic steels
André Schneider,Gerhard Inden +1 more
TL;DR: In this paper, computer simulations of diffusion-controlled phase transformations in model alloys of Fe-Cr-C, FeCr-W-C and FeCrV-V-C are presented.
Journal ArticleDOI
The role of Laves phase on microstructure evolution and creep strength of novel 9%Cr heat resistant steels
TL;DR: In this paper, the influence of Laves phase formation and growth kinetics on the creep strength at 650°C of two different 9%Cr heat resistant steels of the authors' design was investigated.