Prospects for Martensitic 12 % Cr Steels for Advanced Steam Power Plants

Hald, John

doi:10.1007/s12666-015-0793-4

Cited by 22 publications

(11 citation statements)

References 22 publications

(18 reference statements)

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“…There is a distinct difference between kinetics, driving forces, and transformation mechanisms of the MX→Z-phase transformation in the 9% Cr and 11-12% Cr steels [6,9,[16][17][18][19]23,[29][30][31]37,[41][42][43]. The formation of Z-phase results in the creep strength breakdown appearance in the 11-12% Cr steels [16,18,19,33,35,36,42].…”

Section: Introductionmentioning

confidence: 99%

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Effect of creep temperature on Z-phase formation in heat-resistant 9% Cr–3% Co martensitic steel

Fedoseeva

Nikitin

Dudova

et al. 2021

Materials Science and Engineering: A

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The Z-phase (CrVN) precipitation in a 9% Cr-3% Co martensitic steel during creep at 923 K and 948 K has been investigated with aim to establish the effect of temperature on the nucleation mechanism of these particles and their coarsening behavior. Ostwald ripening of VX carbonitrides strongly affects these processes. An increase in creep temperature significantly accelerates the transformation of the nanoscale MX carbonitrides into the Zphase particles causing the Z-phase nucleation in a shorter time. Two different mechanisms of the Z-phase precipitation have been observed. Firstly, for creep tests at 923 K and 948 K with creep rupture time longer than 2000 h, the formation of the stable Z-phase particles with a tetragonal lattice occurs through in-situ transformation of a cubic lattice of the MX carbonitrides leading to a continuous flux of Cr atoms from the ferritic matrix into these particles. The coarsening Z-phase occurs at the expense of dissolution of VX carbonitrides. Secondly, for creep test at 948 K with duration of 773 h, the strain-induced metastable Z-phase with the cubic lattice nucleates on the V-rich MX/ferrite interfaces with following transformation into the stable Z-phase with the tetragonal lattice under creep testing with longer duration. Concurrently, extensive coarsening Cr-rich VX carbonitrides occurs independently. As a result, coarsening Z-phase leads to insignificant dissolution of VX carbonitrides. The creep strength breakdown appearance is not related to the formation and/or coarsening of the Z-phase at both temperatures.

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Section: Introductionmentioning

confidence: 99%

“…Strain and/or stress stimulate the Z-phase precipitation during creep and/or ageing exposure [16,37]. However, if the sizes of the Z-phase and MX carbonitrides are comparable, the Z-phase particles can positively affect the creep strength as MX carbonitrides [5,12,18,19,[30][31][32]37,41].…”

Section: Introductionmentioning

confidence: 99%

Effect of creep temperature on Z-phase formation in heat-resistant 9% Cr–3% Co martensitic steel

Fedoseeva

Nikitin

Dudova

et al. 2021

Materials Science and Engineering: A

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“…Table 1 shows the developing martensitic heat resistant steels over the years [34,35]. Recently, B containing 9% Cr martensitic heat resistant steel (9Cr-B steel) with excellent creep property was developed, i.e., B containing 9Cr-3W-3Co series steels developed by National Institute for Materials Science (NIMS) in Japan [36][37][38][39][40][41][42][43][44][45][46][47][48][49] and FB2 steel in the frame of the European Cooperation in Science and Technology (COST) program [50][51][52][53][54][55][56][57][58][59][60]. More specially, compared with conventional martensitic steel, the difference of creep strength between base metal and weld joint of 9Cr-B steel was negligible [61], as shown in Figure 2 [62].…”

Section: Introductionmentioning

confidence: 99%

A Review of Austenite Memory Effect in HAZ of B Containing 9% Cr Martensitic Heat Resistant Steel

Cai

et al. 2019

Metals

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During the welding process of B containing 9% Cr martensitic heat resistant steel (9Cr-B steel), austenite memory effect (referred to that the prior austenite grains in the heat affected zone (HAZ) after welding inherit the shape and size of prior austenite grains before welding) occurs in its normalized sub-zone of HAZ and the grain refinement is suppressed, which can effectively prevent type IV crack, and improve the service life of the welded joint at high temperatures. In the present article, α/γ reverse transformation behavior in the normalized sub-zone of 9Cr-B steel HAZ is reviewed. Austenite memory effect of 9Cr-B steel is derived from B addition. The main mechanisms of austenite memory effect during α/γ reverse transformation are discussed. Various models of boron causing austenite memory effect are discussed in detail. Matrix microstructure also plays an important role in austenite memory effect. Effects of heating rate, peak temperature, and holding time at peak temperature on austenite memory effect are also discussed.

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“…Cobalt and copper have been the favored additions and the newer 12% chromium steels usually contain one of these elements. However, attempts to apply 12% Cr steels at 650 °C have largely failed, since under this condition the fine MX particles which provide a major strengthening contribution transform into relatively coarse Z ‐phase particles . The development of Z ‐phase has been held responsible for the decrease in long term creep properties as well as the decrease in corrosion resistance, since the formation of Z ‐phase not only causes the dissolution of desirable MX precipitates, but it also might consume some of the chromium in solid solution in the matrix which is required for the formation of a corrosion resistant surface layer.…”

Section: Introductionmentioning

confidence: 99%

“…The development of Z ‐phase has been held responsible for the decrease in long term creep properties as well as the decrease in corrosion resistance, since the formation of Z ‐phase not only causes the dissolution of desirable MX precipitates, but it also might consume some of the chromium in solid solution in the matrix which is required for the formation of a corrosion resistant surface layer. In Hald's research, one possible solution to avoid Z ‐phase in high Cr steels is to eliminate the Z ‐phase forming elements such as V and Nb and replace them by Ti, since TiN is the only nitride in steels which cannot transform into Z ‐phase. However, the TiN nitrides generally do not make a significant contribute to the high temperature strength, hence, the problem how to suppressing Z ‐phase formation in heat resistant martensitic steels with high Cr levels (Cr wt% > 11) operating under a prescribed service temperature of 600–650 °C still remains unsolved …”

Section: Introductionmentioning

confidence: 99%

On the Relationship between the Chromium Concentration, the Z‐Phase Formation and the Creep Strength of Ferritic‐Martensitic Steels

Zwaag

2018

steel research int.

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In this study, the long term creep strength behavior of commercial heat resistant martensitic/ferritic steels with Cr levels ranging from 1 to 15 wt% is analyzed by linking their computed equilibrium compositions to their creep properties. At lower Cr levels, the calculated strength due to precipitation hardening agrees well with the experimental results. At high chromium levels and longer exposure times, an accelerated strength loss due to the formation of Z-phase precipitates has been reported. The accelerated strength loss is computationally analyzed and a correlation between accelerated strength loss and Z-phase formation is confirmed. A study is made to explore the option of adjusting the chemical composition of existing high-chromium steels to reduce the driving force for Z-phase formation. However, no proper composition ranges are found which combine a high Cr concentration with a significantly lower driving force for Z-phase formation.

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Prospects for Martensitic 12 % Cr Steels for Advanced Steam Power Plants

Cited by 22 publications

References 22 publications

Effect of creep temperature on Z-phase formation in heat-resistant 9% Cr–3% Co martensitic steel

Effect of creep temperature on Z-phase formation in heat-resistant 9% Cr–3% Co martensitic steel

A Review of Austenite Memory Effect in HAZ of B Containing 9% Cr Martensitic Heat Resistant Steel

On the Relationship between the Chromium Concentration, the Z‐Phase Formation and the Creep Strength of Ferritic‐Martensitic Steels

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