Vol.:(0123456789) 1 3
Metals and Materials International
https://doi.org/10.1007/s12540-020-00676-y
Effect of Boron in the Coarsening Rate of Chromium‑Rich Carbides
in 9%–12% Chromium Martensitic Creep‑Resistant Steel: Experiment
and Modeling at 650 °C
J. P. Sanhueza
1
· D. Rojas
1
· J. García
2
· M. F. Melendrez
1
· E. Toledo
3
· F. M. Castro Cerda
4
· C. Montalba
5
·
A. F. Jaramillo
6
Received: 19 December 2019 / Accepted: 27 February 2020
© The Korean Institute of Metals and Materials 2020
Abstract
In this study, three martensitic creep-resistant steels with 100, 90, and 70 ppm of boron were investigated. The experimen-
tal data obtained from isothermal aging and creep test at 650 °C were compared with the results of simulation conducted
using TC-PRISMA software. Tungsten was found to be the rate-controlling element in the coarsening of (Cr, Fe, W)
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carbides; however, this result differed in terms of boron-containing steel. Several studies indicate that the low solubility of
boron in ferrite promotes boron enrichment in (Cr, Fe, W)
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carbide, thereby reducing its coarsening rate. However, this
mechanism is not universally agreed upon. In the present study, a comparison between experimental and theoretical results
revealed that in boron-containing steels, the coarsening of (Cr, Fe, W)
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carbide is controlled probably by boron volume
diffusion or by trans-interface diffusion.
Keywords (Cr,Fe,W)
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carbides · Coarsening · ThermoCalc · TC-PRISMA
1 Introduction
Martensitic creep-resistant steels containing 9%–12% Cr
are widely used for high-temperature applications such
as steam pipes, boilers, rotors, bolts, turbine casings, and
turbine blades in supercritical fossil fuel power plants [1,
2]. The high creep strength, oxidation resistance, weld-
ability, and thermal fatigue resistance, and the competitive
production costs compared with austenitic stainless steel
and nickel alloys make martensitic creep-resistant steels
the best choice for the manufacturing of components oper-
ated at temperatures of 500–620 °C [3, 4]. In martensitic
creep-resistant steels, creep strength is achieved through a
combination of sub-boundary, dislocation, precipitation, and
solid-solution-strengthening mechanisms [5, 6]. Although
mechanical resistance of tempered martensite is attributed
to its subgrains, laths, and blocks with free dislocation, pre-
cipitation hardening is fundamental for the stabilization of
tempered martensite at high temperatures [7, 8]. That is, the
precipitation of finely dispersed secondary phases along the
boundaries of subgrains, laths, and blocks exerts a pinning
force over the sub-boundaries and free dislocations, which
prevents the degradation of tempered martensite under long-
term creep conditions [9, 10]. In martensitic creep-resistant
steels, precipitation hardening results from the formation of
three fundamental particles: M
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carbides, Laves-phase
precipitates, and MX carbonitrides [11, 12]. Nevertheless,
M
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carbides are the primary source of the reinforcement
of the creep strength owing to their high volume fraction
of ~ 2.0% and their relatively small size [13, 14].
* J. P. Sanhueza
juanpasanhuezaa@udec.cl
1
Departamento de Ingeniería de Materiales, Universidad de
Concepción, Edmundo Larenas 270, Concepción, Chile
2
AB SandvikCoromant R&D, Lerkrogsvägen 19,
126 80 Stockholm, Sweden
3
Functional Materials, Department of Applied Physics, School
of Engineering Sciences, KTH Royal Institute of Technology,
Isaordsgatan 22, 164 40 Kista, Sotckholm, Sweden
4
Departamento de Metalurgia, Universidad de Santiago de
Chile, Alameda Líbertador Bdo. O´Higgins 3363, Estación
Central, 9170022 Santiago, Chile
5
Departamento de Tecnologías Industriales, Facultad de
Ingeniería, Universidad de Talca, Camino a los Niches km 1,
Curicó, Chile
6
Departamento de Ingeniería Mecánica, Universidad de la
Frontera, Francisco Salazar 01145, Temuco, Chile